On the selectivity of acylation of unprotected diamino acids

p-Nitrophenyl acetate and other esters except formates, will acylate the unprotected diamino acids homolysine, lysine, and ornithine, exclusively at the ω-amino group at pH 11. At lower alkaline pH's, the reaction is preferential but not selective. The reaction with diaminobutyric acid and diaminopropionic acid is not selective at any alkaline pH. ε-N-Acetyllysine can be prepared directly by the action of excess phenyl acetate on lysine at pH 11.