The Therapeutic Potential of Migrastatin-Core Analogs for the Treatment of Metastatic Cancer

molecules

Review The Therapeutic Potential of Migrastatin-Core Analogs for the Treatment of Metastatic Cancer

Ernest Giralt 1,2 and Daniele Lo Re 1,*

1 Institute for Research in Biomedicine (IRB Barcelona), The Barcelona Institute of Science and Technology, C/Baldiri Reixac 10, Barcelona E-08028, Spain; [email protected] 2 Department of Organic Chemistry, University of Barcelona, Marti i Franques 1-11, Barcelona E-08028, Spain * Correspondence: [email protected]; Tel.: +34-635-060-534

Academic Editors: Dong-Kug Choi and Palanivel Ganesan Received: 11 January 2017; Accepted: 2 February 2017; Published: 9 February 2017

Abstract: Tumor metastasis is a complex process in which cells detach from the primary tumor and colonize a distant organ. Metastasis is also the main process responsible for cancer-related death. Despite the enormous efforts made to unravel the metastatic process, there is no effective therapy, and patients with metastatic tumors have poor prognosis. In this regard, there is an urgent need for new therapeutic tools for the treatment of this disease. Small molecules with the capacity to reduce cell migration could be used to treat metastasis. Migrastatin-core analogs are naturally inspired macrocycles that inhibit pathological cell migration and are able to reduce metastasis in animal models. Migrastatin analogs can be synthesized from a common advanced intermediate. Herein we present a review of the synthetic approaches that can be used to prepare this key intermediate, together with a review of the biological activity of migrastatin-core analogs and current hypotheses concerning their mechanism of action.

Keywords: diverted total synthesis; natural products; cancer metastasis

1. Introduction Cell migration is a physiological process and a central feature in embryonic development, tissue repair and immune cell function. Importantly, cell migration is also responsible for angiogenesis, tumor invasion, and metastasis [1]. The cytoskeleton drives cell migration and a key cytoskeletal component is Actin. Several targets have been proposed for the inhibition of Actin dynamics, including the following: (1) actin (e.g., phalloidin (1) an F-actin stabilizer or cytochalasin D (2), an F-actin destabilizer); (2) tubulin and microtubule (e.g., taxol (3), a microtubule stabilizer or vincristine (4), a microtubule destabilizer); (3) actin-binding proteins (ML-7 (5), a myosin light chain kinase inhibitor); and (4) upstream signaling molecules (e.g., Y27632 (6), a Rho-kinase inhibitor) [2] (Figure1). Migrastatin (7) is a natural product that was originally isolated from Streptomyces sp. MK-929-43F1 [3,4] and later found in fermentation broths of Streptomyces platensis [5]. Migrastatin comprises a 14-membered ring macrolactone incorporating two E bonds and one Z double bond, together with three contiguous stereocenters and a pendant alkyl gluturamide side chain. It has been reported that migrastatin inhibits cell migration [3,4], suppresses multi-drug resistance [6], and antagonizes muscarinic acetylcholine receptor [7].

Molecules 2017, 22, 198; doi:10.3390/molecules22020198 www.mdpi.com/journal/molecules Molecules 2017, 22, 198 2 of 26 Molecules 2017, 22, 198 2 of 26

Molecules 2017, 22, 198 2 of 26 Targeting Actin directly Targeting microtubule Targeting Actin-binding protein OH Targeting ActinO directly Targeting microtubuleO Targeting Actin-binding H HN O N OH O O OH protein N O H OH O O N HN H HN NH O NH O O O O N OH O O OH S S N O O N H O O O H N HN H OH O O N NHNHO O NHOHO O O S N O S HO H O O N O O H O I HHOO O N NH O OH OH O PhalloidinN (1) Taxol (3) ML-7 (5) HO H O OF-Actin stabilizer Microtubule stabilizerO Myosin light chain kinaseI inhibitor HO Phalloidin (1) Taxol (3) ML-7 (5) F-Actin stabilizer Microtubule stabilizer Myosin light chain kinase inhibitor OH Targeting upstream signaling OH OH Targeting upstream H H N N O HN signaling OH O N HN H H H O H N H O N N O OAc O HN OAc OH H O O O OH N HN H H NH2 O OMe H O N CytochalasinOAc D (2) O Vincristine (4) OAc Y-27632 (6) OH OH H F-Actin destabilizer MicrotubuleO destabilizerO Rho-kinase inhibitorNH OMe 2 Cytochalasin D (2) Vincristine (4) Y-27632 (6) F-Actin destabilizer Microtubule destabilizer Rho-kinase inhibitor Figure 1. Small-molecule inhibitors of cell mobility. Figure 1. Small-molecule inhibitors of cell mobility. In 2003, Danishefsky andFigure co-workers 1. Small-molecule described inhibitors the first of cell total mobility. synthesis of migrastatin [8]. One Inyear 2003, later, Danishefsky the same group and co-workersdemonstrated described that ablation the ﬁrst of the total glutaramide synthesis ofside migrastatin chain increases [8]. One the year later,biological the sameIn 2003, activity group Danishefsky demonstratedof migrastatin and co-workers analogs that ablation 1000-fold described of with the th glutaramide erespect first total to natural synthesis side migrastatin chain of migrastatin increases [9]. They the [8]. found biologicalOne activityyearthat of simplerlater, migrastatin the analogs same analogs groupat nanomolar demonstrated 1000-fold concentrations with that ablation respect were oftoable the natural to glutaramide inhibit migrastatin cell sidemigration chain [9]. in Theyincreases 4T1 foundmouse the that simplerbiologicalmammary analogs activity tumor at nanomolar cells.of mi Danishefskygrastatin concentrations analogs demonstrated 1000-fold were able thatwith tomigrastatin respect inhibit to cell natural and migration simplified migrastatin in migrastatin 4T1 [9]. mouse They analogs found mammary that simpler analogs at nanomolar concentrations were able to inhibit cell migration in 4T1 mouse tumorcould cells. be Danishefsky easily synthesized demonstrated from a common that migrastatin advanced andintermediate simpliﬁed 8. migrastatinThis result highlights analogscould the be mammarypotential of tumor diverted cells. total Danishefsky synthesis demonstrated drug discovery that (Figure migrastatin 2). and simplified migrastatin analogs easilycould synthesized be easily fromsynthesized a common from advanceda commonintermediate advanced intermediate8. This result 8. This highlights result highlights the potential the of divertedpotential total of synthesis diverted drugtotal synthesis discovery drug (Figure discovery2). (Figure 2).

Figure 2. Diverted total synthesis approach for the preparation of migrastatin (7) and truncated

analogs MGSTA-1,6 from a common advanced intermediate (8). IC50 values (in parentheses) in Figure 2. Diverted total synthesisa approach for the preparation ofb migrastatin (7) and truncated Figureboyden 2. Diverted chamber total assays synthesis against approach 4T1 mouse for mammary the preparation cancer ofand migrastatin A549 human (7) andlung truncatedcancer cells. analogs analogs MGSTA-1,6 from a common advanced intermediate (8). IC50 values (in parentheses) in MGSTA-1,6 from a common advanced intermediate (8). IC values (in parentheses) in boyden boydenSeveral chamber groups have assays been against involved a 4T1 mousein the preparationmammary cancer of 8 (Figure and50 b A549 3 and human table 1)lung [8–14]. cancer The cells. synthesis chamber assays against a 4T1 mouse mammary cancer and b A549 human lung cancer cells. and the biological activity of migrastatin (7) and migrastatin analogs were covered by Reymond and CossySeveral in 2008 groups [15]. haveThe aim been of involved this review in the is preparation to discuss theof 8 recent(Figure synthetic 3 and table approaches 1) [8–14]. The used synthesis for the Severaland the biological groups haveactivity been of migrastatin involved (7 in) and the migrastatin preparation analogs of 8were(Figure covered3 and by Reymond Table1)[ and8 –14]. The synthesisCossy in 2008 and [15]. the biologicalThe aim of activitythis review of migrastatinis to discuss the (7) recent and migrastatin synthetic approaches analogs wereused coveredfor the by

Reymond and Cossy in 2008 [15]. The aim of this review is to discuss the recent synthetic approaches Molecules 2017, 22, 198 3 of 26

Molecules 2017, 22, 198 3 of 26 usedpreparation for the preparation of 8, together of 8 ,with together new findings with new that ﬁndings provide thatinsight provide into the insight anti-metastatic into the potential anti-metastatic of potentialmigrastatin of migrastatin analogs and analogs their targets. and their targets.

FigureFigure 3. Synthetic 3. Synthetic strategies strategies for for thethe preparationpreparation of of advanced advanced intermediate intermediate 8. 8.

Table 1. Synthetic key aspects for the preparation of advanced precursor 8. Table 1. Synthetic key aspects for the preparation of advanced precursor 8. Year Authors n0 Steps Overal Yield Key Steps Notes Reference Overal LACDAC reaction, Multi-gram scale Year2004 Authors Danishefsky et al.n0 Steps 10 22% Key Steps Notes[8,9,16] Reference Yield Ferrier rearrangement synthesis Stereoselective 2006 Cossy et al. 11 (+4) a 11% LACDAC reaction, - [10] 2004 Danishefsky et al. 10 22% crotylmetalation, RCM Multi-gram scale synthesis [8,9,16] Ferrier rearrangement Entry to StereoselectiveStereoselective 2006 Cossy et al. 11 (+4) a 11% isomigrastatin-[ 10] 2007 Cossy et al. 11 (+4) a 35% crotylmetalation,crotylmetalation, RCM Still- [17] analogues, gram StereoselectiveGennari olefination Entry toscale isomigrastatin 2007 Cossy et al. 11 (+4) a 35% crotylmetalation, Still-Gennari [17] Evans aldol analogues, gram scale olefination condensation and Entry to 2006 Lqbal et al. 12 8% Evans aldoldistereoselective condensation isomigrastatin [11] and distereoselective Entry to 2006 Lqbal et al. 12 8% vinylmagnesium analogues [11] vinylmagnesiumbromide additon isomigrastatin analogues bromide additon Upjohn Entry to Upjohn dihydroxilation,dihydroxilation, isomigrastatin-Entry to 2010 Dias et al. 14 1.2% [12] 2010 Dias et al. 14 1.2% Horner-Wadsworth-Horner-Wadsworth- isomigrastatin-corecore epimers, [12] EmmonsEmmons olefination olefination epimers,gram scale gram scale EntryEntry to migrastatin-core to Pd(II)Pd(II) catalyzed catalyzed 2013 Lqbal et al. 11 5.9% migrastatin-corewith different [13] 2013 Lqbal et al. 11 5.9%intramolecular intramolecular C-H oxidation C-H [13] withfunctional different groups oxidation Brown alcoxyallylation, functional groups Entry to isomigrastatin 2014 Murphy et al. 9 30% HWE, Zinc catalyzed [14,18,19] Brown alcoxyallylation, analogues,Entry to gram scale asimmetricHWE, desymmetrization Zinc catalyzed isomigrastatin 2014 Murphy et al. 9 30% [14.67,99] a Precursor of advanced intermediateasimmetric 8. analogues, gram desymmetrization scale a Precursor of advanced intermediate 8. 2. Results 2. Results 2.1. Synthesis of Advanced Intermediate 8 2.1. Synthesis of Advanced Intermediate 8 2.1.1. Synthesis of the Protected Migrastatin-Core (Danishefsky et al.) [16] 2.1.1. Synthesis of the Protected Migrastatin-Core (Danishefsky et al.) [16] The first synthesis of the migrastatin-core was reported by Danishefsky and co-workers in 2002 [16].TheMGSTA-1 first synthesiswas of the synthesized migrastatin-core as its was MOM reported derivative by Danishefsky through and aco-workers precursor in 2002 of advanced [16]. intermediateMGSTA-18 .was The synthesized synthesis as began its MOM with derivative the selective through silylation a precursor of of the advanced primary intermediate hydroxyl 8 group. of (S)-3-benzyloxy-1,2-propanediolThe synthesis began with the selective9 [20 silyla,21],tion followed of the primary by methylation hydroxyl group of the of secondary (S)-3-benzyloxy- hydroxyl 1,2-propanediol 9 [18,19], followed by methylation of the secondary hydroxyl group. Regioselective group. Regioselective deprotection of benzyl ether gave 10, which was subsequently oxidized under Swern conditions. A Lewis acid-catalyzed diene-aldehyde cyclocondensation (LACDAC) [22] reaction between aldehyde 11 and diene 12 gave dihydropyrone 13, which contains the three contiguous stereocenters of the migrastatin core fragment. Dihydropyrone 13 was treated with NaBH4 and Molecules 2017, 22, 198 4 of 26 deprotection of benzyl ether gave 10, which was subsequently oxidized under Swern conditions. A Lewis acid-catalyzed diene-aldehyde cyclocondensation (LACDAC) [20] reaction between aldehyde 11 Molecules 2017, 22, 198 4 of 26 and diene 12 gave dihydropyrone 13, which contains the three contiguous stereocenters of the migrastatin core fragment. Dihydropyrone 13 was treated with NaBH4 and CeCl3·7H2O (Luche CeClreduction)3·7H2 O[21], (Luche followed reduction) by Ferrier [23], followedrearrangement by Ferrier in acidic rearrangement media, to give in acidic lactol media, 14 [22]. to giveReductive lactol 14opening[24]. Reductive of lactol 14 opening using ofLiBH lactol4 gave14 using compound LiBH4 15gave, which compound contains15, the which desired contains (Z) olefin. the desired Diol (15Z) olefin.reacted Diol with15 (Ereacted)-hepta-2,6-dienoyl with (E)-hepta-2,6-dienoyl chloride in the chloridepresence inof theDMAP presence to give of esther DMAP 16 to. The give secondary esther 16. Thehydroxyl secondary group hydroxyl of 16 was group protected of 16 wasas MOM protected ether, as and MOM the ether,TBDPS and group the TBDPS was cleaved group using was cleaved HF.py usingto afford HF ·intermediatepy to afford intermediate17. Oxidation17 of. Oxidationthe primary of hydroxyl the primary group hydroxyl using groupDess-Martin using Dess-Martinperiodinane periodinane(DMP), followed (DMP), by followedolefination by using olefination the Tebbe using reaction the Tebbe [23], reaction gave metathesis [25], gave precursor metathesis 18 precursor. Finally, 18RCM. Finally, reaction RCM of reaction18 with Grubbs of 18 with II catalyst Grubbs [24] II catalyst gave protected [26] gave migrastatin protected migrastatin core compound core compound 19 in 50% 19yieldin 50%(Scheme yield 1). (Scheme 1).

Scheme 1. Danishefsky’s synthesis of protected MGSTA-1 (19). Reagents and conditions ::( (aa)) TBDPSCl, TBDPSCl, 2 2 2 3 imidazole, DMF; DMF; (b (b) )MeI, MeI, NaH, NaH, THF; THF; (c) ( cH)H, Pd(OH)2, Pd(OH), EtOAc,2, EtOAc, 73% 73% over over three three steps; steps; (d) (COCl) (d) (COCl), Et N,2, EtDMSO,3N, DMSO, CH2Cl2 CH; (e)2 ClTiCl2;(4,e CH) TiCl2Cl42;, ( CHf) CSA,2Cl2 ;(PhMe,f) CSA, 71% PhMe, over three 71% steps; over three(g) NaBH steps;4, EtOH, (g) NaBH CeCl4,3·7H EtOH,2O; CeCl(h) CSA,3·7H 2HO;2O, (h THF;) CSA, (i H) 2LiBHO, THF;4, H2 (O,i) LiBHTHF,4 ,H55%2O, over THF, three 55% oversteps; three (j) (E steps;)-hepta-2,6-dienoyl (j)(E)-hepta-2,6-dienoyl chloride, chloride,DMAP, CH DMAP,2Cl2, 65%; CH2 (Clk)2 ,MOMCl, 65%; (k) Bu MOMCl,4NI, DIPEA, Bu4NI, CH DIPEA,2Cl2; (l)CH HF.py,2Cl2 ;(THF,l) HF.py, 79% over THF, two 79% steps; over two(m) steps;DMP, (CHm)2 DMP,Cl2; (n CH) Tebbe2Cl2;( reagent,n) Tebbe pyridine, reagent, pyridine,THF, 60% THF, over 60%two oversteps; two (o) steps; Grubbs (o) II Grubbs catalyst, II catalyst,PhCH3, PhCHreflux,3 50%., reﬂux, 50%.

2.1.2. First Total Synthesis of Migrastatin (Danishefsky(Danishefsky etet al.)al.) [[8]8] In 2003, Danishefsky and co-workers publish thethe ﬁrstfirst totaltotal synthesissynthesis ofof migrastatinmigrastatin ((77)[) [8].8]. In this regard, migrastatin was obtained from advanced intermediate 8, which was prepared using a similar strategy as that used for the synthesis of 15. A slightly optimized procedure for the preparation of 8 was reported one yearyear laterlater [[9]9] andand isis illustratedillustrated inin SchemeScheme2 2.. The synthesis synthesis [9] [9 ]began began with with comme commerciallyrcially available available dimethyl dimethyl 2,3- 2,3-O-isopropylidene-O-isopropylidene-L-tartrateL-tartrate (20), (which20), which was reduced was reduced using using DIBAL. DIBAL. Diastereoselective Diastereoselective divinylzinc divinylzinc addition addition afforded afforded the desired the desired vinyl vinylcarbinol carbinol 21 [25].21 [The27]. two The twofree freehydroxyl hydroxyl groups groups were were then then methylated methylated and and the the acetonide acetonide protecting protecting group was removed to afford diol 22 [26]. Glycol cleavage using Pb(OAc)4 led to vinyl aldehyde 23, group was removed to afford diol 22 [28]. Glycol cleavage using Pb(OAc)4 led to vinyl aldehyde 23which, which was was then then used used for for the the LACDAC LACDAC sequence. sequence. Aldehyde Aldehyde 2323 waswas reacted reacted with with diene diene 1212 inin the presence of TiCl4, affording dihydropyrone 24 as a single diastereoisomer [20]. As above, the presence of TiCl4, affording dihydropyrone 24 as a single diastereoisomer [22]. As above, the reduction ofreduction24, followed of 24, byfollowed Ferrier by rearrangement Ferrier rearrangement [24], gave [22], lactol gave26 lactol, which, 26, which, after reductive after reductive opening opening using using LiBH4 and protection of secondary alcohol as TBS ether, afforded advanced intermediate 8. LiBH4 and protection of secondary alcohol as TBS ether, afforded advanced intermediate 8. With 8 in hand, migrastatin was ﬁnally synthesized (Scheme2). The synthetic procedure leading to migrastatin has already been reviewed elsewhere [15].

Molecules 2017, 22, 198 5 of 26

MoleculesWith2017 8 ,in22 hand,, 198 migrastatin was finally synthesized (Scheme 2). The synthetic procedure leading to5 of 26 migrastatin has already been reviewed elsewhere [15].

