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Turn stabilization in short peptides by Cα-methylated α-amino acids

✍ Scribed by Marco Crisma; Alessandro Moretto; Marta De Zotti; Fernando Formaggio; Bernard Kaptein; Quirinus B. Broxterman; Claudio Toniolo

Publisher
Wiley (John Wiley & Sons)
Year
2005
Tongue
English
Weight
418 KB
Volume
80
Category
Article
ISSN
0006-3525

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✦ Synopsis

Abstract

The crystal‐state conformations of three protected tripeptides, four tetrapeptides, and one pentapeptide, heavily based on the chiral C^α^‐methylated α‐amino acids Iva, (αMe)Nva, and (Me)Val, were assessed by X‐ray diffraction analyses. The eight peptide sequences are as follows: Z(DIva)~2~DValOMe, ZDIvaLIvaGlyO__t__Bu, ZLProDIvaLIvaGlyO__t__Bu, ZLProLIvaDIvaGlyO__t__Bu, ZAib[L(αMe)Nva]~2~O__t__Bu, Ac[L(αMe)Val]~3~D(αMe)ValO__t__Bu, Z[L(αMe)Val]~4~OH, and ZLAla[L(αMe)Nva]~4~O__t__Bu. Two independent molecules were observed in the asymmetric units of ZDIvaLIvaGlyO__t__Bu and ZAib[L(αMe)Nva]~2~O__t__Bu, while three independent molecules were seen in ZLAla[L(αMe)Nva]~4~O__t__Bu. All peptides are folded in a single or multiple β‐turn conformations. Interestingly: (i) a water bridge within the N‐terminal β‐turn is seen in ZLProLIvaDIvaGlyO__t__Bu (dihydrate), and (ii) the hydroxyl group of the C‐terminal carboxyl functionality of Z[L(αMe)Val]~4~OH generates an oxy‐analogue of a β‐turn. The N‐terminal β‐turn is missing in molecules A and B, but it does occur, although poorly stabilized, in molecule C, of ZLAla[L(αMe)Nva]~4~O__t__Bu. © 2004 Wiley Periodicals, Inc. Biopolymers (Pept Sci), 2005

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