Rate of copper extraction and structure of model β-diketones and 4-acyl-5-pyrazolones

The rate of copper extraction with individual 4-acyl-5-pyrazolones and the stability of various enolic and keto forms and their monohydrates were studied. The rate of extraction depends mainly upon the structure of substituent at position 4 and falls when the substituent becomes spacy. The effect of the substituent at position 1 is rather low. The enolic form with intramolecular hydrogen bonding is the most stable. It can form hydrates with water molecules without intramolecular hydrogen bond breaking.     

Preparation and properties of phenyl-substituted cyclopentadienylides

Phenyl-substituted cyclopentadienylides have been prepared, for the most part by carbenic decomposition of diazocyclopentadienes copper-bronze was an effective catalyst and also enabled reaction to be carried out in solution 2,5-Diphenyldiazocyclopentadiene gave triphenylarsonium 2,4-diphenylcyclopentadienylide instead of the expected product. Electrophilic substitution (acetylation, formylation, diazo-coupling) proceeds preferentially at the 2(5)-positions, but if these sites are blocked, may take place at the 3(4)-positions. The spectra of 3(4)-acyl- and 3(4)-phenylazo-derivatives differ markedly from those of their 2(5)-analogues. Unlike their 2(5)-acyl-analogues, triphenylarsonium 3(4)-acyl-derivatives are unstable to hydrolysis.     

Room temperature ICl-induced dehydration/iodination of 1-acyl-5-hydroxy-4,5-dihydro-1H-pyrazoles. a selective route to substituted 1-acyl-4-iodo-1H-pyrazoles

A number of new functionally substituted 1-acyl-5-hydroxy-4,5-dihydro-1H-pyrazoles have been prepared in moderate to excellent yields from the corresponding 2-alkyn-1-ones. The resulting dihydropyrazoles undergo dehydration and iodination in the presence of ICl and Li2CO3 at room temperature to provide 1-acyl-4-iodo-1H-pyrazoles.     

The tautomerism of hydroxy derivatives of five-membered oxygen,nitrogen, and sulfur heterocycles

The unstable enolic tautomers 3-hydroxyfuran, 2- and 3-hydroxythiophene, 3-hydroxy-pyrrole, 3-hydroxy-1-methyl-pyrrole and their benzo-derivatives have been generated in solution and the rate and equilibrium constants for their ketoization determined.     

Density functional theory (DFT) and DRIFTS investigations of the formation and adsorption of enolic species on the Ag/Al2O3 surface

Molecular structure and vibrational frequencies of the novel surface enolic species intermediate on Ag/Al2O3 have been investigated by means of density functional theory (DFT) calculations and in situ infrared spectroscopy. The geometrical structures and vibrational frequencies were obtained at the B3P86 levels of DFT and compared with the corresponding experimental values. Theoretical calculations show that the calculated IR spectra are in good agreement with the experimental spectroscopic results. In addition, the adsorption energy of enolic species on the Ag/Al2O3 catalyst surface was also evaluated. The reaction mechanism from C2H5OH to enolic species on Ag/Al2O3 catalyst was proposed.     

Intramolecular hydrogen bond in enol form of 3-substituted-2,4-pentanedione

The 3-substituent effect on the enolic ring of 2,4-pentanedione has been investigated. A linear relationship between the chemical shifts of the enolic proton and the chelated carbonyl stretching vibrations has been found for the various highly enolized 3-substituted-2,4-pentanediones. The stronger electron-withdrawing resonance effect of the substituent at 3-position results in the lower magnetic field shift of the enolic proton and the lower frequency shift of the chelated carbonyl stretching. Semi-empirical Hückel calculations have been performed to enable discussion of the electronic effect of the substituents.     

