An Enzymatic Carbon-Carbon Bond Cleavage and Aldol Reaction Cascade Converts an Angular Scaffold into the Linear Tetracyclic Core of Ochraceopones

Meroterpenoids of the ochraceopones family featuring a linear tetracyclic scaffold exhibit exceptional antiviral and anti-inflammatory activities. The biosynthetic pathway and chemical logic to generate this linear tetracycle, however, remain unknown. In this study, we identified and characterized all biosynthetic enzymes to afford ochraceopones and elucidated the complete biosynthetic pathway. We demonstrated that the linear tetracyclic scaffold of ochraceopones was derived from an angular tetracyclic precursor. A multifunctional cytochrome P450 OchH was validated to catalyze the free-radical-initiated carbon-carbon bond cleavage of the angular tetracycle. Then, a new carbon-carbon bond was verified to be constructed using a new aldolase OchL, which catalyzes an intramolecular aldol reaction to form the linear tetracycle. This carbon-carbon bond fragmentation and aldol reaction cascade features an unprecedented strategy for converting a common angular tetracycle to a distinctive linear tetracyclic scaffold in meroterpenoid biosynthesis. The linear tetracyclic scaffold of ochraceopones originates from a common angular tetracycle through a cascade of enzymatic C-C bond cleavage and construction. The multifunctional cytochrome P450 OchH facilitates the cleavage of a C-C bond in the angular tetracycle by an unprecedented free-radical-initiated process. The subsequent new aldolase OchL constructs a C-C bond through an aldol reaction to generate the linear tetracycle.+ image