Orally Absorbed Cyclic Peptides
Daniel S. Nielsen,1,2 Nicholas E. Shepherd,1,2 Weijun Xu,1,2 Andrew J. Lucke,1 Martin J. Stoermer,1*
David P. Fairlie1,2*
1Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, Brisbane
Qld 4072, Australia.
2Australian Research Council Centre of Excellence in Advanced Molecular Imaging, Institute for Molecular Bioscience, The
University of Queensland, Brisbane Qld 4072, Australia
ABSTRACT: Peptides and proteins are not orally bioavailable in mammals, although a few peptides are intestinally absorbed in small amounts. Polypeptides are generally too large and polar to passively diffuse through lipid membranes, while most known active transport mechanisms facilitate cell uptake of only very small peptides. Systematic evaluations of peptides with molecular weights above 500 Da are needed to identify parameters that influence oral bioavailability. Here we describe 125 cyclic peptides containing four to thirty-seven amino acids that are orally absorbed by mammals. Cyclisation minimizes degradation in the gut, blood and tissues by removing cleavable N- and C-termini and by shielding components from metabolic enzymes. Cyclisation also folds peptides into bioactive conformations that determine exposure of polar atoms to solvation by water and lipids, and therefore should influence oral bioavailability. Key chemical properties thought to influence oral absorption and bioavailability are analysed, including molecular weight, octanol-water partitioning, hydrogen bond donors/acceptors, rotatable bonds and polar surface area. The cyclic peptides violated to different degrees all of the limits traditionally considered to be important for oral bioavailability of drug-like small molecules, although fewer hydrogen bond donors and reduced flexibility generally favored oral absorption.
CONTENTS 4.9. Pristinamycin and related antibiotics ...... 11
4.10. 1-NMe3 and related cyclic hexapeptides ...... 11 1. INTRODUCTION ...... 2 4.11. Cyclo-[Arg-Arg-Arg-Arg-NaphthylAla-Phe] ...... 13 1.1. Absorption ...... 3 4.12. Kahalalide F ...... 13 1.2. Predicting absorption ...... 3 5. CYCLIC HEPTAPEPTIDES ...... 13 1.3. Metabolism ...... 3 5.1. Sanguinamide A and danamides ...... 13 1.4. Oral bioavailability versus oral activity ...... 3 5.2. Rhizonin A ...... 14 1.5. Formulation and pharmacokinetics ...... 4 5.3. Microcystin LR ...... 14 1.6. Review Scope ...... 4 5.4. YM254890 ...... 14 2. CYCLIC TETRAPEPTIDES ...... 4 5.5. CHEC-7 ...... 14 2.1. CJ-15208 ...... 4
5.6. Polymyxin B1 and B2 ...... 14 2.2. Apicidin and chlamydocin ...... 5 5.7. Bacitracin A ...... 15 2.3. Beauveriolides ...... 5 6. CYCLIC OCTAPEPTIDES ...... 15 2.4. HIV fusion inhibitors ...... 5 6.1. PF1022A and emodepside ...... 15 3. CYCLIC PENTAPEPTIDES ...... 5
3.1. DMP-728 ...... 5 6.2. WH1 Fungin ...... 15
3.2. Cyclochlorotine and astin C ...... 6 6.3. α-Amanitin ...... 15
3.3. BL3020-1 ...... 6 6.4. Griselimycin and synthetic derivatives ...... 16
3.4. Romidepsin ...... 6 6.5. Dihydromycoplanecin and mycoplanecin ...... 16
3.5. Largazole ...... 6 7. CYCLIC NONA- & DECA- PEPTIDES ...... 17
3.6. Complement C5aR antagonist 3D53 ...... 7 7.1. CHEC-9 ...... 17
3.7. Actinomycin D ...... 7 7.2. AFPep ...... 17
3.8. Leucine cyclic peptides ...... 7 7.3. Antamanide and cyclolinopeptide ...... 17
4. CYCLIC HEXAPEPTIDES ...... 8 7.4. Cyclopeptolide 1 ...... 17
4.1. Desmopressin ...... 8 7.5. Permetin A ...... 17
4.2. Melanotan II ...... 8 7.6. Synthetic N-methyl β-strand decapeptides ...... 18
4.3. Oxytocin ...... 8 7.7. Surotomycin ...... 18
4.4. Anidulafungin, caspofungin, micafungin ...... 8 8. CYCLIC UNDECAPEPTIDES ...... 18
4.5. Somatostatin, octreotide and analogues ...... 9 8.1. Cyclosporin A and synthetic derivatives ...... 18
4.6. Beauvericin and enniatins ...... 10 8.2. THR-123 ...... 19
4.7. Nepaduant ...... 10 9. CYCLIC DODECA- AND TRIDECAPEPTIDES ...... 20
4.8. Bouvardin ...... 11 9.1. Cerulide ...... 20 9.2. L-Phenylalanine-dipicolinate macrocycle ...... 20 focussing attention on small molecules restricted to MW < 500. In
10. CYCLIC TETRADECAPEPTIDES AND BEYOND ...... 20 the era of postgenomics, transcriptomics and proteomics, it is time to focus more attention on larger modulators of proteins that can 10.1. Conotoxins and synthetic derivatives ...... 20 span larger surfaces, access new therapeutic mechanisms of 10.2. Duramycin ...... 21 action, and provide greater target specificity.18 This has been 10.3. Kalata B1 and other cyclotides ...... 21 spectacularly demonstrated by antibodies and some proteins that 10.4. Stapled α-helix ...... 22 have spearheaded a paradigm shift in the pharmaceutical industry 11. INFLUENCES ON ORAL BIOAVAILABILITY ……….…...… 22 towards larger therapeutic molecules.19 Proteins and polypeptides
12. CONCLUSIONS and FUTURE PROSPECTS ...... 24 are expensive to manufacture, chemically unstable (degraded by
13. REFERENCES…………………………………………………..25 pH, heat, oxidation, proteases), difficult to store, very flexible in
water, immunogenic, have low membrane permeability and poor
oral bioavailability. Despite these limitations, many peptides and 1. INTRODUCTION polypeptides are in clinical trials and a few are registered drugs,
Proteins and peptides are the largest group of naturally mainly naturally occurring peptides, their semi-synthetic occurring mediators of biological and cellular processes, ranging derivatives, cyclic peptides, or antibodies.18-20 They all need to be in size from small peptide hormones to large multi-domain given by injection, with few peptides known to be orally absorbed
1 polypeptides and proteins. Proteins bind with high specificity and and hardly any being truly orally bioavailable. There is now potency irrespective of whether interactions are localised to one or growing interest in developing molecules with molecular weights
2-4 more small binding pockets (‘hot spots’) or more dispersed between those of conventional drugs and antibodies.18 Here we across larger surface areas. When protein function is localised, describe some examples of orally absorbed peptides, all being protein-protein interactions (PPIs) can potentially be interfered cyclic peptides of 4-37 amino acid residues.
5 with by small drug-like molecules. However, more often than not the bioactive protein interfaces span large surfaces and rely upon 1.1. Absorption multiple weak contacts for affinity and selective recognition. In When a drug is administered by oral, buccal, sublingual, nasal, these cases, an alternative approach to modulating PPIs is to dermal, intramuscular, subcutaneous, pulmonary and rectal routes, mimic one of the interacting protein surfaces by downsizing it to it must be absorbed to enter the bloodstream where it is smaller peptides or peptidomimetics. These are larger than small systemically circulated, distributed into tissues, metabolised, molecule drugs, frequently require molecular constraints to cleared and excreted. Absorption is the process by which a drug stabilise structure in water, and are usually not orally moves unchanged from the site of administration to the site of bioavailable.6-13 measurement in the organism.21 Absorption from the During the last 20 years the pharmaceutical industry has gastrointestinal (GI) tract after oral administration occurs mainly introduced almost universally adopted drug-like-property filters, in the small intestine. Small finger-like folds (villi) coating its such as the ‘rule-of-five’ (RO5)14-16 and related parameters.17 surface generate a much larger surface area (200 m2) for These have guided the design and development of orally compound absorption compared to the stomach (1 m2).21 The bioavailable modulators of macromolecules, deliberately small intestine environment (pH 7-9) aids absorption because and liver, clearance rate and first pass metabolism) also contribute many molecules are uncharged at this pH and can passively to oral bioavailability. diffuse through intestinal membranes. Passive diffusion is the The parallel artificial membrane permeability assay most common way drugs and many nutrients are absorbed from (PAMPA)32 has been used widely in drug discovery as a high the GI tract into plasma. Passive diffusion of drugs is most throughput assay to estimate passive diffusion across a membrane. commonly transcellular (through cell membranes, >90% of drugs) The artificial membrane lacks transporter proteins and so is rather than paracellular (through tight junctions between limited to estimating permeability via passive diffusion. enterocytes, 5-10% of drugs). Charged and hydrophilic molecules Caco-2 cells are heterogeneous human epithelial colorectal such as peptides are not well absorbed via passive diffusion adenocarcinoma cells grown under conditions to mimic absorptive mechanisms. Membrane-bound transporter proteins also mediate cells of the small intestine.33 Their microvilli, metabolic enzymes absorption of amino acids, very small peptides, nucleosides, (e.g. peptidases and esterases), transporter proteins and bile salts sugars, ions and hydrophilic molecules via facilitated diffusion better mimic the physiological environment.34 PAMPA and and active transport.22-26 Studies on peptide and protein transport Caco-2 assays can indicate whether a compound is passively or across gastrointestinal mucosal membranes is still in relative actively transported across epithelial cells. Madin-Darby canine infancy, understanding still confined mainly to single amino acids kidney (MDCK) cells isolated from dog kidney cortex35 retain and small peptides and the biotin, transferrin, and glucose many properties of the kidney tubular epithelium. transporters. The human intestinal peptide transporter SLC15A1 Morphologically, MDCK cells exhibit apical microvilli, is one example of a proton-dependent protein that transports very junctional complexes, and lateral membrane infoldings36-39 small peptides (2-4 residues) via facilitated diffusion.27 SLC15A1 characteristic of transporting epithelia.40 Physiologically, MDCK also facilitates absorption of certain peptide mimetics and peptide- cells transport sodium and water in an apical-to-basal direction like drugs such as ACE inhibitors and β-lactam antibiotics.28 When grown on permeable substrates, MDCK cells generate Conversely, some transporters in enterocytes (e.g. P- transepithelial electrical resistance indicating functioning tight 29,30 glycoproteins) act as a barrier to absorption, actively expelling 41 junctions. These properties resemble Caco-2 cell and other peptides and drugs,31 back into the GI tract. intestinal tract cells, making MDCK cells a viable model for
1.2. Predicting absorption measuring in vitro permeability despite their anatomical origin.
Like Caco-2, MDCK cells have uptake and efflux transporter- Predicting oral absorption of drugs in animals is complex and proteins, but their canine origin may endow different affinity, experimental measurements are low throughput. Therefore selectivity and activity for substrates compared to human attempts have been made to develop in vitro or ex vivo methods to equivalents. Therefore caution should be exercised in interpreting assess membrane permeability. Although no in vitro or ex vivo these results and further validation is best.42 MDCK monolayers model correlates well with in vivo parameters, some methods have are faster to culture (3-7 days)43 than Caco-2 (14-28 days), allowed estimates of relative passive membrane permeability. making them useful for high throughput permeability assays. However, others factors (membrane uptake via endocytosis, Recently, a new cell line, MDCKII-LE (low efflux) was transporter proteins, protein-binding, stability to proteolytic and developed from subpopulations of MDCK cells.44 MDCKII-LE oxidative/reductive enzymes in the gut, intestine, tissues, plasma have greatly reduced expression of canine mRNA/protein and low NADPH-CYP450 oxidoreductases. At this stage the compound active uptake/efflux properties making them a live cell alternative can be: 1) re-absorbed back into the bloodstream, sometimes to the artificial PAMPA assay. There have been many recent unchanged; 2) metabolised and then absorbed into the reviews of cell and membrane permeability of cyclic peptides and bloodstream; or 3) combined with bile salts and excreted back other macrocycles,45-50 so we will not be covering that literature into the GI tract. here. While this is of importance, it is not the only contributor to Metabolism of peptides can occur at all stages, while traversing oral absorption and oral bioavailability. Many membrane and cell the GI tract, in intestinal tissues, in the blood stream, in the liver permeable compounds show negligible oral bioavailability. and other organs and tissues. Peptides can be hydrolysed by a
Instead of measuring transport in vitro across cells, an Ussing myriad of proteases in the gut, plasma and cells. For example, chamber51 can be used to estimate oral absorption by measuring pepsin and HCl in the stomach; trypsin, chymotrypsin, elastase ex vivo membrane transport of ions, nutrients and drugs across and carboxypeptidases in the small intestine; and, by thrombin, mouse52,53 or rat54,55 intestinal tissue. However, such experiments plasmin and clotting factors in blood plasma degrade peptides. also correlate poorly with oral bioavailability (F%) in rodents and The CYP450 monooxygenases and oxidoreductases in the humans. Thus the Ussing chamber has become less popular in intestinal lining and in the liver catalyse carbon hydroxylation and industry over the past decade. epoxidation, heteroatom oxygenation and release. CYP450
56 1.3. Metabolism enzymes account for >75% of drug metabolism within the liver. Substances with good gut absorption can still have low oral Orally administered compounds face many obstacles en route bioavailability if metabolism in the intestinal lining, liver, plasma to the plasma. Compounds of high molecular weight, high or elsewhere is high, or clearance is rapid. It is a misconception lipophilicity or low solubility are recognized and degraded by that high gut permeability equates to high oral bioavailability. metabolic enzymes. Orally ingested compounds are first exposed Stability to metabolic enzymes, especially in the gut, liver and to digestive amylases in the saliva, where glycosidic bonds of blood, is important when predicting oral activity of membrane- starch and other carbohydrates are hydrolysed. Then in the permeable compounds. stomach, acidic (pH 1-2) gastric juice containing peptidases Finally, a relatively new consideration is the influence of the begins to degrade proteins and other nutrients. Upon entering the microbiome on drug and nutrient metabolism. Differences in oral duodenum, the pancreas excretes additional enzymes (proteases, bioavailability between people and species are often attributed to lipases, amylases), bile salts and pH-neutralizing bicarbonate. differences in metabolic enzymes or their efficiencies that change Next, in the jejunum and ileum (small intestine) the pH is 7-9 and with age, genetics and environment. Until now, the influences of most processed nutrients and drugs are absorbed here. Intestinal symbiotic bacteria inhabiting the gut on oral drug stability, P450 enzymes can metabolise compounds even before they enter metabolism and absorption have not been considered much and the bloodstream and thus reduce measurable oral absorption. Once this is likely to be important to study in the future. absorbed from the GI tract, compounds enter the hepatic portal vein, flow into the liver and are perfused into hepatocytes for 1.4. Oral bioavailability versus oral activity first-pass metabolism by cytochrome P450 (CYP450) enzymes Oral bioavailability (F) is the fraction of an orally administered and flavin-containing monooxygenases, monoamine oxidases and compound that reaches the systemic circulation intact. Absorption alone is not a good predictor of oral bioavailability, since measurable response; the effective dose for 50% of the maximal extensive first-pass effects in the liver and intestine can lead to response (ED50); and, the lethal oral dose required to kill 50 or poor systemic exposure. Thus, blood is usually sampled from the 100% of the test population (LD50 and LD100). jugular, rather than portal, vein to take into account first pass 1.5. Formulation and pharmacokinetics metabolism. Oral bioavailability is defined as the ratio of the When comparing pharmacokinetic parameters for compounds amounts of drug found in plasma after intravenous (iv) versus oral tested in separate studies, it is important to note possible (p.o.) dosing, with the iv dose representing 100% differences in experimental design. Compounds are usually bioavailability.21 formulated with a solvent, vehicle or matrix, which can
���!" ����!" � % = 100× × profoundly affect their solubility, rate and location of dissolution, ����!" ���!" and permeability across the intestinal membranes. Formulation For clinical trials, drugs normally need to have F > 20%. Other design is a crucial step in the drug delivery. Some formulations parameters described in this review that relate to oral simply increase chemical stability or solubility at different pH, in bioavailability include: the area under the curve (AUC), used to aqueous or lipophilic environments. Other formulations are express the cumulative amount of drug found in plasma over a optimised to release the compound at a specific location in the period of time; the clearance rate (CL), the volume of plasma gut, in tissues or in targeted organs or cells. Often an excipient is from which a drug is completely removed per unit time; the peak added to enhance membrane permeability or oral absorption. serum concentration (Cmax), the time to reach peak serum Thus, formulation is a key determinant of pharmacokinetic concentration (Tmax); the half life (t1/2), time taken for drug serum parameters, which are highly dependent on the conditions under concentration to decrease by half its original amount; the volume which they are measured. of distribution (VD), the apparent volume in which the drug is Proteins and peptides have been formulated in many ways in distributed at steady state. These parameters provide quantitative attempts to increase oral absorption57-63 including with: (i) estimates of the compound absorbed and surviving first pass enzyme inhibitors to reduce proteolysis in the GI tract (e.g. metabolism. sodium glycocholate, trypsin inhibitors, camostat mesilate, Oral activity is often used as a surrogate to infer oral bacitracin, ovomucoids); (ii) absorption enhancers to improve bioavailability. Orally dosing an animal and observing a intestinal permeability (e.g. detergents, surfactants, bile salts, therapeutic effect provides only qualitative evidence of oral chelating agents); (iii) mucoadhesive polymers to improve bioavailability. We have included reports for orally active delivery & permeability (PEGs, P(MAA-g-EG), lectin peptides in this review even though many such molecules are microparticles, thiolated polymers); (iv) formulation vehicles to poorly absorbed; most peptides and proteins are <1% orally protect drug & improve permeability (emulsions, liposomes, bioavailable. We urge caution in drawing robust conclusions microspheres, micelles, nanoparticles). about oral bioavailability of molecules from such studies. The As shown above, absolute oral bioavailability (F%) is defined observed biological effect could occur by indirect mechanisms, as the dose-corrected ratio of accumulated concentrations in from metabolites or may be due to exceptional potency of trace
plasma (AUC) following an iv injection (AUCiv : 100% material absorbed. The main measures of oral activity used in this
bioavailability by definition) and an oral dose (AUCpo). This review are: the oral dose (mg/kg p.o.) required to induce a dose-corrected absolute value allows direct comparisons to be cyclic peptides reported up until 2016, including some that are made across different studies conducted at different doses. In absorbed in only trace amounts but sufficient to induce a reality, as dose of the test compound is raised, physio-chemical physiological response. Cyclic peptides have been classified boundaries and saturation of the biological system will herein according to the number of residues in their macrocyclic increasingly affect solubility, absorption, active transport portion. For some highly modified cyclic peptide natural products, mechanisms and metabolism. Other pharmacokinetic parameters, we have grouped them with cyclic peptides of equivalent including AUC and Cmax, are dose-dependent as they are macrocycle size (e.g. largazole is grouped with romidepsin). In expressed in terms of compound concentration in plasma, and will cases where a related series of different sized cyclic peptides were therefore depend on the administered dose. developed for the same target, we have grouped them together
The animal model is an important consideration. Biological based on the smallest cyclic peptide in the series in order to variation allows different species, even different strains of the streamline discussion and avoid repetition. The main focus of this same species, to metabolise drugs in different ways, making review is on cyclic peptides larger than four residues because they comparisons across species and even strains difficult. For violate most, often all, rule-of-five (RO5)14-16 and associated17 technical reasons, it also may not be possible to perform identical parameters. We have also included a few representative cyclic experiments in two species, even rodents like mice and rats. tetrapeptides, even though these usually comply with RO5
Pharmacokinetic investigations in rats often involve sampling parameters. We describe 125 cyclic peptides in total for which blood at multiple time points from the same animal through a there is evidence of oral absorption, oral activity or oral surgically implanted line. This is more difficult for mice, for bioavailability. Where possible, we have indicated relevant doses, which studies usually involve larger groups of animals, so that formulations, pharmacokinetic parameters, pharmacological multiple mice can be sacrificed at each time point. activities. In some cases, there was evidence of solid state or
Pharmacokinetic parameters measured by the latter method solution conformations that indicated rigidity or flexibility that provide less accurate results due to variation within animals likely influence absorption. These are referenced to codes in the
(metabolism, total blood, body volume, individual weight, etc) or Protein Data Bank (PDB) or Cambridge Crystallographic Data their environments. It is therefore prudent to carefully consider Centre (CCDC). parameters such as dose, species of test animal and experimental Our review concludes with an analysis of this compound set for design before drawing conclusions. influences of physicochemical parameters normally considered to
1.6. Review Scope affect oral bioavailability. A recent review68 on bioactive linear
and cyclic peptides from the ChEMBL database only examined Most proteins and peptides show negligible oral bioavailability eight cyclic peptides that were orally administered. For the cyclic (F < 1% and usually F < 0.1%). Very few peptides are sufficiently peptides that follow, we have calculated molecular weight (MW), orally absorbed to produce some physiological effect in an the predicted octanol-water partition coefficient (Molinspiration animal. Cyclic peptides are the most orally bioavailable peptides LogP, miLogP), the number of hydrogen bond donors (HBD) and known, but only a handful show F ≥ 10%. Other types of hydrogen bond acceptors (HBA) as strictly defined by Lipinski macrocycles are orally absorbed, but the reader is directed to other and colleagues, the number of rotatable bonds (RotB) and the total reviews for these.64-67 This review covers only orally absorbed polar surface area (tPSA), all determined with the aid of the Molinspiration webportal (http://www.molinspiration.com).69 We O plot each of these six parameters against oral bioavailability (F%), O N HN for those compounds where oral bioavailability has been reported. NH HN O We then discuss how the findings relate to the RO5 and associated NH O guidelines commonly used to predict oral bioavailability of drug- like small molecules. Systematic evaluation of more peptides with 1 MW > 500 are needed to determine allowable upper limits for molecular properties (MW, logP, HBA, HBD, RotB, PSA) that Figure 1. Cyclic tetrapeptide CJ15208 (1). MW = 578; miLogP influence (a) passive (unassisted) permeability of cells & oral = 2.8; HBD = 4; HBA = 9; RotB = 6; tPSA = 120 Å2. bioavailability, and (b) active or facilitated transport mechanisms that promote uptake of peptides >5 amino acids from the gut. This 2.2. Apicidin and Chlamydocin article takes one important step towards identifying how these Cyclic tetrapeptides 2 and 3 are analogues of 1 and are RO5 molecular properties vary in orally absorbed cyclic peptides. compliant except for MW (Fig. 2). Apicidin (2) is a cyclic
2. CYCLIC TETRAPEPTIDES tetrapeptide metabolite isolated from cultures of F.pallidoroseum. It is a histone deacetylase (HDAC) inhibitor and has been shown Cyclic tetrapeptides are generally RO5 compliant, with MW < to kill protozoa such as Plasmodium sporozoites. When 500, HBD = 4, HBA = 8, and LogP 0-5 if bearing hydrophobic administered in DMSO/PEG400/saline (15:20:65) by oral gavage, sidechains. They generally have few rotatable bonds and a small oral bioavailability varied slightly (10 mg/kg p.o.; F = 14 % surface area and so, not surprisingly, they are also often orally (fasting), 19 % (non-fasting); Cmax 235 ng/mL, Tmax 66 min, absorbed and orally bioavailable to some extent. Cyclic -1 -1 71 T1/2 54 min, VdSS 2.5 L/kg, CL 62 mL.min .kg )). The apicidin- tetrapeptides are typically used to stabilize a b-turn conformation, like natural product, chlamydocin (3, Fig. 2), was found to inhibit with proline and D-amino acids often promoting b-turn formation. P-815 cell growth in mastocytoma mouse cells and glial tumor rat 2.1. CJ-15208 cells in vitro (ED50 = 0.36 ng/mL). When 3 was administered to
Cyclic tetrapeptide CJ-15208 cyclo-(Phe-D-Pro-Phe-Trp) (1, tumor-inoculated mice (iv and p.o.) there was no antiproliferative
Fig. 1), isolated from the fungus C.serratus ATCC 15502, showed activity. The difference between cell and animal findings was dose-dependent anti-nociceptive activity in mice measured from attributed to in vivo inactivation of the epoxide in blood.
20-80 minutes after oral administration (1 mg/kg p.o.). When Consistent with this notion, intra-peritoneal injections were more given at a higher dose (10 mg/kg p.o.), 1 antagonized a centrally effective than intravenous injections in inhibiting tumor growth. administered selective κ-opioid receptor agonist, suggesting that 1 For 3, LD50 was 226 (iv) and >850 (p.o.) mg/kg in mice and 66 is brain permeable.70 This cyclic tetrapeptide has only one RO5 (iv) and 141 (p.o.) mg/kg in rats.72 Both 2 and 3 contain one D- violation (MW > 500), a D-proline ring that removes one peptide residue, a D-pipecolic acid in 2 and a D-proline in 3. In solution,73
NH hydrogen bond donor, and hydrophobic side chains, making it two intramolecular hydrogen bonds defined a γ- and β-turn in 2 suitable for oral absorption. but these were replace in the crystal structure from chloroform/methanol73 by intermolecular interactions (CCDC O code: HEWGOG). R O HN O NH H O N O O N O O NH HN O NH HN O
NH N O NH N O 4 (R= D-Leu) O O 5 (R= D-Ile)
O O O 2 3 Figure 3. Beauveriolide I (4) and III (5). 4: MW = 488; miLogP
= 4.1; HBD = 8; HBA = 8; RotB = 12; tPSA = 114 Å2. 5: MW = Figure 2. Apicidin (2) and chlamydocin (3). 2: MW = 624; 488; miLogP = 4.3; HBD = 3; HBA = 8; RotB = 8; tPSA = 114 miLogP = 3.4; HBD = 3; HBA = 11; RotB = 12; tPSA = 139 Å2. Å2. 3: MW = 527; miLogP = 0.9; HBD = 3; HBA = 10; RotB = 9;
2 tPSA = 137 Å . 2.4. HIV fusion inhibitors
2.3. Beauveriolides A critical step in HIV-1 entry into host cells is the protein-
protein interaction between CD4 and gp120. Inhibition of this Beauveriolides (Fig. 3) are cyclic tetradepsipeptides, with three protein-protein interaction (PPI) has been the target of many amide bonds, one D-residue and one ester bond, were isolated research groups.75 A library of cyclic peptides was generated to from the fungus Beauveria sp. FO-6979. Beauveriolides are join two non-continuous regions of CD4-containing key residues potential antiatherosclerotic agents that reduce cholesteryl ester Phe43 and Arg59 that interact with gp120.75 A six residue mimic synthesis in mouse macrophages via inhibition of acyl- cyclized with succinic acid and ethylenediamine gave cyclic CoA:cholesterol acyltransferase (ACAT), leading to a reduction heptapeptide-like 6 (Fig. 4). Optimization of the linker-length by in lipid droplet formation in macrophages. Lipid accumulation is inserting an extra methylene unit and replacing residues Gln-Gly- associated with the development of atherosclerosis, which can be Ser with a pimelic acid moiety enabled inhibition of HIV-1 studied in apoE- or LDL-receptor knockout mice. Beauveriolide infection by analogue 7 (Fig. 4), which resembles a cyclic III (5) was administered to apoE- or LDL-receptor knockout mice tetrapeptide. Despite retention of an arginine, with its protonated for 2 months (25 mg/kg/day p.o.) and was orally active in mouse guanidine at physiological pH usually being an impediment to models of atherosclerogenesis by inhibiting ACAT activity.74 The absorption, 7 still had reasonable pharmacokinetic properties in ester bond in depsipeptides is usually not as stable as the amide rats (1 mg/kg iv: C 102 ± 19 ng/mL, V 0.6 L/kg; 10 mg/kg bond in vivo, but does promote cell permeability before max d p.o. in water: C 866 ± 76 ng/mL, T 18 min, AUC 21,770 ± intracellular ester cleavage by esterases. max max 75 63 min⋅ng/mL, t1/2 73 min, CL 14.5 ± 0.3 mL/min⋅kg, F 10%).
