Proposed mechanism for diterpene synthases in the formation of phomactatriene and taxadiene

To obtain insight into how the cyclization pathway is controlled, the mechanism of diterpene synthase reactions (the putative phomactatriene synthase and taxadiene synthases) involving the same intermediate was investigated in detail. The mechanism of the initial transformation of GGDP to verticillen-12-yl cation (A+) was proposed based on the labelling pattern of phomactatriene (9a) obtained in the feeding experiments with 13C-labelled acetates. To obtain information on the reaction pathway of A+ to 9a and taxadiene, reactions of verticillol with various acids were conducted. Structural determination of products allowed us to propose a reaction pathway via cations A+, D+, E+, F+ and G+. Identification of hydrocarbons in mycelial extracts of phomactin-producing fungus supported the proposed reaction mechanism. Based on the results of ab initio calculations for highly flexible cation intermediates, a mechanism is proposed.     

3,6-Dialkyl-2-hydroxypyrazine 1-oxides as acyl carriers

3,6-Dialkyl-2-hydroxypyrazine 1-oxides were found to be useful as acyl carriers. Benzoyl derivatives were convenient reagents for benzoylation of amines and hydroxy compounds.     

On-Fiber Derivatization of SPME Extracts of Phenol, Hydroquinone and Catechol with GC-MS Detection

A gas chromatography-mass spectrometry (GC-MS) method for the simultaneous determination of phenol (PHE), hydroquinone (HQ) and catechol (CAT) in urine was developed and validated. The method was based on the acidic hydrolysis of conjugated phenolic compounds and further extraction of analytes using solid-phase microextraction (SPME). Analytes were extracted by submersing the polar polyacrylate coated fiber (85 μm) into urine (adjusted to pH 3.0 with glacial acetic acid) for 20 min with magnetic stirring. The extracted compounds on the fiber were exposed to hexamethyldisilazane reagent in the vapor phase for 20 min to yield the corresponding trimethysililylated derivates. This on-fiber derivatization procedure allowed the formation of more amenable compounds for GC analysis, without adversely affecting the lifetime of the fiber. The MS was operated in the selected ion monitoring mode (SIM). The limits of detection were 0.3 μg mL⁻¹ for PHE, 0.15 μg mL⁻¹ for HQ and 0.02 μg mL⁻¹ for CAT. Inter and intra-assay precisions were also verified (coefficient of variation < 8%) with the use of deuterated internal standards. This method of GC-MS analysis can be readily utilized to monitor PHE and its metabolites (HQ and CAT) in urine samples.     

Regular copolymers derived from bis(2-oxazolines). II. Synthesis of polyamides and polyamide-imides containing oxyethylene linkages

New diamines containing amide and oxyethylene linkages were prepared by reduction of the corresponding dinitro compounds which were obtained by the reaction of p-nitrophenol with arylenebis(2-oxazolines) in dimethylformamide at 130°C. Moderate- to high-molecular-weight polyamides and polyamide-imides containing oxyethylene linkages were prepared by the polycondensation of the diamines with diacid chlorides and tetracarboxylic acid dianhydrides, respectively. The polyamides were soluble in dimethylacetamide containing 5% of lithium chloride and dichloroacetic acid, while the polyamide-imides dissolved only moderately in the latter solvent. Thermogravimetric analysis showed that thermo-oxidative decomposition started at 310–330°C and at around 325°C for the polyamides and polyamide-imides, respectively.     

Design and concise synthesis of novel vitamin D analogues bearing a functionalized aromatic ring on the side chain

Five novel vitamin D analogues (2a, 2b, 3a, 3b and 4) bearing an aromatic side chain have been designed and synthesized in a convergent manner. The requisite CD-ring synthons (10a–c) were prepared from C22 aldehyde (5) using four- or five-step procedures. Using turbo-Grignard reagents allowed aromatic side chains with a polar functional moiety to be installed in a single step with excellent yields. A preliminary biological evaluation using bovine thymus vitamin D receptor (VDR) suggested that incorporating a carboxylic acid instead of the C25-hydroxy group had a positive effect on the VDR affinity compared with the corresponding esters.     

Modelling magnetic polarisation J50 by different methods

Two different methods for modelling the angular behaviour of magnetic polarisation at 5000 A/m (J₅₀) of electrical steels were evaluated and compared. Both methods are based upon crystallographic texture data. The texture of non-oriented electrical steels with silicon content ranging from 0.11 to 3%Si was determined by X-ray diffraction. In the first method, J₅₀ was correlated to the calculated value of the average anisotropy energy in each direction, using texture data. In the second method, the first three coefficients of the spherical harmonic series of the ODF and two experimental points were used to estimate the angular variation of J₅₀. The first method allows the estimation of J₅₀ for samples with different textures and Si contents using only the texture data, with no need of magnetic measurement, and this is advantageous, because texture data can be acquired with less than 2 g of material. The second method may give better adjust in some situations but besides the texture data, it requests magnetic measurements in at least two directions, for example, rolling and transverse directions.     

Mechanochemical Tuning of the Binaphthyl Conformation at the Air–Water Interface

Gradual and reversible tuning of the torsion angle of an amphiphilic chiral binaphthyl, from ?90° to ?80°, was achieved by application of a mechanical force to its molecular monolayer at the air–water interface. This 2D interface was an ideal location for mechanochemistry for molecular tuning and its experimental and theoretical analysis, since this lowered dimension enables high orientation of molecules and large variation in the area. A small mechanical energy (<1 kcal mol^?1) was applied to the monolayer, causing a large variation (>50 %) in the area of the monolayer and modification of binaphthyl conformation. Single‐molecule simulations revealed that mechanical energy was converted proportionally to torsional energy. Molecular dynamics simulations of the monolayer indicated that the global average torsion angle of a monolayer was gradually shifted.     

Palladium-catalyzed furylation and thienylation of activated alkenes with 2-furoyl chloride and 2-thenoyl chloride

2-Furoyl or 2-thenoyl chlorides readily react with activated alkenes in the presence of a tertiary amine and a catalytic amount of palladium(II) acetate to give 2-furylated or 2-thienylated alkenes. Under similar conditions, 2-benzofuroyl chloride undergoes facile alkenylation to produce 2-alkenylated benzofurans. The reaction involves a highly efficient decarbonylation of furoyl or thenoyl-palladium species.