Silver(I)-catalyzed addition of zirconocenes to glycal epoxides. A new synthesis of alpha-C-glycosides

[reaction: see text] Hydrozirconation of terminal alkynes, followed by AgClO4-catalyzed in situ addition of the resultant alkenylzirconocenes to 1,2-anhydrosugars (glycal epoxides) leads to alpha-C-glycosides in moderate to high yields.     

Dark Multi-Soliton Solution of the Nonlinear Schrödinger Equation with Non-Vanishing Boundary

The inverse scattering transform for the nonlinear Schrödinger equation in normal dispersion with non-vanishing boundary values is re-examined using an affine parameter to avoid double-valued functions. An operable algebraic procedure is developed to evaluate dark multi-soliton solutions. The dark two-soliton solution is given explicitly as an example, and is verified by direct substitution. The additional motion of the soliton center is given by its asymptotic behavior.     

Hybrid optoelectronic bistability in a fiber Bragg grating by use of a tunable fiber laser

We report the observation of hybrid optoelectronic bistability in a fiber Bragg grating (FBG) by use of an electro-optically tuned cw fiber laser in which another wavelength-matched FBG is employed to constitute a tunable resonant cavity. The potential application of such a device as a fiber-optic sensor is also discussed.     

A novel approach to the synthesis of 6-amino-7-hydroxy-flavone

A novel approach to the synthesis of 6-amino-7-hydroxyflavone (1) is described. Reaction in acetone of 2',4'-dihydroxy-5'-nitroacetophenone and benzoyl chloride in the presence of potassium carbonate affords 3-benzoyl-7-hydroxy-6-nitroflavone, which is cleaved in 5% ethanolic potassium hydroxide to give 1-(2,4-dihydroxy-5-nitrophenyl)-3- phenyl-1,3-propanedione. The 1,3-diketone thus formed is then transformed into 7-hydroxy- 6-nitroflavone, followed by reduction to afford the title compound.     

N-Boc-L-valine-connected amidomonophosphane rhodium(I) catalyst for asymmetric arylation of N-tosylarylimines with arylboroxines

A catalytic asymmetric arylation of sterically tuned imines with arylboroxines was developed by using N-Boc-l-valine-connected amidomonophosphane rhodium(I) catalyst in n-PrOH. The TMS group used for the steric tuning of imines is convertible to other functionalities that are applicable as a key foothold for the carbon-carbon bond-forming coupling reactions.     

Coherent quantum transport in normal-metal/<Emphasis Type="Italic">d</Emphasis>-wave superconductor/normal-metal double tunnel junctions

Taking into account the effects of quantum interference and interface scattering, combining the electron current with hole current contribution to tunnel current, we study the coherent quantum transport in normal-metal/d-wave superconductor/ normal-metal (NM/d-wave SC/NM) double tunnel junctions by using extended Blonder-Tinkham-Klapwijk (BTK) approach. It is shown that all quasiparticle transport coefficients and conductance spectrum exhibit oscillating behavior with the energy, in which periodic vanishing of Andreev reflection (AR) above superconducting gap is found. In tunnel limit for the interface scattering strength taken very large, there are a series of bound states of quasiparticles formed in SC.     

Reactivity and chemical synthesis of L-pyrrolysine- the 22(nd) genetically encoded amino acid

L-pyrrolysine, the 22(nd) genetically encoded amino acid, was previously deduced to be (4R, 5R)-4-substituted-pyrroline-5-carboxylate attached to the epsilon-nitrogen of lysine based on the crystal structure of the M. barkeri monomethylamine methyltransferase (MtmB). To confirm L-pyrrolysine's identity, structures of MtmB have been determined following treatment with hydroxylamine, N-methylhydroxylamine, or dithionite. Analysis of these structures has provided additional support for the presence of the pyrroline ring and, together with previous mass spectroscopy data, has led us to assign the C(4)-substituent to a methyl group. Based on this assignment, synthetic L-pyrrolysine was prepared by chemical methods. Detailed study of this chemically synthesized L-pyrrolysine has allowed us to characterize its physical properties, to study its chemical stability, and to elucidate the role of its C(4) substituent. Future applications of this synthetic L-pyrrolysine include its in vivo incorporation into recombinant proteins.