Converting 6 to 7 increased RO5 compliance for MW, HBD,
HBA, RotB, halved the tPSA and significantly increased
hydrophobicity. Although these changes make 7 smaller and less polar than 6, and are expected to enhance oral bioavailability, no h, AUC 1.38 ± 0.56 µg⋅h/mL, t1/2 2.8 ± 2.1 h, F 14.6 %) and dogs data for 6 has been reported to confirm this point. (2 mg/kg iv, 2 mg/kg p.o. with palmitoylcarnitine chloride; Cmax
0.41 ± 0.10 µg/mL, Tmax 1.0 h, AUC 1.09 ± 0.22 µg⋅h/mL, t1/2 3.3
O ± 0.9 h, F 20.5%).76 Absorption enhancers significantly improved NH2 O O pharmacokinetic parameters compared to controls formulated in O NH O NH HN O O HN microcapsules. The MW, LogP, HBD, tPSA all violate limits NH HO O N O usually associated with passively diffusing, orally bioavailable, NH HN O H NH N 2 NH drug-like small molecules. We speculate that the N-methyl O N O O HN NH HN NH2 arginine might promote active transport of this compound across
NH2 NH2 6 7 the intestinal membrane.
CO H O 2 O Figure 4. HIV fusion inhibitors (6) and cyclic tetrapeptide-like N H O NH HN (7). 6: MW = 775; miLogP = -5.2; HBD = 15; HBA = 22; RotB = H H N N 13; tPSA = 363 Å2. 7: MW = 488; miLogP = -0.3; HBD = 8; 2 N H 2 NH N HBA = 11; RotB = 9; tPSA = 184 Å . O O
3. CYCLIC PENTAPEPTIDES
8 Cyclic pentapeptides generally have HBD = 5, HBA = 10, LogP
0-5 if bearing hydrophobic sidechains, but their molecular weights Figure 5. DMP-728 (8). MW = 561; miLogP = -2.3; HBD = 9; usually exceed 500, resulting in more rotatable bonds and larger HBA = 15; RotB = 8; tPSA = 236 Å2. surface areas. To be orally absorbed, they often require synthetic 3.2. Cyclochlorotine and Astin C modifications. Cyclochlorotine (9, Fig. 6) is a hepatotoxic cyclic pentapeptide
3.1. DMP-728 that was isolated from the common rice-infecting mould
77,78 DMP-728 (8, Fig. 5) is a potent and specific antagonist of P.islandicum. Its structure consists of natural as well as platelet glycoprotein IIb/IIIa complex (GPIIb/IIIa). Like 6 and 7, unnatural L-amino acids, including β-phenylglycine and 3,4- compound 8 contains an arginine residue that is normally dichloro-L-proline. LD50 values were determined in mice (LD50; detrimental to oral absorption. It consists of four conventional iv 0.3, sc 0.5, and p.o. 6.6 mg/kg), suggesting some oral
78 amino acids, including a D-Abu, residues with N- and C-termini absorption. linked by a fifth, unnatural, hydrophobic amino acid, 3- Astin C (or asterin, 10, Fig. 6), a close analogue of 9 is a plant aminomethybenzoic acid. The pharmacokinetic profile for 8 was cyclic peptide isolated from the roots of A.tataricus. The crystal measured following oral administration with or without structure of 10 from chloroform/methanol (CCDC code: absorption enhancers to rats (10 mg/kg iv, 8 mg/kg p.o. with WILXEW) showed a single transannular hydrogen bond from an palmitoylcarnitine chloride; Cmax 0.44 ± 0.212 µg/mL, Tmax 0.75 Abu NH to the (i, i+3) carbonyl of the β-phenylglycine carbonyl.79 The remaining hydrogen bond donors and acceptors enhanced metabolic stability in rat brush border membrane are highly solvent exposed. Inflammatory bowel disease is vesicles (BBMVs). A single oral dose administered to rats (0.5 characterized by activation of T lymphocytes. Astin C has been mg/kg p.o. dissolved in water) led to reduced food consumption,
82 shown to lower mouse serum concentrations of TNFα, IL-4, IL- while repetitive daily oral dosing reduced weight gain in rats.
17 and to induce apoptosis in activated T cells. Daily oral dosing Pharmacokinetic parameters measured in rats following iv of astin C (2 or 4 mg/kg/day p.o. in 5% methylcellulose in saline) administration (1 mg/kg iv in H2O) indicated t1/2 > 105 min and was shown to protect mice against TNBS-induced colonic VD 2.1 L/kg. Oral administration (10 mg/kg p.o. in H2O) to rats
80 inflammation. showed AUC 24980 ng/min/mL, Cmax 202 ± 39 ng/mL, Tmax 37
HO HO ± 10 min, and F 8.5%. We speculate that charged residues in O O O O N N this compound may help promote intestinal absorption via H H NH HN O NH HN O O H O H facilitated transport. Interestingly, concentrations of ~5 ng/mg N N N Cl N Cl were also found in brain tissue, indicating some ability of 11 to O O OH Cl Cl cross the blood brain barrier.82 9 10 O NH O Figure 6. Structures of cyclochlorotine (9) and astin C (10). 9: O NH O N MW = 572; miLogP = -2.5; HBD = 6; HBA = 12; RotB = 4; tPSA NH2 HN O HN = 177 Å2. 10: MW = 570; miLogP = -1.0; HBD = 5; HBA = 11; NH O 2 N RotB = 4; tPSA = 157 Å . O NH H
3.3. BL3020-1 N NH2 H α-Melanocyte stimulating hormone (α-MSH) is a 13-residue 11 peptide (Ac-Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-
Val) that stimulates the release of melanin by skin melanocytes. Figure 7. Structure of BL3020-1 (11). MW = 836; miLogP = -
α-MSH also binds to the melanocortin 4 receptor (MC4R), which 0.8; HBD = 12; HBA = 18; RotB = 13; tPSA = 287 Å2. modulates food intake and energy utilization.81 The tetrapeptide 3.4. Romidepsin sequence His-Phe-Arg-Trp, and other analogues derived from α- Romidepsin (Istodax, FK-228, 12, Fig. 8) is a cyclic peptide MSH decrease food intake and elevate energy utilization upon HDAC inhibitor that possesses potent antitumor activity against a binding to the melanocortin-4 receptor (MC4R), making them variety of human cancer cell lines and xenografts.83,84 It contains a attractive targets as anti-obesity drugs.82 However, they suffer D-cysteine, D-valine, and (3S,4E)-3-hydroxy-7-mercapto-4- from metabolic instability and poor intestinal permeability. heptenoic acid residues. Romidepsin is an RO5-compliant and Backbone cyclized α-MSH analogue based on Phe-D-Phe-Arg- orally active prodrug, reduction leading to a bis-thiol, one of Trp-Gly-NH2, activated MC4R and had increased oral which covalently bonds to the catalytic zinc ion in HDAC bioavailability. One analogue, BL3020-1 (11, Fig. 7) was MC4R enzymes. It was administered orally to mice with human prostate selective, had good permeability in the Caco-2 model and tumor xenographs (3 x 50 mg/kg/wk p.o.),84 and was also 60:15:15:15:10) to female nude mice.95 Oral activities were significantly absorbed after oral administration to rats (10 mg/kg measured through in vivo hyperacetylation of harvested HCT116 iv; Cmax 1829 ± 359 ng/mL, Vdss 22 ± 7 L/kg, t1/2 5.9 ± 1.2 min, tumors. Only 13 produced hyperacetylated histones, however
AUC 25409 ± 8767 ng/mL⋅min., 50 mg/kg p.o.; AUC 19712 ± largazole free thiol was found in tumors from animals orally
9168 ng/mL⋅min, F 16 ± 7%).83 dosed with 13, 14 or 15, indicating that all three derivatives displayed some oral absorption in mice. O
O O O N S S H N N O NH O HN NH O H S N N S N O O O O O O N R H N S S N O H H S S 13 (R = COC7H15) 15 12 14 (R = SCH2C(NHBoc)CO2H)
Figure 9. Structures of largazole (13), its Boc-L-cysteine Figure 8. Structure of Romidepsin (12). MW = 541; miLogP = disulfide derivative (14) and its disulfide dimer (15). 13: MW = 1.6; HBD = 4; HBA = 10; RotB = 2; tPSA = 143 Å2. 623; miLogP = 5.3; HBD = 2; HBA = 9; RotB = 12; tPSA = 127
3.5. Largazole Å2. 14: MW = 716; miLogP = 2.8; HBD = 4; HBA = 13; RotB =
2 Largazole (13, Fig. 9) is a cyclic depsipeptide natural product 12; tPSA = 185 Å . 15: MW = 991; miLogP = 3.6; HBD = 4; 2 85 HBA = 16; RotB = 11; tPSA = 220 Å . isolated from Symploca sp. collected from the Florida Keys.
Largazole is one of the most potent HDAC inhibitors known, with 3.6. Complement C5aR antagonist 3D53 activity at low nM concentrations and selectivity for class I 3D53 (16, Fig. 10), later known as PMX53,96 is a derivative of HDACs. Largazole has been synthesized by multiple routes the C-terminal turn of human complement protein C5a and is a allowing many derivatives to be produced.86-91 A crystal structure potent antagonist of the human C5a receptor (IC50 3 nM against 3 of 13 bound to HDAC 8 (pdb code: 3RQD) shows a single NH nM C5a).96-100 Cyclic pentapeptides97-99 based on this compound directed to the centre of the macrocycle but no strong evidence of feature endocyclic D-cyclohexylalanine and L-arginine that are intramolecular hydrogen bonding.92 Largazole analogues co- important for binding, an aromatic residue (L-tryptophan or L- crystallized with HDAC 8 also do not show any intramolecular phenylalanine) that is required for antagonism, an L-proline turn- hydrogen bonds (PDB codes: 4RN1, 4RN2).93 Pharmacokinetic inducing constraint, and an exocyclic aromatic ring (L- parameters measured in rats showed that 13 was unstable in vivo phenylalanine in 16 or a phenyl propionyl group in 3D624 (later and rapidly cleared after a single iv dose (10 mg/kg iv in called PMX205)) for affinity.99 NMR structural studies of 16 and
EtOH/DMSO/PEG400/saline (1:1:1:2); CL 76 ± 18 L/h⋅kg, t1/2 99 analogues in DMSO-d6 indicated a turn motif. Compound 16 is 0.5 ± 0.1 h, AUC 134 ± 29 µg⋅h/mL, V 27 ± 11 L/kg, C 280 ± D max a classic example where oral activity is independent of oral 64).94 Largazole 13, Boc-L-cysteine-largazole disulfide 14 and bioavailability, due to a long residence time on the receptor (t1/2 disulfide homodimer 15 (Fig. 9) were administered orally (50 ~20 h) overcoming low systemic availability (F 1-2%, rat).100 mg/kg p.o. in polyethylene glycol/glycerol/EtOH/DMSO This compound and its analogues display efficacy in vivo in over determined in mice (LD50 7.8 mg/kg p.o.) and rats (LD50 iv 0.4, po
20 rat and mouse models of human disease following oral 7.2 mg/kg) (Cosmegen®).
96 administration. O O N HN N O N
H N O O HN HN O O O O NH O NH NH2 N O O O O O N O AcHN NH HN NH N 2 O N O H O O N NH H N O N N H O
16
17
Figure 10. Structure of 3D53 (16). MW = 896; miLogP = 1.0; Figure 11. Structure of actinomycin D, (17). MW = 1255;
2 HBD = 11; HBA = 18; RotB = 14; tPSA = 273 Å . miLogP = 0.8; HBD = 6; HBA = 28; RotB = 8; tPSA = 360 Å2.
3.7. Actinomycin D 3.8. Leucine cyclic peptides
Actinomycin D, (17, Fig. 11) is an antibiotic natural product A selection of three all-leucine cyclic peptides (Fig. 12), cyclo- from a family of actinomycins first isolated in 1940.101 It features [(L-Leu)5] (18), cyclo-[(L-Leu)6] (19), and cyclo-[(L-Leu)5(D- two cyclic pentapeptides, each with an L-proline and two N- Leu)] (20), were synthesized and orally administered to rats.106 methyl amino acids, bridged by a phenoxazinone linker. A crystal These compounds are at the boundary limits of RO5 guidelines structure of Actinomycin C in complex with deoxyguanosine for molecular weight, hydrogen bond donors/acceptors. Their showed two intramolecular hydrogen bonds between the two Val other properties (LogP, rotatable bonds, tPSA) depend upon residues keeping the macrocycles close together to help insert the substituents on the cyclic peptide scaffold. NMR, CD and X-ray 102 phenoxazinone into DNA (CCDC code: ACTDGU10). This structural studies on 18-20 did not show intramolecular hydrogen preorganisation minimised solvent exposure to polar atoms. bonds, but intermolecular interactions for 18 were consistent with
Similar structures in the absence of nucleotides (CCDC codes: evidence for aggregation in solution.106 Despite lacking N-methyl
BEJXET, BRAXGU, GIDNUC, POHMUU) show stacking of the groups or depsipeptide bonds to reduce the number of hydrogen cycles but the Val…Val hydrogen bonds remain. These cycle- bond donors, all three compounds showed oral absorption: 18 (1 cycle interactions loosened in crystal structures of 17 bound to mg/kg iv in DMSO: CL 13.1 mL/min⋅kg, VD 0.36 L/kg, t1/2 0.5 h.; short sequences of DNA (PDB codes: 4HIV, 1I3W).103,104 10 mg/kg p.o. in olive oil: AUC 442 ng⋅h/mL, Cmax 187 ng/mL, F Actinomycin D suppresses transcription, is cytotoxic and effective 4%), 19 (1 mg/kg iv in DMSO: CL = 4.7 mL/min⋅kg, VD 0.19 in treating various tumors. It has an estimated bioavailability F = L/kg, t1/2 1.0 h; 10 mg/kg p.o. in olive oil; AUC 6289 ng⋅h/mL, 5% based on adverse systemic effects after oral versus iv Cmax 1900 ng/mL, F 18%), and 20 (1 mg/kg iv in DMSO: CL 24.1 105 administration over 2 weeks. LD50 values for 17 were mL/min⋅kg, VD 0.75 L/kg, t1/2 1.2 h; 10 mg/kg p.o. in olive oil; AUC 642 ng⋅h/mL, Cmax 174 ng/mL, F 9%). Despite being larger OH with more RO5 violations (Fig. 12), 19 had better oral O O bioavailability than 18, and was comparable to cyclosporin A (F O O N H2N HN H 21%) under the same conditions.106 HN NH S O S O HN O H O NH N N N O O HN O N * H H NH O O NH2 NH HN NH HN O 2 O NH O O NH HN O NH HN 2 H H N O N O O O 21
Figure 13. Structure of desmopressin (21). MW = 1069;
18 19 (*L-Leu) miLogP = -4.3; HBD = 18; HBA = 26; RotB = 20; tPSA = 435 20 (*D-Leu)
Å2.
Figure 12. Cyclic pentaleucine (18) and cyclic hexaleucines 4.2. Melanotan II (19, 20). 18: MW = 566; miLogP = 3.9; HBD = 5; HBA = 10; Melanotan II (22, Fig. 14) is a cyclic hexapeptide analogue of RotB = 10; tPSA = 145 Å2. 19: MW = 679; miLogP = 4.7; HBD = α-melanocyte-stimulating hormone that was developed as a 6; HBA = 12; RotB = 12; tPSA = 174 Å2. 20: MW = 679; miLogP tanning agent to help prevent skin cancer. It displayed some = 4.7; HBD = 6; HBA = 12; RotB = 12; tPSA = 175 Å2. bioavailability after oral administration to rats (0.3 mg/kg iv, 6.76
4. CYCLIC HEXAPEPTIDES mg/kg p.o., F 4.6%) despite violating all RO5 and related
parameters (Fig. 14).111 Cyclic hexapeptides and larger macrocycles generally contravene
RO5 parameters, with MW > 500, HBD ≥ 6, HBA ≥ 12, LogP 0-5 NH HN NH if bearing hydrophobic sidechains. They have more rotatable 2
H bonds and larger surface areas than the smaller cyclic peptides HN N NH H above. O O N N O O H HN O HN O N 4.1. Desmopressin NHAc H2N O N H HN Desmopressin (21, Fig. 13) was first reported in 1966 as an O analogue of vasopressin (antidiurectic hormone). Its deaminated cysteine at position 1 and D-arginine at position 8 enhanced 22 metabolic stability and antidiuretic effects. The bioavailability of Figure 14. Structure of melanotan II (22). MW = 1024; miLogP desmopressin in normal healthy adults was low following = -0.1; HBD = 16; HBA = 24; RotB = 18; tPSA = 382 Å2. intranasal administration (F 3-5%) and very low after oral delivery (F 0.08-0.16%).107-110 4.3. Oxytocin dogs following oral and intravenous administration (5 mg/kg iv:
t 15.6 h; CL 0.10 ± 0.02 L/h⋅kg, V 1.76 ± 0.11 L/kg, AUC Oxytocin (23, Fig. 15) is a disulfide-bridged cyclic hexapeptide 1/2 D 0-∞ 49409 ± 10286 ng h/mL; 5 mg/kg p.o.: C 307 ± 61 ng/mL, T hormone with an additional three amino acids outside the cycle. ⋅ max max
118 This mammalian neurotransmitter and hormone is associated with 4.7 ± 1.2 h, AUC0-∞ 4477 ± 768 ng⋅h/mL, F 9%). Region- numerous physiological responses. It is currently used in the dependent intestinal absorption and meal composition effects on
112,113 clinic to induce childbirth and lactation. All physicochemical Cmax and AUC were found for dogs given the same dose via oral, parameters listed in Fig. 15 violate guidelines for oral duodenal, jejunal or colonic administration (250 mg/kg p.o.: bioavailability. An NMR structure for oxytocin in water showed AUC0-48h 23.3, 26.5, 17.7 and 6.9 µg⋅h/mL respectively; Cmax 1.6, two transannular mainchain hydrogen bonds (Asn NH…OC Tyr, 1.5, 0.6, and 0.3 µg/mL respectively). The effect of different meal
Cys NH…OC Tyr),114 which likely reduce the 3D PSA from the treatments (fasted, mixed meal, lipid meal, protein meal, or nominal tPSA value. A crystal structure of a des-amino derivative carbohydrate meal) prior to identical oral dosing was also of oxytocin (PDB codes: 1XY1, 1XY2; CCDC code: DUPFAV) investigated (250 mg/kg p.o.; AUC0-48h 21.2 ± 5.8, 8.9 ± 2.6, 7.5 showed a hydrogen bond defining a β-turn for the YIQN motif, ± 1.8, 8.9 ± 2.8, 25.2 ± 5.1 µg⋅h/mL, respectively. Cmax 1.1 ± and a TyrNH…OC-Asn transannular hydrogen bond along with 0.3, 0.5 ± 0.17, 0.4 ± 0.13, 0.5 ± 0.2, and 1.6 ± 0.3 µg/mL, the disulfide bond bracing the structure.115Nevertheless, the oral respectively).117 Low oral absorption of 24 in humans was bioavailability of oxytocin is very low in rats (F 0.9%), requiring reported in early clincal trials (F 2-7%).119 A similar compound, it to be injected for efficacy.116 caspofungin (25), displayed poor oral absorption in rats (50 mg/kg
120 OH p.o., F < 0.2 %). Micafungin (26) is an antifungal agent approved for intravenous use by the USFDA in 2005 and in O O O H2N O N several other countries. It is a further modified echinocandin H N HN H 2 HN NH S analogue primarily used against Candida infections in HIV- O S O HN O H positive patients. It is an inhibitor of beta-1,3-D-glucan synthase, N N N H O O NH essential for fungal cell wall synthesis. It is poorly orally O 2 121,122 O absorbed. NH2
23
Figure 15. Structure of oxytocin (23). MW = 1007; miLogP = -
3.7; HBD = 16; HBA = 24; RotB = 17; tPSA = 400 Å2.
4.4. Anidulafungin, Caspofungin, Micafungin
Anidulafungin (LY303366, Eraxis, 24, Fig. 16) is a lipid- modified cyclic peptide analogue of echinocandin B.117
Pharmacokinetic parameters were measured in female Beagle R3 Their metabolic stability improved relative to somatostatin-14, R2 OH 123 R4 however, no oral bioavailability was reported. HO N OH N O HN O O H R1 HO R5 O NH O O HN HO HN O O OH N H OH N N H O NH O O O NH NH HO O HN NH2 OH H N HN 2 O R1 R2 R3 R4 R5 HN O NH O H N HN O 2 H 2 N O H H Me HO N OH H 24 O S NH S HO H O N 3 N O H NH2 O O OH
H H 25 H N HN 2 27
H2N
O O O H H SO H N N 3 Me HO N N H H 26 O H2N O O O S O NH O NH N O O H HN O N O NH OH N S H NH HN O O HN O 2 S H HN N S N O O NH NH H H Figure 16. Structures of anidulafungin (24), caspofungin (25) O O OH N N N H H O O and micafungin (26). 24: MW = 1140; miLogP = -0.8; HBD = HO H2N
14; HBA = 24; RotB = 14; tPSA = 377 Å2. 25: MW = 1093; 28 29 miLogP = -4.6; HBD = 18; HBA = 25; RotB = 23; tPSA = 412
Å2. 26: MW = 1268; miLogP = -5.3; HBD = 17; HBA = 32; RotB Figure 17. Structures of somatostatin and cyclic analogues
= 18; tPSA = 510 Å2. (27-29). Somatostatin (27): MW = 1638; miLogP = -5.4; HBD =
26; HBA = 37; RotB = 26; tPSA = 613 Å2. 28: MW = 1403; 4.5. Somatostatin, octreotide and analogues miLogP = -0.7; HBD = 18; HBA = 27; RotB = 19; tPSA = 428 Somatostatin-14 (27) is a growth hormone-inhibiting peptide Å2. 29: MW = 880; miLogP = -0.4; HBD = 11; HBA = 17; RotB resulting from cleavage of its 166 residue pre-proprotein that is = 9; tPSA = 266 Å2. differentially expressed in tissues and regulates endocrine Replacing the -Cys-Aha-Cys- motif in 29 with the simpler - function. Potential therapeutic applications of somatostatin-14 Phe-Pro- motif gave analogue 30. Compounds 27 and 30 both were quickly recognized, however its low half-life in plasma (~2 significantly reduced the effects of growth hormone following sc min) made it an unsuitable drug candidate. Many analogues (e.g. injection to rats. Somatostatin-14, 27 and 30 were administered Fig. 17) were developed to improve pharmacokinetic properties. orally to rats (25 mg/kg p.o.). Somatostatin failed to lower growth Bicyclic 28 displayed potent biological activity. Contracting this hormone levels, 27 reduced levels at 1 h but not at 2 h, while 30 cycle by removing nonessential amino acids gave 29. These reduced levels for at least 3 h . Peptide 27 was cleaved slowly by analogues, in particular 27, retained potency in vitro and in rats. trypsin at a similar rate to 29.124 To improve oral bioavailability
and other pharmacokinetic properties, thirty N-methylated 125 analogues of 30 were synthesised. Compound 30 and tri-N- bonds between side chains. The α-helical conformations methylated analogue 31 (Fig. 18) were administered orally to rats contained 2 internal and 2 side chain-side chain hydrogen bonds.
(10 mg/kg p.o.). Oral bioavailability of 30 could not be In the solid state, crystals of octreotide from aqueous oxalic acid determined, whereas 31 showed some oral absorption (F 10%). (CCDC code: YICMUS) contained two hydrogen bonds in linked
Other pharmacodynamic properties showed that 31 had an β−turns about the FwKT and wKTC motifs which, in conjunction extended elimination half-life (74 vs 15 min) and increased steady with the disulfide, produce a very rigid molecule.129 Octreotide
125 state VD (3.7 vs 0.3 L/kg) relative to 30. resisted degradation by enzymes and tissue homogenates. When
injected into rats and monkeys, octreotide showed the greatest HN HN inhibition of growth hormone, insulin and glucagon production. H N N HN NH 2 HN NH2 Furthermore, octreotide was better tolerated than somatostatin and O O O O NH O O N 126 N O O N O O had ≥ 20 times longer duration of action. Octreotide is orally O O NH NH active126,130,131 but the dose-corrected systemic oral bioavailability N N H 130 OH OH relative to subcutaneous administration is very low (F 0.3%).
