The hexa- and pentapeptide extension of proalbumin. I. Chemical synthesis of serum albumin propeptides.

The proalbumin hexapeptide extension was synthesized beginning from the C-terminal end by stepwise N-terminal peptide chain elongation starting from N-tert-butyloxycarbonyl-(Ng-nitro)arginyl-(Ng-nitro)arginine 4-nitrobenzyl ester; alpha365-12 degrees C (c = 1; dimethylformamide). The other amino acids were incorporated by excess mixed anhydrides of Ddz-amino acids (Ddz; 3,5-dimethoxyphenylisopropyloxycarbonyl) yielding the fully protected hexapeptide in crystalline quality. After removal of the protective groups by acid treatment and hydrogenation the peptide was purified by Dowex ion-exchange and Sephadex chromatography. The purity was confirmed by thin-layer chromatography and amino acid analysis.