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

Phytophthora is one kind of plant pathogenes which could case devastating disease in plants. Phytophthora is a plant pathogen causing devastating disease of plants, and it had led to the1848Irish famine in history. Unfortunately nowadays most but not all kinds of Phytophthora strains have showed strong drug resistance toward long-term using chemical pesticides (such as metalaxyl), therefore it is very important for the whole world to find some novel compounds which can effectively inhibit the growth and reproduction of Phytophthora. Currently many researchers focus on inhibition of mycelia growth or germination of zoospores, while pay little attention on inhibition of sporangia generation which plays a very important role in the process of asexual reproduction. Therefore we established a bioassay system which could selectively obtain some active samples against the generation of sporangia. Under the guidance of the bioassay system, we screened dozens of Chinese traditional medicine. Finally we found the ethyl acetate layer of methanol extract of Allium fistulosum L that showed a remarkable inhibitory activity. Then we separated the active sample by Silica gel open column, and got several active fractions with high amount. We further separated those active fractions by Silica gel/ODS open column and purified them by HPLC. In the end, we obtained nine pure active compounds. We determined six chemical structures of compounds by spectroscopic analysis and compared spectroscopic date with literatures. Their chemical structure types belong to terpenes、ketones、esters class. They are Friedelin、Friedelanol、stigmasta-7,22-dien-3-one、aurantiamideacetate、crotocorylifuran, isololiolide. Among those compounds, Friedelin and Friedelanol showed most obvious biological activity. Their structure-activity relationship showed that functional groups linked with C-3played an important role in their activity. Friedelanol which has a hydroxyl group linked with C-3, showed a high inhibition rate (concentration:30 μg/mL)which reached to the same level of the inhibition rate of metalaxyl (concentration:30μg/mL). For further structure-activity relationship study, a series of esterification reaction were conducted. We made a series of chemical reaction between Friedelanol and different kinds of acid chloride. Bioassay results indicated that with the increase of the length of the carbon chain, compounds’activity gradually enhanced.We not only obtained some active compounds which belong to different types of sturctures, but also got many active fractions which were separated from the ethyl acetate layer of methanol extract of Allium fistulosum L. It is widely known that application of herbal medicines to treat human diseases has thousands of years’history in China. There are numerious practical experience indicating that Chinese herbal medicines do little harm to the human body, therefore exploring and obtaining active fractions with high contents from traditional Chinese medicines to control plant diseases will play an important role in national strategy.