| Abstract: | In the proposed biologically active conformation of vasopressin at its antidiuretic receptor, the side-chain carboxamide moiety of the 5-position asparaginyl residue has been suggested to be an active element for the initiation of the antidiuretic response. [5-Aspartic acid] arginine vasopressin, the analog in which the -NH2 portion of the primary amide has been replaced by an -OH group, has been synthesized and tested for some of the pharmacological activities of vasopressin. The partially protected nonapeptide intermediate was assembled bidirectionally on a poly-N-acrylylpyrrolidine resin. The 6-position cysteinyl residue was attached to the resin via its side-chain through an S-carbamoyl linkage. First the COOH-terminus was extended by coupling with Pro-Arg(Tos)-Gly-NH2, then the NH2-terminus was extended in a stepwise manner. [5-Aspartic acid] arginine vasopressin was found to possess 86.5 ± 4.8 units/mg of antidiuretic potency, 17% of the parent hormone. In addition, the analog possesses rat pressor and rat uterotonic potencies of 6.93 ± 0.15 and 0.38 ± 0.03 units/mg, respectively. This result suggests that a carboxylic acid moiety on the 5-position aspartyl residue retains sufficient steric features and hydrophilicity in common with the carboxamide moiety present in the hormone to substitute for it as an active element at the antidiuretic receptor. |
