Glycosylation of luteolin in hydrophilic organic solvents and structure-antioxidant relationships of luteolin glycosides

An effective approach was developed to biotransform luteolin glycosides in hydrophilic organic solvents. Bacillus cereus A46 cells showed high activity and stability in 5-20% (v/v) DMSO with 90-98% conversion rates of luteolin glycosides. Five glycosides of luteolin 7-O-beta-glucoside, luteolin 4 '-O-beta-glucoside, luteolin 3 '-O-beta-glucoside, luteolin 7,3 '-di-O-beta-glucoside and luteolin 7,4 '-di-O-beta-glucoside were obtained. The addition of DMSO greatly promoted the solubility of luteolin and further regulated the formation of the main products from five luteolin glycosides to luteolin 7-O-beta-glucoside (931.2 mu M). Fourteen flavonoids and anthraquinones were used as tentative substrates. Glycosylation positions were located at the C-7, C-3 ' or C4 ' hydroxyl groups of flavonoids and C-5 hydroxyl group of anthraquinones. The 3 ',4 '-dihydroxy arrangement played the key role for the antioxidant activity of luteolin.