Polypeptides. Part XXI. Synthesis of some sequential macromolecular polypeptolides of L-leucine and L-2-hydroxy-4-methylpentanoic acid

Abstract

Four protected oligopeptolides of L-leucine and L-2-hydroxy-4-methylpentanoic acid, with benzyloxycarbonyl as N-protecting and t-butyl as C-protecting group, have been synthesised; the depside linkage was formed by the action of dicyclohexylcarbodi-imide in ethereal pyridine. The action of triethylamine on the chloride hydrochlorides of the deprotected oligopeptolides gave the macromolecular sequential polypeptolides (I; x= 1, 2, or 3) in 40–45% yield with molecular weights, M_n, of 24,000, 32,000, and 46,000, respectively. An improved method of preparation of L-2-acetoxy-4-methylpentanoic acid from L-leucine is described.