Scheme 2. Danishefsky’s synthesis of 8. Reagents and conditions: (a) DIBALH, then ZnCl2, Scheme 2. Danishefsky’s synthesis of 8. Reagents and conditions:(a) DIBALH, then ZnCl2, H2C=CHMgBr, PhCH3, −78 °C◦ to RT, 75% (ds > 90%); (b) (i) MeI, NaH, DMF, RT, (ii) 2 M HCl, MeOH, H2C=CHMgBr, PhCH3, −78 C to RT, 75% (ds > 90%); (b) (i) MeI, NaH, DMF, RT, (ii) 2 M HCl, reflux, 80%; (c) Pb(OAc)4, Na2CO3, CH2Cl2, 0 °C to RT; (d) (i) TiCl4, CH2Cl2, −78 °C, (ii) TFA, CH2Cl2, MeOH, reflux, 80%; (c) Pb(OAc) , Na CO , CH Cl , 0 ◦C to RT; (d) (i) TiCl , CH Cl , −78 ◦C, (ii) TFA, RT, 87% from 22; (e) LiBH4, MeOH,4 2THF,3 −10 °C;2 (f2) CSA, H2O, THF, reflux; (4g) LiBH2 4, 2H2O, THF, RT, ◦ CH2Cl53%2, RT,from 87% 24; ( fromh) TBSOTf,22;(e) 2,6-lutidine, LiBH4, MeOH, CH2Cl THF,2, RT,− (ii)10 AcOH:HC; (f) CSA,2O:THF H 2(3:1:1),O, THF, RT, reflux; 80%. (g) LiBH4,H2O, THF, RT, 53% from 24;(h) TBSOTf, 2,6-lutidine, CH2Cl2, RT, (ii) AcOH:H2O:THF (3:1:1), RT, 80%. 2.1.3. Synthesis of the Migrastatin-Core Library (Danishefsky et al.) [9,27] 2.1.3. SynthesisAfter achieving of the Migrastatin-Core the total synthesis of Library migrastatin (Danishefsky [8], Danishefsky et al.) and [9 co-workers,29] reported [9,27] the Afterpreparation achieving of a small the total library synthesis of migrastatin-core of migrastatin analogs [8], using Danishefsky advanced and intermediate co-workers 8 (Scheme reported 3).[ 9,29] Reaction of 8 with (E)-hepta-2,6-dienoic acid in the presence of 2,4,6-trichlorobenzoyl chloride and the preparation of a small library of migrastatin-core analogs using advanced intermediate 8 (Scheme3). DIPEA gave acylated compound 27, which, after RCM and protecting group removal, afforded MGSTA-1. ReactionA of similar8 with strategy (E)-hepta-2,6-dienoic was applied for the acid preparation in the of presence MGSTA-2 of. Intermediate 2,4,6-trichlorobenzoyl 8 was coupled chloride to and6-heptenoyl DIPEA gave chloride acylated to give compound 29, which, after27, which,RCM and after de-protection, RCM and afforded protecting MGSTA-2 group. For removal, the affordedpreparationMGSTA-1 of macroketone. analogs, intermediate 8 was converted into allylic bromide 31 using the AAppel similar reaction. strategy Compound was applied 31 was then for thecoupled preparation to β-ketosulfone of MGSTA-2 32 [28], .followed Intermediate reductive8 was removal coupled to 6-heptenoylof the sulfone chloride group to mediated give 29 ,by which, Na/Hg, after to RCMgive ketone and de-protection, 33. RCM and affordedde-protectionMGSTA-2 of 33 gave. For the preparationMGSTA-3 of.macroketone For the preparation analogs, of macrolactam intermediate analogs,8 was compound converted 8 was into converted allylic bromide into allylic31 azideusing the Appel35 reaction. using diphenylphosphoryl Compound 31 was azide then coupledunder Mitsunobu to β-ketosulfone conditions.32 [30Staudinger], followed reduction reductive of removal35, of thefollowed sulfone by group coupling mediated with 6-heptenoic by Na/Hg, acid in to the give presence ketone of33 EDC,. RCM gave andcompound de-protection 36, which, of after33 gave RCM and removal of silyl protecting group, afforded MGSTA-4 (Scheme 3). MGSTA-3. For the preparation of macrolactam analogs, compound 8 was converted into allylic azide 35 using2.1.4. diphenylphosphoryl Synthesis by Cossy et azideal. [10,17] under Mitsunobu conditions. Staudinger reduction of 35, followed by coupling with 6-heptenoic acid in the presence of EDC, gave compound 36, which, after RCM and In 2006, Cossy and co-workers [10] reported the synthesis of a precursor 46 of advanced intermediate removal of silyl protecting group, afforded MGSTA-4 (Scheme3). 8 (Scheme 4). The synthesis began from methyl esther 38. Acetonide cleavage of 38 followed by regioselective protection of primary alcohol in 39 as TBDPS ether afforded 40. Methylation of 2.1.4. Synthesis by Cossy et al. [10,17] secondary alcohol in 40, followed by DIBAL reduction of the ester moiety, gave primary alcohol 42. InAfter 2006, oxidation Cossy of and 42 under co-workers Swern conditions, [10] reported the correspon the synthesisding aldehyde of a precursor was treated46 of with advanced 2- intermediateenyl[tri(n-butyl)]stannane8 (Scheme4). The the synthesispresence of began MgBr2 from·OEt2 to methyl give the esther syn,syn38-stereotriad. Acetonide 43 with cleavage good of 38 followedstereocontrol by regioselective (dr = 90:10) protection [29]. The ofauthors primary claim alcohol that the in 39 stereochemicalas TBDPS ether outcome afforded of that40. reaction Methylation of secondaryresulted from alcohol an open in 40 chair, followed transition by state DIBAL of type reduction A, where of the the carbonyl ester moiety, and the gavemethoxy primary group alcoholof aldehyde are chelated with MgBr2·OEt2 [29]. Compound 43 was treated with methacryloyl chloride 42. After oxidation of 42 under Swern conditions, the corresponding aldehyde was treated with in the presence of TEA and DMAP to give diene 44. RCM of 44 using Grubbs II catalyst gave 2-enyl[tri(n-butyl)]stannane the presence of MgBr ·OEt to give the syn,syn-stereotriad 43 with good unsaturated lactone 45, which contains the olefin with2 desired2 Z configuration and three contiguous dr stereocontrolstereocenters. ( =Treatment 90:10) [31 of]. 45 The with authors LiBH4 in claim the presence that the of stereochemicalCeCl3·7H2O, followed outcome by simultaneous of that reaction resultedprotection from anof openthe two chair hydroxyl transition groups state as TBS of typeetherA and, where regioselective the carbonyl de-protection and the of methoxy the primary group of aldehydealcohol, are afforded chelated precursor with MgBr 46.2 ·ThisOEt 2compound[31]. Compound was therefor43 wase converted treated withinto migrastatin methacryloyl 7 using chloride a in the presencesimilar procedure of TEA and to that DMAP described to give by diene Danishefsky44. RCM and of co-workers44 using Grubbs [8] (Scheme II catalyst 4). gave unsaturated lactone 45, which contains the olefin with desired Z configuration and three contiguous stereocenters. Treatment of 45 with LiBH4 in the presence of CeCl3·7H2O, followed by simultaneous protection of the two hydroxyl groups as TBS ether and regioselective de-protection of the primary alcohol, afforded precursor 46. This compound was therefore converted into migrastatin 7 using a similar procedure to that described by Danishefsky and co-workers [8] (Scheme4). Molecules 2017, 22, 198 6 of 26 Molecules 2017, 22, 198 6 of 26

Molecules 2017, 22, 198 6 of 26

SchemeScheme 3. 3. Danishefsky’sDanishefsky’s synthesis synthesis of the ofmigrastatin-core the migrastatin-core library. Reagents library. and conditionsReagents: (a) and (E)-hepta- conditions : 2,6-dienoic acid, 2,4,6-trichlorobenzoyl chloride, DIPEA, pyridine, PhCH3, RT, 48%; (b) Grubbs II (a)(E)-hepta-2,6-dienoic acid, 2,4,6-trichlorobenzoyl chloride, DIPEA, pyridine, PhCH3, RT, 48%; catalyst (20 mol %), PhCH3 (0.5 mM), reflux, 55% (28), 76% (30), 81% (34), 60% (37); (c) HF.pyridine, (b) GrubbsScheme II3. catalystDanishefsky’s (20 mol synthesis %), PhCH of the migrastatin-core(0.5 mM), reflux, library. 55% Reagents (28), 76%and conditions (30), 81%: (a) ((34E)-hepta-), 60% (37); THF, RT, 66% (MGSTA-1), 94% (MGSTA-23 ), 90% (MGSTA-3), 81% (MGSTA-4); (d) 6-heptenoyl (c) HF2,6-dienoic.pyridine, acid, THF, 2,4,6-trichlorobenzo RT, 66% (MGSTA-1yl chloride,), 94% DIPEA, (MGSTA-2 pyridine,), 90% PhCH (MGSTA-33, RT, 48%;), ( 81%b) Grubbs (MGSTA-4 II ); 2 2 4 3 2 2 chloride, DMAP, CH Cl , RT, 82%; (e) CBr , solid-supported PPh , CH Cl , RT; (f) (i) β-ketosulfone. 32, (d) 6-heptenoylcatalyst (20 mol chloride, %), PhCH DMAP,3 (0.5 mM), CH Clreflux,, RT, 55% 82%; (28), (76%e) CBr (30),, 81% solid-supported (34), 60% (37); ( PPhc) HF,pyridine, CH Cl , RT; DBU, PhCH3, RT, (ii) Na/Hg, Na2HPO24, MeOH,2 RT, 61% from 7;4 (g) DPPA, DBU, PhCH3, RT,3 87%;2 (h)2 THF, RT, 66% (MGSTA-1), 94% (MGSTA-2), 90% (MGSTA-3), 81% (MGSTA-4); (d) 6-heptenoyl (f) (i)(i)β-ketosulfone PPh3, H2O, THF,32, DBU,70 °C, PhCH(ii) 6-heptenoic3, RT, (ii) acid, Na/Hg, EDC, Na DIPEA,2HPO CH4, MeOH,2Cl2, RT, RT, 92%. 61% from 7;(g) DPPA, DBU, chloride, DMAP, CH2Cl2, RT, 82%; (e) CBr4◦, solid-supported PPh3, CH2Cl2, RT; (f) (i) β-ketosulfone 32, PhCH3, RT, 87%; (h) (i) PPh3,H2O, THF, 70 C, (ii) 6-heptenoic acid, EDC, DIPEA, CH2Cl2, RT, 92%. DBU, PhCH3, RT, (ii) Na/Hg, Na2HPO4, MeOH, RT, 61% from 7; (g) DPPA, DBU, PhCH3, RT, 87%; (h) In 2007, Cossy and co-workers [17] reported the synthesis of 46 using a Still–Gennari olefination (i) PPh3, H2O, THF, 70 °C, (ii) 6-heptenoic acid, EDC, DIPEA, CH2Cl2, RT, 92%. Into control 2007, Cossy the formation and co-workers of the (Z)-double [17] reported bond (Scheme the synthesis 5). Compound of 46 using 43 [10] a Still–Gennariwas protected as oleﬁnation TBS ether and therefore subjected to oxidative cleavage using OsO4, followed by treatment with NaIO4. to controlIn the 2007, formation Cossy and of co-workers the (Z)-double [17] reported bond (Scheme the synthesis5). Compound of 46 using a43 Still–Gennari[10] was protected olefination as TBS Theto control aldehyde the obtainedformation was of the treated (Z)-double with Still-Genn bond (Schemeari phosphonate 5). Compound [30,31] 43 in [10] the was presence protected of KHMDS as TBS etherto and give therefore the unsaturated subjected ester to 48 oxidative with a good cleavage Z/E ratio using (97:3). OsO Reduction4, followed of 48 by with treatment DIBAL gave with the NaIO 4. ether and therefore subjected to oxidative cleavage using OsO4, followed by treatment with NaIO4. The aldehyde obtained was treated with Still-Gennari phosphonate [32,33] in the presence of KHMDS precursorThe aldehyde 46. Followingobtained was similar treated steps with to thoseStill-Genn reportedari phosphonate by Danishefsky [30,31] et al.in the[9], presencethis compound of KHMDS was to give the unsaturated ester 48 with a good Z/E ratio (97:3). Reduction of 48 with DIBAL gave the convertedto give the to unsaturated MGSTA-1 esterin 5 steps 48 with (Scheme a good 5). Z /E ratio (97:3). Reduction of 48 with DIBAL gave the precursorprecursor46. Following46. Following similar similar steps steps to to those those reportedreported by by Danishefsky Danishefsky et etal. al.[9], [ 9this], this compound compound was was convertedconverted to MGSTA-1 to MGSTA-1in 5in steps 5 steps (Scheme (Scheme5). 5).

Scheme 4. Cossy’s synthesis of 46. Reagents and conditions: (a) pTSA, MeOH/H2O (1:1), RT, 83%; (b) TBDPSCl, imidazole, CH2Cl2, 0 °C to RT 81%; (c) Ag2O, MeI, MS 4 Å, Et2O, 40 °C, 96%; (d) DIBAL, CH2Cl2, −78 °C to RT 90%; (e) (COCl)2, DMSO, CH2Cl2, −78 °C, then Et3N −78 °C to RT; (f) MgBr2·OEt2, Scheme 4. Cossy’s synthesis of 46. Reagents and conditions: (a) pTSA, MeOH/H2O (1:1), RT, 83%; (b) SchemeCH2Cl 4. 2, Cossy’s−20 °C, then synthesis but-2-enyl-[(tri( of 46. Reagentsn-butyl)]stannane, and conditions −60 °C,:( 87%a) (overpTSA, two MeOH/H steps); (g)2 Omethacryloyl (1:1), RT, 83%; TBDPSCl, imidazole, CH2Cl2, 0 °C◦ to RT 81%; (c) Ag2O, MeI, MS 4 Å, Et2O, 40 °C, 96%;◦ (d) DIBAL, (b) TBDPSCl,chloride, Et imidazole,3N, DMAP, CH CH2Cl2Cl2,2, 0 0 °CC toto RTRT 81%;80%; ( hc) AgGrubbs2O, MeI,II catalyst MS 4 (16.5 Å, Et mol2O, %), 40 CHC,2 96%;Cl2 (c (=d )10 DIBAL,−2 CH2Cl2, −◦78 °C to RT 90%; (e) (COCl)2, DMSO, CH2Cl2, −78 °C,◦ then Et3N −78 °C to◦ RT; (f) MgBr2·OEt2, CH ClM),, −4078 °C, C144 to h, RT 65%; 90%; (i) ( eLiBH) (COCl)4 (7 equiv.),, DMSO, CeCl CH3·7HCl2O ,(1− equiv.),78 C, then THF/H Et 2NO (4:1),−78 RT,C to 74%; RT; ( jf)) TBSOTf, MgBr · OEt , 2 CH2 2Cl2, −20 °C, then but-2-enyl-[(tri(2 n-butyl)]stannane,2 2 −60 °C, 87% (over3 two steps); (g) methacryloyl2 2 ◦ ◦ 2,6-lutidine,− CH2Cl2, 0 °C to RT, 75%;n (k) THF/H2O/AcOH− (1:1:3), 36 h, RT, 75%. g −2 CH2Clchloride,2, 20 EtC,3N, then DMAP, but-2-enyl-[(tri( CH2Cl2, 0 °C -butyl)]stannane,to RT 80%; (h) Grubbs60 IIC, catalyst 87% (over (16.5 twomol steps);%), CH (2Cl)2 methacryloyl (c = 10 ◦ −2 chloride,M), 40 Et 3°C,N, 144 DMAP, h, 65%; CH (i2)Cl LiBH2, 04 (7C equiv.), to RT 80%; CeCl (3h·7H) Grubbs2O (1 equiv.), II catalyst THF/H (16.52O (4:1), mol %),RT, CH74%;2Cl (j2) TBSOTf,(c = 10 M), ◦ 40 C,2,6-lutidine, 144 h, 65%; CH (2iCl) LiBH2, 0 °C4 to(7 RT, equiv.), 75%; (k CeCl) THF/H3·7H2O/AcOH2O (1 equiv.), (1:1:3), THF/H 36 h, RT,2 O75%. (4:1), RT, 74%; (j) TBSOTf, ◦ 2,6-lutidine, CH2Cl2, 0 C to RT, 75%; (k) THF/H2O/AcOH (1:1:3), 36 h, RT, 75%.

Molecules 2017, 22, 198 7 of 26 Molecules 2017, 22, 198 7 of 26

Molecules 2017, 22, 198 7 of 26

Scheme 5. Synthesis of MGSTA-1. Reagents and conditions: (a) TBSOTf, 2,6-lutidine, CH2Cl2, −20 °C, Scheme 5. Synthesis of MGSTA-1. Reagents and conditions:(a) TBSOTf, 2,6-lutidine, CH 2Cl2, ◦93%; (b) (i) OsO4, NMO, t-BuOH/H2O (1/1), RT; (ii) NaIO4, THF/H2O (1/1), RT; (iii) 47, KHMDS, 18- −20 C, 93%; (b) (i) OsO4, NMO, t-BuOH/H2O (1/1), RT; (ii) NaIO4, THF/H2O (1/1), RT; (iii) 47, crown-6,Scheme 5.THF, Synthesis −78 °C, of MGSTA-180% (over. 3Reagents steps); and(c) conditionsDIBAL, CH: (a2)Cl TBSOTf,2, −78 °C 2,6-lutidine, to RT, 94%; CH (d2Cl) 2(,E −)-2,4,6-20 °C, KHMDS, 18-crown-6, THF, −78 ◦C, 80% (over 3 steps); (c) DIBAL, CH Cl , −78 ◦C to RT, 94%; trichlorobenzoic93%; (b) (i) OsO 4(,E) NMO,-hepta-2,6-dienoic t-BuOH/H2O anhydride, (1/1), RT; (ii) Pyridine, NaIO4, PhCHTHF/H3, 2RT,O (1/1), 67%; RT; (2e) NH(iii)2 447F MeOH,, KHMDS, reflux, 18- (d)(E77%;crown-6,)-2,4,6-trichlorobenzoic (f) Dess-Martin THF, −78 °C, Periodinane 80% (E) (over-hepta-2,6-dienoic CH 3 2steps);Cl2, 0 °C (c )to DIBAL, RT; anhydride, (g) Zn,CH 2PbClCl2 Pyridine,, 2− 78cat, °C CH to2 PhCHI 2RT,Ti(O 94%;i-Pr)3, RT,4 ,( THF,d 67%;) (E )-2,4,6-RT (e ()h NH) 4F ◦ MeOH,Grubbstrichlorobenzoic reflux, II catalyst 77%; ((fE) )(20 Dess-Martin-hepta-2,6-dienoic mol %), PhCH Periodinane3, reflux,anhydride, 47%; CH Pyridine, (2i)Cl HF2, 0Py, PhCHC THF, to RT;3 ,RT, RT, ( g67%. )67%; Zn, ( PbCle) NH2 4cat,F MeOH, CH2I 2reflux,Ti(Oi -Pr)4, 77%; (f) Dess-Martin Periodinane CH2Cl2, 0 °C to RT; (g) Zn, PbCl2 cat, CH2I2Ti(Oi-Pr)4, THF, RT (h) THF, RT (h) Grubbs II catalyst (20 mol %), PhCH3, reflux, 47%; (i) HF Py, THF, RT, 67%. 2.1.5.Grubbs Synthesis II catalyst by Iqbal (20 etmol al. %), [11] PhCH 3, reflux, 47%; (i) HF Py, THF, RT, 67%. 2.1.5. Synthesis by Iqbal et al. [11] 2.1.5.In Synthesis 2006, Iqbal by Iqbaland Parthasaratiet al. [11] reported the synthesis of advanced intermediate 8 as its PMB Inderivative 2006, Iqbal 65 in and 12 steps. Parthasarati The synthesis reported started the with synthesis dibutylboron of advanced triflate-mediated intermediate Evans8 as aldol its PMB condensationIn 2006, Iqbalof acrolein and Parthasarati 52 and (S)-benzyl reported oxazolidinone the synthesis 53 toof giveadvanced the desired intermediate aldol product 8 as its 54 PMB [32]. derivativederivative65 in65 12in steps.12 steps. The The synthesis synthesis startedstarted with dibutylboron dibutylboron triflate-mediated triflate-mediated Evans Evans aldol aldol condensationcondensation of acrolein of acrolein52 52and and (S ()-benzylS)-benzyl oxazolidinone oxazolidinone 5353 toto give give the the desired desired aldol aldol product product 54 [32].54 [34].