31 30 O O H2N O N H2N O H Figure 18. Cyclic somatostatin analogues. Cyclic hexapeptide HN HN O S N H S HN O HN O NH S (30) and tri-N-methylated analogue (31). 30: MW = 807; H S H2N N O HN O NH N NH2 H 2 H O O O N miLogP = 0.5; HBD = 9; HBA = 15; RotB = 11; tPSA = 228 Å . HO N NH2 OH H NH O OH 31: MW = 849; miLogP = 1.3; HBD = 6; HBA = 15; RotB = 11; OH tPSA = 201 Å2. 33 32 Bauer (Sandoz Ltd) reported a series of somatostatin-14 analogues based on a disulfide cyclised hexapeptide 32 containing Figure 19. Somatostatin analogue 32 and octreotide (33). 32: an L-Phe-D-Trp-L-Lys motif (Fig. 19).126 Cyclic hexapeptide 32 MW = 784; miLogP = -1.8; HBD = 13; HBA = 16; RotB = 10;
2 was much less active than somatostatin-14 when tested in rats and tPSA = 277 Å . 33: MW = 1019; miLogP = -2.0; HBD = 15;
2 monkeys. To regain activity, D-Phe was added to the N-terminus HBA = 20; RotB = 17; tPSA = 332 Å . to mimic the natural Phe-6 and significantly improved in vivo SDZ CO 611 (Ilatreotide, 34, Fig. 20) is a D(+)-maltose N- potency. Addition of threonol to the C-terminus to mimic the terminally modified amadori derivative of octreotide 33. SDZ CO natural Thr-12 gave octreotide (33, Sandostatin®, Fig. 19). NMR 611 (34) displayed improved metabolic stability supposedly 127 128 solution structural studies of octreotide and close analogues 132 leading to enhanced oral absorption in rats (F 1.1%). in DMSO-d6 (PDB codes: 1SOC, 2SOC, 1YL8, 1YL9) showed a Intravenous infusion of somatostatin and sc injection of octreotide mixture of β−sheet and partially α-helical motifs. The β−sheet 33 suppress pancreatic and gastrointestinal hormones and like structures contained 5 internal hydrogen bonds, 2 accelerate early gastric emptying. Octreotide 33 also prolongs transannular and 1 β−turn in the macrocyclic ring and 2 hydrogen mouth to cecum transit time (MCTT). When administered orally (1 or 5 mg p.o. twice daily) to healthy males, 34 was equally of 35 has been reported in mice (LD50 ip >10 mg/kg, po >100 effective as sc 33 on suppression of preprandial hormone levels, mg/kg).138,139 The beauvericin scaffold is shared by enniatins A- early gastric emptying and prolonging MCTT. 133 C140 (Fig. 21, 36-38), where L-phenylalanine is substituted by L-
OH OH isoleucine (36), L-valine (37) or L-leucine (38), respectively. HO Several crystal structures of 37 and 38 have been reported (CCDC O HO HO OH entries DESYIJ, BICMEF, CIKJAH, ZASQOZ, QEMCAM). As O O N O H O HN O for beauvericin, there were no intramolecular hydrogen HO N H HN bonds.141,142 However, 37 did complex rubidium143 and S S 144 O HN O NH potassium ions, indicating a freely solvent accessible polar H O N OH N NH2 surface (CCDC codes: MVHIRB10, PEKFEQ). Pharmacokinetic H NH O OH data were estimated for 37 from in vitro assays.145 The OH toxicokinetic profile of enniatin B1 (39, Fig. 21) was measured in
34 piglets (0.05 mg/kg iv or p.o. in 2% EtOH/water). Compound 39
was highly orally bioavailable (F 91%) but was cleared rapidly Figure 20. SDZ CO 611 (ilatreotide, 34). MW = 1344; miLogP (t1/2 0.15 h, CL 2.00 L/h⋅kg) with low oral plasma exposure (AUC = -4.9; HBD = 21; HBA = 32; RotB = 23; tPSA = 488 Å2. 25.3 ng⋅h/mL).146 4.6. Beauvericin and enniatins
Beauvericin (35, Fig. 21) is a symmetrical cyclic hexa- O R O O N O depsipeptide consisting of three repeating units of the dipeptides N O O O O O O N-methyl-L-phenylalanine and the D-valine surrogate (R)- O N N O N N R hydroxyisovaleric acid. There are no HBD in 35 or its analogues O O O R O O 36-39, few rotatable bonds and low tPSA, but they do have RO5 O violations for MW, HBA and LogP (Fig. 21). The crystal 35 36 (R=Ile) structure of beauvericin hydrate134 from n-heptane (CCDC code: O 37 (R=Val) O BEVERC) did not showed intramolecular hydrogen bonds, N 38 (R=Leu) O O O however solvent exposure of the hydrogen bond acceptors was O N N evidenced in the solid state by complexation of barium salts O O 135 O (CCDC code: BEAVBA). Compound 35 was first isolated from B.bassiana136 and inhibited cytochrome P450 enzymes. 39 Pharmacokinetic data following oral administration at various doses to rats (0.5, 1.0, 2.0 mg/kg p.o.: Cmax 3.4, 5.4, 13.9 mg/L; Figure 21. Beauvericin (35), enniatins A (R = Ile, 36), B (R =
Tmax 4.1, 4.3, 5.4 h; CL 0.29, 0.21, 0.32 mL/min⋅kg; AUC0-∞ 29, Val, 37) and C (R = Leu, 38), and enniatin B1 (39). 35: MW =
137 784; miLogP = 6.5; HBD = 0; HBA = 12; RotB = 9; tPSA = 140 80, 103 h⋅mg/L; t1/2 2.9, 3.6, 3.0 h, respectively) but no iv data Å2. 36: MW = 682; miLogP = 6.0; HBD = 0; HBA = 12; RotB = was reported making it difficult to estimate oral absorption. LD50 9; tPSA = 140 Å2. 37: MW = 640; miLogP = 4.5; HBD = 0; HBA BOUVAR) did not show internal hydrogen bonds, but was in an
= 12; RotB = 6; tPSA = 140 Å2. 38: MW = 682; miLogP = 6.1; extended conformation induced by the oxidatively fused tyrosine
HBD = 0; HBA = 12; RotB = 9; tPSA = 140 Å2. 39: MW = 654; sidechains. This bridged constraint also introduced a cis-amide miLogP = 5.0; HBD = 0; HBA = 12; RotB = 7; tPSA = 140 Å2. bond between the two residues.149 It was isolated from
B.ternifolia150 and showed in vitro cytotoxicity against P388 4.7. Nepaduant lymphocytic leukemia and B16 melanotic melanoma cell lines. Nepaduant (40, Fig. 22) is a glycosylated, bicyclic hexapeptide Bouvardin and its acetate ester derivative 42 (Fig. 23) had LD50 tachykinin NK2 receptor antagonist. Cyclisation is achieved values of 10 mg/kg (42, ip), 229 mg/kg (41, p.o.) and 20 mg/kg through both head-to-tail and sidechain-to-sidechain linkages and (42, iv) in mice, indicating that 41 is orally absorbed. These an aminohexose is attached to an asparagine side chain. The compounds have few hydrogen bond donors and few rotatable aminohexose moiety gives the structure amphiphilic character. bonds, but they have high polar surface areas and low LogP. Compound 40 was given orally to mice (38 mg/kg p.o. in castor O OH oil; Tmax 2.7 ± 0.7 h, Cmax 1401 ± 220 nM, t1/2 11.7 ± 0.9 h, AUC
147 8463 ± 2635 nmol⋅h/mL, F 5%). Pediatric phase 1 clinical RO studies confirmed oral activity in infants by determining the N concentration of 40 in urine 24 h post oral dosage.148 N O O O NH O HN O O O O O H N N NH NH HN H N O O NH 41 (R = H) O H 42 (R = Ac) HN N N H O O O O NH HO O Figure 23. Bouvardin (41) and acetate ester derivative 42. 41: HO N H OH MW = 773; miLogP = 0.5; HBD = 5; HBA = 16; RotB = 3; tPSA
= 207 Å2. 42: MW = 815; miLogP = 1.3; HBD = 4; HBA = 17; 40 RotB = 5; tPSA = 213 Å2. Figure 22. Nepaduant (40). MW = 947; miLogP = -1.6; HBD = 4.9. Pristinamycin and related antibiotics 11; HBA = 22; RotB = 11; tPSA = 348 Å2. Pristinamycin is an oral antibiotic consisting of two synergistic, 4.8. Bouvardin but structurally unrelated, components. Separately, the Bouvardin (41, Fig. 23) is a cyclic hexapeptide containing three compounds exhibit bacteriostatic activity, while the combination N-methyl amides, one O-methylated tyrosine, one D-Ala and an of Pristinamycin IA (43) and IIA (44, Figure 24) have bactericidal additional diphenylether-bridge between two tyrosine side chains. activity. 43 has one L-Pro, one N-methylated amide, a D-Abu, and The crystal structure of 41 from methanol/water (CCDC code: a 4-oxopiperidine incorporated into its backbone. 44 bears a hybrid terpenoid/peptide backbone rigidified by three alkenyl HO bonds, a 4,5-dehydroproline and an oxazole ring. A study in an O N O O Australian hospital investigated the effectiveness of oral NH O 151 NH N Pristinamycin in patients with various bacterial infections. O O Patients were dosed orally with 500-1000 mg of 43 and 44 on N O O HN O O O NH O N multiple days. Of 46 patients, five were excluded due to side O N effects, 10 were cured from infection and 21 had infections N F OH suppressed. N N O
HO 46 45 O N O NH O Figure 25. The antibacterial drug, NXL103 consisting of NH O O HO N linopristin (45) and floprestin (46). 45: MW = 950; miLogP = N O O O N O O NH 2 O O 1.6; HBD = 4; HBA = 19; RotB = 9; tPSA = 223 Å . 46: MW = N NH O N 532; miLogP = 1.5; HBD = 2; HBA = 9; RotB = 1; tPSA = 122 O O Å2. N 43 44
4.10. 1-NMe3 and related cyclic hexapeptides
Figure 24. The antibacterial combination drug, Pristinamycin To permeate through membranes, molecules must transition consisting of pristinamycins IA (43) and IIA (44). 43: MW = from aqueous to hydrophobic and back to aqueous phases. 867; miLogP = 0.7; HBD = 4; HBA = 18; RotB = 7; tPSA = 228 Conformational changes might facilitate this process by lowering Å2. 44: MW = 526; miLogP = 0.7; HBD = 2; HBA = 10; RotB = desolvation energies. To test this idea, molecular modelling, H-D 1; tPSA = 139 Å2. exchange experiments and permeability measurements were
NXL103 (XRP2868) (Fig. 25) is also an antibiotic cocktail combined to produce passively permeable cyclic hexapeptide
153 made of linopristin 45 and floprestin 46 (30:70 mixture). These diastereomers from cyclo-[Leu-Leu-Leu-Leu-Pro-Tyr] (Fig. compounds replace three hydrogen bond donor NHs with 5 or 6 26). None of the diasteromers had N-methyl groups, however one membered rings and a depsipeptide ester, 45 also has an N-methyl compound, cyclo[Leu-D-Leu-Leu-Leu-D-Pro-Tyr], showed a group. Pharmacokinetic parameters were measured after oral conformational change between CDCl3 and water by molecular administration at multiple doses to cyclophosphamide-induced modelling. This diastereomer was the least permeable in the initial neutropenic mice infected with strains of S. pneumoniae series154 even though higher permeability had previously been
154 (NXL103: 10 mg/kg p.o.: Cmax 0.32 mg/L; 40 mg/kg p.o.: Cmax reported for the same peptide. In further studies, tri-N-
0.8 mg/L, t1/2 21 min; 80 mg/kg p.o.: Cmax 4 mg/L, t1/2 55 min, methylation yielded 1-NMe3 47 which had good PAMPA
AUC0-24h 4.5 mg⋅h/kg; 160 mg/kg p.o.: Cmax 10.4 mg/L, t1/2 76.2 permeability and oral bioavailability in rats (1 mg/kg iv: CL 4.5
152 min, AUC0-24h 11.34 mg⋅h/kg). mL/min⋅kg, VD 1.1 L/kg; 10mg/kg p.o.: AUC 10.5 ng⋅h/mL, Cmax
852 ng/mL, F 28%).155 Analogues of 47 varied a single side chain substitution to learn effects on pharmacokinetic profiles.156 An N- Å2. 48: MW = 729; miLogP = 1.8; HBD = 4; HBA = 14; RotB = methyl-leucine was substituted for N-methyl-serine (48), N- 9; tPSA = 180 Å2. 49: MW = 743; miLogP = 2.1; HBD = 4; HBA methyl-threonine (49), N-methyl-aspartate (50) or N-methyl-lysine = 14; RotB = 9; tPSA = 180 Å2. 50: MW = 757; miLogP = 1.9;
(51). Their pharmacokinetic profiles revealed that increasing side HBD = 4; HBA = 15; RotB = 10; tPSA = 197 Å2. 51: MW = 770; chain polarity reduced oral absorption. Interestingly, threonine miLogP = 2.3; HBD = 5; HBA = 14; RotB = 12; tPSA = 186 Å2. analogue 49 (1 mg/kg iv: CL 63.6 mL/min⋅kg, VD 3.8 L/kg, t1/2 Dotted lines indicate hydrogen bonds observed in crystal structure
1.0 h; 10 mg/kg p.o.: AUC 201 ng⋅h/mL, Cmax 105 ng/mL, F 24%) of 47, and NMR solution structures of analogues. displayed similar pharmacokinetics as 47, while serine analogue The same orally bioavailable scaffold (47) inspired further
48 had low oral absorption (1 mg/ kg iv: CL 60.4 mL/min⋅kg, VD investigations to better understand and improve passive
4.3 L/kg, t1/2 1.5 h; 10 mg/kg p.o.: AUC 42.3 ng⋅h/mL, Cmax 9.86 permeability of cyclic hexapeptides. N-methylamino acid-to- ng/mL, F 2%). Aspartate analogue 50 (1 mg/kg iv: CL 56.4 peptoid substitutions were explored in cyclic hexapeptide/peptoid ml/min⋅kg, VD 0.36 L/kg, t1/2 0.4 h; 10 mg/kg p.o.: AUC 18.7 hybrids,(Fig. 27). Peptoid substitutions that replaced one (52) or ng⋅h/mL, Cmax 17.3 ng/mL, F < 1%) and lysine analogue 51 (1 two (53) of the three N-methyl amides facilitated permeability
across a monolayer of low efflux epithelial MDCK cells. mg/kg iv: CL 10.4 ml/min⋅kg, VD 0.9 L/kg, t1/2 1.0 h; 10 mg/kg
Interestingly, replacing all three N-methyl moieties with peptoid p.o.: AUC 18.1 ng⋅h/mL, Cmax 18.3 ng/mL, F < 1%) had units (54) generated a macrocycle that was less permeable.157 negligible oral bioavailability (F < 1%). NMR structural studies of
153-155 this series of peptides in CDCl3 and DMSO-d6 suggested OH that the pattern of internal hydrogen bonds was strongly HO O O conserved in this class of molecules. N N N N H N H O O OH N O O O O N O O N H H N N N N O O O N N 52 53 N H O O
O O N H N N R HO O O O N N N N H H N O O N OH O O O O N O O OH N H H N N N N 47 (R = Leu) 50 (R = Asp) O O 48 (R = Ser) 51 (R = Lys) 49 (R = Thr) 54 55
Figure 26. 1-NMe3 (47) and derivatives (48-51). 47: MW = Figure 27. Peptoid substituted analogues 52-54 and β-
755; miLogP = 4.1; HBD = 3; HBA = 13; RotB = 10; tPSA = 160 hydroxy-γ-amino acid analogue 55. 52: MW = 741; miLogP = 2 3.5; HBD = 3; HBA = 13; RotB = 10; tPSA = 160 Å ; 53: MW = h, AUCiv 292 nM⋅h; 10 µM/kg p.o.: AUCpo 5.7 nM⋅h, Cmax 2.9
727; miLogP = 3.6; HBD = 3; HBA = 13; RotB = 10; tPSA = 160 nM, Tmax 0.6 h, F 2%) and 47 (3 µM/kg iv: CL 1 mL/min⋅kg, VD
Å2 54: MW = 713; miLogP = 3.6; HBD = 3; HBA = 13; RotB = 0.4 L/kg, t1/2 22 h, AUCiv 29618 nM⋅h; 10 µM/kg p.o.: AUC 8967 10; tPSA = 160 Å2 55: MW = 793; miLogP = 3.6; HBD = 4; HBA nM⋅h, Cmax 534 nM, Tmax 3.8 h, F 30%). These striking results = 14; RotB = 10; tPSA = 180 Å2. Dotted lines indicate conserved highlight good oral absorption for 47 in rodents. hydrogen bonds observed by NMR spectroscopy. Cyclic hexapeptides based on 47 were examined with shuffled
β-hydroxy-γ-amino acids are naturally occurring N-methyl amino acids and inverted stereochemistries. Correlations peptidomimetic surrogates that structurally resemble a peptide between amide NH NMR temperature coefficients, Caco2 and backbone by replacing heteroatoms with carbon to minimize PAMPA permeability yielded cyclic hexapeptide 57 (Fig. 28). polarity. These substructures may have evolved to allow Compared to 47, 57 had one less N-methyl group and a modified molecules to enter cells and interact with intracellular targets. β- N-methylation pattern but was still orally bioavailable in rats (1 hydroxy-γ-amino acids were used to create cyclic hexapeptides mg/kg iv: CL 55 mL/min⋅kg, VD 1.1 L/kg, t1/2 29 min; 10 mg/kg based on 47. Oral bioavailability in rats was reported for one 141 p.o.: AUC 1003 ng⋅h/mL, Cmax 117 ng/mL, F 33%). compound, 55, displaying promising passive permeability (1 OH OH mg/kg iv: CL 10 mL/min⋅kg, VD 1.1 L/kg, t1/2 1.6 h; 5 mg/kg p.o.;
158 O O AUC 1697 ng⋅h/mL, Cmax 324 ng/mL, F 21%). Although good H N N N N permeability was maintained in the less peptidic 55, its oral NH H O O NH O O O O NH O O NH bioavailability and plasma concentration (AUC) were worse than H H N N N N for 47.. Interestingly, NMR evidence suggested that, despite O O variability in the membrane permeability of some peptoid and statin-type analogues of 47, these compounds still retained the 56 57 two internal hydrogen bonds shown in Figure 27.157,158
Other groups have used 47 and analogues to investigate effects Figure 28. Non-N-methylated analogue 56 and bis-N- of N-methylation,159 correlating amide NH NMR temperature methylated analogue 57 with a different N-methylation coefficients with cell permeability160 and flexibility/rigidity.161 A pattern to 47 retained oral bioavailability. 56: MW = 713; crystal structure of 47 (CCDC code: AHELEG) indicated a miLogP = 3.3; HBD = 6; HBA = 13; RotB = 10; tPSA = 186 Å2. saddle-like structure incorporating two β-turns at either end, with 57: MW = 741; miLogP = 3.8; HBD = 4; HBA = 13; RotB = 10;
2 one close hydrogen bond each (2.0, 2.5Å, indicated by dotted tPSA = 168 Å . Dotted lines indicate conserved hydrogen bonds lines, Fig. 26).159 Novartis researchers compared the original observed by NMR spectroscopy. scaffold of 47 with its non-N-methylated counterpart (56, Fig. 28). Peptide 47 was thought to be orally bioavailable due to and showed that N-methylation was important for oral absorption. cyclosporin-like conformational flexibility; however, it showed no
Permeability enhancers did not improve oral bioavailability of 47. conformational difference in polar versus non-polar solvents.161
Pharmacokinetics were measured in mice for non-N-methylated Several analogues of 47 were synthesized and their analogue 56 (3 µM/kg iv: CL 82 mL/min⋅kg, VD 0.8 L⋅kg, t1/2 0.2 pharmacokinetic properties characterized to investigate conformational flexibility versus rigidity. The structure of 47 was 4.11. Cyclo-[Arg-Arg-Arg-Arg-NaphthylAla-Phe] rigidified by introducing a proline (58, Fig. 29), or relaxed by Cell penetrating peptides (CPPs) are a small group of short, introducing N-methylleucine (59, Fig. 29). Both cyclic natural and synthetic, peptides that are often arginine rich, hexapeptides 58 (1 mg/kg iv: CL 11 mL/min⋅kg, t 58 min; 10 1/2 positively charged, amphiphilic and able to cross cell membranes. mg/kg p.o.: AUC 4320 ng⋅h/mL, Cmax 879 ng/mL, F 30%) and 59 How they cross membranes is still not fully resolved but
(1 mg/kg iv: CL 10 mL/min⋅kg, t1/2 121 min; 10 mg/kg p.o.: AUC mechanisms include endocytosis and direct translocation across
162-164 3713 ng⋅h/mL, Cmax 768 ng⋅mL, F 18%) were appreciably orally the membrane. A series of arginine-rich, cell-penetrating, bioavailable in rats.161 For these compounds (59, 47, 58) with cyclic hexapeptides were synthesized and their cellular uptake identical HBD, HBA, tPSA (Fig. 29), reducing the MW (785 > was measured. One analogue, cyclic hexapeptide 60 (Fig. 30),
755 > 725), the number of rotatable bonds (12 > 10 > 8), and the was orally administered to mice and pharmacokinetic parameters
2 hydrophilic surface area (FISA 127.5 > 122.5 > 110.4 Å ) all were measured (1.5 mg/kg iv: Cmax 12174 nmol/L, t1/2 1.02 h, CL
155 improved oral bioavailability (F% 18 ~ 16 (28 ) < 30, under the 0.08 mL/min, VD 7.51 mL; 40 mg/kg p.o.: Cmax 3156 nmol/L, same conditions161). These changes had little effect on the overall AUC 6357 nmol/L, F 4 %) showing it had some oral structure of the macrocycle, as shown by NMR spectroscopy in bioavailability.165
CDCl3 and DMSO-d6, with two rigidifying anti-parallel β-sheets HN NH2 NH connected by type 1 β-turns at each end (dotted lines, Figure 29). NH
NH O N NH2 H O H2N NH N H OH OH NH HN O
O NH HN H O O N O N N H N N H N N O H 2 N O O N H O O NH O O N O O N H H N N N N O O 60
Figure 30. Cyclic cell-penetrating hexapeptide (60). MW =
58 59 969; miLogP = -2.9; HBD = 22; HBA = 24; RotB = 24; tPSA =
422 Å2. Figure 29. Derivatives of 47 with increased (58, left) or decreased (59, right) rigidity. 58: MW = 725; miLogP = 2.8; 4.12. Kahalalide F
HBD = 3; HBA = 13; RotB = 8; tPSA = 160 Å2. 59: MW = 785; Kahalalide F (61, Fig. 31) is the largest depsipeptide in the miLogP = 5.3; HBD = 3; HBA = 13; RotB = 12; tPSA = 160 Å2. family of kahalalides (A-F) and was isolated from the sacoglossan Dotted lines indicate conserved hydrogen bonds observed by mollusk E.rufescens and the green alga Bryopsis.166 61 induced NMR spectroscopy. oncosis in human prostate and breast cancer cells.167
Pharmacokinetic parameters were measured in Phase I clinical
168 trials (iv: t1/2 0.47 h, CL 11.0 L/h, VD 7.0 L). Kahalalide F had LD50 of 300, 980 and 3200 mg/kg p.o. in mouse, rat and rabbit ng/mL, Tmax 240 min, AUC 2647 ng⋅h/mL, F 21 ± 2%). When an respectively, suggesting very low oral absorption. Preclinical N-methyl group was removed, (danamide F, 64, Fig. 32) even
169 toxicity studies determined LD50 in rats at 0.38 – 0.60 mg/kg iv. better oral bioavailability was obtained (1 mg/kg iv in DMSO: CL
23.0 mL/min kg, t1/2 97 min; 10 mg/kg p.o. in olive oil: Cmax 726 H OH N ng/mL, T 240 min, AUC 3372 ng⋅h/mL, F 51 ± 9 %). This O max H H NH HN O N N O O N NH2 O result highlighted the point that N-methylation of solvent H O O O NH O NH O accessible amides does not necessarily always improve oral O O O H HN N N bioavailability.172 N N H H O O
61 R1 R2 O N N O H Figure 31. Kahalalide F (61). MW = 1492; miLogP = 3.0; HBD N O N S = 15; HBA = 30; RotB = 34; tPSA = 442 Å2. H N O O HN 5. CYCLIC HEPTAPEPTIDES N O
5.1. Sanguinamide A and danamides
62 (R1 = H, R2 =Me) Sanguinamide A (62, Fig. 32) is a thiazole-containing cyclic 63 (R1 = Me, R2 = tBu) heptapeptide isolated from H. sanguineus.170 It has six natural 64 (R1 = H, R2 = tBu) amino acids including two prolines that adopt a cis, trans
171 configuration and an isoleucine-derived thiazole. No biological activity is known for sanguinamide A, but it is orally bioavailable in rats (1 mg/kg iv in DMSO: t1/2 23 min, CL 70 mL/min; 10 Figure 32. Sanguinamide A 62 (R1 = H, R2 = Me), danamide D
171 mg/kg p.o.: Tmax 60 min, Cmax 40 nM, F 7 ± 4%). The three 63 (R1 = Me, R2 = tBu), danamide F 64 (R1 = H, R2 = tBu). 62: dimensional structure helped rationalize the pharmacokinetic MW = 722; miLogP = 2.0; HBD = 4; HBA = 13; RotB = 6; tPSA profile of 62. Amide protons formed intramolecular hydrogen = 170 Å2. 63: MW = 778; miLogP = 3.6; HBD = 3; HBA = 13; bonds and were shielded from solvent by bulky side chains, while RotB = 7; tPSA = 161 Å2. 64: MW = 764; miLogP = 3.3; HBD = two prolines and thiazole removed 3 amide NH protons, lowering 4; HBA = 13; RotB = 7; tPSA = 170 Å2. Dotted lines represent the HBD count. NMR studies on analogues of 62 examined H-D hydrogen bonds as determined by NMR spectroscopy.171 exchange rates and amide temperature coefficients and
determined NMR solution structures in d6-DMSO. These data 5.2. Rhizonin A guided introduction of the bulky tert-butylglycine to minimize Rhizonin A (65, Fig. 33) is cyclo-[N(Me)Ala-N(Me)D-Ala(fur- solvent exposed polarity, resulting in danamide D (63, Fig. 32) 3-yl)-D-aIle-D-Val-Val-N(Me)Ala(fur-3-yl)-Leu]. It was isolated that was orally bioavailable (1 mg/kg iv in DMSO: CL 12.5 from fungi R.microspores, a known infection in fruits, vegetables mL/min⋅kg, t1/2 65 min; 10 mg/kg p.o. in olive oil: Cmax 352 176 and malt products. This cyclic heptapeptide consists of L- and D- observed in mice, although the oral toxic dose (LD50 11 mg/kg amino acids, three N-methyl amides and two (2-furyl)-alanines in p.o.) is ~170 fold lower than the lethal dose (LD100 65 mg/kg ip). both (R)- and (S)-configurations.173 In crystals of 65 grown from Distribution studies in mice177 indicated uptake from the small ethyl acetate/hexane, the four bulky side chains including three β- intestine with concentration in the liver, lung and heart. branched residues were at the wide end of the ovoid macrocycle. H HN N O OH The other end showed a transannular hydrogen bond between the O NH2 O IleNH and D-(furylalanine)-carbonyl oxygen.173 Rhizonin A 65 N NH H O NH was given orally to male albino rats (70, 96, 131 or 180 mg/kg O O O NH p.o.) to determine the oral LD50. The lowest dose exceeded LD100 O HO NH as all rats died within 10 days.174 There was no data for i.v. N H N administration, so oral bioavailability could not be quantified. O O
66 N NH O O Figure 34. Microcystin-LR (66). MW = 995; miLogP = -3.5; O N O O 2 O O N HBD = 12; HBA = 22; RotB = 16; tPSA = 341 Å . O NH H N N 5.4. YM254890 H O YM254890 (67, Fig. 35) is a specific Gαq/11 inhibitor produced
by an isolate of the chromobacterium sp. QS3666. The structure is 65 a depsipeptide with 2 ester linkages and a D-phenylalanine Figure 33. Rhizonin A (65). MW = 812; miLogP = 2.6; HBD = derivative. Gαq/11, a G protein implicated in purine nucleotide- 2 4; HBA = 16; RotB = 10; tPSA = 204 Å . Dotted line represents induced platelet aggregation, was inhibited by 67 by targeting the hydrogen bond observed in crystal structure. transformation of GDP to GTP. In rats, 67 inhibited ex vivo
5.3. Microcystin LR platelet aggregation and in vitro thrombus formation, suggesting it may be a clue to a new anti-thrombotic agent. It has been used Microcystin-LR (66, Fig. 34) from M.aeruginosa is one of the orally to treat mice with acute thrombosis and chronic neointima most toxic of over 80 microcystins produced by cyanobacteria in formation after induced vascular injury. Internal bleeding in mice aquatic environments. Its amino acid sequence is: D-alanine, L- was also effectively treated with 67 at 0.03 mg/kg iv or 1 mg/kg leucine, D-methylaspartic acid, variable L-amino acid, a 3-amino- p.o., indicating an oral absorption < 3%.178 9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid
(Adda), D-glutamic acid, N-methyldehydroalanine. The extensively modified cyclic peptide is highly water soluble and a persistent contaminant that bioaccumulates in fish and displays effects on their liver, gastrointestinal tract and kidney.175 Acute hepatotoxic effects especially apoptotic hepatocyte death were treatment with polymyxin B mixture could not neutralize O HN O lipooligosaccharide-induced immune cell activity in mice. O O N However, modulation of this response was observed by oral O O O O O administration in drinking water (29.5 mg/L p.o. suspension in O NH NH O N O O water).180 Human patients with liver disease have been treated H N N HO with enteric coated oral polymyxin B. Plasma endotoxin and O ammonia levels were reduced, even though polymyxin B itself
could not be detected above 0.5 units/mL.181 67 OH Figure 35. YM254890 (67). MW = 960; miLogP = -0.2; HBD = O NH2 NH2 5; HBA = 22; RotB = 13; tPSA = 288 Å2. O NH HN O H H H2N NH H N N N 5.5 CHEC-7 2 N NH H O O HN O O HO O CHEC refers to a series of peptides of various sizes derived O O NH O from the natural survival anti-inflammatory protein Dermicidin. HN H2N N R H CHEC-7 (68, Fig. 36) reduced the incidence of experimental R = H 69 autoimmune encephalomyelitis in a disease model when R = Me 70 administered to rats (1.5 mg/kg p.o. or 0.1 mg/kg/day sc).179
Figure 37. Polymyxin B (69) and B (70). 69: MW = 1189; N 1 2 NH O miLogP = -5.6; HBD = 23; HBA = 29; RotB = 28; tPSA = 491 O OH H N 2 S N Å . 70: MW = 1203; miLogP = -5.5; HBD = 23; HBA = 29; RotB H S NH O 2 HN O = 29; tPSA = 160 Å2. H N O O O HO NH 5.7 Bacitracin A O N H H2N Bacitracin A (71, Fig. 38) is a cyclic thiazoline-containing O peptide from a family of cyclic peptides isolated from the “Tracy 68 I" strain of B. subtilis. Bacitracins are an intriguing group of non-
ribosomal peptides containing a sequence of alternating L- and D-
amino acids. Bacitracin A was compared to vancomycin for
Figure 36. CHEC7 (68). MW = 759; miLogP = -5.6; HBD = 3; treating antibiotic-associated diarrhoea. Plasma and urine
2 HBA = 21; RotB = 9; tPSA = 347 Å . concentrations were measured to quantify unwanted systemic
absorption. 71 was found in plasma at low non-toxic 5.6 Polymyxin B1 and B2 concentrations after oral administration.182 Another study in Polymyxin B (Fig. 37) is a mixture of two natural product which 71 was administered orally to dogs found significant levels cyclic peptides, polymyxin B1 69 and B2 70, containing multiple in blood and urine, confirming absorption from the intestinal unusual diaminobutyric acids and a D-Phe residue. Prolonged tract.183 Bacitracin A has been investigated for the treatment of vancomycin-resistant E.faecium in humans. In combination with different crystal forms have been reported from methanol.192 With doxycycline, 71 was not efficacious beyond the 2-week interval no possibility of forming transannular hydrogen bonds, the during which they were given.184 71 has oral toxicity in mice carbonyl groups are directed above and below the plane of the
185 (LD50 >3750 mg/kg p.o.). macrocycle and are highly solvent exposed, one D-lactate
OH sidechain occupying the interior (CCDC code: DOMZOW). O HN O N Compound 73 was orally active against nematodes and orally
H N 2 NH HN bioavailable (F 47-54%). It had a long elimination half-life NH 189,190 NH O O following intravenous administration to rats (t 39-51 h) . A 2 O NH O 1/2 O OH HN O S phase I clinical trial investigating oral dosing of 73 in normal N O O O HN healthy male volunteers is ongoing. 193 H H HN N N N N O H H O O NH2 O O
O O N O N R O 71 O N O R Figure 38. Bacitracin A (71). MW =1437; miLogP = -1.8; HBD N O O 2 = 20; HBA = 33; RotB = 32; tPSA = 531 Å . O O
6 CYCLIC OCTAPEPTIDES
72 (R = H); 73 (R = morpholino) 6.1 PF1022A and emodepside
PF1022A (72, Fig. 39) is a cyclic octapeptide natural product Figure 39. PF1022A (72) and emodepside (73). 72: MW = 949;
2 with anthelmintic activity first isolated in 1992 from the fungus miLogP = 7.9; HBD = 0; HBA = 16; RotB = 12; tPSA = 186 Å .
