STUDIES ON POLYPEPTIDES .54. SYNTHESIS OF A PEPTIDE CORRESPONDING TO POSITIONS 24-104 OF THE PEPTIDE-CHAIN OF RIBONUCLEASE-T1

A synthesis is described of a partially (S-cysteine and Nε-lysine) protected peptide containing 81 amino acid residues corresponding to positions 24-104 of the peptide chain of the enzyme ribonuclease T1. The peptide was assembled by condensing suitably protected fragments in a sequential manner by azide couplings. Every intermediate was purified, characterized, and analyzed. Small intermediates were characterized by thin-layer chromatography, elemental analysis, optical rotation, and amino acid analyses of acid and in some instances aminopeptidase M digests. Large fragments were characterized by thin-layer chromatography, amino acid analyses of acid, and aminopeptidase M digests (except for insoluble compounds) and dan-syl end-group determinations. Certain sparingly soluble fragments obtained by azide coupling of acyl components not C-terminating in glycine or proline were acid hydrolyzed and the digests exposed to L-amino acid oxidase to assess the stereochemical homogeneity of certain amino acid residues. Based on the method of synthesis and the results of extensive analytical evaluation, it is concluded that the final peptide does not contain failure sequences and major backbone imperfections. However, the analytical methods employed are not sensitive enough to exclude some racemization. © 1979, American Chemical Society. All rights reserved.