Germacrone epoxide

Hikino et al. [153] have investigated by enzymatic means the stereospecific epoxidation reactions of olefinic double bonds in the plant Curcuma zedoaria Roscoe. They studied the bioconversion of germacrone (207), a constituent of C. zedoaria, by microorganisms in the hope of obtaining stereoselective epoxidation as in the case of the plant. Cuminghamella blakesleeana yielded three major products (208 - 210) from germacrone, Fig. (42). 

A further examination of the essential oil of Asarum caulescens Maxim, has resulted in the isolation and identification of caulolactone A (338) and B (339). Interestingly both these compounds co-occur with germacrone 4,5-epoxide (337), and in fact treatment of this epoxide With anhydrous aluminium chloride gives both these lactones in 10% and 8% yields respectively. Mechanistically this has been rationalized in terms of two conformations of the epoxide as depicted in... 

The microbial transformation of humulene, a substrate showing a structure similar to that of germacrone, was studied by Abraham and Stumpf using a screen of about 300 strains1175 . This led the authors to select the fungi Diplodia gossypina and Chaetonium cochlioides for preparative scale experiments. It was thus observed that the main reaction path starts with the epoxidation of the 1,2-double bond, as shown by direct biotransformation of this monoepoxide obtained by chemical synthesis. This is then further oxidized to yield a multitude of products including diepoxides and hydroxy-epoxides (Fig. 16.1-28). 

Germacrone (118), (+) -germacrone-4,5-epoxide (119), and curdione (120) isolated from Curcuma aromatica, which has been used as crude drug, were incubated with A. niger. From compound 119 (700 mg), two naturally occurring metabolites, zedoarondiol (121) and isozedoarondiol (122), were obtained (Takahashi, 1994). Compound 119 was cultured in callus of Curcuma zedoaria and C. aromatica to give the same secondary metabolites 121, 122, and 124 (Sakui et al., 1988) (Figures 20.40 and 20.41). 

Hikino, H., T. Konno, T. Nagashima, T. Kohama, and T. Takemoto, 1971. Stereoselective epoxidation of germacrone by Cunninghamella blakesleeana. Tetrahedron Lett., 12 337-340. 

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