Total syntheses of Tetrodotoxin and 9-epiTetrodotoxin

Tetrodotoxin and congeners are specific voltage-gated sodium channel blockers that exhibit remarkable anesthetic and analgesic effects. Here, we present a scalable asymmetric syntheses of Tetrodotoxin and 9-epiTetrodotoxin from the abundant chemical feedstock furfuryl alcohol. The optically pure cyclohexane skeleton is assembled via a stereoselective Diels-Alder reaction. The dense heteroatom substituents are established sequentially by a series of functional group interconversions on highly oxygenated cyclohexane frameworks, including a chemoselective cyclic anhydride opening, and a decarboxylative hydroxylation. An innovative SmI₂-mediated concurrent fragmentation, an oxo-bridge ring opening and ester reduction followed by an Upjohn dihydroxylation deliver the highly oxidized skeleton. Ruthenium-catalyzed oxidative alkyne cleavage and formation of the hemiaminal and orthoester under acidic conditions enable the rapid assembly of Tetrodotoxin, anhydro-Tetrodotoxin, 9-epiTetrodotoxin, and 9-epi lactone-Tetrodotoxin.