Quinones fractionation

Several studies have explored the anti-platelet effect produced by naturally occurring quinones. For example, the quinone fraction isolated from Auxemma oncocalyx (Allem/Eo) is a reversible and concentration-dependent inhibitor of human platelet aggregation induced by ADP, arachidonic acid, collagen and thrombin [298], Zhang et al. [299] studied the antiplatelet effects of 2-chloro-3-(4-acetophenyl)-amino-l,4-naphthoquinone. This... 

One of the problems with all the current phenol conversions is that a certain amount of other phenols, such as resorcinol and hydro-quinone, will be formed along with the catechol (don t ask). These species are very hard to separate from the catechol because they are all so similar. Aside of carefully monitored fractional distillation there are some vague strategies which can be found in the Chemical Abstract references 116-118. 

The second study was performed using either cytosolic or microsomal fractions from rat liver as the in vitro metabolic mammal models [238]. The studied compound, benzofuroxan (128, Fig. 20), is metabolized to o-quinone dioxime and 2,3-diaminophenazine (Scheme 4). 

Applications Sollinger and Sawatzki [793] have reported the use of TLC-Raman for routine applications, e.g. TLC of hydroxybenzenes (including hydro-quinone and pyrogallol) on conventional, silica gel and specific Raman-TLC plates (coated with spherical silica gel). Databases were used for identification of substances. Typical detection limits were in the low p,g region per application, Micro-Raman spectrometry has been employed in analysing TLC fractions from polymer additives within a detection limit... 

Air (NB) Collection in ethanol reaction with concentrated HCl and zinc dust react with sodium salt of 1,2-naphtho-quinone-4 sulfonic acid at pH 8.0 extraction with CCl concentration separation by paper chromatography extraction of fractions with CCl ... 

The sample sizes collected by our PMj 5 sampling systems are insufficient to conduct detailed chemical analyses. However, available data for size-fractionated fine particulate matter indicates that PAH quinones, including 1,4-naphthoquinone, 5,12-naphthacenequinone, benz[a]anthracene-7,12-dione, and anthracene-9,10-dione, are important organic components (41, 42). The detection of these molecular species that are similar in structure to semiquinone-type radicals supports the assignment of our EPR signals. 

Zhao, S.X. et al. (2007) NADPH-dependent covalent binding of [3H] paroxetine to human liver microsomes and S-9 fractions identification of an electrophilic quinone metabolite of paroxetine. Chemical Research in Toxicology, 20 (11), 1649-1657. 

Among minor constituents some 0- and S-heterocycles and their alkyl derivatives were detected. No non-PAH-type compound or polar derivatives of PAHs (e.g., quinones) were detected in this fraction by mass spectrometry indicating the effectiveness of the isolation procedure. 

Scheme 34 shows the synthesis of the bc portion (336), which possessed three of the nine asymmetric centers present in cobyric acid. Retrosynthesis determined that (336) could be obtained, via sulfide contraction, from the two intermediates (337) and (338). Ring c was synthesized from (+)-camphor quinone (not shown). Ring b (337) was obtained from 8-methyl-j8-acetylacrylic acid (339), the two adjacent chiral centers being generated in the required relative orientation by a Diels-Alder cycloaddition with butadiene in the presence of tin(IV) chloride. Fractional crystallization served to resolve the diastereomeric a-phenethylamine salts derived from them, eventually affording the compound (340). Oxidation with chromic acid cleaved the double bond in (340) and one of the newly generated... 

C-benzoquinone was used in some of the experiments (37). It was shown that the combined quinone was contained in polymer of comparatively low molecular weight which could be removed from the whole polymer by a fractionation technique the polymer formed during stage (b) was free from combined quinone. 

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