Divergent Total Syntheses of (+)-Vulgarisins A–E

The asymmetric total syntheses of (+)-vulgarisins A–E, which share a rare and highly oxygenated [5-6-4-5] tetracyclic core structure that were isolated from P. vulgaris Linn., have been described for the first time in a divergent manner. Key transformations include: 1) a catalytic asymmetric intramolecular cyclopropanation to forge the A ring bearing desired stereochemistry at C14; 2) a one-pot borylation/conjugate addition process for creation of the C1−C11 bond; 3) a Wolff ring contraction to assemble the bicyclo[3.2.0]heptane subunit (CD rings); and 4) a stereocontrolled pinacol cyclization for construction of the central B ring of the natural products.     

Total synthesis of violaceimides A–E and consideration of the reported stereochemistry

Here we report the first total synthesis of violaceimides A–E, a family of sulfur-containing metabolites from Aspergillus violaceus, a sponge-associated fungus. A concise, convergent and enantioselective synthesis was developed for all five family members, from a common advanced intermediate. However, while the NMR spectral data matched that of the reported natural products, the optical rotations were of opposite sign. This result prompted the enantioselective synthesis of all four diastereomeric pairs of violaceimide E, and suggests that the stereochemistry might have been misassigned.     

Agrocybynes A–E from the culture broth of Agrocybe praecox

Five novel compounds (1–3, 5, and 6), and two known ones (4 and 7) were isolated from the culture broth of Agrocybe praecox. Their structures were determined by the interpretation of spectroscopic data. Compounds 1–4 inhibited hypocotyl growth of lettuce, and 1, 3, and 4 inhibited the root growth.     

Chromatography of E. coli tRNA on 5–20 μm Agarose Beads

Abstract

Escherichia coli transfer RNAs have been separated by chromatography on 5–20 μm beads of divinylsulfone-crosslinked agarose with the use of isocratic elution combined with a negative salt gradient. For example, tRNA^Leu was resolved into six isoacceptor species and tRNA^Ser into four. Leucine-charged tRNA's were eluted after their corresponding uncharged isoacceptor species. By optimizing flow rate, column length and elution buffer the fractionation of tRNA could be performed within 3 hours.     

Total Synthesis of Kopsinitarine E

Kopsinitarines A–E are complex octacyclic caged Kopsia alkaloids with strained cage skeletons and a unique cyclic hemiaminal bridge that makes total synthesis challenging. Herein, we disclose the first total synthesis of kopsinitarine E. The key synthetic features include a SmI₂-mediated radical cascade cyclization and a subsequent semi-pinacol rearrangement to install the key carbocyclic skeleton, a chemoselective hydrosilyl amide reduction to construct the hemiaminal ether bridge, and an intramolecular Mannich reaction to establish the highly strained cage system.     

Studies of aminolysis of acrylonitrile–divinylbenzene–methyl methacrylate copolymers

Aminolysis of nitrilacrylate–divinylbenzene–methyl methacrylate copolymers by diethylenetriamine is studied under various conditions. The effect of temperature and catalyst concentration on the properties of synthesized anion exchangers depending on the duration of aminolysis is investigated. The conditions for synthesizing anion exchangers with high capacity characteristics are proposed according to the study results.     

Computational Analysis of Solute–Solvent Coupling Magnitude in the Z/E Isomerization Reaction of Nitroazobenzene and Benzylideneanilines

The dynamic solvent effect often arises in solution reactions, where coupling between chemical reaction and solvent fluctuation plays a decisive role in the reaction kinetics. In this study, the Z/E isomerization reaction of nitoroazobenzene and benzylideneanilines in the ground state was computationally studied by molecular dynamics simulations. The non-equilibrium solvation effect was analyzed using two approaches: (1) metadynamics Gibbs energy surface exploration and (2) solvation Gibbs energy evaluation using a frozen solvation droplet model. The solute–solvent coupling parameter (C_coupled) was estimated by the ratio of the solvent fluctuation Gibbs energy over the corresponding isomerization activation Gibbs energy. The results were discussed in comparison with the ones estimated by means of the analytical models based on a reaction–diffusion equation with a sink term. The second approach using a frozen solvation droplet reached qualitative agreement with the analytical models, while the first metadynamics approach failed. This is because the second approach explicitly considers the non-equilibrium solvation in the droplet, which consists of a solute at the reactant geometry immersed in the pre-organized solvents fitted with the solute at the transition state geometry.     

Nonlinear optical properties of dye-doped E7 liquid crystals at the nematic–isotropic transition

This work shows the influence of a 2,1,3-benzothiadiazole-based dye in the nonlinear optical refraction and nonlinear optical absorption of the thermotropic liquid crystal E7 at the nematic–isotropic transition in the ms time-scale using the Z-scan technique. The addition of dye does not modify the critical exponent of the nonlinear birefringence observed for the undoped sample at the transition, confirming the tricritical character. Also, the order parameter based in the nonlinear absorption shows, for the samples with higher dopings, a critical exponent that deviates from the expected value in the tricritical hypothesis.     

