Submitted to: Chemistry and Biodiversity
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/5/2011
Publication Date: 12/20/2011
Citation: Wang, X., Habib, E., Leon, F., Radwan, M.M., Gao, J., Tabanca, N., Wedge, D.E., Cutler, S.J. 2011. Antifungal metabolites from the roots of Diospyros virginiana by overpressure layer chromatography. Chemistry and Biodiversity. 8:2231-2340. Interpretive Summary: Discovery of new crop protections from natural products has received considerable interest as alternatives to synthetic agrochemicals for use as pest and disease control agents. Our current research efforts are to identify natural product-based fungicides. In this research program, we evaluated 37 plant extracts using a direct bioautography bioassay to detect antifungal activity against Colletotrichum. Of these, Diospyros virginiana (American persimmon) root extract showed the most promising activity. Based on preliminary screening results, a more in-depth study of D. virginiana root extract was conducted in order to isolate and identify the pure metabolites possessing antifungal activity. The literature shows reports of nine compounds being isolated and identified from either the leaves or the wood of D. virginiana. However, there were no reports in the literature on chemicals from the roots of D. virginiana. Eleven phytochemicals were obtained from the roots of D. virginiana and identified using standard analytical chemical techniques. All the isolated compounds were evaluated for their antifungal activity against our library of seven fungal plant pathogens using in vitro micro-dilution broth assay. The results indicated that two compounds showed high antifungal activity against the fungal pathogens that cause strawberry leaf blight (Phomopsis obscurans), and Phomopsis cane and leaf spot of grape (P. viticola).
Technical Abstract: A preparative overpressure layer chromatography (OPLC) method was successfully used for the separation of two new natural compounds, 4-hydroxy-5,6-dimethoxy-2-naphthaldehyde (1) and (Delta)12,13-20,29-dihydrobetulin (2) together with nine known compounds including 7-methyl-juglone (3), diospyrin (4), isodiospyrin (5), shinanolone (6), lupeol (7), betulin (8), betulinic acid (9), betulinaldehyde (10), and ursolic acid (11) from the acetone extract of the roots of Diospyros virginiana. Their identification was performed with mono and bidimensional NMR spectroscopy and HR-ESI-MS methods. All the isolated compounds were evaluated for their antifungal activity against Colletotrichum fragariae, C. gloeosporioides, C. acutatum, Botrytis cinerea, Fusarium oxysporum, Phomopsis obscurans, and P. viticola using in vitro micro-dilution broth assay. The results indicated that compounds 3 and 5 showed high antifungal activity against P. obscurans at 30 µM with 97.0% and 81.4% growth inhibition and moderate activity against P. viticola (54.3% and 36.6%). It appears that an optimized OPLC system offers a rapid and efficient method of exploiting bioactive natural products.