Generation Of Equivalents Research Articles

Design, Synthesis, and Evaluation of a New Generation of Modular Nucleophilic Glycine Equivalents for the Efficient Synthesis of Sterically Constrained α-Amino Acids

A new generation of modular achiral glycine equivalents have been evaluated with respect to their synthetic utility for the production of tailor-made, sterically constrained alpha-amino acids, which proved to be the most efficient approach developed to date for the synthesis of symmetrical alpha,alpha-disubstituted-alpha-amino acids. Among the new series of achiral glycine equivalents, one was found to be a superior glycine derivative for the Michael additions with various (R)- or (S)-N-(E-enoyl)-4-phenyl-1,3-oxazolidin-2-ones representing a general and practical synthesis of sterically constrained beta-substituted pyroglutamic acids. In particular, the application of these complexes allowed for the preparation of several beta-substituted pyroglutamic acids which include electron-releasing and sterically demanding substituents in the structure thus increasing the synthetic efficiency and expanding the generality of these Michael addition reactions.

In situ Generation and Nucleophilic Capture of 1,n‐Dial Equivalents from 1,n‐Dioates (α,ω‐Diesters).

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

In situ Generation and Nucleophilic Capture of 1,n-Dial Equivalents from 1,n-Dioates (α,ω-Diesters)

A procedure is described for the in situ generation of functional equivalents of glutaric. succinic, and malonic dialdehydes. DIBAL-H reduction of the corresponding 1,n-dioates followed by in situ addition of a nucleophilic trapping agent allows for one-pot. bidirectional homologation. Olefination and Grignard addition classes of reactions are specifically demonstrated.

Generation of Acyl Anion Equivalents from Acylphosphonates via Phosphonate—Phosphate Rearrangement: A Highly Practical Method for Cross‐Benzoin Reaction.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Experimental Studies Using Statistical Algorithms on Transliterating Phoneme Sequences for English–Chinese Name Translation

Machine transliteration is automatic generation of the phonetic equivalents in a target language given a source language term, which is useful in many cross language applications. Transliteration between far distant languages, e.g. English and Chinese, is challenging because their phonological dissimilarities are significant. Existing techniques are typically rule-based or statistically noisy channel-based. Their accuracies are very low due to their intrinsic limitations on modeling transcription details. We propose direct statistical approaches on transliterating phoneme sequences for English–Chinese name translation. Aiming to improve performance, we propose two direct models: First, we adopt Finite State Automata on a process of direct mapping from English phonemes to a set of rudimentary Chinese phonetic symbols plus mapping units dynamically discovered from training. An effective algorithm for aligning phoneme chunks is proposed. Second, contextual features of each phoneme are taken into consideration by means of Maximum Entropy formalism, and the model is further refined with the precise alignment scheme using phoneme chunks. We compare our approaches with the noisy channel baseline that applies IBM SMT model, and demonstrate their superiority.

Chemical Blockage of the Proteasome Inhibitory Function of Bortezomib: IMPACT ON TUMOR CELL DEATH

This work was supported by a Dermatology Foundation Career Development Award and National Institutes of Health Grant R01 CA107237 (to M. S. S). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Generation of Acyl Anion Equivalents from Acylphosphonates via Phosphonate−Phosphate Rearrangement: A Highly Practical Method for Cross-Benzoin Reaction

[reactions: see text] Acylphosphonates are potent acyl anion precursors that generate acyl anion equivalents under the promotion of cyanide anion via phosphonate-phosphate rearrangement. These anions readily react with aldehydes to provide cross-benzoin products. In this way it is possible to synthesize a variety of aromatic-aromatic, aromatic-aliphatic, and aliphatic-aromatic benzoins. Moreover the reaction of benzoylphosphonate with potent electrophile 2,2,2-trifluoroacetophenone provided the corresponding aldehyde-ketone coupling product in high yield.

New generation of nucleophilic glycine equivalents

A new generation of nucleophilic glycine equivalents, designed to contain a functional framework, that allows control over the physical properties as well as the reactivity, is described. The reactivity of these nucleophilic glycine equivalents have been compared to previously described examples with the application of various transformations such as alkyl halide alkylations, Michael additions, and aldol condensations.