Total synthesis of pseudacyclins A–E by an on-resin head-to-side chain concomitant cyclization-cleavage reaction

Taking advantage of the nucleophile-sensitive ester link of oxime resin, a novel synthetic strategy was applied to the first synthesis of a type of cyclic peptides known as pseudacyclins A–E. The endocyclic ornithine side-chain part was incorporated by an on-resin acid-catalyzed concomitant cyclization-cleavage reaction after a selective deprotection of orthogonally protected ornithine. The synthetic methodology gives high macrocyclization yields and low oligomerization side-products. The combination used of solid-phase/solution-phase strategy was efficient to prepare pseudacyclins and could prove useful to prepare other natural cycle-tail peptides.     

Simultaneous HPLC–DAD Determination of Retinol and Eight Vitamin E Isomers in Human Serum

An efficient, high-performance liquid-chromatographic method with diode-array detection (HPLC–DAD) has been established for simultaneous determination of retinol, α, (β + γ), and δ-tocopherols, and α, β, γ, and δ-tocotrienols in human serum. After deproteinization, the target vitamins in serum were extracted with n-hexane and the extract was evaporated under weak nitrogen flow. The residue was redissolved in methanol and the resulting solution was used for HPLC analysis. Retinol acetate and α-tocopherol acetate were used as internal standards. The internal standard calibration curves were linear over the range of 0.010–50.0 µg mL⁻¹, with correlation coefficients >0.999. Mean recoveries of the method were 86.3–110 %, with intra-day and inter-day relative standard deviations less than 12.2 and 14.9 %, respectively. The detection limits of the method ranged from 0.001 to 0. 002 µg mL⁻¹, and the quantification limits ranged from 0.002 to 0.008 µg mL⁻¹. The method was successfully applied to analysis of the target vitamins in 50 human serum samples; all the analytes were detected at concentrations ranging from <0.002–23.0 µg mL⁻¹.

     

Phytochemical characterization of bioactive compounds composition of Rosmarinus eriocalyx by RP–HPLC–ESI–QTOF–MS

Rosmarinus eriocalyx (rosemary or Elyazir) is an endemic species growing in arid steppe and rocky mountain in the South-West Algeria. This plant is well known in Algeria and Morocco due to its medicinal properties. However, little is known about its phytochemical composition. For this purpose, natural antioxidant compounds from R. eriocalyx were recovered by solid-liquid extraction and characterized by reversed-phase high-performance liquid chromatography coupled to quadrupole-time-of-flight mass spectrometry using negative and positive ionization modes. This analytical methodology enabled the characterization of 101 compounds, which were distributed in five major categories namely hydroxycinnamic acid derivatives, hydroxybenzoic acid derivatives, flavonoids, phenolic diterpenes and phenolic triterpenes. Moreover, the studied extract generally showed free radical-scavenging and reductive abilities in the range of butylated hydroxyanisole, butylated hydroxytoluene, α-tocopherol^, and ascorbic acid. Therefore, the result suggests that the aqueous-methanolic extract of R. eriocalyx could serve as a potential source of antioxidants.     

Activity of copper–cerium–zirconium catalysts in oxidation of hydrogen

We have studied the catalytic properties in oxidation of hydrogen for copper–cerium oxide systems deposited on supports obtained by calcination of yttrium-stabilized zirconium dioxide at 300–1000 °C. We have shown that the catalytic activity of the samples obtained depends on the specific surface area of the original supports and the amount of reduced copper within the composition of the catalyst. In samples whose support has high specific surface area, the content of reduced metallic copper is greater and the catalytic activity is higher.     

Surface tension of liquid high-entropy equiatomic alloys of a Cu–Sn–Bi–In–Pb system

An experimental study of the temperature dependences of the surface tension of liquid high-entropy equiatomic alloys of a Cu–Sn–Bi–In–Pb system is conducted. Measurements are made within the temperature range of t _L to 1300°C in the mode of heating and subsequent cooling of a sample. Overcooling of a melt prior to crystallization is detected. The depth of overcooling grows along with the number of components in the melt, while the temperature coefficient of surface tension falls. The experimental results qualitatively interpreted within the concepts of the specific surface entropy of a liquid.     

HPIC–UV–ICP–SFMS study of the interaction of cisplatin with guanosine monophosphate

Interaction of cis-[Pt(NH₃)₂Cl₂] (cisplatin) with 5′-guanosine monophosphate (5′-GMP) has been investigated for the first time by on-line coupling of high performance ion chromatography (HPIC) to inductively coupled plasma sector field mass spectrometry (ICP–SFMS). The time-dependent reaction course of the cisplatin-5′-GMP system was followed after incubation under simulated physiological conditions by monitoring the decrease in the concentration of 5′-GMP and the increase in the concentration of formed adducts, on the basis of speciation analysis. Because of the two-step mechanism an intermediate mono adduct was observed together with the major product, the bis adduct cis-[Pt(NH₃)₂(GMP)₂]^2–. The data obtained correlated well with those from earlier studies employing orthogonal techniques such as capillary electrophoresis (CE). Furthermore, HPIC–ICP–SFMS provided unambiguous stoichiometric information about the major GMP-adduct. For this purpose the platinum-to-phosphorus ratio was determined by simultaneously measuring ³¹P and ¹⁹⁵Pt. To separate significant interferences from ¹⁵N¹⁶O⁺, ¹⁴N¹⁶O¹H⁺, ¹²C¹⁸O¹H⁺, and ¹³C¹⁷O¹H⁺ on ³¹P, high-mass resolution (m/Δm = 4500) proved to be mandatory. The P/Pt signal ratio of 2/1 obtained corresponds to the molar ratio in the bis adduct cis-[Pt(NH₃)₂(GMP)₂]^2–.     

