No abstract

An effective method was developed for the preparative separation and purification of monoterpenoid indole alkaloid epimers from Ervatamia yunnanensis Tsiang using a combination of pH-zone-refining counter-current chromatography and preparative high-performance liquid chromatography. With this method, two pairs of MIA epimers including ervatamine (72 mg, 1), 20-epi-ervatamine (27 mg, 4), dregamine (95 mg, 2), tabernaemontanine (129 mg, 3), along with two MIAs, apparicine (112 mg, 5) and isovoacangine (15 mg, 6), were successfully purified from 2.1 g crude extract of E. yunnanensis, each with a purity of over 95% as determined by HPLC. The structures of the MIAs were identified by ESI-MS, 1D, and 2D NMR.

Flavonoids are important plant natural products with variable structures and bioactivities. All known plant flavonoids are generated under the catalysis of a type III polyketide synthase (PKS) followed by a chalcone isomerase (CHI) and a flavone synthase (FNS). In this study, the biosynthetic gene cluster of chlorflavonin, a fungal flavonoid with acetolactate synthase inhibitory activity, was discovered using a self‐resistance‐gene‐directed strategy. A novel flavonoid biosynthetic pathway in fungi was revealed. A core nonribosomal peptide synthetase‐polyketide synthase (NRPS‐PKS) is responsible for the generation of the key precursor chalcone. Then, a new type of CHI catalyzes the conversion of a chalcone into a flavanone by a histidine‐mediated oxa‐Michael addition mechanism. Finally, the desaturation of flavanone to flavone is catalyzed by a new type of FNS, a flavin mononucleotide (FMN)‐dependent oxidoreductase.