Carotenoids oxygen-containing

Not all carotenoids are hydrocarbons Oxygen containing carotenes called xantho phylls which are often the pigments responsible for the yellow color of flowers are espe cially abundant... 

FIGURE 15.1 Structures of carotenoids important for vision. Oxygen-containing carotenoids belong to a subclass of carotenoids known as xanthophylls. 

The formulae of the carotenoids, from which the yellow, orange and red colours of vegetable and fruit derive, comprise hydrocarbon types and the oxygen-containing xanthophylls. They are depicted namely, for the hydrocarbons, p-carotene (11), a-carotene (12),... 

Carotenoids that contain an oxygenated functionality are collectively referred to as xanthophylls. They retain the systematic naming system of carotenes, with the additional functionalities named according to the usual nomenclature rules previously discussed. For example, p,P-carotene-3,3 -diol (zeaxanthin) (Figure 3.10a). Methoxy, carboxy, aldehyde, epoxy, and ketone derivates are also common. 

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. 

Originally only compounds with 10 carbon atoms (monoterpenes) were considered as T, and the oxygen-containing T. were classified as camphors. According to the mechanism of biosynthesis, however, all compounds derived from active isoprene are now classified as T. or isoprenes, including steroids, carotenoids, etc. 

Carotenoids are yellow pigments that are also involved in the photosynthetic process. The structures of a- and /3-carotene are given in the essay preceding this experiment. In addition, chloroplasts also contain several oxygen-containing derivatives of carotenes, called xanthophylls. 

Mono-, sesqui-, di-, and sesterpenes contain the isoprene units linked in a head-to-tail fashion. The triterpenes and carotenoids (tetraterpenes) contain two C15 and C20 units, respectively, linked head to head. Many terpenes are hydrocarbons, but oxygen-containing compounds such as alcohols, aldehydes, or ketones are also found to fall in the class of terpenes. These derivatives are more frequently named as terpenoids. 

In early vitamin and carotenoid syntheses, the oxidation of j6-isophorone was accomplished by epoxidation of /1-isophorone followed by tbe ring-opening of the epoxide and oxidation (Fig. 16.13). A significant improvement of the three-step synthesis of KIP was made by the one-step liquid phase oxidation of j6-isophorone using oxygen or an oxygen-containing gas in the presence of a transition metal catalyst. In 1975, the aerobic oxidation of j6-isophorone in tbe presence of Cu(II)-or V(III)-acetylacetonate was published, in which KIP was obtained in a yield of up to 55%. ... 

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