Phytochemical and biological investigation on the leaves of Saurauia roxburghii

Abstract

The work in this thesis details the phytochemical and biological investigations of one species of Actinidiaceae, Saurauia roxburghii. Previously some works has been reported on this species, but chemical investigation on this species grown in Bangladesh has not been studied extensively. As the plant is being used in our country as a herbal medicine, it is necessary to have a knowledge of the constituents of the plant of our native species.The leaves of S. roxburghii was cold extracted with ethanol. The ethanol extract was partitioned into n-hexane, chloroform and ethylacetate and then subjected to column chromatography for fractionation over silica gel, successively with mixtures of n-hexane/dichloromethane, dichloromethane, mixtures of dichloromethane/ methanol and methanol respectively. The phytochemical investigation of n-hexane extract of Saurauia roxburghii led to the isolation of three compounds, compound-1 (YSR-9), compound-2 (YSR-10) and compound-3 (YSR-2) as well as the chloroform extract led to the isolation of other three compounds, compound-4 (YSR-7), compound-5 (YSR-3) and compound-6 (YSR-5) in pure form by repeated column chromatography over silica gel. All the compounds were identified by chemical methods and structure elucidation was done by spectroscopic analysis (UV, FT-IR, 1H & 13C NMR) and comparison of their spectral data with those published in the literature. Compound-1 and 2 were identified as steroids and compound-3 to 6 were identified as triterpenes. Compound-1 to 6 were named as Stigmasterol, β-sitosterol, 3β-hydroxy-urs-12-en-28-oic acid, 3β-hydroxy-olea-12-en, 3β-hydroxy-olea-12-en-28-oic acid and 2α,3β-dihydroxyolea-12-en-28-oic acid respectively. All of these compounds were isolated for the first time so far from this species Saurauia roxburghii. From the brine shrimp lethality bioassay, it was found that the LC50 of crude ethanol, n-hexane, chloroform; column fractions H-13 of the crude hexane, C-19 of the crude extract of chloroform and column fractions E-13, E-18 and E-24 of the crude extract of ethanol were found to be 12.59, 14.79, 14.06, 11.75, 10.96,11.88, 4.37 and 6.92 μg/mL respectively. It was evident that all the test samples were very lethal to brine shrimp nauplii. Column fractions E-18 and E-24 (4.37 and 6.92 μg/mL) of the crude extracts of ethanol showed quite potent activity in brine shrimp lethality bioassay. For antibacterial activity, the crude ethanol and n-hexane, chloroform, ethyl-acetate extracts were screened against 14 test bacteria at a concentration of 500μg/disc. The extract showed good activity and other extracts showed moderate activity against most of the test Gram-positive and Gram-negative bacteria respectively but n-hexane, chloroform, ethyl-acetate extracts were found to be resistant to the Bacillus megaterium, Salmonella typhi, Vibrio cholera and Bacillus polymyxa and Bacillus megaterium, Streptococcus pneumonia, Vibrio cholera respectively. The column fraction H-13 of the crude extract of n-hexane, C-15 and C-19 of the crude extract of chloroform and E-18 and E-24 of the crude extract of ethyl-acetate were screened against 8 test bacteria at a concentration of 400μg/disc.. These fractions showed low to mild antibacterial activity. Fourteen (14) bacterial strains were taken to study the antibacterial activity of the pure compounds; compound-3 (YSR-2), compound-5 (YSR-3), compound-4 (YSR-7) and compound-1 (YSR-9) at a concentration of 300μg/disc.These compounds showed moderate activity against all the Gram-positive bacteria Bacillus cereus, Bacillus megaterium, Bacillus subtilis, Staphylococcus aureus, Streptococcus pneumonia, Bacillus polymyxa, Mycobacterium tuberculosis and Gram-negative bacteria E.coli, Klebsiella sp., Proteus sp., Salmonella typhi, Shigella sonnei, Pseudomonas Aureus, Vibrio cholera but compound-1(YSR-9) resistant to Streptococcus pneumonia, Mycobacterium tuberculosis; compound-3 (YSR-2) resistant to Proteus sp., Shigella sonnei; compound-4 (YSR-7) resistant to Salmonella typhi, Pseudomonas Aureus and compound-5 (YSR-3) resistant to Salmonella typhi.