Theoretical conformational analysis of enkephalin analogues related to fluorescence and n.m.r. measurements in aqueous solution

Abstract

The properties related to non-radiative energy transfer of a number of enkephalin analogues with tryptophan substituted for phenylalanine in position 4 and n.m.r. 3JNH-C alpha H coupling constants of corresponding [Phe4]-enkephalin analogues are being derived from semi-empirical conformational energy. The molecules considered contain a glycyl, a D-alanyl or an L-alanyl as second residue; two of the compounds are N-methylated at position 4 or 5. The [Trp4]-enkephalin analogues and the corresponding [Phe4]-enkephalin analogues display nearly parallel affinities in the opiate receptor binding assay (Schiller et al. (1). The comparison of computed and experimental properties shows that an ensemble of conformers is a satisfactory representation of the state of these molecules in water.