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.     

Experimental investigation of amplitude death in delay-coupled double-scroll circuits with randomly time-varying network topology

Nonlinear Dynamics - The present study experimentally investigates amplitude death in delay-coupled double-scroll circuits with a time-varying network topology that randomly changes at a regular...     

New fabrication approach to develop a high birefringence photo-crosslinked film based on a sulfur-containing liquid crystalline molecule with large temperature dependence of birefringence

ABSTRACT

We present a new fabrication approach to achieve a high birefringence film by means of photopolymerization based on an alkylthio-containing rod-like liquid crystalline molecule exhibiting large temperature dependence of birefringence. We designed a new reactive mesogen having alkylthio linkages (BPM–S). It was found that BPM–S had a larger increment of birefringence with decreasing temperature, relative to commercially available alkoxy analog LC242. This result could be thought to be due to enhanced intermolecular attractive interaction for an alkylthio mesogen implied by the proximity of laterally neighboring molecules and cybotactic nematic tendency based on wide-angle X-ray measurement. The uniaxially-aligned photo-polymerized film for BPM–S showed higher birefringence than that for LC 242.     

In silico modeling of PAX8–PPARγ fusion protein in thyroid carcinoma: influence of structural perturbation by fusion on ligand-binding affinity

Journal of Computer-Aided Molecular Design - Paired box 8 (PAX8)–peroxisome proliferator-activated receptor γ (PPARγ) rearrangement is believed to play an important role in...     

Direct Estimation of the Surface Location of Immobilized Functional Groups for Concerted Catalysis Using a Probe Molecule

The location of active sites during concerted catalysis by a metal complex and tertiary amine on a SiO₂ surface is discussed based on the interaction between the functionalized SiO₂ surface and a probe molecule, p‐formyl phenylboronic acid. The interactions of the probe molecule with the surface functionalities, diamine ligand, and tertiary amine, were analyzed by FT‐IR and solid‐state ¹³C and ¹¹B MAS NMR. For the catalyst exhibiting high 1,4‐addition activity, the diamine ligand and tertiary amine base exist in closer proximity than in the catalyst with low activity.     

Backward Terahertz Radiation from a Two-Color Femtosecond Laser Filament

A change in the quasistatic magnetic susceptibility in thin plates of iron borate (FeBO₃), which is a weak ferromagnet, has been revealed at adsorption of water molecules. The measurements have been performed at room temperature with the use of the magneto-optical Faraday effect. The change of the susceptibility in saturated water vapors is about 30%. The observed effect is reversible. The time of establishing the susceptibility after the introduction of water vapors is 1.5 min, which is twice as large as the time of establishing the susceptibility after the evacuation. The effect is explained by the appearance of uniaxial surface magnetic anisotropy in the basal plane because of the adsorption of water molecules.     

A practical synthesis of archaeosine and its base

A practical synthetic route to 7-formamidino-7-deazaguanosine (archaeosine), a hypermodified nucleoside observed in archaeal tRNA, has been developed, which involves the addition of hydroxylamine to the cyano group of 7-cyano-7-deazaguanosine (preQ₀-nucleoside) and a subsequent Pd-catalyzed hydrogenation. PreQ₀-nucleoside was obtained from an optimized β-selective glycosylation developed by Hocek et al. The corresponding archaeosine base was subsequently synthesized in high yield from its precursor 7-cyano-7-deazaguanine (preQ₀).