Quantification of urinary AICAR concentrations as a matter of doping controls

Influencing the endurance in elite sports is one of the key points in modern sports science. Recently, a new class of prohibited substances reached in the focus of doping control laboratories and their misuse was classified as gene doping. The adenosine monophosphate activated protein kinase activator 5-amino-4-imidazolecarboxyamide ribonucleoside (AICAR) was found to significantly enhance the endurance even in sedentary mice after treatment. Due to endogenous production of AICAR in healthy humans, considerable amounts were present in the circulation and, thus, were excreted into urine. Considering these facts, the present study was initiated to fix reference values of renally cleared AICAR in elite athletes. Therefore a quantitative analytical method by means of isotope-dilution liquid chromatography (analytical column: C6-phenyl) coupled to tandem mass spectrometry, after a sample preparation consisting of a gentle dilution of native urine, was developed. Doping control samples of 499 athletes were analysed, and AICAR concentrations in urine were determined. The mean AICAR value for all samples was 2,186 ng/mL with a standard deviation of 1,655 ng/mL. Concentrations were found to differ depending on gender, type of sport and type of sample collection (in competition/out of competition). The method was fully validated for quantitative purposes considering the parameters linearity, inter- (12%, 7% and 10%) and intraday precision (14%, 9% and 12%) at low, mid and high concentration, robustness, accuracy (approx. 100%), limit of quantification (100 ng/mL), stability and ion suppression effects, employing an in-house synthesised ¹³C₅-labelled AICAR as internal standard.     

Diastereoselective synthesis of 6-functionalized 4-aryl-1,3-oxazinan-2-ones and their application in the synthesis of 3-aryl-1,3-aminoalcohols and 6-arylpiperidine-2,4-diones

Halocyclocarbamation of benzyl N-(1-phenyl-3-butenyl)carbamates afforded 6-functionalized 4-aryl-1,3-oxazinan-2-ones with moderate to excellent diastereoselectivity depending on the N-substituent. Importantly, in contrast to reported cyclocarbamations of homoallylic carbamates, which are generally trans-diastereoselective, cyclization of N-unsubstituted Cbz-protected homoallylamines led to cis-1,3-oxazinan-2-ones, predominantly. The use of N-benzylated and in situ prepared N-silylated derivatives resulted however in trans-selectivity. Transition states are proposed to explain the stereochemical influence of the N-substituent on the cyclocarbamations. The functionalized 1,3-oxazinan-2-ones could be further elaborated towards biologically or synthetically important 6-arylpiperidine-2,4-diones and 3-aryl-1,3-aminoalcohols.     

N-Acetyl peak in MR spectra of intracranial metastatic mucinous adenocarcinomas

Absence of N-acetylaspartate (NAA) is one important diagnostic criterion of MR spectroscopy (MRS) that may suggest that an intracranial mass lesion is a metastasis. We report two cases of histopathology-confirmed intracranial metastatic mucinous adenocarcinoma, which predominantly showed a large metabolite peak at 2.0 ppm, mimicking an NAA peak of normal brain tissue. This finding could be of help in the interpretation of MRS in cases of intracranial enhancing mass lesions, metastases or gliomas.     

Dynamic Nuclear Polarization of [1-C]pyruvic acid at 4.6 tesla

Dynamic Nuclear Polarization (DNP) of the ¹³C nucleus has been investigated for [1-¹³C]pyruvic acid, doped with the trityl radical OX063Me, at 4.64 T and 1.15 K. The dependence of the polarization on microwave frequency, radical concentration and electron saturation was studied. For optimized conditions, a ¹³C polarization equal to 64 ± 5% was obtained, an increase by more than a factor of two compared with earlier results at 3.35 T of the same system. It was furthermore observed that the addition of gadolinium, which resulted in a twofold polarization increase at 3.35 T, only resulted in a minor improvement at 4.64 T. The dependence of the electron saturation on microwave frequency and microwave power was quantified by first moment measurements which were obtained by nucleus–electron double resonance (NEDOR) experiments. Complete electron saturation was observed for a microwave frequency close to the centre frequency of the ESR line, and by using maximum power of the microwave source. The DNP build-up time at 4.64 T (3000 s) was prolonged by approximately a factor three over the build-up time at 3.35 T (1200 s). However, after approximately 20 min of microwave irradiation the polarization at 4.64 T exceeded the polarization at 3.35 T.     