Systematic procedure for the reduction of complex biological reaction pathways and the generation of macroscopic equivalents

In this study, a class of dynamic models based on metabolic reaction pathways is analyzed, showing that systems with complex intracellular reaction networks can be represented by macroscopic reactions relating extracellular components only. Based on rigorous assumptions, the model reduction procedure is systematic and allows equivalent `input–output' representations of the system to be derived. The procedure is illustrated with a few examples, and a comparison is made with another recently published method for generating and evaluating macroscopic reaction schemes.

Copper(I) tert -Butoxide-Promoted Allylation of β-Triphenylsilyl Allylic Alcohols­ via 1,3 C sp² -to-O Silyl Migration

The substitution of the silyl group in vinylsilanes by an allylic group proceeded when β-triphenylsilylallyl alcohols were treated with copper(I) tert-butoxide and allylic halides. This reaction is the first synthetic application of 1,3 C s p 2 -to-O silyl migration which provides a useful method for generation of vinyl anion equivalents.

Copper(I) tert‐Butoxide‐Promoted 1,4‐ Csp2‐to‐O Silyl Migration: Generation of Vinyl Copper Equivalents and Their Stereospecific Cross‐Coupling with Allylic, Aryl, and Vinylic Halides.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Cyclization of unsaturated amides with triflic anhydride and samarium diiodide

A new approach to the generation of acyl radical equivalents has been developed. Treatment of amides with triflic anhydride followed by samarium diiodide allows for cyclization onto appropriately substituted olefins.

Why is glycated LDL more sensitive to oxidation than native LDL? A comparative study

It is well established that oxidative modification of low-density lipoprotein (LDL) plays a causal role in human atherogenesis and the risk of atherosclerosis is increased in patients with diabetes mellitus. To examine the influence of different agents which may influence LDL-glycation and oxidation, experiments including glycation with glucose, glucose 6-phosphate, metal chelators (EDTA) and antioxidants (BHT) were perfomed. The influence of time dependence on the glycation process and the alteration of the electrophoretic mobility of LDL under diverse glycation and/or oxidation conditions was also investigated. The formation of conjugated dienes and levels of lipid peroxides in these different LDL-modifications were estimated. The copper-induced oxidation of LDL in vitro was determined by measurement of thiobarbituric acid reactive substances (TBARS) and expressed as nmol MDA/mg of LDL protein. We found that glycated LDL is more prone to oxidation than native LDL. Using native LDL, the maximal oxidation effect was found to reach a value of 49.72 nmol MDA/mg protein after 8 h. The maximum oxidation of the 31 days, glycated LDL with glucose was 71.76 nmol MDA/mg protein amounting to 144.33% of the value found for native LDL. In the case of glucose 6-phosphate glycation, the maximum oxidation under the same conditions amounted to 173.77% of the value found for native LDL. To measure the extent of glycation, fluorescence of advanced glycation end products (AGEs) was determined (370 nm excitation and 440 nm emission). The most potent glycation agent was glucose 6-phosphate leading to the formation of very high amounts of AGEs. This process was promoted in the absence of EDTA, which prevents the oxidative cleavage of modified Amadori products (ketoamines) to AGEs. We therefore conclude that both processes, glycation and oxidation, result in the modification of LDL. The lower the glycation-rate (+/− EDTA) as measured by relative fluorescence units RFU (generation of AGEs), the lower the additional oxidation rate after glycation as measured by TBARS (generation of MDA equivalents). Glycation and/or oxidation change the electrophoretic mobility of LDL.

Anaerobic metabolism of bacteria performing enhanced biological phosphate removal

Enhanced biological phosphate removal (EBPR) is an established activated sludge process although many of the fundamental metabolic mechanisms are still poorly understood. Therefore, the stoichiometry and enzymatic reactions of the anaerobic phase of this process were studied in a laboratory reactor with acetate as organic substrate. Enzyme assays showed that acetate activation is performed by acetyl-CoA synthetase. Results of 13C-NMR measurements after feeding 13C-labeled acetate indicated that glycogen is degraded via the Entner–Doudoroff pathway. Energy is supplied by glycolysis, hydrolysis of polyphosphate and probably also by hydrolysis of pyrophosphate and the efflux of MgHPO 4. The ratio of phosphate released to acetate taken up is variable and apparently dependent on the contents of polyphosphate and glycogen. A biochemical model is proposed explaining the experimental results in terms of carbon, redox, and energy balances. Anaerobic operation of an incomplete tricarboxylic acid cycle (TCA) is proposed to explain the generation of extra reducing equivalents.

