Carotenoic acids

Apo-4 -carotenal, 8-Apo-8 -carotenaI, 8-Apo-8 -carotenoic acid ethyl ester, 8-Apo-8 -carotenoic acid methyl ester, Apocodeine, Apomorphine see entries in Chapter 6. 

B-Apo-8 -carotenoic acid methyl ester [16266-99-2] M 512.7, m 136-137°, A2575 at 446nm and 2160 at 471nm, in pet ether. Crystd from pet ether or pet ether/ethyl acetate. Stored in the dark in an inert atmosphere at -20°. 

Larsen E, Abendroth J, Partali V, Schulz B, Sliwka HR, and Quartey EGK. 1998. Combination of vitamin E with a carotenoid a-Tocopherol and trolox linked to (3-apo-8 -carotenoic acid. Chemistry—A European Journal 4(1) 113-117. 

Partali V, Kvittingen L, Sliwka HR, and Anthonsen T. 1996. Stable, highly unsaturated glycerides—Enzymatic synthesis with a carotenoic acid. Angewandte Chemie-Intemational Edition in English 35(3) 329-330. 

Reddy PV, Rabago-Smith M, and Borhan B. 2002. Synthesis of all-frans-[10 -H-3]-8 -apo-P-carotenoic acid. Journal of labelled Compounds Radiopharmaceuticals 45(1) 79-89. 

Xiang, J., F. S. Rondonuwu, Y. Kakitani, R. Fujii, Y. Watanabe, Y. Koyama, H. Nagae, Y. Yamano, and M. Ito. 2005. Mechanisms of electron injection from retinoic acid and carotenoic acids to Ti02 nanoparticles and charge recombination via the T, state as determined by subpicosecond to microsecond time-resolved absorption spectroscopy Dependence on the conjugation length. J. Phys. Chem. B 109 17066-17077. 

Prakash, P., C. Liu, K. Q. Hu et al. 2004. Beta-carotene and beta-apo-14 -carotenoic acid prevent the reduction of retinoic acid receptor beta in benzo[a]pyrene-treated normal human bronchial epithelial cells. J Nutr 134(3) 667-673. 

The success of the carotenoid extracts led to the commercialization of synthetic carotenoids, some with the same chemical structure as those in the plant extracts and others with modifications to improve their technological properties. The yellow beta-carotene was synthesized in 1950, followed by the orange beta-8-carotenal in 1962 and the red canthaxanthin in 1964. A number of others soon followed, methyl and ethyl esters of carotenoic acid, citraxanthin, zeaxanthin, astaxanthin, and recently lutein. 

The structures of four of the synthetic carotenoids (beta-carotene, canthaxanthin, beta-apo-8 -carotenol, beta-apo-8 -carotenoic acid) are shown in Fig. 8.2. By virtue of their conjugated double bond structure, they are susceptible to oxidation but formulations with antioxidants were developed to minimize oxidation. Carotenoids are classified as oil soluble but most foods require water soluble colorants thus three approaches were used to provide water dispersible preparations. These included formulation of colloidal suspensions, emulsification of oily solutions, and dispersion in suitable colloids. The Hoffman-LaRoche firm pioneered the development of synthetic carotenoid colorants and they obviously chose candidates with better technological properties. For example, the red canthaxanthin is similar in color to lycopene but much more stable. Carotenoid colorants are appropriate for a wide variety of foods.10 Regulations differ in other countries but the only synthetic carotenoids allowed in foods in the US are beta-carotene, canthaxanthin, and beta-8-carotenol. 

Beta-8-carotenal and the methyl and ethyl esters of carotenoic acid were also tested for toxic effects with results similar to beta-carotene. 

Fig. 2.27. Representative HPLC chromatograms of carotenoids found in the plasma of green iguanas after being fed with a carotene-deficient diet (a) or a diet supplemented with /3-carotene (b), can-thaxanthin (c) and /f-apo-8 -carotenoic acid ethyl ester (d) recorded at 450 nm. Enumerated peaks are (1) lutein (21.3min) (2) zeaxanthin (22.2min) (3) undefined peak co-eluted with zeaxanthin (22.2min) (4) canthaxanthin (23.1min) and (5) apo-8 -carotenoic acid ethyl ester (26.7min). Retention times in parentheses. Reprinted with permission from J. Raila et al. [65],...

There are several provitamins A these belong to the carotenoid pigments. The most important one is P-carotene, and some of the pigments that can be derived from it are of practical importance. These are P-apo-8 -carotenal and P-apo-8 -carotenoic acid ethyl ester (Figure 9-2). Other provitamins are a- and y-carotene and cryptoxanthin. 

The Reaction Specificity of Carotene Dioxygenase Whereasthe principal site of carotene dioxygenase attack is the 15,15 -central bond of p-carotene, there is evidence that asymmetric cleavage also occurs, leading to formation of 8 -, 10 -, and 12 -apo-carotenals, as shown in Figure 2.4. These apo-carotenals are metabolized by oxidation to apo-carotenoic acids, which are substrates for /3-oxidation to retinoic acid and a number of other metabolites. 

Fig. 3. Commercially important carotenoids P-carotene (10), canthaxanthin [514-78-3] (11), astaxanthin [472-61-7] (12), p-apo-8 -carotenal [1107-26-2] (13), p-apo-8 -carotenoic acid ethyl ester [1109-11-1] (14), and citranaxanthin [3604-90-8] (15).

The importance of carotenoids in photobiology is well known and there is a continuing interest in their photochemistry. Although they do not normally participate in PET processes because of the short lifetimes of their singlet states, incorporation into organized systems with suitable electron acceptors can lead to photoactivity. The dynamics of photoinduced electron injection and recombination between all-trans-8 -apo-p-caroten-8 -oic acid (125) and a Ti02 colloidal nanoparticle have been studied by means of transient absorption spectroscopy. " " An ultrafast ( 360 fs) electron injection from the initially excited S2 state of the carotenoic acid into the Ti02 conduction band with a quantum... 

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