Scheme 6. Iqbal’s synthesis of 65. Reagents and conditions: (a) n-Bu2BOTf, i-Pr2NEt, CH2Cl2, −78 °C to 0

°C, 1 h, 84%; (b) LiBH4, MeOH, THF, 0 °C, 2 h, 96%; (c) (OMe)2CHC6H4OMe, CSA, CH2Cl2, RT, 12 h,

70%;Scheme (d) 6.DIBAL, Iqbal’s CH synthesis2Cl2, −78 of °C 65 to. Reagents 0 °C, 2 h, and 95%; conditions (e) TBSCl,: (a) imidazole,n-Bu2BOTf, DMF, i-Pr2NEt, RT, 12CH h,2Cl 88%;2, −78 (f )°C OsO to 40,◦ Scheme 6. Iqbal’s synthesis of 65. Reagents and conditions:(a) n-Bu2BOTf, i-Pr2NEt, CH2Cl2, −78 C to ◦ NaIO°C, 1 h,4, 2,6-lutidine,84%; (b) LiBH dioxane/H4, MeOH,2O THF, (3:1), 0 ◦RT,°C, 23 h, 96%;82%; (cg)) (OMe)H2C=CHMgBr,2CHC6H4 OMe,MgBr 2CSA,·OEt2 ,CH CH2Cl2Cl2,2 ,RT, RT, 12 2 h, 0 C, 1 h, 84%; (b) LiBH4, MeOH, THF, 0 C, 2 h, 96%; (c) (OMe)2CHC6H4OMe, CSA, CH2Cl2, RT, 12 h, 72%;70%; (hd) MeOTf,DIBAL, 2,6-di-CH2Cltert2, −78-butyl-4-methylpyridine,◦ °C to 0 ◦°C, 2 h, 95%; (e) CH TBSCl,2Cl2, imidazole,reflux, 6 h, DMF,62%; ( RT,i) TBAF, 12 h, THF,88%; (RT,f) OsO 12 h,4, 70%; (d) DIBAL, CH2Cl2, −78 C to 0 C, 2 h, 95%; (e) TBSCl, imidazole, DMF, RT, 12 h, 88%; (f) OsO4, 94%;NaIO (4j,) 2,6-lutidine, DMP, CH2Cl dioxane/H2, RT, 40 min,2O (3:1), 85%; RT, (k) (PhO)3 h, 82%;2P(O)CH(CH (g) H2C=CHMgBr,3)CO2C2H MgBr5, DBU/NaI,2·OEt2, THF,CH2Cl −278, RT, °C to2 h, 0 NaIO4, 2,6-lutidine, dioxane/H2O (3:1), RT, 3 h, 82%; (g)H2C=CHMgBr, MgBr2·OEt2, CH2Cl2, RT, 2 h, °C,72%; 3 (h,h )60%; MeOTf, (l) DIBAL, 2,6-di-tert CH-butyl-4-methylpyridine,2Cl2, −78 °C, 1 h, 96%. CH2Cl2, reflux, 6 h, 62%; (i) TBAF, THF, RT, 12 h, 72%;94%; (h) MeOTf, (j) DMP, 2,6-di- CH2Cltert2, RT,-butyl-4-methylpyridine, 40 min, 85%; (k) (PhO)2P(O)CH(CH CH2Cl2, reﬂux,3)CO2C2 6H h,5, DBU/NaI, 62%; (i) TBAF, THF, − THF,78 °C to RT, 0 12 h, ◦ 94%;The°C, (j) DMP,3 chiral h, 60%; CH auxiliary (2l)Cl DIBAL,2, RT, was 40CH then min,2Cl 2removed, − 85%;78 °C, (k 1 )using h, (PhO) 96%. LiBH2 P(O)CH(CH4 in THF to3)CO yield2C diol2H 555,, DBU/NaI, which was THF, then −protected78 C to ◦ ◦ 0withC, 34-methoxybenzaldehyde h, 60%; (l) DIBAL, CH2Cl dimethyl2, −78 C,acetal 1 h, 96%.[33] to afford compound 56. Acetal 56 was opened usingThe DIBAL chiral [33], auxiliary and wasthe thencorresponding removed using primary LiBH 4alcohol in THF 57to yieldwas diolthen 55, protected which was as then TBS protected ether to with 4-methoxybenzaldehyde dimethyl acetal [33] to afford compound 56. Acetal 56 was opened Theafford chiral the orthogonally auxiliary was protected then removedcompound using 58. Oxidative LiBH4 incleavage THF toof yield58 using diol OsO55,4-NaIOwhich4 in was the then using DIBAL [33], and the corresponding primary alcohol 57 was then protected as TBS ether to protectedpresence with of 4-methoxybenzaldehyde2,6-lutidine [34] gave aldehyde dimethyl 59 in good acetal yield. [35 ]Lewis to afford acid-mediated compound distereoselective56. Acetal 56 was afford the orthogonally protected compound 58. Oxidative cleavage of 58 using OsO4-NaIO4 in the openedaddition using of DIBAL vinylmagnesi [35], andum thebromide corresponding to aldehyde primary 59 gave the alcohol desired57 compoundwas then protected60 (dr = 7:1), as which TBS ether waspresence separated of 2,6-lutidine from its diastereomer[34] gave aldehyde in the 59next in goodstep. Secondaryyield. Lewis alcohol acid-mediated 60 was methylated distereoselective using to affordaddition the orthogonallyof vinylmagnesi protectedum bromide compound to aldehyde58. 59 Oxidative gave the desired cleavage compound of 58 using 60 ( OsOdr = 7:1),4-NaIO which4 in the presence was separated of 2,6-lutidine from its [36 diastereomer] gave aldehyde in the59 nextin goodstep. Secondary yield. Lewis alcohol acid-mediated 60 was methylated distereoselective using addition of vinylmagnesium bromide to aldehyde 59 gave the desired compound 60 (dr = 7:1), which was separated from its diastereomer in the next step. Secondary alcohol 60 was methylated using Molecules 2017, 22, 198 8 of 26

MeOTfMolecules [37] 2017 to, yield 22, 198 enantiomerically pure 61. TBAF-mediated deprotection of the TBS8 groupof 26 in 61, followed by oxidation using Dees-Martin periodinane [38], gave the corresponding aldehyde, MeOTf [35] to yield enantiomerically pure 61. TBAF-mediated deprotection of the TBS group in 61, which was treated with Ando’s phosphonate 63 [39] in the presence of DBU to afford the (Z)-olefin 64 followed by oxidation using Dees-Martin periodinane [36], gave the corresponding aldehyde, which (Z/E ratiowas treated not reported). with Ando’s Reduction phosphonate of the 63 ester [37] in moiety the presence using DIBALof DBU to gave afford the the advanced (Z)-olefin intermediate 64 (Z/E 65, whichratio not was reported). used for Reduction the preparation of the ester of the moie migrastatinty using DIBAL core MGSTA-1gave the advanced(Scheme intermediate6). 65, which was used for the preparation of the migrastatin core MGSTA-1 (Scheme 6). 2.1.6. Synthesis by Dias et al. [12] The2.1.6. strategy Synthesis used by Dias by Dias et al. and [12] co-workers for the preparation of advanced intermediate 8 involved the formationThe strategy of stereocenters used by Dias at and C4,5 co-workers by means fo ofr the an preparation asymmetric of aldoladvanced addition. intermediate The methoxy 8 involved group at C6the was formation introduced of stereocenters as hydroxyl at C4,5 group by means using of Upjohon an asymmetric dihydroxylation aldol addition. and, The finally, methoxyZ configuration group at at C2,3C6 waswas introducedintroduced as using hydroxyl a HWE group reaction. using Upjohon The synthesis dihydroxylation began with and, asymmetric finally, Z configuration aldol addition of a titaniumat C2,3 enolate was introduced derived using from a (S HWE)-4-benzyl-3-propionyloxazolidin-2-one reaction. The synthesis began with asym53metricwhich aldol was addition reacted with of a titanium enolate derived from (S)-4-benzyl-3-propionyloxazolidin-2-one 53 which was reacted acrolein 52 to give product 54 in 87% (dr = 95:5) [40–48]. The secondary alcohol was then protected as with acrolein 52 to give product 54 in 87% (dr = 95:5) [38–46]. The secondary alcohol was then TBS ether to afford 66 in 93% yield. Treatment of 66 with 4-methylmorpholine oxide and a catalytic protected as TBS ether to afford 66 in 93% yield. Treatment of 66 with 4-methylmorpholine oxide and ◦ 67 68 dr amounta catalytic of OsO amount4 in acetone/H of OsO4 in2O acetone/H at 0 C[249O ]at afforded 0 °C [47] lactonesafforded lactonesand 67( and= 68 74:26) (dr = on74:26) a multigram on a scalemultigram (Scheme7 ).scale.

O TBSO O O O O HO O O O a,bc d N N O + O O N O O TBSO TBSO Bn Bn Bn OH OH 5354 dr = 95:5 66 dr 67/68 = 74:26 O O TBSO OH TBSO OTBS ef g O O h PMBO PMBO TBSO TBSO OH OH OH OPMB 68 69 70 71

EtO2C TBSO OTBS TBSO OTBS TBSO OH i-k lm,n PMBO OMe OMe OMe OTBS 72 73 74 76 OMe

HO 2 O Z/E 85:15

3 4 Ref. 12 O O o 7 5 O 8 6 OTBS P O OEt OMe 75 OH 8 OMe 14 steps 1.2% MGSTA-1 overall yield

Scheme 7. Dias’ synthesis. Synthesis of 8. Reagents and conditions: (a) TiCl4, DIPEA, CH2Cl2, −78 °C to◦ Scheme 7. Dias’ synthesis. Synthesis of 8. Reagents and conditions:(a) TiCl4, DIPEA, CH2Cl2, −78 C to ◦ 0 °C; 1 h; (b) acrolein, −78◦ °C to 0 °C◦ to RT, 12 h, 87% over two steps; (c) TBSOTf, 2,6-ludine, CH2Cl2, 0 °C, 0 C; 1 h; (b) acrolein, −78 C to 0 C to RT, 12 h, 87% over two steps; (c) TBSOTf, 2,6-ludine, CH2Cl2, ◦ 20 min, 93%; (d) NMO, OsO4, cat., acetone/H2O, 0 °C, 45◦ min, 67 (57%), 68 (20%); (e) CSA cat., 4- 0 C, 20 min, 93%; (d) NMO, OsO4, cat., acetone/H2O, 0 C, 45 min, 67 (57%), 68 (20%); (e) CSA cat., methoxybenzyl-2,2,2-trichloroacetimidate, CH2Cl2, RT, 12 h, 67%; (f) LiAlH4, THF, −78 °C, 1 h, 75%; 4-methoxybenzyl-2,2,2-trichloroacetimidate, CH Cl , RT, 12 h, 67%; (f) LiAlH , THF, −78 ◦C, 1 h, 75%; (g) TBSCl, imidazole, CH2Cl2, 0 °C, 1 h, 95%; (h2) proton2 sponge, Me3OBF4, CH24Cl2, RT, 12 h, 75%; (i) ◦ (g) TBSCl,DDQ/H imidazole,2O, CH2Cl2; CHRT, 22Cl h,2 88%;, 0 C,(j) 1NMO, h, 95%; TPAP (h )cat., proton CH2Cl sponge,2; RT, 1 h; Me (k)3 OBFCp2TiMe4, CH2, PhCH2Cl2,3 RT,, 70 °C, 12 12 h, 75%; (i) DDQ/Hh, 50% over2O, CHtwo2 steps;Cl2; RT, (l) HF-Py-THF, 2 h, 88%; ( jTHF,) NMO, RT, 12 TPAP h; 80%; cat., (m CH) NMO,2Cl2 ;TPAP RT, 1cat., h; (CHk)2 CpCl2;2 TiMe1 h, RT,2, ( PhCHn) 3, ◦ 70 C,75 12 in h,THF, 50% NaH, over RT, two 12steps; h, 58% ( lover) HF-Py-THF, two steps; ( THF,o) DIBAL, RT, 12 CH h;2Cl 80%;2, −15 (m °C,) NMO, 1 h, 98%. TPAP cat., CH2Cl2; 1 h, ◦ RT, (n) 75 in THF, NaH, RT, 12 h, 58% over two steps; (o) DIBAL, CH2Cl2, −15 C, 1 h, 98%. After chromatographic separation and recovery of the chiral auxiliary, lactone 68 was reacted with 4-methoxybenzyl 2,2,2 trichloroacetimidate in the presence of 10-camphorsulfonic acid to afford After chromatographic separation and recovery of the chiral auxiliary, lactone 68 was reacted fully protected lactone 69. Reduction of 69 with LiAlH4 gave primary alcohol 70 in good yield. The withprimary 4-methoxybenzyl alcohol in 2,2,270 was trichloroacetimidate then protected as TBS in theether presence (71), and of the 10-camphorsulfonic free secondary alcohol acid was to afford fullymethylated protected using lactone 1,8-bis(dimethylamino)naphthal69. Reduction of 69 withene LiAlH (proton4 gave sponge) primary [48] to alcohol afford compound70 in good 72. yield. The primaryThe p-methoxybenzyl alcohol in 70 protectingwas then group protected was then as TBS selectively ether (71removed), and theusing free DDQ/H secondary2O. Ley’s alcohol was methylatedoxidation of usingthe resulting 1,8-bis(dimethylamino)naphthalene primary alcohol [49] followed by Petasis (proton olefination sponge) [[50]50] gave to afford olefin compound 73 in 72. The44%p yield-methoxybenzyl (from 72). The protecting primary TBS group group was was then regioselectively selectively removed removed usingusing HF·Py·THF DDQ/H2O. to Ley’s 73 oxidation of the resulting primary alcohol [51] followed by Petasis oleﬁnation [52] gave oleﬁn in 44% yield (from 72). The primary TBS group was regioselectively removed using HF·Py·THF to Molecules 2017, 22, 198 9 of 26

Molecules 2017, 22, 198 9 of 26 afford the corresponding primary alcohol 74. Ley’s oxidation followed by HWE reaction using Ando’s afford the corresponding primary alcohol 74. Ley’s oxidation followed by HWE reaction using phosphonate ester 75 [39,53,54] gave compound 76 (Z/E = 85:15) in 58% yield (~100 mg scale) from 74. Ando’s phosphonate ester 75 [37,51,52] gave compound 76 (Z/E = 85:15) in 58% yield (~100 mg scale) Finally,from reduction 74. Finally, of reduction the ester of moiety the ester using moiety DIBAL using affordedDIBAL afforded the advanced the advanced intermediate intermediate8 in 8 14 in steps with14 1.2% steps overall with 1.2% yield. overall Using yield.8, Andricopulo Using 8, Andricopulo et al. prepared et al. prepared the macrolactone the macrolactone of migrastatin, of migrastatin, namely MGSTA-1namely. TheMGSTA-1 coupling. The of coupling8 to (E)-2,6-heptadienoic of 8 to (E)-2,6-heptadienoic acid using acid DCC using and DCC DMAP and [DMAP55–57], [53–55], followed by ring-closingfollowed metathesis by ring-closing (RCM) metathesis [8,9,29] (RCM) and removal [8,9,27] and of TBS removal protecting of TBS group, protecting afforded group,MGSTA-1 afforded . SinceMGSTA-1 undesired. lactone 67 was prepared on multi-gram scale, the authors undertook the preparationSince of undesired the C-8 epimerlactone of67 thewas migrastatinprepared oncore, multi-gramMGSTA-7 scale,. the Lactone authors67 undertookwas converted the to compoundpreparation77 using of the the C-8 same epimer strategy of the as thatmigrastatin described core, above MGSTA-7 for the. Lactone preparation 67 was of 8converted. Coupling to of 77 compound 77 using the same strategy as that described above for the preparation of 8. Coupling of to 6-heptadienoic acid gave 78, which underwent RCM. After removal of the TBS protecting group, 77 to 6-heptadienoic acid gave 78, which underwent RCM. After removal of the TBS protecting group, 78 afforded MGSTA-7. Interestingly, 77 was coupled to (E)-2,6-heptadienoic acid, and the resulting 78 afforded MGSTA-7. Interestingly, 77 was coupled to (E)-2,6-heptadienoic acid, and the resulting compoundcompound79 was 79 was submitted submitted to to RCM RCM using using GrubbsGrubbs II II cataly catalystst . However, . However, no nometathesis metathesis product product was was observedobserved (Scheme (Scheme8). 8).

