DaMocles Telithromycin

First Ketolide antibiotic

A. Zarda; D. Zibulski; M. Wartusch; T. Wörmann; S.Zurmühl 26.6.2017

Table of Contents

The demand for a new antibiotic ...... 2 The differences between Telithromycin and Erythromycin ...... 2 Usage...... 3 Side effects ...... 4 Causes of severe side effects...... 5 Medical effect of Telithromycin ...... 6 Synthesis ...... 6 References ...... 9 Table of figures ...... 10

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The demand for a new antibiotic

It is a widespread health problem to combat community-acquired respiratory tract infections worldwide. With the introduction of Erythromycin in 1952 (Raja, et al., 2004) a new treatment for those diseases was found.

Erythromycin is the first Macrolide compounds which is used as an antibiotic. The Macrolide drug class inhibits the bacterial protein synthesis by interacting with its ribosomes (Haastrup Hansen, et al., 1999). But Erythromycin has got some drawbacks as an antibiotic. The acid medium of the stomach leads to the degradation of Erythromycin (Agouridas, et al., 1998). One year after the introduction of the antibiotic erythromycin-resistant staphylococci were found in the United States, Europe and Japan (Roberts, et al., 1999).

As a result, some semisynthetic Macrolides came out: Roxithromycin, Clarithromycin and Azithromycin (Agouridas, et al., 1998) They are more stable, show fewer side effects and provide the treatment for a variety of infectious bacteria (Roberts, et al., 1999). After the increased use of these Macrolides, bacteria build up resistance against them. Through the addition of one or two methyl groups in the 23S rRNA, they block the binding side of erythromycin. Some other antibiotics like lincosamides and streptogramin B have the same problem and have lost their effect against these bacteria (Roberts, et al., 1999).

Due to the adaption of the bacteria research went into a different direction concentrating on the binding side of the active compound.

The differences between Telithromycin and Erythromycin

As a start of the synthesis of a successful compound, they used the structures of already existing antibiotics as a guideline.

It was known that a supplementary amino group improves the activity against H. influenza. For a long time, the cladinose moiety was understood to be the crucial part of the compound with the antibiotic effect. Further experiments showed that it was not the functional group itself which is important but the position (position 3 of macrolides) in the molecule. Therefor research was focused in finding a moiety which is active against the bacteria (Agouridas, et al., 1998).

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Figure 1 Differences between Erythromycin A and Telithromycin (Raja, et al., 2004)

The exchange of the L-cladinose sugar with a 3-keto function was the breakthrough. A new class of antibiotics, the ketolides, was established. The treatment with ketolides is active against bacteria, which are resistant to macrolides, lincosamides and streptogramin B. To improve the activity and pharmacokinetics a carbamate side chain and a methoxy group were added. The methoxy group leads to the stability of Telithromycin in the acid medium in the stomach (Raja, et al., 2004).

Usage

Telithromycin is the major component of the antibiotic drug Ketek® produced by the pharmaceutical company Sanofi (Sanofi, 2017). The drug is often prescribed to patients suffering from pneumonia caused by strains of antibiotic resistant bacteria such as Streptococcus pneumonia, that cannot be treated by first generation macrolides such as erythromycin A. Furthermore otolaryngologists (specialised ENT doctors) will treat acute exacerbation of chronic bronchitis or acute sinusitis in adults and tonsillitis or pharyngitis in children with drugs based on Telithromycin. Telithromycin was believed to be a breakthrough in treating and eradicating resistant strains, as it stays active and effective against 98% - 100% erythromycin-resistant strains (Leclercq, 2001) (Farrell & Felmingham, 2004). Nevertheless, the widespread use of drugs containing Telithromycin has been reduced in the last decade as dramatic and even lethal side effects were noticed in large groups of patients. In 2007 the Food and Drug Administration went as far as dropping two previously approved indications of the drug Ketek®, furthermore warning labels and a contraindication was added stating that no one with the neurological disease ‘myasthenia gravis’ should take said drug (U.S. Food and Drug, 2016).

