Synthesis and Structure–Activity Relationship Analysis of Enamines as Potential Antibacterial Agents

Abstract

Twenty-four new enamines [(Z)-4–15 and (E)-4–15] were synthesized for the first time. Their chemical structures were determined by means of ¹H NMR spectroscopy, electrospray ionization-mass spectrometry, and elemental analysis. All of the compounds were assayed for antibacterial (Bacillus subtilis ATCC 6633, Escherichia coli ATCC 35218, Pseudomonas fluorescens ATCC 13525, and Staphylococcus aureus ATCC 6538) and antifungal (Aspergillus niger ATCC 16404, Candida albicans ATCC 10231, and Trichophyton rubrum ATCC 10218) activities by the 3-(4,5-dimethyl thiazole-2yl)-2,5-diphenyl tetrazolium bromide (MTT) method. Four compounds, (E)-ethyl 3-(4-fluorophenylamino)-2-(3-methoxyphenyl)acrylate ((E)-6), (E)-ethyl 3-(4-chlorophenylamino)-2-(3-methoxyphenyl)acrylate ((E)-9), (E)-ethyl 3-(4-bromophenylamino)-2-(3-methoxyphenyl)acrylate ((E)-12), and (E)-ethyl 3-(2,4-dibromophenylamino)-2-(3-methoxyphenyl)acrylate ((E)-13) showed considerable antibacterial activity against Pseudomonas fluorescens with minimum inhibitory concentrations of 12.5, 12.5, 3.12, and 6.25 μg mL^–1, respectively. Structure–activity relationship analyses revealed that, in general, an (E)-isomer exhibited higher antibacterial activity than the corresponding (Z)-isomer.