Concise Six-Step Asymmetric Approach to Ramelteon from an Acetophenone Derivative Using Ir, Rh, Cu, and Ni Catalysis.

A concise six-step asymmetric synthesis of nearly enantiomerically pure ramelteon was developed from a monocyclic precursor with a 17% overall yield and a 97% ee in the asymmetric step. The synthetically challenging tricyclic 1,6,7,8-tetrahydro-2H-indeno[5,4-b]furan core of ramelteon was assembled by using Ir-catalyzed O-vinylation and Rh-catalyzed vinyl ether annulation through directed C-H bond activation, while the chirality was introduced with enantioselective reduction of an α,ß-unsaturated nitrile moiety under hydrosilylation conditions using a CuII/Walphos type catalyst. The presented methodology represents the shortest synthetic approach to ramelteon.

Inositol hexakisphosphate kinase products contain diphosphate and triphosphate groups.

Eukaryotic cells produce a family of diverse inositol polyphosphates (IPs) containing pyrophosphate bonds. Inositol pyrophosphates have been linked to a wide range of cellular functions, and there is growing evidence that they act as second messengers. Inositol hexakisphosphate kinase (IP6K) is able to convert the natural substrates inositol pentakisphosphate (IP 5) and inositol hexakisphosphate (IP 6) to several products with an increasing number of phospho-anhydride bonds. In this study, we structurally analyzed IPs synthesized by three mammalian isoforms of IP6K from IP 5 and IP 6. The NMR and mass analyses showed a number of products with diverse, yet specific, stereochemistry, defined by the architecture of IP6K's active site. We now report that IP6K synthesizes both pyrophosphate (diphospho) as well as triphospho groups on the inositol ring. All three IP6K isoforms share the same activities both in vitro and in vivo.

Determination of selected trace elements in airborne aerosol particles using different sample preparation.

Determination of trace element concentrations in atmospheric aerosols is important because of their toxic effects on human health. Additionally, they are now widely used in source apportionment studies. There is a number of methods for sample preparation of ambient particulate matter. One of the most widely used is microwave-assisted digestion of filter-based samples. Since the water-soluble fraction is bioavaliable, the aim of our study was to determine the concentration of selected trace elements (V, Cr, Mn, Ni, Cu, Zn, As, Cd, Sb, Tl, and Pb) in this fraction and compare it to the amounts obtained by two different microwave digestion procedures - one using a mixture of H2O2 and HNO3 and the other using a mixture of HF, HCl, and HNO3. The recoveries of the digestion procedures used were tested on certified reference material (NIST SRM 1648 Urban Particulate Matter). The procedures were applied to filters containing PM10 particles collected at an urban background location in Ljubljana, Slovenia. Among the elements analysed, V, Zn, As, and Cd displayed the highest concentration within the water-soluble fraction, with Cr, Ni, Tl and Pb displaying the lowest concentrations. The comparison between the two applied digestion procedures showed that Cr, Ni, Sb and Tl were strongly bound to the sample matrix.

Determination of bisphosphonates by ion chromatography-inductively coupled plasma mass spectrometry.

An ion chromatography-inductively coupled plasma mass spectrometry (IC-ICP-MS) was introduced in the analysis of bisphosphonates. Two compounds (alendronic acid and etidronic acid) were separated on a Dionex AS-7 anion-exchange column with dilute nitric acid employed as the mobile phase. The analytes were detected at m/z 31, as they contain phosphorus. The detection limits achieved were 0.20 mg l(-1) for alendronic acid and 0.05 mg l(-1) for etidronic acid. Since the determination of phosphorus by ICP-MS is difficult due to polyatomic interferences at m/z 31 (15N16O+, 14N16O1H+, and 12C1H(3)16O+), a detailed study of the influence of plasma parameters on phosphorus and background signal was performed.

Selenium species in selenium-enriched and drought-exposed potatoes.