Mapping Post-translational Modifications of Histones H2A, H2B and H4 in Schizosaccharomyces pombe

Core histones are known to carry a variety of post-translational modifications (PTMs), including acetylation, phosphorylation, methylation and ubiquitination, which play important roles in the epigenetic control of gene expression. The nature and biological functions of these PTMs in histones from plants, animals and budding yeast have been extensively investigated. In contrast, the corresponding studies for fission yeast were mainly focused on histone H3. In the present study, we applied LC-nano-ESI-MS/MS, coupled with multiple protease digestion, to identify PTMs in histones H2A, H2B and H4 from Schizosaccharomyces pombe (S. pombe), the typical model organism of fission yeast. Various protease digestions provided high sequence coverage for PTM mapping, and accurate mass measurement of fragment ions allowed for unambiguous differentiation of acetylation from tri-methylation. Many modification sites conserved in other organisms were identified in S. pombe. In addition, some unique modification sites, including N-terminal acetylation in H2A and H2B as well as K123 acetylation in H2A.β, were observed. Our results provide a comprehensive picture of the PTMs of histones H2A, H2B and H4 in S. pombe, which serves as a foundation for future investigations on the regulation and functions of histone modifications in this important model organism.     

Synthesis of Oligosaccharides Corresponding to Structures Found in Capsular Polysaccharides of Cryptococcus Neoformans. Part 3. Two Regioselectively Acetylated Tetrasaccharides.

Abstract

Regioselective acetylation of a tetrasaccharide has been accomplished using acetyl chloride and collidine in dichloromethane at low temperature. The degree of acetylation depended on the time and equivalents of reagents used. However, only acetylation of primary positions was observed. The acetylated oligosaccharides obtained after hydrogenolysis correspond to structures found in the capsular polysaccharide of Cryptococcus neoformans. The acetylation pattern in the target compounds was determined both by NMR and methylation analysis.     

Synthesis and properties of photosensitive compounds based on bromine-containing 3-acyl-2-furylchromones

Methods have been developed for the synthesis of new photosensitive compounds based on the reaction of N,S,O-nucleophiles with 3-acyl-2-(5-bromofur-2-yl)chromones and 3-acyl-2-(5-bromomethylfur-2-yl)chromones. The relationship between the spectral properties and the structure of compounds has been shown.     

Resorcinarenes的合成及其边缘化学修饰(Ⅱ)

探讨了烷基醛类（丁醛、戊醛、异丁醛）的Ｒｅｓｏｒｃｉｎａｒｅｎｅｓ的合成及其边缘化学修饰（乙酰化、甲基化），研究了烷基取代基对合成的影响，并用ＩＲ，＾１ＨＮＭＲ，ＭＳ和ＵＶ对这些化合物进行了表征。     

Diosphenol-based approach to the a-ring functionalization of advanced Taxol precursors

Several different approaches to the A-ring functionalization of an advanced, highly functionalized diosphenol precursor to Taxol are described. The first phase of the undertaking consists of an assessment of those reagents conducive to reaction at the enolic oxygen (silylation, methylation, allylation, and acylation). Transformations involving an alternative attack at the enol carbon center (bromination, selenation) have also been defined. Sodium borohydride reduction operates from the beta-face of C-14 as long as the C-1 hydroxyl is not protected so as to offer steric exclusion. Complications associated with various aspects of these methodological undertakings are addressed. The most advanced oxygenation achievements were realized by way of a noteworthy sequence involving epoxidation of the O-methyl ether, methanolysis under mildly acidic conditions, and regioselective oxidation of diol 38 to give 39.     

The synthesis of 6,7-dihydro-5H-pyrrolo[3,4-d]pyrimidines. II. 4-Hydroxy, 4-mercapto, 2-amino-4-hydroxy and 2,4-dihydroxy derivatives

Several new types of compounds in the 6,7-dihydro-5H-pyrrolo[3,4-d]pyrimidine series have been prepared. Included are a 6-acyl derivative unsubstituted in the pyrimidine ring, as well as 4-hydroxy, 4-mercapto, 2-amino-4-hydroxy and 2,4-dihydroxy derivatives. These products were derived directly or indirectly from 4-cyano- or 4-carbethoxy-1-acyl-3-amino-3-pyrroline intermediates. 3-Hydroxy, 3-amino, and 3-thioformylamino-1-acyl-3-pyrroline-4-thiocarboxamides have been obtained and the 3-thioformylamino derivatives shown to undergo base-catalyzed cyclization to close a 4-mercaptopyrimidine ring.     

