α-Aryl-N-aryl nitrones: Synthesis and screening of a new scaffold for cellular protection against an oxidative toxic stimulus

α-Phenyl-N-tert-Butylnitrone and Analogous α-Aryl-N-alkylnitrones as Neuroprotective Antioxidant Agents for Stroke

The recent advances in research on the use of the antioxidant and neuroprotective agent α-phenyl-N-tert-butylnitrone (PBN) for the therapy of stroke have been reviewed. The protective effect of PBN in the transient occlusion of the middle cerebral artery (MCAO) has been demonstrated, although there have been significant differences in the neuronal salvaging effect between PBN-treated and untreated animals, each set of data having quite large inter-experimental variation. In the transient forebrain ischemia model of gerbil, PBN reduces the mortality after ischemia and the neuronal damage in the hippocampal cornu ammonis 1 (CA1) area of the hippocumpus caused by ischemia. However, PBN fails to prevent postischemic CA1 damage in the rat. As for focal cerebral ischemia, PBN significantly reduces cerebral infarction and decreases neurological deficit after ischemia using a rat model of persistent MCAO in rats. Similarly, the antioxidant and neuroprotective capacity of a number of PBN-derived nitrones prepared in the author's laboratory have also been summarized here, showing their high potential therapeutic power to treat stroke.

Synthesis, antioxidant and neuroprotective analysis of diversely functionalized α-aryl-N-alkyl nitrones as potential agents for ischemic stroke therapy

Herein, we report the synthesis, antioxidant and biological evaluation of 32 monosubstituted α-arylnitrones derived from α-phenyl-tert-butyl nitrone (PBN) in the search for neuroprotective compounds for ischemic stroke therapy, trying to elucidate the structural patterns responsible for their neuroprotective activity. Not surprisingly, the N-tert-butyl moiety plays beneficious role in comparison to other differently N-substituted nitrone groups. It seems that electron donor substituents at the ortho position and electron withdrawing substituents at the meta position of the aryl ring induce good neuroprotective activity. As a result, (Z)-N-tert-butyl-1-(2-hydroxyphenyl)methanimine oxide (21a) and (Z)-N-tert-butyl-1-(2-(prop-2-yn-1-yloxy)phenyl)methanimine oxide (24a) showed a significant increase in neuronal viability in an experimental ischemia model in primary neuronal cultures, and induced neuroprotection and improved neurodeficit score in an in vivo model of transient cerebral ischemia. These results showed that nitrones 21a and 24a are new effective small and readily available antioxidants, and suitable candidates for further structure optimization in the search for new phenyl-derived nitrones for the treatment of ischemic stroke and related diseases.

Metal-Free Solvent Promoted Oxidation of Benzylic Secondary Amines to Nitrones with H2O2

An environmentally benign protocol for the generation of nitrones from benzylic secondary amines via catalyst-free oxidation of secondary amines using H2O2 in MeOH or CH3CN is described. This methodology provides a selective access to a variety of C-aryl nitrones in yields of 60 to 93%. Several studies have been performed to shed light on the reaction mechanism and the role of the solvent.

Single-Step Approach toward Nitrones via Pyridinium Ylides: The DMAP-Catalyzed Reaction of Benzyl Halides with Nitrosoarenes

A single-step approach is reported for the preparation of nitrones from benzyl halides and nitrosoarenes via pyridinium ylides, utilizing 4-dimethylaminopyridine (DMAP) catalyst and mild reaction conditions (Li₂CO₃, dimethylacetamide, and room temperature). The reaction provides both keto- and aldonitrones in high yields with a wide scope for benzyl halides and nitrosoarenes. In the same reaction system, 2-methyl-2-nitrosopropane, which does not have an aryl group, also affords the corresponding N-tert-butyl nitrones from primary benzyl bromides that have an electron-withdrawing group. As an application of the reaction, methyl 2-bromo-2-phenylacetate was used to prepare the corresponding isoxazolidine by a sequential one-pot synthesis.

Synthesis of chiral anti-1,2-diamine derivatives through copper(I)-catalyzed asymmetric α-addition of ketimines to aldimines

Chiral 1,2-diamines serve as not only common structure units in bioactive molecules but also useful ligands for a range of catalytic asymmetric reactions. Here, we report a method to access anti-1,2-diamine derivatives. By means of the electron-withdrawing nature of 2- or 4-nitro-phenyl group, a copper(I)-catalyzed asymmetric α-addition of ketimines derived from trifluoroacetophenone and 2- or 4-NO₂-benzylamines to aldimines is achieved, which affords a series of chiral anti-1,2-diamine derivatives in moderate to high yields with moderate to high diastereoselectivity and high to excellent enantioselectivity. Aromatic aldimines, heteroaromatic aldimines, and aliphatic aldimines serve as suitable substrates. The nitro group is demonstrated as a synthetical handle by several transformations, including a particularly interesting Fe(acac)₃-catalyzed radical hydroamination with a trisubstituted olefin. Moreover, the aryl amine moiety obtained by the reduction of the nitro group serves as a synthetically versatile group, which leads to the generation of several functional groups by the powerful Sandmeyer reaction, such as -OH, -Br, -CF₃, and -BPin.

Chiral 1,2-diamines are useful chemicals used as ligands in asymmetric catalysis. Here, the authors report a copper(I)-catalyzed asymmetric α-addition of ketimines derived from trifluoroacetophenone and 2- or 4-NO2-benzylamines to aldimines, affording a series of chiral anti-1,2-diamine derivatives.

NO and HNO donors, nitrones, and nitroxides: Past, present, and future

The biological effects attributed to nitric oxide (^• NO) and nitroxyl (HNO) have been extensively studied, propelling their array of putative clinical applications beyond cardiovascular disorders toward other age-related diseases, like cancer and neurodegenerative diseases. In this context, the unique properties and reactivity of the N-O bond enabled the development of several classes of compounds with potential clinical interest, among which ^• NO and HNO donors, nitrones, and nitroxides are of particular importance. Although primarily studied for their application as cardioprotective agents and/or molecular probes for radical detection, continuous efforts have unveiled a wide range of pharmacological activities and, ultimately, therapeutic applications. These efforts are of particular significance for diseases in which oxidative stress plays a key pathogenic role, as shown by a growing volume of in vitro and in vivo preclinical data. Although in its early stages, these efforts may provide valuable guidelines for the development of new and effective N-O-based drugs for age-related disorders. In this report, we review recent advances in the chemistry of NO and HNO donors, nitrones, and nitroxides and discuss its pharmacological significance and potential therapeutic application.

Melatonin and Nitrones As Potential Therapeutic Agents for Stroke

Stroke is a disease of aging affecting millions of people worldwide, and recombinant tissue-type plasminogen activator (r-tPA) is the only treatment approved. However, r-tPA has a low therapeutic window and secondary effects which limit its beneficial outcome, urging thus the search for new more efficient therapies. Among them, neuroprotection based on melatonin or nitrones, as free radical traps, have arisen as drug candidates due to their strong antioxidant power. In this Perspective article, an update on the specific results of the melatonin and several new nitrones are presented.