Influence of solvent and configuration of residues at positions 2 and 3 on distance and mobility of pharmacophore groups at positions 1 and 4 in cyclic enkephalin analogues.

The analgesic activity of opioid peptides is mainly connected with their affinity and selectivity for the mu-receptors. The biological activity of cyclic opioid analogues depends on mutual orientation and conformational freedom of aromatic pharmacophore groups at positions 1 and 4. The distance and distance distributions between chromophores at positions 1 [Phe(p-NO(2)), p-nitrophenylalanine] and 4 [Nal, beta-(2-naphthyl)alanine], which constitute an energy donor-acceptor pair, were calculated based on measured fluorescence intensity decays of a donor (Nal). The influence of the solvent and configuration of the residues at position 2 and 3 on donor-acceptor distance distribution and mobility of pharmacophore groups at position 1 and 4 in cyclic enkephalin analogues are discussed.