Total synthesis 2-epi-α-cedren-3-one via a cobalt-catalysed Pauson-Khand reaction

Herein we target the total synthesis of 2-epi-α-cedren-3-one, a natural compound isolated from the essential oil of Juniperus thurifera. Overall, our synthetic sequence presents an optimised and robust series of chemical transformations, with prominent features including a low temperature and highly (Z)-selective Wittig olefination reaction, which is vital for the establishment of the relative stereochemistry within the final natural product, and a microwave-assisted, catalytic, intramolecular Pauson-Khand cyclisation reaction, which is used to construct the intriguing tricyclic core of the target molecule. Our optimum cyclisation protocol utilises only 20?mol% of transition metal, and delivers the complex tricyclic structure in just 10?min. Further manipulations of the annulation product culminate in the first total synthesis of the described natural target.     

The structure of a tetrabromotetrahydrodibenzocyclooctene

5, 6, 11, 12-Tetrabromo-5, 6, 11, 12-tetrahydrodibenzo[a, e]cyclooctene, C₁₆H₁₂Br₄, crystallizes in monoclinic space group P2₁/c witha=8.6917(7),b=15.135(2),c=12.892(2) Å, =101.836(8)°, V=1660.0(7) ų,Z=4. The structure was refined toR=0.058 for 3137 observed reflections. The molecule has approximate C₂ symmetry, with the eight-membered ring adopting the twist-boat conformation. The planes of the two phenyl rings form a dihedral angle of 117.3(2)°, C–Br distances range 1.965(5)–1.981(5) Å.     

Čech cocycles for characteristic classes

We give general formulae for explicit ech cocycles representing characteristic classes of real and complex vector bundles, as well as for cocycles representing Chern-Simons classes of bundles with arbitrary connections. Our formulae involve integrating differential forms over moving simplices inside homogeneous spaces. An important feature of our cocycles is that they take integer values (as opposed to real or rational values). We find in particular a formula for the instanton number of a connection over a closed four-manifold with arbitrary structure group. For flat connections, our formulae recover and generalize those of Cheeger and Simons. The methods of this paper apply also to the purely geometric construction of the Quillen line bundle with its metric.The first author was supported in part by N.S.F. grant DMS-9203517.The second author was supported in part by N.S.F. grant DMS-9310433.     

Scanning control of a vibrating string

We construct scanning feedback controls {γ _i (t)} for the vibrating string equation $$\begin{gathered} y_{tt} (x,t) = y_{xx} (x,t) + Ry(x,t) + \sum\limits_{i = 1}^N {\phi (x - \gamma _i } (t))y(x,t), \hfill \\ 0< x< 1,y = 0 at x = 0,1. \hfill \\ \end{gathered} $$ so that (y, y _t ) → (0,0) ast → ∞ in the weak topology ofH ₀ ¹ (0,1) ×L ₂ (0,1). In particular we show that ifφ is an even polynomial of degreeN with nonpositive coefficients that forR <π ² we can find such stabilizingγ _i (t), i=1,?,N.     

Synthesis of alpha-L-threofuranosyl nucleoside triphosphates (tNTPs)

[structure: see text] The alpha-l-threofuranosyl nucleoside triphosphates of T, G, and D (tTTP, tGTP, and tDTP) were synthesized from the described 2'-O-DMT-protected derivatives using the Eckstein method, while the corresponding C derivative (tCTP) was prepared from the 2'-O-acetyl derivative. The prepared alpha-l-threofuranosyl nucleoside triphosphates, despite being one carbon shorter than the native 2'-deoxyfuranosyl nucleoside triphosphates, are effective substrates for selected DNA polymerases.     

A portable, photon analysis spectrometer for the assay of X- and gamma-ray emitting radionuclides

A portable, battery-powered, multichannel analyzer (MCA) for use with Ge spectrometers has been developed for in-field use for the assay of x-and γ-ray emitting radionuclides. The spectrometer is capable of operating to rates greater than 150,000 counts per second. The analyzer is a Canberra InSpector MCA, that is equipped with the INEEL ultra-stable dual-energy pulser, and pulse injection with subsequent removal (PISR) circuitry. PCGAP, a set of MCA control and spectral analysis programs, was developed for use on a PC with a Windows NT Operating System. It includes an interactive peak analysis program as well as automatic spectral analysis programs for the X- and γ-ray regions, and a number of utility programs. The pulser peaks are calibrated with radioactive sources in terms of energy (i.e., their energy equivalents are measured) using the PCGAP spectral analysis package so that energy shifts, including those due to changes in temperature or count rate, do not cause a loss of energy calibration. The number of injected low- and high-energy-equivalent pulses is known so the stored pulser pulses can be used for a dead-time and random summing correction. The pulser peaks are also used to monitor any deterioration in spectral quality caused by noise, ground loops, etc. The results of performance tests to demonstrate the capabilities of this pulser-equipped InSpector are reported.     

Kinetic analysis of an efficient DNA-dependent TNA polymerase

alpha-l-Threofuranosyl nucleoside triphosphates (tNTPs) are tetrafuranose nucleoside derivatives and potential progenitors of present-day beta-d-2'-deoxyribofuranosyl nucleoside triphosphates (dNTPs). Therminator DNA polymerase, a variant of the 9 degrees N DNA polymerase, is an efficient DNA-directed threosyl nucleic acid (TNA) polymerase. Here we report a detailed kinetic comparison of Therminator-catalyzed TNA and DNA syntheses. We examined the rate of single-nucleotide incorporation for all four tNTPs and dNTPs from a DNA primer-template complex and carried out parallel experiments with a chimeric DNA-TNA primer-DNA template containing five TNA residues at the primer 3'-terminus. Remarkably, no drop in the rate of TNA incorporation was observed in comparing the DNA-TNA primer to the all-DNA primer, suggesting that few primer-enzyme contacts are lost with a TNA primer. Moreover, comparison of the catalytic efficiency of TNA synthesis relative to DNA synthesis at the downstream positions reveals a difference of no greater than 5-fold in favor of the natural DNA substrate. This disparity becomes negligible when the TNA synthesis reaction mixture is supplemented with 1.25 mM MnCl(2). These results indicate that Therminator DNA polymerase can recognize both a TNA primer and tNTP substrates and is an effective catalyst of TNA polymerization despite changes in the geometry of the reactants.     

Preparation of quinolines from resin-bound esters using titanium reagents

ortho-Amino homobenzylic thioacetals are prepared from ortho-nitrobenzaldehydes via homologation using an alpha-methoxy Wittig reagent. Titanium reagents are generated from the 1,3-dithianes using a low valent titanium reagent and are then used to alkylidenate resin-bound esters. An N-silylated Boc group protects the ortho-amino functionality. Traceless SPS of quinolines is completed by treating the resulting resin-bound enol ethers with TFA and then oxidizing with manganese dioxide to give 2-substituted quinolines in high purity without the need for chromatography.