Synthesis, characterization and structure-activity relationship analysis of novel depsides as potential antibacterials.

Twenty-six depsides were synthesized to screen for their antibacterial activity. All of them were reported for the first time. Their chemical structures were clearly determined by (1)H NMR, (13)C NMR, ESI mass spectra and elemental analyses, coupled with one selected single-crystal structure. All the compounds were assayed for antibacterial activities against three gram-positive bacterial strains (Bacillus subtilis ATCC 6633, Staphylococcus aureus ATCC 6538 and Streptococcus faecalis ATCC 9790) and three gram-negative bacterial strains (Escherichia coli ATCC 35218, Pseudomonas aeruginosa ATCC 13525 and Enterobacter cloacae ATCC 13047) by MTT method. Compound 2-(2-methoxy-2-oxoethyl)phenyl 3-nitrobenzoate (C10) and 2-(2-ethoxy-2-oxoethyl)phenyl 3-nitrobenzoate (C23) showed powerful antibacterial activities against B. subtilis with MIC of 0.78 microg/mL while compound 2-(2-methoxy-2-oxoethyl)phenyl 2-(3,4-diethoxyphenyl)acetate (C8) and 2-(2-ethoxy-2-oxoethyl)phenyl 2-(3,4-diethoxyphenyl)acetate (C21) exhibited significant antibacterial activities against E. coli with MIC of 1.562 microg/mL, which were superior to the positive controls penicillin G and kanamycin B, respectively. On the basis of the biological results, structure-activity relationships were discussed.