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In an effort to discover new imidazolyl nucleus belonging to the family of N-fused heterocyclic compounds which display broad spectrum of biological applications, a series of novel imidazolyl pyrazolopyridines 3a,b–7a,b and imidazolyl pyrazoloquinoxaline 8a–d were synthesized. The structures of all the synthesized compounds were confirmed using spectroscopic data and elemental analyses. The compounds were synthesized using conventional heating besides the environmentally friendly benign techniques and reagents as microwave technique and catalyst under solvent–free conditions and short reaction times by anomeric-based oxidation (ABO) to the products in the final step of the synthetic pathway. Further all the synthesized bioactive molecules are tested for their biological potency: in vitro antimicrobial activity using a disc diffusion technique was performed against various Gram-positive and Gram-negative bacteria as well as fungal strains using Chloramophenicol and Fluconazole as positive controls. Free radical scavenging activity has been investigated using the DPPH scavenging methods. Interestingly, most of the synthesized compounds exhibited good to excellent antibacterial activities against most of bacterial strains and showed the highest antioxidant activity.

3-(Pyridin-3-yl)-1-p-tolyl-1H-pyrazolo[3,4-d]thiazol-5-amine was used as a key synthon for a one-pot two- and three-component synthesis of new fused heterocyclic moieties as pyrazolo[3,4-d]thiazole derivatives containing new fused ring pyrimidines or imidazoles. The compounds were synthesized by using microwave irradiation as an eco-friendly technique besides the conventional heating. All the newly synthesized compounds were characterized on the basis of their physical, spectral and analytical data. Most of the synthesized compounds were evaluated for their in vitro antimicrobial potentialities and antioxidant activities, and the most promising compounds were selected to determine antitumor activity. Molecular docking was performed inside the active site of cathepsin D, and target compounds 5a–c had a good binding energy of − 16.87 to − 11.64 kcal/mol compared to that of original ligand of − 16.02 kcal/mol with different binding interactions, thereby suggesting that these compounds may possibly act as cathepsin D inhibitors and thus may participate in anticancer activity.