Strategies for the efficients ynthesis of peptide macrocyclesh ave been al ong-standing goal. In this paper, we demonstrate the use of the peptide ligase termedo mniligase-1 as av ersatile and broadly applicable enzymatic toolf or peptide cyclization. Severalh ead-to-tail (multi)cyclic peptides have been synthesized, including the cyclotide MCoTI-II. Cyclization ando xidative foldingo ft he cyclotide MCoTI-II were efficiently performed in ao ne-pot reactiono na1 -gram scale.T he native cyclotide was isolated andt he correct disulfide bonding pattern was confirmed by NMRs tructure determination. Furthermore,c ompatibility of chemo-enzymatic peptide synthesis( CEPS) using omniligase1w ith methods such as chemical ligation of peptides onto scaffolds( CLIPS)w as successfully demonstrated by synthesizing ak inase-inhibitor derived tricyclic peptide.O ur studies indicate that the minimal ring size for omniligase-1 mediated cyclization is 11 amino acids,w hereas the cyclization of peptides longer than 12 amino acids proceeds with remarkablee fficiency.I na ddition,s everal macrocycles containing non-peptidic backbones( e.g.,p olyethylene glycol), isopeptide bonds (aminoa cid sidechain attachment) as well as d-amino acids couldbe efficiently cyclized.Keywords: chemo-enzymatic peptide synthesis (CEPS);c yclic peptides; cyclization;c yclotide synthesis;c yclotides;e nzyme catalysis;h ead-to-tail cyclization; ligases;m acrocycles;o mniligase-1;p eptides Peptide macrocyclesr epresent an extremely diverse class of molecules that attracti ncreased attentiona s drug leads and prospective pharmaceuticals,w ith currently over 30 cyclic peptides registered or in clinical trials.[1-3] Togetherw ith linearp eptides, they fill the gap between small-molecule drugs (less than 500 Da) and biologics (over 5000 Da) andh avet he potential to address previously "undruggable" targets. Many cyclicp eptides are characterized by their unique structural and enhancedb iopharmaceutical properties,s uch as an improved metabolic stability due to ar educed sensitivity to proteolytic cleavage.T he increasing number of cyclic peptidesu sed as therapeutics is accompanied by the need for efficient andc osteffectiver outes that enable their synthesis on al arge scale.M oreover, efficients ynthesiso fl arge libraries of cyclic peptides (e.g.,f or screeningp urposes) or of cyclicp eptides containing non-canonical amino acids (e.g., d-o ru nnatural amino acids to increase stability and diversity) is of importance.H owever, efficient cyclization of peptidesu sing traditional synthetic methodsi ss till ac hallenge.[4] Classical coupling reagents are often used to cyclize side-chain protected peptides in anhydrous organic solvents.H owever, heavy dilution to prevent polymerization,r isk of epimerization and ap oors olubility of side-chain protected peptideslimitthis approach, especially for peptides longer than 20 amino acids.[5] Native chemical ligation (NCL) [6] is often used to cyclize unprotected peptides in aqueous solution. However, not all pep...

A broadly applicable one-pot methodology for the facile transformation of linear peptides into tetracyclic peptides through a chemoenzymatic peptide synthesis/chemical ligation of peptides onto scaffolds/copper(I)-catalyzed reaction (CEPS/CLIPS/CuAAC; "triple-C") locking methodology is reported. Linear peptides with varying lengths (≥14 amino acids), comprising two cysteines and two azidohomoalanines (Aha), were efficiently cyclized head-to-tail by using the peptiligase variant omniligase-1 (CEPS). Subsequent ligation-cyclization with tetravalent (T4 ) scaffolds containing two bromomethyl groups (CLIPS) and two alkyne functionalities (CuAAC) yielded isomerically pure tetracyclic peptides. Sixteen different functional tetracycles, derived from bicyclic inhibitors against urokinase plasminogen activator (uPA) and coagulation factor XIIa (FXIIa), were successfully synthesized and their bioactivities evaluated. Two of these (FF-T4 ) exhibited increased inhibitory activity against FXIIa, compared with a bicyclic control peptide. The corresponding hetero-bifunctional variants (UF/FU-T4 ), with a single copy of each inhibitory sequence, exhibited micromolar activities against both uPA and FXIIa; thus illustrating the potential of the "bifunctional tetracyclic peptide" inhibitor concept.

We report a one-pot ligation/cyclization technology for the rapid and clean conversion of linear peptides into tricyclic peptides that is based on using tetravalent scaffolds containing two benzyl bromide and two alkyne moieties. These react via CLIPS/CuAAC reactions with cysteines and azides in the peptide. Flexibility in the scaffolds is key to the formation of isomerically pure products as the flexible scaffolds T4 and T4 mostly promote the formation of single isomeric tricycles while the rigid scaffolds T4 and T4 do not yield clean products. There seems to be no limitation to the number and types of amino acids present as 18 canonical amino acids were successfully implemented. We also observed that azides at the peptide termini and cysteine residues in the center gave better results than compounds with the functional groups placed the other way round.

