Synthesis and properties of human beta-endorphin-(1-9) and its analogs

Four analogs of human beta-endorphin (beta h-EP) were synthesized by the solid-phase method: beta h-EP-(1-9) (I), [D-Ala2]-beta h-EP-(1-9) (II), [Gln8]-beta h-EP-(1-9) (III), and [D-Ala2, Gln8]-beta h-EP-(1-9) (IV). Measurement in a radioreceptor binding assay with use of tritiated beta h-EP as primary ligand gave relative potencies as follows: Met-enkephalin, 100; I, 76; II, 100; III, 200; IV, 200. Two new amino acid derivatives were prepared and used for synthesis of the analogs: N alpha-t-butyloxycarbonyl-O-(cyclopentyl)-tyrosine and N alpha-t-butyloxycarbonyl-gamma-(cyclopentyl)-glutamic acid.