Category: foldamers

Can Heterocyclic γ-Peptides Provide Polyfunctional Platforms for Synthetic Glycocluster Construction?

Chemistry. 2018 May 30. doi: 10.1002/chem.201802032

Simon M, Ali LMA, El Cheikh K, Aguesseau J, Gary-Bobo M, Garcia M, Morère A, Maillard LT.


Sugars play key roles in many molecular and cellular communication processes involving a family of proteins named lectins. The low affinity associated with sugar recognition is generally counterbalanced by the multivalent nature of the interaction. While many polyglycosylated architectures have been described, only a few studies focused on the impact of topology variations of the multivalent structures on the interaction with lectin proteins. One major interest of our group concerns the design of new highly predictable and stable molecular pseudo‐peptide architectures for therapeutic applications. In such a context, we described a class of constrained heterocyclic γ‐amino acids built around a thiazole ring, named ATCs. ATC oligomers are helical molecules resulting from the formation of a highly stable C9 hydrogen‐bonding pattern. Following our program, we herein address the potential of ATC oligomers as tunable scaffolds for the development of original multivalent glycoclusters.

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.

Indoloazepinone-Constrained Oligomers as Cell-Penetrating and Blood-Brain Barrier Permeable Compounds

Chembiochem. 2018 Jan 29. doi: 10.1002/cbic.201700678. [Epub ahead of print]

Van der Poorten O, Legrand B, Vezenkov L, Garcia-Pindado J, Bettache N, Knuhtsen A, Sejer Pedersen D, Sanchez-Navarro M, Martinez J, Teixido M, Garcia M, Tourwe D, Amblard M, Ballet S.


Non-cationic and amphipathic indoloazepinone-constrained (Aia) oligomers have been synthesized as new vectors for intracellular delivery. The conformational preferences of the [L-Aia-Xxx]n oligomers were investigated using circular dichroism and NMR spectroscopy. While Boc-[L-Aia-Gly]2,4-OBn 12-13 and Boc-[L-Aia-β3-h-L-Ala]2,4-OBn 16-17 oligomers were totally or partially disordered, Boc-[L-Aia-L-Ala]2-OBn 14 induced a typical turn stabilized by C5- and C7-membered H-bond pseudo-cycles and aromatic interactions. Boc-[L-Aia-L-Ala]4-OBn 15 exhibited a unique structure with remarkable T-shaped pie-stacking interactions involving the indole rings of the four L-Aia residues forming a dense hydrophobic cluster. All the proposed FITC-6-Ahx-[L-Aia-Xxx]4-NH2 oligomers 19-23, with exception of FITC-6-Ahx-[L-Aia-Gly]4-NH2 oligomer 18, were internalized by MDA-MB-231 cells with higher efficiency than the positive references penetratin and Arg8. In parallel, this series of compounds was successfully explored on an in vitro blood-brain barrier (BBB) permeation assay. While no passive diffusion permeability was observed for any of the tested Ac-[L-Aia-Xxx]4-NH2 oligomers in the PAMPA model, Ac-[L-Aia-L-Arg]4-NH2 26 showed significant permeation in the in vitro cell-based human model of the BBB, suggesting an active mechanism of cell-penetration.

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.

12/14/14-Helix Formation in 2:1 α/β-Hybrid Peptides Containing Bicyclo[2.2.2]octane Ring Constraints

Chemistry – A European Journal, 2016, Volume: 22, Issue: 34, Pages: 11986-11990, DOI: 10.1002/chem.201602746

B. Legrand, C. Andre, L. Moulat, C. Didierjean, P. Hermet, J. L. Bantignies, J. Martinez, M. Amblard, M. Calmes 


In the search for new peptide ligands contg. selenium in their sequences, we investigated L-4-selenazolidine-carboxylic acid (selenazolidine, Sez) as a proline analog with the chalcogen atom in the γ-position of the ring.  In contrast to proteinogenic selenocysteine (Sec) and selenomethionine (SeMet), the incorporation within a peptide sequence of such a non-natural amino acid has never been studied.  There is thus a great interest in increasing the possibility of selenium insertion within peptides, esp. for sequences that do not possess a sulfur contg. amino acid (Cys or Met), by offering other selenated residues suitable for peptide synthesis protocols.  Herein, we have evaluated selenazolidine in Boc/Bzl (Boc = tert-butoxycarbonyl) and Fmoc/tBu (Fmoc = 9-fluorenylmethoxycarbonyl) strategies through the synthesis of a model tripeptide, both in soln. and on a solid support.  Special attention was paid to the stability of the Sez residue in basic conditions.  Thus, generic protocols have been optimized to synthesize Sez-contg. peptides, through the use of an Fmoc-Xxx-Sez-OH dipeptide unit.  As an example, a new analog of the vasopressin receptor-1A antagonist was prepd., in which Pro was replaced with Sez [3-(4-hydroxyphenyl)-propionyl-D-Tyr(Me)-Phe-Gln-Asn-Arg-Sez-Arg-NH2].  Both proline and such pseudo-proline contg. peptides exhibited similar pharmacol. properties and endopeptidase stabilities indicating that the presence of the selenium atom has minimal functional effects.  Taking into account the straightforward handling of Sez as a dipeptide building block in a conventional Fmoc/tBu SPPS strategy, this result suggested a wide range of potential uses of the Sez amino acid in peptide chem., for instance as a viable proline surrogate as well as a selenium probe, complementary to Sec and SeMet, for NMR and mass spectrometry anal. purposes.

