Shimalactone Biosynthesis Involves Spontaneous Double Bicyclo-Ring Formation with 8π-6π Electrocyclization

Shimalactones A and B are neuritogenic polyketides possessing characteristic oxabicyclo[2.2.1]heptane and bicyclo[4.2.0]octadiene ring systems that are produced by the marine fungus Emericella variecolor GF10. We identified a candidate biosynthetic gene cluster and conducted heterologous expression analysis. Expression of ShmA polyketide synthase in Aspergillus oryzae resulted in the production of preshimalactone. Aspergillus oryzae and Saccharomyces cerevisiae transformants expressing ShmA and ShmB produced shimalactones A and B, thus suggesting that the double bicyclo-ring formation reactions proceed non-enzymatically from preshimalactone epoxide. DFT calculations strongly support the idea that oxabicyclo-ring formation and 8π-6π electrocyclization proceed spontaneously after opening of the preshimalactone epoxide ring through protonation. We confirmed the formation of preshimalactone epoxide in vitro, followed by its non-enzymatic conversion to shimalactones in the dark.     

Synthesis and Systematic Structural Analysis of Cationic Half-Sandwich Ruthenium Chalcogenocarbonyl Complexes

Although the chemistry of transition-metal complexes with carbonyl (CO) and thiocarbonyl (CS) ligands has been well developed, their heavier analogues, namely selenocarbonyl (CSe) and tellurocarbonyl (CTe) complexes remain scarce. The limited availability of such CSe and CTe complexes has so far hampered our understanding of the differences between such chalcogenocarbonyl (CE: E=O, S, Se, Te) ligands. Herein, we report the synthesis and properties of a series of cationic half-sandwich ruthenium CE complexes of the type [CpRu(CE)(H₂IMes)(CNCH₂Ts)][BAr^F₄] (Cp=η⁵-C₅H₅⁻; H₂IMes=1,3-dimesitylimidazolin-2-ylidene; Ar^F=3,5-(CF₃)₂C₆H₃). A combination of X-ray diffraction analyses, NMR spectroscopic analyses, and DFT calculations revealed an increasing π-accepting ability of the CE ligands in the order O<S<Se<Te. A variable-temperature NMR analysis of the thus obtained chiral-at-metal CE complexes indicated high stereochemical stability.     

Stereoselective Synthesis of the Proposed C79–C104 Fragment of Symbiodinolide

Stereoselective and streamlined synthesis of the proposed C79–C104 fragment 2 of symbiodinolide ( 1 ), a polyol marine natural product with a molecular weight of 2860, was achieved. In the synthetic route, the proposed C79–C104 fragment 2 was synthesized by utilizing a Julia–Kocienski olefination and subsequent Sharpless asymmetric dihydroxylation as key transformations in a convergent manner. Detailed comparison of the ¹³C NMR chemical shifts between the natural product and the synthetic C79–C104 fragment 2 revealed that the stereostructure at the C91–C99 carbon chain moiety of symbiodinolide ( 1 ) should be reinvestigated.     

An efficient method for 3,4-dihydroisoquinolinium ion formation,leading to a facile introduction of nucleophiles

The ketene silyl acetal derived from ethyl 2-benzyltetrahydroisoquinoline-1-carboxylate undergoes a rapid oxidation reaction with N-bromosuccinimide to form 3,4-dihydroisoquinolinium ion, which reacts with Grignard reagents to give 1,1-disubstituted tetrahydroisoquinolines in good yields.     

Dominant Li+ ion conduction in Li+/Na+ mixed crystal, 15NaI∙LiBH4

Journal of Solid State Electrochemistry - In the present work, the conduction ions in 15NaI∙LiBH4 are investigated by secondary ion mass spectroscopy (SIMS) and galvanostatic measurements. An...     

Reactive regioregular oligothiophenes and polythiophenes with Zincke salt structure: Synthesis,reactions, and chemical properties

