Catalytic asymmetric amination of N-nonsubstituted α-alkoxycarbonyl amides: concise enantioselective synthesis of mycestericin F and G

In an attempt to explore the synthetic utility of a ternary asymmetric catalyst comprising La(NO₃)₃?6H₂O, amide‐based ligand (R)‐ L1 , and D ‐valine tert‐butyl ester H‐D ‐Val‐OtBu, we investigated a catalytic, asymmetric amination of functionalized N‐nonsubstituted α‐alkoxycarbonyl amides using di‐tert‐butyl azodicarboxylate as an electrophilic aminating reagent. A highly functionalized, cyclic N‐nonsubstituted α‐alkoxycarbonyl amide delivered the desired amination product in up to 96 % enantiometric excess, with the requisite functionalities of the polar heads of sphingosines with the appropriate stereochemical arrangement. The rapid asymmetric assembly of these functional groups allowed a concise enantioselective synthetic route to sphingosines to be established with a broad flexibility towards derivative synthesis. These studies have culminated in an efficient catalytic enantioselective total synthesis of immunosuppressive fungal metabolites mycestericin F ( 3 a ) and G ( 3 b ).     

Time and Temperature Dependent Fatigue Strengths for Three Directions of Unidirectional CFRP

This paper is concerned with the characterization of time and temperature dependent fatigue strengths for three loading directions of unidirectional CFRP, that is, the longitudinal tensile and compressive directions as parallel to the fiber direction and the transverse tensile direction as transverse to the fiber direction, within the plane of the unidirectional ply, which are the most basic directions for fiber composites. These three kinds of fatigue strengths were measured at various frequencies and temperatures. The master curves of these fatigue strengths were constructed using measured data based on the time-temperature superposition principle. As results, it was cleared that each of three kinds of fatigue strength shows characteristic time and temperature dependent behavior. The tensile fatigue strength for the longitudinal direction of unidirectional CFRP moderately depends on time and temperature as well as the number of cycles to failure. The compressive fatigue strength for the longitudinal direction strongly depends on time and temperature, however this strength scarcely depends on the number of cycles to failure. The tensile fatigue strength for the transverse direction strongly depends on time and temperature as well as the number of cycles to failure.     

New parameters of subsets in polynomial association schemes

We define new parameters, a zero interval and a dual zero interval, of subsets in P- or Q-polynomial association schemes. A zero interval of a subset in a P-polynomial association scheme is a successive interval index for which the inner distribution vanishes, and a dual zero interval of a subset in a Q-polynomial association scheme is a successive interval index for which the dual inner distribution vanishes. We derive bounds of the lengths of a zero interval and a dual zero interval using the degree and dual degree respectively, and show that a subset in a P-polynomial association scheme (resp. a Q-polynomial association scheme) having a large length of a zero interval (resp. a dual zero interval) induces a completely regular code (resp. a Q-polynomial association scheme). Moreover, we consider the spherical analogue of a dual zero interval.     

On Schweiger’s problems on fully subtractive algorithms

In his monograph [6] on multi-dimensional continued fractions, Schweiger has presented two conjectures on fully subtractive algorithms. We affirm one and refute another.     

Sturm bounds for Siegel modular forms of degree 2 and odd weights

Mathematische Zeitschrift - We correct the proof of the theorem in the previous paper presented by Kikuta, which concerns Sturm bounds for Siegel modular forms of degree 2 and of even weights...     

Neutral strange particle production in proton-proton collisions at\sqrt s = 63 GeV

The inclusive cross section for the production ofK _s ⁰ mesons, Λ and \(\bar \Lambda\) particles in proton-proton interactions at \(\sqrt s = 63\) GeV is presented. The produced particles have been detected in the full phase space. Behaviour of the longitudinal and transversal depandences of the cross sections are discussed. The total production cross sections for _s ⁰ mesons and Λ particles was determined to \(\sigma _{{\rm K}_S^0 } = (25.5 \pm 1.4)\) mb andσ _Λ =(7.8±1.2) mb respectively. A strong energy dependence of the production cross sections is observed.