Asymmetric synthesis of N,O,O,O-tetra-acetyl d-lyxo-phytosphingosine, jaspine B (pachastrissamine), 2-epi-jaspine B, and deoxoprosophylline via lithium amide conjugate addition

The highly diastereoselective anti-aminohydroxylation of (E)-gamma-tri-iso-propylsilyloxy-alpha,beta-unsaturated esters, via conjugate addition of lithium (S)-N-benzyl-N-(alpha-methylbenzyl)amide and subsequent in situ enolate oxidation with (+)-(camphorsulfonyl)oxaziridine, has been used as the key step in the asymmetric synthesis of N,O,O,O-tetra-acetyl d-lyxo-phytosphingosine (20% yield over 7 steps), the anhydrophytosphingosine jaspine B (10% yield over 9 steps), 2-epi-jaspine B (14% yield over 9 steps), and the Prosopis alkaloid deoxoprosophylline (26% yield over 7 steps).     

(p-Cymene)thioglycollatoruthenium(II) dimer; a complex with an ambi-basic S,O-donor ligand

The title compound was prepared from the (p-cymene)ruthenium chloride dimer and thioglycollic acid. The structure is a centrosymmetric dimer bridged by the soft-base S atoms, with the hard-base O atoms of the carboxylate group chelating to form a five-membered twisted-ring. The coordination of the ruthenium atoms is completed by a η⁶-p-cymene ligand, giving an 18-electron count. The Ru–S bonds are essentially equal at 2.396(1) Å.     

Identification of urinary modified nucleosides and ribosylated metabolites in humans via combined ESI-FTICR MS and ESI-IT MS analysis

The physiological response of the human body to several diseases can be reflected by the metabolite pattern in biological fluids. Cancer, like other diseases accompanied by metabolic disorders, causes characteristic effects on cell turnover rate, activity of modifying enzymes, and RNA/DNA modifications. This results in an altered excretion of modified nucleosides and biochemically related compounds. In the course of our metabolic profiling project, we screened 24-h urine of patients suffering from lung, rectal, or head and neck cancer for previously unknown ribosylated metabolites. Therefore, we developed a sample preparation procedure based on boronate affinity chromatography followed by additional prepurification with preparative TLC. The isolated metabolites were analyzed by ion trap mass spectrometry (IT MS) and Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS). IT MS was applied for LC-auto MS³ screening runs and MS ^n(n=4–6) syringe pump infusion experiments, yielding characteristic fragmentation patterns. FTICR MS measurements enabled the calculation of corresponding molecular formulae based on accurate mass determination (mass accuracy: 1–5 ppm for external and sub-ppm values for internal calibration). We were able to identify 22 metabolites deriving from cellular RNA metabolism and related metabolic pathways like histidine metabolism, purine biosynthesis, methionine/polyamine cycle, and nicotinate/nicotinamide metabolism. The compounds 1-ribosyl-3-hydroxypyridinium, 1-ribosyl-pyridinium, and 3-ribosyl-1-methyl-l-histidinium as well as a series of ribosylated histamines, conjugated to carboxylic acids at the N^ω-position were found as novel urinary constituents. The occurrence of the modified nucleosides 2-methylthio-N ⁶-(cis-hydroxyisopentenyl)-adenosine, 5-methoxycarbonylmethyl-2-thiouridine, N ⁶-methyl-N ⁶-threonylcarbamoyladenosine, and 2-methylthio-N ⁶-threonylcarbamoyladenosine in human urine is verified for the first time.     

Time-dependent column performance of cholesterol-based stationary phases for HPLC by LC characterization and solid-state NMR spectroscopy

Three different cholesterol-based stationary phases were investigated with respect to their time-dependent separation behavior. The examined stationary phases differ in the used spacer molecule and the synthesis route and were used under routine laboratory conditions over a period of two years. The chromatographic behavior of the three phases was determined by using a standard reference material in addition to a separation of a steroid mixture. The surface chemistry and the modification of these with the chemically bonded moiety were investigated with nuclear magnetic resonance (NMR) spectroscopy and elemental analysis. Through applying different techniques we determined changes in retention and selectivity; solid-state NMR spectra showed changes in the surface chemistry dependent on the synthesis route. Superior long-term stability was observed for the undecanoate-cholesterol (UDC-Chol) column in terms of hydrophobic retentiveness and selectivity.     

Improved stabilization of a 1.3 microm femtosecond optical frequency comb by use of a spectrally tailored continuum from a nonlinear fiber grating

We report significant enhancement (+24 dB) of the optical beat note between a 657 nm cw laser and the second-harmonic generation of the tailored continuum at 1314 nm generated with a femtosecond Cr:forsterite laser and a nonlinear fiber Bragg grating. The same continuum is used to stabilize the carrier-envelope offset frequency of the Cr:forsterite femtosecond laser and permits improved optical stabilization of the frequency comb from 1.0 to 2.2 microm. Using a common optical reference at 657 nm, a relative fractional frequency instability of 2.0 x 10(-15) is achieved between the repetition rates of Cr:forsterite and Ti:sapphire laser systems in 10 s averaging time. The fractional frequency offset between the optically stabilized frequency combs of the Cr:forsterite and Ti:sapphire lasers is +/-(0.024 +/- 6.1) x 10(-17).     

Synthesis and alkyne-coupling chemistry of cyclomanganated 1- and 3-acetylindoles, 3-formylindole and analogues

The syntheses are reported of new cyclomanganated indole derivatives (1-acetyl-κO-indolyl-κC²)dicarbonylbis(trimethylphosphite)manganese (2), (1-methyl-3-acetyl-κO-indolyl-κC²)tetracarbonylmanganese (4), (3-formyl-κO-indolyl-κC²)tetracarbonylmanganese (5a) and (1-methyl-3-formyl-κO-indolyl-κC²)tetracarbonylmanganese (5b). The unusually complicated crystal structure of 5b has been determined, the first for a cyclomanganated aryl aldehyde.The preparations of a mitomycin-related pyrrolo-indole and related products by thermally promoted and oxidatively (Me₃NO) initiated alkyne-coupling reactions of the previously known complex (1-acetyl-κO-indolyl-κC²)tetracarbonylmanganese (1) are reported for different alkynes and solvents. X-ray crystal structures are reported for the dimethyl acetylenedicarboxylate coupling product of 1 (dimethyl 1-methyl-l-hydroxypyrrolo[1,2a]-indole-2,3-dicarboxylate; 6a), and an unusually-cyclised triple insertion product 8 from the coupling of acetylene with 4, in which a cyclopentadiene moiety is η³-allyl-coordinated to Mn through only one double bond and an exocyclic carbon, but which rearranges on heating to an η⁵-cyclopentadienyl complex.     

ChemInform Abstract: First‐Principles Screening of Complex Transition Metal Hydrides for High Temperature Applications.

Semi‐automated thermodynamic and phase diagram calculations based on DFT and grand canonical linear programming (GCLP) methods are used to screen 102 ternary and quaternary complex transition metal hydrides (CTMHs) and 26 ternary saline hydrides in a library of over 260 metals, intermetallics, binary, and higher hydrides to identify materials that release H₂ at higher temperatures than the associated binary hydrides and at elevated temperatures (T < 1000 K, 1 bar H₂ overpressure).