Synthesis of Bioactive 1,2,3-Triazole Fused Macrocycles via Azide-Alkyne Cyclo-addition

Abstract


Introduction
Over a long period, the evolution of therapeutic development, required for treatment of a wide range of diseases, has revolved around the construction of various natural products as well as their synthetic analogues.2a-d Macrocyclic compounds have been reported to display a wide range of bioactivities viz.anticancer, antibacterial, antifungal, immunosuppressant and more and thus have proven themselves to be extremely effective in the field of medicine. 3In particular, 1,2,3-triazole-fused macrocycles have exhibited promising biological activities like anticancer [4][5][6] , antibacterial 7 , anti-inflammatory 8 , antiviral 9 and more [10][11][12] , and hence, the synthesis of triazole-based macrocycles has become a hot topic for researchers.Literature reports revealed that significant efforts have been attributed towards the synthesis of triazole scaffold involving Ag(I)-, Cu(I)-, Ru(II)-catalyzed azide-alkyne cycloaddition (AAC) reactions, microwave assisted reactions, ultrasound-promoted reactions etc. 13a-e The deep impact of the well-renowned Cu(I)catalyzed azide-alkyne cycloaddition (CuAAC) reaction upon synthetic organic chemistry has persuaded several researchers to utilize this reaction while developing the triazole-based analogues of naturally occurring macrocyclic compounds.Through literature survey, we have realized in our limited knowledge that a recent review on the synthesis of bioactive 1,2,3-triazole fused macrocycles has still not been reported.On being currently engaged in the synthesis of macrocycles 14 , we herein report a review article mentioning the synthetic protocols undertaken while grafting the bioactive triazole fused macrocycles since 2006.Throughout the article, the CuAAC and RuAAC reactions have been utilized for the preparation of 1,2,3-triazoles.We remain optimistic that this review will be extremely beneficial for synthetic organic and medicinal chemistry researchers and provide guidance towards the development of novel macrocycles essential for drug discovery.

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In order to combat with a worldwide health problem, cancer, the researchers have paid avid attention towards the two 'D' s in therapeutic development: Detection and Diagnosis.Early detection of this fatal disease is essential for appropriate diagnosis and the needs of the affected people could only be met through proper treatment via medicinal resources.Scientists have devoted countless number of years in cancer therapy to not just cure the patients but also improve their quality life post treatment.
Continuous activation of signal transducers and activators of transcription 3 (STAT3) has been directly linked with oncogenesis and serves as a target for molecular drug designing.In 2007, Chen et al. designed a conformationally constrained macrocycle 7 by following the 'Click-Chemistry' methodology as a crucial step (Scheme 1). 15The synthetic procedure advanced with the condensation between Boc-L-6hydroxynorleucine 1 and O-t-butyl-L-threonine methyl ester 2, in the presence of 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDCI), hydroxybenzotriazole (HOBt) and N,N-Diisopropylethylamine (DIPEA) in dichloromethane.Three consecutive steps provided the azide moiety 3 which was further converted into the macrocyclic precursor 4 via condensation with (S)propargylglycine methyl ester.On constituting both the azidealkyne groups within itself, 4 was subjected to an intramolecular copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction in the presence of copper sulphate and sodium ascorbate in a t-BuOH/H2O solvent system to furnish the 1,4-disubstituted triazole fused macrocycle 5 in 80% yield.This key intermediate was further exposed to nine more sequential reactions to afford the target macromolecule 7. A fluorescence-polarization-based binding assay was conducted next to prove that 7 expressed an effective binding affinity with STAT3 and was found to be more potent when compared to the peptide 8.The target drug 7 was thus established to be an anticancer agent with a strong inhibition against STAT3.Histone deacetylases (HDACs) are enzymes which play an important part in regulation of gene transcription and over the years inhibition of HDACs have resulted in the evolution of anticancer chemotherapy.Apicidin, a naturally occurring cyclic tetrapeptide, was found to exhibit cytotoxic activity by inhibiting the action of HDACs.In 2009, Horne et al. developed few triazole-modified apicidin analogues 16a,b, 17, 25a-c and carried out the HDAC inhibition assay (Schemes 2 and 3). 4 The synthetic procedure commenced with the preparation of the two key fragments 11 and 14 from the starting materials bromoketal 9 and the Boc-protected lactone 12, respectively.The compound 9 was initially turned into a Grignard reagent and then reacted along with the lactone 10 to produce the amino acid derivative 11.The synthesis of the alkyne moiety 14 proceeded with the conversion of the Boc-protected lactone 12 into the acid 13 which was further subjected to a gradual three stepped reaction.The two synthons 11 and 14 were exposed to solution-phase peptide synthesis via six sequential reactions to prepare the azide-alkyne cycloaddition precursors 15a and 15b which finally underwent intramolecular SynOpen Review / Short Review Template for SynOpen Thieme cycloaddition using catalytic CuI, 2,6-lutidine, tris(benzyltriazolylmethyl)-amine (TBTA) and DIPEA in acetonitrile for 48 h to afford the desired 1,4-disubtituted triazole fused macrocycles 16a and 16b, respectively.The macrocyclic precursor 15a was alternatively exposed to microwave conditions in DMF at 220 ℃ which led to the production of a mixture of 1,5-disubstituted triazole fused macrocycle 17 (8%) and macrocycle 16a in a 2:1 ratio (Scheme 2).Next, multiple conformations of 17 were investigated by replacing the β-substituted amino acid Ile with a Leu residue.The Fmoc-protected 2-amino 8-oxodecanoic acid (Aoda) on resin 18 was treated with piperidine to remove the protection and subsequently the de-protected 19 was coupled with the N3-Ala-OH (D/L) 20 to afford the amide 21.To ensure the intermolecular cycloaddition reaction, the azido-amide 21 and Fmoc-Leu-CCH (D/L) 22 were treated with a Ru-based catalyst [Cp*Ru(cod)Cl] in toluene at 45 ℃ for 16 h and the triazolemoiety 23 was afforded.Four subsequent steps led to the formation of the linear pseudotetrapeptides 24a-c which finally underwent macrolactamization through HATU peptide coupling to afford the desired macrocycles 25a-c differing at the Ala and Leu positions in yields greater than 95% (Scheme 3).The bioactivity of all apicidin analogues were assessed in nuclear extracts of HeLa cells and they were found to exhibit the HDAC inhibitor activity.In 2010, the McAlpine group synthesized a set of macrocyclic triazole derivatives 31 and assessed their HDAC inhibitory activity (Scheme 4). 16The synthetic procedure commenced with the conversion of the aldehyde 26 into the alkyne 27 through Bestmann-Ohira reagent.Four sequential reactions involving condensation of 27 with the Boc-protected amino acids 28, 29 resulted in the development of the residue 30 which was in turn HATU/TBTU coupled with azide 31 to afford the linear precursor 32.Finally, the crucial macrocyclization step was undertaken via CuAAC reaction using copper sulphate and sodium ascorbate in a methanol/water solvent system to afford the desired macrocycles 33 in (3-9) % yields.The biological evaluation of these compounds asserted inhibition of deacetylase activity against HeLa cell lysates.The compounds 33a and 33b were found to be the most potent ones.
The Sewald group, in 2010, developed a bioactive triazole analogue 44 of the antitumor agent 'Cryptophycin-52' using the Cu-mediated cycloaddition reaction as one of the crucial steps (Schemes 5 and 6). 17The synthesis advanced with the creation of the alkyne 35 in two steps from the starting material 34.The other building block 38 was afforded through This article is protected by copyright.All rights reserved.

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Template for SynOpen Thieme 45 using EDC/HOBt in order to achieve the amide 46 which was further subjected to condensation with the silyl protected compound 47.Sequential silyl-deprotection and esterification with acid 36 afforded the macrocyclic precursor 49 which upon exposure to CuAAC reaction with CuI/DIPEA catalytic system in toluene at room temperature for 20 h formed a mixture of triazole fused macrocycles (monomer and dimer) in 84% combined yield.The free diols 42 and 50 were finally obtained through acidic cleavage.The key compound 42 was gradually exposed to diol-epoxide conversion in three steps to afford the target macrocycle 44 in 59% yield (Scheme 5).Biological assay of 44 against the multidrug resistant human cervix carcinoma cell line KB-V1 showed promising results being only five times less potent than the parent compound cryptophycin-52.Thus, the triazole analogue proved its efficiency as an anticancer agent.This article is protected by copyright.All rights reserved.

