Amino Acids and Peptides. XXIII. : Synthesis of N^α-Protected Amino Acid 6-Chloro-2-pyridyl Esters and Their Evaluation for Peptide Synthesis

Abstract

6-Chloro-2-pyridyl esters (OPyCl) of N^α-benzyloxycarbonyl and tert-butyloxycarbonylamino acids were synthesized by the N, N'-dicyclohexylcarbodiimide (DCC) method from the acids and 6-chloro-2-hydroxypyridine in dimethylformamide (DMF). The reactivity of the 6-chloro-2-pyridylester with amino group is much higher than that of the corresponding 2-pyridyl ester (OPy) and p-nitrophenyl esters (ONp) in dioxane and DMF, and a peptide bond is formed without acylation at the side chain hydroxyl group of amino acids. Z-Asp(OBzl)-OPyCl reacted with amino acid methyl esters in dioxane to give the corresponding dipeptide without any detectable aspartimide formation.