V. A. Chertkov

Mitochondria-Targeted Plastoquinone Derivatives as Tools to Interrupt Execution of the Aging Program. 1. Cationic Plastoquinone Derivatives: Synthesis and in vitro Studies*

Synthesis of cationic plastoquinone derivatives (SkQs) containing positively charged phosphonium or rhodamine moieties connected to plastoquinone by decane or pentane linkers is described. It is shown that SkQs (i) easily penetrate through planar, mitochondrial, and outer cell membranes, (ii) at low (nanomolar) concentrations, posses strong antioxidant activity in aqueous solution, BLM, lipid micelles, liposomes, isolated mitochondria, and cells, (iii) at higher (micromolar) concentrations, show pronounced prooxidant activity, the “window” between anti- and prooxidant concentrations being very much larger than for MitoQ, a cationic ubiquinone derivative showing very much lower antioxidant activity and higher prooxidant activity, (iv) are reduced by the respiratory chain to SkQH2, the rate of oxidation of SkQH2 being lower than the rate of SkQ reduction, and (v) prevent oxidation of mitochondrial cardiolipin by OH·. In HeLa cells and human fibroblasts, SkQs operate as powerful inhibitors of the ROS-induced apoptosis and necrosis. For the two most active SkQs, namely SkQ1 and SkQR1, C1/2 values for inhibition of the H2O2-induced apoptosis in fibroblasts appear to be as low as 1·10−11 and 8·10−13 M, respectively. SkQR1, a fluorescent representative of the SkQ family, specifically stains a single type of organelles in the living cell, i.e. energized mitochondria. Such specificity is explained by the fact that it is the mitochondrial matrix that is the only negatively-charged compartment inside the cell. Assuming that the Δψ values on the outer cell and inner mitochondrial membranes are about 60 and 180 mV, respectively, and taking into account distribution coefficient of SkQ1 between lipid and water (about 13,000: 1), the SkQ1 concentration in the inner leaflet of the inner mitochondrial membrane should be 1.3·108 times higher than in the extracellular space. This explains the very high efficiency of such compounds in experiments on cell cultures. It is concluded that SkQs are rechargeable, mitochondria-targeted antioxidants of very high efficiency and specificity. Therefore, they might be used to effectively prevent ROS-induced oxidation of lipids and proteins in the inner mitochondrial membrane in vivo.

High-resolution proton-coupled 13C NMR spectra of monosubstituted benzenes. Theoretical and empirical correlations of JCH

Abstract The high-resolution proton-coupled 13C NMR spectra of several monosubstituted benzenes, C6H5X (X = F, Cl, Br, I, NO2, NH2, CHO, CN, OH, OCH3, and Si(CH3)3), have been completely analyzed, and all the signs and magnitudes of the 13C-1H coupling constants have been determined. INDO MO calculations of JCH have been performed and a comparison with the experimental values is made. The calculations only reproduce the substituent trends for 1 J 44 , 2 J 12 , 3 J 13 , 3 J 26 , and 3J35, and the couplings of the ring carbons with the exocyclic protons in toluene. Empirical correlations of nJCH with nJHH are considered and discussed. Correlations with substituent electronegativity indicate that mesomeric and inductive effects of the substituents have an important influence. This leads to the consideration of correlations with σp and σ1.

Porphyrin-Based Peptide Receptors: Syntheses and NMR Analysis

The synthesis and purification of a water-soluble host compound that contains three pyridinium units and one spacer-connected benzocrown ether unit in the meso-positions of porphyrin and of its Zn(II) or Cu(II) complexes is described. Metalation leads to small (compared to the apo-derivative) changes of selectivities with different peptides, with complexation constants in water of above 10(5)M(-1). One complex containing the tripeptide Gly-Gly-Phe is analyzed in detail by COSY, HSQC, HMBC, and NOESY NMR experiments. Temperature-dependent spectra show activation energies for a intramolecular hydrogen exchange of amide protons with valence isomerization of the porphyrin ring, in accordance with the literature. Sharp signals for the spin system are only found at elevated temperature. Vicinal coupling constants within the crown ether moiety indicate stronger puckering than that reported for benzocrowns. All NMR signals of the complexed peptide are shielded, in particular those of the terminal phenylalanine unit, in line with its stacking on the porphyrin surface. A corresponding structural model, obtained by CHARMm simulation, is also in line with the observed intermolecular NOE cross peaks.

Trans-1,2-Cyclohexanedicarboxylic acid derivatives as pH-trigger for conformationally controlled crowns

Abstract Conversion of trans-1,2-cyclohexanedicarboxylic acid derivatives into dianions under the action of strong bases leads to dramatic conformational changes: a conformer with diaxial position of carboxylate groups becomes predominant. Thus the trans-1,2-cyclohexanedicarboxylic acid moiety can be used for pH-induced conformational switching. The conformational energy changes upon protonation amount to 10 kJ/mol.

