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Issue 5, 2013
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Homooligomers of substituted prolines and β-prolines: syntheses and secondary structure investigation

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Abstract

Homooligomers of enantiomerically pure (2S,3R)-3-methyl-proline, (3R,4R)-4-methyl-β-proline and (3R,4S)-3,4-dimethyl-β-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-β-proline bear the same CD signature as non-substituted β-proline oligomers, suggesting that substitution at position 3 is not sufficient to reduce conformational heterogeneity in β-proline oligomers. In the case of 3,4-disubstituted-β-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 13C labelled oligomers of 3,4-disubstituted-β-prolines revealed a complex mixture of cistrans conformers even for longer oligomers.

Graphical abstract: Homooligomers of substituted prolines and β-prolines: syntheses and secondary structure investigation

  • This article is part of the themed collection: Prolines
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Publication details

The article was received on 06 Nov 2012, accepted on 13 Feb 2013 and first published on 18 Feb 2013


Article type: Paper
DOI: 10.1039/C3NJ00127J
New J. Chem., 2013,37, 1312-1319

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

    C. Caumes, N. Delsuc, R. B. Azza, I. Correia, F. Chemla, F. Ferreira, L. Carlier, A. P. Luna, R. Moumné, O. Lequin and P. Karoyan, New J. Chem., 2013, 37, 1312
    DOI: 10.1039/C3NJ00127J

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