FT-IR and NMR structural markers for thiazole-based γ-peptide foldamers

Organic & Biomolecular Chemistry, 2016, Volume: 14, Issue: 37, Pages: 8664-8669, DOI: 10.1039/C6OB01594H

C. Bonnel, B. Legrand, J. L. Bantignies, H. Petitjean, J. Martinez, N. Masurier, L. T. Maillard 


In the search of new robust and environmental-friendly anal. methods able to answer quant. issues in pharmacol., we explore liq. chromatog. (LC) assocd. with elemental mass spectrometry (ICP-MS) to monitor peptides in such complex biol. matrixes.  The novelty is to use mass spectrometry to replace radiolabelling and radioactivity measurements, which represent up-to now the gold std. to measure org. compd. concns. in life science.  As a proof of concept, we choose the vasopressin (AVP)/V1A receptor system for model pharmacol. assays.  The capacity of ICP-MS to provide highly sensitive quantitation of metallic and hetero elements, whatever the sample medium, prompted us to investigate this technique in combination with appropriate labeling of the peptide of interest.  Selenium, that is scarcely present in biol. media, was selected as a good compromise between ICP-MS response, covalent tagging ability using conventional sulfur chem. and peptide detection specificity.  Applying selenium monitoring by elemental mass spectrometry in pharmacol. is challenging due to the very high salt content and org. material complexity of the samples that produces polyat. aggregates and thus potentially mass interferences with selenium detection.  Hyphenation with a chromatog. sepn. was found compulsory.  Noteworthy, we aimed to develop a straightforward quant. protocol that can be performed in any lab. equipped with a std. macrobore LC-ICP-MS system, in order to avoid time-consuming sample treatment or special implementation of instrumental set-up, while allowing efficient suppression of all mass interferences to reach the targeted sensitivity.  Significantly, a quantification limit of 57 ng Se L-1 (72 fmol of injected Se) was achieved, the samples issued from the pharmacol. assays being directly introduced into the LC-ICP-MS system.  The established method was successfully validated and applied to the measurement of the vasopressin ligand affinity for its V1A receptor through the detn. of the dissocn. const. (Kd) which was compared to the one recorded with conventional radioactivity assays.

Turning Peptide Sequences into Ribbon Foldamers by a Straightforward Multicyclization Reaction

Angewandte Chemie, International Edition, 2015, Volume: 54, Issue: 47, Pages: 13966-13970, DOI: 10.1002/anie.201506955

V. Martin, B. Legrand, L. L. Vezenkov, M. Berthet, G. Subra, M. Calmes, J-L. Bantignies, J. Martinez, M. Amblard


The conformational control of mol. scaffolds allows the display of functional groups in defined spatial arrangement.  This is of considerable interest for developing fundamental and applied systems in both the fields of biol. and material sciences.  Peptides afford a large diversity of functional groups, and peptide synthetic routes are very attractive and accessible.  However, most short peptides do not possess well-defined secondary structures.  Herein, we developed a simple strategy for converting peptide sequences into structured γ-lactam-contg. oligomers while keeping the amino acids side chain diversity.  We showed the propensity of these mols. to adopt ribbon-like secondary structures.  The periodic distribution of the functional groups on both sides of the ribbon plane is encoded by the initial peptide sequence.

Unprecedented Chain-Length-Dependent Conformational Conversion Between 11/9 and 18/16 Helix in α/β-Hybrid Peptides

Angewandte Chemie, 2014, Volume: 53, Issue: 48, Pages: 13131-13135, DOI: 10.1002/anie.201407329

B. Legrand, C. Andre, L. Moulat, E. Wenger, C. Didierjean, E. Aubert, M. Averlant-Petit, J. Martinez, M. Calmes, M. Amblard


α,β-Hybrid oligomers of varying lengths with alternating proteogenic α-amino acid and the rigid β2,3,3-trisubstituted bicyclic amino acid ABOC residues were studied using both x-ray crystal and NMR soln. structures.  While only an 11/9 helix was obtained in the solid state regardless of the length of the oligomers, conformational polymorphism as a chain-length-dependent phenomenon was obsd. in soln.  Consistent with DFT calcns., short oligomers adopted an 11/9 helix, whereas an 18/16 helix was favored for longer oligomers in soln.  A rapid interconversion between the 11/9 helix and the 18/16 helix occurred for oligomers of intermediate length.

Mixed Oligoureas Based on Constrained Bicyclic and Acyclic β-Amino Acids Derivatives: On the Significance of the Subunit Configuration for Folding

Source: Chemistry – A European Journal, 2013, Volume: 19, Issue: 50, Pages: 16963-16971,  DOI: 10.1002/chem.201302829

C. Andre, B. Legrand, L. Moulat, E. Wenger, C. Didierjean, E. Aubert, M. Averlant-Petit, J. Martinez, M. Amblard, M. Calmes


The combination of a nonfunctionalized constrained bicyclo[2.2.2]octane motif along with urea linkages gave a highly rigid 2.512/14 helical system both in soln. and the solid state.  The authors aimed at developing stable and functionalized systems as promising materials for biol. applications in studying the impact of this constrained motif and its configuration on homo and heterochiral mixed-oligourea helix formation.  Di-, tetra-, hexa-, and octa-oligoureas alternating the highly constrained bicyclic motif of (R) or (S) configuration with acyclic (S)-β3-amino acid derivs. were constructed.  CD, NMR expts., and the x-ray crystal structure of the octamer unequivocally proved that the alternating heterochiral R/S sequences form a stable left-handed 2.5-helix in contrast to the mixed (S/S)-oligoureas, which did not adopt any defined secondary structure.  The (-)-synclinal conformation around the Cα[n.63743]Cβ bond of the acyclic residues, although sterically less favorable than the (+)-synclinal conformation, was imposed by the (R)-bicyclic amino carbamoyl (BAC) residue.  This highlighted the strong ability of the BAC residue to drive helical folding in heterochiral compds.  The role of the stereochem. of the BAC unit was assessed and a model was proposed to explain the misfolding of the S/S sequences.