Polypeptides. Part XII. The preparation of 2-pyridyl esters and their use in peptide synthesis

2-Pyridyl esters of N-acyl-amino-acids may be prepared from the acids, 2-hydroxypyridine, and NN′-dicyclohexylcarbodi-imide in pyridine (only N-acylureas are formed in acetonitrile or dichoromethane). The N-t-butoxy-carbonyl-amino-acid 2-pyridyl esters are mostly crystalline, stable, and in non-polar solvents considerably more reactive towards nucleophiles (amines, amino-acid esters and amides, hindered amino-acid derivatives, and hydroxy-compounds) than the corresponding p-nitrophenyl esters. Evidence is presented that they are likely to be particularly useful in solid-phase peptide synthesis, and in the synthesis of O-peptides and depsipeptides.