Chemical synthesis of [des(tetrapeptide B27--30), Tyr(NH2)26-B] and [des(pentapeptide B26--30), Phe(NH2)25-B] bovine insulins.

Two analogs of bovine insulin, des(tetrapeptide B27--30), Tyr(NH2)26-B] and des(pentapeptide B26--30), Phe(NH2)25-B] insulin, which differ from the parent molecule in that the C-terminal tetrapeptide and pentapeptide sequences, respectively, from the B chain have been eliminated and the newly exposed residues are amidated, have been synthesized. The des(tetrapeptide B27--30), Tyr(NH2)26-B] insulin shows potencies of 16.8 IU/mg by the mouse convulsion assay method and 10.8 IU/mg by the radioimmunoassay method. The des(pentapeptide B26--30), Phe(NH2)25-B] insulin possesses a potency of 10.5 IU/mg when assayed by the mouse convulsion method and 14 IU/mg by the radioimmunoassay technique. The potencies of these analogs are higher than the potencies of the respective non-amidated derivatives (Katsoyannis et al., 1973, 1974). It is speculated that the gradual decline of biological activity observed as amino acid residues are eliminated from the C-terminal region of the B chain of insulin is due to the proximity of a hydrophilic carboxyl group to the hydrophobic core of the protein molecule.