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Side effects

Common side effects (1-10% of user affected) of the drug Ketek® include nausea, vomiting, diarrhoea, headaches, anxiety and changes in your sense of taste. A medical tail revealed that 4.4 % of the 4780 test- patients (n=2702) had to terminate the intake of the drug mostly due to gastrointestinal problems. Out of this group of test patients, roughly 9% suffered from diarrhoea and 7% suffered from nausea.

Figure 2 Common side effects (Cunha, 2016)

Uncommon but severe side effects (0.0-2% of the users affected) of the drug include heart palpitations, irreversible liver damage and failure, as well as hallucinations and diplopia1. Later visual side effects affected especially females under the age of 40. The clinical trial reported that out of this group 2.1% of female patients experienced severe visual adverse reactions.

Figure 3 Percentages of patients with severe visual adverse reactions (Cunha, 2016)

1 Diplopia is characterised as a visual adverse reaction, causing the patient to perceive his surroundings in blurry double vision.

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Other adverse reactions to the drug Ketek® are observed when the drug is taken in by the patients along with other drugs such as blood thinners, cholesterol-lowering medicines, ergot medicines, sedatives, Itraconazole, Ketoconazole, heart rhythm medications, Rifampin, seizure medications, Metoprolol, Tacrolimus, Sirolimus, Cyclosporine, or Digoxin.

Causes of severe side effects

Telithromycin’s side chain pyridine moiety blocks nicotinic acetylcholine receptors located in the neuromuscular junction, the ciliary ganglion of the eye and the vagus nerve innervating the liver causing uncommon but severe side effects including hallucinations, diplopia and liver failure.

Figure 4 Telithromycin´s pyridine moiety (Shown in red and green) (Fernandes, et al., 2016)

New macrolides such as azithromycin, clarithromycin and the fluoroketolide, Solithromycin contain a different side chain, as well as a fluorine substituent. These alterations not only positively affect the stability of the macrolide but also do not interfere with the choline dependent receptors as severely as Telithromycin does, thus causing less severe side effects (Fernandes, et al., 2016).

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Medical effect of Telithromycin

Telithromycin prevents bacterial growth by inhibiting protein synthesis. It binds to the 23S rRNA and the 50S ribosomal subunit domain, causing the deactivation of metabolic processes. The crystal structure of the large ribosomal subunit altered by telithromycin suggests that the molecule binds to the ribosome with its lactone ring in a similar position as Erythromycin A would. However, for Telithromycin, its alkyl-aryl side chain extends above the lactone ring enabling the stacking of its pyridine groups on the base of C2644 ribose ring. The additional stacking observed in Telithromycin and the hydrogen bond formed between pyridines nitrogen atom and the 2’OH group of C2644 ribose sugar may explain why telithromycin has a high binding affinity for wild-type bacterial ribosomes. In fact, its binding affinity is 10 times higher than that of Erythromycin, making it far more effective drug against resistant strains (Gribble & Joule, 2012).

Synthesis

From Clarithromycin to Telithromycin

In the first step, the hydroxy-group is transformed into a good leaving group. Afterwards elimination takes place in presence of a base like pyridine.

Figure 5 First step of synthesis (Macher & Souza, 2009)

An aqueous acid solvent is used to remove the acetal at C3 since acetals protect hydroxy-functions in basic synthesis but are not stable in acids. The next step of the synthesis is the protection of the C-2 hydroxy- group. This can be done by forming an ester using acetyl chloride, acetic anhydride, benzoyl chloride or benzoic anhydride.

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The forth step is generating the characteristic group of Ketolides the keto-group on the 3-carbon-atom. Oxidation transforms the hydroxy-function at C3 into a keto-function. This Oxidation is carried out by employing commonly used oxidizing reagents such as activated dimethyl sulfoxide (DMSO) and related reagents.

Figure 6 First part of synthesis (Macher & Souza, 2009)

In the fifth step, the C-12 hydroxy group is substituted with an imidazolyl group. To do so compound 20 is reacted with carbonyldiimidazole in the presence of an organic or inorganic base so that compound 21 can be synthesised (see Figure 7 Second part of synthesis . To achieve a complete reaction, the organic base DBU, the solvent methylene chloride and a reaction temperature between -20°C and 20°C are used. In the sixth step, the pyridine and imidazole moieties are attached to the C-11-C-12 carbamate. Compound 22 is recovered by a condensation reaction between compound 21 and primary amine 18.

