Design, synthesis, and in vitro evaluation of cyclic nitrones as free radical traps for the treatment of stroke

Enantioselective Synthesis of Cyclic Nitrones by Chemoselective Intramolecular Allylic Alkylation of Oximes

The enantio- and chemoselective iridium-catalyzed N-allylation of oximes is described for the first time. Intramolecular kinetic resolution provides access to cyclic nitrones and enantioenriched aliphatic allylic alcohols. Salient features of this transformation are its ability to employ E/Z-isomeric mixtures of oxime starting materials convergently and high functional group tolerance. The implementation of N-allylation/1,3-dipolar cycloaddition reaction sequences furnishes tricyclic isoxazolidines in highly enantio- and diastereoselective fashion. The synthetic utility of the approach is demonstrated by the efficient, formal synthesis of the marine natural product (+)-halichlorine.

5-Aryl-2-(3,5-dialkyl-4-hydroxyphenyl)-4,4-dimethyl-4H-imidazole 3-Oxides and Their Redox Species: How Antioxidant Activity of 1-Hydroxy-2,5-dihydro-1H-imidazoles Correlates with the Stability of Hybrid Phenoxyl-Nitroxides

Cyclic nitrones of the imidazole series, containing a sterically hindered phenol group, are promising objects for studying antioxidant activity; on the other hand, they can form persistent hybrid phenoxyl-nitroxyl radicals (HPNs) upon oxidation. Here, a series of 5-aryl-4,4-dimethyl-4H-imidazole 3-oxides was obtained by condensation of aromatic 2-hydroxylaminoketones with 4-formyl-2,6-dialkylphenols followed by oxidation of the initially formed N-hydroxy derivatives. It was shown that the antioxidant activity of both 1-hydroxy-2,5-dihydroimidazoles and 4H-imidazole 3-oxides increases with a decrease in steric volume of the alkyl substituent in the phenol group, while the stability of the corresponding HPNs generated from 4H-imidazole 3-oxides reveals the opposite tendency.

Oxaazabicyclooctene Oxides, Another Type of Bridgehead Nitrones: Diastereoselective Assembly from Acetylene Gas, Ketones, and Hydroxyl Amine

Unique bridgehead nitrones, 8-oxa-6-azabicyclo[3.2.1]oct-6-ene 6-oxides, have been assembled diastereoselectively via acetyldihydropyrans, products of one-pot self-organization of two molecules of ketones and two molecules of acetylene, which after oximation undergo acid-catalyzed ring closure. The proposed mechanism includes the enol double-bond protonation, followed by intramolecular cyclization involving the interaction of the carbocation formed with a nitrogen atom. A broad range of substrates tolerate this facile transformation, in which the bridgehead nitrones were isolated in high yields.

Nickel-catalysed direct alkylation of thiophenes via double C(sp3)–H/C(sp2)–H bond cleavage: the importance of KH2PO4

A Ni-catalyzed C–H/C–H cross-dehydrogenative coupling (CDC) reaction was developed for constructing various highly functionalized alkyl (aryl)-substituted thiophenes.

Crystal structure of 3-meth-oxy-carbonyl-2-(4-meth-oxy-phen-yl)-8-oxo-1-aza-spiro[4.5]deca-1,6,9-trien-1-ium-1-olate

The title compound, C18H17NO5, was prepared by a synthetic strategy based on the Heck reaction from Morita-Baylis-Hillman adducts. The five-membered ring adopts a slightly twisted conformation on the Ca-Cm (a = aromatic and m = methyl-ene) bond. The dihedral angle between the five-membered ring and the spiro aromatic ring is 89.35 (7)°; that between the five-membered ring and the 4-meth-oxy-benzene ring is 4.65 (7)°. Two short intra-molecular C-H⋯O contacts occur. In the crystal, mol-ecules are linked by C-H⋯O hydrogen bonds to generate a three-dimensional network.

Pyrroles versus cyclic nitrones: catalyst-controlled divergent cyclization of N-(2-perfluoroalkyl-3-alkynyl) hydroxylamines

Divergent cyclizations ofN-(2-(perfluoroalkyl)-3-alkynyl) hydroxylamines1have been realized by subtle choice of the catalyst under mild conditions, leading to two distinct types of synthetic valuable compounds, cyclic nitrones2and pyrroles3, in moderate to excellent yields.

