1,4,5,8-tetra-substituted anthraquinone

Pyrazolone dyes are particularly versatile yellow chromophores the yellow dye developer used in Polacolor, the first instant color film, was based on a pyrazolone dye. The stmctures of the three Polacolor dyes are shown in Figure 3. The study of azo dyes derived from 4-substituted 1-naphthols led to the chromophore used in the Polacolor magenta dye developer. The Polacolor cyan dye developer contained a 1,4,5,8-tetra-substituted anthraquinone as chromophore (20). 

The strength of electron-donor groups iacrease ia the order OH < NH < NHR < HNAr. Tetra-substituted anthraquiaones (1,4,5,8-) are more bathochromic than di- (1,4") 01 trisubstituted (1,2,4-) anthraquiaones. Thus, by an appropriate selection of donor groups and substitution patterns, a wide variety of colors can be achieved (see Dyes, anthraquinone). 

Nucleobases and nucleosides are common motifs for hydrogen-bonded supramolecular arrays. Ng et al. first reported a series of phthalocyanine-nucleobase conjugates [64], The tetra-adenine phthalocyanine 64 was prepared by standard <9-alkylation of zinc(II) tetrahydroxyphthalocyanine with 9-(2-bromoethyl)adenine in the presence of K2CO3. The fluorescence of 64 is quenched substantially upon addition of thymine-substituted 9,10-anthraquinone 65, and the rate is much faster compared with that for the situation when the unsubstituted 9,10-anthraquinone is used as the quencher. These results suggest that 64 forms a supramolecular complex with 65 through the Watson-Crick base-pairing interactions. 

The anthraquinone derivative (2) represents the first example from 1997, with numerous others following in rapid succession, including the dibenzo-phenanthroline derivatives and tri-substituted acridines (3), which were reported to inhibit telomerase action in tumour cell lines with IC50 values of up to 28 and 60 nM, respectively. The tri-substituted acridines (3) were developed from the simple acridine (4) on the basis of structure-based design principles to maximise the quadruplex binding affinity. Thus, inhibition of telomerase by these compounds appears to be correlated to selective stabilisation of the human DNA quadruplex structure. Tetra-(A-methyl-4-pyridyl)-porphyrins... 

Examples of tetrapyrroles include porphyrins and porphyrin derivatives and more specifically, chlorophylls, heme pigments and bilins. Examples of tetra-terpenoids or carotenoids include carotenes and xanthophylls. Examples of quinines include benzo-quinones, anthraquinones and naphthiquinones. Examples of oxygen-containing heterocyclic compounds such as flavonoids include anthocyanins and flavonols. Examples of nitrogen-containing heterocyclic compounds include indigoids and indole derivatives, such as betalaines and eumelanins, and substituted pyrimidines such as pterins and purines. 

Lam et al. 226) have reported syntheses of valsarin and 2,4-di-chloroemodin and a new synthesis of 2-chloroemodin (Scheme 18). Thus Friedel-Crafts acylation of a substituted resorcinol (162) with 3-methoxy-5-methylphthalic anhydride gave a crude benzophenone which was treated with boric oxide-sulfuric acid to yield the anthraquinones, 2-chloroemodin (163) and 2,4-dichloroemodin (164). 2,4-Dichloroemodin on treatment with boric acid and sulfuric acid gave valsarin (165). Tetra-O-methyl-valsarin was also synthesized via chlorination of xanthorin. 

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