Asymmetric synthesis of batrachotoxin: Enantiomeric toxins show functional divergence against NaV.

The steroidal neurotoxin (-)-batrachotoxin functions as a potent agonist of voltage-gated sodium ion channels (Nas). Here we report concise asymmetric syntheses of the natural (-) and non-natural (+) antipodes of batrachotoxin, as well both enantiomers of a C-20 benzoate-modified derivative. Electrophysiological characterization of these molecules against Na subtypes establishes the non-natural toxin enantiomer as a reversible antagonist of channel function, markedly different in activity from (-)-batrachotoxin. Protein mutagenesis experiments implicate a shared binding side for the enantiomers in the inner pore cavity of Na These findings motivate and enable subsequent studies aimed at revealing how small molecules that target the channel inner pore modulate Na dynamics.