Cycloaddition reaction of 1-(4-nitrophenyl)-3-phenylnitrile ylide to buckminsterfullerene[60]

Abstract Cycloaddition of 1-(4-nitrophenyl)-3-phenylnitrile ylide generated in situ from N-benzyl-4-nitrobenzimidoyl chloride to C 60 yields to 1,2-[3,4-dihydro-2-phenyl-5-(4-nitrophenyl)-2 H - pyrrolo]-[60]fullerene and diastereomeric mixture of two 5,6-open isomers. Moreover, double carbon-nitrogen bond of 5,6-open of adduct is located in α position to unsubstituted phenyl ring.

13C isotope effects on the parameters of proton magnetic resonance spectra of benzene

Abstract The proton-coupled 13C NMR spectra and the 13C satellites in the 1H NMR spectra of commercial benzene containing about 6.6% of benzene- l-13C were measured and analyzed using the iterative LACX program; 271 lines were assigned and used in the calculations (105 lines from the proton-coupled 13C NMR spectra, 118 lines from outer satellites, and 48 lines from inner satellites in the 1H NMR spectra). The exact values of the 13Cz.sbnd;1H coupling constants were obtained with the standard deviations not exceeding 0.004 Hz. The 12C/13C-induced proton isotope chemical shifts were found to be 1 Δ = 2.44; 2 Δ = 1.34; 3 Δ = 0.51; and 4 Δ = 0.33 (in parts per billion). The 12C/13C-induced isotope effects on the proton-proton coupling constants do not exceed 0.005 Hz.

Proton-coupled 13C NMR spectra of cyclopentadiene

Abstract The complete high-precision analysis of proton-coupled 13C NMR spectra of cyclopentadiene is presente. The coupling constants J( 13 CH ) in cyclopentadiene are discussed in comparison with the data previously reported for five-membered heterocycles.

Selective, Metal-Free Approach to 3- or 5-CF3-Pyrazoles: Solvent Switchable Reaction of CF3-Ynones with Hydrazines

A detailed study of the reaction of trifluoroacetylated acetylenes and aryl (alkyl) hydrazines was performed, aimed to the regioselective synthesis of 3- or 5-trifluoromethylated pyrazoles. It was found that the regioselectivity of reaction depends dramatically on the solvent nature. Highly polar protic solvents (hexafluoroisopropanol) favor the formation of 3-trifluoromethylpyrazoles. In contrast, when the reaction was performed in polar aprotic solvents (DMSO), the formation of their 5-CF3-substituted isomers was preferentially observed. Alternatively, the regioselective assembly of 3-CF3-substituted pyrazoles can be performed via two-step one-pot procedure. The reaction of trifluoromethylated ynones with aryl (alkyl) hydrazines in the presence of acidic catalysts leads to formation of the corresponding hydrazones. The latter can be smoothly transformed into 3-CF3-pyrazoles by treatment with a base. This solvent-switchable procedure was used for the preparation of such important drugs as Celebrex and SC-560 as well as their isomers in gram scale. The possible reaction mechanism is discussed.

Structures and equilibria involving the [222] cryptand and europium ions

Abstract Complexes of Eu(III) salts and the [222] cryptand show in methanol the presence of at least three species, interconverting slowly on the NMR time scale. Shift changes of up to 75 ppm and line widths of up to 110 Hz characterize the inner sphere complexes, which differ significantly in symmetry. In water at pH 7 there is no stable complex at all; if one dissolves the solid complex, which holds the metal inside the cavity as evidenced from a published solid state analysis, a rapid decay to the protonated ligand is observed, with a rate constant of 8.7×10 −4 s −1 .

STABILIZATION OF A CARBODICATION BY A TETRAHEDRAL MOLYBDENUM-CARBON CLUSTER

Abstract The reaction of Cp 2 Mo 2 (CO) 4 -μ-(HOCH 2 CCCH 2 OH) with HBF 4 gives the monocation [Cp 2 Mo 2 (CO) 4 (CH 2 CCCH 2 OH)] + which can be isolated as its fluoroborate salt, which in FSO 3 H or CF 3 COOH (TFA) solution forms the dication [Cp 2 Mo 2 (CO) 4 (CH 2 CCCH 2 )] 2+ . Treatment of the monocation solution in TFA by (CF 3 CO) 2 O followed by addition of aqueous HBF 4 and ether yielded the stable crystalline fluoroborate. 1 H and 13 C NMR spectra of the mono- and dications in various solvents were investigated.