Esters of 2-iodoxybenzoic acid: hypervalent iodine oxidizing reagents with a pseudobenziodoxole structure

Esters of 2-iodoxybenzoic acid (IBX-esters) were prepared by the hypochlorite oxidation of the corresponding 2-iodobenzoate esters and isolated as chemically stable, microcrystalline products. These hypervalent iodine compounds are potentially valuable oxidizing reagents belonging to a new class of pentavalent iodine compounds with a pseudobenziodoxole structure. Methyl 2-iodoxybenzoate can be further converted to the diacetate or a bis(trifluoroacetate) derivative by treatment with acetic anhydride or trifluoroacetic anhydride, respectively. Single-crystal X-ray diffraction analysis of methyl 2-[(diacetoxy)iodosyl]benzoate 8a reveals a pseudobenziodoxole structure with three relatively weak intramolecular I...O interactions. The dimethyl and diisopropyl esters of 2-iodoxyisophthalic acid were prepared by oxidation of the respective iodoarenes with dimethyldioxirane. Single-crystal X-ray diffraction analysis of diisopropyl 2-iodoxyisophthalate 6b showed intramolecular I...O interaction with the carbonyl oxygen of only one of the two carboxylic groups, while NMR spectra in solution indicated equivalency of both ester groups. IBX-esters, methyl 2-[(diacetoxy)iodosyl]benzoate, and 2-iodoxyisophthalate esters can oxidize alcohols to the respective aldehydes or ketones in the presence of trifluoroacetic acid or boron trifluoride etherate. The bis(trifluoroacetate) derivative can oxidize alcohols to carbonyl compounds without acid catalyst.     

Melatonin prevents doxorubicin-induced cardiotoxicity through suppression of AMPKα2-dependent mitochondrial damage

The clinical application of doxorubicin, one of the most effective anticancer drugs, has been limited due to its adverse effects, including cardiotoxicity. One of the hallmarks of doxorubicin-induced cytotoxicity is mitochondrial dysfunction. Despite intensive research over recent decades, there are no effective approaches for alleviating doxorubicin-induced cytotoxicity. Melatonin, a natural hormone that is primarily secreted by the pineal gland, is emerging as a promising adjuvant that protects against doxorubicin-induced cytotoxicity owing to its pharmaceutical effect of preserving mitochondrial integrity. However, the underlying mechanisms are far from completely understood. Here, we provide novel evidence that treatment of H9c2 cardiomyoblasts with doxorubicin strongly induced AMP-activated protein kinase α2 (AMPKα2), which translocated to mitochondria and interfered with their function and integrity, ultimately leading to cellular apoptosis. These phenomena were significantly blocked by melatonin treatment. The levels of AMPKα2 in murine hearts were tightly associated with cardiotoxicity in the context of doxorubicin and melatonin treatment. Therefore, our study suggests that the maintenance of mitochondrial integrity is a key factor in reducing doxorubicin-induced cytotoxicity and indicates that AMPKα2 may serve as a novel target in the design of cytoprotective combination therapies that include doxorubicin.Subject terms: Biochemistry, Diseases     

Synthesis and complexation properties of "zorbarene": a new naphthalene ring-based molecular receptor

[picture: see text] The syntheses of the first 2,3-dialkoxy-substituted naphthalene ring-based macrocycles which have calixarene-like structures are reported. The complexation properties of these octahomotetraoxaisocalix[4]naphthalenes were investigated. These new members of the calixnaphthalene family did not demonstrate any appreciable complexation with C(60) or C(70) under the conditions studied, but did so with the tetramethylammonium cation, showing relatively strong association constants suggesting among other considerations that stronger cation-pi interactions versus pi-pi interactions are operative with these hosts. An X-ray crystal structure of the octa-O-ethoxy derivative revealed a structure having a "flattened partial-cone" conformation in which two acetonitrile guest molecules are trapped.     

Reactions in aminosilane–epoxy prepolymer systems I. Kinetics of epoxy–amine reactions

The reactions of an epoxy prepolymer based on bisphenol A diglycidylether (DGEBA) with γ-aminopropyltriethoxysilane (γ-APS) are studied. The results of different techniques are compared: size exclusion chromatography, differential scanning calorimetry, chemical titration, and Fourier Transform Infrared absorption. Epoxy amine reactions are shown to be faster than the crosslinking reactions between alkoxysilane and hydroxy groups, and thus, can be studied seprately. The reactivity of the epoxy group in DGEBA is compared with that of phenylglycidylether (PGE). And the reactivity of the amine group of γ-APS is compared with that of hexylamine. The kinetic constants are calculated with a mechanism which takes into account both the catalytic and noncatalytic reactions. The ratio r = k₂/k₁ of the reactivity of the secondary to the primary amino-hydrogens was also determined. The values of r are 1.4 for hexylamine and 1.2 for γ-APS. The reactivity of the epoxy groups are the same for both PGE and DGEBA.     

High-performance liquid chromatographic separation of racemic and diastereomeric mixtures of 2,4-pentadienoate-iron tricarbonyl derivatives

beta-Cyclodextrin chiral stationary phase facilitates the chiral separation of the (+/-)-methyl-5-formyl-2,4-pentadienoate-iron tricarbonyl (1) racemic mixture. The separation of oxazolidine derivatives 2 and 3 diastereomers were achieved with a C18 column but the compounds underwent in-column hydrolysis to give (-)- and (+)-1, respectively. This hydrolysis was exploited for the determination of 2 and 3 by the beta-cyclodextrin column, namely 2 and 3 were initially and completely hydrolyzed in the column to give (-)- and (+)-1 and this racemic mixture was then separated by this chiral column.     