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Pirali et al., in 2010, synthesized certain macrocyclic peptide mimetics 56a,b and 61a,b by utilizing the intramolecular [3+2] cycloaddition and biologically evaluated them as HDAC inhibitors (Schemes 7 and 8). 18Initially, the synthetic procedure for the first set of macrocycles commenced with the preparation of the aldehydes 53a,b from their corresponding alcohols using Dess-Martin reagent through oxidation.After having the other fragments αisocyanoacetamide 51 and the amine 52 in hand, a threecomponent reaction was conducted using NH4Cl as a catalyst to afford the 5-aminooxazole 54a,b.Subsequently, the crucial macrocyclization step was carried out via CuAAC reaction with catalytic CuI and DIPEA in THF at room temperature for 13 h in order to furnish the macrocycles 55a and 55b in 83% and 70% yields, respectively (Scheme 7).Three subsequent reactions upon 55a,b afforded the targeted hydroxamic macrocycles 56a,b in 39% and 37% yields, respectively.To generate the second set of macrocycles, a similar ammonium chloride catalyzed methodology was followed using the aldehyde 53b, the alkyne 58 and the azides 57a,b as starting materials for the development of the macrocyclic precursors 59a,b (Scheme 8).A CuI supported cycloaddition following the aforementioned method took place next to graft the macrocycles 60a and 60b in 61% and 80% yields, respectively.Finally, the desired hydroxamic compounds 61a,b were synthesized in 34% and 42% yields in three subsequent steps.Biological evaluation of 56a,b and 61a,b through MTT assay determined their inhibitory activity in SHSY-5Y cells.It was further predicted through molecular docking that 55b and 61b displayed inhibition on histone deacetylases.
In the same year, Sun et al. synthesized the cyclopeptidic Smac mimetics 70a,b utilizing the CuAAC reaction as the macrocyclization pathway and evaluated their anticancer activities (Scheme 9). 19The progress was initiated with the condensation of L-proline benzyl ester hydrochloride 62 and N-Boc-L-6-hydroxynorleucine to achieve the amide 63.Mesylation of 63 followed by treatment with sodium azide afforded the azido derivative 64 which was further subjected to azide-alkyne cycloaddition with 65a/65b to graft the key intermediates 66a,b, respectively.Four subsequent reaction steps resulted in the development of the macrocyclic precursors 67a,b which underwent the crucial Cu-catalyzed AAC reaction with copper sulphate and sodium ascorbate in t-BuOH/H2O medium to synthesize the macrocycles 68a (38%) and 68b (35%), respectively.After removing the protecting groups, condensation was carried out in between 69a,b and Nmethyl-N-Boc-L-alanine to construct the amides.Ultimate Boc deprotection afforded the desired compounds 70a (79%) and 70b (72%) which were further biologically evaluated.Through an FP-based binding assay, it was found out that the binding affinity of 70a is more than 70b towards binding to XIAP, cIAP-1 and cIAP-2 proteins.When the inhibition activity of the target macrocycles was evaluated against growth in the MDA-MB-231 breast cancer and SK-OV-3 ovarian cancer cell lines, compound 70a was reported to be more potent than parent compound 71 while 70b was noted to be weaker than 71.
Heat shock protein 90 (Hsp90) is a captivating target for medicinal chemists for being associated with cancer therapy.Day et al., in 2010, synthesized a series of macrocyclic analogues (82a-e) of the naturally occurring Hsp90 inhibitor 'radicicol' (Scheme 10). 5 The synthetic route advanced with the conversion of 4-chlororesorcinol 72 into the homophthalate ester 73 in two steps which further underwent six reactions to afford the intermediate 74.The substituted diethyl malonates 75a-d were next transformed into their corresponding acid chlorides 76a-d by treatment with thionyl chloride.Subsequently, the chlorides 76a-d were coupled with the anhydride 74, using tetramethylguanidine (TMG), to produce the compounds 77a-d and which were eventually transformed into the isocoumarins 78a-d.Treatment of 78b-d with excess of lithium hydroxide resulted in their ring-opening to give the alkyne moieties 79a-e which were subsequently treated with either 2-azidoethanol or 3-azidopropanol under Mitsunobu conditions helped achieve the macrocyclic precursors 80a-e.This article is protected by copyright.All rights reserved.

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The crucial macrocyclization took place using copper sulphate and sodium ascorbate in t-BuOH/H2O medium to afford the macrocyclic triazoles 81a-e in (8-33%) yields.Final deprotection of MOM groups was conducted with TFA in dichloromethane to furnish the desired compounds 82a-e in (21-84%) yields.Biological evaluation of 82a-e for Hsp90 inhibition showed reduced binding activity with loss of potency when compared to radicicol and analogue NP261.In 2012, Duan et al. synthesized a triazole fused analogue of epothilone 92 and reported its computational docking studies (Scheme 11). 6Initially, the Weinreb amide 83 was used to prepare the fragment 84 which was later made to react with a Grignard reagent to afford the keto-alcohol 85.The compound 85 underwent subsequent Horner-Wadsworth-Emmons reaction and desilylation to afford the alcohol 86 which was successively coupled with 87 to form the alkyne 88.Five sequential reactions upon 88 furnished the intermediate 89 and further treatment with p-toluenesulphonyl chloride and sodium azide helped to generate the macrocyclic precursor 90.The ring-closure was conducted using Cu2O-nanoparticles in acetonitrile medium at 37 ℃ to afford the triazole fused macrocycles 91 (monomer) and 93 (dimer) in 74% and 6% yields, respectively.Acidic cleavage of both of these compounds finally afforded the target macrocycle 92 (92%) and its corresponding dimer 94 (87%).Through molecular docking studies, it was found out that the binding energy of 92 to that of α,β-tubulin was higher than that of natural epothilones.The target molecule 92 was reported to exhibit lower bioactivity against MCF-7 cell lines on comparison with epothilone.Interestingly, the dimer 94 also showed bioactivity against the same cell lines even though it was about 200 times less potent than parent compound Epothilone D.
Ajay et al., in 2012, reported the synthesis of some triazole fused macrocyclic glycoconjugates and also tested their biological activities (Scheme 12). 20The process advanced with the preparation of glycopyranosyl butenones (97a-c, 98) from D-glucose and D-mannose.In three subsequent steps the azidoglycopyranosyl derivatives (99a-c, 100) were prepared and then subjected to CuAAC reaction with the alkynol moieties in presence of copper sulphate and sodium ascorbate in t-BuOH/H2O medium at room temperature for 3-4 h which afforded the triazole derivatives 101-103 in excellent yields (83-87%).Action of tosyl chloride in dichloromethane with triethylamine resulted in the formation of tosylated products 104a, 105a and 106b in poor yields and hence, an alternate pathway for the synthesis of the desired macrocycles was considered.The previously used alkynols were tosylated to create 107a-c and then made to undergo the CuAAC reaction with 99a-c, 100 under the previously mentioned reaction conditions to furnish the tosyloxy triazoles 104(a-c)-106(a-c) and 108a-c in excellent yields (85-89%).Further exposure to sodium azide in DMF at 80 ℃ formed the macrocyclic precursors 109(a-c)-111(a-c) and 112a-c which underwent subsequent macrocyclization using tetrabutylammonium hydrogen sulfate (TBAHS) in DMF at 100 ℃ for 24-36 h to afford the di-triazole fused macrocyclic compounds 113(a-c)-115(a-c) and 116a-c in 64-76% yields.The glucose derived compounds were further deacetylated to afford 117(a-c)-119(a-c).On conducting the biological assessment of macrocycles 113(a-c)-115(a-c) and 117a against breast cancer MCF-7 cell line, the compounds 113c, 114c, and 115c were noticed to exhibit good to moderate activity.This article is protected by copyright.All rights reserved.

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Template for SynOpen Thieme Scheme 12 Synthesis of macrocyclic glycoconjugates 113c, 114c and 115c In 2012, Davis et al. developed a peptidomimetic macrocycle 126 through CuAAC methodology and investigated its bioactivity (Scheme 13). 21The synthesis was initiated through the amide coupling of the acid 120 and the amine 121 in the presence of TBTU and DIPEA.Subsequent acidic deprotection by TFA afforded the key intermediate 122 which was further subjected with two consecutive reactions to produce the azide 123.Next, the previously prepared alkyne fragment 124 was further coupled with 123 in the presence of TBTU/DIPEA to achieve the macrocyclic precursor 125.The key step of macrocyclization was finally conducted using Lascorbic acid, NaHCO3 and copper sulphate in MeOH/H2O medium to graft the desired macrocycle 126 (7.5%).The synthesized macrocycle 126 was evaluated in HeLa cervical cancer cell lines and was noted to inhibit the growth.Its level of cytotoxicity was found to be at par with its parent compound Sansalvamide A.
In 2013, Neilsen et al. developed two triazole fused macrocyclic inhibitors (138, 139) of CT-L protease using the Cu-mediated click-methodology as the crucial macrocyclization step (Scheme 14). 22The synthetic procedure advanced with the development of the key azide fragments 129 and 130, from the starting materials 127, 128, under standard amide forming conditions with Leu-Ot-Bu using EDCI.Subsequent acidic deprotection led to the formation of 131 and 132 which were individually coupled with the amino-alkyne moiety 133 through similar EDCI conditions to afford the azide-alkyne containing macrocyclic precursors 134 and 135.Next, the key macrocyclization step was undertaken in the presence of CuBr and DBU in dichloromethane which grafted the triazole fused macrocycles 136 and 137 in 70% yields each.Further exposure of these compounds to oxidation with Dess-Martin Periodinane (DMP) afforded the aldehyde-based macrocycles 138 and 139 in 80% yields, respectively.Biological evaluation of against the protease CT-L showed 138 and 139 possessed activity as potential inhibitors.They also exhibited potency when tested against a panel of four sarcoma cancer cell lines WE-68, VH-64, STA-ET-1 and TC-252.
Tahoori et al., in 2014, designed a macrocyclic heptapeptide 145 following Ugi-4CR and Huisgen cycloaddition reactions and reported its anticancer activity (Scheme 15). 23To initiate the synthetic process, the 4cyanobenzaldehyde 140, azide fragment 141, the carboxylic acid with propargyl group 142 and cyclohexyl isocyanide 143 reacted in methanol as a four component Ugi reaction to afford the macrocyclic precursor 144.For the click-reaction, CuI•P(OEt)3 was used as a catalyst with DIPEA in dichloromethane at room temperature for 5 days to obtain the heptapeptidic triazole fused macrocycle 145 in 75% yield.Upon testing its biological properties, the macrocycle 145 was seen to exhibit promising anticancer activity against A549 human lung cancer cell line.
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Scheme 13 Synthesis of Sansalvamide-A analogue 126 In the same year, Goh et al. reported the synthesis of a triazole analogue (157) of natural product LL-Z1640-2 and evaluated its biological activity (Scheme 16). 24Initially, the commercially available 2,4,6-trihydroxybenzoic acid 146 was converted into the triflate 147 in three steps.The reaction progressed as the acetonide 148 underwent Colvin rearrangement in the presence of TMS diazomethane and n-BuLi to produce the alkyne 149 and further hydrostannylation produced the trans-vinyl stannane 150.Subsequently, the triflate 147 and stannane 150 were subjected to Stille coupling with PdCl2(PPh3)2 to afford the alcohol 151 which upon further treatment with diphenylphosphoryl azide constructed the key azide fragment 152.Next, 152 was made to react with (S)pent-4-yn-ol 153 in two different pathways; the first reaction was conducted in the presence of NaH to produce the macrocyclization precursor 154 whereas, the second pathway followed standard CuAAC conditions with copper sulphate and sodium ascorbate in t-BuOH/H2O medium to furnish the triazole 155 in 78% yield.Intramolecular click-reaction of 154 under similar CuAAC conditions established the macrocycle 156 in very poor yield (15%) while the intramolecular transesterification of 155 with NaH afforded the desired compound 156 in 63% yield.Final deprotection of 156 by acidification grafted the target triazole analogue 157 in 76% yield.Biological assessment of 157 with several kinases showed its ability to act as a potent inhibitor with an inhibition higher than or comparable with its parent LL-Z1640-2.Besides exhibiting good activity against MNK2 kinase, the targeted analogue 157 also behaved actively against AXL and MET and thus, served as a good target for anticancer therapy.
Zhang et al., in 2015, synthesized a dimeric macrocycle 169 which served as an inhibitor of apoptosis proteins (Scheme 17). 25 To initiate the synthetic procedure, commercially available 2-naphthyl alanine 158 was coupled with the prolines 159a,b using EDCI and HOAt to achieve the compounds 160a,b which were further subjected to five successive steps to develop the key fragments 161a,b.The starting materials 162 and 163 gave rise to the tyrosine derivatives 164 and 166, which were in turn HATU coupled with 161a,b to afford the pentapeptides 165 and 167, respectively.The crucial macrocyclization took place in between the azide-alkyne fragments 165 and 167 by employing the renowned CuAAC-RCM methodologies.The cycloaddition was conducted overnight at room temperature in the presence of CuSO4 and sodium ascorbic acid in THF/t-BuOH/H2O medium to form the triazole linked moiety 168 in 68% yield.Subsequent RCM reaction with Hoveyda-Grubbs-II catalyst, TFA deprotection and Pd-catalyzed hydrogenation

