Synthesis and some pharmacological properties of [3-.beta.-(2-thienyl)-L-alanine]-8-lysine-vasopressin

Abstract

[3-beta-(2-Thienyl)-L-alanine]-8-lysine-vasopressin was synthesized by solution techniques. The partially protected heptapeptide Boc-Cys(Ec)-Tyr-Thi-Gln-Asn-Cys(Ec)-Pro (1) was synthesized in a stepwise manner using the active ester method or the dicyclohexylcarbodiimide (DCC) coupling technique mediated by 1-hydroxybenzotriazole (HBt). The protected nonapeptide amide Boc-Cys(Ec)-Tyr-Thi-Gin-Asn-Cys(Ec)-Pro-Lys(Coc)-Gly-NH2 (2) was prepared by coupling 1 with Lys(Coc)-Gly-NH2 using DCC-HBt. From 2, [3-thienylalanine]-8-lysine-vasopressin was obtained by removing the Boc-protecting groups with trifluoroacetic acid and ethylcarbamoyl (Ec) protecting groups in refluxing liquid NH3 followed by oxidative cyclization in H2O-MeOH using ICH2CH2I. Purification was effected by partition chromatography followed by gel filtration. The highly purified product possesses activities in the oxytocic, avian vasodepressor, rat pressor, and antidiuretic assays of 19.0 +/- 0.5, 87 +/- 4, 243 +/- 5, and 332 +/- 32 units/mg, respectively. Thus [3-thienylalanine]-8-lysine-vasopressin has higher oxytocic, avian vasodepressor, and antidiuretic potencies than does 8-lysine-vasopressin, whereas its pressor potency is about the same as or slightly lower than that of 8-lysine-vasopressin.