Synthesis, Structure Elucidation, Antioxidant and Antimicrobial Activity of Novel 2-(5-Trifluoromethyl-1H-pyrazol-1-yl)-5-(5-trihalomethyl-1H-pyrazol-1-yl-1- carbonyl)pyridines

This paper describes an efficient approach for the synthesis of a novel series of sixteen 2-(5-trifluoromethyl-1H-pyrazol-1-yl)-5-(5-trihalomethyl-1H-pyrazol-1-yl-1-carbonyl) pyridines, for the first time with non-identical substituents in both pyrazole rings, through the cyclocondensation reaction of 4-methoxy-4-alkyl(aryl/heteroaryl-1,1,1-trihaloalk-3-en-2-ones [CX₃C(O)CH=CR¹OCH₃, in which R¹ = CH₃, C₆H₅, 4-CH₃C₆H₄, 4-OCH₃C₆H₄, 2-furyl and X = F, Cl] or acetylacetone with some 6-[3-alkyl(aryl)-5-trifluoromethyl-1H-pyrazol-1-yl]nicotinohydrazides. Optimized yields of 67-91% were obtained when the reactions were performed in ethanol (green solvent) at reflux for 16 h. Subsequent antioxidant and antimicrobial evaluation revealed promising 1,1-diphenyl-2-picrylhydrazyl (DPPH) inhibition percentage and exhibited fungiostatic and fungicidal activities against yeasts, dermatophytes and filamentous, especially for the pyridine systems, when the both pyrazole rings attached to a pyridine ring contain CX₃ groups (X = H, F, Cl) of different kinds. It is also observed the trichloromethyl substituted compounds presented higher antioxidant activity in comparison to their fluorinated analogous.

Keywords:
pyrazole; pyridine; hydrazide; antimicrobial activity; DPPH