Scheme 15 Synthesis of macrocyclic heptapeptide 145
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Template for SynOpen Thieme  26 The linear precursors were prepared on DNA solid-phase support using a literature reported DPC method.The crucial macrocyclization step took place by exposing the precursors 170a-d to Cu-(II) (Z)-2,2,6,6tetramethyl-5-oxohept-3-en-3-olate, ascorbic acid, DIPEA and 2,6-dimethylpyridine in DMF:THF (1:1) solvent system which provided the desired set of monomeric macrocycles 171a-d after deprotection and resin cleavage with TFA.The dimers 172a-d were simultaneously synthesized as a by-product of the aforementioned reaction but, their yields were increased by utilizing a higher substitution density in the solid-phase synthesis, which resulted in the enhancement of intermolecular cyclization.The monomeric macrocycle 173 was produced by inverting the P2 linker in 170a and exposing it to similar macrocyclization conditions whereas, the dimeric macrocycles 174-176 were produced by modifying the P1, P2 and P3 linkers altogether.The macrocycles 171a and 171b were noted to bind potently to cIAP1 BIR3 and XIAP BIR3 in Fluorescence Polarization Assays (FPA) with IC50 values just about 3-8-fold lower in the case of the latter.The compound 171b showed less potency in the caspase-3 rescue assay, weak inhibition towards cell growth in human triple negative breast cancer type I MDA-MB-231 cell-lines and no inhibition in type II A875 melanoma cell-lines.The dimer 172b displayed an improved affinity against BIR2 and BIR3 when compared to its corresponding monomer 171b.Macrocycle 172b exhibited good caspase-3 rescue activity along with measurable antiproliferative activity in both type I and II cell lines despite being potent towards cIAP1 BIR3 domain.The dimer 172a showed good binding towards BIR domain and good caspase-3 rescue activity but no antiproliferation in either I or II celllines.The compound 173 showed slight effect towards BIR3 affinity but a prominent reduction in BIR2 affinity.Macrocycles 174 and 175 portrayed prominent activity against the type I cancer cell lines while showing sub-μM IC50 values against type II A875 cells.The compounds 172c,d were noted to exhibit low IC50 values when evaluated against MDA-MB-231 cells and A875 cells whereas, the compound 176 was seen to display comparable IC50 values with that of 172b.
Cao et al., in 2016, synthesized a set of triazole fused macrocyclic derivatives 186-193 and investigated their antitumor activities (Scheme 19). 27The synthetic procedure commenced with the conversion of carboxylic acid 177 into the Boc-protected ester 178 in two steps with further insertion of the alkyne group and subsequent Boc-deprotection to afford the synthon 179.Next, the acid 180 was transformed into its corresponding ester 181 in two steps which followed treatment with sodium azide and subsequent hydrolysis to afford the synthon 182.The synthon 179 was coupled with 182 to form the amide 183 under reaction conditions involving HOBt, EDCI with triethylamine in dichloromethane.
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On subjecting the macrocyclic precursor 183 to CuAAC reaction with CuI in refluxing toluene for 2 h, the Migrastatin, an anti-metastatic agent originating from microbes, was isolated by Imoto and co-workers back in 2000.In 2017, Gabba et al. synthesized the migrastatin-triazole derivatives 201, 204 and evaluated their biological activities (Scheme 20). 28In order to prepare the target macrocycles, the synthons 194 and 198a-c were first synthesized.Activation of 5-hexen-1-ol 194 with methanesulfonyl chloride followed by treatment with sodium azide led to the formation of alkenylazide 195.Preparation of synthons 198a-c commenced with the use of aldehyde 196; seven subsequent steps furnished the advanced intermediates 197a-c which were made to react in the presence of trimethylsilyl diazomethane and LDA to afford the required alkynes 198a-c.Next, the azidealkyne cycloaddition reaction was conducted upon the alkyne 198a in two different pathways.Initially, 198a was coupled with the azide 195 in the presence of CuSO4•5H2O and sodium ascorbate within THF:water (1:1) medium through 10 min microwave irradiation (60 W) at 60 ℃ to afford 1,4disubstituted triazole derivative 199 (73%).It was further subjected to macrocyclization in presence of Grubbs' 2 nd generation catalyst to furnish the compound 200 and subsequent removal of the TBS protecting group produced the This article is protected by copyright.All rights reserved.This article is protected by copyright.All rights reserved.

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Template for SynOpen Thieme Exposure to metathesis conditions ensured the macrocyclization process and afforded the triazole fused macrocycle 203.Further deprotection of TBS group yielded their other desired product 204 in 96% yield.The compounds 201 and 204 were biologically evaluated using the MDA-MB-361 cell line (human breast cancer) and were found to exhibit a significant effect to retard the process while being comparable with a well-known inhibitor of human tumor cell migrator 205.

Scheme 20 Synthesis of migrastatin analogues 201 and 204
In 2017, Jithin Raj and Bahulayan developed a three step multi-component coupling (MCR)-Click strategy in order to synthesize a library of coumarin-tagged macrocycles 211 with ring size ranging from 11 to 18 (Scheme 21). 29The protocol commenced with an initial Mannich type reaction conducted in between 3-acetyl coumarin 206, an alkyne 207 and bromo nitriles 208 to afford the alkyne compounds 209.Next, the azide group was introduced within the compound by treatment with sodium azide in DMF using potassium carbonate as a base.This action led to the formation of macrocycle precursor 210 which underwent intramolecular CuAAC reaction using copper sulphate and sodium ascorbate in the solvent system t-BuOH/H2O/DMSO (4:2:1) for 48 h to afford the desired macrocycles 211 in 64-73% yields.The set of macrocycles were biologically evaluated and were found to show excellent cytotoxicity towards human breast cancer cell line (MCF-7) indicating them to appear as potential anticancer agents.
In 2018, Eduardo Hernandez-Vazquez and his co-workers reported the synthesis of a series of 20-22-membered triazole fused macrocycles 219 (Scheme 22). 30They described a multicomponent approach which involved a Ugi fourcomponent reaction (Ugi 4-CR) to assemble an acyclic precursor.Final macrocyclization was then carried out by intramolecular CuAAC reaction.The synthetic procedure commenced as the azido synthon 213 was prepared from phydroxyphenylacetic acid 212 in four consecutive steps and then treated with an aldehyde 215, various amines 216, isonitriles 217, and under Ugi 4-CR conditions to generate the acylamino carboxamides 218.The Ugi adducts were next exposed to microwave radiation with CuBr/DBU in toluene for 1.5 h to ensure the formation of triazoles.Thus, macrocyclization led to the production of the triazole fused compounds 219 in moderate to good yields (29-83%).On being biologically evaluated, most compounds were seen to exhibit cytotoxicity against prostate (PC-3) and breast (MCF-7) cancer cells.IC50 values of 219a,b showed more than 50% PC-3 inhibition and 219a also caused high levels of apoptosis in PC-3.
Prabhakaran et al., in 2018, developed a synthetic route to synthesize a triazole fused macrocycle 223 and evaluated its anticancer activity (Scheme 23). 7The synthesis proceeded with the intermolecular click-reaction between the alkyne 220 and the azide 221 in the presence of copper sulphate and sodium ascorbate, in THF/H2O medium at room temperature.This afforded the triazole based macrocyclic precursor 222 in 88% yield and was consecutively subjected to refluxing toluene with sarcosine in Dean-Stark apparatus to provide the target macrocycle 223 (70%).Biological investigation showed that 223 displayed prominent anticancer activity against human adenocacinoma breast cancer cell lines MCF-7.
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Template for SynOpen Thieme   31 The synthetic pathway commenced as the commercially available 6-chloro-1Hpyrazolo [3,4-d]pyrimidine 224 was iodinated with N-iodosuccinimide followed by propargylation with propargyl bromide to afford the intermediate 225.Subsequent steps ensured the introduction of a second alkyne group within the moiety and led to the development of dialkyne compound 226 which was further assembled with 1,3-bis(azidomethyl)benzene 227 in presence of copper iodide, sodium ascorbate, and triethylamine in dioxane/H2O medium at room temperature for 36 h to achieve the macrocycle 228 (23%).The desired macrocyclic compound 231, analogue of multikinase inhibitor eSM119, was obtained in 51% yield when 228 was cross-coupled with 6-(4-Bocpiperazinyl)pyridyl-3-boronic acid pinacol ester 229 and Boc deprotected under acidic conditions.The desired compound 231 was found to display selective inhibitory activity against the receptor tyrosine kinase AXL.

