FAD-dependent monooxygenase; part of the gene cluster that mediates the biosynthesis of the polyenes aspernidgulenes (PubMed:30302871). The carbon backbone of aspernidgulenes is synthesized by the HR-PKS sdgA, which accepts acetyl-CoA as the starter unit and performs malonyl-CoA extensions as well as regioselective methylation and reduction (PubMed:30302871). The resulting nonaketide offloads the HR-PKS by intramolecular lactonization to yield the 5,6-dihydro-alpha-pyrone-containing hexaenoic acids preaspernidgulene A1 and A2 (PubMed:30302871). The FAD-dependent monooxygenase sdgC then installs the first epoxide on the penultimate double bond (PubMed:30302871). Subsequently, the FAD-dependent monooxygenase sdgF presumably generates a ketone intermediate through Meinwald rearrangement involving a hydride shift (PubMed:30302871). Next, sdgC introduces another epoxide on the last olefin of the ketone intermediate after E/Z isomerization (PubMed:30302871). The epoxide hydrolase sdgD then catalyzes stereospecific cyclization of the 5,6-dihydro-alpha-pyrone and opening of the epoxide ring to form an oxygenated trimethylcyclopentanone and an oxabicyclo[2.2.1]heptane unit (PubMed:30302871). Finally, the bicyclic unit undergoes hydrolytic cleavage, either spontaneously or catalyzed by sdgD, to assemble the dimethyl-gamma-lactone moiety in aspernidgulene A1 (PubMed:30302871). Secondary metabolite biosynthesis. Belongs to the paxM FAD-dependent monooxygenase family.