The Synthesis Of Betulone From Betulin Through Regioselective Oxidation Catalyzed By The Cells Of Dothideomycete Sp.

Since1980’s, cancer and acquired immune deficiency syndrome (AIDS) have been thetwo main diseases that serverly threaten humam health. Searching new medicines fromnatural compounds has attracted more attention in the area of medicinal chemistry.Compared to existing drugs, betulin and its derivatives displayed a different toxicmechanism, and had high potential in the treatment of cancer and AIDS. On the earth, thecontent of betulin is much higher than that of betulone. With readily available betulin as thelead compound, the synthesis of its derivatives with higher activity will lead to substantialsocial and economic benefits. It has been demonstrated that the biological activity ofbetulone is much higher than betulin. Compared with chemical methods, microbialtransformation has many advantages such as mild reaction conditions, beingenvironmentally friendily and high selectivity. Therefore, in this dissertation, a lot ofmicroorganisms including marine microbes were screened for the transformation of betulininto betulone, and the effects of various reaction conditions on the reaction were studied; toimprove its catalytic efficiency, the original strain Dothideomycete sp. HQ316564wassubjected to ultraviolet radiation, and the reaction conditions were optimized systematically.Among52strains tested, the marine fungus Dothideomycete sp. HQ316564was theunique strain that enabled to transform betulin into betulone. The optimum initial culture pH,reaction temperature, concentration of the additive DMSO and reaction time were6.0,33℃,0.4%(v/v) and6days, respectively, under which, the total yield of betulone reached43.4%.Upon mutation of the original strain Dothideomycete sp. HQ316564by ultravioletradiation, a positive mutant strain (Dothideomycete sp. UV14) was isolated. Under theaforementioned optimal conditions, the total yield of betulone reached23.2%with thismutant after the reaction of1day, which is much higher than that with the original (13.4%).With this mutant as biocatalyst, the optimal initial culture pH, reaction pH, pre-culture time,reaction time, pre-culture temperature and reaction temperature for this reaction were5.5,7.0,36h,48h,28℃and33℃, respectively, under which, the total yield of betulone reached71.7%. Compared to the original strain, both the catalytic efficiency of theDothideomycete sp. UV14and the total yield of betulone were improved significantly.In the present study, a marine strain was obtained that enabled to synthesize betulonefrom betulin through regioselective oxidation, and a new and efficient biocatalytic approachto betulone was established. Use of rich marine microorganisms might open up manyopportunies for the development of novel biotransformation processes.