Synthesis and pharmacological properties of [1-L-penicillamine,4-L-leucine]oxytocin

For the synthesis of [1-L-penicillamine,4-L-leucine]oxytocin (2), Z-Tyr(Bzl)-Ile-Leu-Asn-Cys(Bzl)-Pro-Leu-Gly-NH2 was treated with anhydrous HBr, and the resulting partially deprotected octapeptide was coupled with Z-penicillamine(Bzl) in a condensation reaction mediated by dicyclohexylcarbodiimide and 1-hydroxybenzotriazole. The protected nonapeptide Z-penicillamine(Bzl)-Tyr-Ile-Leu-Asn-Cys(Bzl)-Pro-Leu-Gly-NH2 was treated with Na in NH3 and the resulting disulfhydryl compound was subjected to oxidative cyclization in H2O-CH3OH with ICH2CH2I, Purification of 2 was effected by partition chromatography and gel filtration. The analog possesses antioxytocic and antiavian vasodepressor pA2 values of 6.77 and 7.21, respectively, and has no antipressor or anti-ADH activity. Its biological activity spectrum is qualitatively identical with that of [1-penicillamine]oxytocin. In contrast to the marked natriuretic-diuretic and anti-antidiuretic activity of [Leu4]oxytocin, 2 exhibits none of these effects on the rat kidney.