Preparation of new mono- and bis-amide derivatives of L-isoleucine via amidation of carboxyl and amino groups

Abstract

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 1H-HMR, 13C-NMR, FTIR, and micro analysis.