Synthesis pathway of saxitoxin
Biosynthetic pathway for saxitoxin (modified from Shimizu 1993). (1) Claisen condensation between arginine and acetate; (2) amidinotransfer from a second arginine to α-amino group of first intermediate; (3) formation of the first heterocycle by a retro-aldol-like condensation; (4) formation of the remaining two heterocycles by unknown reactions; (5) introduction of methyl side chain by electrophilic attachment; (6) rearrangement involving 1,2-H shift from C-6 to C-5; (7) epoxidation of methyl side chain; (8) opening of epoxide to an aldehyde; (9) reduction of aldehyde to alcohol; (10) O-carbamoyl transfer and oxidation reactions completing the STX molecule. "=X" in the intermediates may be two hydrogens, a keto, or two hydroxy groups.
- Kellmann, R & Neilan, B. 2007. Biochemical characterization of paralytic shellfish toxin biosynthesis in vitro. Journal of Phycology 43 (3), 497-508).
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