Human proinsulin, VIII: studies on the S-tritylation of reduced proinsulin, insulin A and B chains and their detritylation.

Reduced proinsulin and insulin A and B chains were selectively and quantitatively converted to hexa(S-trityl)proinsulin, tetra(S-trityl)A chain and di(S-trityl)B chain. These derivatives were used as models to investigate the quantitative removal of S-trityl groups. Amongst the various detritylation methods studied, the best procedure was found to be acidolytic cleavage with trifluoroacetic acid in the presence of thiophenol or benzylmercaptan as cation scavengers. The detritylated derivatives, upon oxidative sulphitolysis, yielded electrophoretically homogeneous hexa(S-sulphonate)proinsulin, tetra(S-sulphonate)A chain and di(S-sulphonate)B chain. The hexa(S-sulphonate)proinsulin was reduced and reoxidized to proinsulin.