A regioselective synthesis of some new pyrazol-1′-ylpyrazolo[1,5-a]pyrimidines in aqueous medium and their evaluation as antimicrobial agents

An efficient and environmental benign regioselective synthesis of some new pyrazol-1′-ylpyrazolo[1,5-a]pyrimidines (7b–h) has been accomplished via treatment of 3(5)-amino-5(3)-hydrazinopyrazole dihydrochloride (5) with several unsymmetrical 1,3-diketones (6b–h) using water as a solvent without any catalysts or additives. The structure of 7b–h was established on the basis of rigorous analysis of 1H, 13C NMR, IR spectral data and MS. Eight compounds (7a–h) were screened for their antibacterial activity against two gram-positive and two gram-negative bacteria and compounds (7a, b, d and e) for antifungal activity against four phytopathogenic fungi. Compounds 7c and 7e manifest rather broad antibacterial activity than standard antibiotics. One lead compound, 7a (10 mg/ml and 200 mg/ml) exhibited equipotent or more potent antifungal activity against all tested microorganisms than standard drug.

Graphical abstractA series of new pyrazol-1′-ylpyrazolo[1,5-a]pyrimidines has been synthesized regioselectively using water as a solvent and were characterized. The preliminary results revealed that some compounds exhibited promising and pronounced antimicrobial activities.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Mild, efficient and environmental friendly, regioselective synthesis of some new pyrazol-1′-ylpyrazolo[1,5-a]pyrimidines (7b–h). ► Structure 3′-methyl-5′-(R)-pyrazol-1′-yl-5-methyl-7-(R)-pyrazolo[1,5-a]pyrimidine (III) was assigned on the basis of rigorous analysis of NMR, IR spectral data, elemental analysis and MS. ► Compounds 7c and 7e exhibited promising antibacterial activity comparable to Linezolid. ► Compound 7a exhibited fungicidal action higher (2–3.4 fold more active) to that of Mancozeb. ► Antifungal and antibacterial activities depend on the nature of substituents at 5′ and 7-positions of pyrazol-1′-ylpyrazolo[1,5-a]pyrimidines.