| Summary: | A series of new tetracyclic oxathiine-fused quinone-thioglycoside conjugates based on biologically active 1,4-naphthoquinones and 1-mercapto derivatives of per-<i>O</i>-acetyl <span style="font-variant: small-caps;">d</span>-glucose, <span style="font-variant: small-caps;">d</span>-galactose, <span style="font-variant: small-caps;">d</span>-xylose, and <span style="font-variant: small-caps;">l</span>-arabinose have been synthesized, characterized, and evaluated for their cytotoxic and antimicrobial activities. Six tetracyclic conjugates bearing a hydroxyl group in naphthoquinone core showed high cytotoxic activity with EC<sub>50</sub> values in the range of 0.3 to 0.9 μM for various types of cancer and normal cells and no hemolytic activity up to 25 μM. The antimicrobial activity of conjugates was screened against Gram-positive bacteria (<i>Staphylococcus aureus</i>, <i>Bacillus cereus</i>), Gram-negative bacteria (<i>Pseudomonas aeruginosa</i> and <i>Escherichia coli</i>), and fungus <i>Candida albicans</i> by the agar diffusion method. The most effective juglone conjugates with <span style="font-variant: small-caps;">d</span>-xylose or <span style="font-variant: small-caps;">l</span>-arabinose moiety and hydroxyl group at C-7 position of naphthoquinone core at concentration 10 µg/well showed antimicrobial activity comparable with antibiotics vancomicin and gentamicin against Gram-positive bacteria strains. In liquid media, juglone-arabinosidic tetracycles showed highest activity with MIC 6.25 µM. Thus, a positive effect of heterocyclization with mercaptosugars on cytotoxic and antimicrobial activity for group of 1,4-naphthoquinones was shown.
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