Scheme 8. Synthesis of C8 epimer of MGSTA-2. Reagents and conditions: (a) DCC, DMAP, 6-heptanoic Scheme 8. Synthesis of C8 epimer of MGSTA-2. Reagents and conditions:(a) DCC, DMAP, 6-heptanoic acid, CH2Cl2, RT, 12 h, 92%; (b) Grubbs II catalyst, PhCH3, reflux, 30 min, 80%; (c) HF, CH2Cl2/CH3CN, RT, acid, CH2Cl2, RT, 12 h, 92%; (b) Grubbs II catalyst, PhCH3, reflux, 30 min, 80%; (c) HF, CH2Cl2/CH3CN, 24 h, 40%; (d) DCC, DMAP, (E)-2,6-heptadienoic acid, CH2Cl2, RT, 98%. RT, 24 h, 40%; (d) DCC, DMAP, (E)-2,6-heptadienoic acid, CH2Cl2, RT, 98%. 2.1.7. Synthesis by Iqbal et al. [13] 2.1.7. Synthesis by Iqbal et al. [13] Iqbal’s synthesis of advanced intermediate 8 began with an Crimmins modified Evans aldol Iqbal’sreaction synthesis[41,56] of Evan’s of advanced chiral auxiliary intermediate 53 and 3-butenal8 began in with the presence an Crimmins of (−)-spartein modified and EvansTiCl4 to aldol reactiongive [aldol43,58 adduct] of Evan’s 80. The chiral secondary auxiliary alcohol53 wasand protected 3-butenal as TBS in ether the ( presence81), and the of chiral (−)-spartein auxiliary and was removed using sodium borohydride to afford primary alcohol 82. Hence, oxidation of 82 using TiCl4 to give aldol adduct 80. The secondary alcohol was protected as TBS ether (81), and the Dess-Martin periodinane gave the corresponding aldehyde, which reacted with ethyl 2-(diphenyl- chiral auxiliary was removed using sodium borohydride to afford primary alcohol 82. Hence, phosphono)acetate (63) [57] in the presence of DBU to give the corresponding α,β-unsaturated ester oxidation83 with of Z82 configuration.using Dess-Martin The attempt periodinane to promote gave intermolecular the corresponding allylic C-H aldehyde, oxidation on which ester reacted83 withusing ethyl White’s 2-(diphenyl-phosphono)acetate catalyst [58] gave two regioisomers (63)[59] 84 in and the presence85 in equal of ratio DBU [59]. to giveCompound the corresponding 84 was α,β-unsaturatedcharacterized esterand appeared83 with Zasconfiguration. a single product The (1H-NMR attempt evidence); to promote howeve intermolecularr, no further studies allylic C-H oxidationwere performed on ester 83 tousing assign White’s the stereochemistry catalyst [60] of gave the twonewly regioisomers formed stereocenter.84 and 85 Within equalthe aim ratio to [61]. Compoundachieve 84highwas regio- characterized and diastereo-selectivity, and appeared the asauthors a single hydrolyzed product ester (1H-NMR 83 to the evidence); corresponding however, no furthercarboxylic studies acid 86, were which performed was then tosubmitted assign theto intramolecular stereochemistry lactonization of the newlyvia C-H formed allylic activation stereocenter. Withusing the aim White’s to achieve catalyst high [60–62]. regio- After and a brief diastereo-selectivity, optimization, the authors the authors found hydrolyzed that the reaction ester of83 86to the correspondingwith White’s carboxylic catalyst acidin the86, presencewhich wasof DDQ then submittedand Cr(III)salenCl to intramolecular gave lactone lactonization 87 as a single via C-H diastereoisomer in 40% yield with 50% recovery of the starting material. Reduction of lactone 87 with allylic activation using White’s catalyst [62–64]. After a brief optimization, the authors found that DIBAL gave the corresponding diallylic alcohol 88. Regioselective protection of primary alcohol was the reactionachieved of using86 with TBSCl White’s in the presence catalyst of in imidazole the presence to afford of DDQ 89. Methylation and Cr(III)salenCl of the secondary gave lactone alcohol 87 as a single diastereoisomer in 40% yield with 50% recovery of the starting material. Reduction of lactone 87 with DIBAL gave the corresponding diallylic alcohol 88. Regioselective protection of primary alcohol was achieved using TBSCl in the presence of imidazole to afford 89. Methylation of the Molecules 2017, 22, 198 10 of 26

Molecules 2017, 22, 198 10 of 26 90 secondaryusing MeOTf alcohol gave using intermediate MeOTf gave 90. Finally, intermediate regioselective. Finally, deprotecti regioselectiveon of primary deprotection alcohol with of CSA primary alcoholin methanol with CSA gave inmethanol advanced intermediate gave advanced 8 (Scheme intermediate 9). 8 (Scheme9).

Scheme 9. Iqbal’s synthesis of 8. Reagents and conditions: (a) TiCl4, 3-butenal, (−) spartein, CH2Cl2, 0 °C, ◦ Scheme 9. Iqbal’s synthesis of 8. Reagents and conditions:(a) TiCl4, 3-butenal, (−) spartein, CH2Cl2, 0 C, 1 h, 83%; (dr 20:1); (b) TBSOTf, DIPEA, CH2Cl2, 0 °C,◦ 90%; (c) NaBH4, THF:H2O, 90 h, 80%; (d) DMP, 1 h, 83%; (dr 20:1); (b) TBSOTf, DIPEA, CH2Cl2, 0 C, 90%; (c) NaBH4, THF:H2O, 90 h, 80%; (d) DMP, CH2Cl2, 2 h, 90%; (e) 63, NaI, DBU, −78 °C to 0 °C, THF, 3 h, Z:E, 95:5, 60%; (f) White catalyst 10%, CH Cl , 2 h, 90%; (e) 63, NaI, DBU, −78 ◦C to 0 ◦C, THF, 3 h, Z:E, 95:5, 60%; (f) White catalyst 10%, 2 p-benzoquinone,2 p-nitrobenzoic acid, 45 °C, 72 h, 84 (24%) and 85 (20%); (g) LiOH, THF/MeOH/H2O, ◦ p-benzoquinone,4 h, 55 °C, 90%;p-nitrobenzoic (h) White catalyst acid, 10%, 45 pC,-benzoquinone, 72 h, 84 (24%) Cr(III)salenCl, and 85 (20%); 1,4-dioxane, (g) LiOH, 45 THF/MeOH/H °C, 72 h, 40% 2O, ◦ ◦ 4 h, 55(78%C, based 90%; on (h) recovered White catalyst starting 10%, material);p-benzoquinone, (i) DIBAL, −78 Cr(III)salenCl, °C to 0 °C, CH 1,4-dioxane,2Cl2, 2 h, 90%; 45 (j)C, TBSCl, 72 h, 40% ◦ ◦ (78%Imidazole, based on DMF, recovered 2 h, 90%; starting (k) DTBMP, material); CH2Cl (i)2, DIBAL,MeOTf, 6− h,78 reflux,C to 70%; 0 C, (l)CH CSA,2Cl MeOH2, 2 h, 2 90%; h, 90%. (j) TBSCl, Imidazole, DMF, 2 h, 90%; (k) DTBMP, CH2Cl2, MeOTf, 6 h, reflux, 70%; (l) CSA, MeOH 2 h, 90%. 2.1.8. Synthesis by Murphy et al. [14] 2.1.8. SynthesisIn their bysynthesis Murphy of fragment et al. [14 8, ]Murphy and co-worker used Ando’s phosphonate ester [11–13,37,57] to introduce the C2,3 olefin with Z configuration. A diastereoselective Brown alkoxylallylation [63] was In their synthesis of fragment 8, Murphy and co-worker used Ando’s phosphonate ester [11–13,39,59] used to introduce the two contiguous stereocenters at C5,6. The synthesis began with desymmetrization to introduceof 2-methylpropanediol the C2,3 olefin with91 usingZ configuration. a scale-up of the A diastereoselective method reported by Brown Trost alkoxylallylationet al. [64] Diol 91 was [65] was usedtreated to introduce with S the,S-Cat two 92 contiguous and vinyl benzoate stereocenters to afford at monoprotected C5,6. The synthesis alcohol began 93. Subsequent with desymmetrization oxidation of 2-methylpropanediolof 93 using TEMPO and91 BAIBusing gave a scale-up aldehyde of 94 the. Hence, method allyl reportedmethyl ether by was Trost treated et al. with [66] s DiolBuLi 91at was treatedlow with temperature.S,S-Cat 92 Additionand vinyl ofbenzoate (+)-B-methoxydiisopino-campheylbora to afford monoprotected alcoholne gave93 .the Subsequent corresponding oxidation of 93borane,using TEMPOwhich reacted and BAIBwith chiral gave aldehyde aldehyde 94 to94 yield. Hence, 96 with allyl high methyl diastereoselectivity. ether was treated The benzoate with s BuLi at lowprotecting temperature. group Additionwas then re ofmoved (+)-B -methoxydiisopino-campheylborane[65] to give diol 97 as a single diastereoisomer gavethe in good corresponding yield. borane,Both which hydroxyl reacted groups with were chiral protected aldehyde as TBS94 ethersto yield using96 TBSOTfwith high in the diastereoselectivity. presence of triethylamine The benzoate(73). protectingRegioselective group wasde-protection then removed of the primary [67] to TBS give prot diolecting97 as group a single was achieved diastereoisomer by treating in the good fully yield. protected 73 with catalytic p-toluenesulfonic acid in methanol to give 74. Oxidation of 74 using Dess- Both hydroxyl groups were protected as TBS ethers using TBSOTf in the presence of triethylamine Martin periodinane afforded aldehyde 98 in excellent yield. Horner-Wadsworth-Emmons reaction (73).was Regioselective used to introduce de-protection the Z olefin of at theC2,3. primary Treatment TBS of 98 protecting with Ando’s group phosphonate was achieved 63 [11,13] by gave treating the fullythe desired protected alkene73 with76. The catalytic reactionp proceeded-toluenesulfonic with high acid Z selectivity in methanol (Z/E to = give97:3) 74on. a Oxidation 1.0 g scale. of 74 usingThe Dess-Martin authors reported periodinane some erosion afforded of aldehydethe Z selectiv98 ityin excellentwhen the yield.reaction Horner-Wadsworth-Emmons was scaled up to ~4.0 g reaction(Z/E was = 90:10). used Finally, to introduce reduction the Zofolefin ester moiety at C2,3. using Treatment with diisobutylaluminum of 98 with Ando’s hydride phosphonate (DIBAL-H)63 [11 ,13] gave the desired alkene 76. The reaction proceeded with high Z selectivity (Z/E = 97:3) on a 1.0 g scale. The authors reported some erosion of the Z selectivity when the reaction was scaled up to ~4.0 g (Z/E = 90:10). Finally, reduction of ester moiety using with diisobutylaluminum hydride Molecules 2017, 22, 198 11 of 26

Molecules 2017, 22, 198 11 of 26 (DIBAL-H) afforded intermediate 8 in 9 steps with an overall yield of 30% from 91. Using 8, the authors preparedafforded Macroketone intermediateMGSTA-3 8 in 9 stepsin with 100-mg an overall scale, yield which of 30% was from used 91. forUsingin 8 vivo, the studiesauthors prepared [14], and the Macroketone MGSTA-3 in 100-mg scale, which was used for in vivo studies [14], and the natural natural product migrastatin (7) (Scheme 10). Interestingly, MGSTA-3, which was contaminated product migrastatin (7) (Scheme 10). Interestingly, MGSTA-3, which was contaminated by hydrocarbon by hydrocarbon and silicon grease [68], was puriﬁed by distillation under reduced pressure using and silicon grease [66], was purified by distillation under reduced pressure using a Kugelrohr apparatus ◦ a Kugelrohr(0.05 mbar, apparatus T = 90 °C, (0.05 18 h). mbar, T = 90 C, 18 h).

Scheme 10. Murphy’s synthesis of 8. Reagents and conditions: synthesis of 8, migrastatin 7 and MGSTA-3. Scheme 10. Murphy’s synthesis of 8. Reagents and conditions: synthesis of 8, migrastatin 7 and Reagents and conditions: (a) vinyl benzoate, 92, PhCH3, −20 °C, 48 h, 89%; (b) DAIB,◦ TEMPO, CH2Cl2, MGSTA-3. Reagents and conditions: (a) vinyl benzoate, 92, PhCH3, −20 C, 48 h, 89%; (b) DAIB, 2.5 h, RT, 84%; (c) (i) sBuLi, THF, 15 min, −78 °C; (ii) (+)Ipc2BOMe, −78 °C, 1 h; (iii) BF3·Et2O then 94, TEMPO, CH Cl , 2.5 h, RT, 84%; (c) (i) sBuLi, THF, 15 min, −78 ◦C; (ii) (+)Ipc BOMe, −78 ◦C, 1 h; −78 °C, 220 h,2 then 1 M NaOH, 30% H2O2, RT, 20 h; (d) K2CO3, MeOH, RT, 182 h, 73% from 94; · 94 − ◦ d (iii) BF(e3) TBSOTf,Et2O then Et3N,, CH782Cl2C,, 0 °C, 20 h,1.5 then h; (f)1 p M-TSA, NaOH, MeOH, 30% 0 °C, H2 2O h,2 ,84% RT, over 20 h; two ( )K steps;2CO (g3,) MeOH,Dess–Martin RT, 18 h, ◦ ◦ 73% fromreagent,94 ;(CHe)2Cl TBSOTf,2, pyridine, Et3 RT,N, CH18 h,2 Cl93%;2, 0(h)C, 63 1.5in THF, h; (f NaH,) p-TSA, 0 °C, MeOH, 1.5 h, then 0 98C, at 2 − h,7884% °C, 30 over min, two then steps; ◦ (g) Dess–Martin0 °C for 15 h, reagent, 79%; (i) DIBAL, CH2Cl CH2, pyridine,2Cl2, −78 °C, RT, 10 18 min, h, 93%;90%. (h) 63 in THF, NaH, 0 C, 1.5 h, then 98 at ◦ ◦ ◦ −78 C, 30 min, then 0 C for 15 h, 79%; (i) DIBAL, CH2Cl2, −78 C, 10 min, 90%. In 2015 [67], Murphy and co-workers reported the preparation of several migrastatin-core analogs with variations in the macrocycle ring size and functionality. Therefore, advanced In 2015 [18], Murphy and co-workers reported the preparation of several migrastatin-core analogs intermediate 8 was used for the preparation of compounds MGSTA-8 to MGSTA-16. with variationsThe coupling in the macrocycleof advanced intermediate ring size and 8 with functionality. carboxylic acids Therefore, 99a–c under advanced Mitsunobu intermediate conditions8 was usedgave for the the preparation corresponding of esters compounds 29 and 100a,bMGSTA-8 whichto underwentMGSTA-16 ring-closing. metathesis (RCM) using TheGrubbs coupling II catalyst of advanced to give macrolactones intermediate 30 8andwith 101a,b carboxylic. Removal acids of the99a TBS–c groupunder was Mitsunobu achievedconditions using gaveHF the.pyridine corresponding to afford esters MGSTA-229 and and100a,b the 13-which and 15-membered underwent analogs ring-closing MGSTA-8 metathesis and MGSTA-11 (RCM) using Grubbs(Scheme II catalyst 11). to give macrolactones 30 and 101a,b. Removal of the TBS group was achieved using HF·pyridine to afford MGSTA-2 and the 13- and 15-membered analogs MGSTA-8 and MGSTA-11 (Scheme 11).

Molecules 2017, 22, 198 12 of 26 Molecules 2017, 22, 198 12 of 26

Molecules 2017, 22, 198 12 of 26

Scheme 11. Synthesis of macrolacton migrastatin-core analogs. Reagents and conditions: (a) 99a–c, Ph3P, Scheme 11. Synthesis of macrolacton migrastatin-core analogs. Reagents and conditions:(a) 99a–c, Ph3P, DIAD, PhCH3, RT; 100a (69%), 100b (76%); (b) Grubbs II catalyst, PhCH3, reflux, 101a (68%), 101b DIAD, PhCH , RT; 100a (69%), 100b (76%); (b) Grubbs II catalyst, PhCH , reﬂux, 101a (68%), 101b (73%); (c) 3HF.py, THF, RT; MGSTA-8 (61%), MGSTA-11 (54%). 3 (73%);Scheme (c) HF.py, 11. Synthesis THF, RT; ofMGSTA-8 macrolacton(61%), migrastatin-coreMGSTA-11 analogs.(54%). Reagents and conditions: (a) 99a–c, Ph3P, DIAD, PhCH3, RT; 100a (69%), 100b (76%); (b) Grubbs II catalyst, PhCH3, reflux, 101a (68%), 101b (73%);Furthermore, (c) HF.py, migrastatin-core-based THF, RT; MGSTA-8 (61%), macroketones MGSTA-11 (54%). were prepared by the conversion of allylic Furthermore,alcohol 8 into the migrastatin-core-based allylic bromide 31 using macroketones an Appel reaction were [9]. preparedThis was subsequently by the conversion reacted with of allylic alcoholβ-ketosulfones8 Furthermore,into the allylic 32- 102a,bmigrastatin-core-based bromide [9] to 31giveusing ketones an macroketonesAppel 33 and reaction 103a,b were. Ring-closing [ 9prepared]. This was by metathesis the subsequently conversion reaction of reacted allylicusing with β-ketosulfonesalcoholGrubbs 8II into catalyst32- 102a,bthe allylic afforded [9] bromideto givemacroketones ketones 31 using33 34anand and Appel 103a,b104a,b, reaction. which, Ring-closing [9]. after This TBSwas metathesis removalsubsequently using reaction reactedHF·Py, using gavewith Grubbs MGSTA-3, and the 13- and the 15-membered analogs MGSTA-9 and MGSTA-12. In addition, protected II catalystβ-ketosulfones afforded macroketones32-102a,b [9] to34 giveand ketones104a,b, 33which, and 103a,b after. TBS Ring-closing removal usingmetathesis HF·Py, reaction gave MGSTA-3using , macroketone 34 underwent Saeugusa Ito oxidation using LHMDS and TMSCl, followed by treatment and theGrubbs 13- and II catalyst the 15-membered afforded macroketones analogs MGSTA-9 34 and 104a,b,and MGSTA-12 which, after. TBS In addition, removal protectedusing HF·Py, macroketone gave MGSTA-3with Pd(OAc), and2, to the give 13- the and α ,theβ-unsaturated 15-membered macroketone analogs MGSTA-9 MGSTA-13 and after MGSTA-12 TBS de-protection. In addition, (Scheme protected 12). 34 underwent Saeugusa Ito oxidation using LHMDS and TMSCl, followed by treatment with Pd(OAc) , macroketone 34 underwent Saeugusa Ito oxidation using LHMDS and TMSCl, followed by treatment 2 to give the α,β-unsaturated macroketone MGSTA-13 after TBS de-protection (Scheme 12). with Pd(OAc)2, to give the α,β-unsaturated macroketone MGSTA-13 after TBS de-protection (Scheme 12).

Scheme 12. Synthesis of macroketone migrastatin-core analogs. Reagents and conditions: (a) CBr4, Ph3P polymer-bound, CH2Cl2; (b) 32-102a,b, DBU, PhCH3 then 31, RT; (c) Na/Hg, MeOH, RT; (103a (51%) 103b (51%), from 8; (d) Grubbs II catalyst, PhCH3, reflux, 104a (99%), 104b (60%); (e) (i) 34, TMSCl, Scheme 12. Synthesis of macroketone migrastatin-core analogs. Reagents and conditions: (a) CBr4, Ph3P SchemeLHMDS, 12. Synthesis THF, 0 °C, of 2 macroketoneh; (ii) Pd(OAc) migrastatin-core2, CH3CN, RT, 2 h, analogs.78% fromReagents 34; (f) HF·Py, and conditionsTHF, RT, MGSTA-13:(a) CBr4,Ph 3P polymer-bound, CH2Cl2; (b) 32-102a,b, DBU, PhCH3 then 31, RT; (c) Na/Hg, MeOH, RT; (103a (51%) polymer-bound,(90%); (g) HF·Py, CH THF,Cl ;( RT,b) 32-102a,b MGSTA-9, DBU,(84%), PhCHMGSTA-12then (82%).31, RT; (c) Na/Hg, MeOH, RT; (103a (51%) 103b (51%), from2 8; (2d) Grubbs II catalyst, PhCH3, reflux,3 104a (99%), 104b (60%); (e) (i) 34, TMSCl, 103b (51%), from 8;(d) Grubbs II catalyst, PhCH , reﬂux, 104a (99%), 104b (60%); (e) (i) 34, TMSCl, LHMDS, THF, 0 °C, 2 h; (ii) Pd(OAc)2, CH3CN, RT,3 2 h, 78% from 34; (f) HF·Py, THF, RT, MGSTA-13 Macrothiolactones◦ were also prepared using Mitsunobu reaction of thioacids 106a,b with allylic LHMDS,(90%); THF, (g) HF·Py, 0 C, 2THF, h; (ii) RT, Pd(OAc) MGSTA-92, CH (84%),3CN, MGSTA-12 RT, 2 h, 78% (82%). from 34;(f) HF·Py, THF, RT, MGSTA-13 (90%);alcohol (g 8). HFThioacids·Py, THF, 106a RT, MGSTA-9and 106b were(84%), preparedMGSTA-12 by treating(82%). the corresponding carboxylic acids 105a,bMacrothiolactones with Lawesson’s were reagent also underprepared microwave using Mitsunobu irradiation reaction [68]. As of thioacidsdescribed 106a,b above, with RCM allylic and alcoholremoval 8 .of Thioacids the TBS 106agroup and afforded 106b were macrothiolactones prepared by treating MGSTA-10 the corresponding and MGSTA-14 carboxylic (Scheme acids 13). Macrothiolactones were also prepared using Mitsunobu reaction of thioacids 106a,b with allylic 105a,bInterestingly, with Lawesson’s silicon grease reagent impurity under in microwave MGSTA-8 irradiation to MGSTA-14 [68]. Aswas described removed above, after distillation RCM and alcohol 8. Thioacids 106a and 106b were prepared by treating the corresponding carboxylic acids 105a,b removal of the TBS group afforded macrothiolactones MGSTA-10 and MGSTA-14 (Scheme 13). withInterestingly, Lawesson’s reagentsilicon grease under impurity microwave in MGSTA-8 irradiation to [MGSTA-1469]. As described was removed above, after RCM distillation and removal of the TBS group afforded macrothiolactones MGSTA-10 and MGSTA-14 (Scheme 13). Interestingly, Molecules 2017, 22, 198 13 of 26 Molecules 2017, 22, 198 13 of 26 Molecules 2017, 22, 198 13 of 26 siliconunder reduced grease impurity pressure in(KugelrohrMGSTA-8 apparatus:to MGSTA-14 0.05 mbar,was removedT = 90 °C, after 2 to 24 distillation h). Since underMGSTA-3 reduced was ◦ pressuresynthesizedunder reduced (Kugelrohr in 100-mgpressure apparatus: scale, (Kugelrohr the 0.05 authors apparatus: mbar, undertook T =90 0.05C, mbar,the 2 to preparation24 T = h). 90 Since °C, 2ofMGSTA-3 to glucuronidated 24 h). Sincewas MGSTA-3 synthesized migrastatin- was in 100-mgcoresynthesized analogs. scale, in the 100-mg authors scale, undertook the authors the preparation undertook ofthe glucuronidated preparation of migrastatin-coreglucuronidated migrastatinanalogs. core analogs.

