Category: B. Legrand

Prospect of Thiazole-based gamma-Peptides Foldamers in Enamine Catalysis: Exploration of the Nitro-Michael Addition

Chemistry. 2019 May 28;25(30):7396-7401. doi: 10.1002/chem.201901221. Epub 2019 May 7.

Aguesseau-Kondrotas J, Simon M, Legrand B, Bantigniès JL, Kang YK, Dumitrescu D, Van der Lee A, Campagne JM, de Figueiredo RM, Maillard LT.


As three-dimensional folding is prerequisite to biopolymer activity, complex functions may also be achieved through foldamer science. Because of the diversity of sizes, shapes and folding available with synthetic monomers, foldamer frameworks enable a numerous opportunities for designing new generations of catalysts. We herein demonstrate that heterocyclic γ-peptide scaffolds represent a versatile platform for enamine catalysis. One central feature was to determine how the catalytic activity and the transfer of chiral information might be under the control of the conformational behaviours of the oligomer.

How are 1,2,3-triazoles accommodated in helical secondary structures?

Org Biomol Chem. 2018 May 15. doi: 10.1039/c8ob00686e

Ben Haj Salah K, Das S , Ruiz N , Andreu V , Martinez J , Wenger E , Amblard M , Didierjean C , Legrand B , Inguimbert N


1,4-Disubstituted-1,2,3-triazole (Tz) is widely used in peptides as a trans-amide bond mimic, despite having hazardous effects on the native peptide activity. The impact of amide bond substitution by Tz on peptide secondary structures is scarcely documented. We performed a Tz scan, by systematically replacing peptide bonds following the Aib residues with Tz on two model peptaibols: alamethicin F50/5 and bergofungin D, which adopt stable α- and 310 helices, respectively. We observed that the Tz insertion, whatever its position in the peptide sequences, abolished their antimicrobial activity. The structural consequences of this insertion were further investigated using CD, NMR and X-ray diffraction. Importantly, five crystal structures that were incorporated with Tz were solved, showing various degrees of alteration of the helical structures, from minor structural perturbation of the helix to partial disorder. Together, these results showed that Tz insertions impair helical secondary structures.

12/10-Helix in Mixed β-Peptides Alternating Bicyclic and Acyclic β-Amino Acids: Probing the Relationship between Bicyclic Side Chain and Helix Stability

Chemistry. 2018 Dec 12. doi: 10.1002/chem.201804404. Epub 2018 Nov 15

Simon M, Milbeo P, Liu H, André C, Wenger E, Martinez J, Amblard M, Aubert E, Legrand B, Calmès M.


12/10-Helices constitute suitable templates that can be used to design original structures. Nevertheless, they often suffer from a weak stability in polar solvents because they exhibit a mixed hydrogen-bond network resulting in a small macrodipole. In this work, stable and functionalizable 12/10-helices were developed by alternating a highly constrained β2, 3, 3 -trisubstituted bicyclic amino acid (S)-1-aminobicyclo[2.2.2]octane-2-carboxylic acid ((S)-ABOC) and an acyclic substituted β-homologated proteinogenic amino acid (l-β3 -hAA). Based on NMR spectroscopic analysis, it was shown that such mixed β-peptides display well-defined right-handed 12/10-helices in polar, apolar, and chaotropic solvents; that are, CD3 OH, CDCl3 , and [D6 ]DMSO, respectively. The stability of the hydrogen bonds forming the C10 and C12 pseudocycles as well as the benefit provided by the use of the constrained bicyclic ABOC versus typical acyclic β-amino acids sequences when designing 12/10-helix were investigated using NH/ND NMR exchange experiments and DFT calculations in various solvents. These studies showed that the β3 -hAA/(S)-ABOC helix displayed a more stable hydrogen-bond network through specific stabilization of the C10 pseudocycles involving the bridgehead NH of the ABOC bicyclic scaffold.

Synthesis of [1,2,4]Triazolo[4,3- a]piperazin-6-ones: An Approach to the Triazole-Fused Ketopiperazine Scaffold

Org Lett. 2018 Jun 1;20(11):3250-3254. doi: 10.1021/acs.orglett.8b01112. Epub 2018 May 15.