Novel retinoic acid receptor alpha agonists for treatment of kidney disease

Development of pharmacologic agents that protect podocytes from injury is a critical strategy for the treatment of kidney glomerular diseases. Retinoic acid reduces proteinuria and glomerulosclerosis in multiple animal models of kidney diseases. However, clinical studies are limited because of significant side effects of retinoic acid. Animal studies suggest that all trans retinoic acid (ATRA) attenuates proteinuria by protecting podocytes from injury. The physiological actions of ATRA are mediated by binding to all three isoforms of the nuclear retinoic acid receptors (RARs): RARα, RARβ, and RARγ. We have previously shown that ATRA exerts its renal protective effects mainly through the agonism of RARα. Here, we designed and synthesized a novel boron-containing derivative of the RARα-specific agonist Am580. This new derivative, BD4, binds to RARα receptor specifically and is predicted to have less toxicity based on its structure. We confirmed experimentally that BD4 binds to RARα with a higher affinity and exhibits less cellular toxicity than Am580 and ATRA. BD4 induces the expression of podocyte differentiation markers (synaptopodin, nephrin, and WT-1) in cultured podocytes. Finally, we confirmed that BD4 reduces proteinuria and improves kidney injury in HIV-1 transgenic mice, a model for HIV-associated nephropathy (HIVAN). Mice treated with BD4 did not develop any obvious toxicity or side effect. Our data suggest that BD4 is a novel RARα agonist, which could be used as a potential therapy for patients with kidney disease such as HIVAN.

Synthesis of a mitochondria-targeted spin trap using a novel Parham-type cyclization

A new cyclic nitrone spin trap, [4-(3′,3′-dibutyl-2′-oxy-3′H-isoindol-5′-yloxy)butyl]triphenylphosphonium bromide (MitoSpin), bearing a lipophilic cation has been prepared by a route that involves a novel Parham-type lithiation–cyclization of an isocyanate to give the isoindolinone core. MitoSpin accumulates in a membrane potential dependent way in energized mitochondria and its oxidation could potentially be used in the study of oxidative stress resulting from reactive oxygen species generated in mitochondria.

N-[2-(2-Methoxyphenyl)benzylidene]-tert-butyl-amine N-oxide

In the mol­ecule of the title compound, C₁₈H₂₁NO₂, the two benzene rings are oriented at a dihedral angle of 58.19 (3)°. Intra­molecular C—H⋯O hydrogen bonds result in the formation of one six- and one five-membered ring, which adopt twist and envelope conformations, respectively. In the crystal structure, C—H⋯O hydrogen bonds link the mol­ecules.

Intravenous Pharmacokinetics and Metabolism of the Reactive Oxygen Scavenger α-Phenyl-N-Tert-Butyl Nitrone (PBN) in the Cynomolgus Monkey

The pharmacokinetics and metabolism of the antioxidant and reactive oxygen scavenger alpha-phenyl-N-tert-butyl nitrone (PBN) was examined in the male cynomolgus monkey after intravenous administration. Following an i.v. bolus dose of 5 mg/kg, plasma concentrations of PBN declined in a bi-exponential fashion. PBN demonstrated a moderate plasma clearance (CL(p) = 27.02 +/- 6.46 ml/min/kg) and a moderate volume of distribution at steady state (Vd(ss) = 1.70 +/- 0.23 l/kg), resulting in a terminal elimination half-life of 0.76 +/- 0.25 h. The corresponding area under the curve (AUC(0-infinity)) was 3.20 +/- 0.77 microg-h/ml. Scale-up of the in vitro microsomal intrinsic clearance data for PBN afforded a blood clearance (CLb) value of 22 ml/min/kg, which was in reasonable agreement with the observed in vivo CLb. Monkey liver microsomes catalyzed the NADPH-dependent monohydroxylation of PBN to the corresponding alpha-4-hydroxyphenyl-N-tert-butylnitrone (4-HOPBN) metabolite. The formation of 4-HOPBN and its corresponding O-glucuronide was also discernible upon qualitative analysis of pooled (0-24 h) monkey plasma and urine samples. Less than 5% of the administered dose was excreted as unchanged PBN in the urine, suggesting that P450-catalyzed metabolism constituted the major route of PBN clearance in the primate. In conclusion, the pharmacokinetic attributes and the clearance mechanism of PBN in the cynomolgus monkey is similar to that observed in the Sprague-Dawley rat.

Pharmacokinetics and metabolism of the reactive oxygen scavenger alpha-phenyl-N-tert-butylnitrone in the male Sprague-Dawley rat

