Synthesis of 2,2’-Biflavanones from Flavone via Electroreduction and Photolysis

Biflavonoids, widely distributed in natural plants, had strong biological activities including spasmolysis, peripheral vasodilatation, antibradykinin activity and antispasmogenic action against prostaglandin PGE1, inhibition of cyclic GMP and cyclic AMP phosphodiesterase and inhibition of hepatoma cells. Recently, some biflavonoids were demonstrated to enhance suppersion of lymphocyte proliferation, inhibition of phospholipaseCr1, anti-inflammatory activity, anti-HIV activity, anticompleme…

Synthesis of 2,2'-Biflavanones from Flavone via Electroreduction and Photolysis

Biflavonoids, widely distributed in natural plants, had strong biological activities including spasmolysis, peripheral vasodilatation, antibradykinin activity and antispasmogenic action against prostaglandin PGE1, inhibition of cyclic GMP and cyclic AMP phosphodiesterase and inhibition of hepatoma cells. Recently, some bifiavonoids were demonstrated to enhance suppersion of lymphocyte proliferation, inhibition of phospholipaseCrl, anti-inflammatory activity, anti-HIV activity, anticomplementatory activity, antiviral activity and chemoprevention of hepatotoxicity.Several synthetic methods including Ullmann coupling, Baker-Venkataraman rearrangement and cyclization, cyclization from bichalcone, oxidative coupling, reductive coupling, Pd-cathode reduction and photoinduced electron transfer reaction were used for preparations of some bifiavonoids. In this paper, we report synthesis of 2,2'-biflavanones from flavone via electrolytic reductive coupling and photolysis.In the electrochemical reduction, flavone was reduced to give two hydrodimers of rac-2,2'-biflavanone and meso-2,2'-biflavanone and one reductive product of flavanone. The yields were dependent on the nature of electrodes, the kinds of supporting electrolytes and the reaction temperature. It was found to afford higher yields of rac-2,2'-biflavanone and meso-2,2'-biflavanone( 32.4% and 24.8%, 35.8% and 13.4%, respectively,) in the reaction conditions of Pb(-)/C(+)-H2SO4-7F/mol and C(-)/C(+)-H2SOn-5F/mol.In the photolysis with the electron-donating amines including triethylamine or 2-(N,N-dimethylamino)ethanol in acetonitrile, benzene or methylene dichloride, flavone also afford two hydrodimers of rac-2,2'-biflavanone and meso-2,2'-biflavanone and one reductive product of flavanone. Their yields were dependent on the molar ratios of substrate to amine, the kinds of amines,the solvents used and the irradiation sources. Higher yields were afforded rac-2,2'-biflavanone,meso-2,2'-biflavanone and flavanone(30.0%, 20.9% and 15.8%, respectively) in the reaction condition of 1/2 molar ratio of flavone to triethylamine in acetontrile with fourteen hours of irradiation.