Joseph Diaz

A large-scale synthesis of somatostatin for clinical use by a novel alternating solution/solid-phase procedure☆

Abstract A large-scale synthesis of somatostatin was developed. A stepwise C → N approach in solution was used, employing N (α)-t-butoxycarbonyl amino acid active esters. The scheme of semipermanent protection utilized 2-(methylsulfonyl)-ethoxycarbonyl for the e-amino group of lysine; acetamidomethyl for the β-thiol groups of cysteine; the orange-colored 2-[4-(phenylazo)-phenylsulfonyl]-ethoxy group for the C-terminal carboxy group of cysteine. All condensations and N (α)-deprotections were carried out in homogeneous solution, while isolation and purification of peptides carrying the colored group was achieved by precipitation and washing of the solid products. Thus, the “alternating solution/solid-phase peptide synthesis” combines advantages of both the classical solution synthesis and the Merrifield solid-phase technique. The overall yield was 5%, or 16 g of somatostatin from 100 g of the novel amino acid derivative, N (α)-t-butoxycarbonyl- S -acetamidomethyl- l -cysteine 2-[4-(phenylazo)-phenylsulfonyl]-ethyl ester. An improved method for the preparation of S -acetamidomethyl- l -cysteine, free of thiazolidine carboxylic acid, is described.