Scheme 13. 13. SynthesisSynthesis of macrothiolacto of macrothiolactonene migrastatin-core migrastatin-core analogs. Reagents analogs. and Reagentsconditions: and (a) Lawesson’s conditions: Scheme 13. Synthesis of macrothiolactone migrastatin-core analogs. Reagents and conditions: (a) Lawesson’s reagent, CH2Cl2, mw, 100 °C, 10 min; (b)◦ 105a,b, Ph3P, DIAD, PhCH3, RT; 106a (42%), 106b (39%); (a) Lawesson’s reagent, CH2Cl2, mw, 100 C, 10 min; (b) 105a,b, Ph3P, DIAD, PhCH3, RT; 106a (42%), reagent, CH2Cl2, mw, 100 °C, 10 min; (b) 105a,b, Ph3P, DIAD, PhCH3, RT; 106a (42%), 106b (39%); (c) Grubbs II catalyst, CH2Cl2, mw, 100 °C, 30 min, 107b◦ (49%); (d) Grubbs-II catalyst, PhCH3, reflux, 106b (39%); (c) Grubbs II catalyst, CH2Cl2, mw, 100 C, 30 min, 107b (49%); (d) Grubbs-II catalyst, (c) Grubbs II catalyst, CH2Cl2, mw, 100 °C, 30 min, 107b (49%); (d) Grubbs-II catalyst, PhCH3, reflux, PhCH107a (88%);, reﬂux, (e) HF·Py,107a (88%); THF, ( eRT;) HF MGSTA-3·Py, THF, RT;(85%),MGSTA-3 MGSTA-7(85%), (63%).MGSTA-7 (63%). 107a (88%);3 (e) HF·Py, THF, RT; MGSTA-3 (85%), MGSTA-7 (63%). The glucuronidation of small molecules is a physiological process that leads to highly water- The glucuronidation of small molecules is a physiological process that leads to highly solubleThe compounds glucuronidation that areof small therefore molecules excreted is a throughphysiological the kidney process [69]. that Theseleads tocompounds highly water- are water-soluble compounds that are therefore excreted through the kidney [70]. These compounds generallysoluble compounds biologically that inactive. are therefore However, excreted it has been through found thethat kidneyglucuronidated [69]. These small compounds molecules canare are generally biologically inactive. However, it has been found that glucuronidated small molecules displaygenerally increased biologically biological inactive. activity However, through it has a directbeen found or indirect that glucuronidated mechanism [69–71]. small In molecules addition, can β- can display increased biological activity through a direct or indirect mechanism [70–72]. In addition, glucuronidasesdisplay increased are biological generally activity overexpressed through in a directtumor or tissue indirect and mechanismglucuronidation [69–71]. strategy In addition, has been β- β-glucuronidases are generally overexpressed in tumor tissue and glucuronidation strategy has been exploitedglucuronidases for the are preparation generally ofoverexpressed pro-drugs based in tumor on SN-38 tissue or and taxol glucuronidation [72,73]. Murphy strategy and co-workers has been exploited for the preparation of pro-drugs based on SN-38 or taxol [73,74]. Murphy and co-workers demonstratedexploited for the that preparation reaction ofof pro-drugsMGSTA-3 based with ontrichloroacetimidate SN-38 or taxol [72,73]. 109 Murphy[74] in theand presence co-workers of demonstrated that reaction of MGSTA-3 with trichloroacetimidate 109 [75] in the presence of TMSFOTf TMSFOTfdemonstrated leads that to thereaction protected of MGSTA-3 β-glucuronide with trichloroacetimidate110. The resulting compound 109 [74] inwas the subsequently presence of leadsTMSFOTf to the leads protected to theβ -glucuronideprotected β-glucuronide110. The resulting 110. The compound resulting was compound subsequently was subsequently treated with treated with TiCl4 [75–81] to give α-glucuronide 111 as a single product. Finally, removal of benzoate TiCl [76–82] to give α-glucuronide 111 as a single product. Finally, removal of benzoate groups and groupstreated4 withand hydrolysis TiCl4 [75–81] of methylto give αester-glucuronide led to migrastatin 111 as a single analogs product. MGSTA-15 Finally, and removal -16 (Scheme of benzoate 14). hydrolysisgroups and of hydrolysis methyl ester of methyl led to migrastatin ester led to analogsmigrastatinMGSTA-15 analogs andMGSTA-15-16 (Scheme and 14-16). (Scheme 14).

Scheme 14. Reagents and conditions: (a) 109 TMSOTf, MS (AW300), CH2Cl2, −78 °C, 5 h, 60%; Scheme 14. Reagents and conditions: (a) 109 TMSOTf, MS (AW300), CH2Cl2, −78 °C,◦ 5 h, 60%; Scheme(b) TiCl4, 14. CDClReagents3, 4 °C, 69%; and ( conditions:c) NaOH aq., (a MeOH,) 109 TMSOTf, RT, 18 h, MS MGSTA-16 (AW300), (61%), CH2Cl MGSTA-172, −78 C, (73%). 5 h, 60%; (b) TiCl4, CDCl3, 4 °C,◦ 69%; (c) NaOH aq., MeOH, RT, 18 h, MGSTA-16 (61%), MGSTA-17 (73%). (b) TiCl4, CDCl3, 4 C, 69%; (c) NaOH aq., MeOH, RT, 18 h, MGSTA-16 (61%), MGSTA-17 (73%).

Molecules 2017, 22, 198 14 of 26

2.2. Biology

2.2.1. Preliminary Findings [3,6,83] The biological activity of migrastatin was ﬁrst reported in 2000 by Imoto et al. [3] These authors showed that migrastatin inhibits the migration of EC17 (mouse esophageal cancer cells), with an IC50 of 6 µM in a wound-healing assay (WHA) and of 2 µM in a chemotaxicell chamber assay. However, the same authors reported [83] that a migrastatin sample was contaminated with teleocidin-related impurities, which are known for their anti-migratory activity. After careful puriﬁcation, they showed an inhibition of cell migration in EC17 cells, pretreated with pure migrastatin for 24 h, with an IC50 of 20.5 µM (WHA). In addition, they showed that migrastatin inhibits the growth of EC17 cells, with an IC50 of 167.5 µM. These results indicate that inhibition of cell migration was not due to cytotoxicity [83]. In 2006, the same authors reported that migrastatin inhibits the function of P-glycoprotein and is therefore capable of suppressing multidrug resistance (MDR) [6]. They demonstrated that migrastatin increases the intracellular concentration of anticancer drugs vinblastine, vincristine and taxol in P-glycoprotein-overexpressing VJ-300 (vincristine-resistant human epidermoid carcinoma) [84] and P388/VCR (vincristine-resistant mouse leukemia) cells [85]. The cytotoxicity of vincristine and taxol in VJ-300 cells treated with migrastatin (61 µM) increased 40- and 53-fold respectively (migrastatin not toxic up to 102 µM).

2.2.2. Danishefsky’s Work [9,86–88] An important breakthrough with respect to the biological activity of migrastatin was made by Danishefsky et al. in 2005 [9]. Through a diverted total synthesis approach (Figure2), a series of truncated analogs of migrastatin were prepared and tested as inhibitors of cell migration in 4T1 cells (mammary mouse cancer) and HUVECs (human healthy endothelial cells). Migrastatin-core analogs MGSTA-2 to 4 were ≈ 1000 more potent that migrastatin itself (Figure4b) and were not cytotoxic up to 20 µM. Interestingly, while migrastatin was stable in mouse plasma, macrolactone MGSTA-1 and MGSTA-2 were not. On other hand, macroketone MGSTA-3 and macrolactam MGSTA-5 displayed higher stability, as revealed by an unchanged HPLC signal over 60 min of incubation (Figure4c). MGSTA-3 and MGSTA-4 also inhibited the migration of highly invasive and metastatic cancer cell lines, such as MDA-MB-231 (human breast tumor), Lovo (human colon tumor) and PC-3 (human prostate tumor) in WHAs [86]. Importantly, MGSTA-3 and MGSTA-4 did not affect the migration of normal human mammary-gland epithelial cells (MCF-10A), mouse embryonic ﬁbroblasts, or primary mouse leukocytes in WHAs [86]. For in vivo studies [86], the 4T1 mouse mammary model was chosen. In this model, the tumor closely mimics human breast cancer with respect to immunogenicity, metastasis, anatomy and growth characteristics [89]. 4T1 tumors spontaneously metastasize to the lung, bone, brain and liver [90]. MGSTA-3 and MGSTA-4 were administrated daily for 20 days at 10 mg/kg or 20 mg/kg. MGSTA-3 and MGSTA-4 reduced the metastasized 4T1 cells in the lungs by 91%–99% (measured by 6-thioguanine clonogenic assay) (Figure4d). Tumor growth was not affected by MGSTA-3 or MGSTA-4, and no obvious side effects were observed. MGSTA-2, which was not stable in plasma (Figure4c), was considerably less effective at inhibiting metastasis (Figure4). In addition, the authors showed that MGSTA-3 and MGSTA-4 block the activation of RAC (Ras-related C3 botolinum toxic substrate 1), a protein involved in lamellipodia formation and therefore in cell migration. Molecules 2017, 22, 198 15 of 26 Molecules 2017, 22, 198 15 of 26

FigureFigure 4.4. ((aa)) Structures Structures of of migrastatin migrastatin (7 ()7 and) and migrastatin migrastatin analogs analogs MGSTA-1MGSTA-1 to to4; (4b;() Chamberb) Chamber cell cellmigration migration assay assay with with 4T1 4T1 mammary mammary mouse mouse tumor tumor cells cells and and HUVECs; HUVECs; ( (cc)) metabolic stabilitystability ofof migrastatinmigrastatin andand analogs;analogs; (d)) inhibitioninhibition of breast tumor metastasis (4T1) by by MGSTA-2, MGSTA-3,, MGSTA-4MGSTA-4in in a a mouse mouse model. model. LungLung metastasismetastasis waswas measuredmeasured byby thethe 6-thioguanine6-thioguanine clonogenic assay. ResultsResults areare meanmean ±± SD ((nn == 5).5). *, p << 0.01. Adapted with permission from PNAS, 2005, 102,, 3772.3772. CopyrightCopyright (2005)(2005) NationalNational AcademyAcademy ofof Sciences,Sciences, U.S.A.U.S.A. aa IntensityIntensity ofof HPLCHPLC signalsignal unchangedunchanged overover 6060 minmin ofof incubation.incubation.

AA fewfew yearsyears laterlater [ 87[86],], DanishefskyDanishefsky and and co-workers co-workers prepared prepared the the simplified simplified macroether macroetherMGSTA-5 MGSTA- starting5 starting from from advanced advanced intermediate intermediate8 8(Figure (Figure5a). 5a).MGSTA-5 MGSTA-5was was tested tested in in transwell transwell cell-migrationcell-migration assaysassays againstagainst 4T1,4T1, MDA-MB-231MDA-MB-231 (human(human breastbreast cancer),cancer), MDA-MB-435MDA-MB-435 (human(human breastbreast cancer)cancer) cellcell lines. MGSTA-5 inhibited the migration of tested cell lines, with an IC50 in the nanomolar range lines. MGSTA-5 inhibited the migration of tested cell lines, with an IC50 in the nanomolar range (Figure(Figure5 b).5b). Interestingly, Interestingly, a a higher higher concentration concentration of ofMGSTA-5 MGSTA-5was wasnecessary necessaryto to inhibitinhibit thethe migrationmigration ofof MCF10AMCF10A (non-tumor human human breast breast cells), cells), thereb therebyy suggesting suggesting a specific a specific mechanism mechanism of action of action for fortransformed transformed cells. cells. MGSTA-5MGSTA-5 also inhibitedalso inhibited the proliferation the proliferation of MDA-MB-231 of MDA-MB-231 cells, with cells, an IC with50 > 100. an This observation suggesting that the inhibition of migration in MDA-MB-231 cells is not related to IC50 > 100. This observation suggesting that the inhibition of migration in MDA-MB-231 cells is not relatedcytotoxicity. to cytotoxicity. MGSTA-5MGSTA-5 inhibitedinhibited the migration the migration of the ofhighly the highly metastatic metastatic breast breast cancer cancer cell cellline LM2-4175 (LM2), with an IC50 (extrapolated from graph) [86] of around 1.5–2 µM. LM2 cells are line LM2-4175 (LM2), with an IC50 (extrapolated from graph) [87] of around 1.5–2 µM. LM2 cells areaggressive aggressive and and highly highly metastatic metastatic and and are are derived derived from from lung lung metastasis metastasis of of MDA-MB-231 [[90].91]. TheThe abilityability ofof MGSTA-5MGSTA-5 toto inhibitinhibit tumortumor metastasismetastasis inin vivovivowas was assessedassessed usingusing luciferase-basedluciferase-based noninvasivenoninvasive wholewhole animalanimal bioluminescentbioluminescent imaging imaging in in a a xenograft xenograft breast breast cancer cancer model model in in NOD/SCID NOD/SCID micemice transplantedtransplanted withwith MDA-MB-231MDA-MB-231 cellscells stablystably expressingexpressing thethe HSVTK-eGFP-luciferaseHSVTK-eGFP-luciferase (TGL)(TGL) reporterreporter proteinprotein [91]. [92]. After After inoculation inoculation of of MDA-MB-2 MDA-MB-23131 cells, cells, a group a group of five of fivemice mice were were treated treated with withMGSTA-5MGSTA-5 (three(three times/week; times/week; 40 mg/kg) 40 mg/kg) from from day day 1 (pre-treatment). 1 (pre-treatment). Another Another group group of of mice waswas treatedtreated startingstarting fromfrom dayday 1515 (post-treatment).(post-treatment). AtAt thethe timetime ofof surgicalsurgical resection,resection, 50%50% ofof controlcontrol micemice hadhad metastasismetastasis andand 85%85% hadhad tumorstumors invadinginvading thethe musclemuscle layerlayer andand peritonealperitoneal membrane.membrane. TheThe groupgroup ofof micemice treatedtreated withwith MGSTA-5MGSTA-5from from dayday 11 (pre-treatment)(pre-treatment) showedshowed anan 87%87% reductionreduction inin metastases,metastases, whilewhile thatthat treatedtreated withwith MGSTA-5MGSTA-5from from dayday 1515 (post-treatment)(post-treatment) showedshowed aa 47%47% reductionreduction (Figure(Figure5 5c).c). Pre-treatmentPre-treatment withwithMGSTA-5 MGSTA-5also also had hadan an importantimportanteffect effecton on overalloverall survival.survival. MiceMice werewere pre-treatedpre-treated with MGSTA-5 at 40 mg/kg and 200 mg/kg. After 50 days, all the control mice had died; however, with MGSTA-5 at 40 mg/kg and 200 mg/kg. After 50 days, all the control mice had died; however, thethe overalloverall survivalsurvival ofof thethe groupsgroups treatedtreated withwith 4040 andand 200200 mg/kg mg/kg waswas 30%30% andand 50%,50%, respectivelyrespectively (Figure(Figure5 d).5d). After After 9 9 weeks, weeks, a a metastatic metastatic tumor tumor was was detectable detectable in in the theformer formergroup groupbut but notnot inin thethe latter.latter. Importantly, treatment with MGSTA-5 did not attenuate the growth of the primary tumor [86]. Importantly, treatment with MGSTA-5 did not attenuate the growth of the primary tumor [87].

MoleculesMolecules2017 2017, 22,, 22 198, 198 16 16of of26 26 Molecules 2017, 22, 198 16 of 26

Figure 5. (a) Structure of MGSTA-5; (b) Chamber cell migration assay; (c) MGSTA-5 treatment FigureFigure(40 mg/kg) 5. 5.( a()a )begun Structure Structure at day ofof MGSTA-51MGSTA-5 (Pre) or day;(; (bb ))15 ChamberChamber (Post) after cell cell tumor migration migration inoculation assay; assay; ((MDA-MB-231).c ()c MGSTA-5) MGSTA-5 treatment treatmentPrimary (40(40tumor mg/kg) mg/kg) was begun begunresected at dayat dayat 1 2 (Pre) 1weeks (Pre) or dayandor day 15tumor (Post) 15 (Post) metastasis after after tumor tumorwas inoculation determined inoculation (MDA-MB-231). by (MDA-MB-231). bioimaging Primary at 3Primary weeks; tumor wastumor(d resected) MGSTA-5 wasat resected 2 weekstreatment at and 2 weeks(40 tumor or 200and metastasis mg/kg) tumor wasbegunmetastasis determined at day was 1 afterdetermined by bioimaging tumor inoculationby bioimaging at 3 weeks; (MDA-MB-231). (atd )3MGSTA-5 weeks; treatment(Primaryd) MGSTA-5 (40 tumor or 200treatment was mg/kg) resected (40 begun or at 200 3 at weeksmg/kg) day 1and begun after tumor tumor at day metastasis inoculation 1 after tumorwas (MDA-MB-231). determined inoculation by (MDA-MB-231). bioimaging Primary tumor at wasPrimary4 resectedweeks. tumorAdapted at 3 weeks was with resected and permission tumor at 3 metastasis weeks from J. and Am. was tumorChem. determined Socmetastasis. 2010 by, 132 bioimagingwas, 3224. determined Copyright at 4 weeks. by (2010) bioimaging Adapted American withat permission4Chemical weeks. Adapted from Society.J. Am. with Chem. permission Soc. 2010 from, 132 J. Am., 3224. Chem. Copyright Soc. 2010 (2010), 132, 3224. American Copyright Chemical (2010) Society.American Chemical Society. With the aim to identify new compounds with enhanced solubility, bioavailability and pharmacostability,WithWith the the aim aim to Danishefskyto identify identify newandnew co-workers compoundscompounds [87] withsynthesized enhanced the carboxymethylsolubility, solubility, bioavailability bioavailability migrastatin-core and and pharmacostability,pharmacostability,analog MGSTA-6 Danishefsky Danishefsky(Figure 6a).and Theandco-workers co-workersability of this [[87]88 compound] synthesized to theinhibit the carboxymethyl carboxymethyl cell migration migrastatin-core migrastatin-core was assessed analoganalogusingMGSTA-6 theMGSTA-6 WHA(Figure and(Figure transwell6a). 6a). The The ability migration ability ofthis of assaythis compound compound in human to inhibit to non-small inhibit cell migrationcell cell migration lung was carcinoma was assessed assessed cells using theusing(NSCLC) WHA the and andWHA transwell compared and transwell migration with that migration assay of MGSTA-5 in human assay. Both non-smallin humanMGSTA-5 cellnon-small and lung MGSTA-6 carcinoma cell lung efficiently cellscarcinoma (NSCLC) reduced cells and compared(NSCLC)the migration with and thatcompared of A549, of MGSTA-5 H1975 with that and. Both of H1299299 MGSTA-5MGSTA-5 cancer. Bothand cells, MGSTA-5MGSTA-6 with an andefﬁciently IC 50MGSTA-6 in the reduced micro efficiently and the nanomolar migration reduced of A549,therange migration H1975 (Figure and of6b). H1299299 A549, H1975 cancer and cells, H1299299 with ancancer IC50 cells,in the with micro an andIC50 nanomolarin the micro range and nanomolar (Figure6b). range (Figure 6b).