M.sterilia. It contains four N-methyl-L-leucine residues 73: MW =1119; miLogP=7.8; HBD = 0; HBA = 20; RotB = 14;
2 alternating with D-lactic acid or D-phenyllactic acid. PF1022A tPSA = 211 Å .
(72) was orally active (0.5-2.0 mg/kg p.o.) and effective against 6.2 WH1 fungin A.galli nematode (ring worm) infections in chickens (0.5-2.0 WH1 fungin (74, Fig. 40) is a surfactin type lipo-depsipeptide mg/kg p.o.)186 and nematode infections in rats (5 or 10 mg/kg extracted from B.amyloliquefaciens WH1. As an p.o.),187 sheep (1 mg/kg p.o.),188 and other species.189,190 These immunoadjuvant, 74 was orally active in mice (0.2 mg) and data gave no insights into intestinal absorption of 72 following enhanced the immune response to co-administered protein oral dosing, since the nematodes inhabited the gut of the test antigens (chicken ovalbumin or glutathione S-transferase).194 74 animals. Further work on analogs of 72 in chickens suggested that was also shown to reduce blood glucose and increase serum certain functional groups, lipophilicity, and PSA influenced insulin in non-obese diabetic mice following oral administration anthelmintic activity in vivo.191 at two doses (5 or 25 mg/kg p.o. in 100 µL PBS). 195 Emodepside (BY 44-4400, 73, Fig. 39), a dimorpholine derivative of 72 and has been approved for use in animals. Four available, simple OMe and sulfone analogues (CCDC entries OH O O O CAZFIS, CAZFIS10, CAZFOY, CAZFOY10) show broadly O NH HN O N similar structures to the protein bound forms above, with two beta H O HN NH turns, one transannular hydrogen bond is lost in the free OH O O HN O H form.203,204 Interestingly, it appears that that the toxicity of the N C14H29 O O amanitins can be modulated by the degree and stereochemistry of
oxidation at the bridging sulfur, with the sulfone analogues being 74 the most toxic, whilst retaining nearly all structural features of the
peptidic backbone. α-Amanitin causes severe liver damage and in Figure 40. WH1-fungin (74). MW = 1064; miLogP = 8.0; HBD some cases death (50-100 fatalities per year in Europe) through = 9; HBA = 20; RotB = 27; tPSA = 345 Å2. acute liver failure.205 75 is orally active only in certain species.
6.3 α-Amanitin The lethal oral dose in humans has been estimated at 0.1 mg/kg
from accidental deaths. In guinea pigs, identical toxicity following The poisonous mushrooms of the Amanita genus contain a oral, intravenous and intraperitoneal administration (LD 0.1 number of related constrained cyclic peptides of MW 770-920. 50 mg/kg) indicated good intestinal absorption. By contrast, toxicity These are toxic by ingestion and include the phallotoxins, in mice (LD 0.4-0.8 mg/kg iv) and rats (LD 3.5-4.0 mg/kg iv) amatoxins and virotoxins.196,197 Some of these toxins are heat 50 50 is only observed following iv administration. Cats and dogs stable and are not destroyed by cooking. Phallotoxins from A. absorb amatoxins following oral administration, but the phalloides are bicyclic heptapeptides, amatoxins (A. phalloides) absorption rate is slow. In dogs, the toxic oral dose is five times are bicyclic octapeptides, and virotoxins (A. virosa) are higher than the toxic intravenous (LD 0.5 mg/kg p.o. vs. 0.1 monocyclic heptapeptides.198 Despite extensive non-natural 50 mg/kg iv). In cats, the toxic oral dose was more than ten times modifications (e.g. leucine, proline hydroxylation, D- higher than the toxic intravenous dose.206 configuration, thia-crosslink) these are ribosomally generated peptides.199 A systematic examination of their oral absorption has OH not been carried out but they display high toxicity by ingestion.
NH α-Amanitin (75, Figure 41) is a member of the group of OH O H HO N poisonous peptides called amatoxins; all L-configured bicyclic HN NH O O octapeptides found in Amanita species of mushrooms. Amatoxins O O NH O S HN contain an oxidised tryptathionine linkage in addition to backbone O H N N N O H cyclisation. Multiple crystal structures (PDB codes: 1K83, O O 2VUM, 3CQZ)200-202 of α-amanitin (75) bound to RNA NH2 polymerase II showed, in addition to six hydrogen bonding 75 interactions to the enzyme, two transannular hydrogen bonds and two more describing beta turns within the α-amanitin framework. Figure 41. α-Amanitin (75). MW = 889; miLogP = -4.1; HBD =
Although native unbound α-amanitin crystal structures are not 13; HBA = 23; RotB = 7; tPSA = 361 Å2. 6.4 Griselimycin and synthetic derivatives O Griselimycin (76, Figure 42) is a macrocyclic poly-N- N N N N methylated depsipeptide isolated from Streptomyces bacteria H O O O O O NH cultures.207 Griselimycin derivatives exhibit antibiotic activity, N O O O NH oral bioavailability, metabolic stability and antitubercular N O O activity.208,209 Griselimycin has impressive pharmacokinetics for N N O its chemical class and size (3 mg/kg iv: CL 40 mL/min⋅kg, VD 1.2
R2 L/kg, t1/2 120 min; 30 mg/kg po: AUC 5100 ng⋅h/mL, Cmax 3900 R1 ng/mL, F 48%).208 Pharmacokinetics were improved by simple 76 (R = H, R = H) structural modifications. Griselimycin contains an N-methyl-D- 1 2
77 (R1 = Me, R2 = H) leucine, one proline and two 4-methylproline residues. Modification of the 4-position of proline gave methyl- 78 (R1 = Me, R2 = Me) 79 (R = F, R = H) griselimycin 77 (3 mg/kg iv: CL 35 mL/min⋅kg, VD 1.6 L/kg, t1/2 1 2
80 (R1 = Chx, R2 = H) 144 min; 30 mg/kg p.o.: AUC 6600 ng⋅h/mL, Cmax 2820 ng/mL, F
47%), dimethyl-griselimycin 78 (3 mg/kg iv: t1/2 132 min; 30 mg/kg p.o.: AUC 17000 ng⋅h/mL, Cmax 4570 ng/mL, F 59%); (S)- fluoro-griselimycin 79 (3 mg/kg iv: t1/2 120 min; 30 mg/kg p.o.: Figure 42. Natural product griselimycin (76, R1 = R2 = H) and
AUC 5100 ng⋅h/mL, Cmax 1490 ng/mL, F 55%) and cyclohexyl- synthetic derivatives: methyl-griselimycin (77, R1 = Me, R2 =
H), dimethyl-griselimycin (78, R1 = R2 = Me), (S)-fluoro- griselimycin 80 (3 mg/kg iv: CL 18.3 mL/min⋅kg, VD 5.5 L/kg,
griselimycin (79, R1 = F, R2 = H), and cyclohexyl-griselimycin t1/2 258 min; 30 mg/kg p.o.: AUC 23000 ng⋅h/mL, Cmax 2620 (80, R = cyclohexyl, R = H). 76: MW = 1113; miLogP = 4.3; ng/mL, F 89%); all apparently with improved oral bioavailability 1 2 HBD = 3; HBA = 22; RotB = 12; tPSA = 256 Å2. 77: MW = and pharmacokinetic properties.208 Griselimycin and the 1127; miLogP = 5.6; HBD = 3; HBA = 22; RotB = 12; tPSA = cyclohexyl analogue 80 have each been crystallised in complex 256 Å2. 78: MW = 1142; miLogP = 5.1; HBD = 3; HBA = 22; with the sliding clamp of Mycobacterium tuberculosis (PDB code: RotB = 12; tPSA = 256 Å2. 79: MW = 1131; miLogP = 4.3; HBD 5AH2, 5AGU, 5AH4, 5AGV).208 The bound griselimycins = 3; HBA = 22; RotB = 12; tPSA = 256 Å2. 80: MW = 1196; showed 2 internal hydrogen bonds, one γ−turn from the Leu CO miLogP = 7.5; HBD = 3; HBA = 22; RotB = 13; tPSA = 256 Å2. preceding MePro to the Leu NH after it, one transannular hydrogen bond between the Gly NH and the N-Me-Leu carbonyl 6.5 Dihydromycoplanecin and mycoplanecin group, and one transannular hydrogen bond between the GlyNH Dihydromycoplanecin A (81, Fig. 43) was discovered as an and the N-Me-Leu carbonyl group. active metabolite in the urine of dogs and mice treated with the
antibiotic mycoplanecin A (82, Fig. 43). Both 81 and 82 are
cyclised through a depsipeptide linkage between the C-terminus
and a threonine residue. Further modifications include four N- methylated amides, 4-methyl and 4-ethylsubstituted prolines, L- administration to rats (1 mg/kg p.o. in gelatin solution) it was homoleucine and α-hydroxy (81) or α-ketobutanoyl (82) N- found in cytosolic fractions of the frontal cortex tissues . This terminal caps. No oral pharmacokinetic data has been reported for indicated both oral absorption from the gut and blood-brain-
210 212 82, but oral toxicity has been reported (LD50 > 3 g/kg p.o.). barrier penetration, despite violating all RO5 and like
Pharmacokinetic parameters for 81 have been measured in mice parameters (Fig.44).
(t1/2 0.5 h; 50 mg/kg p.o.: Cmax 10 µg/mL at 2 and 4 h) and dogs HN O N O OH (t1/2 5.5 h; 25 mg/kg p.o.: Cmax 9 µg/mL at 3 h; 12.5 mg/kg p.o.: H H N N 2 N Cmax 5 µg/mL at 3 h). Quantification of 81 from urine led to H O O S O N 211 H estimates of F 21% in mice and 22-25% in dogs. S HN OH H HO N NH H O O N O N O O H N N O N N H O O NH2 O O O O NH N 83 O O O NH R N O Figure 44. CHEC-9 (83). MW = 917; miLogP = -6.0; HBD = 16; O N HBA = 26; RotB = 10; tPSA = 425 Å2. N O 7.2 AFPep
81 (R = -CH(OH)-C2H5 AFPep (84, Fig. 45) is a cyclic analogue of the 472-479 82 (R = -COC2H5) fragment from alpha-fetoprotein (AFP). AFP inhibits estrogen-
stimulated growth of immature mouse uterus and estrogen-
dependent proliferation of human breast cancer cells.213 The linear Figure 43. Dihydromycoplanecin (81) and mycoplanecin (82). peptide fragment has a bench life of a few weeks and an 81: MW = 1186; miLogP = 5.2; HBD = 4; HBA = 23; RotB = 16; undesirable biphasic dose-response curve. Cyclization, tPSA = 276 Å2. 82: MW = 1184; miLogP = 5.0; HBD = 3; HBA = substitution of proline for hydroxyproline, and addition of 23; RotB = 16; tPSA = 273 Å2. asparagine to the C-terminus gave AFPep (84).214 AFPep was
orally active and arrested growth of human tumor xenografts in
mice (10 µg/mouse p.o.). It also decreased the incidence and
7 CYCLIC NONA- & DECA-PEPTIDES multiplicity of breast cancers in carcinogen-exposed rats (100
µg/rat p.o.). In these animal models, AFPep had similar effects when administered via oral, ip or sc routes.215,216 7.1 CHEC-9
Disulfide-cyclised nonapeptide CHEC-9 (83, Fig. 44) is a putative inhibitor of secreted phospholipase A2. Following oral O polar atoms, including all hydrogen bond donors. These NH H HO N groups were almost entirely shielded by the hydrophobic side N HO2C O 219 NH2 O chains. Two structures of 86 (CCDC codes: GIPKAR10, NH2 O HN NH O POWWEE) from isopropanol/water and methanol/water both O H H O N O N showed three internal hydrogen bonds.220,221 One formed a β-turn S O N OH around residues LILL and two transannular interactions. A
AFP fragment 472-479 conserved water molecule was tightly held to a polar patch
O OH composed of 2 phenylalanine NH and two proline carbonyl H HN N O oxygens. N HO2C O NH O O NH2 NH O 2 HN NH O O H H O N O O N N N O NH H N N OH O O N NH2 HN O O OH NH O O O O N O 84 NH NH O NH HN O O NH HN HN HN O O Figure 45. AFP fragment 472-479: MW = 844; miLogP = -5.1; O O O HN N 2 O HBD = 12; HBA = 22; RotB = 23; tPSA = 350 Å . AFPep (84): N
MW = 969; miLogP = -5.4; HBD = 17; HBA = 28; RotB = 13; tPSA = 455 Å2. 85 86
7.3 Antamanide and cyclolinopeptide Figure 46. Antamanide (85) and cyclolinopeptide (86). 85: MW
Antamanide (85, Fig. 46) is a cyclic decapeptide derived from = 1147; miLogP = 2.4; HBD = 6; HBA = 20; RotB = 9; tPSA = the same fungus as α-amanitin 75 (A.phalloides). Antamanide 256 Å2. 86: MW = 1040; miLogP = 4.6; HBD = 7; HBA = 8;
198 protects against phalloidin poisoning by blocking the organic RotB = 13; tPSA = 244 Å2. anion transporting polypeptide mechanism. This inhibits the uptake of phalloidins into hepatocytes. Thus, antamanide functions by a mechanism similar to immunosuppressants 7.4 Cyclopeptolide 1
217 cyclosporine A and FK506. A related hydrophobic cyclic Cyclopeptolide 1 (87, Fig. 47) is a cyclic 10-residue peptide nonapeptide cyclolinopeptide (86) ound in linseed oil displayed featuring five N-methyl amides, a depsi-peptide, an O-methyl immunosuppressive activity in a mouse model following oral tyrosine and a pipecolic acid. Isolated from the fungus Septoria
218 administration (10 or 100 µg/mouse p.o. in olive oil). A crystal sp., 87 was used to treat systemic and vaginal candidosis in rats structure of 85 from acetonitrile/water (CCDC code: by twice daily oral dosing for 4 days (8 x 200 mg/kg p.o.). A 90%
ANTAHC10) showed two transannular hydrogen bonds in a large cure rate was observed compared to 100% for the antifungal agent bowl-shaped macrocycle. The concave face displayed most of the Ketoconazole.222 O O
HO O O NH2 O NH N O HN HN N HN O O H O O O HN O NH N O O O N O O O NH NH HN O N O NH H N O NH N N 2 2 O N H O O
OH 88
87 Figure 48. Permetin A (88). MW = 1087; miLogP = -2.0; HBD
Figure 47. Cyclopeptolide 1 (87). MW = 1126; miLogP = 2.6; = 16; HBA = 24; RotB = 18; tPSA = 386 Å2.
HBD = 4; HBA = 23; RotB = 12; tPSA = 282 Å2. 7.6 Synthetic N-methyl β-strand decapeptides
7.5 Permetin A Guided by known permeable and orally bioavailable peptides,
The decadepsipeptide permetin A (88, Fig. 48) has two D- researchers from Novartis prepared a library of highly N-
224,225 residues and an unusual β-hydroxyisoheptanoic acid moiety. It methylated cyclic decapeptides (89-107, Table 1). N-
methylation and stereochemical patterns were preserved while displayed broad antibacterial activity in vitro. LD50 was
223 specific side chains were modified. Their in vitro permeability, determined in mice (LD50 36 mg/kg ip; LD50 2100 mg/kg p.o.).
From these data, the oral absorption of 88 can be estimated at metabolic stability and other pharmacokinetic parameters were around 1-2%. evaluated in rats (Table 1). These were the first examples of
cyclic peptides of comparable size to cyclosporin A (109) with
comparable or greater oral bioavailability.
Table 1. Highly N-methylated model cyclic decapeptides.
O AA6 O AA8 AA N N AA 5 N N 9 H H N O AA7 O O O O AA O N H 2 H N N AA4 N N AA10 AA3 O AA1 O
AA AA AA AA AA AUC‡ MW miLogP HBD HBA RotB tPSA No CL† F % 2 1+8 2+7 3+6 4+9 5+10 (iv / p.o.) (Å ) 89 L L L a A 66 256/69 27 1047 3.9 4 20 12 238
90 L A L a A 64 277/28 10 963 1.2 4 20 8 238
91 L L L G P 121 144/4 3 1043 3.3 4 20 12 238
92 A A A G P 56 377/5 1 791 -4.4 4 20 0 288
93 L A L f P 5 4532/767 18 1139 4.3 4 20 12 238
94 L A L p F 7 2206/1006 46 1139 4.3 4 20 12 238
95 L A L p A 30 579/912 130 987 1.4 4 20 8 238
96 L A L p V 43 379/40 11 1043 2.9 4 20 10 238
97 L F L p A 4 3673/608 17 1139 4.3 4 20 12 238
98 L A L f A 5 5773/487 10 1115 4.2 4 20 12 238
99 L A L l F 1 12368/491 4 1200 6.8 4 20 16 238
100 L A L p F+X 5 3219/1317 40 1140 3.1 4 21 12 251
101 L A L p F+T 16 12368/491 73 1093 2.2 5 21 11 258
102 L G L p F 10 1490/322 22 1111 4.6 4 20 12 238
103 L L G p F 21 723/214 29 1111 3.6 4 20 12 238
104 L A+L L p F 7 2470/788 32 1181 5.6 4 20 14 238
105 L A+D L p F 12 1192/32 2 1184 3.5 5 22 14 276
106 L A+K L p F 8 1700/8 0 1197 3.8 6 21 16 264
107 L A+T L p F 3 4354/728 15 1170 3.7 5 21 13 258
† units = mL/min·kg. ‡ units = nM·h . X= 3-pyridylalanine
mg p.o.) was safe and well tolerated in humans and proved more
227 7.7 Surotomycin effective than vancomycin in the treatment of CDI. CDI occur in the gut, therefore low intestinal absorption and systemic Surotomycin (CB-183315, 108, Fig. 49) is a macrocyclic availability is desirable. Low oral absorption was reported in rats antimicrobial lipodepsipeptide, containing multiple unusual and (F <1%)228 and pharmacokinetic parameters from clinical trials D- amino acids. Originally from Cubist Pharmaceuticals, it was also indicated low systemic absorption in humans at various doses being developed by Merck for treatment of C.difficile infections
(500 mg p.o.: Cmax 10.5 ng/mL, AUC0-∞ 317 ng h/mL; 4000 mg (CDI) and associated diarrhoea. In hamsters, 108 was as effective 229 p.o.: Cmax 86.7 ng/mL, AUC0-∞ 2572 ng h/mL). as vancomycin when administered orally 12 hours post-infection twice-daily for five consecutive days (2, 10 or 25 mg/kg p.o. in water).226 In clinical trials, orally administered 108 (125 and 250 OH 13 O OH cyclophilin complex in aqueous solution, and C enriched CSA O N O H bound to cyclophilin, supported the unusual binding conformation O NH HN O NH2 235,236 O NH (PDB codes 1CYA, 1CYB). When bound to cyclophilin, HO NH O N CO H H O 2 O O O O H H CSA was not stabilized by intramolecular hydrogen bonds. N N HN O N N O H H O O Instead, the four-amide protons were orientated towards the NH HN O HO H H2N N O O exterior of the macrocycle. The existence of multiple different O conformers of CSA suggests that it has a flexible structure. This H2N 108 has been hypothesized to play an important role in its unusual Figure 49. Surotomycin (108). MW = 1681; miLogP = -4.6; passive membrane permeability and oral bioavailability. HBD = 25; HBA = 43; RotB = 33; tPSA = 702 Å2. R O 8 CYCLIC UNDECAPEPTIDES O O N O N N 8.1 Cyclosporin A and synthetic derivatives N O HN O H Cyclosporin A (Cyclosporine, CSA, 109, Fig. 50) is an orally N O O N bioavailable cyclic peptide natural product with a D-Ala and a O NH O butenyl-methyl-L-threonine. It was first isolated from the fungus N N O N H T.inflatum in the early 1970s by scientists at Sandoz (now O Novartis). CSA is most often used in the clinic as an injectable
109 (R=H); immunosuppressive drug to combat organ transplant rejection, but it is also used as an oral treatment for graft versus host disease. It 110 (R=CO2CH2OCOCH2CH2CO2mPEG) binds to cyclophilin in lymphocytes.230 CSA has interesting pharmacokinetics and is a rare example of a large cyclic peptide Figure 50. Cyclosporin A (109) and KI-306 (110). 109: MW = (11 residues, MW = 1202 Da) with appreciable oral 1203; miLogP = 3.6; HBD = 5; HBA = 23; RotB = 15; tPSA = bioavailability (F = 20-70% depending upon formulation and 279 Å2. 110: MW = 1391; miLogP = 3.7 (mPEG not counted); species; 22-29% in rat).106,231 CSA has been used as a model for HBD = 4; HBA = 29; RotB = 24; tPSA = 347 Å2. developing peptides into orally deliverable drugs. The crystal KI-306 110 (Fig. 50), is a monomethoxypoly(ethyleneglycol)) structure of CSA from acetone, and the NMR solution structure modified CSA prodrug developed to improve the water solubility determined in CDCl3, both show that it is stabilised by four relative to CSA. The oral bioavailability of 110 and CSA intramolecular hydrogen bonds between the backbone amide NH (Sandimmune Neoral solution) were compared in rats. PEG- and the backbone carbonyl oxygen atoms (CCDC code:
modified 110 (7 mg/kg p.o.: AUC 32.8 µg/mL·h, Cmax 1.8 µg/mL, DEKSAN).232 In polar solvents like methanol, CSA exists in at
Tmax 1.43 h) had higher bioavailability than CSA (Sandimmune least four conformations, but it is insoluble in water. Co-
Neoral, 7 mg/kg p.o.: AUC 21.4 µg/mL·h, Cmax 1.1 µg/mL, Tmax crystallization of CSA with cyclophillin (PDB code: 1CWA) 2.6 h).237 revealed a single bound conformation that differed from its unbound crystal state.233,234 NMR solution structures of the CSA- NIM811 (111, Fig. 51) is a CSA analogue modified at position clinical trials as a HCV antiviral drug that blocks viral replication.
