Chemoenzymatic Synthesis of Plant‐Derived Kavalactone Natural Products by Dynamic Resolution Using a Biosynthetic O‐Methyltransferase Tailoring Enzyme

Biosynthetic enzymes have enormous potential for the chemoenzymatic synthesis of natural products and other bioactive compounds. Methyltransferases are promising tools for the selective enzymatic modification of complex structures. This paper describes the production, purification and biochemical characterization of the O‐methyltransferase JerF, which catalyzes unique 4‐methoxy‐5,6‐dihydropyranone formation in jerangolid A biosynthesis. Isolation problems had hitherto prevented detailed studies on JerF and were solved by the production of the maltose‐binding protein fusion protein. The differentiation of JerF between styryl‐substituted dihydropyrandion enantiomers was investigated. In combination with a spontaneous racemization occurring with this type of substrates, a new enzymatic dynamic kinetic resolution was observed, which was used for the enantioselective chemoenzymatic synthesis of kavalactone natural products and new derivatives. In combination with an HMT‐based SAM regeneration system, (+)‐kavain, (+)‐11,12‐dimethoxykavain and (+)‐12‐fluorokavain were prepared in 3‐4 steps on the 100 µmol scale with overall yields of 37‐57% and ees of 70‐86%. A mutational study based on an AlphaFold 2 model provided indications for active site residues with an influence on the performance of the enzyme that could be targets for engineering. This example illustrates how the exceptional enzymatic activities and specificities of biosynthetic enzymes can be exploited for the development of new synthesis approaches.