5.8- Dihydroxy-2- -1,4-naphthoquinone

Glycol esters from oxido compounds (o-Dihydroxy) naphthoquinones s. 13, 192 G G G(OAc)G(OAc)... 

Reduction, (a) By sulphurous acid. Benzoquinone, /> toluquinone, 1,2-naphthoquinone are readily reduced by SOj ultimately to the dihydroxy-compound. Thus benzoquinone gives colourless hydro-quinone or quinol, />-C2H4fOH)2. 

Animals caimot synthesize the naphthoquinone ring of vitamin K, but necessary quantities are obtained by ingestion and from manufacture by intestinal flora. In plants and bacteria, the desired naphthoquinone ring is synthesized from 2-oxoglutaric acid (12) and shikimic acid (13) (71,72). Chorismic acid (14) reacts with a putative succinic semialdehyde TPP anion to form o-succinyl benzoic acid (73,74). In a second step, ortho-succmY benzoic acid is converted to the key intermediate, l,4-dihydroxy-2-naphthoic acid. Prenylation with phytyl pyrophosphate is followed by decarboxylation and methylation to complete the biosynthesis (75). 

Naphthazarin (5,8-dihydroxy-1,4-naphthoquinone) [475-38-7] M 190.2, m 220-230°(dec), m 225-230°, pKEst(i) 9.5, pKEst(2) ll-l Red-brown needles with a green shine from EtOH. Also recrystd from hexane and purified by vacuum sublimation. [Huppert et al. J Phys Chem 89 5811 1985.] It is sparingly soluble in H2O but soluble in alkalis. It sublimes at 2-10mm. The diacetate forms golden yellow prisms from CHCI3, m 192-193° and the 5,8-dimethoxy derivative has m 157° (155°) (from pet ether) [Bruce and Thompson J Chem Soc 1089 7955 IR Schmand and Boldt J Am Chem Soc 97 447 1975 NMR Brockmann and Zeeck Chem Ber 101 4221 1968]. The monothiosemicarbazone has m 168°(dec) from EtOH [Gardner et al. J Am Chem Soc 74 2106 7952]. 

Alkylamination of naphthazarin copper complex (37)22 gives predominantly a mixture of 2(or 3),5-bis(alkylamino)-8-hydroxy-l,4-naphthoquinone (38) and 2,6-bis(alkylamino)-4,8-dihydroxy-l, 5-naphthoquinone... 

Lithium aluminum hydride reduced p-benzoquinone to hydroquinone (yield 70%) [576] and anthraquinone to anthrahydroquinone in 95% yield [576]. Tin reduced p-benzoquinone to hydroquinone in 88% yield [174] Procedure 35, p. 214). Stannous chloride converted tetrahydroxy-p-benzoquinone to hexa-hydroxybenzene in 70-77% yield [929], and 1,4-naphthoquinone to 1,4-di-hydroxynaphthalene in 96% yield [180]. Other reagents suitable for reduction of quinones are titanium trichloride [930], chromous chloride [187], hydrogen sulfide [248], sulfur dioxide [250] and others. Yields are usually good to excellent. Some of the reagents reduce the quinones selectively in the presence of other reducible functions. Thus hydrogen sulfide converted 2,7-dinitro-phenanthrene quinone to 9,10-dihydroxy-2,7-dinitrophenanthrene in 90% yield [248]. 

Further reduction of quinones - acquisition of four or more hydrogens per molecule - was achieved with lithium aluminum hydride which reduced, in yields lower than 10%, 2-methyl-1,4-naphthoquinone to 1,2,3,4-tetrahydro-l,4-dihydroxy-2-methylnaphthalene and to l,2,3,4-tetrahydro-4-hydroxy-l-keto-2-methylnaphthalene [931]. Lithium aluminum hydride [931], sodium borohydride, lithium trie thy Iborohydride and 9-borabicyclo[3.3.1Jnomine [100] converted anthraquinone to 9,10-dihydro-9,10-dihydroxyanthracene in respective yields of 67, 65, 77 and 79%. 

This enzyme [EC 1.14.99.27] catalyzes the reaction of 5-hydroxy-l,4-naphthoquinone with AH2 and dioxygen to produce 3,5-dihydroxy-l,4-naphthoquinone, A, and water. The enzyme can also use 1,4-naph-thoquinone, naphthazarin, and 2-chloro-l,4-naphthoquinone as substrates, but not other related compounds. 

Menaquinone. The incorporation of [2- C]mevalonate and [2- C]-2-methyl-l,4-naphthoquinone into MK-4, normally considered a bacterial quinone, has been demonstrated in marine invertebrates such as crabs and starfish." Incorporation into 2,3-epoxy-MK-4 (163) was also observed. Cell-free extracts have been prepared from Escherichia coli which catalyse the conversion of o-succinylbenzoic acid (164) into l,4-dihydroxy-2-naphthoic acid (165) and menaquinones. In the presence of farnesyl pyrophosphate the major menaquinone produced was MK-3. Genetic studies with mutants of E. coli K12 that require (164) offer support for the generally accepted pathway for MK biosynthesis via (164) and (165)." The enzyme system that catalyses the attachment of the polyprenyl side-chain to 1,4-dihydroxy-2-naphthoic acid to form demethylmenaquinone-9 (166) has been isolated from E. colU ... 

As with the simple 1,4-naphthoquinones, most recent research activity in the heteroannelated compounds has been directed towards the development of dyes that absorb in the near-infrared. Noteworthy is the dithiadinaphtho-1,4-naphthoquinone system 16 (X = S), which can be prepared by condensing 2,3-dichloro-5,8-dihydroxy-1,4-naphthoquinone with 2-aminothiophenol [25], The parent compound 16 (X = S) [96692-25-0] shows multiple absorption bands between 400 and 800 nm, with the most intense peak at 725 nm in chloroform (rmax 15 200 L mob1 cm-1) [25], Oxidation of the sulfur atoms to SO groups produces a large bathochromic shift, and 16 (X = SO) shows a peak at 827 nm (emax 17 600 L mol-1 cm-1) in chloroform [25],... 

Some naturally occurring prenylated juglone derivatives have been synthesized from 2,8-dihydroxy-1,4-naphthoquinone as it is illustrated in Fig. (20) [156],... 

The enthalpies of formation of arenolquinones appear in Table 8. In reviewing the data there and in Table 1, note the identical solid phase enthalpies of formation of 1,4-naphthoquinone and 9,10-anthraquinone and the identical solid phase enthalpies of formation of 5,8-dihydroxy-l,4-naphthoquinone and l,4-dihydroxy-9,10-anthraquinone. These... 

Dihydroxy-5,8-naphthoquinones, chemical shifts for, isotope effects on 345... 

This paper reports the syntheses and characterization of complexes of cls-Pta2Cl2 with 5-hydroxy-l,4-naphthoquinone (HNQ), 5,8-dihydroxy-l,4-naphthoqulnone (DHNQ), l,4-dlhydroxy-9,10-anthraqulnone (DHAQ) and with DOXO. In addition It reports preliminary results of to vivo experiments performed with complexes cis-Pta2Cl2/DOXO and cls-Fta2Cl2/qulnlzarto. 

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