Cécile Caumes

The click triazolium peptoid side chain: a strong cis-amide inducer enabling chemical diversity.

Access to homogeneous and discrete folded peptoid structures primarily depends on control of the cis/trans isomerism of backbone tertiary amides. This can be achieved by designing specific side chains capable of forming local interactions with the backbone. This is often undertaken at the expense of side-chain diversity, which is a key advantage of peptoids over other families of peptidomimetics. We report for the first time a positively charged triazolium-type side chain that does not compromise diversity and exhibits the best ability reported to date for inducing the cis conformation. The cis-directing effect was studied in N-acetamide dipeptoid model systems and evaluated in terms of K(cis/trans) using NMR spectroscopy in aprotic and protic solvents. Computational geometry optimization and natural bond orbital analysis in combination with NOESY experiments were consistent with a model in which n → π*(Ar) electronic delocalization [from carbonyl (O(i-1)) to the antibonding orbital (π*) of the triazolium motif on residue i] may be operative. In the computational model (gas-phase) and experimentally in CDCl(3), H-bonding between the triazolium C-H proton and the C(i)═O(i) oxygen was also identified and may act cooperatively with the n → π*(Ar) delocalization, resulting in the absence of the trans rotamers in CDCl(3).

Convenient Solution-Phase Synthesis and Conformational Studies of Novel Linear and Cyclic α,β-Alternating Peptoids

The synthesis of a novel family of peptidomimetics composed of linear and cyclic alpha,beta-alternating peptoids is described. Oligomers consisting of up to six peptoid residues (n = 1-3) were synthesized on large scale with use of an efficient iterative solution-phase method and longer oligomers (n = 4, 5) were obtained by the coupling of appropriately protected shorter oligomers. Preliminary conformational studies of these hybrid peptoids are reported.

The tert-butyl side chain: a powerful means to lock peptoid amide bonds in the cis conformation.

The very simple sterically hindered tert-butyl side chain exerts complete control over the peptoid amide geometry which only exists in the cis conformation. It is exemplified in NtBu glycine homo-oligomers and in linear oligopeptoids designed with an alternating cis-trans backbone amide pattern.

Cyclic α,β-Tetrapeptoids: Sequence-Dependent Cyclization and Conformational Preference

The presence of at least one N-Cα branched side chain is crucial for successful cyclization of α,β-tetrapeptoids. The ctct amide sequence revealed in the crystal structure of the 14-membered cyclotetrapeptoid 8 is also the most populated conformation in solution and is reminiscent of the predominant amide arrangement of the 12-membered cyclic tetrapeptides (CTPs).

Synthesis and binding affinities for sst receptors of cyclic peptoid SRIF-mimetics

Mimicking the tetradecapeptide somatostatin through the design of novel non-peptide small molecules is needed for developing analogues with selective or universal affinity for human somatostatin receptors (hsst1–5) and improved pharmacological properties. We report the synthesis and evaluation of the binding potential of the first all-peptoid SRIF (somatotropin release-inhibiting factor) analogues. Cyclic β and mixed α/β tetra- or pentapeptoids were efficiently obtained by macrocyclisation of the corresponding linear peptoids. In vitro competition binding experiments using [125I]-somatostatin were performed on this first generation of peptoids mimicking the SRIF pharmacophore (Phe7-(D)Trp8-Lys9-Thr10). The selectivity profiles of cyclic compounds 1 to 4 were similar with higher affinity for the sst3, sst5 and sst4 receptors and lower potency on sst1 and sst2 subtypes.

1,2,3-Triazolium-Based Peptoid Oligomers

The cis-directing effect of the 1,2,3-triazolium-type side chain was studied on dimeric peptoid models with various patterns: αα, αβ, βα and ββ. Low influences of the sequence and of the solvent were observed, the cis conformation of the amide carrying the triazolium ranging from 83 to 94% in proportion. The synthesis of peptoid homooligomers with four or eight pendant 1,2,3-triazolium side chains is described. α-, β- and α,β-peptoids carrying propargyl groups were subjected to CuAAC reaction using alkyl azides, and the resulting triazoles were quaternized providing well-defined multitriazolium platforms. The influence of the counteranion (PF6-, BF4- or I-) on the conformation was also studied.