The aim of this work was to study selenium (Se) speciation in the potato ( Solanum tuberosum L.) cultivar Desiree, enriched in Se by foliar spraying with a water solution containing 10 mg of Se/L in the form of sodium selenate. Four combinations of treatments were used: well-watered plants with and without Se foliar spraying and drought-exposed plants with and without Se foliar spraying. Water-soluble Se compounds were extracted from potato tubers by water or enzymatic hydrolysis with the enzyme protease XIV, amylase, or a combination of protease XIV and amylase. Extraction was performed using incubation at a constant temperature and stirring (37 degrees C at 200 rpm) or by ultrasound-assisted extraction (300 W), using different extraction times. Separation of soluble Se species (SeCys2, SeMet, SeMeSeCys, selenite, and selenate) was achieved by ion-exchange chromatography, and detection was performed by inductively coupled plasma-mass spectrometry (ICP-MS). Results showed that the concentration of selenate extracted was independent of the enzymatic extraction technique (approximately 98 ng/g for drought-exposed and 308 ng/g for well-watered potato tubers), whereas the extraction yield of SeMet changed with the protocol used (10-36%). Selenate and SeMet were the main soluble Se species (representing 51-68% of total Se) in potato tubers, regardless of the growth conditions.

Matrix effects during phosphorus determination with quadrupole inductively coupled plasma mass spectrometry.

A quadrupole inductively coupled plasma mass spectrometer was evaluated for use in the detection of phosphorus. The influences of nitric acid and methanol (simulating the composition of a sample solution after nitric acid digestion) on phosphorus determination were studied using two different measuring methods at different plasma conditions: detection of phosphorus ions at m/z 31 and detection of phosphorus oxide ions at m/z 47. The existence of polyatomic interferences at m/z 31 and 47 was explored. Nitric acid and methanol are shown to be the sources of polyatomic ions and therefore cause poorer detection limits. Better detection limits were achieved in such matrices when phosphorus was detected as 31P+. The presence of methanol improves the system sensitivity towards phosphorus sevenfold; however, this positive effect is hindered by the high background signal due to carbon-based polyatomic ions. For samples with an organic matrix an appropriate mineralization procedure should be applied (high excess of nitric acid and high temperature) to quantitatively oxidize organic compounds to carbon dioxide, which is easily removed from the sample, in order to achieve correct results.

The Rv0805 gene from Mycobacterium tuberculosis encodes a 3',5'-cyclic nucleotide phosphodiesterase: biochemical and mutational analysis.

Mycobacterium tuberculosis is an important human pathogen and has developed sophisticated mechanisms to evade the host immune system. These could involve the use of cyclic nucleotide-dependent signaling systems, since the M. tuberculosis genome encodes a large number of functional adenylyl cyclases. Using bioinformatic approaches, we identify, clone, and biochemically characterize the Rv0805 gene product, the first cyclic nucleotide phosphodiesterase identified in M. tuberculosis and a homologue of the cAMP phosphodiesterase present in Escherichia coli (cpdA). The Rv0805 gene product, a class III phosphodiesterase, is a member of the metallophosphoesterase family, and computational modeling and mutational analyses indicate that the protein possesses interesting properties not reported earlier in this class of enzymes. Mutational analysis of critical histidine and aspartate residues predicted to be essential for metal coordination reduced catalytic activity by 90-50%, and several mutant proteins showed sigmoidal kinetics with respect to Mn in contrast to the wild-type enzyme. Mutation of an asparagine residue in the GNHD motif that is conserved throughout the metallophosphoesterase enzymes almost completely abolished catalytic activity, and these studies therefore represent the first mutational analysis of this class of phosphodiesterases. The Rv0805 protein hydrolyzes cAMP and cGMP in vitro, and overexpression in Mycobacterium smegmatis and E. coli reduces intracellular cAMP levels. The presence of an orthologue of Rv0805 in Mycobacterium leprae suggests that the Rv0805 protein could have an important role to play in regulating cAMP levels in these bacteria and adds an additional level of complexity to cyclic nucleotide signaling in this organism.