Study On Chemical Constituents From Myrothecium Sp. And Absolute Configuration Of Natural Products

This thesis consists of four chapters. A general research introduction about Myrothecium sp. is summarized in the first chapter; research details of chemical composition of fungus(Myrothecium sp.) 323023 are discussed and listed in the second chapter; theoretical calculation methods and their application in absolute configuration edtermination for natural products is introduced in chapter three, the fourth chapter contains the discussions of six natural products absolute configuration using quantum theory.In this article the fungi which we found them from extreme environment. After solid-state fermentation for 48 days, it was extracted via ethyl acetate. total 14 compounds were isolated by a variety of modern chromatography method, including silica gel column chromatography, gel Sephadex LH-20 column chromatography, C18 chromatographic column, medium pressure liquid chromatography, and high performance liquid chromatography. Their structures were identified according to the physical and chemical properties and spectral data(1 D and 2 D NMR). At the same time, Absolute Configuration(AC) of six natural products with good biological activity was identified in this paper. Optical rotation and electronic circular dichroism were calculated at the B3LYP/6-311++G(2d,p)// PCM/B3 LYP /6-311++G(2d,p) or other levels in the gas phase and/or in solution. Computational results exhibited that the early reported AC of four among the six may not be the best structures after comparing the computed optical rotations(OR), electron circular dichroism(ECD) to the experimental data. Then four favorable structures are suggested to be used for the AC assignments based on the comparison of predicted OR and ECD to the experimental results. It is the first time to find that the different position of carbonyl group on aromatic ring(planar structure changes) in Griseusins can lead to the ECD curve reversed instead of the stereogenic center changes. In traditional opinion, ECD curve reversal happens only when stereogenic center configuration reverses, such as from AC of(R) to(S).