In vitro Bioactivity Guided Isolation and Partial Characterization of Stigmasterol from Plectranthus esculentus. N.E.Br. Crude Extract

Aim: The study was aimed at the in-vitro antibacterial activity evaluation and isolation of phytocompound (s) from Plectranthus esculentus crude extract.

Place and Duration: This research work was carried out at Gombe State University in the Department of Chemistry for a period of one and half year which involved sample collection, preparation, purification and analysis of isolate.

Methodology: The coarsely powdered plant tuber was extracted with methanol. The filtrate obtained was concentrated on a rotavapor. The crude extract was re-dissolved in water: methanol (9:1) and partitioned with n-hexane, ethyl acetate and n-butanol respectively. The crude fractions were tested against a panel of microbes namely Helicobacter pylori, Shigella flexneri, and Salmonella typhi, using macro-dilution technique. The most active and sufficient n-hexane fraction was purified using column chromatography.

Results: The crude extract (≈172 g) was obtained from 3.1 kg of the stembark sample. Fractionation of the crude extract yielded 18.7g, 13.6 g and 26.4 g for n-hexane, ethylacetate and n-butanol respectively. All the crude fractions displayed moderate to strong activity against the microbes. The n-hexane and ethyl acetate fractions were the most active fractions with MICs ranging from 62.5 - 150 µg/mL where Salmonella typhi and Helicobacter pylori were the most susceptible with MIC of 62.50 μg/mL. The n-butanol fraction was weaker with MIC ranging from 125 - 250 µg/mL. Gradient elution of the n-hexane fraction yielded a phytocompound coded C5 with Rf value of 0.56 in n-hexane: ethyl acetate (6:4) and melting point of 136‐138°C. Characterization of C5 using spectroscopic data from FT-IR, GC-MS, 1H NMR and compared with literature identified C5 as stigmasterol.

Conclusion: The study had shown that Plectranthus esculentus contains bioactive principles and may serve as a potential source of antibacterial agents.