Abstract
Various biological properties of natural and synthetic pyrazole derivatives such as anti-inflammatory, antimicrobial, neuroprotective, anticonvulsant, antidepressant and anticancer activities encouraged us to propose a new, fast, green and eco-friendly procedure for the preparation of some novel 5-amino-3-(aryl substituted)-1-(2,4-dinitrophenyl)-1H-pyrazole-4-carbonitriles. They were efficiently synthesized via one-pot two-step process reaction of malononitrile, 2,4-dinitrophenylhydrazine and different benzaldehydes in deep eutectic solvent (DES) glycerol/potassium carbonate. The products yield and reaction times were considerably improved in the presence of applied DES. Antibacterial effects of all newly synthesized pyrazoles in comparison with several common antibiotics were evaluated against a variety of Gram-positive and Gram-negative pathogenic bacteria. In addition to, their inhibitory activities on three fungi were compared to some current antifungal agents. The moderate to good antimicrobial potentials particularly against fungi were observed in the major heterocyclic compounds according to the IZD, MIC, MBC and MFC results.
Highlights
Pyrazoles are an important class of azoles containing two adjacent nitrogen atoms, which are found as major or minor scaffolds in various medicinal compounds and natural products
The reaction conditions were optimized in terms of solvent, presence or absence of the catalyst and temperature. 1 mmol each of malononitrile (1), 4-acetamidobenzaldehyde (2a) and 2,4-dinitrophenylhydrazine (3) were reacted under different conditions (Table 1)
Three-component reaction in 0.5 g of each of these three deep eutectic solvent (DES) at room temperature have resulted in the Schiff bases and benzylidenemalononitriles as the major products (Entries 7, 9, 11), pyrazoles were obtained in 35–40% yields due to the increase of temperature to 80 °C (Entries 8, 10, 12)
Summary
Pyrazoles are an important class of azoles containing two adjacent nitrogen atoms, which are found as major or minor scaffolds in various medicinal compounds and natural products. Compounds containing pyrazole moiety exhibit a wide variety of biological and pharmacological activities including analgesic, neuroprotective, anticonvulsant, angiotensin converting enzyme (ACE) inhibitory, anti-angiogenesis, antioxidant and antiviral activities.[3,4,5,6,7,8,9] Numerous studies have focused on antibacterial and antifungal properties of pyrazole derivatives.[10,11,12] In a research project, inhibitory activities of some heterocyclic Schiff bases derived from thiocarbohydrazide were assessed against various pathogenic bacterial and fungal strains via measurement of their inhibition zone diameters. One of the synthesized 1,2,4-triazines could block the growth of all selected microorganism.[13]
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