Triazolo[3,4-b]thiadiazoles are a class of heterocyclic compounds, which have attracted great interest in medicinal chemistry owing to their wide range of pharmacological activities. A number of triazoles fused to thiadiazoles are incorporated into a wide variety of therapeutically important compounds possessing a broad spectrum of biological activities. Considering such a significant pharmacological potential, as well as wide synthetic possibilities triazolo-thiadiazoles have received considerable attention from scientific community and are extensively used for construction of prospective drug-likes molecules. In this review, we summarized the literature data about the main synthetic approaches for obtaining condensed heterocyclic compounds based on triazolo[3,4-b][1,3,4]thiadiazole scaffold as promising objects for modern bioorganic and medicinal chemistry.

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.

In the present work, we presented an efficient synthesis and anticancer activity evaluation of some new 3-R-6-(5-arylfuran-2-yl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazoles. We have shown that the proposed synthetic protocols provided the possibility to design triazolothiadiazoles diversity with a considerable chemical novelty. The structures of target substances were confirmed by using 1H NMR spectroscopy, mass spectrometry and elemental analysis. The synthesized compounds were selected by the National Cancer Institute Developmental Therapeutic Program for the in vitro cell line screening. Among all the substances tested, three compounds exhibited significant cytotoxic activity.

A series of some new pyrazole-substituted 7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazines was synthesized in this study. The structures of target substances were confirmed by using 1H and 13С NMR spectroscopy, mass spectrometry and elemental analysis. The synthesized compounds have been evaluated for antimicrobial activity against five bacterial strains (Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Staphylococcus aureus) and two fungal strains (Candida albicans and Cryptococcus neoformans). The antimicrobial screening studies of synthesized substances established that 2 of 12 compounds show pronounced antibacterial activity against the strain Staphylococcus aureus.