Original endomorphin-1 analogues exhibit good analgesic effects with minimal implications for human sperm motility.

To search a novel analgesic characterizes the effects on human sperm motility as minimal as possible. A new class of endomorphin-1 (EM-1) analogues was synthesized by combining successful chemical modifications including N-terminal guanidino modification, Phe was chlorinated, replaced of l-Pro-Trp by d-Ala-Gly or d-Pro-Gly at position 2 and 3. Their bioactivities were measured by radioligand binding assay, metabolic stability, antinociception activity and sperm motility effects.

Original endomorphin-1 analogues exhibit good analgesic effects.

A new class of endomorphin-1 analogues was synthesized by combining successful chemical modifications including N-terminal guanidino modification, Phe was chlorinated, D-Ala-Gly Substituted L-Pro. Their bioactivities were measured by radioligand binding assay, metabolic stability and the tail-flick test. In radioligand binding assays, analogue GAGPC (N-Amidino-Tyr-D-Ala-Gly-Trp-p-Cl-Phe-NH), shown a μ-opioid receptor affinity about 1.