Chemoprofiling of Medicinal Plants and Value Addition of Their Principle Constituents through Synthetic Modifications

Natural products, the greatest treasures of nature, are continous and unending source of inspiration for mankind to haunt potentialy lead molecules for pharmaceutical industry. The search for these natural products in medicine dates back to 1550 BC, but the scientific period of this search is much more recent. Historically, plants were a folkloric source of medicinal agents and as modern medicine developed, numerous useful drugs were developed from lead compounds discovered from medicinal plants. Today, this strategy remains an essential route to new pharmaceuticals with multifaceted biological potential. The present investigation was undertaken to study, in particular, the bioprospection of historically relevant medicinal plant, Cotula anthemoides, and the value addition of its principal bioactive constituent, ursolic acid (UA), through rational structural modifications as potential anti-cancer agents. Cotula, the largest genus of flowering plants in Southern Hemisphere which belongs to family Asteraceae and tribe Anthemideae. It constitutes roughly about 80 species of plants generally known as “water buttons” or “button weeds”. Cotula anthemoides is a well-known member of this genus commonly known as ‘Babuna’ and locally as “Thulla bobul”. In traditional medicine, its roots were taken in Lesotho for colic and in South Africa it is a remedy for head and chest colds. Its extensive use in the world wide flu-epidemic of 1919 makes it an attactive target for future research. Cotula anthemoides plant material was collected from Kelar region of District Pulwama and its identification was assured in the Department of Plant Taxonomy, University of Kashmir. A specimen bearing Voucher Specimen No. KASH-710 was submitted to the same department. The aerial part of plant was dried, crushed and subjected to extraction by various organic solvents. Bioactivity guided extraction directed us to focus on methanolic extract. Owing to its potential cytotoxic and antimicrobial activity, methanolic extract was further subjected to column chromatography which resulted into the isolation of 11 individual constituents. Incisive spectral analysis enabled us to identify unambigously four known constituents (α-pinene, coumarin, ursolic acid, gibberlic acid A-3) and a new coumarin ester, 6-Methoxy-2-oxo-2Hchromene- 8-carboxylic acid methylester all reported for the first time from this plant. All the isolated constituents were reevaluated against a panel of human cancer cell lines for anticancer activity and against bacterial and fungal strains for anti-microbial activity. It was interesting to note that, among the five compounds screened, ursolic acid and 6-Methoxy-2-oxo-2H-chromene-8-carboxylic acid methylester exhibited potential anti-cancer activity against four cancer cell lines, THP-1 (leukaemia), A-549 (lung), PC-3 (Prostate) and HCT-15 (colon) and significant antifungal activity against two fungal strains, Aspergillus niger and Penicillium chrysogenum. Taking cue from the preceeding discussion and as part of our ongoing research program to synthsesize biocative molecules as anti-cancer agents, we aim to undertake a research program to design and structuraly modify the UA in order to fine tune its anti-cancer potential through click chemistry approach. Accordingly, a series of UA- triazolyl derivatives were designed and synthesized by employing Cu (I) catalyzed 1, 3-dipolar cycloaddition reaction of propargylated-UA derivative with various aromatic azides. All the compounds were confimed by 1HNMR, 13C NMR, IR and ESI-MS analysis. In 1HNMR, cyclization of azides to form triazoles, was confirmed by resonance of H-5 of triazole ring in aromatic region as well as by the presence of other protons in aromatic region. The structure was further supported by the 13CNMR and DEPT, which showed all the expected carbon signals corresponding to triazole derivatives. All the UA-triazolyl derivatives were assayed for in vitro cytotoxicity against a panel of four human cancer cell lines including A-549 (lung), MCF-7 (breast), HCT-116 (colon), THP-1 (leukemia) and a normal human epithelial cell line, FR-2 using sulforhodamine-B assay. 5-fluorouracil and mitomycin-C in addition to UA were taken as reference standards. From the anticancer screening data, it was interesting to note that some of the compounds exhibited interresting anticancer activity. Compound 9c which contains the p-bromo substitution at aryl ring was found to be most promising compound with a 2-25 fold decrease in IC50 value. All the UA-triazolyl derivatives were also screened for antimicrobial activity against seven bacteria and two fungal strains. The results indicate that these compounds displayed a broad spectrum and variable degree of antibacterial and antifungal activity against the different tested strains. Compounds 9d, 9j and 9k were most promising antibacterial agents and compound 9b and 9i were found to be most promising antifungal compounds in this study