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 ).     

Recent Studies of Hypernuclei Formation with Electron Beams at MAMI

At the Mainz Microtron MAMI exploratory experiments on the spectroscopy of mesonic weak decays (MWD) of electroproduced Λ-hypernuclei were performed. A unique setup was realized to use the broad momentum-band kaon spectrometer Kaos at zero degree angle with respect to the high-intensity electron beam direction to tag strangeness producing processes. A sample of order 10³ MWD from a beryllium target was collected by the coincidence technique with the high-resolution multi-spectrometer facility of the A1 Collaboration. It is conjectured that this sample contains monochromatic two-body decays from stopped hyperfragment decays as well as a wide momentum distribution of quasi-free produced Λ- and Σ-hyperon decays and three-body decays from hyperfragments. Stopped hyperfragments will be identified as monochromatic peaks in the π ^? momentum spectrum from which their masses can be extracted with a precision of 50 keV/c ².     

Indomethacin solubilization induced shape transition in CnE7 (n=14,16) nonionic micelles

Shape transitions were examined with regard to the solubilization of the poorly water-soluble drug indomethacin (IMC) in the nonionic surfactants heptaethylene oxide tetradecyl (C14E7) and hexadecyl (C16E7) ethers by means of a dynamic light scattering technique. The cloud points of the pure C14E7 and C16E7 micelles ranged from 58 to 62 degrees C and from 52.1 to 55.6 degrees C, respectively, at surfactant concentrations of 1 to 10 mM. The cloud points of IMC-solubilized micelles increased by approximately 1 to 5 degrees . The sizes of the pure C14E7 micelles were 4 to 14 nm at 20 to 40 degrees C at a concentration of 2 to 20 mM. The apparent hydrodynamic radius (R happ) of pure C16E7 micelles varied with temperature and concentration. C16E7 surfactant formed small spherical micelles at 20 and 25 degrees C at concentrations below 5 mM; the size of the micelles was approximately 5 nm. On the other hand, from 30 to 40 degrees C and at a higher concentration, C16E7 formed elongated cylindrical micelles, and these elongated micelles entangled or overlapped each other. The R happ of the IMC-solubilized C14E7 micelles at 20 to 40 degrees C and of C16E7 micelles at 20 degrees C increased compared to that of pure micelles. On the other hand, the cylindrical micelles of C16E7 decreased in size and turned into spherical ones because of the hydrophobicity between the micelles caused by solubilization of IMC. This phenomenon was confirmed by transmission electron microscope (TEM) images.     

Syntheses of a partially benzylated derivative of the anhydro-d-altro-heptulose found in Coriaria japonica A and of its analogs

A partially benzylated derivative of anhydro-d-altro-heptulose found in Coriaria japonica A, which is a synthetically useful unit, was successfully synthesized from a d-mannose derivative by a novel synthetic approach involving the intramolecular O-ketopyranosylation reaction developed by us. This synthetic approach was also applicable to the preparation of its four analogs.     

Fabrication of DNA nanowires by orthogonal self-assembly and DNA intercalation on a Au patterned Si/SiO2 surface

A novel Ru complex bearing both an acridine group and anchoring phosphonate groups was immobilized on a surface in order to capture double-stranded DNAs (dsDNAs) from solution. At low surface coverage, the atomic force microscopy (AFM) image revealed the "molecular dot" morphology with the height of the Ru complex ( approximately 2.5 nm) on a mica surface, indicating that four phosphonate anchor groups keep the Ru complex in an upright orientation on the surface. Using a dynamic molecular combing method, the DNA capture efficiency of the Ru complex on a mica surface was examined in terms of the effects of the number of molecular dots and surface hydrophobicity. The immobilized surface could capture DNAs; however, the optimal number of molecular dots on the surface as well as the optimal pull-up speed exist to obtain the extended dsDNAs on the surface. Applying this optimal condition to a Au-patterned Si/SiO 2 (Au/SiO 2) surface, the Au electrode was selectively covered with the Ru complex by orthogonal self-assembly of 4-mercaptbutylphosphonic acid (MBPA), followed by the formation of a Zr (4+)-phosphonate layer and the Ru complex. At the same time, the remaining SiO 2 surface was covered with octylphosphonic acid (OPA) by self-assembly. The selective immobilization of the Ru complex only on the Au electrode was identified by time-of-flight secondary-ion mass spectrometry (TOF-SIMS) imaging on the chemically modified Au/SiO 2 surface. The construction of DNA nanowires on the Au/SiO 2 patterned surface was accomplished by the molecular combing method of the selective immobilized Ru complex on Au electrodes. These interconnected nanowires between Au electrodes were used as a scaffold for the modification of Pd nanoparticles on the DNA. Furthermore, Cu metallization was achieved by electroless plating of Cu metal on a priming of Pd nanoparticles on the Pd-covered DNA nanowires. The resulting Cu nanowires showed a metallic behavior with relatively high resistance.     

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.     

Dimensional dependence of electronic structure of fullerene polymers

Fullerene polymers made of C(60) are systematically investigated by means of a first-principles pseudopotential approach within the local density approximation of the density functional theory. We assume 10 different structures of fullerene polymers. The first three are C(60) polymer networks cross-linked by [2+2] cycloadditional four-membered rings, and the other seven are composed of peanut-shaped fused C(60) polymer chains cross-linked by either seven-membered rings or eight-membered rings. Owing to the overlap of wave functions as well as the hybrid networks of sp(2)-like (3-fold coordinated) and sp(3)-like (4-fold coordinated) carbon atoms, the electronic structure is considerably different from each other. We find that the resulting electronic structure is either semiconductor or semimetal depending on the spatial dimensionality of materials.     

Chiral exciplex dyes showing circularly polarized luminescence: extension of the excimer chirality rule

A series of axially chiral binaphthyls and quaternaphthyls possessing two kinds of aromatic fluorophores, such as pyrenyl, perylenyl, and 4-(dimethylamino)phenyl groups, arranged alternately were synthesized by a divergent method. In the excited state, the fluorophores selectively formed a unidirectionally twisted exciplex (excited heterodimer) by a cumulative steric effect and exhibited circularly polarized luminescence (CPL). They are the first examples of a monomolecular exciplex CPL dye. This versatile method for producing exciplex CPL dyes also improved fluorescence intensity, and the CPL properties were not very sensitive to the solvent or to the temperature owing to the conformationally rigid exciplex. This systematic study allowed us to confirm that the excimer chirality rule can be applied to the exciplex dyes: left- and right-handed exciplexes with a twist angle of less than 90° exhibit (−)- and (+)-CPL, respectively.

Axially chiral binaphthyls and quaternaphthyls possessing two kinds of fluorophores were synthesized. In the excited state, the fluorophores formed a twisted exciplex and exhibited CPL. This study gave us named the exciplex chirality rule.