Enzymatic formation of an unnatural methylated triketide by plant type III polyketide synthases

Octaketide synthase, a novel plant-specific type III polyketide synthase from Aloe arborescens, efficiently accepted (2RS)-methylmalonyl-CoA as a sole substrate to produce 6-ethyl-4-hydroxy-3,5-dimethyl-2-pyrone. On the other hand, a tetraketide-producing chalcone synthase from Scutellaria baicalensis and a diketide-producing benzalacetone synthase from Rheum palmatum also yielded the unnatural methylated C9 triketide pyrone as a single product by sequential decarboxylative condensations of three molecules of (2RS)-methylmalonyl-CoA.