The pharmacokinetics of the spin-trap alpha-phenyl-N-tert-butylnitrone (PBN) was investigated in male Sprague-Dawley rats. Plasma concentrations after i.v. administration (10 mg/kg) declined monoexponentially with a terminal half-life of 2.01 +/- 0.35 h and total plasma clearance (CL(p)) and volume of distribution at steady state (Vd(ss)) averaged 12.37 +/- 3.82 ml/min/kg and 1.74 +/- 0.5 l/kg, respectively. The observed CL(p) was in close agreement with the blood clearance (CL(b)) value (11.5 ml/min/kg) predicted from in vitro liver microsomal incubations suggesting that PBN CL(p) in rats is predominantly due to hepatic metabolism. Peak plasma concentration (C(max)) following p.o. (20 mg/kg) and s.c. (30 mg/kg) PBN administration was 7.35 +/- 1.92 and 3.56 +/- 0.66 microg/ml, whereas the area under the concentration-time curve from 0 to infinity was 23.89 +/- 5.84 and 15.96 +/- 3.10 microg-h/ml, respectively. The mean oral bioavailability of PBN was 85.63 +/- 20.93%. Biotransformation studies indicated the P450 2C11-catalyzed hydroxylation of PBN to M1. Potential sites of hydroxylation included the benzylic carbon resulting in phenyl-N-tert-butylhydroxamic acid or the phenyl ring that would afford alpha-hydroxyphenyl-N-tert-butylnitrone (HOPBN). The structure of M1 was established as alpha-4-Hydroxyphenyl-N-tert-butylnitrone (4-HOPBN) on the basis of: 1) obvious LC R(t) differences between M1 and the authentic hydroxamate standard, 2) P450 catalyzed hydroxylation of [(2)H]PBN that contained a deuterium instead of a hydrogen atom on its benzylic position and which afforded [(2)H]M1, and 3) comparison of the liquid chromatography-tandem mass spectrometry properties with a synthetic 4-HOPBN standard. We speculate that 4-HOPBN is an "active" PBN metabolite that provides an additive effect to the pharmacological action of PBN in vivo.

Comparison of the radical trapping ability of PBN, S-PPBN and NXY-059

The nitrones alpha-phenyl-N-tert-butyl nitrone (PBN), sodium 2-sulfophenyl-N-tert-butyl nitrone (S-PBN) and disodium 2,4-disulfophenyl-N-tert-butyl nitrone (NXY-059) are neuroprotective in a variety of rodent models. The objective of the current studies was to compare the ability of PBN, S-PBN, and NXY-059 to form radical adducts and to prevent salicylate oxidation in an aqueous system. For the electron spin resonance (ESR) studies, hydroxyl radicals were generated with ultraviolet (UV) light and hydrogen peroxide. Secondary radicals were then produced by the addition of methanol, ethanol, isopropanol, dimethylsulfoxide, tetrahydrofuran or 1,4-dioxane. In addition, competition spin trapping studies were performed using PBN-alpha-(13) C and either S-PBN or NXY-059. In the salicylate studies, PBN, S-PBN and NXY-059 were compared to a variety of other antioxidants and reference compounds (cysteine, glutathione, ascorbate, uric acid, Tempo, Trolox, and Tirilizad) for their ability to prevent 2,3- and 2,5-dihydroxybenzoic acid formation induced by hydroxyl radical generating systems. All 3 nitrones trapped carbon- and oxygen-centered radicals to produce ESR-detectable radical adducts. Each nitrone also prevented salicylate oxidation, with PBN being the most effective. The ability of these 3 nitrones to prevent salicylate oxidation resembled that of most of the other compounds tested.

Synthesis, structure, and neuroprotective properties of novel imidazolyl nitrones

A new series of imidazolyl nitrones spin traps has been synthesized and evaluated pharmacologically. The salient structural feature of these molecules is the presence of an imidazole moiety substituted by aromatic or heteroaromatic cycles. This connectivity imparts to the nitrone superior neuroprotective properties in vivo and in parallel reduced side effects and toxicity. Thus compound 6a (a 2-phenylimidazolyl nitrone) administered intraperitoneally protects (80%) mice from lethality induced by an intracerebroventricular administration of tert-butyl hydroperoxide (t-BHP) an oxidant capable of inducing neurodegenerative processes. Administration of the archetypal nitrone phenyl-tert-butyl nitrone (PBN) at an equimolar dose also affords some protection (60%) in this test. However, this activity is accompanied by hypothermia, whereas no such effect is apparent for 6a. Moreover, previously prepared nonsubstituted or alkyl-substituted imidazolyl nitrones were shown to be extremely toxic to rats in contrast to the compounds prepared in this study. The observed activities in vivo correlate well with the calculated partition coefficients (ClogP) and HOMO energy level.

Pharmacologic properties of phenyl N-tert-butylnitrone

Phenyl N-tert-butylnitrone (PBN) is the parent of a family of nitrones used as spin-trapping agents to trap free radicals. PBN's pharmacological effects in animal models are extensive, ranging from protection against death after endotoxin shock, protection from ischemia-reperfusion injury, to increasing the life span of mice. Recent additions to the list include protection from bacterial meningitis, thalidomide-induced teratogenicity, drug-induced diabetogenesis, and choline-deficient hepatocarcinogenesis. Because PBN reacts with oxygen radicals to produce less reactive species, it has been suggested that this is the basis of its pharmacological effects. However, there has been no hard evidence for this notation. Nevertheless, many investigators have used the presence of PBN's pharmacologic effect as evidence for free radical involvement in their models. Mechanistic studies on the PBN's antisepsis action revealed that PBN inhibits expression of various pro-inflammatory genes, suggesting that the protective action involves more than a straightforward free radical-scavenging mechanism. Previous and recent developments in the investigations on the pharmacologic properties of PBN are described in this review.