Cyclic nitrone free radical traps: isolation, identification, and synthesis of 3,3-dimethyl-3,4-dihydroisoquinolin-4-ol N-oxide, a metabolite with reduced side effects

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.

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.

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.