β‐Endorphin: synthesis and properties of analogs modified in positions 8 and 31

Abstract

Four analogs of human β‐endorphin (βh‐EP) were synthesized by the solid‐phase method: [Gln8.31]‐βh‐EP(I), [Arg8, Gln31] ‐βh‐EP(II), [Ala8, Gln31] ‐βh‐EP (III), and [Val8, Gln31]‐βh‐EP(IV). Radioreceptor binding assay with use of tritiated βh‐EP as primary ligand gave relative potencies as follows: βh‐EP, 100; I, 200; II, 150; III, 150; IV, 120. Relative potencies in an analgesic assay were: βh‐EP, 100; 1,236; II, 254;III, 116; IV, 121. The side‐chain of Glu‐8 in βh‐EP can be replaced by a variety of structures without diminishing biological activity.