Scheme 23 Synthesis of triazole fused macrocycle 223
Rahman et al., in 2020, developed a thymidine analogue with linked triazoles 235 and tested its anti-proliferative activities (Scheme 25). 32Commercially available thymidine 232 was initially converted into its di-azide derivative 233 in three sequential steps and consecutively exposed to CuAAC reaction with 1,3-diethynyl benzene 234 using a CuI/DIPEA system in acetonitrile for 36 h in order to afford the macrocyclic thymidine analogue 235 (56%).Biological assessment showed that 235 expressed significant toxicity when tested against C6 glioblastoma cancer cell lines, MCF7 breast cancer cell lines and HT29 colorectal adenocarcinoma cell lines.
In 2021, Srinivas and Rao reported a series of triazole fused macrocycles 241-243, 250-252 and assessed their anticancer activity (Schemes 26 and 27). 33They implemented their idea by using 1-(2-hydroxyphenyl)ethan-1-one 236 as their starting material (Scheme 26).Gradually 236 was converted into an azide moiety 237 by the action of consequent 1,4-dibromopropane and sodium azide.Subsequently, 237 was subjected to cycloaddition reaction with 238 using copper sulphate and sodium ascorbate in a dichloromethane:water solvent system to afford the triazole 239 in 76% yield.Three steps were followed up next in order to furnish the triazole fused macrocycle 240 in 92% yield.Finally, the compound 240 was refluxed using three different core reagents viz.hydroxylamine, hydrazine hydrochloride and guanidine hydrochloride to achieve the target macrocycles 241 (67%), 242 (63%) and 243 (73%).Another set of macrocycles was prepared using 244 as the starting material (Scheme 27).After subjecting it to three reaction steps, the TBS protected compound 245 was achieved and further propargylated to create the alkyne moiety 246.Deprotection of the TBS group resulted in the formation of 247 which was upon exposure to This article is protected by copyright.All rights reserved.In 2021, Vazquez-Miranda and their co-workers extended their previous synthesis of triazole fused macrocycles 258 and explored the anticancer activity of the reported compounds (Scheme 28). 34Through the Ugi-4 component reaction, the amines 253, the isonitriles 254, the azides 255 and the alkyne moiety 256 were made to react together using catalytic amount of InCl3 in methanol to afford a set of macrocyclic precursors 257.The final macrocyclization was conducted via CuAAC reaction, in the presence of CuBr and DBU in toluene through microwave irradiation, to afford the desired set of compounds 258 in (25-79) % yields.The newly synthesized cyclophanes were biologically evaluated against prostate (PC-3 and DU-145) and breast (MCF-7) tumor cells and were reported to exhibit significant cytotoxicity.The compound 259 (Figure 1) was reported to induce apoptosis in PC-3 in their previous work 30 and was treated as a reference for this work.The compound 258a was noticed to display a two-fold higher inhibition towards PC-3 on being compared with 259 and a lower toxicity towards healthy line COS-7.The derivative 258b was also noted to be one of the most biologically active compounds from the entire set.From all of the observations noted, the Vasquez group concluded that the presence of cyclohexyl and 4-isopropylaniline groups attributes to higher activity.

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Antibacterial Derivatives
Antibiotic resistance, another global threat to mortals, has been an important research scope for scientists.Significant progress has been made so far in this field in order to treat bacterial infections.
Many bioactive molecules are known to have the smallest cyclic peptides, diketopiperazines (DKPs) within their frameworks.The peptide or peptidometric incorporated macrocycles can modulate biological systems and thus being extremely important in the medicinal chemistry field.Isidro-Llobet et al., in 2011, synthesized macrocyclic peptidometric framework 264 whose structure was inspired by a bioactive molecule (+)-piperzainomycin (Scheme 29). 35Amide coupling in between the alkyne moiety 260 and azide 261 using EDC and HOBt led to the production of the macrocyclic precursor 262.Subsequently, it subjected to CuAAC conditions with catalytic CuI and DBU in refluxing toluene which afforded the triazole fused macrocycle 263 in 45% yield.The final DKP formation was done using solid-supported NMM and microwave heating at 150 ℃ for 9 h to furnish the target compound 264 in 40% yield.Biological assessment showed that the target macrocycle 264 exhibited prominent antibacterial property against the gram-positive bacteria Staphylococcus aureus.
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Template for SynOpen Thieme Noor et al., in 2014, reported the development of a set of triazole fused macrocycles which formed stable [Re(CO)3] + complexes 271a,b and evaluated their antibacterial activities (Scheme 30). 36The synthetic procedure progressed with the conversion of the tosylated derivative 265 into the 2,6bis(azidomethyl)pyridine 266 by the action of sodium azide in DMF:H2O at 80 ℃ for 24 h.The azide moiety was then treated with the dialkyne 267 in presence of copper sulphate and sodium ascorbate in DMF: H2O (4:1) medium at room temperature for 72 h to afford the macrocycle 268 in 42% yield.It was further converted into 269 in two reaction steps which was gradually exposed to another intermolecular Cucatalyzed cycloaddition with two alkynes, following similar reaction conditions as mentioned earlier, in order to furnish the compounds 270a,b (77%, 76%).Subsequently, the Rhenium(I) complexes 271a,b were prepared in 92% and 61% yields by refluxing 270a,b in methanol with [Re(CO)3(H2O)3]Br for 24 h.Biological evaluation helped in detection of the inhibitory activity of compounds 271a,b against bacterial strains Staphylococcus aureus and Escherichia coli.
Guo et al., in 2017, constructed the thanatin derived 1,2,3triazole bridged disulfide surrogated peptides 285, 286 and tested their antibacterial activities (Schemes 31 and 32). 37The process commenced by installing the t-butyl group, followed by Fmoc protection on 2-propargyl-Lglycine 272 to afford the fragment 273 which was clicked with the azide 274 via [Cp*RuCl(cod)] catalyzed reaction in DMF at 40 ℃ to form the triazole moiety 275.Three subsequent reactions led to the production of a key fragment 276 in 95% yield.In a separate pathway, 273 was coupled with the azide 277 in presence of CuI/DIPEA system in DMF and the triazole 278 was furnished in 84.1% yield.TFA-mediated deprotection of 278 produced the other key fragment 279 in 96.3% yield.The peptidomimetics 285 and 286 were synthesized from the Rink amide AM resin by proper assembling of Fmoc/t-Bu SPPS, using the coupling reagent HCTU, to create the macrocyclic precursors 281, 282.Successful cleavage of the allyl and Alloc groups with [Pd(PPh3)4]/PhSiH3 was followed by cyclization with PyAOP, NMM and HOAt to graft the cyclic peptides 283, 284.After the remaining amino acids were united, deprotection and acidic cleavage afforded the compounds 285 and 286 in 29.7% and 34.5 yields, respectively.Through biological assessment, it was realized that both of the 1,5-and 1,4-disubstituted triazole peptides showed 50% lesser the inhibition against Pseudomonas aeruginosa when compared to thanatin.

Scheme 29 Synthesis of macrocyclic peptidometric framework 264
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Template for SynOpen Thieme Prabhakaran et al., in 2018, developed a synthetic route to synthesize triazole fused macrocycles 291a-j and then evaluated their bioactivities (Scheme 33). 7The synthesis involved propargylation of salicylaldehyde 287 to afford the derivative 288 followed by aldol condensation with various methyl ketones to achieve the unsaturated ketones 289a-i.In addition, the only unsaturated ester 289j was synthesized via Wittig reaction of 288.Subsequently, intermolecular cycloaddition of 289a-j with O-alkylazidoaldehyde 221 in the presence of copper sulphate and sodium ascorbate in THF-H2O (1:1) at room temperature for 12 h furnished the 1, 2, 3triazole linked moieties 290a-j in 85-95% yields.Final cyclization of the aldehydes 290a-j with sarcosine in toluene at 120 ℃ for 12 h eventually afforded the desired macrocycles 291a-j in 75-85% yields.Several biological assessments conducted on 291a-j concluded that these macrocycles showed significant antibacterial activity against Bacillus cereus and Klebsiella pneumoniae.This article is protected by copyright.All rights reserved.

