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

Nuclear magnetic resonance (NMR) spectroscopy has been established as a potent method for the determination of foldamer structures in solution. However, the NMR techniques could be limited by averaging, so additional experimental techniques are often needed to fully endorse the folding properties of a sequence. We have recently demonstrated that oligo-γ-peptides composed of 4-amino(methyl)-1,3-thiazole-5-carboxylic acids (ATCs) adopt an original helical fold stabilized by hydrogen bonds forming C9 pseudocycles. The main objective of the present work is to reinvestigate the folding of ATC oligomer 1 in order to identify reliable FT-IR and NMR structural markers that are of value for tracking the degree of organization of ATC-based peptides.

[Substituted cyclodextrins: an example of biomimetic catalyzers]. / Les cyclodextrines substituées: un exemple de catalyseurs biomimétiques.

Among all molecules used to develop biomimetic catalysts, cyclodextrins are extremely attractive compounds. These oligosaccharides can form inclusion complexes with various organic substrates and in particular with organophosphorus poisons, which are widely used as chemical weapons and insecticides. Soman, a frightening neurotoxic agent, once "trapped" in the internal cavity of beta-cyclodextrin can moreover undergo the nucleophilic attack of an oligosaccharide hydroxyl group, miming the first step of the enzymatic process. Selective substitution of beta-cyclodextrin by a 2-iodosobenzoic acid derivative has enabled effective synthesis of scavangers against organophosphorus compounds. Hydrolysis trials were carried out with paraoxon, as an organophosphorus model. The OP-hydrolyzing activity could reach more than two order of magnitude compared with free 2-iodosobenzoïc acid. Nevertheless, hydrolysis of paraoxon showed saturation kinetics. Although the activity was strongly dependent on the relative position of the reactive group, these results showed the interest of a strategy, resulting in the "trapping" of the organophosphorus substrate in the internal cavity of the oligosaccharide in order to maintain it near the catalytic function.