An Enzymatic Strategy for the Selective Methylation of High-Value-Added Tetrahydroprotoberberine Alkaloids.

Tetrahydroprotoberberines (THPBs) are plant-specific alkaloids with significant medicinal value. They are present in trace amounts in plants and are difficult to chemically synthesize due to stereoselectivity and an unfavorable environment. In this study, a selective methylation strategy was developed for the biocatalysis of seven high-value-added THPB compounds using 4'--methyltransferase (), norcoclaurine 6--methyltransferase (), and ()-scoulerine 9--methyltransferase ( and ) in engineered . The methyltransferases , , , and were expressed heterologously in . Compound (10-methoxy-2,3,9-tetrahydroxyberbine) was synthesized using the recombinant strain and the substrate 2,3,9,10-tetrahydroxyberbine. Compound (9-methoxy-2,3,10-tetrahydroxyberbine) was produced in the recombinant () strain , and compounds and (discretamine) were produced in the recombinant strain . Compounds (9,10-methoxy-2,3-tetrahydroxyberbine) and (corypalmine) were obtained by co-culturing the recombinant strains and with substrate. Compounds (scoulerine) and (isoscoulerine) were produced by co-culturing the substrate with the recombinant strains and . To increase the yield of novel compound , the flask culture conditions of the engineered strain were optimized, resulting in the production of 165.74 mg/L of this compound. This study thus presents an enzymatic approach to the synthesis of high-value-added THPBs with minimum environmental wastage.