Synthesis of ∈-aspartyl-lysines and of isohexylamides of aspartic acid

Lockhart & Abraham (1956) found that two com- pounds which appeared to be aspartyl-lysine and aspartyl(isoleucyl)-lysine respectively were formed when bacitracin A was hydrolysed with 11 N- hydrochloric acid at 800. The aspartic acid residue in these compounds had the L-configuration and was linked to the e-amino group of L-lysine. How- ever, both compounds carried a net positive charge at pH 7 and this raised the question whether they were simple peptides. The synthesis of peptides in which aspartic acid is joined through its m-and f,carboxyl group respectively to the e-amino group of lysine has therefore been undertaken. For purposes of comparison the a-and f,-i8ohexylamides of aspartic acid have also been synthesized. L-Aspartic acid and L-lysine have been used in this work but no attempt has been made to discover whether significant racemization occurs in the course of any of the reactions.