Reactivity of 1,4-dihydropyridines toward alkyl, alkylperoxyl radicals, and ABTS radical cation

Genotoxic and genoprotective effects of 1,4-dihydropyridine derivatives: a brief review

This review summarises current knowledge about the genotoxic and genoprotective effects of 1,4-dihydropyridines (DHP) with the main focus on the water-soluble 1,4-DHPs. Most of these water-soluble compounds manifest very low calcium channel blocking activity, which is considered "unusual" for 1,4-DHPs. Glutapyrone, diludine, and AV-153 decrease spontaneous mutagenesis and frequency of mutations induced by chemical mutagens. AV-153, glutapyrone, and carbatones protect DNA against the damage produced by hydrogen peroxide, radiation, and peroxynitrite. The ability of these molecules to bind to the DNA may not be the only mechanism of DNA protection, as other mechanisms such as radical scavenging or binding to other genotoxic compounds may take place and enhance DNA repair. These uncertainties and reports of high 1,4-DHP concentrations damaging the DNA call for further in vitro and in vivo preclinical research, pharmacokinetic in particular, as it can help pinpoint the exact mechanism(s) of the genotoxic and/or genoprotective action of 1,4-DHPs.

Quantitative Estimation of the Hydrogen-Atom-Donating Ability of 4-Substituted Hantzsch Ester Radical Cations

The purpose of this study is to investigate thermodynamic and kinetic properties on the hydrogen-atom-donating ability of 4-substituted Hantzsch ester radical cations (XRH•+), which are excellent NADH coenzyme models. Gibbs free energy changes and activation free energies of 17 XRH•+ releasing H• [denoted as ΔG HD o(XRH•+) and ΔG HD ≠(XRH•+)] were calculated using density functional theory (DFT) and compared with that of Hantzsch ester (HEH2) and NADH. ΔG HD o(XRH•+) range from 19.35 to 31.25 kcal/mol, significantly lower than that of common antioxidants (such as ascorbic acid, BHT, the NADH coenzyme, and so forth). ΔG HD ≠(XRH•+) range from 29.81 to 39.00 kcal/mol, indicating that XRH•+ spontaneously releasing H• are extremely slow unless catalysts or active intermediate radicals exist. According to the computed data, it can be inferred that the Gibbs free energies and activation free energies of the core 1,4-dihydropyridine radical cation structure (DPH•+) releasing H• [ΔG HD o(DPH•+) and ΔG HD ≠(DPH•+)] should be 19-32 kcal/mol and 29-39 kcal/mol in acetonitrile, respectively. The correlations between the thermodynamic driving force [ΔG HD o(XRH•+)] and the activation free energy [ΔG HD ≠(XRH•+)] are also explored. Gibbs free energy is the important and decisive parameter, and ΔG HD ≠(XRH•+) increases in company with the increase of ΔG HD o(XRH•+), but no simple linear correlations are found. Even though all XRH•+ are judged as excellent antioxidants from the thermodynamic view, the computed data indicate that whether XRH•+ is an excellent antioxidant in reaction is decided by the R substituents in 4-position. XRH•+ with nonaromatic substituents tend to release R• instead of H• to quench radicals. XRH•+ with aromatic substituents tend to release H• and be used as antioxidants, but not all aromatic substituted Hantzsch esters are excellent antioxidants.

1,4-Dihydropyridine Derivatives: Dihydronicotinamide Analogues-Model Compounds Targeting Oxidative Stress

Many 1,4-dihydropyridines (DHPs) possess redox properties. In this review DHPs are surveyed as protectors against oxidative stress (OS) and related disorders, considering the DHPs as specific group of potential antioxidants with bioprotective capacities. They have several peculiarities related to antioxidant activity (AOA). Several commercially available calcium antagonist, 1,4-DHP drugs, their metabolites, and calcium agonists were shown to express AOA. Synthesis, hydrogen donor properties, AOA, and methods and approaches used to reveal biological activities of various groups of 1,4-DHPs are presented. Examples of DHPs antioxidant activities and protective effects of DHPs against OS induced damage in low density lipoproteins (LDL), mitochondria, microsomes, isolated cells, and cell cultures are highlighted. Comparison of the AOA of different DHPs and other antioxidants is also given. According to the data presented, the DHPs might be considered as bellwether among synthetic compounds targeting OS and potential pharmacological model compounds targeting oxidative stress important for medicinal chemistry.

1,4-Dihydropyridines: Reactivity of Nitrosoaryl and Nitroaryl Derivatives with Alkylperoxyl Radicals and ABTS Radical Cation

In the present paper, a direct quenching of radical species by a number of synthesized nitrosoaryl 1,4-dihydropyridines and their parent nitroaryl 1,4-dihydropyridines was determined in aqueous media at pH 7.4. These two series of compounds were compared with the C-4 unsubstituted 1,4-dihydropyridines derivatives and the corresponding C-4 aryl substituted 1,4-dihydropyridines derivatives. Kinetic rate constants were assessed by UV-Vis spectroscopy. Nitrosoaryl derivatives were more reactive than the parent nitroaryl 1,4-dihydropyridines. Our results strongly support the assumption that the reactivity between the synthesized 1,4-dihydropyridines derivatives with alkylperoxyl radicals involves electron transfer reactions, which is documented by the presence of pyridine as final product of reaction and the complete oxidation of the nitroso group to give rise the nitro group in the case of the nitrosoaryl 1,4-dihydropyridines derivatives.