Figure 6 primary amine (Macher & Souza, 2009)

To provide optimal conditions for this reaction a polar aprotic solvent e.g. methylene chloride in the presence of an organic base such as DBU is used as well as a temperature of 20°C to 40°C. In the last step of the synthesis of Telithromycin (compound 1), the C-2' protecting group is removed to restore the C-2' hydroxy group.

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In the case of an ester protecting group, an alcoholysis is carried out for which methanol and ethanol are used. In addition, an aqueous base e.g. NaOH or KOH can be used while a temperature of 0°C to 20°C is maintained. By crystallising telithromycin with polar protic and polar aprotic solvents such as alcohols, esters and ketones, a high purity can be achieved (Macher & Souza, 2009).

Figure 7 Second part of synthesis (Macher & Souza, 2009)

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References

Agouridas, C. et al., 1998. Synthesis and Antibacterial Activity of Ketolides (6-O-Methyl-3oxoerythromycin Derivatives): A New Class of Antibacterials Highly Potent Against MacrolideResistant and -Susceptible Respiratory. J. Med. Chem., Issue 41, pp. 4080-4100.

Cunha, J. P., 2016. RxList. [Online] Available at: http://www.rxlist.com/ketek-side-effects-drug-center.htm [Accessed 07 June 2017].

Farrell, D. J. & Felmingham, D., 2004. Activities of Telithromycin against 13,874 Streptococcus pneumoniae Isolates Collected between 1999 and 2003. Antimicrobial Agents and Chemotherapy, May, 48(5), p. 1882– 1884.

Fernandes, P., Martens, E., Bertrand, D. & Pereira, D., 2016. The solithromycin journey—It is all in the chemistry. Bioorganic & Medicinal Chemistry, 15 Dec, p. 6420–6428.

Gribble, G. W. & Joule, J. A., 2012. Progress in Heterocyclic Chemistry. 1/2012 ed. Oxford; Amsterdam: Elsevier, p.11.

Haastrup Hansen, L., Mauvais, P. & Douthwaite, S., 1999. The macrolide–ketolide antibiotic binding site is formed by structures in domains II and V of 23S ribosomal RNA. Molecular Microbiology, Issue 31(2), p. 623– 631.

Leclercq, R., 2001. Overcoming antimicrobial resistance: profile of a new ketolide antibacterial, telithromycin. Journal of Antimicrobial Chemotherapy, 01 Sep, Issue 48, pp. 09-23.

Macher, I. & Souza, D. D., 2009. Process for the production of Telithromycin. s.l. Patent No. WO 2009/053259 A1.

Nilius, A. M. & Z, M., 2002. Ketolides: the future of the macrolides?. Curr. Opin. Pharmacol., p. 493–500.

Raja, A., Lebbos, J. & Kirkpatrick, P., 2004. Telithrmycin. Nature reviews, Sept, pp. 733-734.

Roberts, M. C. et al., 1999. Nomenclature for Macrolide and Macrolide-LincosamideStreptogramin B Resistance Determinants. Antimicrobial Agents and Chemotherapy, Dec, Issue 12, pp. 2823-2830.

Sanofi, 2017. Sanofi-Aventis Deutschland GmbH. [Online] Available at: https://mein.sanofi.de/produkte/Ketek [Accessed 07 June 2017].

U.S. Food and Drug, A., 2016. U.S. Food and Drug Administration. [Online] Available at: https://www.fda.gov/Drugs/DrugSafety/ucm107824.htm [Accessed 07 June 2017].

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Table of figures

Figure 1 Differences between Erythromycin A and Telithromycin (Raja, et al., 2004) ...... 3

Figure 2 Common side effects (Cunha, 2016) ...... 4

Figure 3 Percentages of patients with severe visual adverse reactions (Cunha, 2016) ...... 4

Figure 4 Telithromycin´s pyridine moiety (Shown in red and green) (Fernandes, et al., 2016) ...... 5

Figure 5 First step of synthesis (Macher & Souza, 2009) ...... 6

Figure 6 primary amine (Macher & Souza, 2009) ...... 7

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