Deactivation of a mixed oxide catalyst of Mo–V–Te–Nb–O composition in the reaction of oxidative ethane dehydrogenation

The operational stability of a mixed oxide catalyst of Mo–V–Te–Nb–O composition in the oxidative dehydrogenation of ethane (ratio of C₂H₆: O₂ = 3: 1) is studied in a flow reactor at temperatures of 340–400°C, a pressure of 1 atm, and a WHSV of the feed mixture of 800 h^?1. It is found that the selectivity toward ethylene is 98% at 340°C, but the conversion of ethane at this temperature is only 6%; when the temperature is raised to 400°C, the conversion of ethane is increased to 37%, while the selectivity toward ethylene is reduced to 85%. Using physical and chemical means (XPS, SEM), it is found that the lack of oxidant in the reaction mixture leads to irreversible changes in the catalyst, i.e., reduced selectivity and activity. Raising the reaction temperature to 400°C allows the reduction of tellurium by ethane, from the +6 oxidation state to the zerovalent state, with its subsequent sublimation and the destruction of the catalytically active and selective phase; in its characteristics, the catalyst becomes similar to the Mo–V–Nb–O system containing no tellurium.     

FTIR study of the sol–gel synthesis of cementitious gels: C–S–H and N–A–S–H

The study explored the compatibility between the main product of Portland cement hydration and the main product of the alkali activation of fly ash: C–S–H and N–A–S–H gels, respectively. Both gels were synthesized with laboratory reagents at different pH values. Blends of the two were synthesized as well, using the sol–gel procedure. All the gels were characterized with Fourier transform IR spectroscopy (FTIR). The gels synthesized with this procedure were shown to precipitate together with a silica-rich gel. In addition, the pH level was found to play a determinant role in both C–S–H and N–A–S–H gel synthesis. The C–S–H gel is the major phase formed at pH > 11 and N–A–S–H gel for pH > 12. The results relating to the joint synthesis of the two (C–S–H and N–A–S–H) gels were not conclusive. Technique used for the characterization failed to differentiate between them in the blended material.

LC–DAD–ESI-MS–MS Separation and Chemical Characterization of the Inflammatory Fraction of the Roots of Euphorbia kansui

In China the roots of Euphorbia kansui T.N. Liou ex T.P. Wang, known as ‘kansui’, have been used for centuries as a herbal remedy for edema, ascites, and asthma. Kansui, has inflammatory and tumor-promoting toxicity, and other side-effects, however, which have seriously restricted its clinical application. In the work discussed in this paper a simple and rapid LC–DAD–ESI-MS–MS method has been established for separation and characterization of the main compounds in the toxic fraction of E. kansui roots. Twelve diterpene derivatives were identified in the inflammatory fraction of kansui: kansuinine C, kansuinine B, kansuinine A, kansuinine D, 5-O-benzoyl-20-deoxyingenol, kansuinine E, kansuiphorin C, 3-O-benzoyl-20-deoxyingenol, 3-O-(2′E,4′Z-decadienoyl)-5-O-acetylingenol, 3-O-(2′E,4′Z-decadienoyl)-20-deoxyingenol, 20-O-(2′E, 4′E-decadienoyl)ingenol, and 3-O-(2′E,4′Z-decadienoyl)-20-O-acetylingenol. The inflammatory fraction was separated on a C₁₈ reversed-phase column with a mobile phase gradient. The proposed method is a scientific and technical platform enabling the herbal medicine industry to perform quality control and ensure the safety of preparations that contain this class of poisonous diterpenoids.     

MSPD–GC–MS–MS Determination of Residues of 15 Organic Nitrogen-Containing Pesticides in Vegetables

A novel and simple method for determination of 15 organic nitrogen-containing pesticides in vegetables using matrix solid-phase dispersion (MSPD) coupled with gas chromatography tandem mass spectrometry (GC–MS–MS) has been developed. The efficiencies of different sorbents (florisil, silicone, neutral alumina) for the MSPD were compared. Mean recoveries of the method using neutral alumina varied from 73.26 to 111.83% with relative standard deviations of 0.79–15.33% in the concentration range of 0.01, 0.02 and 0.05 mg kg^?1. The limits of detection were typically in the 0.0007–0.0320 mg kg^?1 range, which were 10–100 times lower than the maximum residue levels established by the European Union. This method was applied to residue detection in vegetables, in which organic nitrogen-containing compounds were detected at low concentrations.