New 1,4-Dihydropyridines Endowed with NO-Donor and Calcium Channel Agonist Properties Sonja Visentin, † Barbara Rolando, † Antonella Di Stilo, † Roberta Fruttero, † Monica Novara, ‡ Emilio Carbone, ‡ Christian Roussel, § Nicolas Vanthuyne, § and Alberto Gasco* ,† Dipartimento di Scienza e Tecnologia del Farmaco, Universita ` degli Studi di Torino, via Pietro Giuria 9, I-10125 Torino, Italy, Dipartimento di Neuroscienze, Unita ` di ricerca INFM, Universita ` degli Studi di Torino, Corso Raffaello 30, I-10125 Torino, Italy, and UMR “Chirotechnologies: catalyse et biocatalyse”, Universite ´ Aix-Marseille III, Av. Escadrille Normandie Niemen, F-13397 Marseille Cedex 20, France Received November 24, 2003 A new series of calcium channel agonists structurally related to Bay K8644, containing NO donor furoxans and the related furazans unable to release NO, is described. The racemic mixtures were studied for their action on L-type Ca 2+ channels expressed in cultured rat insulinoma RINm5F cells. All the products proved to be potent calcium channel agonists. All the racemic mixtures, with the only exception of the carbamoyl derivatives 9, 12 endowed with scanty solubility, were separated by chiral chromatography into the corresponding enantiomers; the (+) enantiomers were found to be potent agonists while the (-) ones were feeble antagonists. The racemic mixtures were also assessed for their positive inotropic activity on electrically stimulated rat papillary muscle and for their ability to increase Ca 2+ entry into the vascular smooth muscle of rat aorta strips. The cyanofuroxan 8 proved to be an interesting product with dual Ca 2+ -dependent positive inotropic and NO-dependent vasodilating activity. Introduction 1,4-Dihydropyridines (DHPs) of general structure A (Chart 1) are an important class of drugs able to block the Ca 2+ currents through voltage-dependent L-type channels. 1 It is known that when an appropriate group, such as the nitro group, is substituted in A for one of the two ester functions, the resulting two enantiomers display opposite pharmacological profiles. 2 Bay K 8644 is a typical example (Chart 1). The (-) S-antipode is a potent agonist at L-type Ca 2+ -channels while the (+) R-antipode is a feeble antagonist. The Ca 2+ -channel agonists are potentially useful in therapy as positive inotropic agents, in particular for the treatment of the congestive heart failure (CHF). 3-5 The practical use is limited by their additional capacity to increase Ca 2+ entry into vascular smooth muscle with the consequent constriction. NO donors are a class of products which display potent vasodilating properties. 6 This is because they are able to release NO in physiological conditions. Hybrid structures in which 1,4-dihydropyridines able to activate L-type Ca 2+ channels are connected with suitable NO-donor moieties could represent a new interesting class of positive inotropic agents, devoid of vasoconstrictor properties. Two examples of this ap- proach were recently reported in the literature. 7,8 On these bases, we designed new 1,4-dihydropyridines formally obtained by substitution of appropriately sub- stituted NO-donor furoxan substructures for the CF 3 group in Bay K 8644 (derivatives 8, 9, 10). We herein describe the syntheses of these products and the action of their racemic mixtures on L-type Ca 2+ channels expressed by rat insulinoma cell line (RINm5F cells). The racemic mixtures 8, 10 were resolved by chiral chromatography, and the abilities of the single stere- oisomers to modulate the calcium channels were as- sessed. In the case of these latter racemates, namely of products that release small and large amounts of NO respectively, their actions on rat aorta strips partially depolarized with 10 mM K + as well as their inotropic actions evaluated on electrically stimulated rat papillary muscle are also discussed. For control purposes parallel studies were done on the furazan analogues (derivatives 11, 12, 13) devoid of the properties to release NO. Results and Discussion Chemistry. The aldehydes 3, 4, 5 were used as starting materials for the synthesis of the final products. Aldehydes 4, 5 were described in a previous paper, 9 while 3 was obtained from the related (bromomethyl)- furoxan 2 through nucleophilic substitution of the bromine by o-hydroxybenzaldehyde (1) in DMF, in the presence of potassium carbonate (Scheme 1A). The furoxan 1,4-DHPs 8, 9, 10 were prepared by a modified Hantzsch reaction, namely by condensation of the appropriate aldehydes with nitroacetone 6 and methyl 3-aminocrotonate 7 (Scheme 1B) in 2-propanol. For compound 8 the reaction was conducted at 40 °C to avoid thermal furoxan isomerization. The furazan DHPs 11, 12, 13 were obtained by reduction of the furoxan analogues in boiling trimethyl phosphite. The furoxan compounds were assessed for their ability to produce nitrite (NO 2 - ) (Griess reaction) in buffer * To whom correspondence should be addressed. Telephone: 0039 011 6707670. Fax: 0039 011 6707286. E-mail: alberto.gasco@unito.it. † Dipartimento di Scienza e Tecnologia del Farmaco, Universita ` degli Studi di Torino. ‡ Dipartimento di Neuroscienze, Universita ` degli Studi di Torino. § Universite ´ Aix-Marseille III. Chart 1 2688 J. Med. Chem. 2004, 47, 2688-2693 10.1021/jm031109v CCC: $27.50 © 2004 American Chemical Society Published on Web 04/01/2004