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Scheme 33 Synthesis of antibacterial agents 291a-j Biaryl ethers have always been an interesting scaffold for researchers since they possess various bioactivities.In 2018, Singh et al. developed a vancomycin-like 44-membered biphenyl ether based macrocycles with triazole linkers 294a,b and evaluated their antibacterial activities (Schemes 34 and 35). 38Their syntheses were undertaken by using the azidobiphenyls 293a and 293b along with the propargylated sugar moieties 292 and 296.The initial Cu-catalyzed AAC reaction conducted in between 293a and 292 in the CuI/DIPEA system in acetonitrile/water medium at 30 ℃ for 48 h afforded the target macrocycle 294a and its isomer 295 as an inseparable mixture with a combined yield 12% (Scheme 34).Thus, in order to selectively afford the target compound, the substrate 296 was clicked with the biazides 293a and 293b, respectively in presence of copper sulphate and sodium ascorbate in t-BuOH/water medium at 30 ℃ for 3-4 h.This afforded the key intermediates 297a,b in excellent yields 98% and 96%, respectively (Scheme 35).Two subsequent steps led to the formation of the bialkyne 298 and it was gradually subjected to the final CuAAC reaction with the azides 293a/293b in CuI/DIPEA system following similar reaction conditions mentioned earlier.This afforded the desired triazole fused macrocyclic compounds 294a and 294b in 16% and 18% yields, respectively.Through biological investigation, it was reported that both of them exhibited antibacterial activity against Staphylococcus aureus.It was noted that the fluoro substituted compound 294b displayed significant activity against both Methicillin-resistant SA and Vancomycin-resistant SA strains.
In 2022, the Liskamp group constructed a tricyclic hexapeptide 306 which mimicked the topology of a potent antibiotic vancomycin (Scheme 36). 39The process was initiated with coupling of the amine E-299 and the acid fragment 300 under DCC/HOAt conditions in dichloromethane to achieve the amide 301.After acidic treatment of 301, Boc deprotection resulted in the formation of 302 which was further converted into the macrocyclic precursor 304 in four consecutive reactions.
Subsequently, the crucial intramolecular macrocyclization step was conducted using [Cp*RuCl]4 catalyst in THF/MeOH (4:1) medium at 80 ℃ under microwave irradiation for 2 h to furnish the tricyclic compound 305 in 16% yield.Finally, Boc deprotection with acid yielded the target compound 306 which displayed significant antibacterial activity against Staphylococcus aureus.

Scheme 34 Synthesis of antibacterial agent 294a
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Template for SynOpen Thieme Research upon the synthesis of macrocyclic compounds has led to the development of certain compounds which exhibit dual bioactivities.
Selvarani et al., in 2018, synthesized a series of 1:1 and 2:2 oligomeric triazolophanes 312-321 and evaluated their antibacterial activities (Scheme 37 and Figures 2 and 3). 40The synthetic process advanced with the preparation of bispropargyl-5-nitroisophthalate 307 and the respective bisazides 322, 308-311.The building block 307 was obtained by propargylating 5-nitroisophthaloyl chloride while the bisazides were synthesized using 1,4-dibromobutane and various diols as the starting materials.For the crucial macrocyclization step, the fragment 307 was coupled with each of the bisazides (322, 308-311) using catalytic amount of copper sulphate and sodium ascorbate in THF/H2O (3:1) solvent system at room temperature for 12 h (Scheme 37).The This article is protected by copyright.All rights reserved.

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Antilarval Derivatives
The cowpea aphid or Aphis craccivora Koch has been a major problem for agriculture since it affects the growth of leguminous crops by sucking saps from leaves and transmits viruses which ultimately causes economic damage.Researchers are investing efforts to irradicate these pests by developing new macrocyclic drugs to help flourish vegetation.
In 2017, Rana et al. reported the synthesis of a few triazole fused sugar embedded macrocycles 326, 329, 333 and presented their bioactivities in 2018 (Scheme 38). 10,41The synthetic process was carried out with the preparation of the macrocyclic precursors 325, 328 and 332.The alkyne moiety 323 and the azide moiety 324 were exposed to CuI catalyzed AAC reaction in water at 70 ℃ for 2 h to achieve the intermolecular click product 325 in 78% yield.Subsequently, ring-closing metathesis (RCM) reaction was conducted upon 325 in the presence of Grubbs-II catalyst in two different pathways with varying amount of catalyst added in the reaction mixtures.For the method A, the substrate was refluxed in dichloromethane for 3 h which afforded the triazole fused macrocycle 326 in 83% yield.Simultaneously, for the This article is protected by copyright.All rights reserved.

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Template for SynOpen Thieme method B, the substrate was heated at 75 ℃ in ethyl acetate for 2 h and the desired macrocycle 326 was grafted in 39% yield.
The fragments 327 and 324 were coupled using similar CuAAC reaction conditions to synthesize the macrocyclic precursor 328 (91%) which was further subjected to two different RCM reactions following the conditions mentioned earlier.The target macrocycle 329 was afforded in 82% (method A) and 92% (method B) yields, respectively.Consecutively, 330 and 331 were clicked together to afford 332 (87%) which underwent macrocyclization via RCM and formed the desired compound 333 in 84% (method A) and 56% (method B) yields.Biological screening of these macrocycles was conducted to evaluate their toxicity against larvae of Aphis craccivora Koch.

Anti-inflammatory Derivatives
In order to reduce inflammation caused due to various health issues, particularly arthritis, a focused attention has been paid for the development of few 'clickable' cyclophanes.
In Anandhan et al. synthesized and screened the antiinflammatory activity of certain triazole-based macrocycles (Schemes 39 and 40). 8The synthetic procedure commenced with propargylation of the amine 334 using KOH and TBAP in a toluene/H2O solvent system to afford the alkyne moiety 335.The compound 335 was subjected to three different reaction pathways to afford the macrocyclic precursors 339-342 which were subsequently made to react with the azides 343-345 following the cycloaddition reaction methodology using copper sulphate and sodium ascorbate in THF/H2O medium at room temperature for 10 h in order to furnish a set of triazole based macrocyclic compounds 346-357 All the macrocycles exhibited good anti-inflammatory activity when compared to the reference prednisolone.

Antiviral Derivatives
Viral infection has forever been affecting the lives of people and is an important health concern.In order to combat with such infectious diseases, researchers have applied a significant attention towards drug development required for treatment.
In Mandadapu et al. reported the synthesis and bio evaluation of a macrocyclic inhibitor (364) of 3C and 3C-like proteases of viral pathogens (Scheme 41). 9 The synthetic procedure advanced with the development of the building block 359 from the (L) Boc-protected propargyl glycine 358 in four consecutive steps while the other building block 361 was synthesized from commercially available (L) Boc-Glu-OCH3 360 in two steps.These two were gradually coupled under standard conditions using HOBt and EDCI with DIPEA in DMF to graft the amide 362 which was further subjected to cycloaddition reaction conditions using CuBr, DBU in dichloromethane to afford the triazole fused macrocycle 363 in 45% yield.Further treatment of 363 with lithium borohydride converted it into an alcohol which subsequently formed the desired macrocycle 364 through Dess-Martin periodinane oxidation.Through biological assessment, the compound 364 was noted to exhibit inhibition against novovirus 3CLpro, enterovirus 3Cpro and SARS-CoV 3CLpro.
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Template for SynOpen Thieme Scheme 41 Synthesis of antiviral agent 364 Weerawarna et al., in 2016, developed a series of triazole fused macrocycles 379-390 and evaluated their antiviral property (Schemes 42, 43 and 44). 42The synthesis progressed with the construction of the key intermediates 365a-c, 368a-e and 369a,b.Initially, the commercially available N-Bocprotected L-propargylglycine 358 was transformed into the intermediates 365a-c in four consecutive steps.A subsequent coupling of N-Boc protected glutamic acid 366 and HCl salts of amino azides 367a-e, under standard conditions involving EDCI and HOBt proceeded to furnish the intermediates 368a-e (Scheme 42).Deprotection of Boc-group in presence of HCl yielded the azides 369a,b which further underwent coupling with acid 365a in presence of EDCI and HOBt to afford the macrocyclic precursors 370a,b, respectively.The crucial macrocyclization step was undertaken next via intramolecular CuAAC reaction in presence of CuI with DBU in DCM solvent at room temperature for 24 h to achieve the macrocycles 371a,b in 45% and 50% yields.Sequential reduction with LiBH4 and oxidation through Dess-Martin periodinane afforded the desired triazole based macrocycles 381, 383 in good yields (Scheme 42).In order to synthesize the other macrocycles 379,

Scheme 42 Synthesis of antiviral agents 381, 383
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Template for SynOpen Thieme 380, 382, 384-389, the key intermediates 365a-c and 368a-e were coupled in presence of copper sulphate and sodium ascorbate in THF/H2O at room temperature for 20 h to graft the triazole linked fragments 372a-i (Scheme 43).Subsequent amide bond formation through acid-amine coupling with a sequenced Boc-deprotection constructed the macrocycles 373a-i in fair yields (~60%).A similar reaction methodology of consecutive reduction-oxidation upon 373a-i resulted in the formation of the desired macrocyclic compounds 379, 380, 382, 384-389.The synthesis of the last macrocycle 390 commenced with the reaction of Z-L-ornithine with triflic azide solution in presence of triethylamine and copper sulphate in acetonitrile medium to afford the acid 375.The N-Bocprotected amino acid was transformed into the azide moiety 376 in three consecutive steps and subsequent Bocdeprotection followed by coupling with 375 under standard conditions afforded the macrocyclic precursor 377.The intramolecular cycloaddition with CuI/DBU catalytic mixture in dichloromethane at room temperature for 12 h afforded the macrocycle 378 in 48% yield.Finally, after two consecutive steps, the desired triazole based macrocycle 390 was achieved (Scheme 44).After investigating the biological properties of 379-390, it was reported that these macrocycles showed inhibition against novovirus 3C-Like protease.
Scheme 43 Synthesis of some antiviral agents

