Racemization-free synthesis of C-terminal cysteine-peptide using 2-chlorotrityl resin.

We investigated the effects of bases, resins, and S-protecting groups on the extent of racemization at the C-terminal cysteine during Fmoc-based(Fmoc=fluoren-9-yl-methoxy-carbonyl) solid phase peptide synthesis. The use of 2-chlorotrityl resin was most effective in suppressing the racemization caused by the base treatment for Fmoc-cleavage. Somatostatin was successfully synthesized with practically no racemization using 2-chlorotrityl resin by Fmoc-chemistry.