Synthesis and properties of dermorphin and an analog of beta-endorphin containing the dermorphin sequence

Dermorphin (I) and [D-Ala2, Phe3, Gly4, Tyr5, Pro6]-beta c-EP (II) have been synthesized by the solid-phase method (beta c-EP, camel beta-endorphin). Positions 1 through 7 of II correspond to the sequence of I. Relative potencies of synthetic peptides in the mouse tail-flick test for analgesia by the intracerebroventricular route were: human beta-endorphin, 100; camel beta-endorphin, 164; I, 450; II, 440. The dermorphin was about 670 times more potent than morphine in the assay. Peptide II represents a rare instance where the enkephalin moiety of beta-endorphin has been altered to produce a more potent analgesic.