Synthesis and voltage-clamp studies of methyl 1,4-dihydro-2,6-dimethyl-5-nitro-4-(benzofurazanyl)pyridine-3-carboxylate racemates and enantiomers andof their benzofuroxanyl analogues

Racemic methyl 1,4-dihydro-2,6-dimethyl-5-nitro-4-(benzofurazanyl)pyridine- 3-carboxylates(+/-)-10 and (+/-)-11 and their benzofuroxanyl analogues (+/- )-12 and (+/-)-13 were prepared using a modified Hantzsch reaction that inv olved the condensation of nitroacetone with methyl 3-aminocrotonate and the appropriate aldehydes. The racemic mixtures were resolved into the corresp onding enantiomers. Whole-cell voltage-clamp studies on L-type Ca2+ channel s expressed in a rat insulinoma cell line (RINm5F) showed that all the dext rorotatory antipodes were effective agonists of L-type Ca2+ currents, while the levorotatory ones were weak Ca2+ entry blockers. The (+)-enantiomer of benzofurazan-5'-yl derivative 11 demonstrated unusual activity in that, in addition to producing a potentiation of L-type currents, it interfered wit h the voltage-dependent gating of L-type channels by producing a net delay of their activation at low voltages. This compound represents an interestin g tool to probe L-type Ca2+ channel structure and function.