Pyrazole, isoxazoline and bypyrimidine derivatives from polygonum senegalense and psiadia punctulata flavonoids and their anti- microbial activities

Abstract

Currently, researchers have given special attention to the synthesis of hetero­ cyclic compounds with nitrogen and oxygen five in five­ or six ­membered ring systems. This is mainly due to their wide range of biological activities. Hence, in this study, isoxazoline, pyrazole and bypyrimidine derivatives were synthesized from flavonoids, previously isolated from Polygonum senega - lense and Psiadia panctulata, and assessed for their anti­fungal activity. A flavone was reacted with hydrazine hydrate to afford a pyrazole analogue 5­methoxy ­2­(5­(2,3,4,5­tetramethoxyphenyl)­1 H ­pyrazol­3­yl)benzene­1,3­ diol ( 1 ) Two isoxazoline derivatives namely, 2­(4,5­dihydro­5­phenylisoxazol­ 3­yl)­5­methoxybenzene­1,3­diol ( 2 ) and 2­(­4,5­dihydro­5­phenylisoxazol­ 3­yl)­3,5­dimethoxyphenol ( 3 ) were successfully synthesized by the reaction of chalcones with hydroxylamine hydrochloride. An oxime derivative ( 4 ) was also generated from a similar procedure. A reaction between a chalcone and thiourea gave a bypyrimidine derivative, 4,5­dihydro­6­(2,4­ dihydroxy ­3,6­dimethoxyphenyl)­4­phenylpyrimidine­2­(1H)­thione ( 5 ). The products were then assessed for their anti­bacterial and anti­fungal activity. All compounds showed no significant activity except compound 2 that demonstrated activity against standard anti­bacterial agent, Streptococcus aureus with IC 50 value of 7.56 and anti­fungal Candida neoformans, Candida krusei and Candida glabrata strains with IC 50 values 8.01, 8.11 and 13.74 μg/mL respectively. We, therefore, recommend synthetic optimization of com ­ pound 2 as a potential anti­microbial agent.