Polythiophenes with reactive Zincke salt structure, P4ThPy⁺DNP(Cl^?)‐a and P5ThPy⁺DNP(Cl^?)‐a , were synthesized by the oxidation polymerization of oligothiophenes, such as 3'‐(4‐N‐(2,4‐dinitrophenyl)pyridinium chloride)?2,2':5',2'';5'',2'''‐quarterthiophene ( 4ThPy⁺DNP(Cl^?) ) and 4''‐(4‐N‐(2,4‐dinitrophenyl)pyridinium chloride)?2,2';5',2'';5'',2''';5''',2''''‐quinquethiophene ( 5ThPy⁺DNP(Cl^?) ), with iron(III) chloride. The reaction of P5ThPy⁺DNP(Cl^?)‐a with R‐NH₂ [R = n‐hexyl (Hex) and phenyl (Ph)] substituted the 2,4‐dinitrophenyl group into the R group with the elimination of 2,4‐dinitroaniline to yield P5ThPy⁺R(Cl^?) . Similarly, model compounds, 4ThPy⁺R(Cl^?) and 5ThPy⁺R(Cl^?) (R = Hex and Ph), were also synthesized. In contrast to the photoluminescent 4ThPy and 5ThPy , the compounds P4ThPy⁺DNP(Cl^?)‐a , P5ThPy⁺DNP(Cl^?)‐a , and P5ThPy⁺R(Cl^?) showed no photoluminescence because their internal pyridinium rings acted as quenchers. Cyclic voltammetry measurements suggested that P4ThPy⁺DNP(Cl^?)‐a , P5ThPy⁺DNP(Cl^?)‐a , and P5ThPy⁺R(Cl^?) received an electrochemical reduction of the pyridinium and 2,4‐dinitrophenyl groups and oxidation of the polymer backbone. P4ThPy⁺DNP(Cl^?)‐a and P5ThPy⁺DNP(Cl^?)‐a were electrically conductive (ρ = 3.0 × 10 ^{? 6} S cm ^{? 1} and 2.1 × 10 ^{? 6} S cm ^{? 1}, respectively) in the nondoped state. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 481–492     

Catalytic enantioselective synthesis of atropisomeric 2-aryl-4-quinolinone derivatives with an N–C chiral axis

In the presence of an (R)-MOP-Pd₂(dba)₃ catalyst, the reaction of ortho-tert-butylaniline with 2-bromophenyl arylethynyl ketone proceeded via a tandem amination (1,4-addition of aniline to an ynone and subsequent intramolecular Buchwald–Hartwig amination) to afford axially chiral N-(2-tert-butylphenyl)-2-aryl-4-quinolinone derivatives with moderate enantioselectivity (up to 72% ee).     

High magnetic field solid‐state NMR analyses by combining MAS,MQ‐MAS,homo‐nuclear and hetero‐nuclear correlation experiments

A general strategy of structural analysis of alumina silicate by combining various solid‐state NMR measurements such as single pulse, multi‐quantum magic angle spinning, double‐quantum homo‐nuclear correlation under magic angle spinning (DQ‐MAS), and cross‐polarization hetero‐nuclear correlation (CP‐HETCOR) was evaluated with the aid of high magnetic field NMR (800 MHz for ¹H Larmor frequency) by using anorthite as a model material. The high magnetic field greatly enhanced resolution of ²⁷Al in single pulse, DQ‐MAS, and even in triple‐quantum magic angle spinning NMR spectra. The spatial proximities through dipolar couplings were probed by the DQ‐MAS methods for homo‐nuclear correlations between both ²⁷Al–²⁷Al and ²⁹Si–²⁹Si and by CP‐HETCOR for hetero‐nuclear correlations between ²⁷Al–²⁹Si in the anorthite framework. By combining various NMR methodologies, we elucidated detailed spatial correlations among various aluminum and silicon species in anorthite that was hard to be determined using conventional analytical methods at low magnetic field. Moreover, the presented approach is applicable to analyze other alumina‐silicate minerals. Copyright © 2012 John Wiley & Sons, Ltd.     

Minimization of erase-band in shingled PMR with asymmetric writer

To make the write-field much stronger with sharper cross-track field gradient in Shingled perpendicular Magnetic Recording (SMR), we have successfully developed asymmetric SMR heads with one-side shield design. Using these heads, higher track density capability on the shielded-side was demonstrated, which came from narrower erase-band width at shielded side.     

Growth of large La2−xSrxCuO4 single crystals using tilting-mirror-type infrared heating image furnace

Large single crystals of La_2−xSr_xCuO₄ (LSCO) high-T_c superconductors were grown by the infrared heating floating zone (IR-FZ) method using a tilting-mirror-type image furnace. The maximum diameter of the LSCO crystals increased to 10 mm in the tilting-mirror-type image furnace from 6 mm in the conventional image furnace. CuO rich feeds were required for the crystal growth using the tilting-mirror-type image furnace to compensate for the lack of CuO caused by the significant evaporation of CuO during the growth. The evaporation of CuO was affected by the tilting angle of the mirrors of the image furnace and by feed diameter. The optimized growth conditions were as follows: mirror tilting angle, 20°; feed diameter, 10 mm∅; and feed composition 50.7 mol% CuO.