Natural pigments quinones

Other natural pigments including tannins, betalains, leucoanthocyanins, quinones and... 

Besides playing a vital role in the oxidation-reduction processes of living organisms, quinones occur widely as natural pigments found mainly in plants, fungi, lichens, marine organisms, and insects (see alizarin, Section 28-4A, as representative of a natural anthraquinone-type dye). 

Benzoquinones are highly conjugated molecules and are consequently coloured. 8enzo-1,4-quinone itself is yellow and benzo-1,2-quinones are often red. Chloranil forms glistening yellow platelets on crystallization from fuming nilric acid Quinones occur naturally and some natural pigments contain a quinone unit... 

Various natural pigment classes, such as llavonoids, an-thocyanins, carotenoids, chlorophylls and chlorophyll derivatives, porphyrins, quinones, anthraqinones, be-talains, and so forth are abundant in many famihes of the vegetable and animal kingdoms. As consumers generally dislike the color of synthetic dyes, the concentration and composition of pigments in foods and food products exert a considerable impact on the consumer acceptance and, consequently, on the commercial value of the products. It has been proven many times that one of the main properties employed for the commercial evaluation of the quahty of products is their color that is, an adequate color is an important requirement of marketabihty. 

Other natural pigments existing in selected pi. nt foods include tannin, betalain, leucoanthocyanin, quinone and xanthone. Table I lists the color and stability of natural pigments in fruits and vegetables (10). 

Quinones are colored p-benzoquinone, for exanple, is yellow. Many occur naturally and have been used as dyes. Alizarin is a red pigment extracted from the roots of the madder plant. Its preparation from anthracene, a coal tar derivative, in 1868 was a significant step in the development of the synthetic dyestuff industry. 

Since arucadiol and miltirone both have an aromatic "B" ring, enone 64 served as a common intermediate for both of these quinone pigments. The aromatization of 64 was readily achieved using 2,3-dicyano-5,6-dichloro-l,4-quinone (DDQ) (Equation 5.2). With substrate 65 in hand, only demethylation of the ethers was required to complete a synthesis of arucadiol (58). This transformation was accomplished in nearly quantitative yield using boron tribromide. Our synthetic arcudiol was spectrally identical with the natural material. 

There are few natural representatives of this system. Albidin is a fungistatic red pigment isolated from Penicillium albidum and an X-ray analysis has shown that it has structure 146 (86JCS(P1)1145). From the fungus Nectria haematococca, in addition to the previously known quinones, a new one, nectriafurone (147), was isolated (83PI30I). From 2.5 kg of the root bark of... 

---