CYP719B1 Is Salutaridine Synthase, the C-C Phenol-coupling Enzyme of Morphine Biosynthesis in Opium Poppy

Morphine is a powerful analgesic natural product produced by the opium poppy Papaver somniferum. Although formal syntheses of this alkaloid have been reported, the morphine molecule contains five stereocenters and a C-C phenol linkage that to date render a total synthesis of morphine commercially unfeasible. The C-C phenol-coupling reaction along the biosynthetic pathway to morphine in opium poppy is catalyzed by the cytochrome P450-dependent oxygenase salutaridine synthase. We report herein on the identification of salutaridine synthase as a member of the CYP719 family of cytochromes P450 during a screen of recombinant cytochromes P450 of opium poppy functionally expressed in Spodoptera frugiperda Sf9 cells. Recombinant CYP719B1 is a highly stereo- and regioselective enzyme; of forty-one compounds tested as potential substrates, only (R)-reticuline and (R)-norreticuline resulted in formation of a product (salutaridine and norsalutaridine, respectively). To date, CYP719s have been characterized catalyzing only the formation of a methylenedioxy bridge in berberine biosynthesis (canadine synthase, CYP719A1) and in benzo[c]phenanthridine biosynthesis (stylopine synthase, CYP719A14). Previously identified phenol-coupling enzymes of plant alkaloid biosynthesis belong only to the CYP80 family of cytochromes. CYP719B1 therefore is the prototype for a new family of plant cytochromes P450 that catalyze formation of a phenol-couple.