Biosynthesis of Indole Diterpene Lolitrems: Radical-Induced Cyclization of an Epoxyalcohol Affording a Characteristic Lolitremane Skeleton

Lolitrems are tremorgenic indole diterpenes that exhibit a unique 5/6 bicyclic system of the indole moiety. Although genetic analysis has indicated that the prenyltransferase LtmE and the cytochrome P450 LtmJ are involved in the construction of this unique structure, the detailed mechanism remains to be elucidated. Herein, we report the reconstitution of the biosynthetic pathway for lolitrems employing a recently established genome-editing technique for the expression host Aspergillus oryzae. Heterologous expression and bioconversion of the various intermediates revealed that LtmJ catalyzes multistep oxidation to furnish the lolitrem core. We also isolated the key reaction intermediate with an epoxyalcohol moiety. This observation allowed us to establish the mechanism of radical-induced cyclization, which was firmly supported by density functional theory calculations and a model experiment with a synthetic analogue.     

Effects of polyethylene spacer length in polymeric electrolytes on gelation of ionic liquids and ionogel properties

Polymer electrolytes containing N,N′-(trans-cyclohexane-1,4-diyl)dibenzamide linkages, polyethylene ((CH₂)_m, m = 2, 4, 10) spacers, and bis(trifluoromethanesulfonyl)amide (TFSA) or bis(fluorosulfonyl)amide (FSA) counteranions (polymer abbreviation: CDBAm•X; m = 2, 4, 10; X = TFSA, FSA) have been synthesized, adding to our previous report (m = 6). In addition, their ability to effect the gelation of six ionic liquids and the properties of the resulting ionogels have been examined. The polymers, except for CDBA10•TFSA, effect the gelation for all ionic liquids used in this study at fairly low concentrations (0.9–50 g/L). Ionogel ionic conductivity is not dependent on the spacer length, but does decrease slightly as increasing amounts of the gelatinizer are introduced. In contrast to ionic conductivity, the temperatures at which these ionogels transition into isotropic fluids is dependent on the spacer length; the gel composed of [EMI][FSA] and 100 g/L of CDBA6•FSA transforms at 120 °C, while the gel composed of [EMI][FSA] and 5 g/L of CDBA2•FSA does not transform into a sol even when temperatures become 155 °C. In brief, ionogel heat resistance can be improved by changing the spacer length of the polyelectrolyte. Finally, it has been determined using cyclic voltammetry that the potential window of the polyelectrolytes is particularly wide, ranging from −1.6 to 2.5 V. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 249–255     

Synthesis of C12-Keto Saxitoxin Derivatives with Unusual Inhibitory Activity Against Voltage-Gated Sodium Channels

A novel series of C12-keto-type saxitoxin (STX) derivatives bearing an unusual nonhydrated form of the ketone at C12 has been synthesized, and their Na_V-inhibitory activity has been evaluated in a cell-based assay as well as whole-cell patch-clamp recording. Among these compounds, 11-benzylidene STX ( 3 a ) showed potent inhibitory activity against neuroblastoma Neuro 2A in both cell-based and electrophysiological analyses, with EC₅₀ and IC₅₀ values of 8.5 and 30.7 nm , respectively. Interestingly, the compound showed potent inhibitory activity against tetrodotoxin-resistant subtype of Na_V1.5, with an IC₅₀ value of 94.1 nm . Derivatives 3 a – d and 3 f showed low recovery rates from Na_V1.2 subtype (ca 45–79 %) compared to natural dcSTX ( 2 ), strongly suggesting an irreversible mode of interaction. We propose an interaction model for the C12-keto derivatives with Na_V in which the enone moiety in the STX derivatives 3 works as Michael acceptor for the carboxylate of Asp¹⁷¹⁷.     

Supramolecular Sensor for Astringent Procyanidin C1: Fluorescent Artificial Tongue for Wine Components

An artificial tongue that detects astringent components for a comprehensive evaluation of taste has not been established to date. Herein, we first propose fluorescent polythiophene (PT) derivatives ( S1 – S3 ) modified with 3-pyridinium boronic acid as supramolecular chemosensors for wine components including astringent procyanidin C1. After numerous attempts for the synthetic conditions, more than 95 mol % of the PT unit was modified with the pyridinium boronic acid moiety. To evaluate the PT derivatives as chemosensors of the artificial tongue, qualitative and quantitative analyses were performed with four types of wine components (i.e., sweet, sour, bitter, and astringent tastes) in combination with pattern recognition models. Notably, procyanidin C1 in the actual wine sample was successfully detected in a quantitative manner. In other words, we have established an authentic artificial tongue using PT based supramolecular chemosensors.     

