The Steric Hindrance of the Stepwise Reaction of N-Carboxy α-Amino Acid Anhydride with the α-Amino Acid Ester

Article abstract of DOI:10.1246/bcsj.54.2705

The mechanisms of the reactions of 4-alkyloxazolidinediones (1) (N-carboxy α-amino acid anhydrides(NCAs)) with α-amino acid benzyl ester p-toluenesulfonates (2) were investigated in acetonitrile containing triethylamine at low and room temperatures.Two types of reactions were observed: (1) the polymerization of NCAs was initiated with a small amount of 2 to produce polypeptides (6), and (2) the dipeptide benzyl esters (4) were produced by the stepwise reaction of NCAs with the esters.Both the polymerization and the dipeptide formation (1+2) seemed to be initiated by the nucleophilic attack of the amino group of the ester on the C-5 carbon of NCAs.The polymerization proceeded when the side chains of the amino acid esters (R²) were more bulky than those of the NCAs (R¹).On the contrary, dipeptide esters were produced when the side chains of the NCAs (R¹) were more bulky than those of the esters (R²).