Conformational features of benzoyl N-alkylated amino-acids (N-alkylated benzamido-acids) determined by nuclear magnetic resonance spectroscopy

Abstract

cis–trans Rotational isomerism about the benzoyl amide bond has been detected in a series of N-alkylated benzamido-acids. The proportions of cis–trans rotamers appear to be different for N-methylvaline and N-methylisoleucine when compared with other imino-acids studied. A singlet peak for the aromatic protons in the ¹H n.m.r. spectra of a number of derivatives, shows that the ortho-protons are not deshielded and that conjugation between the benzene ring and the amide group is reduced because of the steric environment created by N-alkylation of the amide. U.v. measurements also confirm this phenomenon.