Synthesis and biological evaluation of N-methyl-laudanosine iodide analogues as potential SK channel blockers

• Published in: Bioorganic & medicinal chemistry Vol. 13; no. 4; pp. 1201 - 1209
• Main Authors: Graulich, A., Mercier, F., Scuvée-Moreau, J., Seutin, V., Liégeois, J.-F.
• Format: Journal Article Web Resource
• Language: English
• Published: Oxford Elsevier Ltd 15.02.2005; Elsevier Science
• Subjects: Animals; Biological and medical sciences; Human health sciences; Isoquinolines - chemical synthesis; Isoquinolines - pharmacology; Isoquinolines/chemical synthesis/pharmacology; Magnetic Resonance Spectroscopy; Male; Medical sciences; Miscellaneous; Neuropharmacology; Pharmacie, pharmacologie & toxicologie; Pharmacology. Drug treatments; Pharmacy, pharmacology & toxicology; Potassium Channels, Calcium-Activated - antagonists & inhibitors; Rats; Rats, Wistar; Sciences de la santé humaine; Spectrophotometry, Infrared; Organic cation; Rat; Potassium channel antagonist; Nitrogen heterocycle; Rodentia; Central nervous system; Benzene derivatives; Electrophysiology; In vitro; Encephalon; Quaternary ammonium compound; SK potassium channel; Vertebrata; Alkaloid; Mammalia; Neuromodulator; Structure activity relation; Animal; Enantiomer; Bicyclic compound; Dopaminergic neuron; Aromatic compound; Chemical synthesis
• ISSN: 0968-0896; 1464-3391; 1464-3391
• DOI: 10.1016/j.bmc.2004.11.025

[Display omitted] Neuronal action potentials are followed by an afterhyperpolarisation (AHP), which is mediated by small conductance Ca 2+-activated K + channels (SK channels or KCa2 channels). This AHP plays an important role in regulating neuronal activity and agents modulating AHP amplitude could have a potential therapeutic interest. It was previously shown that N-methyl-bicuculline iodide blocks SK channels but its GABA A activity represents a serious drawback. In view of the structural analogy between bicuculline and laudanosine 14, several N-quaternary analogues of the latter were developed. It was shown that N-methyl-laudanosine 15 (NML) and N-ethyl-laudanosine 16 induce a reversible and relatively specific blockade of the apamin sensitive AHP in dopaminergic neurones with mean IC 50s of 15, and 47 μM, respectively. Laudanosine 14, N-butyl- 17 and N-benzyl- 18 derivatives were less potent. In order to find pharmacophore elements, modifications were performed at different positions such as C-1, C-6 and C-7. Intracellular recordings on rat midbrain dopaminergic neurones were made in order to evaluate the putative blockade of SK channels by these molecules. Simplified structures such as tetrahydroisoquinoline derivatives with H or Me at C-1 1– 6 presented no significant activity at 300 μM. The presence of a 1-(3,4-dimethoxybenzyl) moiety seems an important feature. Indeed, compound 8 showed a blockade of the AHP of only 33% at 300 μM while compound 13 blocked it by 67%, respectively, at the same concentration. Binding experiments were also performed. Binding affinities for SK channels are in good agreement with electrophysiological data. These results indicate that the presence of a charged nitrogen group is an essential point for the affinity on SK channels. Finally, because of the similar activity of both enantiomers of NML 19 and 20, the interaction site may present a symmetrical configuration.