Scheme 44 Synthesis of antiviral agent 390
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Template for SynOpen Thieme In 2019, the Groutas group extended their previous synthetic work 9 and established a few macrocyclic inhibitors of novovirus 3CLpro, 1-3, utilizing similar multistep synthesis and click-methodology as described earlier (Figure 4). 43The FRET NV 3CL protease assay along with the examination of the effects of macrocycles on virus replication against NV or MNV portrayed comparable results with few previously synthesized macrocycles. 9American trypanosomiasis, also known as Chagas disease, is a life-threatening condition caused by the parasite Trypanosoma cruzi transmitted through the faeces of triatomine bugs.Millions of people especially in regions like Latin America are affected every year with this fatal disease causing a desperate need for treatment.
Campo et al., in 2015, showed their interest in developing triazole linked macrocyclic inhibitors of T. cruzi trans-sialidase (TcTS) which was found to be a potential drug target for the aforementioned disease (Scheme 45). 44In order to achieve the galactose monomer 399, O-propargyl-D-galactopyranose 394, was chosen as the starting material.With proper benzoylation of 394 followed by exposure to ammonia in methanolic-THF medium, the hemiacetal 396 was synthesized.With further treatment with trichloroacetonitrile and DBU, the compound 397 was formed and subsequently activated with trimethylsilyl trifluoromethanesulfonate and 2-(2-(2chloroethoxy)ethoxy)ethanol to give the β-glycoside 398.Through two sequential reactions the chlorinated fragment 398 was converted into the azide 399 and then tested under two different CuAAC reaction conditions.The first method (A) involved subjecting 399 to CuSO4/Cu turnings in DMF to microwave irradiation at 110 °C for 30 min while the second reaction (B) was conducted at ambient temperature and continued for 2 days; both the reactions afforded linear as well as cyclic products.The cyclic oligomers of various ring sizes (monomer 400, dimer 401, trimer 402 and so on) were obtained by utilizing the 1,4-disubstituted triazole as connectors.When the component 399 was separately exposed to an uncatalyzed microwave conditions for 30 min (Method C), the 1,4-disubstituted triazole based macrocycle 400 and the 1,5-disubstituted triazole based macrocycle 403 were obtained as products along with their respective linear oligomers.The synthetic procedure commenced with the preparation of key fragment 409a,b using the alkyne moiety 404 as the starting material.After being refluxed in ethanol with hydrazine, the amine thus produced was further coupled with N-Boc L-Asn using HOBT and EDC to afford the Boc-protected amide 405.TFA-mediated deprotection of 405 formed the compound 406 which was next subjected to two This article is protected by copyright.All rights reserved.

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Template for SynOpen Thieme subsequent steps to synthesize the tripeptide 407.On attaining this compound in the form of an inseparable epimeric mixture, further N-Fmoc removal resulted in separation of the amines and production of the diastereomers 408a and 408b.The macrocyclic precursors 409a, b were next prepared by treating 408a, b with bromoacetic anhydride and consequent addition of sodium azide.Subsequently, removal of t-Bu group and exposure to copper sulphate, L-ascorbate and DIPEA in acetonitrile-t-BuOH-H2O solvent system at room temperature afforded the monomeric macrocycles 411a, b along with the dimers 4513a,b.The cycloaddition reaction produced the monomers in majority at 1µM substrate concentration whereas, the dimers were obtained predominantly at 2µM substrate concentration.Finally, cleavage of the t-butyl esters produced the target monomeric (412a,b) and dimeric (414a,b) macrocycles.Surface Plasmon Resonance (SPR) used to evaluate the Grb2 SH2 domain-binding affinities of the newly synthesized macrocycles.It was found that the (R)isomeric-macrocycles 412b and 414b displayed binding constants above 1 µM.The monomeric (S)-macrocycle 412a bound with sub-micromolar affinity while its corresponding dimer 414a exhibited more than fifty-fold higher binding affinity.A potent tyrosinase inhibitor cyclo-[Pro-Tyr-Pro-Val] was isolated from the "good bacteria" L. helveticus.On being interested in developing synthetic analogues of the natural cyclotetrapeptide, in 2007, the Maarseveen group achieved two triazole analogues (425, 431) of the aforementioned compound (Schemes 47 and 48). 11The process began with the preparation of the linear precursor 423 through an initial coupling of the acid 415 and protected proline 416 to develop the azido-amide 417.Further deprotection of 417 led to the synthesis of a key fragment 418 (Scheme 47).A similar EDC-HOBt-mediated coupling in between the alkyne 419 and protected valine 420 afforded 421 which upon Boc deprotection afforded the other key fragment 422.Subsequently, the macrocyclic precursor 423 was synthesized through peptide coupling of 418 and 422 in the presence of EDC, HOBt, DIPEA in dichloromethane and finally subjected to macrocyclization through CuBr mediated CuAAC reaction with DBU in refluxing toluene to furnish the triazole fused macrocycle 424 in 56% yield.Pd-catalyzed hydrogenation of 424 finally afforded the desired analogue 425 in 91% yield (Scheme 48).In order to prepare the other triazole analogue 431, the alkyne moiety 426 was initially coupled with the azide moiety 427 to graft the triazole based key fragment 428.The compound 428 was further exposed to three consecutive reactions to obtain the linear macrocyclic precursor 429.A similar CuAAC methodology was applied upon 429 which furnished the cyclotetrapeptide 430 in 36% yield.Benzyl group deprotection of 430 finally helped in grafting the desired analogue 431 in 90% yield (Scheme 48).The biological investigation of the synthesized macrocycles 425 and 431 was carried out by comparison of their inhibitory activity with their parent compound 432.It was reported that the analogues exhibited three-fold increase in inhibition against mushroom tyrosinase.
In 2011, Ingale and Dawson described the synthesis of structurally constrained peptides through side-chain macrocyclization following CuAAC reaction (Scheme 49). 46ommercially available Tenta-gel resin was treated through Fmoc SPPS protocol to produce the protected resin bound peptide 433.The key macrocyclization was conducted with CuBr, sodium ascorbate, 2,6-lutidine and DIPEA in DMSO for 16-18 h at room temperature to afford the triazole based intermediate 434.Subsequent removal of protecting groups and resin cleavage provided the cyclized product 435 in 70% yield.In order to show the usefulness of this reaction in complex systems, full-length MPER epitope of gp41 668-683 was produced.The resin bound peptide 436 was exposed to similar macrocyclization conditions as stated earlier followed This article is protected by copyright.All rights reserved.

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Template for SynOpen Thieme by deprotection and resin cleavage to afford the triazole fused product 437 in 65% yield.Upon evaluating the binding of the triazole-constrained peptides to 4E10 and Z13e1, they were noticed to alter the structure of helical peptides obtained from HIV gp41.

Scheme Synthesis of tyrosinase inhibitor
Sunflower trypsin inhibitor-1 (SFTI-1) is a cyclic peptide framework favoured by researchers while synthesizing peptide-based pharmaceuticals as it acts a potent inhibitor of trypsin.With a wide range of applications in drug designing, SFTI-1 is particularly targeted onto serine proteases and The Kolmar group, in 2011, developed three triazolebased derivatives (440, 441 and 444) of a peptide variant of SFTI-1 (445) by utilizing both CuAAC and RuAAC methodologies (Scheme 50). 47Commercially available SPPS building blocks Fmoc-L-propargylglycine (Fmoc-Pra-OH) and Fmoc-L-azidoalanine (Fmoc-Aza-OH) or Fmoc-Lazidohomoalanine (Fmoc-Aha-OH) were utilized to afford the macrocyclic precursors 438 and 439, respectively.Subsequent TFA-mediated cleavage with further macrocyclization undertaken in presence of copper sulphate, sodium ascorbate and DIPEA at room temperature resulted in the formation of the 1,4-disubstituted triazole linked peptides 440 and 441, respectively.Application of RuAAC methodology upon unprotected peptide 439 led to a mixture of undesired products thus initiating the researchers to develop a different linear precursor 442.The protected peptide 442 was subjected to [Cp*RuCl(cod)] catalyzed microwave irradiation at 60 ℃ for 5 h and the 1,5-disubstituted triazole linked macrocycle 443 was obtained.The desired macrocycle 444 was obtained after the introduction of SPPS building block and consecutive acidic cleavage.Kinetic studies using active-site titrated trypsin made it clear that different modes of macrocyclization significantly affected the inhibitory activity of the peptides.The 1,5-disubstitued triazole based macrocycle 444 was reported to retain inhibition in a range comparable with its parent peptide 445 (Figure 5) whereas, the 1,4disubstituted triazole based macrocycles 440 and 441 showed a decline in inhibition.
2013, Pehere et al. designed a few triazole fused macrocyclic protease inhibitors (Schemes 51 and 52). 48the preparation of the macrocycle 450, initially coupling in between the dipeptide 446 with the azide moiety 447 under standard EDCI-HOBt conditions gave rise to the tripeptide 448 which further underwent macrocyclization in the presence of CuBr and DBU in dicholoromethane for 7 h at room temperature to afford the macrocycle 449 (71%).