4 with N-methylisoleucine and a D-Ala at position 8,. and iIt has It has excellent pharmacokinetic and safety profiles and been investigated as a therapeutic agent for the treatment of significantly decreased viral load in HCV-infected patients (1200 hepatitis C. 111 suppresses hepatitis C virus replication but, mg/day p.o.: Cmax 1052 ng/mL, Tmax 2.0 h, AUC0-12h 3858 unlike CSA, was not immunosuppressive. It was found to have ng·h/mL).241,242 similar oral bioavailability to CSA in mice (10 mg/kg p.o.: C max H O 2.1 µg/mL, Tmax 2-5 h, AUC0-24 23.7 µg/mL⋅h), rats (10 mg/kg O O N O p.o.: Cmax 1.4 µg/mL, Tmax 4-8 h, AUC0-24 13.1 µg/mL⋅h), dogs N N N O HN (20 mg/kg p.o.: Cmax 5.2 µg/mL, Tmax 1 h, AUC0-24 38.2 µg/mL⋅h) O H N O and monkeys (10 mg/kg p.o.: Cmax 1.7 µg/mL, Tmax 3-8 h, AUC0- O N O 11.3 g/mL h).238 24 µ ⋅ NH O R1 N N O N R H H 2 O O R3 O O N O N N 112 (R1 = S(CH2)2NMe2, R2=Me, R3=CH2C(Me2)OH) N O HN 113 (R1 = Me, R2 = Et, R3 = CH(Me2) O H N O O N
O NH O N N Figure 52. SCY-635 (112) and alisporivir (113). 112: MW = O N H O 1322; miLogP = 2.9; HBD = 6; HBA = 25; RotB = 19; tPSA =
302 Å2. 113: MW = 1217; miLogP = 3.8; HBD = 5; HBA = 23;
RotB = 15; tPSA = 279 Å2. 111
8.2 THR-123 Figure 51. NIM811 (111). MW = 1203; miLogP = 3.6; HBD = 5; The 16-residue disulfide bridged cyclic peptide THR-123 (114, HBA = 23; RotB = 15; tPSA = 279 Å2. Fig. 53) was designed to mimic a loop in the structure of human
BMP7; a protein from the TGF-β superfamily that binds Alk2/3/6 SCY-635 112 (Fig. 52) is CSA analogue recently developed as and antagonizes TGF-β–mediated activity. The disulfide bridge a potent inhibitor of hepatitis C Virus RNA replication and stabilizes the conformation. Compound 114 was active against showed oral bioavailability in rats (5 mg/kg p.o.: C 900 ng/mL, max kidney fibrosis by inhibiting the Alk3 receptor after oral T 4.0 h, AUC 13000 ng·h/mL, t 19.2 h, F 23.1%) and max 0-∞ 1/2 administration (5-15 mg/kg p.o.) to mice.243 monkeys (5 mg/kg p.o.: Cmax 1810 ng/mL, Tmax 2.0 h, AUC0-∞
239 27900 ng·h/mL, t1/2 24.6 h, F 17.7%). Alisporivir (also Debio-
025, DEB025, UNIL025, 113, Fig. 52) is an orally bioavailable
CSA analogue with N-methyl-D-alanine at position 3 and N-ethyl- valine at position 4.240 Alisporivir completed Phase I and II OH HT3 antagonist, ondansetron (iv) had no emetic effect. The O H authors concluded that cerulide causes emesis through central 5- N O HO O HT3 receptor stimulation of the vagus afferent. Cerulide had ED50 HO N H HN O 12.9 µg/kg (p.o.) and 9.8 µg/kg (ip) for inducing emesis in
245 H2N NH S.murinus rodents. HN NH2 NH O NH O
H2N O O HN O O H H N S NH N O 2 O N H O O O NH O S NH O HN O HO O NH OH O NH2 NH O O O O O HN HN O O O O NH O HN NH O O N OH N O H H O O HO O O HO 115
114 Figure 54. Cereulide (115). MW = 1153; miLog P = 6.6; HBD = 6; HBA = 24; RotB = 12; tPSA = 332 Å2. Figure 53. THR-123 (114). MW = 1926; miLogP = -6.2; HBD = 9.2 L-Phenylalanine-dipicolinate macrocycle 35; HBA = 49; RotB = 42; tPSA = 833 Å2.
A series of linear and macrocyclic L-phenylalanine-dipicolinic 9 CYCLIC DODECA- AND TRIDECAPEPTIDES acid based compounds were synthesized and tested for anti-
There are a number of cyclic dodecapeptides that are orally active. inflammatory activity. Anti-inflammatory activity was evaluated
One example is the antibiotic valinomycin, which contains 3 L- by oral administration (7 mg/kg p.o.) to rats with carrageenan- valines, 3 D-valines, 6 depsipeptide components including 3 L- induced paw edema. Two known non-steroidal anti-inflammatory lactic acids and 3 D-alpha-hydroxyisovaleric acid. The 36- drugs (NSAIDs), indomethacin and diclofenac, were used as membered macrocycle is a potassium-selective ionophore (LD50 4 controls. Compound 116 (Fig. 55) caused 72% inhibition of paw
244 mg/kg p.o, rat). Unfortunately, there is little pharmacokinetic inflammation compared to 82% and 61% for indomethacin and data available for most dodecapeptides. diclofenac.246
9.1 Cerulide
O O O The cyclic dodecadepsipeptide cerulide (115, Fig. 54) contains O H N N N N O N H seven L-residues, five D-residues, six depsipeptide and six peptide H HN O NH O O N O H bonds. It is an emetic toxin (induces vomiting) produced by the O O H 245 N O O O HN O bacteria B.cereus. Cerulide was administered (p.o. or ip) to the NH H H N O N N N N S.murinus rodents to test for emetic effects at doses from 2-32 H O O O O µg/kg. The maximal oral dose (32 µg/kg p.o.) resulted in emesis in 5 of 5 test animals. 115 (50 µg/kg p.o.) in combination with 5- α-Conotoxin MII (118) and lipidated analogue 119 (Fig. 57) are 116 16-residue bis-disulfide bridged natural peptides that are orally Figure 55. L-Phenylalanine-dipicolinic acid based macrocycle absorbed. Following oral administration of 118 and a lipophilic (116). MW = 1930; miLogP = 8.6; HBD = 12; HBA = 36; RotB = analogue 119 (1 mg/kg p.o.) to male Sprague–Dawley rats, ~6% 16; tPSA = 505 Å2. of both peptides crossed the GI tract and were found in a variety
of body tissues based on radioactive labelling.248
O 10 CYCLIC TETRADECAPEPTIDES AND H2N BEYOND N HN O O N 10.1 Conotoxins and synthetic derivatives HO O O H NH HN O HN N Linaclotide® (117, Fig. 56) is a 14-residue peptide toxin that is S S NH HN cyclized through three cysteine disulfide bridges. It is a treatment O O O for irritable bowel syndrome with constipation and for chronic S HN R NH O constipation. 117 was stable in simulated gastric fluid up to 3 h HN H2N O and was not hydrolysed by pepsin. Following oral administration O O S O to rats, 117 was found in plasma despite minimal oral absorption O NH H OH H N NH HO N 247 2 (10 mg/kg p.o.: AUC0–6h 19.7 ng·h/mL, F 0.1%). O NH N NH HN HO O O O NH2 O O O H2N H O N N HO HN NH 118 (R = H) O NH O S HN O 119 (R = (CH2)8-Me HN O S O O
S NH HN S
O S O NH Figure 57. α-Conotoxin MII (118) and lipidated analogue NH2 S O OH O (119). 118: MW = 1711; miLogP = -5.8; HBD = 27; HBA = 45; O NH N RotB = 21; tPSA = 718 Å2. 119: MW = 1837; miLogP = -4.6; H NH HBD = 27; HBA = 45; RotB = 29; tPSA = 718 Å2.
HO O OH A head-to-tail cyclized analogue of α-conotoxin Vc1.1 (120,
Fig. 58) from the cone snail C.victoriae was administered orally 117 to rats (0.3 or 3.0 mg/kg p.o.) and produced a significant dose-
Figure 56. Linaclotide (117). MW = 1527; miLogP = -5.7; HBD dependent relief of neuropathic pain.249
= 21; HBA = 36; RotB = 13; tPSA = 574 Å2. O H N NH2 HO NH OH N H N O HN 2 OH O H O O O N N H HO O O H NH NH N HN O N NH H2N O H HN O O O O S S NH O H O HN O N OH HN O O O OH S S O HN S O O NH O H NH O H N HN 2 N N H2N H O OH O HN HN HN O O S O O NH O O O NH H O HN NH NH O NH S O N H N NH HN O N N N O NH HN H N NH O H N O NH 2 O N O H O O O O O HO
120 121
Figure 58. Head-to-tail cyclized analogue of α-conotoxin Vc1.1 Figure 59. Duramycin (121). MW = 2013; miLogP = -6.1; HBD (120). MW = 2160; miLogP = -6.3; HBD = 32; HBA = 59; RotB = 29; HBA = 48; RotB = 19; tPSA = 760 Å2. = 21; tPSA = 909 Å2. 10.3 Kalata B1 and other cyclotides 10.2 Duramycin The cyclotides are a rapidly expanding family of cyclic Duramycin (lancovutide, Moli1901, 121, Fig. 59) is a highly peptides, which owe their stability to a remarkably conserved crosslinked 19-residue peptide with three lanthione bridges and cyclic cysteine knot (CCK) motif. Cyclotides have a range of one lysoalanine bridge, all derived from L-cysteine. 121 was biological activities (e.g. antiviral, antitumor, antibacterial) and given to rats via pulmonary, intravenous or oral administration. are actively being investigated for their potential in drug Faeces, urine, blood and tissue were collected over a 7-day period. development.251 The prototypic cyclotide, kalata B1 (122, Figure Analysis indicated minimal systemic availability following oral 60) is a 29-residue peptide from the African medicinal plant administration with almost 100% of the oral dose recovered from O.affinis. Kalata B1 is a uterotonic agent252 and by virtue of its faeces. Nevertheless, 121 was detected in serum of rats seven knotted structure is chemically and enzymatically stable and can days after oral administration (231 mg/kg p.o.).250 be made into tea by infusing its parent plant with boiling water.
This tea is an indigenous medicinal agent used to accelerate
childbirth by inducing uterine contractions. Recently, orally active
peptidic bradykinin B1 receptor antagonists were grafted onto
kalata B1 to replace the entire loop 6 unit.253 The grafted analogue
CKB-KAL (123, Fig. 60) was the most potent compound studied
and inhibited acetic acid induced abdominal contraction (the
writhing assay) after injection (1 mg/kg ip) or oral administration
(10 mg/kg p.o.). Maximum inhibition was similar for both routes (49% ip and 42 % p.o.).253 All the cysteine crosslinks have L- mice were given 125 by oral gavage (10 and 20 mg/kg p.o.), it stereochemistry. was found in plasma in a dose dependent manner (10 mg/kg p.o.:
Recently a lysine mutant of kalata B1, KB1[T20K] (124, Fig. Cmax 1.5 µg/mL; 20 mg/kg p.o.: 2.3 µg/mL). The non-stapled
60),254 was investigated in an experimental autoimmune linear analogue was not detected in plasma after oral
257 encephalomyelitis model of multiple sclerosis. 124 was administration. We are not aware of any other similar helix- efficacious when administered orally to mice (10 or 20 mg/kg constrained peptide reported to show any significant oral p.o.) and impeded disease progression at 20 mg/kg p.o. compared absorption at all. to the control group dosed with an inactive kalata B1 derivative
H C H C 255 3 3 H3C H3C [V10K]. X X N L L S X X L B 1 W E D E N Y S I S I E Q Q E N Q L E T W I T H E N K E 37 1 29 1 31 G G F S N L P P P R V P L T C 125 C C R G S G V S S K E C E P S T V T Figure 61. HIV fusion inhibitor helical peptide SAH-gp41 W (626– S C P S C S S V W V (125). B = Norleucine, X = (S)- -methyl(4- C 666) α G S G X S S S G G 20 C C S S pentenyl)alanine. 125: MW = 4589; QPLogP = -23.1*; HBD = T T G C T P T N C C G N 2 P T 72; HBA = 117; RotB = 132; tPSA* = 2173 Å . “*”: Data
calculated with QikProp256 due to structures exceeding 122 (X = T) 123 Molinspiration maximum size.
124 (X = K) 11 INFLUENCES ON ORAL BIOAVAILABILITY
Oral bioavailability is a specific term that indicates how much
Figure 60. Cyclotides kalata B1 (122), CKB-KAL (123), and intact peptide can be measured in the circulation after oral
KB1[T20K] (124). 122: MW = 2892; QPLogP = -15.8*; HBD = ingestion. By definition this parameter is dictated not just by
42; HBA = 74; RotB = 23; tPSA* = 1207 Å2. 123: MW = 3135; compound absorption through an intestinal membrane, but also by
QPLogP = -17.6*; HBD = 42; HBA = 77; RotB = 26; tPSA* = compound stability, interactions and metabolism before intestinal
1224 Å2. 124: MW = 2919; QPLogP = -16.6*; HBD = 43; HBA = absorption as well as compound stability, metabolism, tissue
74; RotB = 26; tPSA* = 1212 Å2. “*”: Data calculated with distribution and clearance after uptake. Most proteins and peptides
QikProp256 due to structures exceeding Molinspiration maximum simply do not get absorbed from the GI tract, and those that do are size. often rapidly metabolized, cleared or distributed into tissues. Key
problems for peptides are their high polarity and large polar 10.4 Stapled α-helix surface areas, large sizes, low membrane permeability, high
SAH-gp41(626-662) (125) is a doubly-stapled 37 residue peptide clearance and rapid metabolism. Cyclization of peptides reported to be a stable α-helix and resistant to pepsin and frequently aids formation of intramolecular hydrogen bonds and chromtrypsin. The bridging residues are of normal S- orientation of sidechains, properties that can help shield polar configuration, but possess an additional α-methyl group. When atoms from the solvent medium (water/lipid) and protect against proteolytic degradation, reduce flexibility, reduce polar surface lipophilic that it cannot partition out. The compromise for small area, and promote permeability through cell membranes. We molecule drugs is LogP 0-5, with some support for the variation - describe one hundred and twenty five cyclic peptides above that 0.4 to 5.6.259 are orally absorbed, orally active or have a measured oral bioavailability (F%). Physicochemical parameters traditionally associated with limits on oral bioavailability have been calculated here for each compound (see Figure legends). For cyclic peptides with reported oral bioavailability, we now plot key molecular properties, such as MW (Fig. 62A), miLogP (Fig. 62B), HBD
(Fig. 63A), HBA (Fig. 63B, Fig. 64), RotB (Fig. 65A) and tPSA
(Fig. 65B), against F%.
The plot of molecular weight versus oral bioavailability (Fig.
62A) shows that cyclic peptides with molecular weights ranging from 500-1350 can have some oral bioavailability (F = 0.1 -
10%). Cyclic peptides with higher oral bioavailability clustered into two distinct MW ranges 700-800 and 1000-1200, the latter possibly skewed by the high number of decapeptide- and cyclosporine-like cyclic peptides. It is encouraging that 14 cyclic peptides with MW 500-850 (2, 8, 12, 19, 31, 36, 47, 49, 55, 57-
59, 63, 64) had 10-50 % oral bioavailability. A further 23 cyclic peptides (73, 76-81, 89, 90, 93-98, 100-104, 107, 109, 112) with
MW 960-1350 had ≥10% oral bioavailability. These data demonstrate that a higher MW (> 500) does not necessarily preclude oral bioavailability for cyclic peptides, even though it is important for most small molecules,17,64,65,123,124
Oral bioavailability for each cyclic peptide in this review was next plotted against the predicted octanol-water partition Figure 62. Plots of oral bioavailability (F%) versus A) coefficient (miLogP) in Fig. 62B. The calculated miLogP value is molecular weight, and B) octanol-water partition coefficient one of the better predictors of octanol-water partition (miLogP), of orally absorbed cyclic peptides 2-112.
258 coefficients. The partition coefficient P (or distribution Figure 62B shows that most cyclic peptides in this review with coefficient D) is a ratio of hydrophobicity:hydrophilicity and a F ≥ 10% oral bioavailability also had miLogP 1-5 (e.g. 2, 12, 19, measure of relative compound solubility in the two solvents. To 31, 46, 47, 49, 57, 63, 64, 76, 79, 89, 90, 93-98, 100-103, 107, be orally absorbed, a cyclic peptide must permeate intestinal 109, 112). The extent of oral bioavailability did not correlate with membranes by partitioning into the lipid, but it must not to be so miLogP within this range. Seven orally bioavailable (F > 10%) cyclic peptides (36, 38, 73, 77, 78, 80, 81, 104) had miLogP > 5. Two RO5 criteria that guide oral bioavailability of drug-like
Eleven cyclic peptides with miLogP < 0 had measurable oral small molecules are the numbers of hydrogen bond donors (HBD) bioavailability but this was limited to F < 10% (7, 8, 21-25, 33, and acceptors (HBA). A small molecule is considered more likely
34, 40, 92). These data suggest that hydrophobicity (and to be orally bioavailable if it contains ≤ 5 HBD and ≤ 10 HBA,14- lipophilicity) is likely an important contributor to oral 16 This implies that hydrogen bond donors are more detrimental bioavailability of these cyclic peptides. This data shows that this to oral bioavailability. Figure 63A shows that cyclic peptides with parameter is more accommodating for cyclic peptides (miLogP 1- 1–6 HBD are much more likely to be orally bioavailable than
8) than it is for small molecules (LogP 0-5). those with HBD > 6. A few compounds (19, 20, 31, 112) with
HBD = 6 had F 9-25%, but all compounds with HBD > 6 except 8
(15%) had F ≤ 10%. If this dataset is representative of all cyclic
peptides, HBD do indeed limit oral bioavailability for this class of
molecules.
Figure 63B shows that all cyclic peptides examined had HBA >
10, and those with F > 50% had HBA = 12–22. Thus, almost all
of the orally bioavailable cyclic peptides in this review apparently
violate the RO5 limit on HBA (Fig. 63B), a guideline developed
from small molecule drugs. This suggests that optimising cyclic
peptides to reduce HBD, rather HBA, is likely to improve oral
bioavailability. However, Fig. 63B uses the originally definition
of HBA 14,15, which was simply the total count of all nitrogen and
oxygen atoms, irrespective of their actual hydrogen bond
accepting properties. This is important because the amide nitrogen
is not a hydrogen bond acceptor due to electron delocalisation of
the nitrogen lone pair, indeed protonation always occurs
preferentially on the amide oxygen, not the nitrogen.260 Thus, if
HBA alone is recounted without amide nitrogens, the result
changes dramatically (Fig. 64). As shown, twenty four of the
cyclic peptides for which F ≥ 10% now have HBA ≤ 10 (e.g. 2, 7,
8, 12, 19, 31, 36, 47, 49, 55, 57-59, 63, 64, 89, 93, 95-98, 102-
104). Only twelve cyclic peptides with F ≥ 10% now have HBA
>10 (e.g. 73, 76-81, 100, 101, 107, 109, 112). Thus, the HBA Figure 63. Plots of oral bioavailability (F%) versus A) count is still violated by one third of the cyclic peptides with F ≥ hydrogen bond donors (HBD), or B) hydrogen bond acceptors 10% oral bioavailability, but two-thirds of the cyclic peptides now (HBA), for orally absorbed cyclic peptides 12-112. conform to conventional RO5 guidelines. We conclude that HBA count is somewhat important for oral bioavailability of cyclic to be 13.262 Figure 65A shows that most of the cyclic peptides peptides but not as restrictive as the HBD count. examined here with oral bioavailability had 6-16 rotatable bonds.
Compounds 12 (RotB = 2, F = 16%) and 112 (RotB = 19, F =
23%) were outside this range. Twenty four compounds exceeded
RotB ≤ 10; compounds 2, 19, 31, 93, 97, 98, 107 had F% > 10,
while 36, 73, 76, 77, 78, 79, 80, 81, 89, 94, 100, 101, 102, 103,
104, 109, 112 had F ≥ 20%. . This is consistent with a degree of
conformational rigidity being favorable for oral bioavailability of
cyclic peptides.
Figure 64. Plot of oral bioavailability (F%) versus hydrogen bond acceptors (HBA), where the amide nitrogen is not counted as a HBA atom, for orally absorbed cyclic peptides
12-112.
Rotatable bonds (RotB) reflect the degree of conformational flexibility in a molecule. RO5 compliant drug-like compounds typically have ≤ 10 rotatable bonds.17 However, care must be taken in the use of RotB itself, or as part of any prediction model for oral bioavailability. Firstly, it is notable that strict Ro5 rules describe any bond in a cycle of any ring size as being non- rotatable. However, as cyclic peptide ring size increases, the energy required to rotate Φ/Ψ bonds within the macrocycle decreases, reducing the utility of this RotB metric. As observed above, from cyclic tetrapeptide 2 to cyclosporin A, solution structures and crystal structures can often differ greatly due to such rotations or ring flips. Secondly, studies in rats and humans have shown that the calculation method, therapeutic class of compounds, and desired F% all influence the acceptable number of RotB. In rats, certain therapeutic classes of drugs had Figure 65. Plots of oral bioavailability (F%) versus: A)
261 acceptable F% with RotB >12. Recently, a study on the oral rotatable bonds (RotB), or B) total polar surface area (tPSA), bioavailability of 1014 molecules in humans found the RotB limit for orally absorbed cyclic peptides 12-112. The plot of total polar surface area (tPSA) versus oral four most orally bioavailable (F > 70%) cyclic peptides (36, 80, bioavailability (Fig. 65B) indicated that large polar surfaces (tPSA 95, 101), which respectively had MW > 500 (724, 1196, 987,
> 300 Å2) were a barrier to appreciable oral bioavailability (F > 1079), HBA > 10 (12, 22, 20, 21), three had tPSA > 200 Å2 (140,
10 %), likely due to low absorption and high clearance. Sixteen of 256, 238, 258). On the other hand, all four compounds the smaller cyclic peptides with still large polar surfaces (tPSA respectively had HBD ≤ 5 (0, 3, 4, 5), three had RotB ≤ 12 (12,
100-200) had F = 5-30% (2, 7, 12, 18-20, 31, 36, 38, 47, 49, 55, 13, 8, 10), two had milogP < 5 (6.8, 7.5, 1.4; 2.0) and, without
57, 62, 63,64) and four had F > 30% (36, 38, 57, 64). Twenty four counting amide nitrogens, two had HBA ≤ 10 (9, 12, 10, 11). compounds with tPSA 200-300 were still orally bioavailable Further systematic evaluations of new orally bioavailable cyclic with F ≥ 10% (8, 31, 73, 76-81, 89, 93-98, 100-104, 107, 109, peptides with MW > 500 are needed to support these observations
112), and violate the prediction limit17 for most drug-like small and better define limits of these parameters on oral bioavailability. molecules (tPSA < 140 Å2). This may enable prediction and optimization of orally
bioavailable cyclic peptides larger than 5 amino acids. 12 CONCLUSIONS and FUTURE PROSPECTS The above data set supports current and new chemical This compilation of data on oral activity, oral absorption and strategies to enhance oral absorption. These include reducing oral bioavailability for 125 cyclic peptides, composed of 4 to 37 HBD by removing backbone amide NH protons through amino acids and derivatives. It indicates that there are substitution with N-alkyl groups, esters, ethers, or hydrocarbons; opportunities to expand the molecular weight range beyond the incorporating the nitrogen into a heterocycle; or substituting RO5 limit of small molecules (MW ≤ 500) for cyclic peptides and amides with other surrogates. Thus, cyclic hexapeptide 36 has 3 still obtain appreciable oral bioavailability. This is encouraging depsipeptide linkages, 3 NMe substituents and no NH protons; for therapeutic targeting of protein-protein interactions that may cyclic octapeptide 80 has 1 depsipeptide linkage, 2 NMe require modulators with larger surface areas. The cyclic peptides substituents, 2 prolines and 3NH protons; while cyclic show great variation in the parameters (MW, HBD, HBA, LogP, decapeptides 90 and 101 both have 6 NMe substituents and 4 NH RotB, tPSA) conventionally associated with limiting oral protons. However, these approaches may not be a panacea to the bioavailability (F%) of drug-like molecules. Such parameters are problem of poor oral bioavailability. Biological activity is usually of course all interdependent. As molecules get bigger, they either dependent on three-dimensional structure, and N-methylation or increase in the number of polar components (increasing HBD and insertion of amide isosteres263 that reduce NH protons (HBD) can HBA) or nonpolar components (increasing LogP), generally alter peptide structure, which may negatively impact on function. become more flexible (increasing RotB), and thus expose more of For example, amide protons might be required for direct binding their surface area to water (tPSA) and membranes. The RO5 has to a target or for maintaining the bioactive conformation through been used very successfully to guide development of orally intramolecular hydrogen bonds. N-methylation or amide isosteres bioavailable small molecule drugs over the past two decades. can disrupt either or both of these properties. Intramolecular However, it is clear from Figures 62-65 that orally bioavailable hydrogen bonds are often desirable because they reduce the cyclic peptides can violate all of these parameters, especially exposed polar surface of a peptide. Introducing an amide isostere MW, tPSA, HBA and, but not to the same extent, HBD, RotB, also normally requires additional synthetic steps, the value of LogP. Interestingly, Figures 62, 63, 65 show this to be true for the which must be weighed up against potential pharmacokinetic benefits. Ester bonds are present in many naturally occurring structural compression to shield polar residues in the interior of a cyclic depsipeptides and are thought to be evolutionary adaptions cyclic peptide and expose outer hydrophobic substituents to lipid that facilitate permeability through biological membranes. bilayers. Compact structures that undergo minimal change in
Romidepsin 12, largazole 13, kahalalide F 61, and Gq inhibitor going from water through a lipid membrane to water again should
YM254890 67, are among many examples of depsipeptides that pay a lower entropy penalty to overcome this transition. Thus, are active in mammalian cells and bind to intracellular targets, rigidity may be more desirable than flexibility for oral supporting this hypothesis. However, ester bonds are also unstable bioavailability, although this brings an accompanying problem of and hydrolysed by esterases in cells and in vivo. Although lower aqueous solubility. esterification has been widely exploited for delivering carboxylic The nature and extent of water solvation is likely to be a key acids as prodrugs, ester substitution can also jeopardize in vivo consideration for oral absorption. Water molecules need to be stability. For example, orally bioavailable romidepsin 12, stripped away from polar surfaces to facilitate uptake from the gut largazole 13 and kahalalide F 61 have very short half-lives at 37° via passive diffusion or for interaction with proteins that promote
C (t1/2 6, 0.3, 28 min), probably due to poor in vivo stability of active transport. Experimental determination and comparison of their cleavable ester moieties. In Enniantin B1 31, every second solvation energies can be very helpful for predicting oral amino acid linkage is a depsipeptide bond. It displays unusually absorption as well as solubility. The nature of amino acid high oral bioavailability (F = 91%), but also has a very short half- substituents and the degree of flexibility of the macrocycle not life (t1/2 9 min). only dictates solvation, but also susceptibility to oxidative and
Two important considerations missing from the above analysis degradative metabolism. Amino acid substituents and peptide are three dimensional polar surface area and metabolic stability. backbone conformation also determine interactions with proteins,
There were only a few reported three-dimensional structures for including transporters and efflux promoters, metabolising cyclic peptides in this review, but the effect of three-dimensional enzymes, albumen, plasma and cellular proteins. All of these structure and conformational preference of cyclic peptides in factors contribute to oral bioavailability and need to be studied to water versus lipid membranes is very important. Three- better understand how metabolism and clearance, in addition to dimensional structure can significantly change the solvent- absorption, are affected by structural modifications to cyclic exposed polar surface area. Large macrocycles might be folded peptides. through intramolecular hydrogen bonds that are shielded from This collection of cyclic peptides has the potential to stimulate solvent. This could produce much smaller exposed polar surface chemists to reach for new horizons in the design, synthesis and areas than suggested by tPSA calculations on 2D structures. application to humans of larger, biologically active, compounds
Structural compression may enable larger molecules (MW) with including macrocycles. To date extensive research has focused on more polar atoms (HBD/HBA) and larger tPSA (but low 3D-PSA) membrane and cell permeability of peptides and macrocycles but, to be tolerated in a cyclic peptide for oral absorption. Compaction as revealed in this review, membrane permeability is only one of or hydrophobic collapse is a dominant feature of protein folding many contributors to oral bioavailability. More details on that enables proteins to shield their hydrophobic residues in their solvation, absorption, metabolism, tissue distribution, clearance interiors away from water. Conversely, passive diffusion through and three-dimensional structures of cyclic peptides can provide a a lipid membrane would be favored by the reverse effect, deeper understanding of how to better exploit the different factors Weijun Xu was a lecturer at the School of Chemical and Life that influence their oral bioavailability and their promise as new Sciences (Singapore Polytechnic), an undergraduate (B.Sc. Hons. oral therapeutics. Biochemistry, 2006) and postgraduate of University of
Queensland (PhD, 2013-2016), where he is a research assistant. AUTHOR INFORMATION He was an International Postgraduate Research Scholar and
Corresponding Author University of Queensland Advantage Scholar with Professor
* Institute for Molecular Bioscience, The University of Fairlie on computer-aided molecular modeling of protein-ligand
Queensland, Brisbane, QLD 4072, Australia, Fax: +61- and protein-protein interactions, involving discovery of ligands
733462990, E-mail: [email protected]. for GPCRs, proteases, enzymes and other proteins involved in human immune systems. Present Address Andrew J. Lucke obtained a PhD in organic chemistry at †Andrew J. Lucke, La Trobe Institute of Molecular Sciences, La Griffith University, followed by postdoctoral research in the Trobe University, Melbourne, VIC 3083, Australia. United Kingdom and Australia. He has published in organic,
Notes medicinal, physical and macromolecular chemistry. His recent
research has used molecular simulation techniques to model The authors declare no competing financial interests. interactions between small organic molecules and large
BIOGRAPHIES biomolecules. He is a molecular modeller at La Trobe University
Daniel S. Nielsen obtained a B.Sc and M.Sc from the Faculty with interests in organic synthesis, medicinal chemistry (drug of Pharmaceutical Sciences at University of Copenhagen (2011). design and development), peptidomimetics and protein molecular
He received a University of Queensland International Ph.D. dynamics.
