Phosphine‐Catalyzed Enantioselective Synthesis of Oxygen Heterocycles

Chiral phosphepine 1 catalyzes the transformation of an array of hydroxy‐2‐alkynoates into saturated oxygen heterocycles with good enantioselectivity. Phenols are also shown to participate in such phosphine‐catalyzed cyclizations, including an asymmetric variant. This method provides a new approach to the enantioselective synthesis of tetrahydrofurans, tetrahydropyrans, and dihydrobenzopyrans.

     

Sampling with Bessel Functions

The paper deals with sampling of σ-bandlimited functions in R^m with Clifford-valued, where bandlimitedness means that the spectrum is contained in the ball B(0, σ) that is centered at the origin and has radius σ. By comparing with the general setting, what is new in the sampling is using the explicit Bochner-type relations involving spherical harmonics and monogenics in the Clifford algebra setting. Convergence of the sampling formulas in the L² sense and in the uniform and absolute pointwise sense are studied. The study was supported by Research Grant of the University of Macau No. RG059/05- 06S/QT/FST.     

A model of the elastodynamic interaction of a thin-walled inclusion with a matrix under antiplanar shear

Using the example of antiplanar shear we give a generalized scheme for constructing models of elastodynamic interaction of an elastic matrix with a thin-walled elastic curvilinear inclusion lying in the matrix under conditions of ideal contact subject to steady vibrations, by introducing suitable conditions on the middle line of the inhomogeneity. The procedure for the study is based on the application of the methods of the theory of singular perturbations. We describe the behavior of the stress-strain state of the body near the edges of the inhomogeneity, where boundary-layer phenomena appear. Translated fromMatematychni Metody ta Fizyko-Mekhanichni Polya, Vol. 41, No. 1, 1998, pp. 54–61.     

Evidence for the Prerequisite Formation of Phenoxyl Radicals in Radical-Mediated Peptide Tyrosine Nitration In Vacuo

The elementary mechanism of radical-mediated peptide tyrosine nitration, which is a hallmark of post-translational modification of proteins under nitrative stress in vivo, has been elucidated in detail by using an integrated approach that combines the gas-phase synthesis of prototypical molecular tyrosine-containing peptide radical cations, ion–molecule reactions, and isotopic labeling experiments with DFT calculations. This reaction first involves the radical recombination of ^.NO₂ towards the prerequisite phenoxyl radical tautomer of a tyrosine residue, followed by proton rearrangements, finally yielding the stable and regioselective 3-nitrotyrosyl residue product. In contrast, nitration with the π-phenolic radical cation tautomer is inefficient. This first direct experimental evidence for the elementary steps of the radical-mediated tyrosine nitration mechanism in the gas phase provides a fundamental insight into the regioselectivity of biological tyrosine ortho-nitration.     

Study of the reaction of methyltris(dimethylamino)silane with diamines

Tris(dimethylamino)methylsilane reacts with N,N′-dialkyldiamines to give the corresponding substituted 1,3,2-diazasilacycloalkanes. In contrast, the reaction with an N-alkyldiamine yields the corresponding polycyclic silazane.