β‐ENDORPHIN: SYNTHESIS OF ANALOGS WITH EXTENSION AT THE CARBOXYL TERMINUS WITH HIGH RADIORECEPTOR BINDING ACTIVITY

Abstract
Four analogs of human β-endorphin (βh-EP) have been synthesized: [Gly31]-βh-EP-Gly-NH2, [CH3(CH2)4NH312]-βh-EP, [Gly31]-βh-EP-Gly-Gly-NH2, and [Gln8, Gly31]-βh-EP-Gly-Gly-NH2. All are more active than βh-EP in an opiate receptor binding assay. Stepwise extension at the COOH-terminus shows a progressive increase in binding activity. The last analog, which combines extension at the COOH-terminus with elimination of the remaining anionic charge in βh-EP, is nine times more active than the parent molecule.