Reaction of alkynyltrimethylsilanes with a hypervalent organoiodine compound: A new general synthesis of alkynyliodonium salts

New general methods for the synthesis of alkynyl(phenyl)iodonium tetrafluoroborate 2 from alkynyltrimethylsilanes 1 utilizing the combination of iodosylbenzene and triethyloxonium tetrafluoroborate or boron trifluoride etherate were developed. The medium effect observed in the reaction was also discussed.     

Practical version of the Asymptotic Linearity Theorem with applications to the additivity problems of thermodynamic quantities

By using fundamental notions and theorems of the Lesbesgue integral, a practical version of the Asymptotic Linearity Theorem has been derived. From this new version of the theorem, it easily follows that the theorem is also applicable to the additivity problems of thermodynamic quantities of molecules having many identical moieties, as well as to those of the zero-point vibrational energy of hydrocarbons and the total pi electron energies of altemant hydrocarbons.On leave from: Institute for Fundamental Chemistry, 34-4 Nishihiraki-cho, Takano, Sakyo-ku, Kyoto 606, Japan.     

Possibility of a non-amino acid pathway in the biosynthesis of marine-derived oxazoles

A novel avenue for oxazoles via Beckmann rearrangement of alpha-formyl ketoxime dimethyl acetals is described that indicates the possibility of a non-amino acid biosynthetic pathway in marine natural products.     

Measurements of the complex degree of spectral coherence by use of a wave-front-folded interferometer

A wave-front-folded interferometer composed of a K?sters prism and an image-forming lens provides a good way of measuring the complex degree of spectral coherence. Demonstrative experiments are implemented by incorporation of uncorrelated two-point spectral sources in the primary-source plane; these sources establish a spatially partially coherent wave field over the secondary source plane just in front of the interferometer. The complex degree of spectral coherence of the secondary source is successfully measured after an a priori calibration is made for the interferometer that was constructed.     

Studies toward the total synthesis of nakiterpiosin: construction of the CDE ring system by a transannular Diels-Alder strategy

The transannular Diels-Alder (TADA) reaction was applied to the synthesis of the CDE ring system of nakiterpiosin (1). Tetracyclic compound 25 may be a key intermediate in the total synthesis of 1.     

Structural analysis of certain linear operators representing chemical network systems via the existence and uniqueness theorems of spectral resolution. III

By extending the methodology given in Parts I and II of this series of articles, certain dynamical systems of chemical kinetic equations are analyzed in the setting of the Banach algebra B(ℬ︁) of all bounded operators acting on a Banach space ℬ︁. In this article, we proceed from the general setting of B(ℬ︁), which played a central role in Part II, toward its specific application to the dynamical systems. In our analysis, crucial initial steps are taken by (i) equipping the abstract space ℬ︁ with the “positive quadrant,” which we denote by Γ(ℝ⁺ⁿ), and by (ii) investigating the asymptotic behavior of the solution χ_ϵ(t) of the initial-value problem is suitably specified for our application purposes. The main theorem and its two specialized versions, together with the notions of Γ-semipositive operators and semipositive matrices presented here, serve as fundamental tools for the analysis of a class of dynamical systems of chemical kinetic equations whose examples were illustratively treated in the previous parts of this series of articles. The techniques developed here for an asymptotic analysis of chemical kinetic dynamical systems will be linked and unified with those for the asymptotic analysis of quantum mechanical systems in a forthcoming part of this series of articles. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 149–163, 1997     

Elucidation of the Active Conformation of Vancomycin Dimers with Antibacterial Activity against Vancomycin‐Resistant Bacteria

Covalently linked vancomycin dimers have attracted a great deal of attention among researchers because of their enhanced antibacterial activity against vancomycin‐resistant strains. However, the lack of a clear insight into the mechanisms of action of these dimers hampers rational optimization of their antibacterial potency. Here, we describe the synthesis and antibacterial activity of novel vancomycin dimers with a constrained molecular conformation achieved by two tethers between vancomycin units. Conformational restriction is a useful strategy for studying the relationship between the molecular topology and biological activity of compounds. In this study, two vancomycin units were linked at three distinct positions of the glycopeptide (vancosamine residue (V), C terminus (C), and N terminus (N)) to form two types of novel vancomycin cyclic dimers. Active NC‐VV‐linked dimers with a stable conformation as indicated by molecular mechanics calculations selectively suppressed the peptidoglycan polymerization reaction of vancomycin‐resistant Staphylococcus aureus in vitro. In addition, double‐disk diffusion tests indicated that the antibacterial activity of these dimers against vancomycin‐resistant enterococci might arise from the inhibition of enzymes responsible for peptidoglycan polymerization. These findings provide a new insight into the biological targets of vancomycin dimers and the conformational requirements for efficient antibacterial activity against vancomycin‐resistant strains.     

Completeness of Trigonometric System with Integer Indices {e; x }

Necessary and sufficient conditions are given which ensure the completeness of the trigonometric systems with integer indices; {e^inx; x }^∞_n=−∞ or {e^inx; x }^∞_n=1 in L^α(μ,  ), α1. If there exists a support Λ of the measure μ which is a wandering set, that is, Λ+2kπ, k=0, ±1, ±2, … are mutually disjoint for different k's, then the linear span of our trigonometric system {e^inx; x }^∞_n=−∞ is dense in L^α(μ,  ) α1. The converse statement is also true.     

Activation and inhibition of lipoprotein lipase in mixed monolayers of medium or long chain-triglycerides and phospholipids

 We evaluated the activation and inhibition effects of phosphatidylcholine (PC) and sphingomyelin (SM) on lipoprotein lipase (LPL) for medium or long chain-triglycerides (TG) in monolayers at the air/water interface. Monolayers of medium chain-TG, being in an expanded state at a surface pressure of 15 mN/m, showed low susceptibility to LPL in the subphase. Adding 50 mole% of PC or SM into these monolayers reduced the partial molecular area of the TG and enhanced the LPL activity. Monolayers of long chain-TG, being in a condensed state, showed high susceptibility of LPL either with or without PC. SM added to the long chain-TG monolayers, however, inhibited the LPL action. We investigated the interaction between TG and phospholipid on the basis of the collapse pressure-measurements of mixed monolayers. For medium chain-TG monolayers, PC and SM gave similar collapse pressure-composition profiles. Contrary to this, SM gave a markedly higher collapse pressure of long chain-TG than PC: SM stabilized the monolayer state of long chain-TG. These results suggested that I) orientation of the acyl chains of TG molecule in a monolayer is crucial for the LPL activity, and that II) strong interaction between SM and long chain-TG retards the substrate-transfer from the mixed monolayer to the catalytic pocket of LPL. Received: 6 March 1996 Accepted: 19 July 1996