Pyrazole, Isoxazoline and Bypyrimidine Derivatives from Polygonum senegalense and Psiadia punctulata Flavonoids and their Anti-Microbial Activities

Evans Okemwa Kenanda^a, Leonidah Kerubo Omosa^b
aDepartment of Chemistry, School of Pure and Applied Sciences, Kisii University, P.O. Box 408-40200 Kisii, Kenya
^bDepartment of Chemistry, School of Physical Sciences, University of Nairobi, P.O. Box 30197-00100 Nairobi, Kenya

Pharmacognosy Communications,2017,7,1,47-52.
DOI:10.5530/pc.2017.1.7
Published: October 2016
Type: Original Article

ABSTRACT

Currently, researchers have given special attention to the synthesis of heterocyclic 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 senegalense and Psiadia panctulata, and assessed for their anti-fungal activity. A flavone was reacted with hydrazine hydrate to afford a pyrazole analogue 5-methoxy-2-(5-(2,3,4,5-tetramethoxyphenyl)-1H-pyrazol-3-yl)benzene-1,3- diol (1) Two isoxazoline derivatives namely, 2-(4,5-dihydro-5-phenylisoxazol- 3-yl)-5-methoxybenzene-1,3-diol (2) and 2-(-4,5-dihydro-5-phenylisoxazol- 3-yl)-3,5-dimethoxyphenol (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, 4,5-dihydro-6-(2,4- dihydroxy-3,6-dimethoxyphenyl)-4-phenylpyrimidine-2-(1H)-thione (5). The products were then assessed for their anti-bacterial and anti-fungal activity. All compounds showed no significant activity except compound 2 that demonstrated activity against standard anti-bacterial agent, Streptococcus aureus with IC₅₀ value of 7.56 and anti-fungal Candida neoformans, Candida krusei and Candida glabrata strains with IC₅₀ values 8.01, 8.11 and 13.74 μg/mL respectively. We, therefore, recommend synthetic optimization of compound 2 as a potential anti-microbial agent.

Key words: Bypyrimidine, Isoxazolines, Oxime, Pyrazole, Chalcones.