Catalytic asymmetric synthesis of ferrocenes and P-stereogenic bisphosphines

The catalytic asymmetric synthesis of planar chiral ferrocenes and P-stereogenic phosphines and bisphosphines (important classes of chiral ligands for metal-catalyzed asymmetric processes) is successfully demonstrated using n-BuLi or s-BuLi in combination with substoichiometric quantities (0.1-0.5 equiv) of (-)-sparteine or the (+)-sparteine surrogate.     

Site-specific cleavage of RNA by a metal-free artificial nuclease attached to antisense oligonucleotides

RNA cleaving tris(2-aminobenzimidazoles) have been attached to DNA oligonucleotides via disulfide or amide bonds. The resulting conjugates are effective organocatalytic nucleases showing substrate and site selectivity as well as saturation kinetics. The benzimidazole conjugates also degrade enantiomeric RNA. This observation rules out contamination effects as an alternative explanation of RNA degradation. The pH dependency shows that the catalyst is most active in the deprotonated state. Typical half-lifes of RNA substrates are in the range of 12-17 h. Thus, conjugates of tris(2-aminobenzimidazoles) can compete with the majority of metal-dependent artificial nucleases.     

Systematic DFT study of gas phase and solvated uranyl and neptunyl complexes [AnO2X4]n (An = U, Np; X = F, Cl, OH, n = -2; X = H2O, n = +2)

The six-valent uranyl and neptunyl complexes [An(VI)O2X4]n (An = U, Np; X = F, Cl, OH, n = -2; X = H2O, n = +2) have been studied within the framework of density functional theory. The relative stabilities of the cis and trans isomers, structural properties, charge distribution, and ligand binding energies have been determined using the modified Perdew-Burke-Ernzerhof functional at the all-electron scalar relativistic level. Uranyl and neptunyl complexes with different ligands have been compared in a systematic fashion, demonstrating close similarity of these actinides in oxidation state VI. In addition, the effect of an aqueous solution has been taken into account with the polarizable continuum model COSMO. Computed averaged ligand binding energies permit one to rationalize the observed different stabilities of the title species in aqueous media.     

A density functional study of uranyl monocarboxylates

We studied uranium(VI) monocarboxylate complexes by a relativistic density functional method using simple carboxylic acids as ligands, i.e. [UO2(OOCR)]+ (R = H, CH3, CH2CH3). These complexes exist in aqueous solution and, for R = CH3 and CH2CH3, may also be considered as models of uranyl complexated by humic substances. We investigated mono- and bidentate coordination modes. Short-range solvent effects were accounted for explicitly via aqua ligands of the first hydration shell and long-range electrostatic interactions were described via a polarizable continuum model. The calculated results for the uranyl U=O bond, the bond to aqua ligands, and the averaged uranium distances to equatorial oxygen atoms, U-Oeq, agreed quite well with EXAFS-derived interatomic distances. However, the uranyl-carboxylate bond was calculated to be notably shorter than the experimentally determined value. Experimental differences between mono- and bidentate coordination, obtained mainly from crystal structures, were qualitatively reproduced for the U-C distance but not for the average bond length, U-Oeq. We discuss these discrepancies between calculated and experimental results in some detail and suggest changes in the coordination number rather than variations of the coordination geometry as the main source of the experimentally observed variation of the U-Oeq distance.     

Numerical Simulation of Spot-Weld Joints under Crash Loading

This paper compares FE simulations of spot-weld joints for dual-phase steel under different load cases by using damage models of Gurson-Tvergaard-Needleman (GTN) and its two extensions, GTN-Johnson-Cook and GTN-Hutchinson. Spot-weld specimens have three zones depending with different material properties: Base material, heat-affected zone and fusion zone. The characterization of the base material is straightforward. The other two zones are characterized with specifically heat-treated specimens. For each zone, flat smooth tensile, flat notched tensile and Iosipescu-shear specimen are used in order to obtain the damage behavior for different triaxiality values. GTN damage model parameters are calibrated with the help of smooth and notched flat tensile specimens. The parameters of the above mentioned extensions of GTN damage model are identified with the help of Iosipescu-shear specimen. Finally, the calibrated material models are used in the FE simulation of the spot-weld specimens under quasi static-load case (10 mm/min) for loading directions of 0°, 30°, 60°, 90°. The numerical force-displacement results are in good agreement with experimental results. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)