Hydroxynaphthoquinone

Brimble and McEwan (206) investigated the Diels-Alder reaction between naphthoquinones and cyclopentadiene using these catalysts. Acetylnaphthoqui-none reacts with cyclopentadiene in the presence of 67 Cu(OTf)2 to provide the cycloadduct in low selectivity (30% ee). Catalysts 269c and 269d afford lower selectivities. Improved selectivities are observed using 5-hydroxynaphthoquinone [50% ee with 67 Cu(OTf)2]. 

In this case, a plot of log krcl versus h(W) for a series of substituted nitrobenzenes should yield a straight line with a slope of (1/0.059), which as is shown in Figure 9, is actually found for the compounds listed in Table 7. Hence, for the reduction of neutral substituted nitrobenzenes in homogeneous aqueous hydrogen sulfide solution with lawson as electron-transfer mediator, the relative reaction rate of a given compound may be predicted from its one-electron reduction potential. Similar results have been obtained for the same set of compounds with another quinone (i.e., 5-hydroxynaphthoquinone (reaction 10 in Table 5) see Schwarzenbach et al. (in press b). 

The black walnut tree has often been observed to inhibit the growth of numerous species of plants (see Table 18.11). The area of inhibition usually corresponds closely with the spread of the root system. Juglone (5-hydroxynaphthoquinone), which is present in both the roots and aerial parts of the plant is thought to be the toxic factor. 

Binaphthol (B1N0L)-Ti complexes 100 are found to be effective catalysts in NED D-A reactions. It catalyzes the reaction of 5-hydroxynaphthoquinone with butadienyl acetate in 86 % yield and 96 % ee of cnJo-product. This intermediate is useful in the synthesis of anthracycline antibiotics [86]. 

Atovaquone, a hydroxynaphthoquinone, selectively inhibits the respiratory chain of protozoan mitochondria at the cytochrome bcl complex (complex III) by mimicking the natural substrate, ubiquinone. Inhibition of cytochrome bcl disrupts the mitochondrial electron transfer chain and leads to a breakdown of the mitochondrial membrane potential. Atovaquone is effective against all parasite stages in humans, including the liver stages. 

HPLC ESI MS is also a useful tool in the analysis of non-anthraquinone red dyestuffs. The use of this technique allows the identification of carthamin as the main colour component of safflower.[34] Ten species of the genus Alkanna are extracted with hexane, and dissolved in water-methanol solution after evaporation. [47] Ammonium formate buffer (pH 3.0) was used as the mobile phase modifier. In the preparations, alkannin and many hydroxynaphthoquinones (alkannin derivatives) were identified by comparison of retention times, as mass spectra (in the NI mode) for all compounds consisted only of quasi-molecular peaks. 

Without ion-radical initiation, the yield of the resulted product reaches 50% for 24 h. Practically the same yield can be achieved for the same time in the presence of tris(4-bromophenyl)ammoniumyl hexachloroantimonate and for only 6 h on sonication (Nebois et al. 1996). Sonication accelerates the rate-determining formation of the diene cation-radical. Of course, hydroxynaphthoquinone is strong enough as an electron-acceptor with respect to 2-butenal Af,Af-dimethylhydrazone. Therefore, the question remains whether sonication is more or less the general method for the initiation of ion-radical cycloaddition. A possible role of sonication in optimization of ion-radical reactions was considered in Section 5.2.5. 

Atovaquone, a hydroxynaphthoquinone (Figure 52-2), was initially developed as an antimalarial agent, and as a component of Malarone is recommended for treatment and prevention of malaria. Atovaquone has also been approved by the FDA for the treatment of mild to moderate P jiroveci pneumonia. 

Crystallization from alcohol containing a trace of acetic acid gives glistening yellow needles, melting with decomposition at about 191-1920. The red samples of hydroxynaphthoquinone often mentioned in the literature are not completely pure. Such material, or crude material of any kind, is best purified through either the sodium salt or the methyl ether. 

The second method is that described above /3-naphthol is converted through the nitroso derivative and i-amino-2-naph-thol-4-sulfonic acid into naphthoquinone sulfonate, and this is subjected to acid hydrolysis. The sulfonate can be converted directly into hydroxynaphthoquinone by the action of concentrated sulfuric acid,3,4 but the process is not so easily controlled as when the quinone is etherified as it is formed, and the ether subsequently hydrolyzed.4 The overall yield from /3-naphthol is 46 per cent of the theoretical amount, but all the reagents are inexpensive, and with ordinary apparatus, 150 g. of hydroxynaphthoquinone can be made conveniently in one run (from 300 g. of /3-naphthol). 

The classical forerunner of metallizable hydroxyanthraquinones was alizarin (1), which was widely used in the production of very fast, bright red shades on cotton by the mordant technique (Section 58.1). Early studies by Pfeiffer140 demonstrated that metal complex formation involved the carbonyl group and the a-hydroxy group (208) rather than the two hydroxy groups and led to intensive research on metal complexes of 1 -hydroxyanthraquinones and related compounds such as 8-hydroxynaphthoquinone. This is the subject of a number of reviews3a Jc141 and will only be considered briefly here. 

A major problem in the use of the antiparasitic 4-hydroxyquinolones and 2-hydroxynaphthoquinones is resistance that can develop with extraordinarily high frequency. It may be attributable to their mitochondrial site of action, which is known to have a high frequency of mutation. 

Pd(II)/Cu(I)-promoted reactions of the 2-hydroxynaphthoquinone ylide 283 with terminal alkynes or their tributylstannane derivatives afford moderate yields of furonaphthoquinones 284 (Scheme 81) (97TL837). It was... 

When a brown natural dyeing turns yellow upon vatting with sodium dithionite and ammonia and the original shade returns upon reoxidation, the dyeing probably was produced with walnut shells (C.I. Natural Brown 7) or some other hydroxynaphthoquinone. 

The reaction of resorcinols with a,P-unsaturated aldehydes and ketones catalysed by ethylenediamine diacetate has been used to synthesise the naturally occurring chromenes confluentin and daurichromenic acid <05OBC3955, 05TL7539>. 2-Hydroxynaphthoquinone behaves similarly providing a useful route to pyranonaphthoquinones <05S3026>. 

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