Cytochrome P450 monooxygenase; part of the gene cluster that mediates the biosynthesis of burnettramic acids, an unusual class of bolaamphiphilic pyrrolizidinediones that display potent antibacterial, antifungal, and cytotoxic activities (PubMed:30735051). The first step of the biosynthesis of burnettramic acids is the hydroxylation of proline by the proline hydroxylase buaE to generate 4-hydroxyproline (PubMed:30735051). The PKS-NRPS buaA and trans-enoyl reductase buaC construct the highly reduced polyketide chain, and the condensation (C) domain of buaA then catalyzes the amide bond formation with the activated 4-hydroxyproline (PubMed:30735051). This is followed by the R domain releasing the nascent polyketide-peptide directly via a Dieckmann condensation to afford a tetramic acid fused to the hydroxyproline, generating the bicyclic pyrrolidinedione moiety (PubMed:30735051). The cytochrome P450 monooxygenases buaD and buaG are likely responsible for the multiple hydroxylations on the polyketide chain and its terminus, although in the heterologous context, buaD does not appear to be required. Therefore, while buaG may be a multifunctional cytochrome P450 monooxygenase, it cannot be ruled out that the two secondary alcohols on the polyketide chain could have an acetate origin (PubMed:30735051). Finally, the glycosyltransferase buaB transfers beta-D-mannose to the aglycone burnettramic acid A to form burnettramic acid A (PubMed:30735051). Burnettramic acid B is a minor cis-pyrrolizidine epimer of burnettramic acid A and it is likely that small amounts of it form naturally in acidic environments (PubMed:30735051). Mycotoxin biosynthesis. Belongs to the cytochrome P450 family.