Figure 2.

Some unique reactions catalyzed by P450 enzymes found in the IQA pathway. CYP719A1 from C. japonica catalyzes the oxidative cyclization of an ortho-hydroxymethoxy-substituted aromatic ring (i.e. methylenedioxy bridge formation) and converts only tetrahydrocolumbamine to (S)-tetrahydroberberine. CjCYP80G2 not only catalyzes the intramolecular C-C phenol coupling reaction and converts (S)-reticuline to (S)-corytuberine, but also 4-O-demethylates codamine to form the demethylated product. The reaction mechanism has been discussed in the text.