Anabaseine causes paralysis in crustaceans and insects, but not in vertebrates, presumably by acting as an agonist on peripheral neuromuscular nicotinic acetylcholine receptors.[2]
Structure
The anabaseine molecule consists of a non-aromatic tetrahydropyridine ring connected to the 3rd carbon of a 3-pyridyl ring. It can exist in three forms at physiological pH: a ketone, imine, or iminium structure.[2] Due to conjugation between the imine and 3-pyridyl ring, anabaseine exists as a nearly coplanar molecule.
Spath and Mamoli first synthesized anabaseine in 1936.[4] The researchers reacted benzoic anhydride with δ-valerolactam to yield N-benzoylpiperidone. Then, N-benzoylpiperidone is reacted with nicotinic acid ethyl ester to produce α-nicotinoyl-N-benzoyl-2-piperidone. This product then is decarboxylated, undergoes a ring closure, and amide hydrolysis to form anabaseine.
Additional synthetic strategies have since been developed by Bloom,[5] Zoltewicz,[6] Smith,[7] and Villemin.[8]
Derivatives
Due to anabaseine’s fairly non-specific binding to nicotinic acetylcholine receptors, the molecule was largely discarded as a useful tool in research or medicine. However, anabaseine derivatives have been identified with a more selective α7 binding profile. One such derivative (GTS-21, 3-(2,4-dimethoxybenzylidene)-anabaseine) has been studied as a drug candidate for cognitive and memory deficits, particularly associated with schizophrenia; it has been studied in phase II clinical trials without progression to phase III.[9] Moreover, the modification of the anabaseine pyridine nucleus led to the obtainment of new derivatives endowed with binding and functional selectivity for the α3β4 nicotinic acetylcholine receptor subtype.[10]
