Tocinoic acid, the 20-membered cyclic disulfide ring of cysteinyltyrosylisoleucylglutaminylasparaginyl-cysteine, which possesses the tocin ring of oxytocin, was synthesized by the stepwise p-nitrophenyl ester method. All protecting groups of the protected intermediate Z-Cys(Bzl)-Tyr-Ile-Gln-Asn-Cys(Bzl)-ONB were removed on addition of this peptide to Na in NH3. The reduced peptide was converted to purified tocinoic acid by oxidation, followed by partition chromatography and gel filtration. Deaminotocinoic acid was synthesized by similar methods. No C-terminal carboxamide derivatives could be detected. Tocinoic acid possessed 0.2–0.3 unit/mg of oxytocic activity and no detectable avian vasodepressor activity, while deaminotocinoic acid had 3.7 ± 0.3 units/mg of oxytocic activity and no detectable avian vasodepressor activity. Deaminotocinoic acid possessed a slight inhibitory effect on the avian vasodepressor activity of synthetic oxytocin.
ASJC Scopus subject areas
- Colloid and Surface Chemistry