Opiate-like peptides. Part XII. Synthesis and some biological properties of Met-enkephalin analogues modified in position 2 by D-alanyl residue in positions 2 and 4 by 3-(2-naphthyl)-D-alanyl residue.

: Nine Met-enkephalin analogues containing D-alanyl residue in position 2 and/or 3-(2-naphthyl)-D-alanyl residue in positions 2 and 4 have been obtained. Their biological activity has been determined after intracerebroventricular administration to rats. Almost all compounds appeared strongly toxic causing the death of the animals. Only [D-2-Nal2,4, Met5-OMe]--enkephalin exerted an analgesic effect after the administration in the form of fine suspension.