Studies On The Extraction And Separation Of The Active Components In The White Birch Bark And The Synthesis Of Betulin Derivatives

Betulin and betulinic acid are remarkable natural products. They are obtained from a variety of botanical sources. Betulin, betulinic acid and many of their derivatives exhibit great promise as bioactive agents for the treatment of HIV infection and cancer. In our country, birch sources are enriched, but the little have been explored. In consequence, we decide to study the sources of Changbai Mountain birch.Betulinic acid, a pentacyclic triterpene, has recently been reported to possess antitumor activity against cultured human melanoma cells. Furthermore, the ability of betulinic acid to induce apoptosis in melanoma and other cell types and the favoral therapeutic index suggests that betulinic acid is an attractive and promising antitumor agent. It has been isolated from the stem bark of Ziziphum mauritiana Lam but only in low content. Betulin, a naturally occurring triterpene, available in abundance up to 10% dry weight of bark from white birch bark, seems to be an ideal starting material for the synthesis of betulinic acid.During a discovery effort from natural resources, in order to seek new biologically active compounds, reaearch on chemical modifications of valuable precursors have been demonstrated to be an effective path to resolve the water solubility problem and increase bioavailability. It was envisioned that a series of simple modifications of the parent structures could produce a number of potentially important derivatives that could improve the selective antitumor activity. In this paper we synthesized some derivatives of betulin with modifications at the positions C-3 and C-28.The main content of this thesis is as following:In the first chapter of this thesis, we summarize the references about our research and introduce the corrlelative reaearch background. The current developments were summarized and the research contents of this thesis were described.In the second chapter, a simple procedure is described for the simultaneous extraction and determination of betulin and betulinic acid in white birch bark. To compare extraction efficiency, effect of white birch bark growing in different locations and different extract solvents on the content of betulin and betulinic acid were evaluated. In this thesis betulin was purified by recrystallization with chloroform and methanol mixture, and orthogonal design had been taken to optimize the conditions of recrystallization including the volume and ratio of chloroform and methanol mixtures. In addition a simple process was also developed to obtain purified betulin using chloroform / NaOH two-phase solvent extraction.In the third chapter, the solubilities of betulin in fourteen commonly used organic solvents, chloroform + methanol, acetone + water and ethanol + water mixed solvents were determined using HPLC method at different temperatures. From the solubility data, we can conclude that the proper crystallization solvent for betulin is ethanol + water. Moreover, UNIQUAC equation and NRTL equation were used to correlate the experimental data. As a result the UNIQUAC activity coefficient model was better than NRTL model, UNIQUAC activity coefficient model with its optimally fitted binary interaction parameters can be used to predict the solubility of betulin in a wide range of temperature.In the forth chapter, betulin was oxidized by Jones oxidation in step 1 and converted to betulonic acid, then betulonic acid was reduced by sodium borohydride in step 2 and converted to betulinic acid. Optimized reaction condition was also studied. And the asymmetric reduction mechanism of betulonic acid by sodium borohydride was investigated. Four-member ring mechanism has been studied.In the fifth chapter, a series of betulin derivatives including 28-acetoxybetulin, 28-tritylbetulin, 28-benzoylbetulin, 3-0-P-D-glucopyranoside of betulin and some betulinic acid conjugate containing amino acid were synthesized and confirmed by MS and NMR.In the last chapter, all of the experimental work was summarized. We find the deficiencies in this thesis and propose the idea of the latter research.