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.

Determining permeability of a given compound through human skin is a principal challenge owing to the highly complex nature of dermal tissue. We describe the application of an ambient mass spectrometry imaging method for visualizing skin penetration of sodium channel modulators, including novel synthetic analogs of natural neurotoxic alkaloids, topically applied ex vivo to human skin. Our simple and label-free approach enables successful mapping of the transverse and lateral diffusion of small molecules having different physicochemical properties without the need for extensive sample preparation.

A novel family of small molecule inhibitors of voltage-gated sodium channels (Navs) based on the structure of batrachotoxin (BTX) – a well-known channel agonist – is described. Protein mutagenesis and electrophysiology experiments reveal the binding site as the inner pore region of the channel, analogous to BTX, alkaloid toxins, and local anesthetics. Homology modeling of the eukaryotic channel based on recent crystallographic analyses of bacterial NaVs suggests a mechanism of action for ion conduction block.

Non-alcoholic steatohepatitis (NASH) is a serious chronic liver disease characterized by progressive fibrosis that can lead to cirrhosis, liver failure, and death. Compound 1 is a farnesoid X receptor (FXR) agonist that was investigated for use as a treatment for NASH. This paper describes process development efforts enabling the first multikilogram scale-up.