Ab initio study of the structure of enolic and ketonic forms of β-diketones with the general formula R″COCH2COR′ (R′ and R″ = H, CH3, CF3)

Geometric parameters, values of force constants and vibration frequencies for different geometric configurations of enolic and ketonic forms of molecules of β-diketones, R″COCH₂COR′ (R″ and/or R′ are H, CH₃, CF₃) have been computed by the ab initio method MO LCAO SCF using wide bases of Cartesian Gaussians. The enolic form of the considered molecules is most energetically favorable. Values of isomerization energy, the height of internal rotation barriers, and energies of the intramolecular hydrogen bond were obtained for it. The stabilization of the enolic form was shown to be caused by the presence of the intramolecular hydrogen bond in the chelate ring. The effect of a substituent on the computed values of molecular parameters was examined. The comparison with the available experimental data testifies to a sufficiently high reliability of the data obtained.     

Electrochemical study on the keto-enol tautomerization of p-hydroxyphenylpyruvic acid in aqueous solution

The keto-enol tautomerization of p-hydroxyphenylpyruvic acid (pHPP) in aqueous solutions and the complexation reaction between enolic pHPP and boric acid have been studied by electrochemical techniques including linear sweep voltammetry (LSV), pulse voltammetry, and cyclic voltammetry (CV), combining with UV spectrometry. Electrochemical techniques reveal that in aqueous solution, there are two tautomers of pHPP: enolic form and ketonic form; the former exists mainly in freshly prepared pHPP solution, and the latter exists mainly in equilibrium solution. Both enolic and ketonic pHPP are electroactive. The electrochemical oxidation of enolic pHPP gives rise to two anodic waves, I(a) and II(a), while the electrochemical oxidation of ketonic pHPP only results in the observation of the second wave II(a). The oxidation process I(a) is revealed to be associated with the quasi-reversible, two-electron two-proton oxidation of "C=C"group at the side chain of enolic pHPP, and the oxidation process II(a) is proposed to result from the irreversible oxidation of phenolic hydroxyl group. It is observed that in aqueous solution, enolic pHPP can quickly complex with boric acid to yield enol-borate complex that can also oxidize at a glassy carbon electrode to yield an anodic wave.     

Copper(II) triflate catalyzed amination and aziridination of 2-alkyl substituted 1,3-dicarbonyl compounds

A method to prepare α-acyl-β-amino acid and 2,2-diacyl aziridine derivatives efficiently from Cu(OTf)(2) + 1,10-phenanthroline (1,10-phen)-catalyzed amination and aziridination of 2-alkyl substituted 1,3-dicarbonyl compounds with PhI═NTs is described. By taking advantage of the orthogonal modes of reactivity of the substrate through slight modification of the reaction conditions, a divergence in product selectivity was observed. In the presence of 1.2 equiv of the iminoiodane, amination of the allylic C-H bond of the enolic form of the substrate, formed in situ through coordination to the Lewis acidic metal catalyst, was found to selectively occur and give the β-aminated adduct. On the other hand, increasing the amount of the nitrogen source from 1.2 to 2-3 equiv was discovered to result in preferential formal aziridination of the C-C bond of the 2-alkyl substituent of the starting material and formation of the aziridine product.     