Behaviour of 1-phenylethyl chloride in aqueous ethanol: α-deuterium isotope effect on solvolysis rates

α-Deuterium effects on the voltolysis rates of 1-phenylethyl chloride in ethanol-water mixtures within the 80–100% etOH range are reported. According to Shiner's investigations,⁹ a monotonical decrease of K_H/k_D with decreasing water content was expected. Results show the existence of a minimum for k_H/k_D in approximately 90 vol.% EtOH. This behaviour might be accounted for in the framework of Shiner's mechanistic scheme if (i) H-bonded intermolecular associations, in which ethanol water should have their reactivity changed (ii) the structure of such clusters should depend upon the solvent composition.     

Potent, selective pyrone-based inhibitors of stromelysin-1

In an effort to develop alternatives to hydroxamate-based matrix metalloproteinase inhibitors (MPIs), we have utilized the drug discovery program LUDI enhanced with the structural coordinates of a bioinorganic model complex. This method has yielded the first pyrone-based MPIs. The inhibitors demonstrate nanomolar potency against MMP-3 and are selective for MMP-3 over MMP-2 and MMP-1. We postulate that the potency and unusual selectivity profile of these MPI is attributable to the pyrone chelating group.     

Computational evidence for methyl-donated hydrogen bonds and hydrogen-bond networking in 1,2-ethanediol-dimethyl sulfoxide

The 1:1 complex of 1,2-ethanediol with dimethyl sulfoxide was studied using density functional theory. A network of three hydrogen bonds holds the complex together, including two in which each methyl group donates to the same hydroxyl oxygen. Four lines of evidence support the existence of methyl-donated hydrogen bonds. The interaction energy is 36 +/- 5 kJ/mol using Becke's three parameter hybrid theory with the 1991 nonlocal correlation functional of Perdew and Wang, and a moderately large basis set (B3PW91/6-311++G**//B3PW91/6-31+G**). To determine the energy of each hydrogen bond, a relaxed potential energy scan was performed in a smaller basis set to break the weaker hydrogen bonds by forced systematic rotation of the methyl groups. Two cross-checking analyses show cooperative effects that cause individual hydrogen bond energies in the network to be nonadditive. When one methyl hydrogen bond is broken, the remaining interactions stabilize the complex by storing an additional 2-3 kJ/mol. With all hydrogen bonds intact, the O[bond]H...O[bond]S hydrogen bond contributes 26 +/- 2 kJ/mol stability, and each weak methyl bond stores 5 +/- 2 kJ/mol.     

Surface reactivity of polypyrrole/iron-oxide nanoparticles: electrochemical and CS-AFM investigations

Composite materials based on iron-oxide nanoparticles (magnetite, hematite, and maghemite) and tetraoxalate-doped polypyrrole (PPy) were electrochemically generated from aqueous solutions. Their composition was determined using electrochemical quartz crystal microbalance experiments. The oxide percentage in mass was found to vary from 17 to 27% depending on the oxide identity. They were all shown to be fascinating candidates as protective materials against corrosion of iron and carbon steel materials although maghemite-nanoparticle-loaded polypyrrole films offer the best performances. An anionic surfactant (sodium dodecylsulfate) was added to the electrodeposition solution to avoid the formation of clusters. These anions were also shown to improve the conductivity of the resulting PPy films, while the presence of oxide nanoparticles tends to decrease this same surface conductivity. On the other hand, the correlation between the morphology and the local conductivity appears to be more obvious in the absence of anionic surfactants than in their presence. This aspect is discussed although it still needs further investigation. Contribution to the International Workshop on Electrochemistry of Electroactive Materials (WEEM-2006), Repino, Russia, 24–29 June 2006.     

Role of the Na+ ion on phenol derivatives/hydroxypropyl-beta-cyclodextrin complex formation on porous graphitic carbon phase

The reversed-phase liquid chromatography retention of phenol derivatives was investigated over a concentration range of sodium chloride (0-10(-2) M) and hydroxypropyl-beta-cyclodextrin (HP-beta-CD) (0-35x10(-3) M) using a porous graphitic carbon (PGC) stationary phase and a methanol/water mixture (50:50 (v/v)) as the mobile phase. A theoretical treatment was developed to investigate the effect of the sodium chloride and hydroxypropyl-beta-cyclodextrin on the equilibrium between the solutes with the PGC surface and the aqueous medium, respectively. The thermodynamic parameter variations were calculated using van't Hoff plots. It was expected that the sodium ion acted on the solute-PGC association process by modifying the surface tension of both the bulk solvent and the PGC surface. The phenol derivative/HP-beta-cyclodextrin complexation was shown to be entropically controlled for all the solutes except for the one which contained the -NO2 group in its structure, i.e. the nitro phenol derivative. A comparison of the compensation temperature of the solute-PGC association process when sodium chloride and HP-beta-CD concentration changed in the mobile phase led to the conclusion that these two modifiers acted via a variation in the hydrophobic effect.