Synthesis of artificial receptors as potential candidates for recognition and binding of pterin analogs

Open chain podands 2a-c and macrocycles 2d-e have been synthesized as potential candidates for 4-aminopterin recognition and binding, featuring H? bonding characteristics and “stacking interaction” 2e. Preliminary binding studies between 6, 7 , and 8 (simpler analogs of the above 2a-e ) as “bosts” and appropriate “guests”, showed that carbamates 2a and 2e are the most promising receptors for 4-aminopterin binding.     

Synthetic studies on the molybdenum cofactor: Total synthesis of pterindithiolenes by direct dithiolene formation from suitable pterin alkynes

A novel, efficient total synthesis of a series of pterindithiolenes (15, 16, 17 and 18) [(5,6-dihydro-[1,4]dithiin or 6,7-dihydro-5H-[1,4]dithiepin systems respectively for six and seven membered dithiolenes] has been reported. The six membered quinoxaline thioketal 9 and seven membered quinoxaline dithiolene 11 have also been synthesized from quinoxaline acetylenic alcohol 5 and the corresponding acetylenic ketone 10 respectively. The synthesis of five membered pterin thioketals 12 and 13 along with the conversion of 13 to the dithiolene 14 by the reaction with NBS is also reported.     

An automated direct sample insertion system for the inductively coupled plasma

A new sample introduction system for inductively coupled plasma emission spectrometry is described. With this system, sample carrying cups can be sequentially and automatically inserted into an ICP discharge using a pneumatically activated transport system. The system carousel holds up to 24 cups (graphite or metal) and is located below a modified plasma torch that accommodates pneumatic injection of the entire sample carrying cup. The torch-insertion subassembly allows height programming of the final insertion and hence steps such as drying and ashing can be performed in situ. The system is applicable to the analysis of small volumes of liquids (10 μl) and small amounts (10 mg) of powders. The analytical characteristics will be presented including signal temporal behavior, detection limits and precision. Preliminary results indicate that the direct quantitative analysis of powdered botanicals and coal is feasible.     

Synthesis of new fluorinated Tebufenpyrad analogs with acaricidal activity through regioselective pyrazole formation

In previous studies, our group has shown that the use of fluorinated alcohols such as trifluoroethanol (TFE) and hexafluoroisopropanol (HFIP) as solvents dramatically increases the regioselectivity in the pyrazole formation from 1,3-diketone with methylhydrazine. We have now applied this synthetic method to the preparation of new fluorinated pyrazoles, which have then been used as synthetic intermediates in the preparation of fluorinated analogs of Tebufenpyrad, a commercial acaricide. These compounds display a strong acaricidal activity that is either comparable to or better than that of the commercial compound.     

Synthesis of benzaldehyde-functionalized LewisX trisaccharide analogs for glyco-SAM formation

LewisX (Le^x) antigen based carbohydrate–carbohydrate interactions are mediated by complexation of metal ions. Although theoretical studies about the influence of participating hydroxyl groups in the Le^x trisaccharide head group (Galβ(1-4)[Fucα(1-3)]GlcNAc) could gave same rudimental information about the basic mechanism behind this interaction, a little is known about orientation and configuration of the hydroxyl groups required for the specific interaction mediated by Ca²⁺ complexation. Therefore, there is a need of non-natural derivatives to provide detailed information about the requirements for hydroxyl group arrangement in Le^x head group surface plasmon resonance and gold nanoparticle techniques have shown to be powerful tools to investigate carbohydrate–carbohydrate interactions. Benzaldehyde-functionalized glycans can be used for attachment to both gold nanoparticles and surface plasmon resonance sensor surfaces. Therefore, seven benzaldehyde equipped Le^x analogs including the natural trisaccharide were synthesized utilizing convergent approach. The derivatives were applied in ongoing carbohydrate–carbohydrate interaction studies by surface plasmon resonance experiments to prove theoretical postulate about the structural requirements of hydroxyl group arrangements in Le^x trisaccharides.     

A computer-controlled direct sample insertion device for inductively coupled plasma-mass spectrometry

A direct sample insertion (DSI) device has been developed for application to inductively coupled plasma-mass spectrometry (ICP-MS). In a DSI device for use with ICPs, the sample is placed into or onto a probe with subsequent introduction of the sample carrying probe, via the central tube of the ICP torch, into the plasma. A mechanical, stepper-motor driven, computer controlled DSI device and software support system has been designed and developed that can easily be attached to a commercial ICP-MS system (Perkin-Elmer/SClEX Elan). This system allows the direct introduction of microliter volumes of liquids and milligram quantities of powdered/solid samples into the ICP-MS with little or no sample pre-treatment.     

