Conformational studies of N‐acetyl‐N′‐methylamide derivatives of α‐aminobutyric acid, norvaline, and valine. II. Conformational energy calculations and comparison with experimental results

Abstract

AbstractConformational analyses on a series of dipeptides CH3—C*O—NH—CH(R)—C*O—HN—CH3 with side chains such as R = CH2CH3, CH2CH2CH3, and CH(CH3)2 are described. Calculations were carried out by using semiempirical potential energy functions of Brant et al. The results were compared with those reported by Vásquez et al. and Chuman et al., who employed the ECEPP program in their analyses. The averages of the vicinal coupling constant J and the side‐chain conformer fractions p(χ1) and p(χ2)′ were estimated therefrom for preferred conformations. The characteristic features of the experimental observations derived from the 1H‐nmr measurements are reasonably well reproduced by these calculations.