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Scheme 50 Synthesis of trypsin inhibitors 440, 441 and 444 Figure 5 A peptide variant of SFTI-1 Subsequently, 449 was reduced with lithium borohydride and the resultant alcohol was oxidized by DMP to provide the target compound 450 (52%) (Scheme 51).The triazole linked macrocyclic precursor 453 was next grafted in 60% yield by the intermolecular click reaction in between the alkyne 451 and the azide 452 in the presence of copper sulphate and sodium ascorbate in dichloromethane-water medium at room temperature for 15 h.TFA-mediated Boc deprotection formed the moiety 454 which subsequently underwent HATU coupling to provide the triazole fused macrocyclic ester 455 in 13% yield.Gradual reduction of 455 with lithium borohydride followed by oxidation with DMP helped achieve the target compound 456 (80%).In a similar manner, the alkyne fragment 457 was coupled with 452 under AAC reaction conditions using copper sulphate and sodium ascorbate to furnish the triazole linked moiety 458 (63%).Further Boc deprotection followed by HATU/HOAt mediated amide formation resulted in the development of the triazole fused macrocycle 460 in 48% yield (Scheme 52).Two subsequent steps finally afforded the desired compound 461 in 80% yield.The macrocyclic precursor 462 constituting both the azide and alkyne parts underwent intramolecular CuAAC reaction with CuBr following the aforementioned conditions to give the compound 463 (70%), which upon further oxidation with DMP to afforded the macrocycle 465 in 73% yield.To their amazement, when the compound 462 was left at room temperature for a few months, the 1,5-disubstituted triazole 464 (65%) was received.Upon further oxidation, the macrocycle 466 was obtained in 71% yield.Biological evaluation of the macrocycles showed all compounds displayed inhibition towards Cathepsin S (Cat S), a protease related to tumor growth, autoimmune diseases, osteoporosis etc.The compound 466 was found to be at par with 465 when tested for inhibition towards the proteases calpain II (implied in stroke, cataracts etc.), Cat S, and Chymotrypsin-like (CT-L) (anticancer therapeutic target).It was also found to exhibit a 4fold decrease in potency for Cathepsin L on comparison with 465.
After being isolated in 2010, the natural product Palmyrolide A had been identified as with neuroprotective activity as it suppressed neuronal spontaneous calcium ion oscillations via its voltage-gated sodium channel (VGSC) blocking ability.Thus, researchers have always considered Palmyrolide A to be a favourable target in CNS drug discovery.In 2016, Philkhana et al. synthesized two triazole based analogues (471, 472) of Palmyrolide A and investigated their bioactivities (Scheme 53). 12The process began by subjecting the compound 467 to ozonolysis with subsequent Seyferth-Gilbert homologation using the Ohira Bestmann reagent to afford the alkyne 468.TCBC-mediated esterification of 468 with 6-azidohexanoic acid 469 produced the macrocyclic precursor 470 which was finally clicked intramolecularly with CuI in MeOH: PEG400 (1:2) medium at 80 °C under sealed conditions.The desired triazole fused macrocycles 472 and 471 were obtained in a combined yield of 66% in a 2:1 ratio.Biological evaluation of the macrocycles was conducted to check their interaction with VGSC.Their inhibitory activity against the veratridine-stimulated Na + influx in murine primary neuronal cultures proved that the triazole containing moieties did not show much potency, instead 472 exhibited a five-fold decrease in activity when compared to its parent compound Palmyrolide A (Figure 6).This article is protected by copyright.All rights reserved.

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Template for SynOpen Thieme Jogula et al., in 2017, synthesized some 'Geldanamycin' inspired triazole based macrocycles by employing CuAAC reaction as the crucial macrocyclization step and evaluated their bioactivities (Scheme 54). 49The preparation of the target molecules was initiated from L-ascorbic acid (473) as it was converted to ester fragment 474 following a literature reported method.Several consecutive steps afforded the fragment 475 which was subsequently acidified to cleave the dioxolane moiety and treated with triisopropylsilyl chloride to achieve 476.The macrocyclic precursor 478 was next achieved through DCC-DMAP coupling of the separately synthesized azido-acid 477 and the alcohol 476.The final macrocyclization occurred via intramolecular cycloaddition reaction by utilizing CuI/DIPEA catalytic system in refluxing THF resulted the desired product 479 in 63% yield.Following a similar methodology, the ester 480 was converted into the TBSprotected alkyne fragment 481 which was further coupled with 477 to produce the macrocyclic precursor 482.This moiety was intramolecularly clicked using the aforementioned catalyst at 70 ℃ to graft the macrocycle 483 (70%).In order to assess these novel macrocycles biologically, initially the molecular docking simulations of 479 and 483 were investigated with Hsp90.It was reported that 483 exhibited better binding with the ATP binding site of Hsp90 protein than geldanamycin.The synthesized macrocycles exhibited the ability to trans-differentiate human umbilical cord tissuederived mesenchymal stem cells to neurons.By monitoring the phenotypic changes occurring within the cells, some selected biomarkers viz.nestin, agrin and RTN4 were identified to be present in the transformed neuronal cells with 483.This article is protected by copyright.All rights reserved.

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Melanocortin system is known to be involved in the regulation of physiological functions like feeding behavior, inflammation, pigmentation, exocrine gland function and more.In 2018, Tala et al. reported the synthesis of some triazolebridged peptidomimetics evaluated them at the mouse melanocortin receptors (Schemes 55 and 56). 50Initially, the linear peptide 484 was synthesized by replacing following the Fmoc/t-Bu SPPS method on Rink-amide MBHA resin.The solid phase assembly in furnishing 484 had introduced both the alkyne and azide groups within the system by replacing the N α -Fmoc-Cys-OH residues with N α -Fmoc-L-Pra-OH and N α -Fmoc-L-Aza-OH amino acids within the peptide template 494 (Figure 7).The macrocyclic precursor 484 favourably underwent intramolecular CuAAC reaction conducted overnight using copper sulphate-sodium ascorbate in H2O-tBuOH solvent system at room temperature and afforded the desired 1,4disubstituted triazole-fused macrocyclic peptide 485 (Scheme 55).In a similar manner, the linear peptide 486 was also prepared by coupling the amino acids on resin using the aforementioned strategy.Subsequently, macrocyclization was conducted with catalytic [Cp*RuCl(cod)] under microwave (30 W) at 60 °C for 3 h to graft the compound 487 on resin.After subjecting to further coupling of Tyr and subsequent TFAmediated cleavage, the 1,5-substituted triazole-fused macrocyclic peptide 488 was obtained.The effects of ring size on macrocyclization were further investigated by the team and henceforth, the N α -Fmoc-L-Aza-OH residues in 494 were replaced by N α -FmocL-Orn(N3)-OH amino acids to develop the linear peptide 489 through the Fmoc/tBu SPPS method.
Subsequently, 489 was coupled with 1,3-diethynylbenzene 490 following the intermolecular copper sulphate-sodium ascorbate catalyzed reaction in the presence of tris(3hydroxylpropyltriazolylmethyl) amine in a similar ambience mentioned earlier.This yielded the target macrocyclic 1,4disubstituted bis-triazole-fused peptide 491 in majority (Scheme 56).The peptide resin 492 afforded in a way same as the other linear precursors, was coupled with 490 through intermolecular RuAAC reaction using [Cp*RuCl(cod)] under microwave conditions stated earlier.Through subsequent deprotection, resin-cleavage and purification, the 1,5disubstituted bis-triazole-macrocyclic peptide 493 was obtained as the major product.With the generated macrocycles in hand, the pharmacological assessment at the mouse melanocortin receptors mMC1R, mMC3R, mMC4R, and mMC5R was conducted.Their ability to stimulate intracellular cAMP signalling was tested in HEK293 cells.The macrocyclic peptide 485 showed 41-, 13-, 14-, and 7-fold decrease in potency at the mMC1R, mMC3R, mMC4R, and mMC5R, respectively in comparison to the template peptide 494.The peptide 488 was noted to exhibit an increase in potency at the mMC3R and mMC5R while maintaining potent nanomolar agonist activity at the mMC1R and mMC4R in contrast with the potency of 488.The compound 488 was also found to show a five-fold decrease in potency at the mMC4R on comparison with 494 and a twenty-nine-fold reduced potency at the mMC1R.The peptides 491 and 493 were seen to display modest selectivity for the mMC5R.This article is protected by copyright.All rights reserved.

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Scheme 56 Synthesis of macrocyclic peptides 491, 493 Figure 7 A peptide template White et al., in 2020, established a series of triazole linked cyclic peptides using SFTI-1 framework and assayed them against serine protease inhibitors (Scheme 57). 51Commercially available β-azidoalanine (Aza) or γ-azidohomoalanine (hAza) and propargylglycine (Prg) were assembled by Fmoc SPPS upon 2-chlorotrityl chloride resin 495.Subsequent resin cleavage and backbone cyclization brought the azide and alkyne groups close to each other.Further TFA-cleavage was followed by CuAAC reaction with copper sulphate, THPTA and sodium ascorbate at 37 ℃ for 3 h resulted in the formation of 1,4-disubstituted triazole linked peptide macrocycles 500d-f and 501d-f.On exposing the protected peptide to RuAAC reaction with [Cp*RuCl(cod)] catalyst in DMF at 80 ℃ for 18 h yielded the 1,5-disubstituted triazole linked peptide.Final deprotection led to the production of the target compounds 500b, c; 502b, 501b, c and 503b.The inhibitory activity of triazoles 500b-f were evaluated against trypsin using SFTI-1 as a reference.The compounds 500b,c were found to be more potent compared to the others while 500b was reported to retain maximum inhibition when compared to SFTI-1.The other triazole based peptide analogues 502b, 501b and 503b were screened for inhibition against kallikrein-related peptidase 7 (KLK7), plasmin and matriptase.The compound 502b exhibited a seven-fold lower inhibitory activity than its parent 502a when assayed upon KLK7 protease involved in skin disorders.Compound 501b showed sixty-two-fold less inhibition when compared to 501a after being evaluated against plasmin, a protease related to fibrinolysis.Furthermore, the analogues 501c-f exhibited extreme loss in potency (>6300-fold) when assayed against the same proving 501b to remain as the most favourable disulphide mimetic.The other analogue 503b was noted to display one hundredtwenty-fold lesser inhibition than 503a after being screened against matriptase, a membrane-anchored protease involved in epithelial tumors.The triazole linked peptides 500b-503b were tested against human serum and were found to resist degradation.On being investigated against liver S9 assays, 500b-503b were reported to be stable with half-lives greater than 200 min.
Kulsi et al., in 2020, designed an amide based triazole fused macrocycle 511 through cyclo-oligomerization (Scheme 58). 52he synthetic route progressed with the azide-alkyne cycloaddition between O-phthalimide-protected propargyl alcohol 504 and azido-glucose 505 using copper sulphate and sodium ascorbate in t-BuOH/H2O medium to afford the triazole 506 in 88% yield.Five consecutive steps led to the production of the intermediate 507 which was further subjected to sequential protection-deprotection to furnish 509.Subsequently, the fragments 507 and 509 were coupled together to form the amide 510 under EDC/HOBt conditions.The final macrocyclization to yield the cyclic peptide 511 (55%) took place via hydrolysis and activation with pentafluorophenyl ester (PFP) with gradual peptide coupling.Through several assessments, the macrocycle 511 was found to be an electroneutral and anion receptor.With an incredible ability to distinguish in between ions, the macrocycle exhibited a preference towards Cl -ion and served as a scaffold for ion This article is protected by copyright.All rights reserved.