Scholarship (2012) and obtained a PhD (2016) on orally Martin Stoermer obtained a B.Sc. Hons (1986) and Ph.D. bioavailable cyclic peptides with Professor Fairlie. He conducted (1991) from University of Sydney in organic synthesis and postdoctoral research in the same lab. In 2017, he is a postdoctoral organometallic reaction mechanisms. He worked in drug design at fellow in Professor Meldal’s group at University of Copenhagen. the Centre for Drug Design and Development, University of
Research interests are in pharmaceutical sciences, natural Queensland (1991-1995) and in the Institute for Molecular products, cyclic peptides, organic synthesis and drug discovery. Bioscience since 2001 as a Senior Research Officer. He has also
Nicholas E. Shepherd developed bioactive helical peptide collaborated with the pharmaceutical industry while at the mimics during his PhD at the University of Queensland. As a Technical University of Clausthal-Zellerfeld, Germany (1995- postdoctoral researcher at the University of Tokyo he identified 1996) and the Victorian College of Pharmacy, Monash University novel bimetallic catalysts to enantioselectively synthesize (1996-2000). pharmaceutically important chiral small molecules. As an ARC David Fairlie studied at Adelaide, Australian National, New
DECRA fellow at the University of Sydney he used chemical South Wales, Stanford and Toronto universities. At University of tools to define the structural basis for R/DNA-binding proteins Queensland, he led the Chemistry Group in the Centre for Drug and epigenetic multi-protein complex function. He is currently a Design and Development and is Head of the IMB Division of senior research officer at the University of Queensland. Chemistry and Structural Biology. Interests are medicinal/organic chemistry, protein mimics, and modulators of GPCRs, PPIs and milligrams per kilogram; MC4R melanocortin 4 receptor ; Me enzymes in inflammation, infection, neurodegeneration and methyl; miLogP Molinspiration octanol-water coefficient; α- cancer. He studies mechanisms of chemical, immunological and MSH alpha-melanocyte stimulating hormone; MW molecular biological reactions, disease development and drug action. weight; NH amide proton; NK2 neurokinin 2; NMR nuclear
magnetic resonance; N-Me N-methyl; NSAIDs non-steroidal anti- ACKNOWLEDGMENT inflammatory drugs; PAMPA parallel artificial membrane We acknowledge grants from the National Health and permeability assay; PEG400 polyethyleneglycol average Medical Research Council (Senior Principal Research molecular weight of 400; p.o. peroral; RO5 rule-of-five; RNA Fellowships 1027369, 1117017 to D.P.F.) and the Australian ribonucleic acid; RotB rotatable bonds; SAH stabilised alpha Research Council (DP150104609, DP130100629, DP160104442, helix; sc subcutaneous; SLC15A1 solute carrier family 15 CE140100011). member 1; t1/2 half life, the time taken for drug concentration to
decrease by half its original value; TGF-beta transforming growth ABBREVIATIONS
factor beta; Tmax time to reach the peak serum concentration; AFP alpha-fetoprotein; AFPep alpha-fetoprotein 472-479 TNBS trinitrobenzene sulfonic acid; tPSA total polar surface area; cyclic analogue; Aha 6-aminohexanoic acid; Alk3 bone VD volume of distribution, the apparent volume in which the drug morphogenetic protein receptor, type IA; AUC area under the is distributed at steady state. curve, the integral of the concentration time curve (0-∞ = after a single dose; or τ,ss = at steady state); BBMV brush border 13. REFERENCES membrane vesicles; BMP7 bone morphogenic protein 7; CL (1) Otvos, L., Jr.; Wade, J. D. Current Challenges In Peptide-Based clearance, the volume of plasma cleared of the drug per unit time; Drug Discovery. Front. Chem. 2014, 2, 62, 1–4.
CSA cyclosporin A; Cmax peak serum concentration; C5a (2) Clackson, T.; Wells, J. A. A Hot Spot Of Binding Energy In A complement factor 5a; CDI C. difficile infection; CCK cyclic Hormone-Receptor Interface. Science 1995, 267, 383–6. (3) Moreira, I. S.; Fernandes, P. A.; Ramos, M. J. Hot Spots - A cysteine knot; CDCl3 deuterochloroform; CYP cytochrome P450 Review Of The Protein-Protein Interface Determinant Amino-Acid enzyme; Da Daltons; DMSO dimethylsulfoxide; EtOH ethanol; Residues. Proteins 2007, 68, 803–12. ED50 dose required to give 50% of the maximal response; EM (4) Hall, D. R.; Kozakov, D.; Whitty, A.; Vajda, S. Lessons From electron microscopy; F% fraction of orally absorbed compound in Hot Spot Analysis For Fragment-Based Drug Discovery. Trends plasma; GI gastro-intestinal; HCV hepatitis C virus; HDAC Pharmacol. Sci. 2015, 36, 724–36. Histone deacetylase; HBA hydrogen bond acceptors; HBD (5) Sheng, C.; Dong, G.; Miao, Z.; Zhang, W.; Wang, W. State-Of- hydrogen bond donors; H-D hydrogen deuterium exchange; HIV The-Art Strategies For Targeting Protein-Protein Interactions By human immunodeficiency virus; HCT116 human colon carcinoma Small-Molecule Inhibitors. Chem. Soc. Rev. 2015, 44, 8238–8259. cell line 116; 5-HT3 5-hydroxytryptamine subtype 3; iv (6) Modell, A. E.; Blosser, S. L.; Arora, P. S. Systematic Targeting intravenous; ip intraperitoneal; LD dose required to kill 50% of 50 Of Protein-Protein Interactions. Trends Pharmacol. Sci. 2016, 37, the test population; LD dose required to kill 100% of the test 100 702–713. population; MDCK Madin-Darby canine kidney cells; MDCKII-
LE Madin-Darby canine kidney cells - low efflux; mg/kg (7) Giannis, A.; Kolter, T. Peptidomimetics For Receptor Ligands - (19) Nisen, M. The Best Selling Prescription Drugs In The World
Discovery, Development, And Medical Perspectives. Angew. Chem. Last Year. Gen. Eng. Biotech. News 2015, Feb 25,
Int. Edit. 1993, 32, 1244–1267. Http://Qz.Com/349929/Best-Selling-Drugs-In-The-World/.
(8) Fairlie, D. P.; Abbenante, G.; March, D. R. Macrocyclic (20) Vlieghe, P.; Lisowski, V.; Martinez, J.; Khrestchatisky, M.
Peptidomimetics - Forcing Peptides Into Bioactive Conformations. Synthetic Therapeutic Peptides: Science And Market. Drug Discov.
Curr. Med. Chem. 1995, 2, 654–686. Today 2010, 15, 40–56.
(9) Hruby, V. J. Designing Peptide Receptor Agonists And (21) Rowland, M.; Tozer, T. N. Clinical Pharmacokinetics:
Antagonists. Nat. Rev. Drug Discov. 2002, 1, 847–858. Concepts And Applications; Third Ed.; Williams & Wilkins:
(10) Tyndall, J. D. A.; Pfeiffer, B.; Abbenante, G.; Fairlie, D. P. Baltimore, United States, 1995.
Over One Hundred Peptide-Activated G Protein-Coupled Receptors (22) Rubio-Aliaga, I.; Daniel, H. Peptide Transporters And Their
Recognize Ligands With Turn Structure. Chem. Rev. 2005, 105, 793– Roles In Physiological Processes And Drug Disposition. Xenobiotica
826. 2008, 38, 1022–1042.
(11) Walensky, L. D.; Bird, G. H. Hydrocarbon-Stapled Peptides: (23) Giacomini K. M.; Huang, S.-M.; Tweedie, D. J. Et Al, The
Principles, Practice, And Progress. J. Med. Chem. 2014, 57, 6275– International Transporter Consortium. Membrane Transporters In
6288. Drug Development. Nat. Rev. Drug Discov. 2010, 9, 215–236.
(12) Azzarito, V.; Long, K.; Murphy, N. S.; Wilson, A. J. Inhibition (24) Brandsch, M. Drug Transport Via The Intestinal Peptide
Of Α-Helix-Mediated Protein-Protein Interactions Using Designed Transporter PEPT1. Curr. Opin. Pharmacol. 2013, 13, 881–887.
Molecules. Nat. Chem. 2013, 5, 161–173. (25) Hillgren, K. M.; Keppler, D.; Zur, A.A.; Giacomini, K. M.;
(13) Hill, T. A.; Shepherd, N. E.; Diness, F.; Fairlie, D. P. Stieger, B.; Cass, C. E.; Zhang, L. Emerging Transporters Of Clinical
Constraining Cyclic Peptides To Mimic Protein Structure Motifs. Importance: An Update From The International Transporter
Angew. Chem. Int. Edit. 2014, 53,13020–13041. Consortium. Clin. Pharmacol. Thera. 2013, 94, 52–63.
(14) Lipinski, C. A.; Lombardo, F.; Dominy, B. W.; Feeney, P. J. (26) Li, X.; Yu, M.; Fan, W.; Gan, Y.; Hovgaard, L.; Yan, M.
Experimental And Computational Approaches To Estimate Solubility Orally Active-Targeted Drug Delivery Systems For Proteins And
And Permeability In Drug Discovery And Development Settings. Peptides. Expert Opin. Drug Deliv. 2014, 11, 1435-1447.
Adv. Drug Del. Rev. 1997, 23, 3–25. (27) Bhutia, Y. D.; Babu, E.; Ramachandran, S.; Yang, S.;
(15) Lipinski, C. A. Lead- And Drug-Like Compounds: The Rule- Thangaraju, M.; Ganapathy, V. SLC Transporters As A Novel Class
Of-Five Revolution. Drug Discov. Today: Technol. 2004, 1, 337–341. Of Tumour Suppressors: Identity, Function And Molecular
(16) Leeson, P. D.; Springthorpe, B. The Influence Of Drug-Like Mechanisms. Biochem J. 2016, 473, 1113–1124.
Concepts On Decision-Making In Medicinal Chemistry. Nat. Rev. (28) Boll, M.; Markovich, D.; Weber, W. M.; Korte, H.; Daniel, H.;
Drug. Discov. 2007, 6, 881–890. Murer, H. Expression Cloning Of A cDNA From Rabbit Small
(17) Veber, D. F.; Johnson, S. R.; Cheng, H. Y.; Smith, B. R.; Intestine Related To Proton-Coupled Transport Of Peptides, Beta-
Ward, K. W.; Kopple, K. D. Molecular Properties That Influence The Lactam Antibiotics And Ace-Inhibitors. Pflugers Arch. 1994, 429,
Oral Bioavailability Of Drug Candidates. J. Med. Chem. 2002, 45, 146–149.
2615–2623. (29) Dietrich, C. G.; Geier, A.; Oude Elferink, R. P. J. ABC Of Oral
(18) Craik, D. J.; Fairlie, D. P.; Liras, S.; Price, D. The Future Of Bioavailability: Transporters As Gatekeepers In The Gut. Gut 2003,
Peptide-Based Drugs. Chem. Biol. Drug Des. 2013, 81, 136–147. 52, 1788–1795. (30) Lown, K. S.; Mayo, R. R.; Leichtman, A. B.; Hsiao, H. L.; Of Papillary Adenocarcinoma And Of Renal Tubular Epithelium.
Turgeon, D. K.; Schmiedlin-Ren, P.; Brown, M. B.; Guo, W.; Rossi, Cancer 1970, 26, 1022–1028.
S. J.; Benet, L. Z. et al Pharmacokinetics And Drug Disposition: Role (40) Lodish H, B. A., Zipursky Sl, Et Al. In Molecular Cell
Of Intestinal P-Glycoprotein (MDR1) In Interpatient Variation In The Biology; 4th Edition Ed.; Freeman, W. H., Ed. New York, 2000.
Oral Bioavailability Of Cyclosporine. Clin. Pharmacol. Ther. 1997, (41) Fromter, E.; Diamond, J. Route Of Passive Ion Permeation In
62, 248–260. Epithelia. Nat. New Biol. 1972, 235, 9–13.
(31) Schinkel, A. H.; Jonker, J. W. Mammalian Drug Efflux (42) Goh, L. B.; Spears, K. J.; Yao, D.; Ayrton, A.; Morgan, P.;
Transporters Of The Atp Binding Cassette (ABC) Family: An Roland Wolf, C.; Friedberg, T. Endogenous Drug Transporters In In
Overview Adv. Drug Del. Rev. 2003, 55, 3–29. Vitro And In Vivo Models For The Prediction Of Drug Disposition In
(32) Kansy, M.; Senner, F.; Gubernator, K. Physicochemical High Man. Biochem. Pharmacol. 2002, 64, 1569–1578.
Throughput Screening: Parallel Artificial Membrane Permeation (43) Volpe, D. A. Drug-Permeability And Transporter Assays In
Assay In The Description Of Passive Absorption Processes. J. Med. CACO-2 And MDCK Cell Lines. Future Med. Chem. 2011, 3, 2063–
Chem. 1998, 41, 1007–1010. 2077.
(33) Hidalgo Ij Fau - Raub, T. J.; Raub Tj Fau - Borchardt, R. T.; (44) Di, L.; Whitney-Pickett, C.; Umland, J. P.; Zhang, H.; Zhang,
Borchardt, R. T. Characterization Of The Human Colon Carcinoma X.; Gebhard, D. F.; Lai, Y.; Federico, J. J.; Davidson, R. E.; Smith, R.
Cell Line (CACO-2) As A Model System For Intestinal Epithelial et al. Development Of A New Permeability Assay Using Low-Efflux
Permeability. Gastroenterol. 1989, 96, 736–749. Mdckii Cells. J. Pharm. Sci. 2011, 100, 4974–4985.
(34) Press, B.; Di Grandi, D. Permeability For Intestinal (45) Chatterjee, J.; Gilon, C.; Hoffman, A.; Kessler, H. N-
Absorption: CACO-2 Assay And Related Issues. Curr. Drug Metab. Methylation Of Peptides: A New Perspective In Medicinal Chemistry.
2008, 9, 893–900. Acc. Chem. Res. 2008, 41, 1331–1342.
(35) Gaush, C. R.; Hard, W. L.; Smith, T. F. Characterization Of An (46) Bockus, A. T.; Mcewen, C. M.; Lokey, R. S. Form And
Established Line Of Canine Kidney Cells (MDCK). Proc. Soc. Exp. Function In Cyclic Peptide Natural Products: A Pharmacokinetic
Biol. Med. 1966, 122, 931–935. Perspective. Curr. Top. Med. Chem. 2013, 13, 821–836.
(36) Rabito, C. A.; Tchao, R.; Valentich, J.; Leighton, J. (47) Whitty, A.; Zhong, M.; Viarengo, L.; Beglov, D.; Hall, D. R.;
Distribution And Characteristics Of The Occluding Junctions In A Vandja, S. Quantifying The Chameleonic Properties Of Macrocycles
Monolayer Of A Cell Line (MDCK) Derived From Canine Kidney. J. And Other High-Molecular-Weight Drugs. Drug Discov. Today 2016,
Membr. Biol. 1978, 43, 351–365. 21, 712– 717.
(37) Cereijido, M.; Robbins, E. S.; Dolan, W. J.; Rotunno, C. A.; (48) Over, B.; Mccarren, P.; Artursson, P.; Foley, M.; Giordanetto,
Sabatini, D. D. Polarized Monolayers Formed By Epithelial Cells On F.; Gronberg, G.; Hilgendorf, C.; Lee, M. D.; Matsson, P.;
A Permeable And Translucent Support. J. Cell Biol. 1978, 77, 853– Muncipinto, G. et al. Impact Of Stereospecific Intramolecular
880. Hydrogen Bonding On Cell Permeability And Physicochemical
(38) Misfeldt, D. S.; Hamamoto, S. T.; Pitelka, D. R. Properties. J. Med. Chem. 2014, 57, 2746–2754.
Transepithelial Transport In Cell Culture. Proc. Natl. Acad. Sci. U. S. (49) Over, B.; Matsson, P.; Tyrchan, C.; Artursson, P.; Doak, B. C.;
A. 1976, 73, 1212–1216. Foley, M. A.; Hilgendorf, C.; Johnston, S. E.; Lee, M. D. T.; Lewis,
(39) Leighton, J.; Estes, L. W.; Mansukhani, S.; Brada, Z. A Cell R. J. et al. Structural And Conformational Determinants Of
Line Derived From Normal Dog Kidney (Mdck) Exhibiting Qualities Macrocycle Cell Permeability. Nat. Chem. Biol. 2016, 12, 1065–1074. (50) Wang, C. K.; Craik, D. J. Cyclic Peptide Oral Bioavailability: (62) Fox, C. B.; Kim, J.; Le, L. V.; Nemeth, C. L.; Chirra, H. D.;
Lessons From The Past. Biopolymers 2016, 106, 901–909. Desai, T. A. Micro/nanofabricated Platforms for Oral Drug Delivery.
(51) Ussing, H. H.; Zerahn, K. Active Transport Of Sodium As The J. Control Release 2015, 219, 431–444.
Source Of Electric Current In The Short-Circuited Isolated Frog Skin. (63) Bak, A.; Leung, D.; Barrett, S. E.; Forster, S.; Minnihan, E. C.;
Acta Physiol. Scand. 1951, 23, 110–127. Leithead, A. W.; Cunningham, J., Toussaint, N.; Crocker, L. S.
(52) Kato, Y.; Miyazaki, T.; Kano, T.; Sugiura, T.; Kubo, Y.; Tsuji, Physicochemical and Formulation Developability Assessment for
A. Involvement Of Influx And Efflux Transport Systems In Therapeutic Peptide Delivery—A Primer. AAPS J. 2015, 17, 144–
Gastrointestinal Absorption Of Celiprolol. J. Pharm. Sci. 2009, 98, 155.
2529–2539. (64) Giordanetto, F.; Kihlberg, J. Macrocyclic Drugs And Clinical
(53) Clarke, L. L. A Guide To Ussing Chamber Studies Of Mouse Candidates: What Can Medicinal Chemists Learn From Their
Intestine. Am. J. Physiol.-Gastr. L. 2009, 296, G1151–G1166. Properties? J. Med. Chem. 2014, 57, 278–295.
(54) Motlekar, N. A.; Srivenugopal, K. S.; Wachtel, M. S.; Youan, (65) Doak, B. C.; Over, B.; Giordanetto, F.; Kihlberg, J. Oral
B. B. C. Evaluation Of The Oral Bioavailability Of Low Molecular Druggable Space Beyond The Rule Of 5: Insights From Drugs And
Weight Heparin Formulated With Glycyrrhetinic Acid As Permeation Clinical Candidates Chem. Biol. 2014, 21, 1115–1142.
Enhancer (Retraction Of Vol 67, Pg 166, 2006). Drug Dev. Res. 2008, (66) Matsson, P.; Doak, B. C.; Over, B.; Kihlberg, J. Cell
69, 535. Permeability Beyond The Rule Of 5. Adv. Drug Deliv. Rev. 2016,
(55) Dietrich, C. G.; De Waart, D. R.; Ottenhoff, R.; Schoots, I. G.; 101, 42-61.
Elferink, R. P. J. O. Increased Bioavailability Of The Food-Derived (67) Matsson, P.; Kihlberg, J. How Big Is Too Big for Cell
Carcinogen 2-Amino-1-Methyl-6-Phenylimidazo[4,5-B]Pyridine In Permeability? J. Med. Chem. 2017, 60, 1662-1664.
MRP2-Deficient Rats. Mol. Pharmacol. 2001, 59, 974–980. (68) Santos, G. B.; Ganesan, A.; Emery, F. S. Oral Administration
(56) Guengerich, F. P. Cytochrome P450 And Chemical Of Peptide-Based Drugs: Beyond Lipinski's Rule. ChemMedChem
Toxicology. Chem. Res. Toxicol. 2008, 21, 70–83. 2016, 11, 2245–2251.
(57) Park, K.; Kwon, I. C.; Park, K. Oral protein Delivery: Current (69) Ertl, P.; Rohde, B.; Selzer, P. Fast Calculation Of Molecular
Status and Future Prospect. Reactive Functional Polymers 2011, 71, Polar Surface Area As A Sum Of Fragment-Based Contributions And
280-287. Its Application To The Prediction Of Drug Transport Properties. J.
(58) Lee, E.; Lee, J.; Jon, S. A Novel Approach To Oral Delivery Med. Chem. 2000, 43, 3714–3717.
Of Insulin By Conjugating With Low Molecular Weight Chitosan. (70) Aldrich, J. V.; Senadheera, S. N.; Ross, N. C.; Ganno, M. L.;
Bioconjug. Chem. 2010, 21, 1720-1723. Eans, S. O.; Mclaughlin, J. P. The Macrocyclic Peptide Natural
(59) Henriksen, K.; Bay-Jensen, A. C.; Christiansen, C.; Karsdal, Product CJ-15,208 Is Orally Active And Prevents Reinstatement Of
M. A. Oral Salmon Calcitonin - Pharmacology In Osteoporosis. Extinguished Cocaine-Seeking Behavior. J. Nat. Prod. 2013, 76, 433–
Expert Opin. Biol. Therapy 2010, 10, 1617-1629. 438.
(60) Aungst, B. J. Absorption Enhancers: Applications and (71) Shin, B. S.; Chang, H. S.; Park, E. H.; Yoon, C. H.; Kim, H.
Advances. AAPS J. 2012, 14, 10–18. Y.; Kim, J.; Ryu, J. K.; Zee, O. P.; Lee, K. C.; Cao, D. et al.
(61) Renukuntla, J.; Vadlapudi, A. D.; Patel, A.; Boddu, S. H.; Pharmacokinetics Of A Novel Histone Deacetylase Inhibitor,
Mitra, A. K. Approaches for Enhancing Oral Bioavailability of Apicidin, In Rats. Biopharm. Drug Disposition 2006, 27, 69–75.
Peptides and Proteins. Int. J. Pharm. 2013, 447, 75–93. (72) Stahelin, H.; Trippmacher, A. Cytostatic Activity Of (81) Cummings, D. E.; Schwartz, M. W. Melanocortins And Body
Chlamydocin, A Rapidly Inactivated Cyclic Tetrapeptide. Eur. J. Weight: A Tale Of Two Receptors. Nat. Genet. 2000, 26, 8–9.
Cancer 1974, 10, 801–808. (82) Hess, S.; Linde, Y.; Ovadia, O.; Safrai, E.; Shalev, D. E.;
(73) Kranz, M.; Murray, P.J.; Taylor, S.; Upton, R.J.; Clegg, W.; Swed, A.; Halbfinger, E.; Lapidot, T.; Winkler, I.; Gabinet, Y. et al.
Elsegood, M.R.J. Solution, Solid Phase And Computational Backbone Cyclic Peptidomimetic Melanocortin-4 Receptor Agonist
Structures Of Apicidin And Its Backbone-Reduced Analogs. J. Pept. As A Novel Orally Administrated Drug Lead For Treating Obesity. J.
Sci., 2006, 12, 383-388. Med. Chem. 2008, 51, 1026–1034.
(74) Namatame, I.; Tomoda, H.; Ishibashi, S.; Omura, S. (83) Chan, K. K.; Bakhtiar, R.; Jiang, C. Depsipeptide (FR901228,
Antiatherogenic Activity Of Fungal Beauveriolides, Inhibitors Of Nsc-630176) Pharmacokinetics In The Rat By LC/MS/MS. Invest.
Lipid Droplet Accumulation In Macrophages. Proc. Natl. Acad. Sci. New Drugs 1997, 15, 195–206.
U. S. A. 2004, 101, 737–742. (84) Lai, M.-T.; Yang, C.-C.; Lin, T.-Y.; Tsai, F.-J.; Chen, W.-C.
(75) Hurevich, M.; Swed, A.; Joubran, S.; Cohen, S.; Freeman, N. Depsipeptide (FK228) Inhibits Growth Of Human Prostate Cancer
S.; Britan-Rosich, E.; Briant-Longuet, L.; Bardy, M.; Devaux, C.; Cells. Urol. Oncol: Sem. Orig. Invest. 2008, 26, 182–189.
Kotler, M. et al. Rational Conversion Of Noncontinuous Active (85) Taori, K.; Paul, V. J.; Luesch, H. Structure And Activity Of
Region In Proteins Into A Small Orally Bioavailable Macrocyclic Largazole, A Potent Antiproliferative Agent From The Floridian
Drug-Like Molecule: The HIV-1 CD4:Gp120 Paradigm. Biorg. Med. Marine Cyanobacterium Symploca SP. J. Am. Chem. Soc. 2008, 130,
Chem. 2010, 18, 5754–5761. 1806–1807.
(76) Burcham, D. L.; Aungst, B. A.; Hussain, M.; Gorko, M. A.; (86) Bowers, A.; West, N.; Taunton, J.; Schreiber, S. L.; Bradner, J.
Quon, C. Y.; Huang, S. M. The Effect Of Absorption Enhancers On E.; Williams, R. M. Total Synthesis And Biological Mode Of Action
The Oral Absorption Of The GP IIb/IIIa Receptor Antagonist, Dmp Of Largazole: A Potent Class I Histone Deacetylase Inhibitor. J. Am.
728, In Rats And Dogs. Pharm. Res. 1995, 12, 2065–2070. Chem. Soc. 2008, 130, 11219–11222.
(77) Terao, K.; Ito, E.; Tatsuno, T. Liver Injuries Induced By (87) Bowers, A. A.; Greshock, T. J.; West, N.; Estiu, G.; Schreiber,
Cyclochlorotine Isolated From Penicillium Islandicum. Arch. Toxicol. S. L.; Wiest, O.; Williams, R. M.; Bradner, J. E. Synthesis And
1984, 55, 39–46. Conformation-Activity Relationships Of The Peptide Isosteres Of
(78) Uraguchi, K.; Saito, M.; Noguchi, Y.; Takahashi, K.; Enomoto, Fk228 And Largazole. J. Am. Chem. Soc. 2009, 131, 2900–2905.
M. Chronic Toxicity And Carcinogenicity In Mice Of The Purified (88) Ghosh, A. K.; Kulkarni, S. Enantioselective Total Synthesis Of
Mycotoxins, Luteoskyrin And Cyclochlorotine. Food Cosmet. (+)-Largazole, A Potent Inhibitor Of Histone Deacetylase. Org. Lett.
