The formation of peptides from glycine thioesters

The condensation products obtained from 0.01M S-glycyl-N-acetyl-cysteamine at different pH's were investigated. The highest yields of diketopiperazine (approx. 50%) were observed in phosphate buffers between pH 7.5 and 8.5. The highest yields of diglycine (46%), triglycine (10%) and tetraglycine (2%) were observed in carbonate buffers at pH 9.5. At pH 8.0, over 90% of the glycyl residues of 0.15M S-glycyl-N-acetylcysteamine were incorporated into condensation products, mainly DKP (60--70%). The yields of products from the condensation of S-glycyl-ethanethiol under similar conditions closely resembled those obtained with S-glycyl-N-acetylcysteamine.