Diels-Alder approaches to model compounds related to fredericamycin A

Evans, Jonathan; Klix, Russell C.; Bach, Robert D.

doi:10.1021/jo00258a022

Cited by 47 publications

(22 citation statements)

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Section: Discussionmentioning

confidence: 99%

“…Organic compounds like CHD are known to undergo aromatization during oxidation, yielding hydroquinone (H 2 Q) and finally quinone (Q) as products. [21][22][23] A simple skeleton scheme for the uncatalyzed CHD oscillator is This scheme neglects reactions of hydroquinone.An alternative simple scheme can be obtained by substituting reactions R11-R15 for reactions R6, R7, R9, and R10:Here HQ • is semiquinone. In reality, all the above reactions can take place, together with many others.…”

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confidence: 99%

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Bromate−1,4-Cyclohexanedione−Ferroin Gas-Free Oscillating Reaction. 1. Basic Features and Crossing Wave Patterns in a Reaction−Diffusion System without Gel

et al. 1996

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We present a study of the bromate-1,4-cyclohexanedione-ferroin oscillating reaction in both well-stirred and reaction-diffusion systems. We investigate the dependence of the system dynamics on the initial reagent concentrations, with the initial concentration of ferroin varied from 0 to 5 × 10 -3 M, and show that the system behaves like a typical BZ oscillator if the concentration of ferroin exceeds 5 × 10 -5 M. We demonstrate spontaneous formation of spiral waves and transverse wave fronts in quasi-two-dimensional systems and formation of crossing wave patterns in thin layers of solution open to air. IntroductionThe Belousov-Zhabotinsky (BZ) reaction-diffusion system is perhaps the most commonly employed tool for experiments on chemical waves and pattern formation. [1][2][3][4][5][6][7] The ferroincatalyzed reaction with malonic acid as the initial reductant has been the most frequently used BZ system for this purpose. An important drawback of this reaction is the production of carbon dioxide, which results in the formation of bubbles that disturb the reaction-diffusion patterns and make it difficult to conduct lengthy experiments in either batch or open reactors. Attempts have been made to develop gas-free versions of the BZ reaction. 8 Unfortunately, these variants do not generate the range of chemical wave behavior found in the ferroin-malonic acid BZ reaction. Recently, showed that target patterns develop in the bromate-1,4-cyclohexanedione-ferroin reaction-diffusion system without formation of bubbles. They used ferroin at a concentration of 5 × 10 -4 M and considered it to be only an indicator, implying that the reaction is an uncatalyzed bromate oscillator (UBO). [9][10][11][12] Here we present further results related to both the uncatalyzed and the ferroin-catalyzed systems. We study the dependence of the system dynamics on the initial reagent concentrations, with that of ferroin varied from 0 to 5 × 10 -3 M, and show that the system behaves like a typical BZ oscillator if the concentration of ferroin exceeds 5 × 10 -5 M.The absence of bubbles and precipitate makes the present system an excellent tool for experiments on chemical waves and patterns. We demonstrate spontaneous formation of spiral waves and transverse wave fronts in quasi-two-dimensional systems and the formation of crossing wave patterns in thin layers of solution open to air.Some preliminary mechanistic considerations are also suggested. Experimental SectionMaterials. Stock solutions of 1.0 M NaBrO 3 (Janssen Chimica, 99+%), 0.3 M 1,4-cyclohexanedione (abbreviated as CHD) (Aldrich, 98%) dissolved in 1.0 M H 2 SO 4 by stirring the solution on a hot plate (40-50°C) for about 30 min, 0.025 M ferroin (prepared from the calculated amount of FeSO 4 ‚7H 2 O (Fisher, certified) and 1,10-phenanthroline (Aldrich, 99+%)), 0.2 M NaBr (Fisher, certified), and 1.0-10.0 M H 2 SO 4 were used to prepare the working solutions.Apparatus and Procedures. Batch experiments with the bromate-CHD and the bromate-CHD-ferroin systems were performed in a thermosta...

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Section: Discussionmentioning

confidence: 99%

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confidence: 99%

Bromate−1,4-Cyclohexanedione−Ferroin Gas-Free Oscillating Reaction. 1. Basic Features and Crossing Wave Patterns in a Reaction−Diffusion System without Gel

et al. 1996

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“…In the following only reaction times, chromatography details (eluant, Rf), isolated yield, physical constants and spectroscopic data are given. 5 . To a solution of (15.4 g, 0.1 mol) of 2,4-dihydroxybenzoic acid in 20% NaOH (50 mL) was added (10.41 mL, 0.11 mol) of dimethyl sulfate.…”

Section: Resultsmentioning

confidence: 99%

Base-promoted acetal formation employing aryl salicylates

Boontheung¹,

Perlmutter²,

Puniani³

2001

Arkivoc

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“…detected lipids from a single cell (length, ~100 µm) with a resolution of ~7 µm . However, when imaging tissue sections with a length of several centimeters is carried out, the clustering of DHB can affect the intensity of the MS spectra . Recently, Hankin et al .…”

Section: Discussionmentioning

confidence: 99%

Improved spatial resolution of matrix-assisted laser desorption/ionization imaging of lipids in the brain by alkylated derivatives of 2,5-dihydroxybenzoic acid

Stoyanovsky

Sparvero

Amoscato

et al. 2014

Rapid Commun. Mass Spectrom.

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RATIONALE Matrix‐assisted laser desorption/ionization (MALDI) is one of the major techniques for mass spectrometry imaging (MSI) of biological systems along with secondary‐ion mass spectrometry (SIMS) and desorption electrospray mass spectrometry (DESI). The inherent variability of MALDI‐MSI signals within intact tissues is related to the heterogeneity of both the sample surface and the matrix crystallization. To circumvent some of these limitations of MALDI‐MSI, we have developed improved matrices for lipid analysis based on structural modification of the commonly used matrix 2,5‐dihydroxybenzoic acid (DHB). METHODS We have synthesized DHB containing ‐C6H13 and ‐C12H25 alkyl chains and applied these matrices to rat brain using a capillary sprayer. We utilized a Bruker Ultraflex II MALDI‐TOF/TOF mass spectrometer to analyze lipid extracts and tissue sections, and examined these sections with polarized light microscopy and differential interference contrast microscopy. RESULTS O‐alkylation of DHB yields matrices, which, when applied to brain sections, follow a trend of phase transition from crystals to an oily layer in the sequence DHB → DHB‐C6H13 → DHB‐C12H25. MALDI‐MSI images acquired with DHB‐C12H25 exhibited a considerably higher density of lipids than DHB. CONCLUSIONS Comparative experiments with DHB and DHB‐C12H25 are presented, which indicate that the latter matrix affords higher lateral resolution than the former. Copyright © 2014 John Wiley & Sons, Ltd.

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Diels-Alder approaches to model compounds related to fredericamycin A

Cited by 47 publications

References 5 publications

Bromate−1,4-Cyclohexanedione−Ferroin Gas-Free Oscillating Reaction. 1. Basic Features and Crossing Wave Patterns in a Reaction−Diffusion System without Gel

Bromate−1,4-Cyclohexanedione−Ferroin Gas-Free Oscillating Reaction. 1. Basic Features and Crossing Wave Patterns in a Reaction−Diffusion System without Gel

Base-promoted acetal formation employing aryl salicylates

Improved spatial resolution of matrix-assisted laser desorption/ionization imaging of lipids in the brain by alkylated derivatives of 2,5-dihydroxybenzoic acid

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