Resorcinarenes的合成及其边缘化学修饰（Ⅰ）

探讨了烷基醛类（乙醛,丙醛）的Ｒｅｓｏｒｃｉｎａｒｅｎｅｓ的合成及其边缘化学修饰（乙酰化,甲基化）,研究了各种因素对Ｒｅｓｏｒｃｉｎａｒｅｎｅｓ的影响。确定了较佳反应条件。     

Theoretical and experimental study on formation and adsorption of enolic species on Ag-Pd/Al2O3 catalyst

The formation and adsorption of enolic species on a palladium promoted Ag/Al2O3 catalyst (denoted Ag-Pd/Al2O3) during the selective catalytic reduction (SCR) of NOx by C3H6 has been studied by means of DRIFTS and density functional calculations. The structure of the enolic species adsorbed on Ag-Pd/Al2O3 catalyst has been established based on the in situ DRIFTS spectra and simulated results. The reaction mechanism from C3H6 to enolic species on Ag-Pd/Al2O3 catalyst was proposed and the hypothesis about the Pd promotion was discussed.     

Chemistry of 1,1,1,5,5,5-hexafluoro-2,4-pentanedione on Si(100)-2x1

The surface chemistry of 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (hfacH), a hydrogenated form of the most common ligand in metal and metal oxide deposition, on Si(100)-2x1 has been investigated using multiple internal reflection Fourier transform infrared spectroscopy (MIR-FTIR), Auger electron spectroscopy (AES), thermal desorption mass spectrometry, and computational analysis. The main goal of these studies was to understand if hfacH is a source of fluorine, carbon, and oxygen contamination for a variety of deposition processes where the hfac ligand is involved. In its molecular form, hfacH may potentially have up to 10 isomers including two ketonic and eight enolic forms. One of the enolic forms is shown to be the most stable upon adsorption on a clean Si(100)-2x1 surface at submonolayer coverages at cryogenic temperatures. Even though only the enolic form is present at cryogenic temperatures, at room temperature any of these isomers can exist and all the possibilities of their interaction with the Si(100)-2x1 surface, including several [2 + 2] and [2 + 4] addition pathways as well as O-H dissociation, should be considered. Despite such an array of possibilities, the room-temperature adsorption is governed by the thermodynamic stability of the final addition products between the hfacH and silicon surface. These adducts are stable at room temperature and decompose upon surface annealing.     

N-Acyl-beta-D-glycopyranosylamines and 2-alkylamido-2- deoxy-alpha / beta-D-glucopyranoses: relationship between molecular structure and mesomorphism

A variety of N -acyl- beta -D-glucopyranosylamines, N -acyl- beta -D-mannopyranosylamines and 2-alkylamido-2-deoxy- alpha / beta -D-glucoses has been prepared regiospecifically and in good yield in a one step reaction of the appropriate acid chloride with D-mannosylamine, 2-amino-2-deoxyD-glucopyranose (prepared in one step from glucose and mannose according to literature methods) and D-glucosamine liberated in situ from the commercially available hydrochloride. The dependence of the liquid crystal transition temperatures and mesophase formation on the degree and nature of intermolecular hydrogen bonding has been studied by choosing two different carbohydrate cores and by attaching aliphatic terminal chains via an amide linkage in two different positions. Comparison is made with related compounds reported in the literature. Whereas the N -acyl- beta -D-mannopyranosylamines and N -acyl- beta-D-glucopyranosylamines possess wide-range smectic A* phases, the corresponding 2-alkylamido-2-deoxy- beta-Dglucopyranoses do not exhibit observable mesomorphism. Although some homologues of the compounds synthesized have already been reported in the literature, their liquid crystalline behaviour was not reported. These investigations confirm the general view that it is the number and type of hydrogen bonding groups on the carbohydrate moiety and the aliphatic chain length that primarily determine thermotropic mesophase behaviour, as well as the absolute values of the transition temperatures.     

Fluorinated heterocyclic compounds. 2. 2,4-difluoro and 4-amino-2-fluoropyrimidines,nucleoside base analogs

Nucleoside base analogs in which fluoro substituents replace the enolic hydroxy groups of uracil, thymine and cytosine have been prepared. Improved methods for the preparation and isolation of the known 2,4-di-fluoropyrimidine, 2,4-difluoro-6-methylpyrimidine and the new 2,4-difluoro-5-methylpyrimidine, 2-fluoro-4-aminopyrimidine, 4-fluoro-2-aminopyrimidine, and other alkylaminofluoropyrimidines are described.