PT  - JOURNAL ARTICLE
AU  - McDonald, Allwin
AU  - Nakamura, Yoko
AU  - Schotte, Carsten
AU  - Lau, Kin
AU  - Alam, Ryan
AU  - Lopes, Adriana A.
AU  - Buell, C. Robin
AU  - O’Connor, Sarah
TI  - Enzymatic epimerization of monoterpene indole alkaloids in Kratom
AID  - 10.1101/2024.12.13.628308
DP  - 2024 Jan 01
TA  - bioRxiv
PG  - 2024.12.13.628308
4099  - http://biorxiv.org/content/early/2024/12/13/2024.12.13.628308.short
4100  - http://biorxiv.org/content/early/2024/12/13/2024.12.13.628308.full
AB  - Monoterpene indole alkaloids (MIAs) are a large, structurally diverse class of bioactive natural products. These compounds are biosynthetically derived from a stereoselective Pictet-Spengler condensation that generates a tetrahydro-β-carboline scaffold characterized by a 3S stereocenter. However, a subset of MIAs contain a non-canonical 3R stereocenter. Herein, we report the basis for 3R-MIA biosynthesis in Mitragyna speciosa (Kratom). We discover the presence of the iminium species, 20S-3-dehydrocorynantheidine, which led us to hypothesize that isomerization of 3S to 3R occurs by oxidation and stereoselective reduction downstream of the initial Pictet-Spengler condensation. Isotopologue feeding experiments implicated young leaves and stems as the sites for pathway biosynthesis, facilitating the identification of an oxidase/reductase pair that catalyzes this epimerization. This enzyme pair has broad substrate specificity, suggesting that the oxidase and reductase may be responsible for the formation of many 3R-MIAs and downstream spirooxindole alkaloids in Kratom. These enzymes allow biocatalytic access to a range of previously inaccessible pharmacologically active compounds.Competing Interest StatementThe authors have declared no competing interest.