Purification, solubility, and pKa of veratridine

The alkaloid neurotoxin veratridine is widely used by cell physiologists to increase membrane sodium permeability. The compound is only sporadically available from commercial sources, but can be purified (Kupchan et al., 1953, J. Amer. Chem. Soc. 75, 5519-5524) from veratrine, a mixture of several alkaloids. We describe here a purification procedure only slightly modified from that of Kupchan et al., and include important details not mentioned in the original paper. Ultraviolet and infrared spectra are presented. We have also determined the pKa and solubility of veratridine in 150 mM NaCl at 25 degrees C. The solubility is steeply pH dependent, ranging from 0.61 +/- 0.02 mM above pH 12 to 18.5 mM at pH 8.07. The pKa, determined from the solubility versus pH curve, was found to be 9.54 +/- 0.02.