A stereoselective route towards heliannuol A

Both epimers of Heliannuol A, first heliannane reported in the literature, isolated from Heliannthus annuus, have been prepared individually in a stereoselective route using a ring closing metathesis (RCM) as a key step to obtain the eight-membered ring. Very good overall yield was obtained in both cases.     

A Hydrochlorothiazide-Imprinted Polymer

ABSTRACT

Hydrochlorothiazide (HCT) is a medicine commonly used as a diuretic. A series of HCT-imprinted polymers were prepared using 4-vinylpyridine or methacrylic acid or none as a functional monomer. Liquid chromatographic analysis using the polymers as a stationary phase showed that 4-vinylpyridine was suitable for synthesizing HCT-selective polymers. It appeared that the sulfonamide groups on HCT molecule could interact with 4-vinylpyridine through ionic interaction, and thus could be used as a functional group for molecular imprinting. The prepared HCT-specific polymers should have applications for clinical analysis of HCT.     

A Study of Monodispersed Polydimethylsiloxanes

A series of monodispersed polydimenthylsiloxanes (PDMS) with molecular weights from 3K to 156K were synthesized. The intrinsic viscosity and absolute molecular weight of each monodispersed PDMS was measured and the Mark-Houwink equation for the PDMS series in toluene at 25°C was derived: [eta;]=2.88 × 10^?4 M^0.613. It was proven that the accurate molecular weight determination of polysiloxanes is not possible using polystyrene (PS) standards. It can be achieved either by using a gel permeation chromatographic method with PDMS standards or by a calculation from the Mark-Houwink equation using experimental values of intrinsic viscosity.     

A Fluorescence-Based Sensor for Ammonium and Nitrate

Abstract

Measurement of nitrite and nitrate in rain samples was performed using a fluorescence based sensor. Nitrite and nitrate were reduced to ammonia using Devarda's alloy, and the gas was then passed through a membrane and reacted with o-phthalaldehyde. A linear relationship between the nitrate concentration and the luminescence intensity was observed over the concentration range of 1 – 5 mg/1, with a relative standard deviation (RSD) of 2.3% at a nitrate concentration of 1 mg/1 (n = 5). The system did not show any response toward sulfate or chloride. Results obtained from the measurement of river water samples using the sensor showed good agreement with those obtained using a conventional method.     

Temperature-programmed crystallization of zeolite A

Crystallization rates of zeolite A were studied in a constant-temperature mode and a temperature-programmed mode. The crystallization rate in the constant-temperature mode was examined using the engineering reaction model. Activation energy for crystal growth was determined to be 32.8 kJ/mol. The crystallization curves in the temperature-programmed mode could be simulated by using the rate constants and the fractions of soluble species determined from the constant-temperature mode experiments.     

Phomoxanthone A Targets ATP Synthase

Phomoxanthone A is a naturally occurring molecule and a powerful anti-cancer agent, although its mechanism of action is unknown. To facilitate the determination of its biological target(s), we used affinity-based labelling using a phomoxanthone A probe. Labelled proteins were pulled down, subjected to chemoproteomics analysis using LC-MS/MS and ATP synthase was identified as a likely target. Mitochondrial ATP synthase was validated in cultured cells lysates and in live intact cells. Our studies show sixty percent inhibition of ATP synthase by 260 μM phomoxanthone A.     

A microwave-assisted stereoselective synthesis of polyandrocarpamines A and B

A stereoselective synthesis of the marine natural products, polyandrocarpamines A and B, has been achieved using a high-yielding one-step aldol condensation reaction under microwave conditions. The structures of both synthetic compounds were confirmed following 1D and 2D NMR, UV, IR and MS spectral analysis, and by comparison with literature data. Both synthetic natural products were assigned Z geometry about their exocyclic double bond on the basis of ¹³C/¹H long-range coupling constants, which were measured using a gHSQMBC experiment. Polyandrocarpamines A and B were evaluated for their cytotoxicity towards the tumour cell lines, MCF-7 (breast), H460 (lung) and SF268 (central nervous system). Polyandrocarpamine A displayed selective cytotoxicity towards the SF268 cell line with a GI₅₀ value of 65 μM.     

A Molecularly Imprinted Nicotine-Selective Polymer

Abstract

A (-)-nicotine-selective polymer was prepared by molecular imprinting technique using methacrylic acid as a functional monomer. Liquid-chromatographic tests, using the polymers as a stationary phase, exhibited that the basicity of the functional group of (-)-nicotine is crucial for rebinding by the molecularly imprinted polymer. Scatchard analysis implied that the binding sites generated within the polymer are heterogeneous in terms of affinity, and the apparent dissociation constant of the highest affinity binding sites was estimated as 3.7 μM.     

A data-oriented CI program system

A program system has been developed for calculation of molecular electronic structure using the configuration interaction (CI) method. Emphasis is placed on the inherent genealogical data structure of the files which a program system produces. Based on this genealogy, a language is provided for users which allows easy and consistent manipulation of files in the new system. Users need only specify a file which contains the desired data, using this file manipulation language. If the desired file does not exist, the new system creates it automatically by calling appropriate modules. The new system may be regarded as a data base equipped with computational ability.     

