Conformational studies on peptides having chiral five-membered ring amino acid with two azido or triazole functional groups within the sequence of Aib residues

The chiral cyclic α,α-disubstituted α-amino acid, (3R,4R)-1-amino-3,4-diazido-1-cyclopentanecarboxylic acid [(R,R)-Ac5cdN3], was introduced into achiral α-aminoisobutyric acid (Aib) peptides. The azido groups of (R,R)-Ac5cdN3 in the peptides were efficiently converted into 1,2,3-triazole functional groups. FTIR, 1H NMR, and CD spectra revealed that the dominant conformations of all peptides in solution were 310-helical structures without controlling the helical-screw sense. X-ray crystallographic analyses of peptides containing (R,R)-Ac5cdN3 showed that both the right-handed (P) and left-handed (M) 310-helical structures were present in the crystal state