Cyclization

Abstract

The protected peptide amide, 1-desamino-S,S’-diacetamidomethyl-oxytocein [1] (115 mg, 0.10 mmol) is dissolved in 75% aqueous methanol (600 ml) and a solution of iodine (64 mg, 0.25 mmol) in methanol (150 ml) is added, with stirring, during one hour [2]. After four more hours at room temperature the solution is concentrated in vacuo at a bath temperature of 30 °C to about 25–30 ml. The concentrated solution is filtered through a Sephadex G10 column: elution of the peptide is monitored by u.v. absorption at 275 nm. The peptide is further purified by countercurrent distribution in the solvent system n-butanol-toluene −0.05% acetic acid (3:2:5) [3]. The target compound migrates with a K value of 0.5. It is recovered by concentration of the solution in vacuo and liophilization of the concentrated solution: 55 mg. Crystallization from water (2 ml) in the presence of a trace of acetic acid affords the trihydrate (34 mg; 32.5%) melting at 174–175 °C; [a]_D−90° (c 0.5, 1 M AcOH). It is homogeneous in chromatography on thin layer plates of silica gel, Rf 0.35 (nbutanol-acetic acid-water, 4:1:1); Rf 0.43 (chloroform-methanol, 1:1). Correct values are obtained on elemental analysis and the expected ratios on amino acid analysis. The synthetic peptide has 6001U uterotonic activity per mg.