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

The steroidal neurotoxin (-)-batrachotoxin functions as a potent agonist of voltagegated sodium ion channels (Na(V)s). 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-V 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-V. These findings motivate and enable subsequent studies aimed at revealing how small molecules that target the channel inner pore modulate Na-V dynamics.