Evidence for formation of diphenylphosphinic peroxy radical intermediate: Spin trapping and chemical reactivity of the new phosphorus radical generated from diphenylphosphinic chloride and superoxide

Diphenylphosphinic chloride reacts with the superoxide anion radical in acetonitrile under mild conditions to form a peroxyphosphorus radical intermediate which shows strong oxidizing abilities for the epoxidation of olefins, oxidation of sulfides to sulfoxides, desulfurization of thioamides to amides, and oxidation of triarylphosphines to phosphine oxides. The radical can be trapped using a spin trapping method.     

Method for analysis of polymer-supported organic compounds using mass spectrometry direct insertion

A new approach on the use of mass spectrometry direct-insertion and a quadrupole detector for analysis of organic compounds supported in solid phase has been developed. This is a simple and efficient method based on cleavage due to the thermal-instability of the benzylic group of most commercial resins. The cleavage of supported compounds takes place in the spectrometer as a consequence of the high temperature in the instrument's chamber. These compounds are detected using a similar fragmentation pattern and a molecular ion corresponding to the same compound obtained by traditional synthesis. Polymer degradation fragments do not interfere with the spectrum interpretation, because only a few peaks and low intensities are detected. We report here the identification of different types of compounds supported in Merrifield resin, such as bis-o-aminobenzamides and simple aromatic and aliphatic compounds, using this new approach.     

Synthesis of heterocyclic compounds using radical reactions and evidence for the formation of spiro radical intermediates

Synthesis of novel heterocycles using radical reactions have been described. Reaction mechanism of their formation is also presented.     

姜黄素类似物的合成及其清除自由基的研究

姜黄素(见图1)为中药姜黄的主要成分,是一种黄色色素。研究报道姜黄素具有抗氧化、抗炎、抗病毒、抗癌等生物活性[1-4]。本文通过芳香醛和环己酮催化缩合反应合成了一系列姜黄素类似物(见图2),研究了它们抗自由基的活性。图1姜黄素的化学结构F ig.1 Chem ical structure of cur     

Catalytic carbene insertion into an aminoporphyrin and formation of a new chiral supramolecular porphyrin system

The catalytic insertion of ethyl diazoacetate into a porphyrin derivative bearing an NH₂ substituent, in the presence of a Rh-based catalyst, was investigated. The X-ray analysis of one of the isolated products reveals the formation of a chiral supramolecular system.     

Heat of formation for the SH radical by photoionization mass spectrometry

Photoionization mass spectrometry has been used to measure the appearance energies for [C₂H₅]⁺ from ethanethiol, [C₃H₇]⁺ from 2-propanethiol and [C₃H₅]⁺ from 2-methylthiirane. From the known thermochemistry of these cations and their precursor molecules, a 298 K heat of formation of 138.6±0.4 kJ mol^?1 for the SH radical has been derived.     

Dual-level direct dynamics studies for the reactions of OH radical with bromine-substituted ethanes

The dynamic properties of the multichannel hydrogen abstraction reactions of CH(3)CH(2)Br + OH --> products and CH(3)CHBr(2) + OH --> products are studied by dual-level direct dynamics method. For each reaction, three reaction channels, one for alpha-hydrogen abstraction and two for beta-hydrogen abstractions, have been identified. The minimum energy paths (MEPs) of both the reactions are calculated at the Becke's half-and-half (BH&H)-Lee-Yang-Parr (LYP)/6-311G(d, p) level and the energy profiles along the MEPs are further refined with interpolated single-point energies (ISPE) method at the G2M(RCC5)//BH&H-LYP level. There are complexes with energies less than those of the reactants or products located at the entrance or exit channels, which indicates that the reactions may proceed via an indirect mechanism. By canonical variational transition-state theory (CVT) the rate constants are calculated incorporating the small-curvature tunneling (SCT) correction in the temperature range of 220-2000 K. The agreement of the rate constants with available experimental values for two reactions is good in the measured temperature range. The calculated results show that alpha-hydrogen abstraction channel is the major reaction pathway in the lower temperature for two reactions, while the contribution of beta-hydrogen abstraction will increase with the increase in temperature.