**Synthesis and Evaluation of Antimicrobial and Cytotoxic Activity of Oxathiine-Fused Quinone-Thioglucoside Conjugates of Substituted 1,4-Naphthoquinones**

**Yuri E. Sabutski 1,\*, Ekaterina S. Menchinskaya 1, Ludmila S. Shevchenko 1, Ekaterina A. Chingizova 1, Artur R. Chingizov 1, Roman S. Popov 1, Vladimir A. Denisenko 1, Valery V. Mikhailov 1, Dmitry L. Aminin 1,2 and Sergey G. Polonik 1,\***


Academic Editor: Luisella Verotta

Received: 22 July 2020; Accepted: 5 August 2020; Published: 6 August 2020

**Abstract:** A series of new tetracyclic oxathiine-fused quinone-thioglycoside conjugates based on biologically active 1,4-naphthoquinones and 1-mercapto derivatives of per-*O*-acetyl d-glucose, d-galactose, d-xylose, and l-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 EC50 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 (*Staphylococcus aureus*, *Bacillus cereus*), Gram-negative bacteria (*Pseudomonas aeruginosa* and *Escherichia coli*), and fungus *Candida albicans* by the agar diffusion method. The most effective juglone conjugates with d-xylose or l-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.

**Keywords:** 1,4-naphthoquinones; quinoid compounds; thioglycosides; quinone-sugar conjugates; cytotoxic activity; antibiotic activity