Toxicol. 1972, 10, 193–207. 2008, 10, 3907–3909.
(79) Xu, H.-M.; Zeng, G.-Z.; Zhou, W.-B.; He, W.-J.; Tan, N.-H. (89) Nasveschuk, C. G.; Ungermannova, D.; Liu, X.; Phillips, A. J.
Astins K–P, Six New Chlorinated Cyclopentapeptides From Aster A Concise Total Synthesis Of Largazole, Solution Structure, And
Tataricus. Tetrahedron , 2013, 69, 7964-7969. Some Preliminary Structure Activity Relationships. Org. Lett. 2008,
(80) Shen, Y.; Luo, Q.; Xu, H. M.; Gong, F. Y.; Zhou, X. B.; Sun, 10, 3595–3598.
Y.; Wu, X. F.; Liu, W.; Zeng, G. Z.; Tan, N. H. et al. Mitochondria- (90) Seiser, T.; Kamena, F.; Cramer, N. Synthesis And Biological
Dependent Apoptosis Of Activated T Lymphocytes Induced By Astin Activity Of Largazole And Derivatives. Angew. Chem. Int. Ed. Engl.
C, A Plant Cyclopeptide, For Preventing Murine Experimental 2008, 47, 6483–6485.
Colitis. Biochem. Pharmacol. 2011, 82, 260–268. (91) Ying, Y.; Taori, K.; Kim, H.; Hong, J.; Luesch, H. Total Leukocytes. Relationships Between Structures And Activity. Mol.
Synthesis And Molecular Target Of Largazole, A Histone Pharmacol. 2004, 65, 868–879.
Deacetylase Inhibitor. J. Am. Chem. Soc. 2008, 130, 8455–8459. (100) Seow, V.; Lim, J.; Cotterell, A. J.; Yau, M. K.; Xu, W.;
(92) Cole, K.E.; Dowling, D.P.; Boone, M.A.,;Phillips, A.J.; Lohman, R. J.; Kok, W. M.; Stoermer, M. J.; Sweet, M. J.; Reid, R. C.
Christianson, D.W. Structural Basis Of The Antiproliferative Activity et al. Receptor Residence Time Trumps Drug-Likeness And Oral
Of Largazole, A Depsipeptide Inhibitor Of The Histone Deacetylases. Bioavailability In Determining Efficacy Of Complement C5a
J. Am. Chem. Soc. 2011, 133, 12474-12477. Antagonists. Sci. Rep. 2016, 6, 24575.
(93) Decroos, C.; Clausen, D.J.; Haines, B.E.; Wiest, O.; Williams, (101) Waksman, S. A.; Woodruff, H. B. Bacteriostatic And
R.M.; Christianson, D.W. Variable Active Site Loop Conformations Bactericidal Substances Produced By A Soil Actinomyces. Proc. Soc.
Accommodate the Binding of Macrocyclic Largazole Analogues to Exp. Biol. Med. 1940, 45, 609–614.
HDAC8. Biochemistry, 2015, 54, 2126-2135. (102) Jain, S.C.;l Sobell,. H.M. Stereochemistry Of Actinomycin
(94) Yu, M.; Salvador, L. A.; Sy, S. K.; Tang, Y.; Singh, R. S.; Binding To DNA. I. Refinement And Further Structural Details Of
Chen, Q. Y.; Liu, Y.; Hong, J.; Derendorf, H.; Luesch, H. Largazole The Actinomycin-Deoxyguanosine Crystalline Complex. J. Mol. Biol.
Pharmacokinetics In Rats By LC-MS/MS. Mar. Drugs 2014, 12, 1972, 68, 1-20.
1623–1640. (103) Lo, Y.S.; Tseng, W.H.; Chuang, C.Y.; Hou, M.H. The
(95) Salvador, L. A.; Park, H.; Al-Awadhi, F. H.; Liu, Y.; Kim, B.; Structural Basis Of Actinomycin D-Binding Induces Nucleotide
Zeller, S. L.; Chen, Q. Y.; Hong, J.; Luesch, H. Modulation Of Flipping Out, A Sharp Bend And A Left-Handed Twist In CGG
Activity Profiles For Largazole-Based Hdac Inhibitors Through Triplet Repeats. Nucleic Acids Res. 2013, 41, 4284-4294.
Alteration Of Prodrug Properties. ACS Med. Chem. Lett. 2014, 5, (104) Robinson, H.; Gao, Y.G.; Yang, X.; Sanishvili, R.;
905–910. Joachimiak, A.; Wang, A.H. Crystallographic Analysis Of A Novel
(96) Monk, P. N.; Scola, A-M.; Madala, P.K.; Fairlie, D. P. Complex Of Actinomycin D Bound To The DNA Decamer
Function, Structure And Therapeutic Potential Of Complement C5a CGATCGATCG. Biochemistry, 2001, 40, 5587-92.
Receptors. Br. J. Pharmacol. 2007, 152, 429–448. (105) Tan, C. T.; Dargeon, H. W.; Burchenal, J. H. The Effect Of
(97) Wong, A.K.; Finch, A.M.; Pierens, G.K.; Craik, D.J.; Taylor, Actinomycin D On Cancer In Childhood. Pediatrics 1959, 24, 544–
S.M.; Fairlie, D.P. Small Molecular Probes For G-Protein-Coupled 561.
C5a Receptors: Conformationally Constrained Antagonists Derived (106) Hill, T. A.; Lohman, R. J.; Hoang, H. N.; Nielsen, D. S.;
From The C-Terminus Of The Human Plasma Protein C5a. J. Med. Scully, C. C.; Kok, W. M.; Liu, L.; Lucke, A. J.; Stoermer, M. J.;
Chem. 1998, 41, 3417-3425. Schroeder, C. I. et al. Cyclic Penta- And Hexa-Leucine Peptides
(98) Finch, A. M.; Wong, A. K.; Wadi, S. K.; Paczkowski, N. J.; Without N-Methylation Are Orally Absorbed. ACS Med. Chem. Lett.
Fairlie, D. P.; Taylor, S. M. Low Molecular Weight Peptidic And 2014, 5, 1148–1151.
Cyclic Antagonists Of The Receptor For The Complement Factor (107) Robson, W. L. M.; Leung, A. K. C.; Norgaard, J. P. The
C5a. J. Med. Chem. 1999, 42, 1965–1974. Comparative Safety Of Oral Versus Intranasal Desmopressin For The
(99) March, D. R.; Proctor, L. M.; Stoermer, M. J.; Sbaglia, R.; Treatment Of Children With Nocturnal Enuresis. J. Urol. 2007, 178,
Abbenante, G.; Reid, R. C.; Wadi, K.; Paczkowski, N.; Tyndall, J. D. 24–30.
A.; Taylor, S. M.; Fairlie, D. P. Potent Cyclic Antagonists Of The (108) Rembratt, A.; Graugaard-Jensen, C.; Senderovitz, T.;
Complement C5a Receptor On Human Polymorphonuclear Norgaard, J. P.; Djurhuus, J. C. Pharmacokinetics And
Pharmacodynamics Of Desmopressin Administered Orally Versus Intravenously At Daytime Versus Night-Time In Healthy Men Aged Of Permeable Cyclic Peptides. ACS Med. Chem. Lett. 2014, 5, 1167–
55–70 Years. Eur. J. Clin. Pharmacol. 2004, 60, 397–402. 1172.
(109) Fjellestad-Paulsen, A.; Hoglund, P.; Lundin, S.; Paulsen, O. (117) Zornes, L. L.; Stratford, R. E. Development Of A Plasma
Pharmacokinetics Of 1-Deamino-8-D-Arginine Vasopressin After High-Performance Liquid Chromatographic Assay For LY303366, A
Various Routes Of Administration In Healthy Volunteers. Clin Lipopeptide Antifungal Agent, And Its Application In A Dog
Endocrinol 1993, 38, 177–182. Pharmacokinetic Study. J. Chromatog. B: Biomed. Sci. Appl. 1997,
(110) D'agay-Abensour, L.; Fjellestad-Paulsen, A.; Höglund, P.; 695, 381–387.
Ngô, Y.; Paulsen, O.; Rambaud, J. C. Absolute Bioavailability Of An (118) Li, C.; Fleisher, D.; Li, L.; Schwier, J. R.; Sweetana, S. A.;
Aqueous Solution Of 1-Deamino-8-D-Arginine Vasopressin From Vasudevan, V.; Zornes, L. L.; Pao, L. H.; Zhou, S. Y.; Stratford, R. E.
Different Regions Of The Gastrointestinal Tract In Man. Eur. J. Clin. Regional-Dependent Intestinal Absorption And Meal Composition
Pharmacol. 1993, 44, 473–476. Effects On Systemic Availability Of LY303366, A Lipopeptide
(111) Lan, E.-L.; Ugwu, S. O.; Blanchard, J.; Fang, X.; Hruby, V. Antifungal Agent, In Dogs. J. Pharm. Sci. 2001, 90, 47–57.
J.; Sharma, S. Preformulation Studies With Melanotan-Ii: A Potential (119) Raasch, R. H. Anidulafungin: Review Of A New
Skin Cancer Chemopreventive Peptide. J. Pharm. Sci. 1994, 83, Echinocandin Antifungal Agent. Expert Rev. Anti Infect. Ther. 2004,
1081–1084. 2, 499–508.
(112) Meyer-Lindenberg A.; Domes, G.; Kirsch, P.; Heinrichs, M. (120) Denning, D. W. Echinocandin Antifungal Drugs. The Lancet
Oxytocin And Vasopressin In The Human Brain: Social 2003, 362, 1142.
Neuropeptides For Translational Medicine. Nat. Rev. Neurosci. 2011, (121) Ikeda, F.; Tanaka, S.; Ohki, H.; Matsumoto, S.; Maki, K.;
12, 524–538. Katashima, M.; Barrett, D.; Aoki, Y. Role Of Micafungin In The
(113) Manning, M.; Misicka, A.; Olma, A.; Bankowski, K.; Stoev, Antifungal Armamentarium. Curr. Med. Chem. 2007, 14, 1263-1275.
S.; Chini, B.; Durroux, T.; Mouillac, B.; Corbani, M.; Guillon, G. (122) Morris, M. I.; Villmann, M. Echinocandins In The
Oxytocin And Vasopressin Agonists And Antagonists As Research Management Of Invasive Fungal Infections, Part 1. Am. J. Health-
Tools And Potential Therapeutics. J. Neuroendocrinol. 2012, 24, System Pharmacy 2006, 63, 1693-1703.
609–628. (123) Veber, D. F.; Holly, F. W.; Nutt, R. F.; Bergstrand, S. J.;
(114) de Araujo, A. D.; Mobli, M.; Castro, J.; Harrington, A. M.; Brady, S. F.; Hisrschmann, R.; Glitzer, M. S.; Saperstein, R. Highly
Vetter, I.; Dekan, Z.; Muttenthaler, M.; Wan, J.; Lewis, R. J.; King, Active Cyclic And Bicyclic Somatostatin Analogues Of Reduced
G. F.; Brierley, S. M.; Alewood, P. F. Selenoether Oxytocin Ring Size. Nature 1979, 280, 512–514.
Analogues Have Analgesic Properties In A Mouse Model Of Chronic (124) Veber, D. F.; Freidinger, R. M.; Perlow, D. S.; Paleveda, W.
Abdominal Pain. Nat. Commun. 2014, 5, 3165. J.; Holly, F. W.; Strachan, R. G.; Nutt, R. F.; Arison, B. H.; Homnick,
(115) Wood, S.P.; Tickle, I.J.; Treharne, A.M. Pitts, J.E.; C.; Randall, W. C. et al. A Potent Cyclic Hexapeptide Analogue Of
Mascarenhas, Y.; Li, J.Y.; Husain, J.; Cooper, S.; Blundell, T.L.; Somatostatin. Nature 1981, 292, 55–58.
Hruby, V.J. et al. Crystal Structure Of Deamino-Oxytocin: (125) Biron, E.; Chatterjee, J.; Ovadia, O.; Langenegger, D.;
Conformational Flexibility And Receptor Binding. Science, 1986, Brueggen, J.; Hoyer, D.; Schmid, H. A.; Jelinek, R.; Gilon, C.;
232, 633–636. Hoffman, A. et al. Improving Oral Bioavailability Of Peptides By
(116) Goetz, G. H.; Philippe, L.; Shapiro, M. J. Epsa: A Novel Multiple N-Methylation: Somatostatin Analogues. Angew. Chem. Int.
Supercritical Fluid Chromatography Technique Enabling The Design Ed. Engl. 2008, 47, 2595–2599. (126) Bauer, W.; Briner, U.; Doepfner, W.; Haller, R.; Huguenin, (134) Geddes, A.J.; Akrigg, D. The Crystal Structure of Hydrated
R.; Marbach, P.; Petcher, T. J.; Pless, J. SMS 201–995: A Very Potent Beauvericin. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst.
And Selective Octapeptide Analogue Of Somatostatin With Chem, 1976, 32, 3164-3171.
Prolonged Action. Life Sci. 1982, 31, 1133–1140. (135) Braden, B.; Hamilton, J.A.; Sabesan, M.N.; Steinrauf, L.K.
(127) Melacini, G.; Zhu, Q.; Goodman, M. Multiconformational Crystal Structure Of A Beauvericin-Barium Picrate Complex. J. Am.
NMR Analysis Of Sandostatin (Octreotide): Equilibrium Between Chem. Soc. 1980, 102, 2704-2709.
Beta-Sheet And Partially Helical Structures. Biochemistry, 1997, 36, (136) Plattner, R. D.; Nelson, P. E. Production Of Beauvericin By A
1233-1241. Strain Of Fusarium Proliferatum Isolated From Corn Fodder For
(128) Spyroulias, G.A.; Galanis, A.S.; Petrou, C.H.; Vahliotis, D.; Swine. Appl. Environ. Microbiol. 1994, 60, 3894–3896.
Sotiriou, P.; Nikolopoulou, A.; Nock, B.; Maina, T.; Cordopatis, P. (137) Mei, L.; Zhang, L.; Dai, R. An Inhibition Study Of
3D Solution Structure Of [Tyr3]Octreotate Derivatives In DMSO: Beauvericin On Human And Rat Cytochrome P450 Enzymes And Its
Structure Differentiation Of Peptide Core Due To Chelate Group Pharmacokinetics In Rats. J. Enzyme Inhib. Med. Chem. 2009, 24,
Attachment And Biologically Active Conformation. Med. Chem. 753–762.
2005, 1, 487-499. (138) Streit, E.; Schwab, C.; Sulyok, M.; Naehrer, K.; Krska, R.;
(129) Pohl, E.; Heine, A.; Sheldrick, G.M.; Dauter, Z.; Wilson, Schatzmayr, G. Multi-Mycotoxin Screening Reveals The Occurrence
K.S.; Kallen, J.; Huber, W.; Pfaffli, P.J. Structure of Octreotide, a Of 139 Different Secondary Metabolites In Feed And Feed
Somatostatin Analogue. Acta Crystallogr., Sect. D: Biol. Crystallogr., Ingredients. Toxins (Basel) 2013, 5, 504–523.
1995, 51,48-59. (139) Jestoi, M. Emerging Fusarium-Mycotoxins Fusaproliferin,
(130) Köhler, E.; Duberow-Drewe, M.; Drewe, J.; Ribes, G.; Beauvericin, Enniatins, And Moniliformin: A Review. Crit. Rev.
Loubatières-Mariani, M. M.; Mazer, N.; Gyr, K.; Beglinger, C. Food Sci. Nutr. 2008, 48, 21–49.
Absorption Of An Aqueous Solution Of A New Synthetic (140) Ovchinnikov, Y. A.; Ivanov, V. T.; Evstratov, A. V.;
Somatostatin Analogue Administered To Man By Gavage. Eur. J. Mikhaleva, I. I.; Bystrov, V. F.; Portnova, S. L.; Balashova, T. A.;
Clin. Pharmacol. 1987, 33, 167–171. Meshcheryakova, E. N.; Tulchinsky, V. M. The Enniatin Ionophores.
(131) Williams, G.; Burrin, J. M.; Ball, J. A.; Joplin, G. F.; Bloom, Conformation And Ion Binding Properties. Int. J. Pept. Protein Res.
S. R. Effective And Lasting Growth-Hormone Suppression In Active 1974, 6, 465–498.
Acromegaly With Oral Administration Of Somatostatin Analogue (141) Kratky, C.; Dobler, M. The Crystal Structure of Enniatin B.
SMS 201-995. The Lancet 1986, 328, 774–778. Helv. Chim. Acta , 1985, 68, 1798-1803.
(132) Albert, R.; Marbach, P.; Bauer, W.; Briner, U.; Fricker, G.; (142) Tishchenko, G.N.; Zhukhlistova, N.E. Crystal and Molecular
Brums, C.; Pless, J. SDZ CO 611: A Highly Potent Glycated Analog Structure of the Membrane-Active Antibiotic Enniatin C
Of Somatostatin With Improved Oral Activity. Life Sci. 1993, 53, Kristallografiya (Russ.) Crystallogr. Rep., 2000, 45, 677-683.
517–525. (143) Tishchenko, G.N.; Karimov, Z. Structure Of Rubidium(1+)
(133) Nelson-Piercy, C.; Hammond, P. J.; Gwilliam, M. E.; Complex Of The LDLLDL Analog Of Enniatin B In Crystals.
Khandan-Nia, N.; Myers, M. J.; Ghatei, M. A.; Bloom, S. R. Effect Kristallografiya (Russ.) Crystallogr.Rep. 1978, 23,729-742.
Of A New Oral Somatostatin Analog (SDZ CO 611) On Gastric (144) Zhukhlistova, N.E.; Tishchenko, G.N.; Refaat, L.; Woolfson,
Emptying, Mouth To Cecum Transit Time, And Pancreatic And Gut M.M. Crystal And Molecular Structure Of (Enniatin B)2.KI Complex.
Hormone Release In Normal Male Subjects. J. Clin. Endocrinol. Kristallografiya (Russ.) Crystallogr. Rep. 1998, 43, 50-57.
Metab. 1994, 78, 329–336. (145) Faeste, C. K.; Ivanova, L.; Uhlig, S. In Vitro Metabolism Of (154) Rezai, T.; Bock, J. E.; Zhou, M. V.; Kalyanaraman, C.;
The Mycotoxin Enniatin B In Different Species And Cytochrome Lokey, R. S.; Jacobson, M. P. Conformational Flexibility, Internal
P450 Enzyme Phenotyping By Chemical Inhibitors. Drug Metab. Hydrogen Bonding, And Passive Membrane Permeability: Successful
Dispos. 2011, 39, 1768–1776. In Silico Prediction Of The Relative Permeabilities Of Cyclic
(146) Devreese, M.; Broekaert, N.; De Mil, T.; Fraeyman, S.; De Peptides. J. Am. Chem. Soc. 2006, 128, 14073–14080.
Backer, P.; Croubels, S. Pilot Toxicokinetic Study And Absolute Oral (155) White, T. R.; Renzelman, C. M.; Rand, A. C.; Rezai, T.;
Bioavailability Of The Fusarium Mycotoxin Enniatin B1 In Pigs. Mcewen, C. M.; Gelev, V. M.; Turner, R. A.; Linington, R. G.;
Food Chem. Toxicol. 2014, 63, 161–165. Leung, S. S. F.; Kalgutkar, A. S. et al. On-Resin N-Methylation Of
(147) Lecci, A.; Carini, F.; Tramontana, M.; D'aranno, V.; Cyclic Peptides For Discovery Of Orally Bioavailable Scaffolds. Nat.
Marinoni, E.; Crea, A.; Bueno, L.; Fioramonti, J.; Criscuoli, M.; Chem. Biol. 2011, 7, 810–817.
Giuliani, S. et al. Nepadutant Pharmacokinetics And Dose-Effect (156) Rand, A. C.; Leung, S. S.; Eng, H.; Rotter, C. J.; Sharma, R.;
Relationships As Tachykinin NK2 Receptor Antagonist Are Altered Kalgutkar, A. S.; Zhang, Y.; Varma, M. V.; Farley, K. A.; Khunte, B.
By Intestinal Inflammation In Rodent Models. J. Pharmacol. Exp. et al. Optimizing PK Properties Of Cyclic Peptides: The Effect Of
Ther. 2001, 299, 247–254. Side Chain Substitutions On Permeability And Clearance.
(148) http://Clinicaltrials.Gov/Ct2/Show/Nct00655083. MedChemComm. 2012, 3, 1282–1289.
(149) Jolad, S.D.; Hoffmann, J.J.; Torrance, S.J.; Wiedhopf, R.M.; (157) Schwochert, J.; Turner, R.; Thang, M.; Berkeley, R. F.;
Cole, J.R.; Arora, S.K.; Bates, R.B.; Gargiulo, R.L. Kriek, G.R. Ponkey, A. R.; Rodriguez, K. M.; Leung, S. S.; Khunte, B.; Goetz, G.;
Bouvardin and Deoxybouvardin, Antitumor Cyclic Hexapeptides Limberakis, C. et al. Peptide To Peptoid Substitutions Increase Cell from Bouvardia ternifolia (Rubiaceae). J. Am. Chem. Soc. 1977, 99, Permeability In Cyclic Hexapeptides. Org. Lett. 2015, 17, 2928–2931.
8040-8044. (158) Bockus, A. T.; Lexa, K. W.; Pye, C. R.; Kalgutkar, A. S.;
(150) Jolad, S. D.; Hoffmann, J. J.; Torrance, S. J.; Wiedhopf, R. Gardner, J. W.; Hund, K. C.; Hewitt, W. M.; Schwochert, J. A.;
M.; Cole, J. R.; Arora, S. K.; Bates, R. B.; Gargiulo, R. L.; Kriek, G. Glassey, E.; Price, D. A. et al. Probing The Physicochemical
R. Bouvardin And Deoxybouvardin, Antitumor Cyclic Hexapeptides Boundaries Of Cell Permeability And Oral Bioavailability In
From Bouvardia Ternifolia (Rubiaceae). J. Am. Chem. Soc. 1977, 99, Lipophilic Macrocycles Inspired By Natural Products. J. Med. Chem.
8040–8044. 2015, 58, 4581–4589.
(151) Reid, A. B.; Daffy, J. R.; Stanley, P.; Buising, K. L. Use Of (159) Lewis, I.; Schaefer, M.; Wagner, T.; Oberer, L.; Sager, E.;
Pristinamycin For Infections By Gram-Positive Bacteria: Clinical Wipfli, P.; Vorherr, T. A Detailed Investigation On Conformation,
Experience At An Australian Hospital. Antimicrob. Agents Permeability And PK Properties Of Two Related Cyclohexapeptides.
Chemother. 2010, 54, 3949–3952. Int. J. Pept. Res. Ther. 2015, 21, 205–221.
(152) Andes, D.; Craig, W. A. Pharmacodynamics Of A New (160) Wang, C. K.; Northfield, S. E.; Colless, B.; Chaousis, S.;
Streptogramin, XRP 2868, In Murine Thigh And Lung Infection Hamernig, I.; Lohman, R. J.; Nielsen, D. S.; Schroeder, C. I.; Liras,
Models. Antimicrob. Agents Chemother. 2006, 50, 243–249. S.; Price, D. A. et al. Rational Design And Synthesis Of An Orally
(153) Rezai, T.; Yu, B.; Millhauser, G. L.; Jacobson, M. P.; Lokey, Bioavailable Peptide Guided By NMR Amide Temperature
R. S. Testing The Conformational Hypothesis Of Passive Membrane Coefficients. Proc. Natl. Acad. Sci. U. S. A. 2014, 111, 17504–17509.
Permeability Using Synthetic Cyclic Peptide Diastereomers. J. Am. (161) Nielsen, D. S.; Lohman, R. J.; Hoang, H. N.; Hill, T. A.;
Chem. Soc. 2006, 128, 2510. Jones, A.; Lucke, A. J.; Fairlie, D. P. Flexibility Versus Rigidity For Orally Bioavailable Cyclic Hexapeptides. ChemBioChem 2015, 16, (171) Nielsen, D. S.; Hoang, H. N.; Lohman, R. J.; Diness, F.;
2289–2293. Fairlie, D. P. Total Synthesis, Structure, And Oral Absorption Of A
(162) Bechara, C.; Sagan, S. Cell-Penetrating Peptides: 20 Years Thiazole Cyclic Peptide, Sanguinamide A. Org. Lett. 2012, 14, 5720-
Later, Where Do We Stand? FEBS Lett. 2013, 587,1693-1702. 5723.
(163) Kauffman, W. B.; Fuselier, T.; He, J.; Wimley, W. C. (172) Nielsen, D. S.; Hoang, H. N.; Lohman, R. J.; Hill, T. A.;
Mechanism Matters: A Taxonomy Of Cell Penetrating Peptides. Lucke, A. J.; Craik, D. J.; Edmonds, D. J.; Griffith, D. A.; Rotter, C.
Trends Biochem. Sci. 2015, 40, 749-764. J.; Ruggeri, R. B. et al. Improving On Nature: Making A Cyclic
(164) Tashima, T. Intelligent Substance Delivery Into Cells Using Heptapeptide Orally Bioavailable. Angew. Chem. Int. Edit. 2014, 45,
Cell-Penetrating Peptides. Bioorg. Med. Chem. Lett. 2017, 27, 121- 12059–12063.
130. (173) Steyn, P. S.; Tuinman, A. A.; Van Heerden, F. R.; Van
(165) Qian, Z.; Martyna, A.; Hard, R. L.; Wang, J.; Appiah-Kubi, Rooyen, P. H.; Wessels, P. L.; Rabie, C. J. The Isolation, Structure,
G.; Coss, C.; Phelps, M. A.; Rossman, J. S.; Pei, D. Discovery And And Absolute Configuration Of The Mycotoxin, Rhizonin A, A
Mechanism Of Highly Efficient Cyclic Cell-Penetrating Peptides. Novel Cyclic Heptapeptide Containing N-Methyl-3-(3-Furyl)Alanine,
Biochemistry 2016, 55, 2601–2612. Produced By Rhizopus Microsporus. J. Chem. Soc., Chem. Commun.
(166) Hamann, M. T.; Scheuer, P. J. Kahalalide-F - A Bioactive 1983, 47–49.
Depsipeptide From The Sacoglossan Mollusk Elysia-Rufescens And (174) Wilson, T.; Rabie, C. J.; Fincham, J. E.; Steyn, P. S.;
The Green-Alga Bryopsis Sp. J. Am. Chem. Soc. 1993, 115, 5825– Schipper, M. A. Toxicity Of Rhizonin A, Isolated From Rhizopus
5826. Microsporus, In Laboratory Animals. Food Chem. Toxicol. 1984, 22,
(167) Suarez, Y.; Gonzalez, L.; Cuadrado, A.; Berciano, M.; 275–281.
Lafarga, M.; Munoz, A. Kahalalide F, A New Marine-Derived (175) Ernst, B.; Hoeger, S. J.; O'brien, E.; Dietrich, D. R. Oral
Compound, Induces Oncosis In Human Prostate And Breast Cancer Toxicity Of The Microcystin-Containing Cyanobacterium
Cells. Mol. Cancer Ther. 2003, 2, 863–872. Planktothrix Rubescens In European Whitefish (Coregonus
(168) Rademaker-Lakhai, J. M.; Horenblas, S.; Meinhardt, W.; Lavaretus). Aquat. Toxicol. 2006, 79, 31–40.
