Novel ethyl 1,5-disubstituted-1H-pyrazole-3-carboxylates as a new class of antimicrobial agents.

A series of pyrazole derivatives 9-22 were designed and synthesized. All the newly synthesized compounds were assayed for their antimicrobial activity against the Grampositive bacteria Staphyllococcus aureus and Bacillius subtilis and the Gram-negative bacteria Escherichia coli, Pseudomonas aeruginosa, in addition to the fungi organisms, Candida albicans, C. parapsilosis and C. tropicalis. Ethyl 5-(2,5-dimethylthiophen-3-yl)-1-phenyl-1H-pyrazole-3-carboxylate (21) (MIC(E.coli) = 0.038 μmol mL⁻¹, MIC(P. aerug.) = 0.067 μmol mL⁻¹) is nearly as active as ampicillin (MIC = 0.033 and 0.067 μmol mL⁻¹), respectively. Ethyl 5-(4-bromo-2-chlorophenyl)-1-phenyl-1H-pyrazole-3-carboxylate (16) (MIC = 0.015 μmol mL⁻¹) is more active than fluconazole (0.020 μmol mL⁻¹) as a reference drug against C. parapsilosis.