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Turn stabilization in short peptides by C α ‐methylated α‐amino acids
Author(s) -
Crisma Marco,
Moretto Alessandro,
De Zotti Marta,
Formaggio Fernando,
Kaptein Bernard,
Broxterman Quirinus B.,
Toniolo Claudio
Publication year - 2004
Publication title -
peptide science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.20181
Subject(s) - chemistry , tripeptide , stereochemistry , molecule , pentapeptide repeat , amino acid , peptide , turn (biochemistry) , crystallography , biochemistry , organic chemistry
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 ValOMe, Z D Iva L IvaGlyO t Bu, Z L Pro D Iva L IvaGlyO t Bu, Z L Pro L Iva D IvaGlyO t Bu, ZAib[ L (αMe)Nva] 2 O t Bu, Ac[ L (αMe)Val] 3 D(αMe)ValO 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 IvaGlyO t Bu and ZAib[ 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 IvaGlyO 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