Figure 6. (a) Structure of MGSTA-6 a; (b) Chamber cell migration assay with non-small lung carcinoma Figure 6. (a) Structure of MGSTA-6 a; (b) Chamber cell migration assay with non-small lung carcinoma Figure(NSLC) 6. A549, (a) Structure H1975, H1299of MGSTA-6 cells; (c )a; Bioluminescent (b) Chamber cell imaging migration of tumor assay metastasis with non-small at endpoint. lung carcinomaLung (Lu), (NSLC) A549, H1975, H1299 cells; (c) Bioluminescent imaging of tumor metastasis at endpoint. Lung (Lu), (NSLC)liver (Li), A549, heart H1975, (H), kidneys H1299 (K),cells; and (c) Bioluminescentspleen (S). Adapted imaging with of permission tumor metastasis from PNAS at endpoint., 2011, 108 Lung, 15074. (Lu), liverliver (Li), (Li), heart heart (H), (H), kidneys kidneys (K),(K), and spleen spleen (S). (S). Adapted Adapted with with permission permission from from PNASPNAS, 2011, 2011, 108,, 10815074., 15074. The capacity of MGSTA-5 and 6 to inhibit tumor metastasis generated from human primary smallTheThe lung capacity capacity carcinoma of ofMGSTA-5 MGSTA-5 cells (SLCL)and and was6 6to toalsoinhibit inhibit evaluate tumortumord. Primary metastasis tumors generated generated were obtained from from human human from primarypatients, primary smallsmalland lung cells lung carcinomawere carcinoma stably cells cellstransduced (SLCL) (SLCL) waswithwas alsoalsoa triplefusi evaluated.evaluateond. protein Primary Primary reporter tumors tumors construct were were obtained obtained (AC3-TGL) from from patients,and patients, then andandtransplanted cells cells were were stablyby stably subcutaneous transduced transduced injection with with aa triplefusionwithtriplefusi Matronigel protein into NOD/SCID reporter reporter construct constructIL2R gamma (AC3-TGL) (AC3-TGL) null (NSG) and and mice.then then transplantedtransplantedMice were treated by by subcutaneous subcutaneous with both MGSTA-5 injection injection withand with 6 Matr from Matrigeligel day into 1 at into NOD/SCID doses NOD/SCID of 10, IL2R 40 and gamma IL2R 200 mg/kg gamma null (NSG) (MGSTA-5 null mice. (NSG)) mice.Miceand Mice 12were and weretreated 49 mg/kg treated with (MGSTA-6 both with MGSTA-5 both) (bothMGSTA-5 and analogs 6 fromand were day6 from administered1 at doses day of 1 at10, by doses 40 intraperitoneal and of 200 10, mg/kg 40 andinjection (MGSTA-5 200 mg/kgthree) (MGSTA-5andtimes/week; 12 and) and 49 doses mg/kg 12 and adjusted (MGSTA-6 49 mg/kg to molecular) (both (MGSTA-6 analogs weight).) (bothwere Mice administered analogs were treated were by administered forintraperitoneal 55 days and by injection intraperitonealmonitored three by injectiontimes/week;serial noninvasive three doses times/week; adjustedbioluminescent doses to molecular adjusted imaging weight). to (BLI). molecular Mice At day were weight). 55, treated mice Mice werefor were55 killed, days treated andand monitored forthe 55spread days by of and monitoredserialmetastasis noninvasive by in serial lungs, noninvasivebioluminescent liver, heart, bioluminescent kidneys imaging and (BLI). spleen imaging At wasday (BLI).evaluated55, mice At daywere using 55, killed, miceBLI (Figure and were the killed, 6c). spread Neither and of the spreadmetastasisanalog of metastasisaffected in lungs, the in liver,inhibition lungs, heart, liver, of kidneys tumor heart, and kidneysgrowth. spleen andNo was toxicity spleen evaluated waswas evaluatedusingdetected BLI in using(Figure mice BLI treated6c). (Figure Neither with6c). NeitheranalogMGSTA-6 analog affected. In affected addition, the inhibition the treatment inhibition of tumorwith oftumor the growth. low growth. dose No of toxicity No MGSTA-6 toxicity was was(12 detected mg/kg) detected in was mice in approximatively mice treated treated with with MGSTA-6MGSTA-6four times. In. moreIn addition, addition, potent treatment thantreatment MGSTA-5 with with the theat the lowlow same dosedose dose of MGSTA-6 (10 mg/kg). (12(12 mg/kg) mg/kg) was was approximatively approximatively four times more potent than MGSTA-5 at the same dose (10 mg/kg). four times more potent than MGSTA-5 at the same dose (10 mg/kg).

Molecules 2017, 22, 198 17 of 26

2.2.3.Molecules Mechanism 2017, 22,of 198 Action [93] 17 of 26 In 2010, Chen and co-worker [93] attempted to elucidate the mechanism of action of MGSTA-3. 2.2.3. Mechanism of Action [92] The authors claimed that the target of MGSTA-3 was fascin. Fascin is an actin-bundling protein responsibleIn 2010, for cell Chen migration and co-worker and therefore [92] attempted for cell to invasionelucidate andthe mechanism metastasis. of Fascin action of mRNA MGSTA-3 transcript. and proteinThe authors levels claimed are elevated that the target in aggressive of MGSTA-3 tumors was[ 94fascin.,95], Fascin and overexpression is an actin-bundling of fascin protein is also responsible for cell migration and therefore for cell invasion and metastasis. Fascin mRNA transcript linked to increased cell migration and invasion [96,97]. Using an affinity protein purification approach, and protein levels are elevated in aggressive tumors [93,94], and overexpression of fascin is also they demonstrated that a MGSTA-3 biotin-labeled analog [9] (Figure7a) binds to fascin in cancer cell linked to increased cell migration and invasion [95,96]. Using an affinity protein purification extracts.approach, F-actin they pelleting demonstrated assays that [98 a] MGSTA-3 revealed that biotin-labeledMGSTA-3 analogsignificantly [9] (Figure decreases 7a) binds fascin-inducedto fascin in bundlingcancer of cell F-actin extracts. polymers. F-actin pelleting The authors assays [97] also revealed published that anMGSTA-3 X-raycrystal significantly structure decreases of fascin co-crystalizedfascin-induced with bundlingMGSTA-3 of F-actinand claimed polymers. that TheMGSTA-3 authors alsobinds published at the samean X-ray site crystal of actin. structure However, this X-rayof fascin structure co-crystalized was found with MGSTA-3 to be incorrect and claimed and was that thereforeMGSTA-3 retracted binds at the [93 same], since site theof actin. chemical structureHowever, of MGSTA-3 this X-raybound structure to was fascin found shown to be in in thecorrect X-ray and picture was therefore was not retractedMGSTA-3 [92], butsince rather the its isomerchemical [99]. Furthermore, structure of MGSTA-3 the authors bound showed to fascin that shown selective in the mutation X-ray picture of fascin was innot the MGSTA-3 proposed but region of bindingrather reducedits isomer the [98]. actin-bundling Furthermore, the activity authors of fascinshowed (mutation that selective on H392, mutation Lys471, of fascin Ala488, in the F-actin proposed region of binding reduced the actin-bundling activity of fascin (mutation on H392, Lys471, pelleting assay, Figure7b). On other hand, mutation of His 474 to Ala did not reduce the activity Ala488, F-actin pelleting assay, Figure 7b). On other hand, mutation of His 474 to Ala did not reduce of fascin but rendered fascin resistant to MGSTA-3 treatment (Figure7c). These results were also the activity of fascin but rendered fascin resistant to MGSTA-3 treatment (Figure 7c). These results validatedwere inalso 4T1 validated cancer in cells 4T1 incancer a boyden cells in chamber a boyden assay chamber (Figure assay7 d).(Figure 7d).

Figure 7. (a) Structure of Biotin-conjugated MGSTA-3; (b) Quantification of actin bundling assay for Figure 7. (a) Structure of Biotin-conjugated MGSTA-3;(b) Quantiﬁcation of actin bundling assay for the wild-type fascin and mutants; results are means and ± SD (n = 3); * p < 0.05 (c) Mutant sensitivity the wild-type fascin and mutants; results are means and ± SD (n = 3); * p < 0.05 (c) Mutant sensitivity to MGSTA-3. Wild-type fascin and the E391A and H474A mutants of fascin were assayed for their MGSTA-3 to actin-bundling. Wild-type activity fascin in the andabsence the or E391A presence and of H474A MGSTA-3 mutants (10 µM); of results fascin are were means assayed and ±SD for their actin-bundling(n = 3). * p

10 and MGSTA-13 in canine mammary cell lines. The study was carried out using CMT-W1 and CMT-W2 cells and their corresponding lung metastasis CMT-W1M and CMT-W2M cells [100,101]. Molecules 2017, 22, 198 18 of 26 A preliminary screen using the wound-healing assay (WHA) showed that MGSTA-3 and MGSTA-13 werecorresponding the most promising lung metastasis analogs. CMT-W1M Further singleand CMT-W2M concentration cells [100,101]. studies (BoydenA preliminary chamber screen assay) showedusing that theMGSTA-13 wound-healingwas assay the most(WHA) promising showed that compound. MGSTA-3MGSTA-13 and MGSTA-13inhibited were cellthe migrationmost of CMT-W1,promising CMT-W1M, analogs. Further CMT-W2 single cells, concentration with an IC studies50 in the (Boyden molar chamber range (Figure assay)8 b).showed Surprisingly, that no effectMGSTA-13 was observed was the inmost CMT-W2M promising cells. compound. Theynext MGSTA-13 examined inhibited the invasive cell migration phenotype of CMT-W1, [102,103 ] of CMT-W1,CMT-W1M, CMT-W1M, CMT-W2 CMT-W2 cells, with cells an cultured IC50 in the on reconstitutedmolar range (Figure basement 8b). Surprisingly, membrane (Matrigel no effectTM was) in the observed in CMT-W2M cells. They next examined the invasive phenotype [102,103] of CMT-W1, presence or the absence of MGSTA-13. After 24 h, cells cultured in control conditions showed typical CMT-W1M, CMT-W2 cells cultured on reconstituted basement membrane (MatrigelTM) in the branching formation. In contrast, all cells treated with MGSTA-13 showed a remarkable inhibition of presence or the absence of MGSTA-13. After 24 h, cells cultured in control conditions showed typical branchbranching formation formation. (Figure In7 c).contrast, This observationall cells treated indicates with MGSTA-13 that this showed compound a remarkable has an effect inhibition on actin machinery,of branch which formation is responsible (Figure 7c). forThis filopodia observation formation indicates that and this thus compound for cell migration.has an effect on Given actin these findings,machinery, the authors which is focused responsible their for attention filopodia on formation fascin, anand actin-bundling thus for cell migration. protein Given responsible these for the developmentfindings, the authors and maintenance focused their ofattention straight on and fascin, tight an actin-bundling F-actin bundles protein [104 –responsible106]. Using for confocalthe microscopy,development they demonstratedand maintenance that of actinstraight strongly and ti co-localizedght F-actin bundles with fascin1 [104–106]. in CMTW1 Using confocal cells, while aftermicroscopy, treatment with they MGSTA-3demonstratedthis that co-localization actin strongly co-localized decreased dramaticallywith fascin1 in (Figure CMTW18d). cells, In while addition, CMT-W1after cellstreatment in control with MGSTA-3 conditions this showed co-localization several filopodia decreased and dramatically protrusions, (Figure which 8d). disappeared In addition, after CMT-W1 cells in control conditions showed several filopodia and protrusions, which disappeared treatment with MGSTA-13 (Figure8e). Similar results were obtained with CMT-W1 and CMT-W2 after treatment with MGSTA-13 (Figure 8e). Similar results were obtained with CMT-W1 and CMT-W2 cells. With these results in hand, the authors analyzed the expression of phospho-fascin1 protein cells. With these results in hand, the authors analyzed the expression of phospho-fascin1 protein (phospho-FSCN1(ser39))(phospho-FSCN1(ser39)) in in the the four four cell cell lines. lines. TheThe expression expression of of fascin1 fascin1 in CMT-W2M in CMT-W2M cells, cells, which which werewere not sensitivenot sensitive to MGSTA-3 to MGSTA-3and and13 13, was, was lower lower thanthan in in the the other other cell cell lines lines (Figure (Figure 8f).8 f).

Figure 8. (a) Structure of MGSTA-13; (b) Chamber cell migration assay with canine mammary cancer Figure 8. (a) Structure of MGSTA-13;(b) Chamber cell migration assay with canine mammary cell lines; (c) Growth characteristics of CMT-W1, cell lines cultured on Matrigel and treated with cancer cell lines; (c) Growth characteristics of CMT-W1, cell lines cultured on Matrigel and treated MGSTA-13 100 µM for 24 h; (d) Quantification of fascin1 and F-actin co-localization at merge images; µ with theMGSTA-13 unpaired t-test100 wasM forapplied. 24 h; p (

Molecules 2017, 22, 198 19 of 26 of expression of a mutant form of the tumor suppressor p53 [115]. MGSTA-3 had no effect on the immobile fraction of E-cadherin, a measure of the amount of E-cadherin immobilized at cell-cell junctions. PDAC cells were therefore injected subcutaneously into nude mice, and tumors were allowed to grow for Molecules 2017, 22, 198 19 of 26 seven days. The mice were treated with MGSTA-3 (20 mg/kg) for three days, and E-cadherin dynamics werecell-cell studied junctions. using FRAP. PDACMGSTA-3 cells weretreatment therefore injected increased subcutaneously the immobile into fraction, nude mice, an effect and tumors expected to strengthenwere allowed cell-cell to adhesion grow for andseven therefore days. The impede mice were metastasis. treated with MGSTA-3 (20 mg/kg) for three Indays, 2015, and E-cadherin Murphy and dynamics co-workers were studied reported using theFRAP. biological MGSTA-3 activity treatment of increa severalsed migrastatinthe immobile core analogs.fraction,MGSTA-8 an effect expectedto 16 were to strengthen tested against cell-cell three adhesion breast and (MCF7,therefore MCF7-Dox,impede metastasis. MDA-MB361) and In 2015, Murphy and co-workers reported the biological activity of several migrastatin core one pancreatic (HPAC) cancer cell lines in WHA. All analogs inhibited cell migration, and none analogs. MGSTA-8 to 16 were tested against three breast (MCF7, MCF7-Dox, MDA-MB361) and one were toxic up to 100 µM. Selected analogs (MGSTA-3, MGSTA-12 to 13, MGSTA-15 to 16) were pancreatic (HPAC) cancer cell lines in WHA. All analogs inhibited cell migration, and none were thereforetoxic up tested to 100 in µM. transwell Selected assays analogs in (MGSTA-3 MCF7, MDA-MB-361, MGSTA-12 to and13, MGSTA-15 HPCA cells to 16 (Figure) were 9therefore). All these compoundstested in inhibitedtranswell assays cell migration in MCF7, MDA-MB-361 in the nanomolar and HPCA range, cells with (Figure the exception9). All these of compoundsMGSTA-13 in MCF-7inhibited cells. Sincecell migrationMSTA-13 in inhibitedthe nanomo celllar migrationrange, with in the the exception highly metastaticof MGSTA-13 MDA-MB-361 in MCF-7 cells. cell but not inSince the lessMSTA-13 invasive inhibited MCF7 cell cells, migration the authors in the claimedhighly metastatic that this MDA-MB-361 effect couldbe cell related but not to incytoskeleton the less proteinsinvasive targeted MCF7 by cells, migrastatin the authors analogs claimed [14 that,93]. this Interestingly, effect couldMGSTA-13 be related towas cytoskeleton tested against proteins a panel of 55targeted targets knownby migrastatin to be related analogs to [14,92]. adverse Interestingly, drug reactions MGSTA-13 (ADRs). wasMGSTA-13 tested againstshowed a panel only of 55 weak inhibitorytargets capacity known to over be related adenosine to adverse receptor drug A2Areactions (27%) (ADRs). and prostanoidMGSTA-13 showed EP4 receptor only weak (39%). inhibitory It has been capacity over adenosine receptor A2A (27%) and prostanoid EP4 receptor (39%). It has been reported reported that a promiscuity index (percentage of targets giving more than 50% inhibition at 10 µM in that a promiscuity index (percentage of targets giving more than 50% inhibition at 10 µM in a set of a set of at least 50 targets) of more than 20% is linked to market withdrawal and clinical trial failure. at least 50 targets) of more than 20% is linked to market withdrawal and clinical trial failure. UnsaturatedUnsaturated macroketone macroketoneMGSTA-13 MGSTA-13registered registered a promiscuity index index of ofbetween between 0% 0%and and5%, and 5%, is and is thereforetherefore a promising a promising candidate candidate for for further further biological biological studies.

