Abstract
Conformations of two pairs of dehydropeptides with the opposite configuration of the Delta Phe residue, Boc-Gly-Delta(z)Phe-Gly-Phe-OMe (Z-OMe), Boc-Gly-Delta(E)Phe-Gly-Phe-OMe (E-OMe), Boc-Gly-Delta(z)Phe-Gly-Phe-p-NA (Z-p-NA), and Boc-Gly-Delta(E)Phe-Gly-Phe-p-NA (E-p-NA) were compared on the basis of CD and NMR studies in MeOH, trifluoroethanol (TFE), MeCN, chloroform, and dimethylsulfoxide (DMSO). The CD results were used as the additional input data for the NMR-based determination of the detailed solution conformations of the peptides. It was found that E-OMe is unordered and Z-OMe, Z-p-NA, and E-p-NA adopt the beta-turn conformation. There are two overlapping beta-turns in each of those peptides: type II and type III' in Z-OMe and Z-p-NA, and two type III in E-p-NA. The ordered structure-inducing properties of Delta(z)Phe and Delta(E)Phe in the peptides studied depend on the C-terminal blocking group. In methyl esters, the Delta(z)Phe residue is a strong inducer of ordered conformations whereas the Delta(E)Phe one has no such properties. In p-nitroanilides, both isomers of Delta Phe cause the peptides to adopt ordered structures to a similar extent. (C) 2010 Wiley Periodicals, Inc. Biopolymers 93: 1055-1064, 2010.