Insulin peptides. XXI. A synthesis of the B chain of sheep (bovine, porcine) insulin and its isolation as the S-sulfonated derivative

Reexamination of sodium-liquid ammonia reduction in the peptide chemistry

Sodium-liquid ammonia reduction has been used for over 50 years for removal of benzyl-type protecting groups in peptide chemistry. Up until now a definitely blue end-point has generally been accepted for detection of the completion of reaction. Systematic investigation with model compounds has revealed that this is not only unnecessary for the complete removal of the protecting groups but also that the application of sodium in excess results in many undesired transformations which can simply be suppressed or even eliminated by optimizing the sodium consumption. Cleavage of tert.-butyloxycarbonyl group and N-C alpha bond, reduction of carboxamide groups to carbinol derivatives, transpeptidation and formation of a hydantoin derivative have been observed in model experiments by using sodium in excess.

Synthesis of human [9-leucine-B] Insulin

The synthesis and isolation in purified form of [Leu9-B]insulin, a biologically active analogue of human insulin, is described. This analogue differs from the parent molecule in that the polar residue, serine, occupying position 9 in the B chain and located on the outside of the insulin molecule, has been replaced with the hydrophobic leucine residue. For the synthesis of this analogue the [Leu9]B chain of human insulin was chemically synthesized by the fragment condensation approach and isolated in the S-sulfonated form. Combination of this compound with the sulfhydryl form of human A chain afforded [Leu9-B]insulin. Separation of this analogue from the combination mixture and isolation as the hydrochloride in purified form were accomplished by chromatography on a carboxymethylcellulose column with an acetate buffer (pH 3.3) and an exponential sodium chloride gradient. [Leu9-B]Insulin possesses a potency of 13-14 IU/mg when assayed by the mouse convulsion method and 11-12 IU/mg by the radioimmunoassay method as compared to 23-25 IU/mg possessed by the natural hormone.