Relative toxicities and neuromuscular nicotinic receptor agonistic potencies of anabasine enantiomers and anabaseine

Abstract

Anabasine occurring in wild tree tobacco ( Nicotiana glauca) and anabaseine occurring in certain animal venoms are nicotinic receptor agonist toxins. Anabasine lacks the imine double bond of anabaseine; the two possible enantiomers of anabasine occur in N. glauca. A comparision of the relative potencies of S- and R-anabasine has not been previously reported. We separated the enantiomers of anabasine by reaction of the racemic N. glauca natural product with 9-fluorenylmethoxycarbonyl- l-alanine (Fmoc- l-Ala-OH) to give diastereomers, which were separated by preparative reversed phase HPLC. The S- and R-anabasine enantiomer fractions were then obtained by Edman degradation. A mouse bioassay was used to determine the relative lethalities of S- and R-enriched anabasine enantiomers. The intravenous LD 50 of the (+)- R-anabasine rich fraction was 11 ± 1.0 mg/kg and that of the (−)- S-anabasine-rich fraction was 16 ± 1.0 mg/kg. The LD 50 of anabaseine was 0.58 ± 0.05 mg/kg. Anabaseine was significantly more toxic in the mouse bioassay than S-anabasine (27-fold) and R-anabasine (18-fold). The relative agonistic potencies of these three alkaloids on human fetal nicotinic neuromuscular receptors were of the same rank order: anabaseine ≫ R-anabasine > S-anabasine.