title: Homoanatoxin: a potent analogue of anatoxin-A.
abstract: The natural toxin anatoxin-a (AnTx) is a potent nicotinic agonist that is valuable for the study of nicotinic receptors. We have synthesized 2-(propan-1-oxo-1-yl)-9-azabicyclo[4.2.1]non-2-ene, the homologue of AnTx in which the side-chain is extended by one methylene unit from a methyl to an ethyl ketone. This chemistry would allow the generation of a tritiated product and the homologue, designated homoanatoxin (HomoAnTx), has been characterized here with that aim in mind. In competition binding assays at neuronal nicotinic ligand binding sites characterized by [3H]nicotine and [125I]-alpha bungarotoxin, HomoAnTx retained the same potency as the parent molecule, with Ki values of 7.5 nM and 1.1 microM, respectively. In contrast, it showed little inhibition of muscarinic binding defined by [3H]-quinuclidinyl benzilate. HomoAnTx is a potent nicotinic agonist in frog muscle contracture assays, having four times the potency of carbamylcholine and one tenth of the activity of AnTx itself. The N-methylated version of HomoAnTx was more than two orders of magnitude weaker in both functional and binding assays. The successful synthesis of HomoAnTx with retention of high nicotinic potency offers a route for the generation of novel, potent radiolabelled nicotinic ligands.
authors.affiliation: Department of Biochemistry, University of Bath, Claverton Down, U.K.
authors.forename: S
authors.initials: S
authors.lastname: Wonnacott
authors.forename: K L
authors.initials: KL
authors.lastname: Swanson
authors.forename: E X
authors.initials: EX
authors.lastname: Albuquerque
authors.forename: N J
authors.initials: NJ
authors.lastname: Huby
authors.forename: P
authors.initials: P
authors.lastname: Thompson
authors.forename: T
authors.initials: T
authors.lastname: Gallagher
mesh_terms: D000818:Animals; D001372:Aza Compounds / Q000138:chemical synthesis* / Q000494:pharmacology; D001427:Bacterial Toxins / Q000737:chemistry*; D001665:Binding Sites / Q000187:drug effects; D001667:Binding, Competitive; D001643:Bridged Bicyclo Compounds / Q000138:chemical synthesis* / Q000494:pharmacology; D019086:Bridged Bicyclo Compounds, Heterocyclic; D000087522:Cyanobacteria Toxins; D007553:Isotope Labeling; D008387:Marine Toxins / Q000737:chemistry*; D052998:Microcystins; D009119:Muscle Contraction / Q000187:drug effects; D011978:Receptors, Nicotinic / Q000187:drug effects; D014326:Tropanes
chemical_list: D001372:Aza Compounds; D001427:Bacterial Toxins; D001643:Bridged Bicyclo Compounds; D019086:Bridged Bicyclo Compounds, Heterocyclic; D000087522:Cyanobacteria Toxins; D008387:Marine Toxins; D052998:Microcystins; D011978:Receptors, Nicotinic; D014326:Tropanes; C073221:homoanatoxin; C509783:anatoxin a