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Role of a two-residue spacer in an α,β-didehydrophenylalanine containing hexapeptide: crystal and solution structure of Boc-Val-ΔPhe-Leu-Ala-ΔPhe-Ala-OMe

✍ Scribed by Anil K. Padyana; S. Ramakumar; Puniti Mathur; N. R. Jagannathan; V. S. Chauhan

Book ID
105360243
Publisher
John Wiley and Sons
Year
2003
Tongue
English
Weight
152 KB
Volume
9
Category
Article
ISSN
1075-2617

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✦ Synopsis

Abstract

The peptide Boc‐Val^1^‐ΔPhe^2^‐Leu^3^‐Ala^4^‐ΔPhe^5^‐Ala^6^‐OMe has been examined for the structural consequence of placing a two‐residue segment between the ΔPhe residues. The peptide is stabilized by four consecutive β‐turns. The overall conformation of the molecule is a right‐handed 3~10~‐helix, with average (ϕ, ψ) values (−67.7°, −22.7°), unwound at the C‐terminus. The ^1^H NMR results also suggest that the peptide maintains its 3~10~‐helical structure in solution as observed in the crystal state. The crystal structure is stabilized through head‐to‐tail hydrogen bonds and a repertoire of aromatic interactions laterally directed between adjacent helices, which are antiparallel to each other. The aromatic ring of ΔPhe^5^ forms the hub of multicentred interactions, namely as a donor in aromatic C–H···π and aromatic C–H···OC interactions and as an acceptor in a CH~3~···π interaction. The present structure uniquely illustrates the unusual capability of a ΔPhe ring to host such concerted interactions and suggests its exploitation in introducing long‐range interactions in the folding of supersecondary structures. Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd.

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## Abstract The structures of two dehydropentapeptides, Boc–Pro–ΔPhe–Val–ΔPhe–Ala–OMe (**I**) and Boc–Pro–ΔPhe–Gly–ΔPhe–Ala–OMe (**II**) (Boc: __t__‐butoxycarbonyl), have been determined by nuclear magnetic resonance (NMR), circular dichroism (CD), and X‐ray crystallographic studies. The peptide **

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An N a -protected model pentapeptide containing two consecutive DPhe residues, Boc-Leu-DPhe-DPhe-Ala-Phe-NHMe, has been synthesized by solution methods and fully characterized. 1 H-nmr studies provided evidence for the occurrence of a significant population of a conformer having three consecutive, i