Amino acids and peptides. XXII. Preparation and antinociceptive effect of [D-Ala2]Leu-enkephalin-poly(ethylene glycol) hybrid.

The hybrid of poly(ethylene glycol) and [D-Ala2]Leu-enkephalin was prepared by the solution method and its antinociceptive effect and inhibitory effect on the electrically induced contractions of mouse vas deferens were examined. The hybrid was synthesized by the coupling of Boc-Tyr-D-Ala-Gly-Phe-Leu-OH and amino-poly(ethylene glycol), followed by trifluoroacetic acid treatment. The hybrid showed more potent antinociceptive activity in mice and 120 times higher inhibitory activity in mouse vas deferens preparation than intact [D-Ala2]Leu-enkephalin.