Nitroaryl-1,4-dihydropyridines as antioxidants against rat liver microsomes oxidation induced by iron/ascorbate, nitrofurantoin and naphthalene

1,4-Dihydropyridines (DHPs) used in the treatment of cardiovascular diseases, are calcium channel antagonists and also antioxidant agents. These drugs are metabolized through cytochrome P(450) oxidative system, majority localized in the hepatic endoplasmic reticulum. Several lipophilic drugs generate oxidative stress to be metabolized by this cellular system. Thus, DHP antioxidant properties may prevent the oxidative stress associated with hepatic biotransformation of drugs. In this work, we tested the antioxidant capacity of several synthetic nitro-phenyl-DHPs. These compounds (I-IV) inhibited the microsomal lipid peroxidation, UDPGT oxidative activation and microsomal thiols oxidation; all phenomena induced by Fe(3+)/ascorbate, a generator system of oxygen free radicals. As the same manner, these compounds inhibited the oxygen consumption induced by Cu(2+)/ascorbate in the absence of microsomes. Furthermore, compound III (2,6-dimethyl-4-(4-nitrophenyl)-1,4-dihydropyridin-3,5-ethyl-dicarboxylate) and compound V (N-ethyl-2,6-dimethyl-4-(4-nitrophenyl)-1,4-dihydropyridin-3,5-methyl-dicarboxylate) inhibited the microsomal lipid peroxidation induced by Nitrofurantoin and naphthalene in the presence of NADPH. Oxidative stress induced on endoplasmic reticulum may alter the biotransformation of drugs, so, modifying their plasmatic concentrations and therapeutic effects. When drugs which are activated by biotransformation are administered together with antioxidant drugs, such as DHPs, oxidative stress induced in situ may be prevented.

Analyses by GC–MS and GC–MS–MS of the hantzsch synthesis products using hydroxy- and methoxy-aromatic aldehydes

EI mass spectra of products of the dihydropyridine Hantzsch synthesis using hydroxy and methoxy aldehydes as starting materials are reported. The reaction products (C-4 hydroxy- and methoxyphenyl-1,4-dihydropyridines and chromeno[3,4,c]-pyridines) were derivatized with N-methyl-N-(trimethylsilyl)-trifluoracetamide to be analyzed by gas chromatographic techniques. Fragmentation pathways for 1,4-dihydropyridines and chromeno-pyridines are proposed. The study provides (mainly through MS-MS technique) useful data for the confirmation of the structure of the compounds and also is a valuable tool for further analytical purposes to follow both photostability and reactivity studies with free radicals for these types of compounds.

Intramolecular electron transfer in the photochemistry of some nitrophenyldihydropyridines

4-Phenyl-1,4-dihydropyridine-3,5-dicarboxylates contain two pi chromophores separated by an sp3 carbon. The lowest singlet is localized on the dihydropyridine moiety (1PyH2-Ph) and emits a blue fluorescence (with close to unitary efficiency in glass at 77 K). In 3-nitrophenyl derivatives (PyH2-PhNO2, some of which are photolabile drugs) the fluorescence is completely quenched. Reasonably, this is due to intramolecular electron transfer between the close-lying donor and acceptor moieties to give the charge-separated species (PyH2*+-PhNO2*-). In EPA glass at 77 K, back-electron transfer gives the dihydropyridine-localized triplet (3PyH2-PhNO2), which emits a yellow phosphorescence. In solution, deprotonation from the radical cation on the dihydropyridine moiety initiates rearomatization, finally giving Py-PhNO2 with low quantum yield (5 x 10(-4) to 5 x 10(-3), increasing up to 0.013 by irradiation at 254 nm, where direct excitation of the nitrophenyl chromophore contributes). In the presence of triethylamine, the reaction changes to neat reduction of the nitro group. When a tethered alkylamino group is present, oxidative degradation of that moiety occurs, again via an electron-transfer intramolecular process. This has been found with the drug nicardipine, where photodegration is more efficient (phi 0.02 to 0.1). Donor-acceptor dyads of this type, easily available through the Hantzsch synthesis, may be useful for building new photoinduced electron-transfer systems.

Structural effects on the reactivity 1,4-dihydropyridines with alkylperoxyl radicals and ABTS radical cation

A series of eight commercial C-4 substituted 1,4-dihydropyridines and other synthesized related compounds were tested for direct potential scavenger effect towards alkylperoxyl radicals and ABTS radical cation in aqueous Britton-Robinson buffer pH7.4. A direct quenching radical species was established. The tested 1,4-dihydropyridines were 8.3-fold more reactive towards alkylperoxyl radicals than ABTS cation radical, expressed by their corresponding kinetic rate constants. Furthermore, NPD a photolyte of nifedipine and the C-4 unsubstituted 1,4-DHP were the most reactive derivatives towards alkylperoxyl radicals. The pyridine derivative was confirmed by GC/MS technique as the final product of reaction. In consequence, the reduction of alkylperoxyl and ABTS radicals by 1,4-dihydropyridines involved an electron transfer process. Also, the participation of the hydrogen of the 1-position appears as relevant on the reactivity. Results of reactivity were compared with Trolox.