Katrina M Miranda

Nitroxyl (HNO) donors have been shown to elicit a variety of pharmacological responses, ranging from tumoricidal effects to treatment of heart failure. Isopropylamine-based diazeniumdiolates have been shown to produce HNO on decomposition under physiological conditions. Herein, we report the synthesis and HNO release profiles of primary alicyclic amine-based diazeniumdiolates. These compounds extend the range of known diazeniumdiolate-based HNO donors. Acetoxymethyl ester-protected diazeniumdiolates were also synthesized to improve purification and cellular uptake. The acetoxymethyl derivative of cyclopentylamine diazeniumdiolate not only showed higher cytotoxicity toward cancer cells as compared to the parent anion but was also effective in combination with tamoxifen for targeting estrogen receptor α-negative breast cancer cells.

PMID: 18682867;Abstract:

The synthesis of [Ru(NO2)L(bpy)2]⁺ (bpy = 2,2′-bipyridine and L = pyridine (py) and pyrazine (pz)) can be accomplished by addition of [Ru(NO)L(bpy)2](PF6) 3 to aqueous solutions of physiological pH. The electrochemical processes of [Ru(NO2)L(bpy)2]⁺ in aqueous solution were studied by cyclic voltammetry and differential pulse voltammetry. The anodic scan shows a peak around 1.00 V vs. Ag/AgCl attributed to the oxidation process centered on the metal ion. However, in the cathodic scan a second peak around -0.60 V vs. Ag/AgCl was observed and attributed to the reduction process centered on the nitrite ligand. The controlled reduction potential electrolysis at -0.80 V vs. Ag/AgCl shows NO release characteristics as judged by NO measurement with a NO-sensor. This assumption was confirmed by ESI/MS⁺ and spectroelectrochemical experiment where cis-[Ru(bpy) 2L(H2O)]²⁺ was obtained as a product of the reduction of cis-[Ru^II(NO2)L(bpy)2] ⁺. The vasorelaxation observed in denuded aortic rings pre-contracted with 0.1 μmol L^-1 phenylephrine responded with relaxation in the presence of cis-[Ru^II(NO2)L(bpy)2]⁺. The potential of rat aorta cells to metabolize cis-[Ru^II(NO 2)L(bpy)2]⁺ was also followed by confocal analysis. The obtained results suggest that NO release happens by reduction of cis-[Ru^II(NO2)L(bpy)2]⁺ inside the cell. The maximum vasorelaxation was achieved with 1 × 10^-5 mol L^-1 of cis-[Ru^II(NO2)L(bpy)2] ⁺ complex. © 2008 The Royal Society of Chemistry.

Nitroxyl anion (NO-) is the one-electron reduction product of nitric oxide (NO.) and is enzymatically generated by NO synthase in vitro. The physiologic activity and mechanism of action of NO- in vivo remains unknown. The NO- generator Angeli's salt (AS, Na2N2O3) was administered to conscious chronically instrumented dogs, and pressure-dimension analysis was used to discriminate contractile from peripheral vascular responses. AS rapidly enhanced left ventricular contractility and concomitantly lowered cardiac preload volume and diastolic pressure (venodilation) without a change in arterial resistance. There were no associated changes in arterial or venous plasma cGMP. The inotropic response was similar despite reflex blockade with hexamethonium or volume reexpansion, indicating its independence from baroreflex stimulation. However, reflex activation did play a major role in the selective venodilation observed under basal conditions. These data contrasted with the pure NO donor diethylamine/NO, which induced a negligible inotropic response and a more balanced veno/arterial dilation. AS-induced positive inotropy, but not systemic vasodilatation, was highly redox-sensitive, being virtually inhibited by coinfusion of N-acetyl-L-cysteine. Cardiac inotropic signaling by NO- was mediated by calcitonin gene-related peptide (CGRP), as treatment with the selective CGRP-receptor antagonist CGRP-(8-37) prevented this effect but not systemic vasodilation. Thus, NO- is a redox-sensitive positive inotrope with selective venodilator action, whose cardiac effects are mediated by CGRP-receptor stimulation. This fact is evidence linking NO- to redox-sensitive cardiac contractile modulation by nonadrenergic/noncholinergic peptide signaling. Given its cardiac and vascular properties, NO- may prove useful for the treatment of cardiovascular diseases characterized by cardiac depression and elevated venous filling pressures.

