Liquid-phase synthesis of naturally occurring peptides, I. Syntheses of leucine-enkephalin and methionine-enkephalin of a p-alkoxybenzyl-modified soluble support.

The liquid-phase synthesis of two pentapeptides corresponding to the amino acid sequence of Leu- and Met-enkephalin is described. Modified monofunctional poly(ethylene glycol) containing a p-alkoxybenzyl alcohol functional group was employed as the soluble polymeric support. Cleavage of the peptides from the polymer, as well as the removal of protecting groups, was achieved with trifluoroacetic acid at room temperature. The free peptides were purified by column chromatography on DEAE-Sephadex, and were identical in both physical and biological characteristics with reference material. The results showed that the proposed support is effective for a mild cleavage of peptides from the soluble polymer during liquid-phase synthesis.