Thiazolo[3,2-a]pyrimidines are structural analogues of biogenic purine bases, thus may be considered as potential purine antagonists. The synthesis of these heterocyclic systems attracts significant attention from researchers in the field of organic and medicinal chemistry due to their wide range of biological activities, e.g. anti-inflammatory, antimicrobial, antioxidant, antiviral, and anticancer. The high bioactivity of thiazolo[3,2-a]pyrimidine derivatives stimulates the development of fundamentally new synthesis options, which include modern catalytic, microwave and ultrasonic methods for activating cycloaddition reactions, and the improvement of already known methods. This, in turn, became a strong basis for summarizing and systematizing the existing array of literature sources from 2000 to 2024 relating to the methods of obtaining and biomedical profile of thiazolo[3,2-a]pyrimidines and their hydrogenated analogues.

Angular pyrrolo(pyrido)[1,2-a]quinazolinones, being structurally isomeric to linear pyrrolo(pyrido)[2,1-b]quinazolinone alkaloids, are attractive molecular systems for both synthetic transformations and targeted biomedical research. The pyrrolo(pyrido)[1,2-a]quinazolinone scaffold has proven to be quite effective in the search for compounds with a wide range of pharmacological activities, e.g. anti-inflammatory, antioxidant, antibacterial, antiarrhythmic, and inhibitors of important biotargets. The present review summarises the methods for the synthesis of pyrrolo(pyrido)[1,2-a]quinazolinones as a comprehensive research object, especially in the past decade. They are systematised according to the type of heteroannulation and include the processes of cascade annulation of the pyrimidine and pyrrole (pyridine) cycles to anthranilamides (hydrazides); formation of a pyrimidine nucleus based on ortho-pyrrolyl(pyridinyl) substituted aromatic compounds; annulation of the pyrrole (pyridine) nucleus to a quinazolinone scaffold. It is expected that the generalised material presented will serve as a reliable guide for the rational design of new pharmacologically oriented compounds.

A number of 3-aryl-5,6-dihydroimidazo[2,1-b][1,3]thiazoles were synthesized by cyclocondensation of imidazolidine-2-thione with phenacyl bromides, and their antimicrobial and antioxidant activity was evaluated. Bioscreening confirmed the moderate antibacterial activity against the reference strains of bacteria Staphylococcus aureus, Escherichia coli and Proteus vulgaris and excellent antifungal activity against Candida albicans. It was found that 3-(4-chlorophenyl)-5,6-dihydroimidazo[2,1-b]thiazole 4h (MIC = 15.625 μg/ml) has twice the antifungal effect compared to the control drug Furacilin. The study of the antioxidant activity of the synthesized compounds proved their ability to inhibit 60–97% of DPPH radicals. The best antiradical effect was found for 4-(5,6-dihydroimidazo[2,1-b]thiazol-3-yl)phenol 4e (I = 97%). A probable mechanism of its action was proposed involving the formation of a radical cation by the SET process. For the most active antioxidants 4e-g, reactivity and electrostatic surface potential were evaluated using the DFT method, and molecular docking was studied on the human peroxiredoxin 5 protein model.

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.

The current study presents the synthesis of thiophene-appended pyrazoles through 3+2 annulations of chalcones 3(a-g)with aryl hydrazine hydrochlorides 4(a-d) in acetic acid (30%) under reflux conditions produced the thiophene-pyrazole hybrids 5(a-g) in good yields. Structures of synthesized new pyrazoles were confirmed by spectral studies, and elemental analysis. Further, preliminary biological evaluation studies show that compounds 5b and 5f having chloro substitution only in the thiophene ring exhibited excellent inhibition (12.5-25.0 µg/mL) against all the tested organisms in comparison with that of the standard. Compounds, 5a, 5c and 5g having electronegative chloro substitutions each in the aromatic and thiophene rings showed excellent (12.423-31.213 µg mL^-1) DPPH radical scavenging potencies. The synthesis of pyrazoline derivatives and the efficacy of some of the synthesized molecules as antimicrobial and antioxidant agents validate the significance of this study.