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91.
Cheng A Diller DJ Dixon SL Egan WJ Lauri G Merz KM 《Journal of computational chemistry》2002,23(1):172-183
Very large data sets of molecules screened against a broad range of targets have become available due to the advent of combinatorial chemistry. This information has led to the realization that ADME (absorption, distribution, metabolism, and excretion) and toxicity issues are important to consider prior to library synthesis. Furthermore, these large data sets provide a unique and important source of information regarding what types of molecular shapes may interact with specific receptor or target classes. Thus, the requirement for rapid and accurate data mining tools became paramount. To address these issues Pharmacopeia, Inc. formed a computational research group, The Center for Informatics and Drug Discovery (CIDD).* In this review we cover the work done by this group to address both in silico ADME modeling and data mining issues faced by Pharmacopeia because of the availability of a large and diverse collection (over 6 million discrete compounds) of drug-like molecules. In particular, in the data mining arena we discuss rapid docking tools and how we employ them, and we describe a novel data mining tool based on a ID representation of a molecule followed by a molecular sequence alignment step. For the ADME area we discuss the development and application of absorption, blood-brain barrier (BBB) and solubility models. Finally, we summarize the impact the tools and approaches might have on the drug discovery process. 相似文献
92.
Barnes JH Schilling GD Stone SF Sperline RP Denton MB Young ET Barinaga CJ Koppenaal DW Hieftje GM 《Analytical and bioanalytical chemistry》2004,380(2):227-234
The use of a separation step, such as liquid chromatography, prior to inductively coupled plasma mass spectrometry (ICP–MS) has become a common tool for highly selective and sensitive analyses. This type of coupling has several benefits including the ability to perform speciation analysis or to remove isobaric interferences. Several limitations of conventional instruments result from the necessity to scan or pulse the mass spectrometer to obtain a complete mass spectrum. When the instrument is operated in such a non-continuous manner, duty cycle is reduced, resulting in poorer absolute limits of detection. Additionally, with scanning instruments, spectral skew can be introduced into the measurement, limiting quantitation accuracy. To address these shortcomings, a high-performance liquid chromatograph has been coupled to an ICP–MS capable of continuous sample introduction and simultaneous multimass detection. These features have been realized with a novel detector array, the focal plane camera. Instrument performance has been tested for both speciation analysis and for the elimination of isobaric interferences. Absolute limits of detection in the sub picogram to tens of picograms regime are obtainable, while the added mass dimension introduced by simultaneous detection dramatically increases chromatographic peak capacity. 相似文献
93.
Armstrong A Ahmed G Dominguez-Fernandez B Hayter BR Wailes JS 《The Journal of organic chemistry》2002,67(24):8610-8617
Several alpha-substituted N-carbethoxytropinones have been evaluated as catalysts for asymmetric epoxidation of alkenes with Oxone, via a dioxirane intermediate. alpha-Fluoro-N-carbethoxytropinone (2) has been studied in detail and is an efficient catalyst which does not suffer from Baeyer-Villiger decomposition and can be used in relatively low loadings. This ketone was prepared in enantiomerically pure form using chiral base desymmetrization of N-carbethoxytropinone. Asymmetric epoxidation catalyzed by 2 affords epoxides with up to 83% ee. Among other derivatives tested, the alpha-acetoxy derivative 7 affords the highest enantioselectivities. 相似文献
94.
Fry B Silva SR Kendall C Anderson RK 《Rapid communications in mass spectrometry : RCM》2002,16(9):854-858
Elemental analyzers have been successfully coupled to stable-isotope-ratio mass spectrometers for online measurements of the delta(34)S isotopic composition of plants, animals and soils. We found that the online technology for automated delta(34)S isotopic determinations did not yield reproducible oxygen isotopic compositions in the SO(2) produced, and as a result calculated delta(34)S values were often 1-3 per thousand too high versus their correct values, particularly for plant and animal samples with high C/S ratio. Here we provide empirical and analytical methods for correcting the S isotope values for oxygen isotope variations, and further detail a new SO(2)-SiO(2) buffering method that minimizes detrimental oxygen isotope variations in SO(2). 相似文献
95.
Hodgson DM Kirton EH Miles SM Norsikian SL Reynolds NJ Coote SJ 《Organic & biomolecular chemistry》2005,3(10):1893-1904
Organolithium-induced deprotonation of terminal epoxides in the presence of appropriate diamine ligands allows trapping with a range of electrophiles, yielding functionalised di- and tri-substituted epoxides in good yields and with control of stereochemistry at the epoxide. 相似文献
96.
