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Isomeric oxathiolone fused chalcones were prepared by condensation of appropriate acetylbenzo[1,3]-oxathiol-2-ones with benzaldehydes under acidic conditions. The synthesized compounds were screened for cytotoxic activity using HeLa cells, as well as for antibacterial activity against Micrococcus luteus, Staphylococcus aureus, Salmonella typhimurium, Escherichia coli, Proteus vulgaris, antifungal activity against Candida albicans, and tuberculostatic activity against Mycobacterium tuberculosis H 37 Rv and Mycobacterium kansasii strains.

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Three structurally related oxathiolone fused chalcone derivatives appeared effective chemosensitizers, able to restore in part sensitivity to fluconazole of multidrug-resistant C. albicans strains. Compound 21 effectively chemosensitized cells resistant due to the overexpression of the MDR1 gene, compound 6 reduced resistance of cells overexpressing the ABC-type drug transporters CDR1/CDR2 and derivative 18 partially reversed fluconazole resistance mediated by both types of yeast drug efflux pumps. The observed effect of sensitization of resistant strains of Candida albicans to fluconazole activity in the presence of active compounds most likely resulted from inhibition of the pump-mediated efflux, as was revealed by the results of studies involving the fluorescent probes, Nile Red, Rhodamine 6G and diS-C3(3).

The synthesis of substituted chalcones, thioflavanones, and thioflavones hydroxylated in both A and B rings is described. Acetoquinone (1) was transformed into 2,5-dihydroxy-6-(p-methoxybenzylmercapto)acetophenone (2) and subsequently into its 2,5-dimethoxy (3) and 2,5-dibenzyloxy (4) derivatives. Compounds 3 and 4 were condensed with suitable benzaldehydes to give chalcones 5−10. The thiol group of the chalcones was deprotected by a cleavage of the p-methoxybenzyl protecting group using a new, mild method (silver nitrate in boiling ethanol, 2 h), and the products were cyclized to thioflavanones (15−20). Dehydrogenation of the thioflavanones gave related thioflavones (25−27). Deprotection of methoxy and benzyloxy groups is also described.