Ben Haj Salah K, Legrand B, Bibian M, Wenger E, Fehrentz JA, Denoyelle S.


A stereoconservative synthesis to access the triazole-fused ketopiperazine (TKP) scaffold is presented. This underexplored platform offers a wide range of structural modulations with several points of diversity and chiral centers. A series of [1,2,4]triazolo[4,3- a]piperazin-6-ones was synthesized from optically pure dipeptides. The methodology was then successfully applied to access the pyrrolo[1,2- a]triazolo[3,4- c]piperazin-6-one tricycle. Importantly, the crystal structures of representative TKPs confirmed that the configuration of the chiral centers was controlled during the synthetic route and facilitated description of the orientation of the substituents depending on their nature and position on the TKP scaffold.

Selectivity Modulation and Structure of α/aza-β3 Cyclic Antimicrobial Peptides

Chemistry 2018 Apr 20;24(23):6191-6201. doi: 10.1002/chem.201800152. Epub 2018 Mar 26.

 Simon MLaurencin M, Fleury Y, Baudy-Floc’h M, Bondon A, Legrand B.


Potent and selective antimicrobial cyclic pseudopeptides (ACPPs) mixing α- and aza-β3 -amino acids were developed. Cyclopseudopeptide sequences were designed to investigate the impact of some intrinsic molecular parameters on their biological activities. Fine changes in the nature of the side chains strongly modulated the selectivity of the ACPPs with regard to hemolysis versus antimicrobial activity. The conformational preference of such compounds in various media was extensively studied, and the typical structure of cyclic α/aza-β3 -pseudopeptides is described for the first time. Interestingly, such scaffolds are stabilized by successive inverse γ- and N-N turns (hydrazino turns), a unique feature due to the aza-β3 residues. The α-amino acid side chains form a cluster on one face of the ring, while the aza-β3 -amino acid side chains are projected around the ring in the equatorial orientation. Such structural data are particularly valuable to fine-tune the bioactivity of these ACPPs by a structure-based approach.

C9/12 Ribbon-Like Structures in Hybrid Peptides Alternating α- and Thiazole-Based γ-Amino Acids

Chemistry. 2017 Dec 11;23(69):17584-17591. doi: 10.1002/chem.201704001. Epub 2017 Nov 15.

Bonnel C, Legrand B, Simon M, Martinez J, Bantignies JL, Kang YK, Wenger E, Hoh F, Masurier N, Maillard LT.


According to their restricted conformational freedom, heterocyclic γ-amino acids are usually considered to be related to Z-vinylogous γ-amino acids. In this context, oligomers alternating α-amino acids and thiazole-based γ-amino acids (ATCs) were expected to fold into a canonical 12-helical shape as described for α/γ-hybrid peptides composed of cis-α/β-unsaturated γ-amino acids. However, through a combination of X-ray crystallography, NMR spectroscopy, FTIR experiments, and DFT calculations, it was determined that the folding behavior of ATC-containing hybrid peptides is much more complex. The homochiral α/(S)-ATC sequences were unable to adopt a stable conformation, whereas the heterochiral α/(R)-ATC peptides displayed novel ribbon structures stabilized by unusual C9/12 -bifurcated hydrogen bonds. These ribbon structures could be considered as a succession of pre-organized γ/α dipeptides and may provide the basis for designing original α-helix mimics.

Ribbon-like Foldamers for Cellular Uptake and Drug Delivery

Chembiochem 2017 Nov 2;18(21):2110-2114. doi: 10.1002/cbic.201700455. Epub 2017 Sep 22.

Vezenkov LL, Martin V, Bettache N, Simon M, Messerschmitt A, Legrand B, Bantignies JL, Subra G, Maynadier M, Bellet V, Garcia M, Martinez J, Amblard M.


