Studies On The Synthesis Of Two Natural Products Of Plant Origins

This M.S. degree thesis concentrates on synthesis of two natural products originated from plant. One is a new melilotic ester Meliloester with biologically active ingredient isolated from the Melilotus alba in2012; another is a natural product which was extracted from Ravensara crassifolia and showed antifungal activity against the phytopathogenic fungus. The thesis is divided into three parts:Fristly, in an attempt to establish the absolute configuration of meliloester, the literature structure was firstly synthesized in an enantiopure form. The carboxylic unit was gained from salicylaldehyde after three-step conversion, and constructed the chiral centers by Evans’aldol reaction. The desired optically active alcohol was afforded by modified, then condensed with the free acid gave the end product with high yield. Comparing the data with those reported for the natural product, it is concluded that the previously assigned structure for meliloester is incorrect.Then, attention was paid to the enantiopure epoxy chiral building blocks (S)-1-((R)-2,2-dimethyl-1,3-dioxolan-4-yl)-2-(S)-oxiran-2-yl ethanol (3-2) derived from inexpen sive and readily available D-glucolactone. Efforts were first made in improving the access to the enantiopure epoxy chiral building blocks required for the later endeavors directed towards synthesis of natural products.Finally, the synthesis of the antimicrobial substances extracted from Ravensara crassifolia (the natural product is (6S)-5,6-dihydro-6-[(2R)-2-hydroxy-6-phenylhexyl]-2H-pyran-2-one) is studied on by three synthetic routes which began with the elaboration of the enatiopure epoxy chiral building block. Wherein using the third route, its6-epimer4-2has been successfully synthesized in high yield and short steps, and the synthesis of the natural isomers4-1has come to the precursor4-33, which could afford the final product after deprotection, the work has to be further studied.