PEPTIDE-SYNTHESIS IN WATER AND THE USE OF IMMOBILIZED CARBOXYPEPTIDASE-Y FOR DEPROTECTION

We report here a method for peptide synthesis in aqueous systems in which coupling and deblocking are carried out at pH 6 and 8.5, respectively (Scheme I). Water-soluble carbodiimide and amino acid ethyl esters are used to elongate the chain from the carboxyl end (Scheme II). The removal of the ethyl ester blocking group is accomplished by treatment with immobilized carboxypeptidase Y (CPY) at pH 8.5 and room temperature. The bound enzyme is removed by filtration and the filtrate used directly for the addition of the next amino acid. Peptides were grown on carboxymethyl-poly(ethylene glycol)-glycylmethionine (CM-PEG-Gly-Met). The use of this handle provides solubility for the growing chain and permits facile release of finished peptide using CNBr.1 The advantages of a polymeric handle have been pointed out by Mutter et al., who used underivatized PEG in synthesis of peptides by extension of the amino terminus in organic solvents.2 The preparation of chemically and optically pure H-Leu-Phe-Leu-OEt is illustrated below. © 1979, American Chemical Society. All rights reserved.