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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

The peptide Boc‐Val1‐ΔPhe2‐Leu3‐Ala4‐ΔPhe5‐Ala6‐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 310‐helix, with average (ϕ, ψ) values (−67.7°, −22.7°), unwound at the C‐terminus. The 1H NMR results also suggest that the peptide maintains its 310‐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 ΔPhe5 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 CH3···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.