Highly regioselective synthesis of betulone from betulin by growing cultures of marine fungus Dothideomycete sp. HQ 316564

The synthesis of betulone from betulin through highly regioselective oxidation catalyzed by growing microorganism cells was reported for the first time. Fifty-two microbial strains including many marine fungi were examined for their capability of transformation of betulin and betulinic acid. Among the strains tested, the marine fungus Dothideomycete sp. HQ 316564 was the unique strain that regioselectively catalyzed the oxidation of betulin to betulone and the regioselectivity toward 3-hydroxyl was exclusive; nonetheless, no strains could transform betulinic acid into its 3-carbonyl derivative betulonic acid. The effects of several key culture and reaction conditions on the synthesis of betulone were studied. The optimum initial culture pH, reaction temperature and the concentration of the co-solvent dimethyl sulfoxide were 6.0, 33 °C and 0.4% (v/v), respectively, under which the yield of betulone reached 43.4%.

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► Microbial synthesis of betulone from betulin was described for the first time.
► Dothideomycete sp. HQ 316564 favored oxidation of the secondary 3-hydroxyl rather than the primary 28-hydroxyl in betulin.
► The regioselectivity of this biocatalytic approach is exclusive.
► Dothideomycete sp. HQ 316564 proved to be a good biocatalyst for betulone synthesis.
► The yield of betulone (43.4%) is satisfactory.