Abstract:

Described are the spectra and kinetics of transients formed by laser flash photolysis of the ruthenium nitrosyl nitrito complexes Ru(P)(NO)(ONO), P= TPP (meso-tetraphenylporphyrin), OEP (octaethylporphyrin), TmTP (tetra(m- tolyl)porphyrin); and FTTP (tetra(m-trifluoromethylphenyl)porphyrin)in benzene solutions. Two transient decay processes are seen on the time frame ( 1 ms) of the flash photolysis experiment, and a residual difference spectrum, which decays to baseline on a longer time frame, is noted as well. The accumulated evidence points to the formation of two primary photoproducts, Ru(P)(ONO) (A) formed by NO photolabilization and Ru(P)(NO) (B) formed by NO2 photolabilization. Both decay by NO dependent pathways, the reaction of A with NO to re-form Ru(P)(NO)(ONO) being substantially faster (2.4-5.5 x 10⁸ M^-1 s^-1 in ambient temperature benzene) than the reaction of B with NO (2.4-10 x 10⁷ M^-1 s^-1). The product of the latter reaction is apparently the dinitrosyl complex Ru(P)(NO)2, which undergoes a much slower thermal reaction with excess NO to give again Ru(P)(NO)(ONO). The possibility of B being the oxo complex O=Ru(P)(No) formed by NO loss from coordinated nitrite was considered but concluded to be a minor pathway at best. Isotopic exchange reactions using either labeled complex or labeled NO in cyclohexane demonstrate photochemical exchange of NO into both the nitrosyl and nitrito complexes, and time-resolved infrared experiments are consistent with formation of a long-lived nitrosyl-containing intermediate. Flash photolysis studies of the respective nitrosyl chloro complexes Ru(TPP)(NO)Cl and Ru(OEP)(NO)Cl indicate that only a single transient species, presumably Ru(P)Cl, is formed in each case, and this decays by a single NO dependent pathway back to starting material.

Abstract:

The synthesis, X-ray crystal structures, and some spectroscopic and chemical properties of the nitrosylruthenium(II) porphyrin complexes Ru(TPP) (NO) (ONO), Ru(TPP) (NO) (OH), Ru(OEP) (NO) (ONO), and Ru(OEP) (NO)-(OH) (TPP = tetraphenylporphyrinato dianion; OEP = octaethylporphyrinato dianion) derived from the analogous Ru(II) carbonyl complexes are reported. Also described are experiments which quantitatively demonstrate that N2O is formed as a product of the synthesis scheme and that NO serves as the principal oxidant in the transformation of N(II) to N(III). The two TPP complexes are isostructural and consist of columns of molecules stacked along the c axis. The two OEP complexes are also isostructural and can be considered as layers of OEP complexes stacked along the b axis with solvent molecules situated at the cavities between layers. The nitrite ions are coordinated in a unidentate fashion through the oxygen atom. Crystal data for Ru(TPP) (NO) (ONO) (1): M = 789.79, space group I4/m (No. 87), a = 13.6529(6) Å, c = 9.7904(5) Å, V = 1825.0(2) ų, Z = 2, ρ = 1.437 g cm^-3, purple bipyramid, 2θmax = 50.0°, R(F) = 4.87% for 86 parameters and 838 reflections with I > 2σ(I). Crystal data for Ru(TPP) (NO) (OH) (2): M = 760.79, space group I4/m (No. 87), a = 13.5423(4) Å, c = 9.7150-(4) Å, V= 1781.7(1) ų, Z = 2, ρ = 1 .418 g cm^-3, dark red plate, 2θmax = 50.0°, R(F) = 3.92% for 83 parameters and 811 reflections with I > 2σ(I). Crystal data for Ru(OEP) (NO)(ONO)·CH2Cl2 (3): M = 794.77, space group P21 (No. 4), a = 10.7687(2) Å, b = 21.0320(2) Å, c = 8.5936(2) Å, β= 102.683(1)°, V= 1898.85(6) ų, Z = 2, ρ = 1.390 g cm^-3, black plate, 2θmax = 50.0°, R(F) = 6.23% for 453 parameters and 4702 reflections with I > 2σ(I). Crystal data for Ru(OEP) (NO) (OH)·C2H5OH (4): M = 726.91, space group P21 (No. 4), a = 10.8474-(7) Ǎ, b = 21.002(1) Å, c = 8.3646(5) Å, β= 103.571(1)°, V= 1852.4(2) ų, Z= 2, ρ = 1.303 g cm^-3, brown plate, 2θmax = 45.0°, R(F) = 6.74% for 421 parameters and 3527 reflections with I > 2σ(I).