A series of N-(5-(alkylthio)-1,3,4-thiadiazol-2-yl)acetamides and their 2-chloro analogues were synthesized via the acylation of 2-alkylthio-5-amino-1,3,4-thiadiazoles using acetyl chloride and chloroacetyl chloride. Structural characterization was performed using spectroscopic methods, with selected derivatives further confirmed by single-crystal X-ray analysis. The in vitro cytotoxic activity of the synthesized compounds was evaluated against a panel of cancer cell lines (CCRF-CEM, HEp-2, HeLa, and HBL-100) and normal cells. While the parent compounds and acetyl derivatives exhibited negligible activity, the chloroacetyl-substituted derivatives showed significantly enhanced cytotoxicity. The most potent derivatives demonstrated IC50 values of approximately 10 μM against CCRF-CEM cells, comparable to the reference drug cytarabine. However, the compounds displayed low selectivity toward cancer cells over normal cell lines. These results indicate that the incorporation of a chloroacetyl moiety is critical for increasing the cytotoxic potency, although its high reactivity may reduce therapeutic selectivity. Therefore, further structural optimization is required to improve selectivity and therapeutic potential.

3-aryl-6-phenyl-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazines were obtained with good yields (81-95%) via the heterocyclization reaction of 1-phenyl-2-((5-aryl-1,3,4-oxadiazole-2-yl)thio)ethane-1-ones in acetic acid. The physicochemical characteristics of the synthesized compounds were established, the structures were confirmed by the data of IR, ¹H and ¹³C NMR spectra, as well as the results of X-ray diffraction analysis. The cytotoxic, antibacterial and antifungal properties of these compounds were evaluated. In vitro screening results showed that compounds 8, 9 and 12 significantly inhibit (54-65%) the growth of HeLa, HBL-100 and CCRF-CEM cancer cell lines. It was found that the cytotoxicity of the synthesized compounds increases in the series of oxadiazoltiones (1-4) - S-derivatives (5-8) - triazolothiadiazines (9-12). Compounds 5-16 do not exhibit antimicrobial properties.

Amidoalkylation of secondary heterocyclic amines by N-[5-(alkylsulfanyl)-1,3,4-thiadiazol-2-yl]-2'-chloroacetamide resulted the new compounds 5-10 that contain 1,3,4-thiadiazole-5-thione moiety alongside pyperidine, morpholine, and cytisine fragments. In vitro screening of antimicrobial activity of synthesized compounds showed that N-[5-(amylsulfanyl)-1,3,4-thiadiazol-2-yl]-2'-morpholinacetamide exhibited an appreciable antibacterial activity against gram-negative bacteria of Escherichia coli (inhibition zone diameter of 16 mm) and gram-positive bacteria of Staphylococcus aureus and Bacillus subtilis (10-13 mm).