Accepted Manuscript
Template for SynOpen Thieme transportation thus imposing cancer cell death by disruption of ionic homeostasis.In 2022, Cheekatla et al. developed a few aza-oxa based macrocycles by employing CuAAC reaction and evaluated their biological properties (Scheme 59). 53The synthetic procedure commenced by subjecting the amine-hydroxyl derivatives 512a-d to O-propargylation with propargyl bromide by using NaH in DMF at 0 ℃ and subsequent N-propargylation in the presence of DIPEA in refluxing chloroform to afford the alkyne moieties 513a-d.These alkynes underwent intermolecular CuAAC reaction with bis(2-azidoethyl)amine 514 using catalytic CuI and DIPEA in acetonitrile medium at room temperature for 12-24 h to afford the triazole fused macrocycles 515a-d.For the other macrocycle 518, the diol 516 was initially converted to its corresponding dipropargylated moiety 517 by the action of propargyl bromide and NaH in DMF at 0 ℃ and was further treated with similar click-conditions as described earlier.By studying the fluorescence properties for the interaction between the macrocycles with bovine serum albumin (BSA) and human serum albumin (HSA), it was reported that all the compounds exhibited a varied range of interactions.The macrocycles which interacted well with the proteins, showed fluorescence quenching.Upon calculating the binding constants for the interaction of macrocycles and BSA, 518 was noted to have the highest binding while the other macrocycles 515a-d exhibited moderate binding.Furthermore, the fluorescence studies of 518 with HSA showed that it had the highest interaction and quenching while the other macrocycles displayed moderate results.
Scheme 57 Synthesis of macrocyclic peptides 500b-f, 501b-f, 502b and 503b Scheme 58 Synthesis of triazole fused macrocycle 511 This article is protected by copyright.All rights reserved.

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Thurakkal et al. synthesized a triazole based macrocyclic fluorescence sensor in 2023 for the detection of antibiotics containing nitro groups (Scheme 60). 54The envisioned procedure commenced with the reaction of dansyl chloride 519 with diethanolamine 520 in presence of triethylamine to afford 521.After subsequent exposure to proparyl bromide, 521 was converted into the dialkyne-moiety 522.The final macrocyclization was conducted in presence of the azide moiety 514 through CuAAC reaction with copper sulphate and sodium ascorbate in MeOH/H2O medium at room temperature for 30 min to furnish the macrocycle 523.The photophysical studies of 523 along with its interaction with several antibiotic drugs like dimetridazole (DMI), nitrofurantoin (NFT), nitrofurazone (NFZ) etc. were conducted.Fluorescence spectroscopy and molecular docking exhibited that DTMC sensed the nitro-containing compounds and also showed favourable interaction with proteins.In conclusion, we have reported several synthetic methodologies for the preparation of biologically active 1,2,3triazole fused macrocyclic compounds having ring size of 12 to 60 members.Many of them have been constructed through peptide linkages.In most of the cases the renowned Cucatalyzed azide-alkyne cycloaddition reaction led to the 1,4disubstituted 1,2,3-triazoles whereas, the 1,5-disubstituted 1,2,3-triazoles fused macrocycles were obtained via Rucatalyzed cycloaddition.Thorough literature survey proved that the azide-alkyne cycloaddition is a versatile method and does not require any drastic reaction condition.It was observed that when further functionalization of the triazole linked scaffolds was conducted, in order to obtain the target bioactive compounds, the triazole moieties remained unaffected.Researchers also synthesized analogues of a few naturally occurring bioactive macrocycles involving azide-alkyne cycloaddition strategy. 4,17,21,24The macrocycles described herein This article is protected by copyright.All rights reserved.

Scheme 16
Scheme 16 Synthesis of triazole analogue 157 of natural product LL-Z1640-2 furnished the desired dimeric macrocycle 169 in 57% yield.Biological assessment of 169 showed its binding ability to XIAP and cIAP proteins.The target compound also exhibited inhibition towards growth of human melanoma and colorectal cell lines by demonstrating prominent antitumor activity in the A875 human melanoma xenograft mode.In 2015, Seigal et al. established a DNA-programmed library of cyclic peptidomimetics 171a-d, 172a-d, and 173-176 utilizing the Cu-catalyzed 1,3-dipolar cycloaddition reaction (Scheme 18).26The linear precursors were prepared on DNA solid-phase support using a literature reported DPC method.The crucial macrocyclization step took place by exposing the precursors 170a-d to Cu-(II) (Z)-2,2,6,6tetramethyl-5-oxohept-3-en-3-olate, ascorbic acid, DIPEA and 2,6-dimethylpyridine in DMF:THF (1:1) solvent system which provided the desired set of monomeric macrocycles 171a-d after deprotection and resin cleavage with TFA.The dimers 172a-d were simultaneously synthesized as a by-product of the aforementioned reaction but, their yields were increased by utilizing a higher substitution density in the solid-phase synthesis, which resulted in the enhancement of intermolecular cyclization.The monomeric macrocycle 173 was produced by inverting the P2 linker in 170a and exposing it to similar macrocyclization conditions whereas, the dimeric macrocycles 174-176 were produced by modifying the P1, P2 and P3 linkers altogether.The macrocycles 171a and 171b were noted to bind potently to cIAP1 BIR3 and XIAP BIR3 in Fluorescence Polarization Assays (FPA) with IC50 values just about 3-8-fold lower in the case of the latter.The compound 171b showed less potency in the caspase-3 rescue assay, weak

Scheme 28 Synthesis of anticancer agents 258 Figure 1
Scheme 28 Synthesis of anticancer agents 258

Scheme 30
Scheme 30 Synthesis of antibacterial agents of Re-complexes 271a,b

Scheme 35
Scheme 35 Synthesis of antibacterial agents 294a, b

Scheme 51
Scheme 51 Synthesis of macrocyclic protease inhibitors 450 and 456

Scheme 59
Scheme 59 Synthesis of a few aza-oxa macrocycles 1,4disubstituted triazole fused macrocycle 184 was achieved in 55% yield whereas, exposure to RuAAC reaction with catalytic [Cp*RuCl]4 in toluene at 80 ℃ for 4 h, afforded the 1,5disubstituted triazole fused macrocycle 185 in 42% yield.Subsequently, the macrocyclic esters 184, 185 were changed into their respective acid derivatives 186 and 190 which were further made to undergo condensation with several amines to form the amide derivatives 187-189 and 191-193 in good yields.Biological evaluation of macrocycles 186-193 against lung cancer cell line A549, breast cancer cell line MDA-MB-231 and hepatocarcinoma cell line Hep G2 explained moderate antitumor activity.
Template for SynOpen Thieme desired compound 201 in 60% yield.A Ru-catalyzed azidealkyne cycloaddition of 198a and 195 was also conducted by Adele Gabba and her co-workers using catalytic [Cp*Ru(cod)Cl] in DMA through 100 W irradiation at 100 ℃ for 30 min to prepare the derivative 202 (40%).
Scheme 18 Synthesis of a few macrocyclic anticancer agents Scheme 19 Synthesis of antitumor agents 186-193 Template for SynOpen Thieme azide-alkyne cycloaddition reaction conditions with 237 furnished the triazole 248 in 77% yield.Two subsequent steps helped graft the intermediate 249 (70.58%) and finally, it was allowed to react in three different pathways to afford the target macrocycles 250 (64%), 251 (68%) and 252 (61%) following up a similar methodology mentioned earlier.Biological evaluation of these compounds showed promising anticancer activity of 241 and 252 against MCF-7 cell line whereas, compounds 242, 243, 250 and 251 were noted to exhibit activity against MDA-MB-231 and HeLa cell lines.
Macrocycle 317 was seen to display a stronger inhibition towards the Gram-positive bacteria S. aureus and B. subtilis than the Gram-negative bacteria E. coli and S. typhi.Further molecular docking studies via Glide XP established the binding ability of macrocycles 313-316 with the target protein CTXMenzyme in complex with cefotaxime.Selvarani et al. also investigated the bioactivities of 312-321 against the larvae of vector Aedes aegypti.The compounds shown in figures 2 and 3 exhibit larvicidal activity with 90% mortality rate in case of 316.The macrocycles 314 and 315 were reported to display 80% mortality rate while 312-313 showed moderate rate and 317-321 showed low mortality.