Studies on analgesic oligopeptides. IV. Synthesis and analgesic activity of N-terminal shorter analogs of (D-Arg2)dermorphin and des-Tyr1-dermorphin analogs.

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Abstract
Des-Tyr1-dermorphin, des-Tyr1-[D-Arg2]dermorphin, and the N-terminal di-, tri-, tetra- and hexapeptide amides of [D-Arg2]dermorphin were synthesized by a conventional solution method and their analgesic activities were assayed by means of the tail pressure test after subcutaneous administration (s.c.) to mice. The des-Tyr1 analogs of both dermorphin and [D-Arg2]dermorphin did not show analgesic activity even at a dose of up to 50 mg/kg, s.c. The N-terminal tetrapeptide amide, H-Tyr-D-Arg-Phe-Gly-NH2, showed extremely potent activity, being 31 times more active than morphine on a molar basis, whereas the N-terminal tri- and dipeptide amides showed no activity seen at a dose of up to 40 mg/kg, s.c.