Biotransformation to synthesize the methylated derivatives of baicalein using engineered Escherichia coli.

Oroxylin A and negletein are flavonoid compounds existing in plants, with excellent pharmacological activities such as anti-inflammatory, anti-viropexis, and anti-cancer. Nevertheless, the natural abundance of these compounds in plants is extremely low. Here, a biotransformation pathway was developed in engineered strains to synthesize oroxylin A and negletein from baicalin by using the crude extract of Scutellaria baicalensis as the substrate. Briefly, the precursor baicalin in this crude extract was hydrolyzed by a β-glucuronidase to form the intermediate baicalein, then O-methyltransferases utilize this intermediate to synthesize oroxylin A and negletein. Through screening strains and carbon sources, regulating intercellular S-adenosyl L-methionine synthesis, and optimizing culture conditions, the titers of the target products increased gradually, with 188.0 mg/L for oroxylin A and 222.7 mg/L for negletein finally. The study illustrates a convenient method to synthesize oroxylin A and negletein from a low-cost substrate, paving the way for the mass acquisition and further bioactivities development and utilization of these rare and high-value compounds.