Synthesis of diospongin A

A stereoselective synthesis of Diospongin A using a cross-metathesis-intramolecular Michael addition has been achieved.     

A six-dimensional quadrature procedure

An account is given of the use of Gaussian quadrature product formulae in the evaluation of certain six-dimensional, two-centre integrals involving one-electron Green's functions. These integrals occur in a new molecular variational principle recently proposed by Hall, Hyslop and Rees [1] from which an approximate energy may be derived which can be shown to be at least as good as that obtained from the Rayleigh-Ritz principle. Reductions in computing time are realized by removing certain singularities using a subtraction technique and also by using an empirically determined Richardson-type extrapolation formula.This paper was presented during the session on numerical integration methods for molecules of the 1970 Quantum Theory Conference in Nottingham. It has been revised in the light of the interesting discussion which followed.     

单根聚己内酯电纺亚微米纤维的动力学特性分析

通过静电纤维制造技术得到直径范围在100～500nm的PCL亚微米纤维,并使用信号发生器和压电片联用对收集到的单根纤维进行振动实验,由共振频率数据得到单根纤维的弹性模量,并同时对直径的测量方法进行了修正.实验结果显示,PCL亚微米纤维的弹性模量随直径变化而显著增加,存在明显的尺寸效应.通过引入应变梯度的振动模型对实验中观测到的尺寸效应进行了理论解释,等效弹性模量的理论预测值与实验数据吻合良好.     

A general catalytic allylation using allyltrimethoxysilane

A general and mild catalytic allylation of carbonyl compounds, applicable to aldehydes, ketones, and imines is developed using allyltrimethoxysilane as the allylating reagent. The reaction proceeds smoothly with 1-10 mol % of CuCl and TBAT in THF at ambient temperature. Mechanism studies indicated that the copper alkoxide, allylfluorodimethoxysilane, and allyltrimethoxysilane are essential to promote the reaction efficiently. Preliminary extension of the reaction to the first catalytic enantioselective allylation of ketones using an allylsilane produced the product with 61% ee from acetophenone, using a CuCl-p-tol-BINAP-TBAT catalyst (15 mol %).     

A short stereoselective synthesis of (+)-boronolide

A short and stereoselective synthesis of (+)-boronolide via oxidative functionalization of an olefin using a pendant sulfinyl group is described. Diastereoselective allylation was performed using Keck’s protocol and the lactone moiety was prepared by ring closing metathesis.     

A New Class of Non‐Racemic Chiral Macrocycles: A Conformational and Synthetic Study

Amino alcohols have been used to introduce non‐racemic chirality into macrocycles using a modular approach that relies on a Heck macrocyclisation reaction. A wide variety of macrocycles have been synthesised, and their structures studied using X‐ray crystallography and molecular modelling. A fragmentation reaction encountered during the use of (S)‐1,1‐dimethylvalinol revealed that carboxylic acids generate acylals under reaction conditions often used for Heck reactions.     

A stereoselective synthesis of (+)-herboxidiene/GEX1A

A stereoselective synthesis of (+)-herboxidiene is described. The convergent synthesis utilized a Suzuki cross-coupling reaction to assemble the key segments. The synthesis of the functionalized tetrahydropyran ring utilized an Achmatowicz reaction as the key step. The synthesis of the C10-C19 segment was accomplished using Brown's crotylboration, asymmetric alkylation, and a stereoselective allylic chlorination reactions.     

A predictive vapor-pressure equation

A simple equation is presented for predicting the temperature dependence of the vapor-pressure of a pure substance along the entire (liquid + vapor) coexistence curve, from the triple point to the critical point. The proposed equation is based on the use of a dimensionless temperature reduced by using critical and triple point values, and of the Clausius–Clapeyron equation as a zeroth-order approximation. The pressure and temperature at the triple point, the normal boiling temperature, and the pressure and temperature at the critical point are required as input data. The proposed equation is verified for 53 fluids by using NIST data. These data are reproduced with an overall average deviation of 0.55%.     

A synergistic approach to anion antiport

A synergistic approach to Cl(-)/HCO(3)(-) antiport has been demonstrated in POPC lipid bilayers using an ion selective electrode assay showing that, when using combinations of carriers each optimised for a particular component of the transport process, enhanced rates of transport are observed.     

Approach toward the total synthesis of 5-hydroxyaloin A

The synthesis of a thiomethyl analogue of 5-hydroxyaloin A has been achieved using benzyne and naphthyne [4 + 2] cycloadditions with substituted furans. A regiocontrolled cycloaddition was achieved using a silicon tether, and a regioselective ring opening was accomplished using a sulfide as a directing group.     

A linear multiporphyrinic

A linear multiporphyrinic [2]-rotaxane has been synthesized using the transition metal-templating method for threading a gold(III)-incorporating macrocycle onto a rodlike, phenanthroline-derived chelate bearing carboxylate end groups. Stoppering has been performed by reacting the resulting prerotaxane with the amino derivative of a zinc tetraarylporphyrin under EDC-HOBt activation. A 34% yield has been realized for this one-pot, double amide bond formation.