Method of conjugating oligopeptides

Claim 1

An improved method for preparing a polypeptide product capable of forming a peptide bond in an aqueous medium, said method being of the type wherein an oligopeptide is formed by the sequential addition of amino acids to an initial amino acid which is bound to a 4-alkoxybenzyl alcohol resin or chloromethyl resin through an ester linkage, said improvement comprising: reacting a cyclic carboxylic acid anhydride with an available amino group on the oligopeptide to form an amic acid to provide a single free reactive carboxyl group on said oligopeptide; esterifying said carboxyl group with an hydroxyl compound selected from the group consisting of 4-hydroxy-3-nitrobenzenesulfonic acid salt, pentachlorophenol, N-hydroxy succinimide, and p-nitrophenol to provide an activated ester stable to cleavage of the oligopeptide from the resin and capable of forming a peptide bond in an aqueous medium; cleaving said oligopeptide from said resin employing hydrofluoric acid or trifluoroacetic acid in an inert organic solvent to provide a mixture of said resin and said oligopeptide in an acid solution; neutralizing said acid solution to a mildly basic pH in the absence or presence of a peptide having an available amino group, whereby said oligopeptide reacts either (1) intramolecularly or intermolecularly with itself or (2) with said amino containing peptide to form a peptide bond.