Influence of pancreatic islets on growth and differentiation of hepatocytes in co-culture.

Improvement of cell culture conditions in hepatic tissue engineering may permit cell/tissue banking and the generation of liver tissue equivalents for transplantation. In these systems, continuous hepatotrophic stimulation is still necessary. We investigated the stimulatory effects of pancreatic islets on hepatocytes in co-culture and characterized the stimulatory mechanisms. Hepatocytes and pancreatic islets were harvested from Lewis rats. Cells were cultured on collagen dishes either with nonstimulated media (controls and co-cultures with low or high islet rate) or stimulated media (controls and co-cultures). To characterize stimulatory mechanisms, additional co-cultures with membrane separation, with antiinsulin, antiglucagon, and with both antibodies were examined. Hepatocyte numbers, albumin secretion rate by enzyme-linked immunoadsorbent assay, and monoethylglycinxylidid biotransformation values by fluorescence polarization immunoassay were assessed. A radioimmunoassay measured insulin and glucagon concentrations. In groups with nonstimulated media, cell number was higher in co-cultures with low islet rate, and albumin secretion rate was increased in co-cultures with high islet rate compared to controls. MEGX biotransformation was decreased in co-cultures. In groups with stimulated media, co-culture had no impact on cell number or albumin secretion rate. Hepatocyte numbers and albumin secretion rates were not changed in co-cultures after membrane separation. Islet effects on hepatocytes were reduced in co-cultures with antiinsulin, antiglucagon, or both antibodies. Pancreatic islets provide stimulation for hepatocytes in vitro. Islet effects were mediated by soluble factors, and are dependent on insulin and glucagon. These results permit further investigations towards three-dimensional transplantable hepatocyte-islet devices for continuous in vitro and in vivo stimulation.

On the Generation of Operator Equivalents and the Calculation of Their Matrix Elements

To find all components T(k)±q = Nk,qJq± ∑k−qm=0 (±1)k−ma(k, q; m)Jmz (0 ≤ q ≤ k) of an irreducible tensor operator of rank k, a recursion formula for the coefficients a(k, q; m) is derived. Various kinds of operator equivalents and forms of their expression are examined. Matrix elements of operator equivalents are expressed through the coefficients a(k, q; m). A table for the coefficients a(k, q; m) with k = 2, 4, and 6 is given.

Heteroatom-directed lithiations of chiral alkyl carbamates: A powerful tool for enantioselective synthesis

Abstract

ChemInform Abstract: Generation of Acyl Radical Equivalents by Cathodic Reduction of Acyl Tributylphosphonium Ions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Generation of Acyl Anion Equivalents by In Situ Cathodic Reduction of Acyl Tributylphosphonium Ions Anodically Generated from Tributylphosphine and Carboxylic Acids: Preparation of α‐Hydroxy Cycloalkanones from Keto Acids

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Xylitol formation and reduction equivalent generation during anaerobic xylose conversion with glucose as cosubstrate in recombinant Saccharomyces cerevisiae expressing the xyl1 gene.

Glucose was used as a cosubstrate under anaerobic conditions in the conversion of xylose to xylitol by a recombinant Saccharomyces cerevisiae strain expressing the xyl1 gene. Glucose was metabolized mainly through glycolysis, with carbon dioxide, acetate, and ethanol as end products and with reduction equivalents generated in the glyceraldehyde-3-phosphate dehydrogenase and acetaldehyde dehydrogenase reactions. At a high glucose supply rate, generation of surplus reduction equivalents resulted in simultaneous ethanol formation. On the other hand, at a low glucose supply rate, additional reduction equivalents were generated by simultaneous ethanol consumption. A significantly lower xylitol formation rate was observed.