Soonam Park Feng Liao John M. Larson Steven L. Girshick Michael R. Zachariah 《Plasma Chemistry and Plasma Processing》2004,24(3):353-372
A molecular beam mass spectrometry system for in situ measurement of the concentration of gas phase species including radicals impinging on a substrate during thermal plasma chemical vapor deposition (TPCVD) has been designed and constructed. Dynamically controlled substrate temperature was achieved using a variable thermal contact resistance method via a backside flow of an argon/helium mixture. A high quality molecular beam with beamtobackground signal greater than 20 was obtained under film growth conditions by sampling through a small nozzle (75 m) in the center of the substrate. Mass discrimination effects were accounted for in order to quantify the species measurements. We demonstrate that this system has a minimum detection limit of under 100 ppb. Quantitative measurements of hydrocarbon species (H, H2, C, CH3, CH4, C2H2, C2H4) using Ar/H2/CH4 mixtures and silicon species (Si, SiH, SiH2, SiCl, SiCl2, Cl, HCl) using Ar/H2/SiCl4 mixtures were obtained under thermal plasma chemical vapor deposition conditions. 相似文献
97.
Richardson NA Wesolowski SS Schaefer HF 《Journal of the American Chemical Society》2002,124(34):10163-10170
The adiabatic electron affinity (AEA) for the Watson-Crick guanine-cytosine (GC) DNA base pair is predicted using a range of density functional methods with double- and triple-zeta plus polarization plus diffuse (DZP++ and TZ2P++) basis sets in an effort to bracket the true electron affinity. The methods used have been calibrated against a comprehensive tabulation of experimental electron affinities (Chem.Rev. 2002, 102, 231). Optimized structures for GC and the GC anion are compared to the neutral and anionic forms of the individual bases as well as Rich's 1976 X-ray structure for sodium guanylyl-3',5'-cytidine nonahydrate, GpC.9H(2)O. Structural distortions and natural population (NPA) charge distributions of the GC anion indicate that the unpaired electron is localized primarily on the cytosine moiety. Unlike treatments using second-order perturbation theory (MP2), density functional theory consistently predicts a substantial positive adiabatic electron affinity for the GC pair (e.g., TZ2P++/B3LYP: +0.48 eV). The stabilization of C(-) via three hydrogen bonds to guanine is sufficient to facilitate adiabatic binding of an electron to GC and is also consistent with the positive experimental electron affinities obtained by photoelectron spectroscopy of cytosine anions incrementally microsolvated with water molecules. The pairing (dissociation) energy for GC(-) (35.6 kcal/mol) is determined with inclusion of electron correlation and shows the anion to have greater thermodynamic stability; the pairing energy for neutral GC (TZ2P++/B3LYP 23.9 kcal/mol) compares favorably to previous MP2/6-31G (23.4 kcal/mol) results and a debated experiment (21.0 kcal/mol). 相似文献
98.
Steven P. Hopper Michael J. Tremelling Emma W. Goldman 《Journal of organometallic chemistry》1978,156(2):331-340
The heterogeneous gas-solid reaction of trimethylchlorosilane and an equal molar mixture of potassium t-butoxide and sodium methoxide gave exclusively trimethyl-t-butoxysilane. A similar reaction utilizing dimethyldichlorosilane as the vapor phase substrate gave predominant incorporation of butoxide. The heterogeneous reaction of chloromethyldimethylchlorosilane with these two bases was extensively studied. The parameters investigated for the latter system include the dependence of the product distribution on temperature, nitrogen flow rate and the relative hydroxide content of the solid alkoxide base. These studies allow the assessment of the relative reactivities of these bases under the conditions of heterogeneous gas/solid reaction. Under these conditions and with partially hydrolyzed bases a substantial amount of displacement of the chloromethyl group from chloromethyldimethylchlorosilane is observed. The role of hydroxide ion in this reaction is discussed. Convenient syntheses of t-butyl methyl ether and dimethylchloromethoxysilane are reported. 相似文献
99.
Nathan L. Bauld Dennis J. Bellville Steven A. Gardner Yoelit Migron Garrett Cogswell 《Tetrahedron letters》1982,23(8):825-828
Cation radical polymers which have cation radical functions at up to 5% of the poly(styrene) monomer sites have been prepared, and their effectiveness in catalyzing the cation radical Diels-Alder reaction is demonstrated. 相似文献
100.
We present results of exact calculations on a three-level Morse oscillator modeling HF which suggest that multiphoton absorption proceeds by sequential single-level transitions, transitions arising from coupling between non-adjacent states being dynamically negligible. The time-dependent Schrödinger equation is integrated in the Floquet formalism. 相似文献