N-Benzhydryl-glycolamide: the first protecting group in peptide synthesis with a strong conformational bias

We have synthesized and examined the preferred conformation of a set of N-benzhydrylglycolamide esters from N-alpha-protected (or N-alpha-blocked) alpha-amino acids. Experiments were performed in CDCl3 solution by Fourier transform infrared absorption and H-1-NMR techniques, and in the crystalline state by x-ray diffraction. The results of our analysis strongly support the view that this type of N-alpha-acylated alpha-aminoacyl esters has a marked tendency to fold into a beta-turn conformation, the nature of which is dictated by the structural propensity of the amino acid constituent at the i + 1 position.