Enantiomerically pure 2,6-disubstituted piperidinones were synthesized from furfural involving an organocatalyzed Mannich reaction, aza-Achmatowicz reaction, and an N-acyliminium ion-mediated coupling step. This approach was also successfully applied to a total synthesis of (-)-sedacryptine and one of its epimers.

We report aone-pot ligation/cyclization technology for the rapid and clean conversion of linear peptides into tricyclic peptides that is based on using tetravalent scaffolds containing two benzyl bromide and two alkyne moieties.These react via CLIPS/CuAACreactions with cysteines and azides in the peptide.Flexibility in the scaffolds is key to the formation of isomerically pure products as the flexible scaffolds T4 1 and T4 2 mostly promote the formation of single isomeric tricycles while the rigid scaffolds T4 3 and T4 4 do not yield clean products. There seems to be no limitation to the number and types of amino acids present as 18 canonical amino acids were successfully implemented. We also observed that azides at the peptide termini and cysteine residues in the center gave better results than compounds with the functional groups placed the other wayr ound.Cyclic peptides have emerged as ap romising class of drug compounds [1][2][3][4] showing aw ide therapeutic window that ranges from antifertility [5] to anticancer [6][7][8] and antiviral [9][10][11] applications.A st he number of cyclic peptides entering clinical trials has drastically increased over the last years, [6] the search for novel synthetic routes to multicyclic peptides has received significant interest. [12][13][14][15][16][17][18][19][20][21][22][23] In 2005, our group introduced "CLIPS technology" (chemical linkage of peptides onto scaffolds), which involves the tandem ligation/cyclization of tris(cysteine)-containing linear peptides with a,a',a''-tribromomesitylene (T3)t og ive the corresponding bicyclic peptides. [12] Heinis and co-workers applied this technology in phage display libraries,r eaching diversity levels as high as 10 9 -10 13 different bicycles. [13] Biological evaluation against various proteins [13][14][15][16] identified potent bicyclic peptides with K i values in the nanomolar range.I ns ome cases,t he best inhibitors displayed only (sub)micromolar activities, [24] suggesting that higher-order structures,such as tricycles,may be needed to reach improved activity levels.V ancomycin, alast-resort antibiotic consisting of aglycopeptide wrapped around an aromatic core,provides an illustrative example of such ac omplex architecture (Figure 1). [25] Currently,c omplex syntheses impede the large-scale production of vancomycin-like drugs,and complicate structural diversification processes aimed at optimizing their biological activities. [26] Examples of synthetic tricyclic peptides have been reported as the groups of both Ruchala [17] and Wu [18] used either a T h -o raD 2h -symmetric scaffold to assemble linear peptides into tricycles,w hile Suga, [19] Nuijens, [20] and our group [21] used various types of backbone cyclization in combination with T3 CLIPS.T hese and other examples emphasize the interest in multicyclic peptides although the formation of multiple isomers,laborious reaction procedures, as well as difficulties in generating structural diversity remain delicate issues.CLIPS reactions of tetrakis(cysteine)-containing pept...

The inside cover picture, provided by Nuijens and co‐workers, illustrates the power and versatility of the peptide ligase omniligase‐1. This ligase provides a promising green and clean alternative to chemical approaches used for peptide cyclization, peptide fragment condensation and protein labelling. The ligations are traceless, proceed with very high catalytic efficiency and result in high product yields. Details on omniligase‐mediated peptide cyclization can be found in the communication on pages 2050–2055 (M. Schmidt, A. Toplak, P. J. L. M. Quaedflieg, H. Ippel, G. J. J. Richelle, T. M. Hackeng, J. H. van Maarseveen, T. Nuijens, Adv. Synth. Catal. 2017, 359, 2050–2055; DOI: 10.1002/adsc.201700314).

A scaffold‐assisted one‐pot CLIPS/CuAAC ligation/multicyclization reaction based on the use of flexible tetravalent scaffolds enables the conversion of linear peptides into single‐isomeric tricyclic peptides. In their Communication on page 501 ff., J. H. van Maarseveen, P. Timmerman et al. show that there are no practical limitations to the nature and amount of amino acids present in the loops. This method can be used for the high‐throughput synthesis of tricyclic peptides followed by subsequent screenings for the identification of potent peptide therapeutics.

Organocatalytic Entry into 2,6-Disubstituted Aza-Achmatowicz Piperidinones: Application to (-)-Sedacryptine and Its Epimer. -(-)-Sedacryptine (XIII) and its epimer (XVI) are prepared via organocatalyzed Mannich, aza-Achmatowicz, and an N-acyliminium ion addition reaction from boc-protected furanyl amines. -(VAN DER PIJL, F.; HARMEL, R. K.; RICHELLE, G. J. J.; JANSSEN, P.; VAN DELFT, F. L.; RUTJES*, F. P. J. T.; Org. Lett. 16 (2014) 7, 2038-2041, http://dx.doi.org/10.1021/ol500633u ; Inst. Mol. Mater., Radboud Univ. Nijmegen, NL-6525 AJ Nijmegen, Neth.; Eng.) -F. Berndt