Chemical Studies On Specific Inhibitors Of Sporangia Formation Of Phytophthora From Natural Products

Phytophthora is a notorious kind of strong phytopathogenic oomycetes which caused several billion dollars annual economic losses of agricultural production in the world. It can spread rapidly. However, many fungicides have less effect while long-term use because of the resistance. So, it is important to search for new active substances against Phytophthora.Firstly, more than six hundred Actinomycetes metabolites samples were screened against the hyphae growth of Phytophthora. Six samples showed remarkable activity. All of them showed inactive after large scale.On the other land, the spread of the Blight was caused by zoospores released from sporangium in asexual reproduction. Many researchers were focus on the hyphae frowth inhibition study and zoospores germination study while little literature reported the inhibition of the sporangium formation, which was the key process in asexual reproduction. We established a stable new bioassay system for screening active sample against the Phytophthora sporangium formation. More than one hundred samples from traditional Chinese medicine were screened. The Helianthus annuus L. extract which showed remarkable activity was conducted by solvent partition, silica gel/ODS open column separation. More than ten active fractions were obtained. The most active fraction was conducted by HPLC purification guided by biological activity test. A pure active compound was obtained, which was identified as angeloygrandifloric acid using the 1D/2D NMR measurement, MS measurement and comparison with literature data. For structure-activity relationship study, deacylation, hydrogenation, methylation were done. Bioassay results indicated that, the acyl group played an important role for the inhibition activity. In addition, another active fatty acid compound was obtained from Centella asiatica (L.) Urban by similar methods.More than ten active fractions along with one pure active compound from Helianthus annuus L. were obtained guided by the screening system. The study results showed that, it has potential value for supression of Phytophthora asexual reproduction by using Helianthus annuus L. crude sample, active fractions or active compounds.