Discovery of an Unexpected 1,4-Oxazepine-Linked -Fluostatin Heterodimer by Inactivation of the Oxidoreductase-Encoding Gene .

Fluostatins belong to the atypical angucyclinone aromatic polyketides featuring a distinctive tetracyclic benzo[]fluorene skeleton. To understand the formation of the heavily oxidized A-ring in fluostatins, a flavin adenine dinucleotide-binding oxidoreductase-encoding gene was inactivated, leading to the production of an unprecedented 1,4-oxazepine-linked -fluostatin heterodimer difluostatin I () and five new fluostatin-related derivatives, fluostatins T-X (-). Their structures were elucidated by mass spectrometry, nuclear magnetic resonance, X-ray diffraction analysis, and biosynthetic considerations. Difluostatin I () represents the first example with an A-ring-cleaved 3',4'--fluostatin skeleton. The absolute configuration of fluostatin T () was determined by X-ray diffraction analysis. Fluostatin W () contains an uncommon isoxazolinone ring. These findings highlight the structural diversity of fluostatins.