Stokvis, E.; De Reijke, T. M.; Jimeno, J. M.; Lopez-Lazaro, L.; Lopez (176) Yoshida, T.; Makita, Y.; Nagata, S.; Tsutsumi, T.; Yoshida,
Martin, J. A.; Beijnen, J. H.; Schellens, J. H. Phase I Clinical And F.; Sekijima, M.; Tamura, S.; Ueno, Y. Acute Oral Toxicity Of
Pharmacokinetic Study Of Kahalalide F In Patients With Advanced Microcystin-LR, A Cyanobacterial Hepatotoxin, In Mice. Nat. Toxins
Androgen Refractory Prostate Cancer. Clin. Cancer Res. 2005, 11, 1997, 5, 91–95.
1854–1862. (177) Ito, E.; Kondo, F.; Harada, K. First Report On The
(169) Brown, A. P.; Morrissey, R. L.; Faircloth, G. T.; Levine, B. S. Distribution Of Orally Administered Microcystin-LR In Mouse
Preclinical Toxicity Studies Of Kahalalide F, A New Anticancer Tissue Using An Immunostaining Method. Toxicon 2000, 38, 37–48.
Agent: Single And Multiple Dosing Regimens In The Rat. Cancer (178) Kawasaki, T.; Taniguchi, M.; Moritani, Y.; Uemura, T.;
Chemother. Pharmacol. 2002, 50, 333–340. Shigenaga, T.; Takamatsu, H.; Hayashi, K.; Takasaki, J.; Saito, T.;
(170) Dalisay, D. S.; Rogers, E. W.; Edison, A. S.; Molinski, T. F. Nagai, K. Pharmacological Properties Of YM-254890, A Specific
Structure Elucidation At The Nanomole Scale. 1. Trisoxazole G(Alpha)q/11 Inhibitor, On Thrombosis And Neointima Formation In
Macrolides And Thiazole-Containing Cyclic Peptides From The Mice. Thromb. Haemost. 2005, 94, 184–192.
Nudibranch Hexabranchus Sanguineus. J. Nat. Prod. 2009, 72, 732– (179) Cunningham, T. J.; Greenstein, J.; Yao, L. Uncompetitive
738. Phospholipase A2 Inhibition By CHEC Sequences Including Oral Treatment Of Experimental Autoimmune Myeloencephalitis. Open (189) Harder, A.; Holden–Dye, L.; Walker, R.; Wunderlich, F.
Enzyme Inhib. J. 2009, 2, 1–7. Mechanisms Of Action Of Emodepside. Parasitol. Res. 2005, 97, S1–
(180) Kicielinska, J.; Szczygiel, A.; Rossowska, J.; Anger, N.; S10.
Kempinska, K.; Switalska, M.; Kaszowska, M.; Wietrzyk, J.; (190) Harder, A.; Schmitt-Wrede, H.-P.; Krucken, J.; Marinovski,
Boratynski, J.; Pajtasz-Piasecka, E. Oral Administration Of P.; Wunderlich, F.; Willson, J.; Amliwala, K.; Holden-Dye, L.;
Polymyxin B Modulates The Activity Of Lipooligosaccharide E. Coli Walker, R. Cyclooctadepsipeptides - An Anthelmintically Active
B Against Lung Metastases In Murine Tumor Models. PloS One Class Of Compounds Exhibiting A Novel Mode Of Action. Int. J.
2016, 11, E0148156. Antimicrob. Agents 2003, 22, 318–331.
(181) Adachi, Y.; Enomoto, M.; Adachi, M.; Suwa, M.; Nagamine, (191) Ohyama, M.; Okada, Y.; Takahashi, M.; Sakanaka, O.;
Y.; Nanno, T.; Hashimoto, T.; Inoue, H.; Yamamoto, T. Enteric Matsumoto, M.; Atsumi, K. Structure-Activity Relationship Of
Coated Polymyxin B In The Treatment Of Hyperammonemia And Anthelmintic Cyclooctadepsipeptides. Biosci. Biotechnol. Biochem.
Endotoxemia In Liver Cirrhosis. Gastroenterol. Jpn. 1982, 17, 550– 2011, 75, 1354–1363.
557. (192) Baronsky, J.; Bongaerts, S.; Traeubel, M. Weiss, H.-C.;
(182) Dudley, M. N.; Mclaughlin, J. C.; Carrington, G.; Frick, J.; Urbanetz, N. The Study Of Different Solid Forms Of Emodepside.
Nightingale, C. H.; Quintiliani, R. Oral Bacitracin Vs Vancomycin Eur. J. Pharm. and Biopharm. 2009 , 71, 88-99.
Therapy For Clostridium Difficile-Induced Diarrhea. A Randomized (193) Https://Clinicaltrials.Gov/Ct2/Show/Nct02661178.
Double-Blind Trial. Arch. Intern. Med. 1986, 146, 1101–1104. (194) Gao, Z. Q.; Zhao, X. Y.; Lee, S.; Li, J. J.; Liao, H.; Zhou, X.
(183) Bond, G. C.; Vanderbrook, M. J.; Et Al. Oral Administration H.; Wu, J.; Qi, G. F. Wh1fungin A Surfactin Cyclic Lipopeptide Is A
Of Bacitracin. Proc. Soc. Exp. Biol. Med. 1948, 68, 395–400. Novel Oral Immunoadjuvant. Vaccine 2013, 31, 2796–2803.
(184) Weinstein, M. R.; Dedier, H.; Brunton, J.; Campbell, I.; (195) Gao, Z. Q.; Zhao, X. Y.; Yang, T.; Shang, J.; Shang, L.; Mai,
Conly, J. M. Lack Of Efficacy Of Oral Bacitracin Plus Doxycycline H. Z.; Qi, G. F. Immunomodulation Therapy Of Diabetes By Oral
For The Eradication Of Stool Colonization With Vancomycin- Administration Of A Surfactin Lipopeptide In Nod Mice. Vaccine
Resistant Enterococcus Faecium. Clin. Infect. Dis. 1999, 29, 361–366. 2014, 32, 6812–6819.
(185) http://www.Drugbank.Ca/Drugs/Db00626. (196) Wieland, T.; Faulstich, H. Amatoxins, Phallotoxins,
(186) Sasaki, T.; Takagi, M.; Yaguchi, T.; Miyadoh, S.; Okada, T.; Phallolysin, And Antamanide: The Biologically Active Components
Koyama, M. A New Anthelmintic Cyclodepsipeptide, PF1022a. J. Of Poisonous Amanita Mushrooms. CRC Crit. Rev. Biochem. 1978, 5,
Antibiot. 1992, 45, 692–697. 185–260.
(187) Kachi, S.; Ishih, A.; Terada, M. Effects Of Pf1022a On Adult (197) Faulstich, H.; Buku, A.; Bodenmuller, H.; Wieland, T.
Angiostrongylus Cantonensis In The Pulmonary Arteries And Larvae Virotoxins: Actin-Binding Cyclic Peptides Of Amanita Virosa
Migrating Into The Central Nervous System Of Rats. Parasitol. Res. Mushrooms. Biochemistry 1980, 19, 3334–3343.
1995, 81, 631–637. (198) Wong, J. H.; Ng, T. B. In Handbook Of Biologically Active
(188) Von Samson-Himmelstjerna, G.; Harder, A.; Sangster, N. C.; Peptides; Abba, J. K., Ed.; Academic Press: Burlington, 2006, 131–
Coles, G. C. Efficacy Of Two Cyclooctadepsipeptides, Pf1022a And 135.
Emodepside, Against Anthelmintic-Resistant Nematodes In Sheep (199) Walton, J. D.; Hallen-Adams, H. E.; Luo, H. Ribosomal
And Cattle. Parasitology 2005, 130, 343–347. Biosynthesis Of The Cyclic Peptide Toxins Of Amanita Mushrooms.
Biopolymers 2010, 94, 659–664. (200) Bushnell, D.A.; Cramer, P.; Kornberg, R.D. Structural Basis (211) Haneishi, T.; Nakajima, M.; Shiraishi, A.; Katayama, T.; of Transcription: Alpha-Amanitin-RNA Polymerase II Cocrystal at Torikata, A.; Kawahara, Y.; Kurihara, K.; Arai, M.; Arai, T.; Aoyagi,
2.8 Å Resolution. Proc. Natl. Acad. Sci. U. S. A. 2002, 99, 1218-122. T.; Et Al. Antimycobacterial Activities In Vitro And In Vivo And
(201) Brueckner, F.; Cramer, P. Structural Basis of Transcription Pharmacokinetics Of Dihydromycoplanecin A. Antimicrob. Agents
Inhibition by Alpha-Amanitin and Implications for RNA Polymerase Chemother. 1988, 32, 110–116.
II Translocation. Nat. Struct. Mol. Biol. 2008, 15, 811-818. (212) Cunningham, T. J.; Greenstein, J. I.; Loewenstern, J.;
(202) Kaplan, C.D.; Larsson, K.M.; Kornberg, R.D. The RNA Degermentzidis, E.; Yao, L. H. Anti-Inflammatory Peptide Regulates
Polymerase II Trigger Loop Functions in Substrate Selection and is The Supply Of Heat Shock Protein 70 Monomers: Implications For
Directly Targeted by Alpha-Amanitin., Mol. Cell, 2008, 30, 547-556. Aging And Age-Related Disease. Rejuv. Res. 2015, 18, 136–144.
(203) Wieland, T.; Gotzendorfer, C.; Dabrowski, J.; Lipscomb, (213) Mesfin, F. B.; Bennett, J. A.; Jacobson, H. I.; Zhu, S.;
W.N.; Shoham, G. Unexpected Similarity of the Structures of the Andersen, T. T. Alpha-Fetoprotein-Derived Antiestrotrophic
Weakly Toxic Amanitin (S)-Sulfoxide and the Highly Toxic (R)- Octapeptide. Biochim. Biophys. Acta 2000, 1501, 33–43.
Sulfoxide and Sulfone As Revealed by Proton Nuclear Magnetic (214) Defreest, L. A.; Mesfin, F. B.; Joseph, L.; Mcleod, D. J.;
Resonance and X-ray Analysis. Biochemistry , 1983, 22, 1264-1271. Stallmer, A.; Reddy, S.; Balulad, S. S.; Jacobson, H. I.; Andersen, T.
(204) Shoham, G.; Lipscomb, W.N.; Wieland, Th. Conformations T.; Bennett, J. A. Synthetic Peptide Derived From Α-Fetoprotein of Amatoxins in the Crystalline State. J. Am. Chem. Soc. 1989, 111, Inhibits Growth Of Human Breast Cancer: Investigation Of The
4791-4809. Pharmacophore And Synthesis Optimization. J. Pept. Res. 2004, 63,
(205) Mas, A. Mushrooms, Amatoxins And The Liver. J. Hepatol. 409–419.
2005, 42, 166–169. (215) Bennett, J. A.; Defreest, L.; Anaka, I.; Saadati, H.; Balulad,
(206) Wieland, T. Peptides Of Poisonous Amanita Mushrooms; S.; Jacobson, H. I.; Andersen, T. T. Afpep: An Anti-Breast Cancer
Springer-Verlag, 1986. Peptide That Is Orally Active. Breast Cancer Res. Treat. 2006, 98,
(207) Terlain, B.; Thomas, J. P. Structure Of Griselimycin, 133–141.
Polypeptide Antibiotic Extracted Streptomyces Cultures. I. (216) Mesfin, F. B.; Andersen, T. T.; Jacobson, H. I.; Zhu, S.;
Identification Of The Products Liberated By Hydrolysis. Bull. Soc. Bennett, J. A. Development Of A Synthetic Cyclized Peptide Derived
Chim. Fr. 1971, 6, 2349–2356. From Alpha-Fetoprotein That Prevents The Growth Of Human Breast
(208) Kling, A.; Lukat, P.; Almeida, D. V.; Bauer, A.; Fontaine, E.; Cancer. J. Pept. Res. 2001, 58, 246–256.
Sordello, S.; Zaburannyi, N.; Herrmann, J.; Wenzel, S. C.; Konig, C. (217) Fehrenbach, T.; Cui, Y.; Faulstich, H.; Keppler, D. et al. Antibiotics. Targeting Dnan For Tuberculosis Therapy Using Characterization Of The Transport Of The Bicyclic Peptide Phalloidin
Novel Griselimycins. Science 2015, 348, 1106–1112. By Human Hepatic Transport Proteins. Naunyn Schmiedebergs Arch.
(209) Holzgrabe, U. New Griselimycins For Treatment Of Pharmacol. 2003, 368, 415–420.
Tuberculosis. Chem. Biol. 2015, 22, 981–982. (218) Siemion, I. Z.; Pçdyczak, A.; Trojnar, J.; Zimecki, M.;
(210) Nakajima, M.; Torikata, A.; Ichikawa, Y.; Katayama, T.; Wieczorek, Z. Immunosuppressive Activity Of Antamanide And
Shiraishi, A.; Haneishi, T.; Arai, M. Mycoplanecins, Novel Some Of Its Analogues. Peptides 1992, 13, 1233–1237.
Antimycobacterial Antibiotics From Actinoplanes Awajinensis (219) Karle, I.L.; Wieland, T.; Schermer, D.; Ottenheijm, H.C.J.
Subsp. Mycoplanecinus Subsp. Nov. II. Isolation, Physico-Chemical Conformation Of Uncomplexed Natural Antamanide Crystallized
Characterization And Biological Activities Of Mycoplanecin A. J. From CH3CN/H20. Proc. Nat. Acad. Sci. U. S. A. 1979, 76, 1532-
Antibiot. (Tokyo) 1983, 36, 961–966. 1536. (220) Di Blasio, B.; Rossi, F,; Benedetti, E.; Pavone, V.; (229) https://Clinicaltrials.Gov/Ct2/Show/Study/Nct01597505.
Pedone, C.; Temussi, P.A.; Zanotti, G,; Tancredi T. Bioactive (230) Grevel, J.; Nuesch, E.; Abisch, E.; Kutz, K. Pharmacokinetics
Peptides: Solid-State And Solution Conformation Of Of Oral Cyclosporin A (Sandimmun) In Healthy Subjects. Eur. J.
Cyclolinopeptide A. J. Am. Chem. Soc. 1989, 111, 9089-9098. Clin. Pharmacol. 1986, 31, 211–216.
(221) Quail, J.W.; Shen, J.; Reaney, M.J.T.; Sammynaiken R. (231) Jin, M.; Shimada, T.; Shintani, M.; Yokogawa, K.; Nomura,
Cyclolinopeptide A Methanol Solvate. Acta Crystallogr. Sect. E: M.; Miyamoto, K. Long-Term Levothyroxine Treatment Decreases
Struct. Rep. Online , 2009, 65, 1913-1914. The Oral Bioavailability Of Cyclosporin A By Inducing P-
(222) Emmer, G.; Grassberger, M. A.; Meingassner, J. G.; Schulz, Glycoprotein In Small Intestine. Drug Metab. Pharmacokinet. 2005,
G.; Schaude, M. Derivatives Of A Novel Cyclopeptolide. 1. 20, 324–330.
Synthesis, Antifungal Activity, And Structure-Activity Relationships. (232) Loosli, H.-R.; Kessler, H.; Oschkinat, H.; Weber, H.-P.;
J. Med. Chem. 1994, 37, 1908–1917. Petcher, T. J.; Widmer, A. Peptide Conformations. Part 31. The
(223) Takahara, Y.; Takeuchi, Y.; Komura, I.; Hirose, Y.; Murao, Conformation Of Cyclosporin A In The Crystal And In Solution.
S. Isolation Of A New Peptide Antibiotic, Permetin A, From Bacillus Helv. Chim. Acta 1985, 68, 682–704.
Circulans. J. Antibiot. (Tokyo) 1979, 32, 115–120. (233) Pflugl, G.; Kallen, J.; Schirmer, T.; Jansonius, J. N.; Zurini,
(224) Fouche, M.; Schafer, M.; Berghausen, J.; Desrayaud, S.; M. G.; Walkinshaw, M. D. X-Ray Structure Of A Decameric
Blatter, M.; Piechon, P.; Dix, I.; Martin Garcia, A.; Roth, H. J. Design Cyclophilin-Cyclosporin Crystal Complex. Nature 1993, 361, 91.
And Development Of A Cyclic Decapeptide Scaffold With Suitable (234) Mikol, V.; Kallen, J.; Pflugl, G.; Walkinshaw, M. D. X-Ray
Properties For Bioavailability And Oral Exposure. ChemMedChem Structure Of A Monomeric Cyclophilin A-Cyclosporin A Crystal
2016, 11, 1048–1059. Complex At 2.1Å Resolution. J. Mol. Biol. 1993, 234, 1119–1130.
(225) Fouche, M.; Schafer, M.; Blatter, M.; Berghausen, J.; (235) Weber, C.; Wider, G.; Von Freyberg, B.; Traber, R.; Braun,
Desrayaud, S.; Roth, H. J. Pharmacokinetic Studies Around The W.; Widmer, H.; Wuthrich, K. The NMR Structure Of Cyclosporin A
Mono- And Difunctionalization Of A Bioavailable Cyclic Bound To Cyclophilin In Aqueous Solution. Biochemistry 1991, 30,
Decapeptide Scaffold. ChemMedChem 2016, 11, 1060–1068. 6563–6574.
(226) Mascio, C. T.; Mortin, L. I.; Howland, K. T.; Van Praagh, A. (236) Fesik, S.W.; Gampe, R.T. Jr.; Eaton, H.L.; Gemmecker, G.,
D.; Zhang, S.; Arya, A.; Chuong, C. L.; Kang, C.; Li, T.; Silverman, Olejniczak, E.T.; Neri, P.; Holzman, T.F.; Egan, D.A.; Edalji, R.;
J. A. In Vitro And In Vivo Characterization Of CB-183,315, A Novel Simmer, R. et al. NMR studies of [U-13C]cyclosporin A bound to
Lipopeptide Antibiotic For Treatment Of Clostridium Difficile. cyclophilin: bound conformation and portions of cyclosporin involved
Antimicrob. Agents Chemother. 2012, 56, 5023–5030. in binding. Biochemistry, 1991, 30, 6574-83.
(227) Snydman, D. R.; Jacobus, N. V.; Mcdermott, L. A. Activity (237) Cho, H.; Chung, Y. Water Soluble Cyclosporine
Of A Novel Cyclic Lipopeptide, CB-183,315 Against Resistant Monomethoxy Poly(Ethyleneglycol) Conjugates As Potential
Clostridium Difficile And Other Gram Positive Aerobic And Prodrugs. Arch. Pharm. Res. 2004, 27, 662–669.
Anaerobic Intestinal Pathogens. Antimicrob. Agents Chemother. 2012, (238) Rosenwirth, B.; Billich, A.; Datema, R.; Donatsch, P.;
56, 3448–3452. Hammerschmid, F.; Harrison, R.; Hiestand, P.; Jaksche, H.; Mayer,
(228) Knight-Connoni, V.; Mascio, C.; Chesnel, L.; Silverman, J. P.; Peichl, P. Inhibition Of Human Immunodeficiency Virus Type 1
Discovery And Development Of Surotomycin For The Treatment Of Replication By SNZ NIM 811, A Non-Immunosuppressive
Clostridium Difficile. J. Ind. Microbiol. Biotechnol. 2016, 43, 195– Cyclosporine Analog. Antimicrob. Agents Chemother. 1994, 38,
204. 1763–1772. (239) Hopkins, S.; Scorneaux, B.; Huang, Z.; Murray, M. G.; Solinga, R. M.; Sun, L. J. et al. Linaclotide, Through Activation Of
Wring, S.; Smitley, C.; Harris, R.; Erdmann, F.; Fischer, G.; Ribeill, Guanylate Cyclase C, Acts Locally In The Gastrointestinal Tract To
Y. SCY-635, A Novel Nonimmunosuppressive Analog Of Elicit Enhanced Intestinal Secretion And Transit. Eur. J. Pharmacol.
Cyclosporine That Exhibits Potent Inhibition Of Hepatitis C Virus 2010, 649, 328–335.
RNA Replication In Vitro. Antimicrob. Agents Chemother. 2010, 54, (248) Blanchfield, J. T.; Gallagher, O. P.; Cros, C.; Lewis, R. J.;
660–672. Alewood, P. F.; Toth, I. Oral Absorption And In Vivo Biodistribution
(240) Ptak, R. G.; Gallay, P. A.; Jochmans, D.; Halestrap, A. P.; Of [Alpha]-Conotoxin MII And A Lipidic Analogue. Biochem.
Ruegg, U. T.; Pallansch, L. A.; Bobardt, M. D.; De Béthune, M.-P.; Biophys. Res. Commun. 2007, 361, 97–102.
Neyts, J.; De Clercq, E. et al. Inhibition Of Human Immunodeficiency (249) Clark, R. J.; Jensen, J.; Nevin, S. T.; Callaghan, B. P.; Adams,
Virus Type 1 Replication In Human Cells By DEBIO-025, A Novel D. J.; Craik, D. J. The Engineering Of An Orally Active Conotoxin
Cyclophilin Binding Agent. Antimicrob. Agents Chemother. 2008, 52, For The Treatment Of Neuropathic Pain. Angew. Chem. Int. Ed. 2010,
1302–1317. 49, 6545–6548.
(241) Flisiak, R.; Horban, A.; Gallay, P.; Bobardt, M.; Selvarajah, (250) Mcnulty, M. J.; Hutabarat, R. H.; Findlay, J. W.; Devereux,
S.; Wiercinska-Drapalo, A.; Siwak, E.; Cielniak, I.; Higersberger, J.; K.; Knick, V. C.; Harvey, R. J.; Molina, L. Pharmacokinetics And
Kierkus, J. et al. The Cyclophilin Inhibitor DEBIO-025 Shows Potent Tissue Distribution Of The Nonadecapeptide MOLI-1901 In Rats
Anti–Hepatitis C Effect In Patients Coinfected With Hepatitis C And And Mice. Xenobiotica 2003, 33, 197–210.
Human Immunodeficiency Virus. Hepatology 2008, 47, 817–826. (251) Pinto, M. F. S.; Almeida, R. G.; Porto, W. F.; Fensterseifer, I.
(242) Gallay, P.; Lin, K. Profile Of Alisporivir And Its Potential In C. M.; Lima, L. A.; Dias, S. C.; Franco, O. L. Cyclotides: From Gene
The Treatment Of Hepatitis C. Drug Des. Devel. Ther. 2013, 7, 105– Structure To Promiscuous Multifunctionality. J. Evid. Based
115. Complementary Altern. Med. 2012, 17, 40–53.
(243) Sugimoto, H.; Lebleu, V. S.; Bosukonda, D.; Keck, P.; (252) Gran, L. On The Effect Of A Polypeptide Isolated From
Taduri, G.; Bechtel, W.; Okada, H.; William, C.; Bey, P.; "Kalata-Kalata" (Oldenlandia Affinis DC) On The Oestrogen
Rusckowski, M. et al. Activin-Like Kinase 3 Is Important For Kidney Dominated Uterus. Acta Pharmacol. Toxicol. 1973, 33, 400–408.
Regeneration And Reversal Of Fibrosis. Nat. Med. 2012, 18, 396– (253) Wong, C. T. T.; Rowlands, D. K.; Wong, C.-H.; Lo, T. W. C.;
404. Nguyen, G. K. T.; Li, H.-Y.; Tam, J. P. Orally Active Peptidic
(244) Rose, L.; Jenkins, A. T. A. The Effect Of The Ionophore Bradykinin B1 Receptor Antagonists Engineered From A Cyclotide
Valinomycin On Biomimetic Solid Supported Lipid DPPTE/EPC Scaffold For Inflammatory Pain Treatment. Angew. Chem. Int. Ed.
Membranes. Bioelectrochem. 2007, 70, 387–393. 2012, 51, 5620–5624.
(245) Agata, N.; Ohta, M.; Mori, M.; Isobe, M. A Novel (254) Henriques, S. T.; Craik, D. J. Importance Of The Cell
Dodecadepsipeptide, Cereulide, Is An Emetic Toxin Of Bacillus- Membrane On The Mechanism Of Action Of Cyclotides. ACS Chem.
Cereus. FEMS Microbiol. Lett. 1995, 129, 17–19. Biol. 2012, 7, 626–636.
(246) Amr, A. E.-G. E.; Abo-Ghalia, M. H.; Abdalah, M. M. (255) Thell, K.; Hellinger, R.; Sahin, E.; Michenthaler, P.; Gold-
Synthesis Of New (N-Α-Dipicolinoyl)-Bis-L-Valyl-L-Phenylalanyl Binder, M.; Haider, T.; Kuttke, M.; Liutkeviciute, Z.; Goransson, U.;
Linear And Macrocyclic Bridged Peptides As Anti-Inflammatory Grundemann, C. et al. Oral Activity Of A Nature-Derived Cyclic
Agents. Arch. Pharm. 2007, 340, 304–309. Peptide For The Treatment Of Multiple Sclerosis. Proc. Natl. Acad.
(247) Busby, R. W.; Bryant, A. P.; Bartolini, W. P.; Cordero, E. A.; Sci. U. S. A. 2016, 113, 3960–3965.
Hannig, G.; Kessler, M. M.; Mahajan-Miklos, S.; Pierce, C. M.; (256) QikProp, Schrödinger, LLC, New York, NY, 2016.
Schrödinger Release 2016-1.
(257) Bird, G. H.; Madani, N.; Perry, A. F.; Princiotto, A. M.;
Supko, J. G.; He, X.; Gavathiotis, E.; Sodroski, J. G.; Walensky, L. D.
Hydrocarbon Double-Stapling Remedies The Proteolytic Instability
Of A Lengthy Peptide Therapeutic. Proc. Natl. Acad. Sci. U. S. A.
2010, 107, 14093–14098.
(258) Mannhold, R.I.; Poda, G. I.; Ostermann, C.; Tetko, I. V.
Calculation Of Molecular Lipophilicity: State-Of-The-Art And
Comparison Of Log P Methods On More Than 96,000 Compounds. J.
Pharm. Sci. 2009, 98, 861–893.
(259) Ghose, A. K.; Viswanadhan, V. N.; Wendoloski, J. J. A knowledge-based approach in designing combinatorial or medicinal chemistry libraries for drug discovery. 1. A qualitative and quantitative characterization of known drug databases. J. Comb.
Chem. 1999, 1, 55–68.
(260) Stewart, W. E.; Siddall, T. H. Nuclear Magnetic Resonance
Studies Of Amides. Chem. Rev. 1970, 70, 517–551.
(261) Lu, J. J.; Crimin, K.; Goodwin, J. T.; Crivori, P.; Orrenius, C.;
Xing, L.; Tandler, P. J.; Vidmar, T. J.; Amore, B. M.; Wilson, A. G.
E.; Stouten, P. F. W.; Burton, P. S. Influence Of Molecular Flexibility
And Polar Surface Area Metrics On Oral Bioavailability In The Rat.
J. Med. Chem. 2004, 47, 6104–6107.
(262) Tian, S.; Li, Y.; Wang, J., Zhang, J.; Hou, T. ADME
Evaluation In Drug Discovery. 9. Prediction Of Oral Bioavailability
In Humans Based On Molecular Properties And Structural
Fingerprints. Mol. Pharmaceutics 2011, 8, 841–851.
(263) Meanwell, N. E. Synopsis Of Some Recent Tactical
Application Of Bioisosteres In Drug Design. J. Med. Chem. 2011, 54,
2529–2591.
Table of Contents Graphic