The Synthesis of [1-Deamino,4-L-leucine]-oxytocin and [1-Deamino,4-L-isoleucine]-oxytocin and Some of Their Pharmacological Properties

[1-Deamino,4-L-leucine]-oxytocin and [1-deamino,4-L-isoleucine]-oxytocin have been synthesized by the solid phase method, and some of their pharmacological properties have been determined. [1-Deamino,4-L-leucine]-oxytocin was also synthesized by the p-nitrophenyl ester stepwise procedure and compared to that synthesized by the solid phase method. The two preparations were found to be identical. The oxytocic and avian vasodepressor potencies of [1-deamino,4-L-leucine]-oxytocin and [1-deamino,4-L-isoleucine]-oxytocin are two- to threefold higher than those of [4-L-leucine]-oxytocin and [4-L-isoleucine]-oxytocin respectively. The two deamino analogs also exhibit milk-ejecting activities of approximately 150 units/mg. Neither analog possesses appreciable pressor or antidiuretic activity. A similar enhancement of oxytocic and avian vasodepressor activities had been observed when the free amino group of [4-L-valine]-oxytocin was replaced by hydrogen.