Bioassay-guided Isolation and Identification of Fungitoxic Coumarins from Angelica dahurica

Bio-prospecting of natural products allows for the discovery of new agrochemicals for pest management and chemistry found from plants used in traditional medicines have often not been evaluated as bio-pesticides. TCM Bai Zhi is the root of Angelica dahurica which has been used as early as 400 BC in Ancient China for the treatment of illnesses such as headaches, nasal obstruction, detoxification of the blood, swollen gums, toothaches, anti-inflammatory, a laxative, sedative, and an anti-fungal cream for skin. The root of A. dahurica is also widely known to contain furanocoumarins. Our preliminary evaluations of several Angelica species were completed in 2012 for antifungal and mosquito deterrent activity. Several species of Angelica were shown to be active. TLC-bioautography with Colletotrichum species as the antifungal detection agents demonstrated that the ethyl acetate extract of A. dahurica showed strong antifungal activity. Current mosquito testing with new plant material failed to show significant biting deterence, or toxicant activity. In order to isolate and identify the antifungal constituents in the root of A. dahurica, a systematic bioassay-guided fractionation of the ethyl acetate extract was performed. Several active fractions were obtained by combining biotage with direct-bioautography. Two coumarins “bergapten (1)” and “suberosin (2)” were isolated from active fractions using biotage and HPLC and the structures were confirmed by ¹H and ¹³C NMR spectroscopic analyses. Other active antifungal fractions are being purified. Our current goal is to test all pure compounds in a micro-dilution broth assay in comparison to bergapten, suberosin and commercial fungicide standards. Development of natural fungicides with low mammalian and environmental toxicity will help guarantee food safety and sustainability of the U.S. and Chinese agricultures.

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