An improved synthesis of crystalline mammalian glucagon.

Mammalian glucagon was synthesized by the stepwise solid-phase method using several improvements developed in recent years. Peptide was assembled on a 4-(oxymethyl)phenylacetamidomethyl-copoly(styrene-divinyl benzene) resin support with N alpha-t-butoxycarbonyl and benzyl-based side-chain protection for most of the trifunctional amino acids. Crude synthetic glucagon was obtained in 75% yield by deprotection and cleavage from the resin with a new modified HF procedure. Pure material was isolated in 48% overall yield by a one-step purification on preparative C18 reverse-phase chromatography. It was crystallized from aqueous solution at pH 9.2. The synthetic glucagon activated adenylate cyclase in rat liver membranes in the same manner as natural glucagon, with both achieving half-maximum activation at a concentration of 7 nM.