Preparation of New Mono- and Bis-Amide Derivatives of L-isoleucine Via Amidation of Carboxyl and Amino Groups

N,N'-Dicyclohexylcarbodiimide and hydroxybenzotriazole mediated amination of free COOH group of N-tert-butyloxyoxycarbonyl-L-isoleucine 1 with three aromatic amines gave the corresponding amides 2a-c. Deprotection of N-tert-butyloxyoxycarbonyl groups of 2a-c with AcOH yielded the related amine derivatives 3a-c. The amidation of the free NH2 groups of (3a-c) with phthaloyl dichloride yielded the bis-amide products 4a-c. The synthesized compounds were purified by crystallization and their structures were elucidated by spectroscopic methods such as H-1-HMR, C-13-NMR, FTIR, and micro analysis.