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Article Dans Une Revue New Journal of Chemistry Année : 2013

Homooligomers of substituted prolines and beta-prolines: syntheses and secondary structure investigation

Fabrice Chemla

Résumé

Homooligomers of enantiomerically pure (2S,3R)-3-methyl-proline, (3R,4R)-4-methyl-beta-proline and (3R,4S)-3,4-dimethyl-beta-proline were synthesized and studied using circular dichroism (CD) in water, methanol and propanol and using NMR in water. Changes in the far-UV CD spectrum were observed from dimers to hexamers, but little change was observed from hexamers to octa-or nonamers, both in water and methanol. CD and NMR data allowed us to conclude that oligomers of 3-substituted prolines with more than six residues adopt a characteristic PPII secondary structure both in water and aliphatic alcohols. Oligomers of (3R, 4R)-4-methyl-beta-proline bear the same CD signature as non-substituted beta-proline oligomers, suggesting that substitution at position 3 is not sufficient to reduce conformational heterogeneity in beta-proline oligomers. In the case of 3,4-disubstituted-beta-proline oligomers, an atypical signature with an extra negative band at around 225 nm was observed, together with a concentration dependent CD spectrum indicating association properties. Nevertheless, NMR studies of C-13 labelled oligomers of 3,4-disubstituted-beta-prolines revealed a complex mixture of cis-trans conformers even for longer oligomers.
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Dates et versions

hal-01362673 , version 1 (09-09-2016)

Identifiants

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Cécile Caumes, Nicolas Delsuc, Redouane Beni Azza, Isabelle Correia, Fabrice Chemla, et al.. Homooligomers of substituted prolines and beta-prolines: syntheses and secondary structure investigation. New Journal of Chemistry, 2013, 37 (5), pp.1312-1319. ⟨10.1039/c3nj00127j⟩. ⟨hal-01362673⟩
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