Synthesis and biological evaluation of nucleoside dicarboxylates as potential mimics of nucleoside diphosphates

A series of nucleotide analogues wherein the diphosphate moiety has been replaced by a dicarboxylate were synthesized and tested for inhibitory activity against nucleoside diphosphate (NDP) kinase as well as several pathogenic bacterial strains.     

Unexpected formation of aryl ketones by palladium-catalyzed coupling of aryl bromides with vinylic acetates

A palladium-catalyzed coupling reaction of aryl bromides with vinylic acetates in the presence of tributyltin methoxide has been described. Unexpected formation of aryl ketones was obtained. Preliminary mechanistic studies indicated that the reaction proceeded by the addition of the aryl moiety in the coordination sphere of palladium to a ketene.     

Total synthesis of rhein and diacerhein via a directed ortho metalation of an aromatic substrate

An efficient total synthesis of rhein and diacerhein has been accomplished by relying on a remarkable regioselective directed ortho metalation (DOM) followed by a one-pot two step addition-cyclization reaction, generating phthalide 5 intermediate efficiently.     

Synthesis of pyridine-based polyaminocarboxylic ligands bearing a thioalkyl anchor

A bicyclic tetraazatriacetic chelating agent containing a thioalkyl pendant group was prepared. Four synthetic routes have been investigated via a Mitsunobu reaction from 2,4-[bishydroxymethyl]-3-hydroxy-pyridine 1. Deprotection of trityl thioether compound 5c led to ligand 6c in 22% overall yield from the starting 3-hydroxypyridine.     

A nonradioactive method for detecting phosphates and polyphosphates separated by PAGE

Nonradioactive polyphosphate (poly(P); (PO(3) (-))(n)) species resolved by PAGE can be detected by hydrolytic degradation of the polyphosphates into orthophosphates (P(i)) with a 5 M HCl solution saturated with NaCl, followed by staining the P(i) degradation products in a 1 M HCl solution of 0.25% w/v methyl green and 1% w/v ammonium molybdate. This method detects down to 0.5 nmol of phosphate as P(i), linear poly(P) (condensed phosphate), pyrophosphate (P(2)O(7) (4) (-)), or cyclic trimetaphosphate ion (P(3)O(9))(3) (-) species. This method improves the current method of staining linear poly(P) longer than four phosphate units with Toludine blue-O after PAGE. This study also shows that Stains-All can visualize resolved linear poly(P) shorter than those visualized by Toluidine blue-O. It is hoped that this sequential hydrolytic degradation and phosphate visualization method for detecting ortho-, linear, and cyclic poly(P) species will be a useful tool, as poly(P) are being discovered in a wide variety of biological systems, and their biochemical roles are still largely unknown.     

Adiabatic and non-adiabatic concerted proton-electron transfers. Temperature effects in the oxidation of intramolecularly hydrogen-bonded phenols

The one-electron electrochemical and homogeneous oxidations of two closely similar aminophenols that undergo a concerted proton-electron transfer reaction, in which the phenolic proton is transferred to the nitrogen atom in concert with electron transfer, are taken as examples to test procedures that allow the separate determination of the degree of adiabaticity and the reorganization energy of the reaction. The Marcus (or Marcus-Hush-Levich) formalism is applicable in both cases, but not necessarily in its adiabatic version. Linearization of the activation-driving force laws simplifies the treatment of the kinetic data, notably allowing the use of Arrhenius plots to treat the temperature dependence of the rate constant. A correct estimation of the adiabaticity and reorganization energy requires the determination of the variation of the driving force with temperature. Application of these procedures led to the conclusion that, unlike previous reports, the homogeneous reaction is non-adiabatic, with a transmission coefficient of the order of 0.005, and that the self-exchange reorganization energy is about 1 eV lower than previously estimated. With such systems, the intramolecular reorganization energy, although sizable, is in fact rather modest, being only slightly larger than that for the outer-sphere electron transfer that produced the cation radical. The electrochemical reaction is, in contrast, adiabatic, as revealed by the temperature dependence of its standard rate constant obtained from cyclic voltammetric experiments. This difference in behavior is deemed to derive from the effect of the strong electric field within which the electrochemical reaction takes place, stabilizing a zwitterionic form of the reactant (in which the proton has been transferred from oxygen to nitrogen). Taking this difference in adiabaticity into account, the magnitudes of the reorganization energies of the two reactions appear to be quite compatible with one another, as revealed by an analysis of the solvent and intramolecular contributions in both cases.     

Metabolism of <Superscript>14</Superscript>C-labelled and non-labelled sulfadiazine after administration to pigs

The behaviour of sulfadiazine (SDZ) and its metabolites was investigated by administering the ¹⁴C-labelled veterinary drug to fattening pigs. The excretion kinetics were determined after daily collection of manure. Two known metabolites, N-acetylsulfadiazine and 4-hydroxysulfadiazine, and two hitherto unidentified minor metabolites were recovered. Various mass spectrometric techniques such as parent, product ion scans and accurate mass measurement were used. The new compounds were identified as N-formylsulfadiazine (For-SDZ) and N-acetyl-4-hydroxysulfadiazine (Ac-4-OH-SDZ). The identification of SDZ, Ac-SDZ and For-SDZ was confirmed by comparison of the spectroscopic and chromatographic data of the synthesized authentic references. The identification of the hydroxylated compounds 4-OH-SDZ and Ac-4-OH-SDZ was performed by MSⁿ, and accurate mass measurements. Only 4% of the administered radioactivity remained in the pig after ten days and SDZ accounted for 44% of the 96% radioactivity excreted. More than 93% of the labelled compounds were detected and identified in the manure. The key analytical problem, namely a high concentration of matrix in sample extracts, was overcome by advanced measurement techniques and with the use of a suitable internal standard. The mean recoveries for all compounds were ≥96%. Linearity was established over a concentration range of 0.5 to 10,000 μg kg⁻¹ manure with a correlation coefficient ≥0.99. The same experiment was carried out simultaneously with non-labelled SDZ to obtain manure for outdoor soil experiments.