Different intracellular delivery systems of bioactive compounds have been developed, including cell-penetrating peptides. Although usually nontoxic and biocompatible, these vectors share some of the general drawbacks of peptides, notably low bioavailability and susceptibility to protease degradation, that limit their use. Herein, the conversion of short peptide sequences into poly-α-amino-γ-lactam foldamers that adopt a ribbon-like structure is investigated. This template is used to distribute critical cationic and/or hydrophobic groups on both sides of the backbone, leading to potent short, cell-permeable foldamers with a low positive-charge content. The lead compound showed dramatically improved protease resistance and was able to efficiently deliver a biologically relevant cargo inside cells. This study provided a simple strategy to convert short peptide sequences into efficient protease-resistant cell-penetrating foldamers.

A General Approach to the Aza-Diketomorpholine Scaffold

Organic Letters, 2017, Volume: 19, Issue: 3, Pages: 492-495, DOI: 10.1021/acs.orglett.6b03656

M. Berthet, B. Legrand, J. Martinez, I. Parrot


A stereoconservative three-step synthesis to access to 1,2,4-oxadiazine-3,6-dione is presented. This underexplored platform could be considered as a constrained oxy-azapeptide or an aza-diketomorpholine, the methodol. being then successfully applied to produce enantiopure aza-analogs of diketomorpholine natural products. Importantly, the 1st crystal structures were obtained and compared to diketomorpholine and diketopiperazine structures. Finally, a straightforward procedure concerning the coupling of this heterocyclic scaffold with various amino acids to afford original pseudodipeptide analogs was described.

A switchable stapled peptide

Journal of Peptide Science, 2016, Volume: 22, Issue: 3, Pages: 143-148, DOI: 10.1002/psc.2851

A. Kalistratova, B. Legrand, P. Verdie, E. Naydenova, M. Amblard, J. Martinez, G. Subra


The O-N acyl transfer reaction has gained significant popularity in peptide and medicinal chem.  This reaction has been successfully applied to the synthesis of difficult sequence-contg. peptides, cyclic peptides, epimerization-free fragment coupling and more recently, to switchable peptide polymers.  Herein, we describe a related strategy to facilitate the synthesis and purifn. of a hydrophobic stapled peptide.  The staple consists of a serine linked through an amide bond formed from its carboxylic acid function and the side chain amino group of diaminopropionic acid and through an ester bond formed from its amino group and the side chain carboxylic acid function of aspartic acid.  The α-amino group of serine was protonated during purifn.  Interestingly, when the peptide was placed at physiol. pH, the free amino group initiated the O-N shift reducing the staple length by one atom, leading to a more hydrophobic stapled peptide.

Selective homodimerization of unprotected peptides using hybrid hydroxydimethylsilane derivatives

RSC Advances, 2016, Volume: 6, Issue: 39, Pages: 32905-32914, DOI: 10.1039/C6RA06075G

C. Echalier, A. Kalistratova, J. Ciccione, A. Lebrun, B. Legrand, E. Naydenova, D. Gagne, J. A. Fehrentz , J. Marie, M. Amblard, A. Mehdi, J. Martinez, G. Subra 


We developed a simple and straightforward way to dimerize unprotected peptide sequences that relies on a chemoselective condensation of hybrid peptides bearing a hydroxydimethylsilyl group at a chosen position (either C-ter, N-ter or side-chain linked) to generate siloxane bonds upon freeze-drying. Interestingly, the siloxane bond sensitivity to hydrolysis is strongly pH-dependent. Thus, we investigated the stability of siloxane dimers in different exptl. conditions. For that purpose, 29Si, 13C and 1H NMR spectra were recorded to accurately quantify the ratio of dimer/monomer. More interestingly, we showed that 1H resonances of the methylene and Me groups connected to the Si can be used as sensitive probes to monitor siloxane hydrolysis and to det. the half-lives of the dimers. Importantly, we showed that the dimers were rather stable at pH 7.4 (t1/2 ≈ 400 h) and we applied the dimerization strategy to bioactive sequences. Once optimized, three dimers of the growth hormone releasing hexapeptide (GHRP-6) were prepd. Interestingly, their pharmacol. evaluation revealed that the activity of the dimeric ligands could be switched from agonist to inverse agonist depending on the position of dimerization.