Preparation of free‐standing silicone particles in aqueous heterogeneous system

To prepare cross‐linked silicone (silicone rubber) particles in an aqueous medium, we investigated two synthesis methods involving a miniemulsion system. The first method was based on cationic ring‐opening polymerization of cyclic siloxane, which is a common synthetic route for linear silicone oil and uses octamethylcyclotetrasiloxane (D₄) as the monomer and dimeric D₄ (bis‐D₄) as the cross‐linker. Although this method produces silicone particles, the particles do not remain in the particulate state after drying because of low cross‐linking density. The polymerization mechanism of this method was also investigated, which proceeds under the ring‐opening reaction of D₄ in monomer droplets and upon polycondensation of hydrolyzed D₄, which occurs in the water phase (ie, outside the monomer droplets). This mechanism implied that introducing the cross‐linking structure into particles is difficult because of the low solubility of bis‐D₄ in water. To overcome these difficulties, we demonstrated a second method of preparing silicone particles based on the thiol‐Michael addition reaction between thiol‐terminated silicone oil and triacrylate in miniemulsion systems. Transmission electron microscopy images indicated that the silicone particles obtained in the particulate state upon drying and the aggregates of these particles showed elasticity.     

Designing Cross-Coupling Reactions using Aryl(trialkyl)silanes

Organo(trialkyl)silanes have several advantages, including high stability, low toxicity, good solubility, easy handling, and ready availability compared with heteroatom-substituted silanes. However, methods for the cross-coupling of organo(trialkyl)silanes are limited, most probably because of their exceeding robustness. Thus, a practical method for the cross-coupling of organo(trialkyl)silanes has been a long-standing challenging research target. This article discusses how aryl(trialkyl)silanes can be used in cross-coupling reactions. A pioneering example is Cu^II catalytic conditions with the use of electron-accepting aryl- or heteroaryl(triethyl)silanes and aryl iodides. The reaction forms biaryls or teraryls. This design concept can be extended to Pd/Cu^II-catalyzed cross-coupling polymerization reactions between such silanes and aryl bromides or chlorides and to Cu^I-catalyzed alkylation using alkyl halides.     

Fe K‐Edge X‐ray Absorption Fine Structure Determination of γ‐Al2O3‐Supported Iron‐Oxide Species

The structure of FeO_x species supported on γ‐Al₂O₃ was investigated by using Fe K‐edge X‐ray absorption fine structure (XAFS) and X‐ray diffraction (XRD) measurements. The samples were prepared through the impregnation of iron nitrate on Al₂O₃ and co‐gelation of aluminum and iron sulfates. The dependence of the XRD patterns on Fe loading revealed the formation of α‐Fe₂O₃ particles at an Fe loading of above 10 wt %, whereas the formation of iron‐oxide crystals was not observed at Fe loadings of less than 9.0 wt %. The Fe K‐edge XAFS was characterized by a clear pre‐edge peak, which indicated that the Fe?O coordination structure deviates from central symmetry and that the degree of Fe?O?Fe bond formation is significantly lower than that in bulk samples at low Fe loading (<9.0 wt %). Fe K‐edge extended XAFS oscillations of the samples with low Fe loadings were explained by assuming an isolated iron‐oxide monomer on the γ‐Al₂O₃ surface.     

Total Biosynthesis of Melleolides from Basidiomycota Fungi: Mechanistic Analysis of the Multifunctional GMC Oxidase Mld7

Mushroom terpenoids are biologically and chemically diverse fungal metabolites. Among them, melleolides are representative sesquiterpenoids with a characteristic protoilludane skeleton. In this study, we applied a recently established hot spot knock-in method to elucidate the biosynthetic pathway leading to 1α-hydroxymelleolide. The biosynthesis of the sesquiterpene core involves the cytochrome P450 catalyzing stepwise hydroxylation of the Δ⁶-protoilludene framework and a stereochemical inversion process at the C5 position catalyzed by short-chain dehydrogenase/reductase family proteins. The highlight of the biosynthesis is that the flavoprotein Mld7 catalyzes an oxidation-triggered double-bond shift accompanying dehydration and acyl-group-assisted substitution with two different nucleophiles at the C6 position to afford the Δ⁷-protoilludene derivatives, such as melleolide and armillarivin. The complex reaction mechanism was proposed by DFT calculations. Of particular importance is that product distribution is regulated by interaction with the cell membrane.     

A generalized technique for the encapsulation of nano‐sized NiO particles by styrene‐2‐hydroxyethyl methacrylate copolymer

Encapsulation of nickel oxide (NiO) particles is of great interest to the researchers as such modification produces remarkable improvement in properties and versatility in application potential. In this investigation, nanosized NiO particles were first prepared by calcination of nickel hydroxide precursor obtained using a simple liquid‐phase process. The produced NiO particles were stabilized with oleic acid and then treated with tetraethylorthosilicate to produce NiO/SiO₂ composite seed particles. Finally tri‐layered inorganic/organic composite particles were prepared by seeded copolymerization of styrene and 2‐hydroxyethyl methacrylate (HEMA) in the presence of NiO/SiO₂ composite seed particles. The produced composite particles named as NiO/SiO₂/P(S‐HEMA) were colloidally stable, and the obtained particles were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy and thermogravimetric analyses. Copyright © 2015 John Wiley & Sons, Ltd.