[4-(0-methyl)-L-threonine] -oxytocin. Synthesis and uterotonic activity.

[4-(0-methyl)-L-threonine]-oxytocin, a new analogue of neurohypophyseal hormone oxytocin, was synthesized. Its uretonic activity was found to be 150 I. U./mg. The comparison of the potency of [4-(0-methyl)-threonine]-oxytocin with a very active analogue [4-threonine]-oxytocin and low active analogue [4-isoleucine] -oxytocin supports the hypothesis of high uterotonic activity of 4-substituted analogue of oxytocin to be related to the presence of suitably located hydrophilic and lipophilic grouper in the side chain in position 4, and to the proton donor/proton acceptor properties of hydrophilic group.