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Issue 5, 2020
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Elusive π-helical peptide foldamers spotted by chiroptical studies

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A series of oligomers containing alternate L-Ala and pGlu (pyroglutamic acid) both in the L and D form have been prepared and conformationally investigated by X-ray, NMR, UV/ECD, IR/VCD and molecular modelling. X-ray diffraction analysis was possible for the shortest oligomers LL-1 and LD-1. Molecular dynamics simulations of the oligomers demonstrated that the energy landscapes of the LL-series are broad. In contrast, the energy landscapes of the LD-series are characterized by well-defined minima corresponding to specific conformational structures. A single well-defined minimum exists in the energy landscape of the largest oligomer LD-8, corresponding to a precise conformation, characterized by i + 5 → i N–H⋯O[double bond, length as m-dash]C hydrogen bonds, typical of a π-helix. ECD and VCD spectra were measured to identify the chiroptical profiles of the oligomers. The most striking element in the ECD spectra of the LD-series is their exceptionally strong intensity, which confirms that these polypeptides attain a high degree of helical order. VCD spectra for the LD-series are well reproduced by frequency calculations when π-helix folds are employed as input structures, suggesting that a symmetrical VCD couplet around 1720 cm−1 can be taken as the VCD signature of π-helices.

Graphical abstract: Elusive π-helical peptide foldamers spotted by chiroptical studies

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Article information

25 Oct 2019
10 Dec 2019
First published
10 Dec 2019

Org. Biomol. Chem., 2020,18, 865-877
Article type

Elusive π-helical peptide foldamers spotted by chiroptical studies

S. Di Silvio, F. Bologna, L. Milli, D. Giuri, N. Zanna, N. Castellucci, M. Monari, M. Calvaresi, M. Górecki, G. Angelici, C. Tomasini and G. Pescitelli, Org. Biomol. Chem., 2020, 18, 865
DOI: 10.1039/C9OB02313E

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