FigureFigure 9. Structures 9. Structures of selectedof selected migrastatin migrastatinanalogs analogs and and effect effect on on human human breast breast cancer cancer cell lines cell linesMCF7 MCF7 and MDA MB-361 assessed with Boyden chamber assay. and MDA MB-361 assessed with Boyden chamber assay. The biological activity of migrastatin-core analogs has attracted the attention of cancer biologists Thein recent biological years. activitySeveral synthetic of migrastatin-core approaches ha analogsve been has developed attracted for the these attention compounds, of cancer and biologiststheir in recentrelatively years. simple Several structure synthetic has allowed approaches the preparation have been of small developed libraries and for scale-up these compounds, for in vivo studies. and their relativelyMigrastatin simple structure analogs has act allowed as anti-metastatic the preparation agents by of smallinhibition libraries of the and cell scale-upmotility machinery for in vivo andstudies. Migrastatinthey have no analogseffect in tumor act as anti-metastaticgrowth or prolifer agentsation. byThe inhibition mechanism of by the which cell motilitymigrastatin machinery analogs and theyinterfere have no with effect cell in migration tumor growth is still debated or proliferation. and further The studies mechanism are necessary by whichin order migrastatin to confirm their analogs primary target. Preliminary data suggest that migrastatin analogs selectively reduced cell migration interfere with cell migration is still debated and further studies are necessary in order to confirm their in cancer cells without interfering with non-transformed cells. New findings in this direction will primarydefinitely target. help Preliminary medicinal chemist data suggest to design that new migrastatin analogs with analogs enhanced selectively biological activity reduced and cell stability. migration in cancerIn cells addition, without this interferingclass of compound with non-transformed displayed low cytotoxic cells. activity New findings and recently in this it have direction been will definitelydemonstrated help medicinal that MGSTA-13 chemist to present design low new affinity analogs for with several enhanced targets biological related to activity adverse and drug stability. Inreactions addition, (ADRs). this classSince ofhigh compound affinity of displayedtargets related low with cytotoxic ADRs activity result in and preclinical/clinical recently it have or been demonstratedmarket withdrawal, that MGSTA-13 migrastatinpresent analogs low affinity could forbe severalvaluable targets molecules related for to adversefurther preclinical drug reactions (ADRs).development. Since high Efforts affinity in of this targets direction related could with lead ADRs to the result identification in preclinical/clinical of preclinical or candidates market withdrawal, with migrastatinenhanced analogs safety profile. could be valuable molecules for further preclinical development. Efforts in this direction couldWe also lead believe to the that identification the preparation of preclinical of synthetic candidates migrastatin with analogs enhanced with safety enhanced profile. water solubility and plasma stability it is also necessary. It has been demonstrated that free hydroxyl group in migrastatin core could be modified with the introduction of a carboxymethyl moiety or sugar

Molecules 2017, 22, 198 20 of 26

We also believe that the preparation of synthetic migrastatin analogs with enhanced water solubility and plasma stability it is also necessary. It has been demonstrated that free hydroxyl group in migrastatin core could be modified with the introduction of a carboxymethyl moiety or sugar moiety without drastically affect the biological activity. Moreover, modification of hydrophobic left hand side of migrastin-core analogs has not be explored. From the clinical point of view, migrastatin analogs could act as prophylactic agents that prevent tumor cells to metastasize. Safe and efficient migrastatin analogs could be administrated after liver or lung metastasis resection and this could prevent metastasis relapse. Alternatively, migrastatin analogs could be administrated during or after chemotherapy standard treatment. We hope that this review serves to inspire the preparation of novel analogs with enhanced pharmacological properties, thus paving the way for their application in the treatment of patients with metastatic cancer.

Acknowledgments: This work was supported by Generalitat de Catalunya (XRB, 2014-SGR-521), AGAUR—Ajuts programa Beatriu de Pinós (Modalitat B) REF: 2014_BP_B_00075, from the European Union’s Seventh Framework Programme for research, technological and demonstration under grant agreement no 600404 and from MINECO-FEDER (Bio2016-75327-R). IRB Barcelona is the recipient of a Severo Ochoa Award of Excellence from MINECO (Government of Spain). IRB Barcelona is a member of the CERCA network of research centers of the Generalitat de Catalunya. Conﬂicts of Interest: The authors declare no conﬂict of interest.

Abbreviations List of Abbreviations Used 2,6-lutidine 2,6-dimethylpyridine BAIB (Diacetoxyiodo) benzene CSA camphorsulfuric acid DCC N,N’-dicyclohexylcarbodiimide DIBAL diisobutylaluminium hydride DIPEA N,N-Diisopropylethylamine DMP Dess-Martin periodinane DMAP 4-dimethylaminopyridine DPPA diphenylphosphoryl azide DTBMP 2,6-di-tert-butyl-4-methylpyridine DBU 1,8-Diazabicyclo[5.4.0]undec-7-ene EDC 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide (1,3-Bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene)dichloro(phenylmethylene) Grubbs II (tricyclohexylphosphine) ruthenium (+)Ipc2BOMe (+)-B-methoxydiisopinocampheylborane MS molecular sieves MeOTf methyl trifluormethanesulfonate MOMCl chloromethyl methyl ether NMO N-methylmorpholine-N-Oxide Proton sponge 1,8-bis(dimethylamino)naphthalene TBDPSCl tert-butyldiphenylsilyl chloride TBAF tetrabutylammonium fluoride TBSCl tert-butyldimethylsilyl chloride TBSOTf tert-butyldimethylsilyl trifluoromethanesulfonate Tebbe reagent Bis(cyclopentadienyl)-µ-chloro-(dimethylaluminum)-µ-methylenetitanium TEMPO 2,2,6,6,-tetramethyl-1-piperidinyloxy TPAP tetrapropylammonium perruthenate p-TSA p-toluenesulfonic acid White catalyst 1,2-bis(phenylsulfinyl)ethane palladium (II) acetate WHA wound-healing assay Molecules 2017, 22, 198 21 of 26

List of Cell Lines 4T1 (mammary mouse cancer) A549 (lung carcinoma) CMT-W1 (canine mammary cancer) CMT-W2 (canine mammary cancer) CMT-W1M (canine lung metastasis) CMT-W2M (canine lung metastasis) EC17 (mouse esophageal cancer) H1299 (lung cancer) H1975 (lung adenocarcinoma) HPAC (human pancreas adenocarcinoma) HUVECs (human healthy endothelial cells) LM2-4175 (lung metastatic cells derived from MDA-MB-231) Lovo (human colon cancer) MCF7 (human breast cancer) MDAB-MB-361 (human breast cancer) MCF-10A normal human mammary-gland epithelial MDA-MB-231 (human breast cancer) MDA-MB-435 (human breast cancer) P388/VCR (vincristine-resistant mouse leukemia) PC-3 (human prostate cancer) PDAC (pancreatic ductal adenocarcinoma) VJ-300 (vincristine-resistant human epidermoid carcinoma)

References

1. Yamaguchi, H.; Wyckoff, J.; Condeelis, J. Cell migration in tumors. Curr. Opin. Cell Biol. 2005, 17, 559–564. [CrossRef][PubMed] 2. Fenteany, G.; Zhu, S. Small-molecule inhibitors of actin dynamics and cell motility. Curr. Top. Med. Chem. 2003, 3, 593–616. [CrossRef][PubMed] 3. Nakae, K.; Yoshimoto, Y.; Sawa, T.; Homma, Y.; Hamada, M.; Takeuchi, T.; Imoto, M. Migrastatin, a new inhibitor of tumor cell migration from Streptomyces sp. MK929-43F1. Taxonomy, fermentation, isolation and biological activities. J. Antibiot. 2000, 53, 1130–1136. [CrossRef][PubMed] 4. Nakae, K.; Yoshimoto, Y.; Ueda, M.; Sawa, T.; Takahashi, Y.; Naganawa, H.; Takeuchi, T.; Imoto, M. Migrastatin, a novel 14-membered lactone from Streptomyces sp. MK929-43F1. J. Antibiot. 2000, 53, 1228–1230. [CrossRef][PubMed] 5. Woo, E.J.; Starks, C.M.; Carney, J.R.; Arslanian, R.; Cadapan, L.; Zavala, S.; Licari, P. Migrastatin and a new compound, isomigrastatin, from Streptomyces platensis. J. Antibiot. 2002, 55, 141–146. [CrossRef][PubMed] 6. Takemoto, Y.; Tashiro, E.; Imoto, M. Suppression of Multidrug Resistance by Migrastatin. J. Antibiot. 2006, 59, 435–438. [CrossRef][PubMed] 7. Nakae, K.; Nishimura, Y.; Ohba, S.; Akamatsu, Y. Migrastatin Acts as a Muscarinic Acetylcholine Receptor Antagonist. J. Antibiot. 2006, 59, 685–692. [CrossRef][PubMed] 8. Gaul, C.; Njardarson, J.T.; Danishefsky, S.J. The Total Synthesis of (+)-Migrastatin. J. Am. Chem. Soc. 2003, 125, 6042–6043. [CrossRef][PubMed] 9. Gaul, C.; Njardarson, J.T.; Shan, D.; Dorn, D.C.; Wu, K.-D.; Tong, W.P.; Huang, X.-Y.; Moore, M.A.S.; Danishefsky, S.J. The Migrastatin Family: Discovery of Potent Cell Migration Inhibitors by Chemical Synthesis. J. Am. Chem. Soc. 2004, 126, 11326–11337. [CrossRef][PubMed] 10. Reymond, S.; Cossy, J. Total Synthesis of (+)-Migrastatin. Eur. J. Org. Chem. 2006, 2006, 4800–4804. [CrossRef] 11. Sai Baba, V.; Das, P.; Mukkanti, K.; Iqbal, J. A convergent synthesis of the macrolide core of migrastatin. Tetrahedron Lett. 2006, 47, 6083–6086. [CrossRef] 12. Dias, L.C.; Finelli, F.G.; Conegero, L.S.; Krogh, R.; Andricopulo, A.D. Synthesis of the Macrolactone of Migrastatin and Analogues with Potent Cell-Migration Inhibitory Activity. Eur. J. Org. Chem. 2010, 2010, 6748–6759. [CrossRef] Molecules 2017, 22, 198 22 of 26

13. Gade, N.R.; Iqbal, J. Stereoselective formal synthesis of macrolidecore of migrastatin using late stage C–H oxidation. Tetrahedron Lett. 2013, 54, 4225–4227. [CrossRef] 14. Lo Re, D.; Zhou, Y.; Nobis, M.; Anderson, K.I.; Murphy, P.V. Synthesis of migrastatin and its macroketone analogue and in vivo FRAP analysis of the macroketone on E-cadherin dynamics. Chembiochem. Eur. J. Chem. Biol. 2014, 15, 1459–1464. [CrossRef][PubMed] 15. Reymond, S.; Cossy, J. Migrastatin and analogues: New anti-metastatic agents. C. R. Chim. 2008, 11, 1447–1462. [CrossRef] 16. Gaul, C.; Danishefsky, S.J. Synthesis of the macrolide core of migrastatin. Tetrahedron Lett. 2002, 43, 9039–9042. [CrossRef] 17. Reymond, S.; Cossy, J. Synthesis of migrastatin and its macrolide core. Tetrahedron 2007, 63, 5918–5929. [CrossRef] 18. LoRe, D.; Zhou, Y.; Mucha, J.; Jones, L.F.; Leahy, L.; Santocanale, C.; Krol, M.; Murphy, P.V. Synthesis of Migrastatin Analogues as Inhibitors of Tumour Cell Migration: Exploring Structural Change in and on the Macrocyclic Ring. Chem. A Eur. J. 2015, 21, 18109–18121. [CrossRef][PubMed] 19. Majchrzak, K.; Lo Re, D.; Gajewska, M.; Bulkowska, M.; Homa, A.; Pawlowski, K.; Motyl, T.; Murphy, P.V.; Krol, M. Migrastatin analogues inhibit canine mammary cancer cell migration and invasion. PLoS ONE 2013, 8, e76789. [CrossRef][PubMed] 20. Kitaori, K.; Furukawa, Y.; Yoshimoto, H.; Otera, J. CsF in organic synthesis. Regioselective nucleophilic reactions of phenols with oxiranes leading to enantiopure β-blockers. Tetrahedron 1999, 55, 14381–14390. [CrossRef] 21. Xiang, G.; McLaughlin, L.W. A cytosine analogue containing a conformationally flexible acyclic linker for triplex formation at sites with contiguous G-C base pairs. Tetrahedron 1998, 54, 375–392. [CrossRef] 22. Danishefsky, S.J.; Pearson, W.H.; Harvey, D.F.; Maring, C.J.; Springer, J.P. Chelation-controlled facially selective cyclocondensation reactions of chiral alkoxy aldehydes: Syntheses of a mouse androgen and of a carbon-linked disaccharide. J. Am. Chem. Soc. 1985, 107, 1256–1268. [CrossRef] 23. Luche, J.L.; Gemal, A.L. Lanthanoids in organic synthesis. 5. Selective reductions of ketones in the presence of aldehydes. J. Am. Chem. Soc. 1979, 101, 5848–5849. [CrossRef] 24. Ferrier, R.J. Unsaturated carbohydrates. Part II. Three reactions leading to unsaturated glycopyranosides. J. Chem. Soc. (Resum.) 1964, 5443–5449. [CrossRef] 25. Tebbe, F.N.; Parshall, G.W.; Reddy, G.S. Olefin homologation with titanium methylene compounds. J. Am. Chem. Soc. 1978, 100, 3611–3613. [CrossRef] 26. Scholl, M.; Ding, S.; Lee, C.W.; Grubbs, R.H. Synthesis and Activity of a New Generation of Ruthenium-Based Olefin Metathesis Catalysts Coordinated with 1,3-Dimesityl-4,5-dihydroimidazol-2-ylidene Ligands. Organ. Lett. 1999, 1, 953–956. [CrossRef] 27. Jørgensen, M.; Iversen, E.H.; Paulsen, A.L.; Madsen, R. Efficient Synthesis of Enantiopure Conduritols by Ring-Closing Metathesis. J. Organ. Chem. 2001, 66, 4630–4634. [CrossRef] 28. Lee, W.-W.; Chang, S. A new and concise synthetic route to an enantiopure (+)-conduritol-E derivative from diethyl l-tartrate. Tetrahedron Asymm. 1999, 10, 4473–4475. [CrossRef] 29. Njardarson, J.T.; Gaul, C.; Shan, D.; Huang, X.-Y.; Danishefsky, S.J. Discovery of Potent Cell Migration Inhibitors through Total Synthesis: Lessons from Structure–Activity Studies of (+)-Migrastatin. J. Am. Chem. Soc. 2004, 126, 1038–1040. [CrossRef][PubMed] 30. Chun, J.; Li, G.; Byun, H.-S.; Bittman, R. Synthesis of New Trans Double-Bond Sphingolipid Analogues: ∆4,6 and ∆6 Ceramides. J. Org. Chem. 2002, 67, 2600–2605. [CrossRef][PubMed] 31. Keck, G.E.; Savin, K.A.; Cressman, E.N.K.; Abbott, D.E. Effects of Olefin Geometry on the Stereochemistry of Lewis Acid Mediated Additions of Crotylstannanes to Aldehydes. J. Org. Chem. 1994, 59, 7889–7896. [CrossRef] 32. Still, W.C.; Gennari, C. Direct synthesis of Z-unsaturated esters. A useful modification of the horner-emmons olefination. Tetrahedron Lett. 1983, 24, 4405–4408. [CrossRef] 33. Patois, C.; Savignac, P.; About-Jaudet, E.; Collignon, N. A Convenient Method for the Synthesis of bis-Trifluoroethyl Phosphonoacetates. Synth. Commun. 1991, 21, 2391–2396. [CrossRef] 34. Evans, D.A.; Gage, J.R.; Leighton, J.L. Total synthesis of (+)-calyculin A. J. Am. Chem. Soc. 1992, 114, 9434–9453. [CrossRef] Molecules 2017, 22, 198 23 of 26

35. Anderson, J.C.; McDermott, B.P.; Griffin, E.J. Asymmetric Epoxide Cyclisation Route to the F-pyran Fragment of the Altohyrtins and Key Aldol Studies. Tetrahedron 2000, 56, 8747–8767. [CrossRef] 36. Yu, W.; Mei, Y.; Kang, Y.; Hua, Z.; Jin, Z. Improved Procedure for the Oxidative Cleavage of Olefins by OsO4–NaIO4. Org. Lett. 2004, 6, 3217–3219. [CrossRef][PubMed] 37. Smith, N.D.; Kocienski, P.J.; Street, S.D.A. A Synthesis of (+)-Herboxidiene A. Synthesis 1996, 1996, 652–666. [CrossRef] 38. Dess, D.B.; Martin, J.C. A useful 12-I-5 triacetoxyperiodinane (the Dess-Martin periodinane) for the selective oxidation of primary or secondary alcohols and a variety of related 12-I-5 species. J. Am. Chem. Soc. 1991, 113, 7277–7287. [CrossRef] 39. Ando, K.; Oishi, T.; Hirama, M.; Ohno, H.; Ibuka, T. Z-Selective Horner–Wadsworth–Emmons Reaction of Ethyl (Diarylphosphono)acetates Using Sodium Iodide and DBU. J. Org. Chem. 2000, 65, 4745–4749. [CrossRef][PubMed] 40. Evans, D.A.; Bartroli, J.; Shih, T.L. Enantioselective aldol condensations. 2. Erythro-selective chiral aldol condensations via boron enolates. J. Am. Chem. Soc. 1981, 103, 2127–2129. [CrossRef] 41. Evans, D.A.; Taber, T.R. Enantioselective aldol condensations via boron enolates. A steric model for asymmetric induction. Tetrahedron Lett. 1980, 21, 4675–4678. [CrossRef] 42. Crimmins, M.T.; She, J. An Improved Procedure for Asymmetric Aldol Additions with N-Acyl Oxazolidinones, Oxazolidinethiones and Thiazolidinethiones. Synlett 2004, 2004, 1371–1374. [CrossRef] 43. Crimmins, M.T.; King, B.W.; Tabet, E.A.; Chaudhary, K. Asymmetric Aldol Additions: Use of Titanium Tetrachloride and (−)-Sparteine for the Soft Enolization of N-Acyl Oxazolidinones, Oxazolidinethiones, and Thiazolidinethiones. J. Org. Chem. 2001, 66, 894–902. [CrossRef][PubMed] 44. Dias, L.C.; Meira, P.R.R. Synthesis of C13-C22 fragment of the marine sponge polyketide callystatin A. Tetrahedron Lett. 2002, 43, 185–187. [CrossRef] 45. Dias, L.C.; de Oliveira, L.G.; de Sousa, M.A. Total Synthesis of (−)-Pironetin. Org. Lett. 2003, 5, 265–268. [CrossRef][PubMed] 46. Dias, L.C.; de Oliveira, L.G.; Vilcachagua, J.D.; Nigsch, F. Total Synthesis of (+)-Crocacin D. J. Org. Chem. 2005, 70, 2225–2234. [CrossRef][PubMed] 47. Dias, L.C.; de Oliveira, L.G. Total Synthesis of (+)-Crocacin C. Org. Lett. 2001, 3, 3951–3954. [CrossRef] [PubMed] 48. Dias, L.C.; de Oliveira, L.G. Short Synthesis of the 6,6-Spiroketal Cores of Spirofungins A and B. Org. Lett. 2004, 6, 2587–2590. [CrossRef][PubMed] 49. Dias, L.C.; de Castro, I.B.D.; Steil, L.J.; Augusto, T. A short approach to trisubstituted γ-butyrolactones. Tetrahedron Lett. 2006, 47, 213–216. [CrossRef] 50. Evans, D.A.; Ratz, A.M.; Huff, B.E.; Sheppard, G.S. Total Synthesis of the Polyether Antibiotic Lonomycin A (Emericid). J. Am. Chem. Soc. 1995, 117, 3448–3467. [CrossRef] 51. Ley, S.V.; Norman, J.; Griffith, W.P.; Marsden, S.P. Tetrapropylammonium Perruthenate, Pr4N+RuO4-, TPAP: A Catalytic Oxidant for Organic Synthesis. Synthesis 1994, 1994, 639–666. [CrossRef] 52. Petasis, N.A.; Bzowej, E.I. Titanium-mediated carbonyl olefinations. 1. Methylenations of carbonyl compounds with dimethyltitanocene. J. Am. Chem. Soc. 1990, 112, 6392–6394. [CrossRef] 53. Ando, K. Practical synthesis of Z-unsaturated esters by using a new Horner-Emmons reagent, ethyl diphenylphosphonoacetate. Tetrahedron Lett. 1995, 36, 4105–4108. [CrossRef] 54. Ando, K. Highly Selective Synthesis of Z-Unsaturated Esters by Using New Horner–Emmons Reagents, Ethyl (Diarylphosphono)acetates. J. Org. Chem. 1997, 62, 1934–1939. [CrossRef][PubMed] 55. Dias, L.C.; Ferreira, E.L. Allyltrichlorostannane additions to chiral dipeptide aldehydes. Tetrahedron Lett. 2001, 42, 7159–7162. [CrossRef] 56. Dias, L.C.; Ferreira, A.A.; Diaz, G. Short Total Synthesis of Aspartyl Protease Inhibitors L-685,434, L-682,679 and L-685,458. Synlett 2002, 2002, 1845–1849. [CrossRef] 57. Dias, L.C.; Diaz, G.; Ferreira, A.A.; Meira, P.R.R.; Ferreira, E. Allyltrichlorostannane Additions to α-Amino Aldehydes: Application to the Total Synthesis of the Aspartyl Protease Inhibitors L-682,679, L-684,414, L-685,434, and L-685,458. Synthesis 2003, 2003, 0603–0622. [CrossRef] 58. Crimmins, M.T.; Katz, J.D.; McAtee, L.C.; Tabet, E.A.; Kirincich, S.J. An Aldol Approach to the Synthesis of the EF Fragment of Spongistatin 1. Org. Lett. 2001, 3, 949–952. [CrossRef][PubMed] Molecules 2017, 22, 198 24 of 26

