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.     

A simple high‐performance liquid chromatography for the determination of linezolid in human plasma and saliva

Linezolid is an antimicrobial agent for the treatment of multiresistant Gram‐positive infections. A practical high‐performance liquid chromatography method was developed for the determination of linezolid in human plasma and saliva. Linezolid and an internal standard (o‐ethoxybenzamide) were extracted from plasma and saliva with ethyl acetate and analyzed on a Capcell Pak C₁₈ MG column with UV detection at 254 nm. The calibration curve was linear through the range 0.5–50 µg/mL using a 200 μL sample volume. The intra‐ and interday precisions were all <6.44% for plasma and 5.60% for saliva. The accuracies ranged from 98.8 to 110% for both matrices. The mean recoveries of linezolid were 80.8% for plasma and 79.0% for saliva. This method was used to determine the plasma and saliva concentrations of linezolid in healthy volunteers who were orally administered a 600 mg dose of linezolid. Our liquid–liquid extraction procedure is easy and requires a small volume of plasma or saliva (200 μL). This small volume can be advantageous in clinical pharmacokinetic studies, especially if children participate. Copyright © 2015 John Wiley & Sons, Ltd.     

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     

Synthesis and characterization of 9,9‐bis(4‐hydroxyphenyl and 4‐aminophenyl)dibenzofluorenes: Novel fluorene‐based monomers

Two novel 9,9‐difunctionalized fluorene‐type monomers, 9,9‐bis(4‐hydroxyphenyl‐ and 4‐aminophenyl)‐2,3:6,7‐dibenzofluorenes, are synthesized by the reaction of dibenzenzofluorenone with phenol and aniline. These monomers are used for the preparation of polyester and polyimide as the typical polymers to evaluate the property change such as thermal stability caused by the benzene rings fused to the fluorene skeleton with keeping good solubility, in comparison with the polymers derived from simple fluorenone. In fact, these two new polymers have the fairly enhanced thermal stability and refractive index value along with satisfactory solubility in organic solvents, enough to emphasize the fusion effect. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2602–2605