Carotenoids derivatives

As has already been stated, the carotenoids are lipophilic and are therefore absorbed and transported in association with the lipoprotein particles. In theory, this fortuitous juxtaposition of lipid and carotenoid should confer protection on the lipid through the antioxidant properties of the carotenoid. No doubt some antioxidant protection is afforded by the presence of the carotenoids derived from the diet. However, with one or two exceptions, human supplementation studies have not supported a role for higher dose carotenoid supplements in reducing the susceptibility of the low-density lipoproteins to oxidation, either ex vivo or in vivo (Wright et al, 2002 Hininger et al, 2001 Iwamoto et al, 2000). 

In the natural world, carotenoid oxidation products are important mediators presenting different properties. Volatile carotenoid-derived compounds such as noriso-prenoids are well known for their aroma properties. Examples include the cyclic norisoprenoid P-ionone and the non-cyclic pseudoionone or Neral. Carotenoid oxidation products are also important bioactive mediators for plant development, the best-known example being abscisic acid. Apo-carotenoids act as visual and volatile signals to attract pollination and seed dispersal agents in the same way as carotenoids do, but they are also plant defense factors and signaling molecules for the regulation of plant architecture. 

Winterhalter, P. and Rouseff, R., Carotenoid-Derived Aroma Compounds, Series, A.S. Ed., American Chemical Society, Washington, 2001, 1. 

Foss BJ. 2005. Synthesis and physical properties of hydrophilic carotenoid derivatives, PhD thesis, Norwegian University of Science and Technology, Trondheim, Norway. 

Oliveros E, Braun AM, Aminiansaghafi T, and Sliwka HR. 1994. Quenching of singlet oxygen ( A0) by carotenoid derivatives—Kinetic analysis by near-infrared luminescence. New Journal of Chemistry 18(4) 535-539. 

El-Agamey, A. and McGarvey, D.J. 2005. First direct observation of reversible oxygen addition to a carotenoid-derived carbon-centered neutral radical. Org. Lett. 18 3957-3960. 

Kalariya, NM, Ramana, KV, Srivastava, SK, and van Kuijk, FJ, 2008. Carotenoid derived aldehydes-induced oxidative stress causes apoptotic cell death in human retinal pigment epithelial cells. Exp Eye Res 86, 70-80. 

Kanofsky, JR and Sima, PD, 2006. Synthetic carotenoid derivatives prevent photosensitised killing of retinal pigment epithelial cells more effectively than lutein. Exp Eye Res 82, 907-914. 

Schwartz, S. H., X. Q. Qin et al. (2004). The biochemical characterization of two carotenoid cleavage enzymes from Arabidopsis indicates that a carotenoid-derived compound inhibits lateral branching. J. Biol. Chem. 279(45) 46940 16945. 

Winterhalter B. and R. L. Rouseff (2002). Carotenoid-Derived Aroma Compounds An Introduction. Washington DC Amercian Chemical Society. 

These assays measure the level of protection provided to the naturally occurring carotenoid derivative crocin from bleaching by the radical generator AAPH. The assay was originally suggested by Bors and others (1984) and modified by Tubaro and others (1998), who used it to show that plasma antioxidant capacity is deeply influenced by the consumption of wine. The addition of a sample containing chain-breaking antioxidants results in the decrease in the rate of crocin decay. The sample is monitored for 10 min at 443 nm. 

Thiophene chains also make serviceable wires. The terthiophene 11, measured by MCBJ, gives two conductance maxima, at 10 nS and 80 nS [67]. Even simple polyene chains can be wires the carotenoid derivative 12 has a conductance of 2 nS, measured by STM-BJ [68]. 

Ru complex and (CH3)3COK [(S, R)-34B] is also an excellent catalyst for hydrogenation of the cyclic enone [111]. The allylic alcohol product is a useful intermediate for the synthesis of carotenoid-derived odorants and other bioactive ter-penes. Hydrogenation of 2-cyclohexenone in the presence of the (S,S)-DIOP-Ir catalyst gives (R)-2-cyclohexenol in 25% ee (Fig. 32.43) [137]. 

