biostudies-literatureUnknownMann SGANatural Sciences and Engineering Research Council of CanadaSarpagan and akuammiline monoterpenoid indole alkaloids (MIAs) are a class of bioactive plant-derived compounds with significant pharmaceutical potential. These alkaloids are formed through oxidative cyclization of geissoschizine, catalyzed by homologous cytochrome P450 monooxygenases (CYP) known as sarpagan bridge enzymes (SBEs) and rhazimal synthases (RHSs). However, a long-standing discrepancy exists between the expected C16 stereochemistry of enzymatic products and the stereochemistry of naturally occurring derivatives. This study investigates C16 stereochemistry outcomes after geissoschizine cyclization and subsequent enzymatic transformations in six MIA-producing species. We combine comparative gene discovery, in planta gene silencing of Catharanthus roseus SBE, in vitro enzyme charaThe New phytologisthttps://www.ebi.ac.uk/biostudies/studies/S-EPMC12222928biostudies-literatureStereochemical insights into sarpagan and akuammiline alkaloid biosynthesis.PMC12222928Paz-Galeano MPerley JOGuo JMann SGAQu YShahsavarani MGarza-Garcia JJOfalseStereochemical insights into sarpagan and akuammiline alkaloid biosynthesis.Sarpagan and akuammiline monoterpenoid indole alkaloids (MIAs) are a class of bioactive plant-derived compounds with significant pharmaceutical potential. These alkaloids are formed through oxidative cyclization of geissoschizine, catalyzed by homologous cytochrome P450 monooxygenases (CYP) known as sarpagan bridge enzymes (SBEs) and rhazimal synthases (RHSs). However, a long-standing discrepancy exists between the expected C16 stereochemistry of enzymatic products and the stereochemistry of naturally occurring derivatives. This study investigates C16 stereochemistry outcomes after geissoschizine cyclization and subsequent enzymatic transformations in six MIA-producing species. We combine comparative gene discovery, in planta gene silencing of Catharanthus roseus SBE, in vitro enzyme chara2025-01-01T00:00:00Z2025 Jun2025-07-28T03:04:09.852Z2025-07-28T03:04:09.852ZS-EPMC122229284045897310.1111/nph.70272