Exploring Novel Indazole and Pyrazole Nucleoside Analogues: Enzymatic Synthesis, Characterization, and Biological Evaluation

New indazole and pyrazole nucleoside analogues were synthesized by enzymatic transglycosylation using E. coli purine nucleoside phosphorylase (PNP). Indazoles substituted at position 5 or 6 with bromine, pyrazole or pyrimidine fragments were used as heterocyclic bases. In the case of indazole-pyrazole hybrids, the selectivity of PNP in glycosylation of the pyrazole fragment, rather than the indazole one, was established. Molecular modeling methods allowed the identification of the preferred orientations of substrates in the active site of the enzyme, leading to the formation of N1- and N2-regioisomers of indazole. Unique substrate specificity ensured the possibility of glycosylation of the bases with conversion rates of 65–100% (according to HPLC analysis of the reaction mixtures) and isolated yields of 19–94%. It was shown that the synthesized nucleoside analogues are not inhibitors of E. coli adenosine deaminase (ADA). They do not exhibit cytotoxicity towards cancer cell lines (SH-SY5Y neuroblastoma cell lines, K-562 lymphoblastic cells, and HL-60 promyeloblastic cells). The activity of indazole derivatives against Mycobacterium tuberculosis (strain H37Rv) was determined by the microdilution method. 1-(β-D-2′deoxyribofuranosyl)-5-bromo-indazole and 5-(pyrimidin-5-yl)-1H-indazole at a concentration of 50 μg/mL were able to inhibit 50% and 90% of the culture growth, correspondingly.