Synthesis and biological evaluation of novel benzoquinones as potential antimicrobial agents

New series of 2,5-dihydroxyphenyl-1,3-thiazoles 4a–l was synthesized by reacting 2,5-dihydroxyphenacyl bromide with various 4-aryl thiosemicarbazones 3a–l that on oxidation with ferric chloride yielded the corresponding N 1-substituted benzylidene-N 2-[3-aryl-4-(1,4-benzoquinon-2-yl)-1,3-thiazol-2-ylidene]hydrazines 5a–l. They were evaluated for antibacterial activity against Staphylococcus aureus and Bacillus subtilis as Gram-positive bacteria, Escherichia coli and Pseudomonas aeruginosa as Gram-negative bacteria. They were also evaluated for their in vitro antifungal potential against Candida albicans. Almost all tested compounds were found to possess variable degrees of antimicrobial activity. The obtained data revealed that compounds 4b–h and 5e, 5f and 5l exhibited promising antimicrobial activity against the tested organisms of which compound 4b proved to be the most active.