A Naphthoquinone

Determination of structural features. The ultraviolet spectrum has been of value in the determination of the structure of several vitamins. Thus the presence of an a-naphthoquinone system in vitamin K was first detected by this means. Also the 4-methylthiazole and the 2 5-dimethyl-6-aminopyridine system was first identified in vitamin Bj (thiamine), a- and /3-Ionones can be distinguished since the former contains two conjugated chromophores and the latter three conjugated chromophores. 

The epoxide of vitamin K is involved in the regeneration of the anticoagulant vitamin (a naphthoquinone) from the active hydroquinone form (81JA5939). 

Dibydropteridine reductase (from human liver) [9074-11-7] Mr52,000 [EC 1.6.99.7]. Purified to homogeneity on a naphthoquinone affinity adsorbent, followed by DEAE-Sephadex and CM-Sephadex... 

A) -Naphthoquinone.—For the best results this preparation must be carried out rapidly. The vessels and reagents required should be made ready in advance. The oxidizing solution is prepared by dissolving 240 g. (0.89 mole) of ferric chloride hexahydrate in a mixture of go cc. of concentrated hydrochloric acid and 200 cc. of water with heating, cooling to room temperature by the addition of 200-300 g. of ice, and filtering the solution by suction. 

Most investigators have purified a-naphthoquinone by steam distillation, but for the efficient handling of any but very small quantities it appears necessary to use superheated steam in vacuum,and the recovery amounts to only 70 per cent. 

When just a trace of dark impurity is present, as in some of the commercial preparations, a completely pure product is easily obtained by vacuum distillation, but the ordinary crude reaction product is likely to decompose when treated in this manner. The ether method introduced in the present procedure has the advantage of being simple and efficient. It is equally applicable to the purification of the homologues of a-naphthoquinone. 

The allylidenephosphorane (64) with phenanthraquinone gave the pyran (65) together with small amounts of (66) and (67). Similar pyrans were also obtained from (64) and a-naphthoquinone and tetrachloro-o-benzoquinone. 

The introduction of a substituent, especially a free or methylated hydroxyl group, determines a bathochromic shift of band II in the visible region. The 1,4-naphthoquinone absorption bands are at 245, 257, and 335 nm and the bands are at 243, 263, 332, and 405 nm for anthaqninone. The introduction of a substituent (especially a hydroxyl group) in the aromatic ring of a naphthoquinone determines a strong bathochromic effect (up to 100 nm) and some UV bands are shifted into the visible (vis) region. 

Reduction of monocyclic aromatic nitro compounds has been demonstrated (a) with reduced sulfur compounds mediated by a naphthoquinone or an iron porphyrin (Schwarzenbach et al. 1990), and (b) by Fe(II) and magnetite produced by the action of the anaerobic bacterium Geobacter metallireducens (Heijman et al. 1993). Quinone-mediated reduction of monocyclic aromatic nitro compounds by the supernatant monocyclic aromatic nitro compounds has been noted (Glaus et al. 1992), and these reactions may be signihcant in determining the fate of aromatic nitro compounds in reducing environments (Dunnivant et al. 1992). 

Oxidation of the aminonaphthols 91 gives the quinone spiroketals 92, analogues of palmarumycin <00TL9105>. The first total synthesis of (+)-diepoxin a 93 has been achieved from a naphthoquinone . 

The novolac sample, which was provided by Kodak, was synthesized from pure meta-cresol and formaldehyde. It has a weight average molecular weight of 13,000 and a very broad polydispersity of 8.5. The polymer was purified by two precipitations from tetrahydrofuran into hexane. The PAC was a naphthoquinone-1,2-(diazide-2-)-5-sulfonyl ester provided by Fairmount Chemical (Positive Sensitizer 1010). A hydroxyl substituted benzophenone is attached to the sulfonyl ester. The spreading solvent was isopropyl acetate, which was obtained from Aldrich Chemicals and used as received. 

As the final example of the simplified treatment of an aromatic ring, a novel potential energy calculation of a naphthoquinone derivative (36) with a program called EENY will be briefly mentioned (155). This program seems to resemble WMIN in that it calculates only van der Waals energy. The rotation around the cyclopropyl-quinonoid bonds is calculated to have a barrier of about 10 kcal/mol. In this and another case (156), the results could be considerably improved by full relaxation MM calculations. 

