A Hydroxyquinones

Note The detection limits for a-hydroxyquinones and 5-hydroxyflavones are 5 pg [1] and for histidine 20 ng substance per chromatogram zone [3]. 

The biological mechanism of action is helieved to involve the production of superoxides near the DNA strand, resulting in DNA backbone cleavage and cell apoptosis. The actual mechanism is not yet known, but is believed to proceed from the reduction of molecular oxygen into superoxide via an unusual auto-redox reaction on a hydroxyquinone moiety of the compound following. There is also some speculation the compound becomes activated into its reactive oxazolidine form. 

Humic acido from ooilo and ligniteo have been examined by ERR spectrometry. All samples showed a stable free organic radical content of about 1018 spins per gram. When these samples were converted to their sodium salts, a marked increase in radical content occurred. This was interpreted to indicate that a quinhydrone moiety exists in the humic acid macromolecule. Synthetic humic acid, prepared by oxidizing catechol in the presence of amino acids, also showed similar ERR spectra, as did selected quinhydrone model compounds. The radical moiety appeared to be stable to severe oxidation and hydrolytic conditions. Reduction in basic media caused an initial decrease in radical species continued reduction generated new radical species. A proposed model for humic acid based on a hydroxyquinone structure is proposed. 

Hydroxyquinone annelation. The lithio anion (2) of 1 adds to the vinylogous silyl ether 3 to provide the adduct 4. Conversion to the aldehyde and epoxidation results in 6, which undergoes cyclization in base to a hydroxyquinone, best isolated as the methyl ether 7. This quinone annelation fails when applied to an acyclic vinylogous silyl ether. 

FIGURE 12.5 A hydroxyquinone is a minor but important side product in the reaction of alkaline peroxide with f-hutyl-o-quinone. (After Gellerstedt, G., Hardell, H-L., and Lindfors, E-L., Acta. Chem. Scand., B 34, 669-673, 1980.)... 

Herz et al.hli assigned to the yellow adduct of levopimaric acid (1) and 1,4-benzo-quinone the structure (2) and found that a solution of 5 g. of (2) in 75 ml. of /-butanol treated with a solution prepared from 0.7 g. of potassium and 50 ml. of /-butanol and then with a stream of oxygen for 3 hrs. developed a deep purple color. Addition of 60 ml. of water and removal of the solvent left a purple residue from which by acidification, solvent extraction, and chromatography a hydroxyquinone (3) was isolated in 20% yield. A distinction was not made between the two possible positions for the hydroxyl group. 

This small group of hydroxyquinone (1.16), arylaminoquinone (1.17) and aminophthalimide (1.18) derivatives has contributed a few members of some application ranges, mainly yellow disperse dyes and reddish brown vat dyes, but there are superior alternatives available from the major chemical classes. 

The oxygens of methoxynaphthazarin 247 (Scheme 65) (white arrows) can be selectively ortho acetylated/methylated. Starting from the acetates or polyacetates of Scheme 65, it is possible to prepare a variey of polycyclic hydroxyquinone... 

Rueping has further developed this theme by showing that diarylprolinol ether 55 efficiently catalyses the addition of hydroxyquinones to a variety of a,P-unsatu-rated aldehydes as a method for the preparation of both 1,4- and 1,2-naphthoquinones with remarkable levels of enantioselectivity [98],... 

The sulfur tetrafluoride fluorination of most nonhalogenated quinones and hydroxyquinones is erratic in behavior and generally occurs with isomerization, substitution of a hydrogen atom by fluorine, and addition of fluorine to the carbon atom / to the carbonyl group. Thus, the fluorination of benzo-l,4-quinone results in aromatization to give 1,2,4-trifluorobenzene (8) as the sole product.41... 

An EPR spectral survey of a selected number of hydroxyquinones showed that they all formed stable radical salts which could be reversibly converted to the acid form of low or negligible spin content. Significantly, many of these hydroxyquinones were stable free radicals in the acid form although the radical content was quite low (Table IV). 

In a recent study S. E. Moschopedis (II) produced some direct evidence for the presence of quinones and hydroxyquinones in coal and humic acid, and infrared examination of products obtained in the course of the present investigation clearly indicated the existence of five-membered cyclic anhydrides in the reactant mixtures. 

Quinone Diazides. E. von Herz (Ref 1) proposed the use of nitrated quinone diazides and tetra-zides of polyhydric phenols or their metallic salts in percussion caps and primers, either as a top charge over a main charge (Tetryl, PETN or TNT), or in mixts with usual primary expls such as LA, MF, etc. Typical compds were 4,6-dinitro-2-quinone diazide, the K salt of dinitro-3-hydroxy quin one diazide, metallic salts of dinitro-4-hydroxyquinone diazide, the Pb salt of dinitro-3,5-dihydroxyquinone diazide, and sym-tetra-nitrodihydroxydiphenylolquinone tetrazide J.E. Burns (Ref 2) proposed the use of nitrated quinone diazides, such as the 2,6-dinitro-2-diazide, with Pb pic rate, Na nitrate, Pb thio-... 

Conjugate addition of acyl groups to naphthoquinones (3, 211).2 The acyl nickel carbonylate anion (1) undergoes conjugate addition to the ethylene ketal 2 to form a lithium adduct that can be trapped by allyl iodide to give 3 in 81% yield. This product can be converted in a few steps to the hydroxyquinone 4, a precursor of the naphthoquinone antibiotic deoxyfrenolicin (5). 

The most common chelating agents used to extract metals from water samples are ammonia pyrolidine dithiocarbamate (APDC) and 8-hydroxyquinone. Methyl isobutyl ketone (MIBK) is generally used as a solvent. In a typical extraction, 1 mL of APDC is added to 50 to 100 mL of aqueous sample in a volumetric flask. The pH of the aqueous sample is adjusted for maximum extraction of the analyte of interest. Then 10 mL of MIBK is added (the volumetric ratio of sample to MIBK is usually less than 40) and the mixture is vigorously shaken for 30 seconds. The metal chelate partitions into the organic phase, which floats on the water. More water can be added to raise the organic level into the neck of the flask so that it can be... 

Preincubation of human liver microsomes (HLMs) with cannabidiol decreased the formation of all detectable metabolites of cyclosporine, a substrate of CYP3A (9). Cannabidiol is metabolized by CYP3A to form a cannabidiol hydroxyquinone. This metabolite binds to the apoprotein of CYP3A and renders it inactive (10). 

Bomheim L, Grille M. Characterization of cytochrome P450 3A inactivation by cannabidiol possible involvement of cannabidiol-hydroxyquinone as a P450 inactivator. Chem Res Toxicol 1990 11 1209-1216. 

Natural sunlight induced photooxidation of naphthalene in aqueous solution has also been reported by McConkey et al. to produce six major products including 1-naphthol, coumarin, and two hydroxyquinone [9]. The authors proposed that the initially formed 2 + 2 and 2 + 4 photo cyclo addition products undergo subsequent oxidation and/or rearrangement to form the observed products [9]. Grabner et al. have studied solvent effects on the photophysics of naphthalene and report that fluorescence lifetime decreases by a factor of 2.5 in aqueous solution compared to organic solvents (e.g. ethanol, hexane, acetonitrile) [10]. Based on the observed differences in naphthalene excited triplet state properties in aqueous and organic media, the decrease... 

---