Lycopene, structure

LUMO, see Lowest unoccupied molecular orbital Lyase, 1041-1042 Lycopene, structure of, 483 Lysergic acid diethylamide, structure of, 963... 

It has been established that carotenoid structure has a great influence in its antioxidant activity for example, canthaxanthin and astaxanthin show better antioxidant activities than 3-carotene or zeaxanthin. 3- 3 3-Carotene also showed prooxidant activity in oil-in-water emulsions evaluated by the formation of lipid hydroperoxides, hexanal, or 2-heptenal the activity was reverted with a- and y-tocopherol. Carotenoid antioxidant activity against radicals has been established. In order of decreasing activity, the results are lycopene > 3-cryptoxanthin > lutein = zeaxanthin > a-carotene > echineone > canthaxanthin = astaxanthin. ... 

The second major difficulty is that cells and tissues in the body are exposed to numerous metabolites displaying different structures compared to the parent molecules present in plant foods. For example, it has been suggested that the metabolites of lycopene may be responsible for reducing the risk of developing prostate cancer. These metabolites may interact with nuclear receptors such as PPARs, LXR, and others. " Future research is needed to produce metabolites (enzymatically or chemically) in order to elucidate their cellular mechanisms and thus clarify their effects on human health. 

Carotenoid oxidation products were not only formed from the parent molecules in order to elucidate structure, they were also obtained by partial or total synthesis or by direct oxidation of carotenoid precursors. Thus, apo-8 -lycopenal was synthesized in 1966 more recently, the ozonide of canthaxanthin was obtained by chemical oxidation of canthaxanthin. ... 

Freeze-dried tomato powders obtained from whole tomato fruits and from their pulp after centrifugation, containing 474 and 5399 pg/g dry weight, respectively, were developed for use as additives for food fortification. Cis isomers of lycopene were determined in only a few smdies. The 5-cis-, 9-cis-, and 13-d5 --El5-d5 -lycopene were the isomers found in commercial tomato products. The structures of lycopene cis isomers are shown in Figure 4.2.1 and the structure of the dll-trans isomer is displayed in Figure 6.2.1 in Chapter 6. 

Lycopene is the typical substrate for cyclization. One or both ends of the acyclic precursor can be cyclized. Cyclization can occur in one of two ways to create two different ring structures, differing only by the position of the double bond in the cyclohexane ring. Different enzymes form each of the rings, the lycopene-(3-cyclase (LCYB) and the lycopene-e-cyclase (LCYE), as shown in Figure 5.3.3. 

Plant apocarotenoids have a wide variety of structures and functions. As expected, there is a small gene family of CCDs with different cleavage sites and somewhat promiscuous substrate selection. Some CCDs are stereo-specific, for example, 9-cis epoxycarotenoids are the substrates for NCEDs (9-cis expoxy dioxygenases) that produce the precursor of ABA biosynthesis, xanthoxin. Both linear carotenoids (lycopene) and cyclic carotenoids are substrates for cleavage at various double bonds including the central 15-15 and eccentric 5-6, 7-8, 9-10, 9 -10, and 11-12 bonds. Some CCDs cleave both linear and cyclic carotenoids and may cleave the same molecule twice, e.g., both 9-10 and 9 -10 positions. 

Figure 4.7 shows the structures of important carotenoids (all-E) lutein, (all-E) zeaxanthin, (all-E) canthaxanthin, (all-E) p-carotene, and (all-E) lycopene. Employing a self-packed C30 capillary column, the carotenoids can be separated with a solvent gradient of acetone water=80 20 (v/v) to 99 1 (v/v) and a flow rate of 5 pL min, as shown in Figure 4.8 (Putzbach et al. 2005). The more polar carotenoids (all-E) lutein, (all-E) zeaxanthin, and (all-E) canthaxanthin elute first followed by the less polar (all-E) p-carotene and the nonpolar (all-E) lycopene. Figure 4.9 shows the stopped-flow II NMR spectra of these five carotenoids. The chromatographic run was stopped when the peak maximum of the compound of interest reached the NMR probe detection volume.

FIGURE 4.7 Structures of important carotenoids (all-E) lutein, (all-/ ) zeaxanthin, (all-E) canthaxanthin, (all-E) P-carotene, and (all-E) lycopene. 

Carotenoids are a class of lipophilic compounds with a polyisoprenoid structure. Most carotenoids contain a series of conjugated double bonds, which are sensitive to oxidative modification and cis-trans isomerization. There are six major carotenoids (ji-carotenc, a-carotene, lycopene, P-cryptoxanthin, lutein, and zeaxanthin) that can be routinely found in human plasma and tissues. Among them, p-carotene has been the most extensively studied. More recently, lycopene has attracted considerable attention due to its association with a decreased risk of certain chronic diseases, including cancers. Considerable efforts have been expended in order to identify its biological and physiochemical properties. Relative to P-carotene, lycopene has the same molecular mass and chemical formula, yet lycopene is an open-polyene chain lacking the P-ionone ring structure. While the metabolism of P-carotene has been extensively studied, the metabolism of lycopene remains poorly understood. 

FIGURE 20.1 Schematic illustration of lycopene metabolic pathway by CM02. (a) 5-cis Lycopene and 13-cis lycopene are preferentially cleaved by CM02 at 9, 10 -double bond. The cleavage product, apo-lO -lycopenal, can be further oxidized to apo-lO -lycopenol or reduced to apo-lO -lycopenoic acid, depending on the presence of NAD+ or NADH. (b) Chemical structures of apo-lO -lycopenoic acid, acyclo-retinoic acid, and all-frans retinoic acid. (Adapted from Hu, K.Q. et al., J. Biol. Chem., 281, 19327, 2006. With permission.)... 

Khachik, F., A. Steck, U.A. Niggli, and H. Pfander. 1998. Partial synthesis and structural elucidation of the oxidative metabolites of lycopene identified in tomato paste, tomato juice and human serum. J Agric Food Chem 46 4885 1890. 

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