Tetrahedral intermediates 3: The kinetics and mechanism of the breakdown of some hemiorthoesters

The kinetics of the breakdown of hemiorthoesters generated from dialkoxyalkyl acetates or ketene acetals have been investigated. The following compounds were studied: dimethyl hemiorthoformate (1b), diethyl hemiorthoformate (2b), 2-hydroxy-1,3-dioxolane (3b), 2-hydroxy-4,4,5,5-tetramethyl-1, 3-dioxolane, (4b), 2-hydroxy-2-methyl-1,3-dioxolane (5b),and 2-hydroxy-2,4,4,5,5-pentamethyl-1,3-dioxolane (6b).The whole series was studied in aqueous acetonitrile (c_H2O= 8.33 M); 4b, 5b, and 6b were studied in aqueous acetonitrile (c_H2O = 2.22 M) and 4b and 6b in water. Complete pc_H-rate or pH-rate profiles were obtained for each reaction. The mechanisms of the hydronium-ion, hydroxide-ion and “water” catalysed reactions are discussed and compared to those for the breakdown of hemiacetals and the hydrolysis of orthoesters.     

Polyenylpyrroles and polyenylfurans from an Australian Isolate of the soil ascomycete Gymnoascus reessii

[structure: see text] An Australian isolate of the soil ascomycete Gymnoascus reessii yielded a series of cytotoxic metabolites, including the known polyenylpyrroles rumbrin (1) and auxarconjugatin A (2), and the new rumbrin stereoisomer 12E-isorumbrin (3), as well as an unprecedented class of polyenylfurans exemplified by gymnoconjugatins A (4) and B (5). Structures were assigned with detailed spectroscopic analysis.     

FTIR Emission Spectra, Molecular Constants, and Potential Curve of Ground State GeO

Extensive new high-temperature, high-resolution FTIR emission spectroscopy measurements for the five common isotopomers of GeO are combined with previous diode laser and microwave measurements in combined isotopomer analyses. New Dunham expansion parameters and an accurate analytical potential energy function are determined for the ground X1Sigma+ state. Copyright 1999 Academic Press.     

Aspergillicins A-E: five novel depsipeptides from the marine-derived fungus Aspergillus carneus

A search for new antiparasitic agents from a strain of the fungus Aspergillus carneus isolated from an estuarine sediment collected in Tasmania, Australia, yielded the known terrestrial fungal metabolite marcfortine A (1) as an exceptionally potent antiparasitic agent. This study also yielded a series of new depsipeptides, aspergillicins A-E (2-6) and the known terrestrial fungal metabolite acyl aszonalenin (7). Marcfortine A (1) and acyl aszonalenin (7) were identified by spectroscopic analysis, with comparison to literature data. Complete stereostructures were assigned to aspergillicins A-E (2-6) on the basis of detailed spectroscopic analysis, together with ESIMS analysis of the free amino acids generated by acid hydrolysis, and HPLC analysis of Marfey derivatives prepared from the acid hydrolysate. The peptide amino acid sequence for all aspergillicins was unambiguously assigned by MS(n) ion-trap ESI mass spectrometry.     

Sesquiterpene metabolites from laurencia filiformis

The major lipid components of Laurencia filiformis have been shown to be aplysistatin 1 and 6β-hydroxyaplysistatin 2. The structure and absolute configuration of these sesquiterpenes has been confirmed by X-ray diffraction methods. An interesting thermal rearrangement of2 is described.     

Microscale analysis of mucin-type O-glycans by a coordinated fluorophore-assisted carbohydrate electrophoresis and mass spectrometry approach

The total glycan moiety was released in a single step from native glycoproteins by a nonreductive beta-elimination procedure. The generated oligosaccharides were further derivatized either with the hydrophobic fluorophore 2-aminoacridone (AMAC) or the charged 8-aminonaphthalene-1,3,6-trisulfonic acid (ANTS) fluorophore, and the resulting fluorescent derivatives were separated according to their hydrodynamic size or charge with high-resolution gel electrophoresis. Both N- and O-glycans released by this beta-elimination procedure might be analyzed simultaneously. AMAC derivatization allows a rapid separation of neutral and charged oligosaccharides without prior fractionation. Derivatized oligosaccharide species were then eluted from the gel slices and analyzed by mass spectrometry. This methodology allowed the rapid structural characterization of each glycan in term of monosaccharide composition and sequence. Using this technique we were able to screen several heterogeneous O-glycan mixtures isolated at the picomolar range from reference glycoproteins or mucins.     

A unified formalism in mechanics

Summary A method is described by which the paths of mechanical systems, whether relativistic or non-relativistic, holonomic or non-holonomic, may be obtained from a single principle, the Principle of Stationary Curvature. The systems may include electric charges and fields.The formalism is invariant, irrespective of the type of system, for a form of contact transformation differing from that commonly used in mechanics.The generating function (metric) is initially a quadratic function of the coordinates. In the last two paragraphs the metric is generalized.     

Wide angle electron-positron bremsstrahlung at adone a new limit for the existence of a heavy electron

The cross section for the reaction e⁺+e^?→e⁺+e^?+γ has been measured at the Adone storage ring. The results in agreement with the QED predictions, establish a new limit for the mass and the coupling constant $\text{e}{}^1\text{e}\text{γ}$ of a heavy electron e¹.     

Search for the radiative η′(958)+γ decay of the J/Ψ (3100) resonance produced in e+e− annihilation

The decay J/Ψ (3100)→ η(958) + γ has been searched for at tthe Adone e⁺e^+- storage ring. No candidate event has been found. This allows to set an upper limit of 1.0 keV (90% C.L.) for this decay partial width.     

Sydowiols A–C: Mycobacterium tuberculosis protein tyrosine phosphatase inhibitors from an East China Sea marine-derived fungus, Aspergillus sydowii

Chemical analysis of an East China Sea marine-derived fungus, Aspergillus sydowii (MF357) returned three new tris-pyrogallol ethers, sydowiols A–C (1–3), and two known bis-pyrogallol ethers, violaceols I (4) and II (5). Structures were assigned on the basis of detailed spectroscopic analysis and by consideration of symmetry. Sydowiols A (1) and C (3) were responsible for the inhibitory activity detected in the crude fungal extract against Mycobacterium tuberculosis protein tyrosine phosphatase A (PtpA).