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Methyllycaconitine (MLA, 1) is a novel, potent probe for mammalian and insect nicotinic acetylcholine receptors (nAChR) and displays remarkable selectivity toward neuronal [125I]-alpha-bungarotoxin (alpha BgTX) binding sites that correspond to alpha 7-type nAChR in mammalian brain. We have shown that, among a number of selected norditerpenoid alkaloids, elatine (2) and nudicauline (3) are equipotent with, or better than, MLA (1) in binding to brain [125I]-alpha BgTX binding sites, with IC50 values of 6.1, 1.7, and 7.6 nM, respectively. The 2-((S)-methylsuccinimido)benzoyl moiety of these ligands is crucial for high-affinity binding, whereas structural modifications to the norditerpenoid core of the ligand can be tolerated without loss of activity or selectivity. In addition to MLA (1), elatine (2), and nudicauline (3), we have examined lycoctonine (4), inuline (6), lappaconitine (7), N-desacetyllappaconitine (8), delsoline (10), delcorine (11), deltaline (12), condelphine (13), and karacoline (14). This study therefore extends the range of norditerpenoids, other than MLA, which can be used to probe this important class of nAChR. All 12 alkaloids were assessed for activity at [3H]nicotine binding sites which are considered to represent alpha 4 beta 2 nAChR. Furthermore, the 1H and 13C NMR spectroscopic data of MLA and elatine have been critically compared.

Original publication

DOI

10.1021/jm9604991

Type

Journal article

Journal

J Med Chem

Publication Date

22/11/1996

Volume

39

Pages

4860 - 4866

Keywords

Aconitine, Alkaloids, Animals, Binding Sites, Binding, Competitive, Brain, Bungarotoxins, Cell Membrane, Magnetic Resonance Spectroscopy, Protein Binding, Rats, Receptors, Nicotinic, Structure-Activity Relationship, Succinimides