Semi-Synthetic Pyrazoline Derivatives from Polygonum senegalense Chalcones and their Anti-Microbial Activities

This paper describes the semi-synthesis and anti-microbial activity of novel pyrazoline derivatives of Polygonum senegalense chalcones. The study was carried out on the understanding that heterocycles with pyrazoline ring systems are known to possess a broad spectrum of biological activities. The derivatives were afforded by refluxing mixtures of chalcones and phen- ylhydrazine, hydrazine hydrate, and / or acetic acid in DMSO or ethanol at low temperatures between 40-60°C in an oil-bath. The products were characterized in by 1H-NMR (200 or 400 MHz), 13C-NMR spectroscopy and ESI-HRMS. NMR data was described in detail for each derivative. The compounds 6-15 have been screened for their in vitro anti-bacterial activity against one gram positive bacteria (S. aureus) and anti-fungal activity against five strains C. krusei, C. neoformans, and C. glabrata. They all showed insignificant antimicrobial activities with lower IC50 as compared to positive control, except compound 7 that demonstrated moderate anti- fungal activity with IC50 values ranging between 8.01 - 13.74 µg/mL against C. krusei, C. neoformans and C. glabrata. The compound also showed anti- bacterial activity of IC50 value 7.56µg/mL against S. aureus. Based on these findings, we recommend that compound 7 should undergo further structural modification in order to optimize its anti-microbial activity.