Biotransformation of Coreopsis tinctoria major flavonoids marein and flavanomarein

Coreopsis tinctoria Nutt. is a medicinal plant that is cultivated in many countries around the world. The major bioactives of C. tinctoria include marein, flavanomarein, okanin, isookanin and others; among them, marein and flavanomarein are the dominant components, whereas the others present in minor amounts, although they have demonstrated significant biological activities. Continued pharmacological research of flavanomarein, okanin, and isookanin requires sufficient amounts of these components, therefore, this study investigated the efficient biotransformation of marein to flavanomarein, okanin, and isookanin. By screening different enzyme types and optimizing reaction conditions (temperature, concentration, time, and pH), the optimal enzymatic conditions for converting marein to its corresponding cyclic isomer and aglycone were determined. Under enzymatic catalysis, marein and flavanomarein were transformed into their aglycones, okanin and isookanin, respectively. The optimal conditions were as follows: enzyme activity 25 U/mL (VinoTaste^® proline enzyme), 37 ℃, pH 8.0, and a reaction time of 2 h. Under these conditions, marein yielded 34.56% okanin and 18.31% isookanin, while flavanomarein yielded 92.25% isookanin. This study reports, for the first time, the efficient enzymatic conversion of Coreopsis tinctoria flavonoid glycosides into their aglycones.