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Triterpenoids from Psidium guajava with Biocidal Activity P. GHOSH*, A. MANDAL, P. CHAKRABORTY, M. G. RASUL, MADHUMITA CHAKRABORTY AND A. SAHA1 Natural Product and Polymer Chemistry Laboratory, Department of Chemistry and 1Department of Botany, University of North Bengal, Darjeeling – 734 013
Ghosh, et al.: Triterpenoids from Psidium guajava In continuation of our studies on the phytochemical investigation of medicinal plants available in the foothills of Darjeeling and Teri, we report herein the isolation of two triterpenoids betulinic acid and lupeol from the leaf extract of Psidium guajava and their potential antimicrobial and phytotoxic activities. All the structures of the isolated compounds were confirmed by spectral (IR, NMR) analysis and by comparison with the literature reports. Key words: Betulinic acid, lupeol, minimum inhibitory concentration, myrtaceae, Psidium guajava, triterpenoid
The Himalayan region of Darjeeling and Terai are rich in bio diversity with plants having pronounced
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medicinal activities as evidenced by recent literature reports[1-3] as well as by the tribal medicinal practice in this region. Plants of the family Myrtaceae are extensively used in indigenous medicine from prehistoric ages. Psidium guajava is an important representative of this family. Present day reports
Indian Journal of Pharmaceutical Sciences
July - August 2010
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about P. guajava are attracting because of their highly encouraging biological activities[3-11]. Different parts of these plants are used in the traditional system of medicine for the treatment of various human ailments such as ulcers, bronchitis, eye sores, bowels, diarrhoes and cholera[3-6]. It is reported in the literature that the leaf extract of P. guajava has antitussive, antibacterial, hemostatic, antioxidant and narcotic properties[7-10]. Recently Abreu et al, have reported that guava extract can alter the labelling of blood with technetium99m[11]. In view of the attributed medicinal properties and in an ongoing search for bioactive triterpenoids from plants of Myrtaceae available in Darjeeling foothills, the toluene extract of leaves of P. guajava was selected for further investigation. The leaf extract of P. guajava was found to contain two new triterpenoids (1 and 2) along with earlier reported guajanoic acid (3)[6], -sitosterol (4), uvaol (5), ursolic acid (6) and oleanolic acid (7)(fig. 1). Compounds 1 and 2 have been characterized as betulinic acid and lupeol respectively. This is the first report of the isolation of these two triterpenoids from the leaf extract of P. guajava available plenty in the foothills of Darjeeling. In addition to that preliminary studies towards the antimicrobial and phytotoxic activities of these two compounds, which have not yet reported so far from this source, have also been carried out against some fungal and bacterial pathogens. All the melting points were determined by open capillary method and are uncorrected. The NMR spectra were recorded in CDCl3 solutions at ambient temperature on a Bruker Avance 300 MHz-FT NMR spectrometer using 5 mm BBO probe. The chemical shift are given in ppm related to tetra methyl silane (TMS) as internal standard. The coupling constant (J) are reported in Hz. The IR spectra were recorded in Shimadzu FT-IR spectrophotometer in KBr discs.
Fresh leaves of P. guajava were collected in bulk from young mature plants at the Sukna belt of Darjeeling foothills during early summer, washed, shade dried and milled into coarse powder by a mechanical grinder. The prepared powdered leaves were then used for further studies. The powdered plant material was extracted with toluene using Soxhlet apparatus for 72 h. The solvents were then removed under reduced pressure and a sticky brown residue was obtained. This residue was then purified by column chromatography using silica gel (60-120) mesh and suitable proportions of petroleum ether and ethyl acetate were used as the eluent. In this present work the in vitro antifungal antibacterial activities and the phytotoxicity of the two isolated triterpenoids have been studied. Five different fungal pathogens namely, Calletotricheme camellie, Fussarium equisitae, Alterneria alternate, Curvularia eragrostidies, Colletrichum Gleosproides were used for the antifungal study. For antibacterial study Escherichia Coli, Bacillus Subtilis, Staphylococcus aureus, Enterobactor were used as bacterial pathogen. Suitable strains of these organisms were procured from the microbiology laboratory of our institute. MICs (minimum inhibitory concentration) of the triterpenoids against bacterial and fungal pathogens are reported in Tables 1 and 2, respectively. DMSO (dimethyl sulfoxide) was used as solvent to prepare different concentrations of the triterpenoids. Solvent control (DMSO) was also maintained throughout the experiment. All experiments were performed in petridishes and were incubated at 37o for 48 h. TABLE 1: MIC OF 1 AND 2 AGAINST DIFFERENT BACTERIA Compounds
MIC in μg/ml against different strains of bacteria EC BS SA EB 150