59. Ando, K. Z-Selective Horner–Wadsworth–Emmons Reaction of α-Substituted Ethyl (Diarylphosphono) acetates with Aldehydes1. J. Org. Chem. 1998, 63, 8411–8416. [CrossRef] 60. Chen, M.S.; Prabagaran, N.; Labenz, N.A.; White, M.C. Serial Ligand Catalysis: A Highly Selective Allylic C−H Oxidation. J. Am. Chem. Soc. 2005, 127, 6970–6971. [CrossRef][PubMed] 61. Gormisky, P.E.; White, M.C. Synthetic Versatility in C–H Oxidation: A Rapid Approach to Differentiated Diols and Pyrans from Simple Olefins. J. Am. Chem. Soc. 2011, 133, 12584–12589. [CrossRef][PubMed] 62. Fraunhoffer, K.J.; Prabagaran, N.; Sirois, L.E.; White, M.C. Macrolactonization via Hydrocarbon Oxidation. J. Am. Chem. Soc. 2006, 128, 9032–9033. [CrossRef][PubMed] 63. Stang, E.M.; White, M.C. Total synthesis and study of 6-deoxyerythronolide B by late-stage C-H oxidation. Nat. Chem. 2009, 1, 547–551. [CrossRef] 64. Stang, E.M.; White, M.C. On the Macrocyclization of the Erythromycin Core: Preorganization is Not Required. Angew. Chem. Int. Ed. 2011, 50, 2094–2097. [CrossRef][PubMed] 65. Brown, H.C.; Jadhav, P.K.; Bhat, K.S. Chiral synthesis via organoboranes. 13. A highly diastereoselective and enantioselective addition of [(Z)-.gamma.-alkoxyallyl]diisopinocampheylboranes to aldehydes. J. Am. Chem. Soc. 1988, 110, 1535–1538. [CrossRef] 66. Trost, B.M.; Malhotra, S.; Mino, T.; Rajapaksa, N.S. Dinuclear Zinc-Catalyzed Asymmetric Desymmetrization of Acyclic 2-Substituted-1,3-Propanediols: A Powerful Entry into Chiral Building Blocks. Chem. A Eur. J. 2008, 14, 7648–7657. [CrossRef][PubMed] 67. Maddess, M.L.; Tackett, M.N.; Watanabe, H.; Brennan, P.E.; Spilling, C.D.; Scott, J.S.; Osborn, D.P.; Ley, S.V. Total Synthesis of Rapamycin. Angew. Chem. Int. Ed. 2007, 46, 591–597. [CrossRef][PubMed] 68. Gottlieb, H.E.; Kotlyar, V.; Nudelman, A. NMR Chemical Shifts of Common Laboratory Solvents as Trace Impurities. J. Org. Chem. 1997, 62, 7512–7515. [CrossRef][PubMed] 69. Rao, Y.; Li, X.; Nagorny, P.; Hayashida, J.; Danishefsky, S.J. A simple method for the conversion of carboxylic acids into thioacids with Lawesson’s reagent. Tetrahedron Lett. 2009, 50, 6684–6686. [CrossRef][PubMed] 70. Shipkova, M.; Wieland, E. Glucuronidation in therapeutic drug monitoring. Clin. Chim. Acta Int. J. Clin. Chem. 2005, 358, 2–23. [CrossRef][PubMed] 71. Kilpatrick, G.J.; Smith, T.W. Morphine-6-glucuronide: Actions and mechanisms. Med. Res. Rev. 2005, 25, 521–544. [CrossRef][PubMed] 72. Van Heek, M.; Farley, C.; Compton, D.S.; Hoos, L.; Alton, K.B.; Sybertz, E.J.; Davis, H.R. Comparison of the activity and disposition of the novel cholesterol absorption inhibitor, SCH58235, and its glucuronide, SCH60663. Br. J. Pharmacol. 2000, 129, 1748–1754. [CrossRef][PubMed] 73. Stachulski, A.V.; Meng, X. Glucuronides from metabolites to medicines: A survey of the in vivo generation, chemical synthesis and properties of glucuronides. Nat. Prod. Rep. 2013, 30, 806–848. [CrossRef][PubMed] 74. El Alaoui, A.; Schmidt, F.; Monneret, C.; Florent, J.-C. Protecting Groups for Glucuronic Acid: Application to the Synthesis of New Paclitaxel (Taxol) Derivatives. J. Org. Chem. 2006, 71, 9628–9636. [CrossRef][PubMed] 75. Shimawaki, K.; Fujisawa, Y.; Sato, F.; Fujitani, N.; Kurogochi, M.; Hoshi, H.; Hinou, H.; Nishimura, S.-I. Highly Efficient and Versatile Synthesis of Proteoglycan Core Structures from 1,6-Anhydro-β-lactose as a Key Starting Material. Angew. Chem. Int. Ed. 2007, 46, 3074–3079. [CrossRef][PubMed] 76. Pilgrim, W.; Murphy, P.V. SnCl4- and TiCl4-Catalyzed Anomerization of Acylated O- and S-Glycosides: Analysis of Factors That Lead to Higher α:β Anomer Ratios and Reaction Rates. J. Org. Chem. 2010, 75, 6747–6755. [CrossRef][PubMed] 77. O’Brien, C.; Poláková, M.; Pitt, N.; Tosin, M.; Murphy, P.V. Glycosidation–Anomerisation Reactions of 6,1-Anhydroglucopyranuronic Acid and Anomerisation of β-D-Glucopyranosiduronic Acids Promoted by SnCl4. Chem. A Eur. J. 2007, 13, 902–909. [CrossRef][PubMed] 78. Pilgrim, W.; Murphy, P.V. α-Glycosphingolipids via Chelation-Induced Anomerization of O- and S-Glucuronic and Galacturonic Acid Derivatives. Org. Lett. 2009, 11, 939–942. [CrossRef][PubMed] 79. O’Reilly, C.; Murphy, P.V. Synthesis of α-S-Glycosphingolipids Based on Uronic Acids. Org. Lett. 2011, 13, 5168–5171. [CrossRef][PubMed] 80. Farrell, M.; Zhou, J.; Murphy, P.V. Regiospecific Anomerisation of Acylated Glycosyl Azides and Benzoylated Disaccharides by Using TiCl4. Chem. A Eur. J. 2013, 19, 14836–14851. [CrossRef][PubMed] 81. McDonagh, A.W.; Mahon, M.F.; Murphy, P.V. Lewis Acid Induced Anomerization of Se-Glycosides. Application to Synthesis of α-Se-GalCer. Org. Lett. 2016, 18, 552–555. [CrossRef][PubMed] Molecules 2017, 22, 198 25 of 26

82. McDonagh, A.W.; Murphy, P.V. Synthesis of α-galactosyl ceramide analogues with an α-triazole at the anomeric carbon. Tetrahedron 2014, 70, 3191–3196. [CrossRef] 83. Takemoto, Y.; Nakae, K.; Kawatani, M.; Takahashi, Y.; Naganawa, H.; Imoto, M. Migrastatin, a novel 14-membered ring macrolide, inhibits anchorage-independent growth of human small cell lung carcinoma Ms-1 cells. J. Antibiot. 2001, 54, 1104–1107. [CrossRef][PubMed] 84. Kohno, K.; Kikuchi, J.; Sato, S.; Takano, H.; Saburi, Y.; Asoh, K.; Kuwano, M. Vincristine-resistant human cancer KB cell line and increased expression of multidrug-resistance gene. Jpn. J. Cancer Res. 1988, 79, 1238–1246. [CrossRef][PubMed] 85. Tsuruo, T.; Iida, H.; Tsukagoshi, S.; Sakurai, Y. Overcoming of vincristine resistance in P388 leukemia in vivo and in vitro through enhanced cytotoxicity of vincristine and vinblastine by verapamil. Cancer Res. 1981, 41, 1967–1972. [PubMed] 86. Shan, D.; Chen, L.; Njardarson, J.T.; Gaul, C.; Ma, X.; Danishefsky, S.J.; Huang, X.Y. Synthetic analogues of migrastatin that inhibit mammary tumor metastasis in mice. Proc. Natl. Acad. Sci. USA 2005, 102, 3772–3776. [CrossRef][PubMed] 87. Oskarsson, T.; Nagorny, P.; Krauss, I.J.; Perez, L.; Mandal, M.; Yang, G.; Ouerfelli, O.; Xiao, D.; Moore, M.A.S.; Massagué, J.; et al. Diverted Total Synthesis Leads to the Generation of Promising Cell-Migration Inhibitors for Treatment of Tumor Metastasis: In vivo and Mechanistic Studies on the Migrastatin Core Ether Analog. J. Am. Chem. Soc. 2010, 132, 3224–3228. [CrossRef][PubMed] 88. Lecomte, N.; Njardarson, J.T.; Nagorny, P.; Yang, G.; Downey, R.; Ouerfelli, O.; Moore, M.A.; Danishefsky, S.J. Emergence of potent inhibitors of metastasis in lung cancer via syntheses based on migrastatin. Proc. Natl. Acad. Sci. USA 2011, 108, 15074–15078. [CrossRef][PubMed] 89. Pulaski, B.A.; Ostrand-Rosenberg, S. Reduction of Established Spontaneous Mammary Carcinoma Metastases following Immunotherapy with Major Histocompatibility Complex Class II and B7.1 Cell-based Tumor Vaccines. Cancer Res. 1998, 58, 1486–1493. [PubMed] 90. Aslakson, C.J.; Miller, F.R. Selective Events in the Metastatic Process Defined by Analysis of the Sequential Dissemination of Subpopulations of a Mouse Mammary Tumor. Cancer Res. 1992, 52, 1399–1405. [PubMed] 91. Minn, A.J.; Gupta, G.P.; Siegel, P.M.; Bos, P.D.; Shu, W.; Giri, D.D.; Viale, A.; Olshen, A.B.; Gerald, W.L.; Massague, J. Genes that mediate breast cancer metastasis to lung. Nature 2005, 436, 518–524. [CrossRef] [PubMed] 92. Minn, A.J.; Kang, Y.; Serganova, I.; Gupta, G.P.; Giri, D.D.; Doubrovin, M.; Ponomarev, V.; Gerald, W.L.; Blasberg, R.; Massagué, J. Distinct organ-specific metastatic potential of individual breast cancer cells and primary tumors. J. Clin. Investig. 2005, 115, 44–55. [CrossRef][PubMed] 93. Chen, L.; Yang, S.; Jakoncic, J.; Zhang, J.J.; Huang, X.Y. Migrastatin analogues target fascin to block tumour metastasis. Nature 2010, 464, 1062–1066. [CrossRef][PubMed] 94. Yoder, B.J.; Tso, E.; Skacel, M.; Pettay, J.; Tarr, S.; Budd, T.; Tubbs, R.R.; Adams, J.C.; Hicks, D.G. The expression of fascin, an actin-bundling motility protein, correlates with hormone receptor-negative breast cancer and a more aggressive clinical course. Clin. Cancer Res. 2005, 11, 186–192. [PubMed] 95. Grothey, A.; Hashizume, R.; Sahin, A.A.; McCrea, P.D. Fascin, an actin-bundling protein associated with cell motility, is upregulated in hormone receptor negative breast cancer. Br. J. Cancer 2000, 83, 870–873. [CrossRef][PubMed] 96. Hashimoto, Y.; Parsons, M.; Adams, J.C. Dual Actin-bundling and Protein Kinase C-binding Activities of Fascin Regulate Carcinoma Cell Migration Downstream of Rac and Contribute to Metastasis. Mol. Biol. Cell 2007, 18, 4591–4602. [CrossRef][PubMed] 97. Vignjevic, D.; Schoumacher, M.; Gavert, N.; Janssen, K.P.; Jih, G.; Lae, M.; Louvard, D.; Ben-Ze’ev, A.; Robine, S. Fascin, a novel target of beta-catenin-TCF signaling, is expressed at the invasive front of human colon cancer. Cancer Res. 2007, 67, 6844–6853. [CrossRef][PubMed] 98. Yamashiro-Matsumura, S.; Matsumura, F. Purification and characterization of an F-actin-bundling 55-kilodalton protein from HeLa cells. J. Biol. Chem. 1985, 260, 5087–5097. [PubMed] 99. Nagorny, P.; Krauss, I.; Njardarson, J.T.; Perez, L.; Gaul, C.; Yang, G.; Ouerfelli, O.; Danishefsky, S.J. Confirmation of the Structures of Synthetic Derivatives of Migrastatin in the Light of Recently Disclosed Crystallographically Based Claims. Tetrahedron Lett. 2010, 51, 3873–3875. [CrossRef][PubMed] Molecules 2017, 22, 198 26 of 26

100. Krol, M.; Polanska, J.; Pawlowski, K.M.; Turowski, P.; Skierski, J.; Majewska, A.; Ugorski, M.; Morty, R.E.; Motyl, T. Transcriptomic signature of cell lines isolated from canine mammary adenocarcinoma metastases to lungs. J. Appl. Genet. 2010, 51, 37–50. [CrossRef][PubMed] 101. Majchrzak, K.; Pawłowski, K.M.; Orzechowska, E.J.; Dolka, I.; Mucha, J.; Motyl, T.; Król, M. A role of ghrelin in canine mammary carcinoma cells proliferation, apoptosis and migration. BMC Vet. Res. 2012, 8, 170. [CrossRef][PubMed] 102. Król, M.; Pawłowski, K.M.; Majchrzak, K.; Gajewska, M.; Majewska, A.; Motyl, T. Global gene expression profiles of canine macrophages and canine mam mary cancer cells grown as a co-culture in vitro. BMC Vet. Res. 2012, 8, 16. 103. Manuali, E.; De Giuseppe, A.; Feliziani, F.; Forti, K.; Casciari, C.; Marchesi, M.C.; Pacifico, E.; Pawłowski, K.M.; Majchrzak, K.; Król, M. CA 15–3 cell lines and tissue expression in canine mammary cancer and the correlation between serum levels and tumour histological grade. BMC Vet. Res. 2012, 8, 86. [CrossRef] [PubMed] 104. Vignjevic, D.; Kojima, S.; Aratyn, Y.; Danciu, O.; Svitkina, T.; Borisy, G.G. Role of fascin in filopodial protrusion. J. Cell Biol. 2006, 174, 863–875. [CrossRef][PubMed] 105. Mattila, P.K.; Lappalainen, P. Filopodia: Molecular architecture and cellular functions. Nat. Rev. Mol. Cell Biol. 2008, 9, 446–454. [CrossRef][PubMed] 106. Mejillano, M.R.; Kojima, S.; Applewhite, D.A.; Gertler, F.B.; Svitkina, T.M.; Borisy, G.G. Lamellipodial versus filopodial mode of the actin nanomachinery: Pivotal role of the filament barbed end. Cell 2004, 118, 363–373. [CrossRef][PubMed] 107. Thiery, J.P.; Acloque, H.; Huang, R.Y.J.; Nieto, M.A. Epithelial-Mesenchymal Transitions in Development and Disease. Cell 2009, 139, 871–890. [CrossRef][PubMed] 108. Christofori, G. Snail1 links transcriptional control with epigenetic regulation. EMBO J. 2010, 29, 1787–1789. [CrossRef][PubMed] 109. David, J.M.; Rajasekaran, A.K. Dishonorable Discharge: The Oncogenic Roles of Cleaved E-Cadherin Fragments. Cancer Res. 2012, 72, 2917–2923. [CrossRef][PubMed] 110. Berx, G.; van Roy, F. Involvement of Members of the Cadherin Superfamily in Cancer. Cold Spring Harb. Perspect. Biol. 2009, 1, a003129. [CrossRef][PubMed] 111. Birchmeier, W.; Behrens, J. Cadherin expression in carcinomas: Role in the formation of cell junctions and the prevention of invasiveness. Biochim. Biophys. Acta (BBA) Rev. Cancer 1994, 1198, 11–26. [CrossRef] 112. Risinger, J.I.; Berchuck, A.; Kohler, M.F.; Boyd, J. Mutations of the E-cadherin gene in human gynecologic cancers. Nat. Genet. 1994, 7, 98–102. [CrossRef][PubMed] 113. Berx, G.; Cleton-Jansen, A.M.; Nollet, F.; de Leeuw, W.J.; van de Vijver, M.; Cornelisse, C.; van Roy, F. E-cadherin is a tumour/invasion suppressor gene mutated in human lobular breast cancers. EMBO J. 1995, 14, 6107–6115. [PubMed] 114. Efstathiou, J.A.; Liu, D.; Wheeler, J.M.D.; Kim, H.C.; Beck, N.E.; Ilyas, M.; Karayiannakis, A.J.; Mortensen, N.J.M.; Kmiot, W.; Playford, R.J.; et al. Mutated epithelial cadherin is associated with increased tumorigenicity and loss of adhesion and of responsiveness to the motogenic trefoil factor 2 in colon carcinoma cells. Proc. Natl. Acad. Sci. USA 1999, 96, 2316–2321. [CrossRef][PubMed] 115. Morton, J.P.; Timpson, P.; Karim, S.A.; Ridgway, R.A.; Athineos, D.; Doyle, B.; Jamieson, N.B.; Oien, K.A.; Lowy, A.M.; Brunton, V.G.; et al. Mutant p53 drives metastasis and overcomes growth arrest/senescence in pancreatic cancer. Proc. Natl. Acad. Sci. USA 2010, 107, 246–251. [CrossRef][PubMed]

© 2017 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).