The phytochemical reducibility of quinones was first demonstrated in the case of p-xyloquinone. This compound is worthy of interest since it is very easily formed from diacetyl by purely chemical means through a type of aldol condensation followed by ring closure. It is reduced to p-xylohydroquinone by fermenting yeast. Benzoquinone, thymoquinone and a-naphthoquinone similarly yield the corresponding hydroquinones. Tetrabromo-o-quinone and anthraquinone proved resistant to attack, while phenanthraquinone could be reduced phyto-chemically to phenanthrahydroquinone in poor yield (9%). Phytochemical reduction can also be accomplished in the dicyclic terpene series. According to unpublished experiments by Neuberg and Peiser, 2,3-dihy-... 

Atovaquone is a naphthoquinone whose mechanism of action involves inhibition of the mitochondrial electron transport system in the protozoa. Malaria parasites depend on de novo pyrimidine biosynthesis through dihy-droorotate dehydrogenase coupled to electron transport. Plasmodia are unable to salvage and recycle pyrimidines as do mammalian cells. 

A. Liposomal amphotericin B was approved by the US. Food and Drug Administration to treat visceral leishmaniasis. Pentavalent antimony compounds, pentamidine, amphotericin B, and aminosi-dine (paromomycin) have all been demonstrated efficacious here. The liposomal amphotericin appears to be better taken up by the reticuloendothelial system, where the parasite resides, and partitions less in the kidney, where amphotericin B traditionally manifests its toxicity. In addition to being better tolerated by patients, it has proved to be very effective in India, where resistance to antimony drugs is widespread. This patient appears to have acquired his infection there, where many infected patients develop darkening of the skin, hence the name kala-azar, or black sickness. Albendazole, an anthelmintic, has no role here. Atovaquone, a naphthoquinone, is used to treat malaria, babesiosis, and pneumocystosis. Pyrimethamine-sulfadoxine is used to treat malaria and toxoplasmosis. Proguanil inhibits the dihydrofolate reductase of malaria parasites and is used in combination with atovaquone. 

Combs AB, Porter TH, Folkers K. Anticoagulant activity of a naphthoquinone analog of vitamin K and an inhibitor of coenzyme Qjo-enzyme systems. Res Commun Chem Pathol Pharmacol 1976 13 109-114. 

Stabilization of a radical anion of humic acid may be caused by an adsorption effect. Bijl (3) observed that solid barium hydroxide octahydrate turned blue when placed in a solution of quinhydrone the blue solid was highly paramagnetic. Under the conditions we used for preparing these salts, insoluble sodium humate (with a large surface area) could have stabilized the anion radical by adsorption from the basic solution. Weiss and McNeil (18) observed a similar phenomenon with base soluble xanthenes, and proposed that biradicals may be formed in such a system. His compounds, however, do not appear to have the structural requirements to satisfy such a stabilized system. The recent report by Weber (29) on the spin content increase associated with the basification of a naphthoquinone-naphthohydroquinone system seems to parallel our observations quite closely. 

In some instances, the electrophilic ring closure reaction can be replaced by a nucleophilic reaction in an alkaline medium, such as used for polyfluorinated derivatives the compound obtained by condensing 2,3-dichloro-a-naphthoquinone with ethyl acetoacetate thus undergoes ring closure344 (Scheme 1). 

Reaction centers of purple bacteria typically contain three polypeptides, four molecules of bacteriochlorophyll, two bacteriopheophytins, two quinones, and one nonheme iron atom. In some bacterial species, both quinones are ubiquinone. In others, one of the quinones is menaquinone (vitamin K2), a naphthoquinone that resembles ubiquinone in having a long side chain (fig. 15.10). Reaction centers of some species, such as Rhodopseudomonas viridis, also have a cytochrome subunit with four c-type hemes. 

The complexes obtained in this way are converted to the corresponding a-naphthoquinones by CAN, I2, FeCl3, or FeCl3-DMF in 65-70%yield.3 The reaction is somewhat regioselective with unsymmetrical alkynes (equations II, III, and IV). 

Oxidation of the dye during chroming with dichromate creates a naphthoquinone structure in the molecule. Two other important black dyes are C.I. Mordant Black 3, 14640 [3564-14-5] (25, R = H), and C.I. Mordant Black 11 (see Section 3.9.3). 

A naphthoquinone unit is located at the end of a molecular wire to fit into the pocket (so-called quinone pocket) from which VKi has been extracted. 

The oxidative effect of the DMSO/PhNCO system on cellulose was confirmed by means of alcoholic model compounds (60, 62, 64) that were neatly oxidized into the corresponding ketones. The presence of the active species, the oxidatively acting sulfonium ylide 66, in the cellulose carbanilation mixture was proven by trapping with two reagents, a tocopherol-based compound (48) and a naphthoquinone (68) that was also used in a facile color test to estimate the degrading effect of certain carbanilation mixtures and conditions on cellulose. 

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