(+)-Laburnamine, a natural selective ligand and partial agonist for the alpha4beta2 nicotinic receptor subtype

(+)-Laburnamine (1), a rare alkaloid extracted from Laburnum anagyroides seeds (~ 4 mg from 1 kg), was shown to bind with high affinity (Ki, 293 nM) to the ?4?2 nicotinic receptor subtype, which is, respectively, 126 and 136 times higher than that to the ?3?4 (Ki 37 ?M), and ?7 subtypes (Ki 40 ?M). When its ability to release [3H]-dopamine from striatal slices was tested in a functional assay, compound 1 behaved as a partial agonist with an EC50 of 5.8 ?M and an Emax that was 43% that of nicotine. When incubated with nicotine in the same assay, 1 prevented a maximal effect from being reached.