Formation of optically pure N-acyl-N,N'-dicyclohexylurea in N,N'-dicyclohexylcarbodiimide-mediated peptide synthesis.

N-acylurea, a side product in peptide synthesis from DCC, preserves its chiral integrity although peptides formed simultaneously in the same reaction are racemized to a large extent. This observation is inconsistent with the generally accepted opinion that racemization-prone O-acylisourea is a common intermediate for both peptides and N-acylurea. Chiral purity of N-acylureas and peptides was determined by HPLC using chiral stationary phases. An efficient method of synthesis of chirally pure N-acylureas is also presented.