Syndyphalins are enkephalin-like synthetic tripeptides with analgesic action 1,2.

Kiso, et al., in 1981, synthesized tripeptide hydroxyalkylamide derivatives in order to obtain more stable and potent ENK analogues and reported that a simple peptide, Tyr-D-Met(O)-Gly-MePheol, named 'syndyphalin(SD)-25' was 23300 times and 9 times as active as morphine in the in vitro assay using guinea pig ileum and in the tail flick analgesic test after administration, respectively 3.

Structural Characteristics
Syndyphalin-33: Tyr-D-Met(O)-Gly-MPA; (Tyr-D-Met(O)-Gly-N-methylphenethylamide;Syndyphalin-25: Tyr-D-Met (O)-Gly-MePheol.

Mode of Action
The ability of naloxone to block SD33-stimulated growth hormone (GH) secretion suggests that this peptide acts via µ­opiate receptors 1.

A simple tripeptide alkylamine, syndyphalin 33 (SD33, Tyr-DMet (O)-Gly-methylphenethylamide) was shown to stimulate GH secretion in sheep, hogs and rats following peripheral administration 1.SD-25 possesses potent central nervous system actions closely similar to those of morphine, but its effect on blood pressure and respiration is weaker than that of morphine 2.



1.      Nakamura H, Kiso Y, Motoyoshi S, Yoshida N, Ishii K, Yokoyama Y, Kadokawa T, Shimizu M (1982). Analgesic and other pharmacological activities of an enkephalin analogue, syndyphalin (SD)-25. Eur J Pharmacol., 85(2):133-142.

2.      Buonomo FC, Tou JS, Kaempfe LA (1991). Stimulation of somatotropin secretion following peripheral administration of the tripeptide, syndyphalin 33 in sheep, pigs and rats. Life Sci., 48(20):1953-1961.

3.      Kiso Y, Yamaguchi M, Akita T, Moritoki H, Takei M, Nakamura H (1981). Super-active Enkephalin Analogues.Simple Tripeptide Hydroxyalkylamides Exhibit Surprisingly High and Long-lasting Opioid Activities. Naturwissenschaften, 68(4):210-212.

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