Molecular mechanics (MM3) study of the conformations of methyl esters and N,N-dimethylamides of diastereoisomeric 4-cyano-3,4-diphenyl-butanoic acids

Molecular mechanics (MM3 force field) was used to examine an unexpected observation by NMR for a preference of conformations with synclinal protons around the C(3)-C(4) bond in methyl esters and dimethylamides of diastereoisomeric 4-cyano-3,4-diphenyl-butanoic acids. After the reoptimization of three torsional parameters, related to structural units containing a cyano group, we obtained a good correlation between the MM3 computed populations of the conformations and the estimates from vicinal coupling constants. The electrostatic interactions have the decisive contribution for lowering the energies of the preferred conformations. (C) 3000 Elsevier Science B.V. All rights reserved.