Restore Filter Topoisomerase Inhibitors Based On Plant Extracts -D- 1-deoxy-xylulose 5-phosphate

Due to the abuse of antibiotics and the increasing incidences of bacterial drug resistance, there is an urgent need to find new targets for antibiotic screening. Terpenoids are one of the biggest families of natural products, which play importance roles in all living organisms. There are two biosynthetic pathways for the formation of terpenoids in nature, one is the classic mevalonate pathway (MVA pathway), and the other is the newly established2-methyl-D-erythritol4-phosphate pathway (MEP pathway). Research has shown that the MEP pathway is essential for most pathogenic bacteria, but is absent in humans. Thus, the enzymes in MEP pathway can be regarded as ideal targets for screening new antibacterials.1-Deoxy-D-xylulose5-phosphate reductoisomerase (DXR) is the rate-limiting enzyme of the MEP pathway, which catalyzes the conversion reaction of1-deoxy-D-xylulose5-phosphate (DXP) to MEP. That provides a perfect target for novel antibacterial screening. According to clinical and pharmacological studies, many pharmaceutical plants possess good anti-microbial activity. In this thesis, we wish to find DXR inhibitors from some plants.First,15traditional Chinese medicines with activities against pathogenic microorganisms were extracted and preliminarily separated. Then, the inhibitory activity of different extracts against EcDXR(DXR of E. coli) and PaDXR(DXR of P. aeruginosa)were tested by using a precolumn derivatization-HPLC method. The results showed that the extract of green tea possessed significant DXR inhibitory activity. Further fractionation of the extract with petrol ether, ethyl acetate and n-butanol, respectively generated four parts and each part showed over50%inhibitory activity against DXR and among which the ethyl acetate fraction gave the best inhibition. In addition, we also found that the ethyl acetate fraction of Sophora flavescens and Salvia miltiorrhiza Bge. possessed over30%inhibitory activity against DXR. Although Chrysanthemum indicum L. exhibited DXR inhibitory activity, it seemed that its activity was source and batch dependent.Based on the above results, the ethyl acetate fraction of green tea was further separated using silica gel column chromatography and15fractions were thus obtained among which the parts9-15showed over50%inhibitory effect. Subsequent separation of the part9resulted in the isolation of two compounds. The first compound showed45%inhibitory activity on DXR at a concentration of1μg/μL, but its structure is still pending. And the second compound which showed20%inhibitory activity on DXR (end cone.1μg/μL) was kaempferol as determined by spectroscopic methods.