Component of the seco-iridoid and derivatives monoterpenoid indole alkaloids (MIAs, e.g. vinblastine, catharanthine, tabersonine, vincadifformine, vindoline, vincristine, quinine and strychnine) biosynthesis pathway. Converts O-acetylstemmadenine (OAS) to reactive acetylated intermediates, likely dihydroprecondylocarpine acetate. O-acetyl-15alpha-stemmadenine + O2 = H2O2 + precondylocarpine acetate Alkaloid biosynthesis. First targeted to endoplasmic reticulum (ER) and progressively secreted to vacuole by ER-derived vesicles. Expressed in leaf epidermis. Accumulates O-acetylstemmadenine (OAS) at the expense of catharanthine and vindoline (PubMed:30256480, PubMed:29724909). Strong accumulation of stemmadenine acetate (PubMed:29724909). Belongs to the oxygen-dependent FAD-linked oxidoreductase family.