N-Methyl peptides: VII. Conformational perturbations induced by N-methylation of model dipeptides

摘要: The natural occurrence of N-methyl peptides in various plant metabolites has made N-methylation a subtle and attractive possible modification for structure-activity relationship studies endogeneous peptides. However, little is known about the conformational specificity induced by given peptide, particularly concerning β-turn conformation. A spectroscopic investigation (i.r., n.m.r., CD) X-ray diffraction experiments have been carried out on tBuCO-X-Me-Y-NHMe blocked dipeptides (X = Gly, L-Ala, L-Pro, Y L- or D-Ala, Leu, Phe) with reference to homologous desmethylated species. influence conformation depends large extent chirality X residues. Homochiral sequences are most affected, strong preference βVI-folded containing middle cis amide bond. Heterochiral essentially unaffected retain βII-folded trans Glycine-containing undergo more complex perturbation according position Gly residue. available data larger consistent our observations, suggesting that these simple well reflect perturbations