HNS-32, a novel azulene-1-carboxamidine derivative, inhibits nifedipine-sensitive and -insensitive contraction of the isolated rabbit aorta

Synthesis of bicyclo[5.3.0]azulene derivatives

Azulene has been recognized for its application in medicinal therapy against inflammation. Recently, azulene analogs have been used in optical technology. Nevertheless, synthesis of this family of compounds is always associated with multiple challenges. In this protocol, we describe a time-efficient and cost-effective procedure for the preparation of azulene derivatives from 2-hydroxycyclohepta-2,4,6-trienone (tropolone), a readily available starting material. The technique illustrated here involves a cycloaddition reaction of a lactone with the in situ-generated vinyl ether from 2,2-dimethoxypropane during the thermolysis reaction. The three-step synthesis should take <4 d, resulting in an overall yield of 74% with a final step yield of 91%.

Functional contribution of voltage-dependent and Ca2+ activated K+ (BK(Ca)) channels to the relaxation of guinea-pig aorta in response to natriuretic peptides

We examined the relaxant effects of natriuretic peptide family on the isolated guinea-pig aorta to determine the receptor subtype which primarily mediates this vascular relaxation, with particular attention to the apparent contribution of voltage-dependent and Ca2+-activated KS (BK(Ca)) channels to the response. Three endogenous natriuretic peptide ligands (natriuretic peptide, ANP; brain natriuretic peptide, BNP; C-type natriuretic peptide, CNP) produced a concentration-dependent relaxation in de-endothelialized guinea-pig aorta pre-contracted by noradrenaline (NA), with a potency order of ANP > or = BNP >> CNP. Although the relaxations elicited by these three natriuretic peptide ligands were significantly diminished by iberiotoxin (IbTx, 10(-7) M), a selective BK(Ca) channel blocker, the inhibitory effect of IbTx was most pronounced for the CNP-induced relaxation; when estimated at 10(-7) M of each peptide, the apparent extent of BK(Ca) channel contribution to the total relaxant response was approximately 60% for CNP > approximately 20% for either ANP or BNP. Supporting the substantial role of BK(Ca) channels in the vascular responses, high-KCl (80 mM) potently suppressed the relaxations induced by these natriuretic peptide ligands. The relaxant response to 8-Bromo-cyclic GMP, a membrane permeable cyclic GMP analogue, was also diminished by IbTx (10(-7) M) and high-KCl (80 mM), which indicates the key role of cyclic GMP in the BK(Ca) channel-mediated, natriuretic peptide-elicited vascular relaxation. These results indicate that the A-type receptor (NPR-A, which is more selective for ANP and BNP) rather than the B-type receptor (NPR-B, which is more selective for CNP) predominates in the guinea-pig aorta as the natriuretic peptide receptor which mediates this vascular smooth muscle relaxation. Although activation of BK(Ca) channels substantially contributes to both NPR-A- and NPR-B-activated relaxations, particularly in the NPR-B-activated relaxation, this K channel may function as a primary relaxant mediator in this conduit artery.

Cardiovascular effects of orally administered HNS-32, an originally synthesized azulene-1-carboxamidine derivative, assessed in the in vivo rat model

HNS-32, an azulene-1-carboxamidine derivative, is an originally synthesized antiarrhythmic compound. Its cardiovascular effects after oral administration (1-10 mg/kg) were assessed using the pentobarbital-anesthetized in vivo rat model in comparison with those of verapamil (3 mg/kg, p.o.). Verapamil decreased the heart rate and mean blood pressure and prolonged the PR interval without changing the QRS width (n = 6). Similar results were observed for HNS-32 except that the QRS width was prolonged by the highest dose and the effects occurred slowly and lasted longer. These results suggest that HNS-32 is an orally active slowly-acting calcium plus sodium channel blocker.

A review of HNS-32: a novel azulene-1-carboxamidine derivative with multiple cardiovascular protective actions

HNS-32 [N(1),N(1)-dimethyl-N(2)-(2-pyridylmethyl)-5-isopropyl-3,8-dimethylazulene-1- carboxamidine] (CAS Registry Number: 186086-10-2) is a newly synthesized azulene derivative. Computer simulation showed that its three dimensional structure is similar to that of the class Ib antiarrhythmic drugs, e.g., lidocaine or mexiletine. HNS-32 potently suppressed ventricular arrhythmias induced by ischemia due to coronary ligation and/or ischemia-reperfusion in dogs and rats. In the isolated dog and guinea pig cardiac tissues, HNS-32 had negative inotropic and chronotropic actions, prolonged atrial-His and His-ventricular conduction time and increased coronary blood flow. In the isolated guinea pig ventricular papillary muscle, HNS-32 decreased maximal rate of action potential upstroke (Vmax) and shortened action potential duration (APD). These findings suggest that HNS-32 inhibits inward Na+ and Ca2+ channel currents. In the isolated pig coronary and rabbit conduit arteries, HNS-32 inhibited both Ca2+ channel-dependent and -independent contractions induced by a wide variety of chemical stimuli. HNS-32 is a potent inhibitor of protein kinase C (PKC)-mediated constriction of cerebral arteries. It is likely to block both, Na+ and Ca2+ channels expressed in cardiac and vascular smooth muscles. These multiple ion channel blocking effects are largely responsible for the antiarrhythmic and vasorelaxant actions of HNS-32. This drug may represent a novel approach to the treatment of arrhythmias.