An interesting study [52] of the protonation kinetics and equilibrium of radical cations and dications of three carotenoid derivatives involved cyclic voltammetry, rotating-disk electrolysis, and in situ controlled-potential electrochemical generation of the radical cations. Controlled-potential electrolysis in the EPR cavity was used to identify the electrode reactions in the cyclic volt-ammograms at which radical ions were generated. The concentrations of the radicals were determined from the EPR amplitudes, and the buildup and decay were used to estimate lifetimes of the species. To accomplish the correlation between the cyclic voltammetry and the formation of radical species, the relative current from cyclic voltammetry and the normalized EPR signal amplitude were plotted against potential. Electron transfer rates and the reaction mechanisms, EE or ECE, were determined from the electrochemical measurements. This study shows how nicely the various measurement techniques complement each other. 

Of special interest are push-pull polyenes composed of a polyolefinic chain bearing a donor group on one end and an acceptor on the other (see 96). Push-pull carotenoid derivatives (Figure 20) are highly polarizable conjugated polyenes that also represent polarized molecular wires. 

Hydrogenation of 2,4,4-trimethyl-2-cyclohexenone with rrans-RuCl2(tolbinap)(dpen) and (CH3)3COK under 8 atm of hydrogen gives 2,4,4-trimethyl-2-cyclohexenol quantitatively with 96% ee (Scheme 1.70) [256,275,276]. In this case, unlike in the reaction of aromatic ketones, the combination of the R diphosphine and S,S diamine most effectively discriminates the enantiofaces. The chiral allylic alcohol is a versatile intermediate in the synthesis of carotenoid-derived odorants and other bioactive terpens such as a-damascone and dihydroactinidiolide [277]. 

On a molecular level, exactly the same characteristics are required of supramolecular components and hence a molecular rectifier shoufd comprise an eiectron donor and an eiectron acceptor, separated by an insulating spacer. Compounds 11.49 and 11.50 are based on c-insulating framework, while donor-acceptor carotenoid derivatives such as 11.51 are separated by a more conducting n system. 

Winterhalter, R, Rouseff, R.(2000). Carotenoid-derived aroma compounds. In P. Winterhalter R. Rouseff (Eds.),Carotenoid-derived aroma compounds an introduction (pp. 1-17). Washington, DC ACS Symposium Series 802. 

Schaeffer P., Adam P., Wehrung P., and Albrecht P. (1997) Novel aromatic carotenoid derivatives from sulfur photosynthetic bacteria in sediments. Tetrahedron Lett. 38, 8413 - 8416. 

Gunata, Z., Wirth, J.L., Guo, W. and Baumes, R.L. (2002) C13-norisoprenoid aglycon composition of leaves and grape berries from Muscat of Alexandria and Shiraz culti-vars, In Carotenoid-derived aroma compounds, ACS Symp. Series 802, Am. Chem. Soc., Washington DC. 

Carotenes and Carotenoid Derivatives From Tobacco and Tobacco Smoke... 

Tobacco, unlike most other commodities, is not produced as a food crop, but it is used for manufacture of smoking materials and other products. The essential oils in tobacco are important for impact and balance in smoking (11). Smoking pleasure is derived from a balance of nicotine and volatile components. Tobacco chemists and flavorists are certain that carotenoid derivatives contribute to smoke flavor and aroma (5) Over a hundred compounds related to carotenoids have been isolated from tobacco and tobacco smoke. 

The effect of carotenoids upon smoke flavor and aroma has resulted in new endeavors in research to increase levels of carotenoid derivatives. Plant breeders, attempting to improve tobacco quality, have developed cultivars with higher carotenoid levels. Beatson and Wernsman increased carotenoid content 40% by back-crossing and selection in only five generations. Statistical analyses of these data showed positive correlations between carotenoids and nicotine in these flue-cured tobaccos (r=.8l) (12). 

Figure 4. Carotenoid derivatives as flavor compounds. found in blank e tea identified...

Figure 6. Compounds identified as carotenoid derivatives in flue-cured tobacco.

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