New Natural Carotenoids

AcycBc Carotenoids.—Diphenylamine-inhibited Rhodospiritlum rubrum 

Two new acyclic end-groups have been found. Phytoene-1,2-oxide (15) was isolated from tomatoes. In the bacteria Rhodopseudomonas viridis it was found that although neurosporene and lycopene (16) were present, most of the carotenoids previously thought to be these two compounds, were in fact the corresponding 1,2-dihydro-derivatives [e.g. (17)]. In addition, l,2-dihydro-3,4-dehydrolycopene (18) was present. 

A reinvestigation of lycoxanthin (19) and lycophyll (20) showed that the allylic hydroxy-group is on the terminal carbon atom. This result was confirmed by nickel peroxide oxidation to the corresponding aldehydes. 

Cholnoky, J. Szabolcs, and E. S. Waight, Tetrahedron Letters, 1968, 1931 M. C. Markham and S. Liaaen-Jensen, Phytochem., 1968, 7, 839. 

The diapo-carotenoid crocetindial (25) and the corresponding oxoacid were isolated from Jacquinia augustifolia.  

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Carotenoid synthesis has a long and distinguished history. It also has an exciting future. The old objectives remain valid, namely to synthesize new natural carotenoids and to improve methods both in laboratory and industrial scale processes. But now there are new and more diverse challenges as carotenoid science expands into new areas. 

Today the total synthesis of a carotenoid for structure elucidation is often no longer necessary because of advances in high resolution spectroscopic methods but, when only small amounts of a new natural carotenoid, metabolite or degradation product are available, full spectroscopic characterization may not be possible, and total synthesis of the proposed structure then becomes indispensable, especially to establish its stereochemistry. 

Degraded Carotenoids. Several new natural products have structures similar to carotenoid end-groups and thus may be considered as degraded carotenoids. A new abscisic acid (31) metabolite from seeds of Robinia pseudacacia has been identified as the 3-hydroxy-3-methylglutaryl ester of hydroxyabscisic acid (32). 

New Natural Products Related to Carotenoids. Tobacco continues to yield volatile constituents with carotenoid-like rings, described by some authors as nor-carotenoids . New structures reported are 5-hydroxy-5,6-dihydro-3,6-epoxy-/3-ionol [carotene numbering (19)] and the related 5,8-epoxide (20). An epoxymegastigmadiene (21) has been identified in Osmanthus absolute/ The... 

New Natural Products Related to Carotenoids Carotenoid-Protein Complexes Synthesis and Reactions Carotenoids Retinoids... 

Nir, Z, Hartal, D and Raveh, Y (1993) Lycopene from tomatoes. A new commerical natural carotenoid. Int. Food Ingredients, 3, 45-51. 

New research has demonstrated that carotenoids may also lend additional health benefits that may possibly reduce the risk of certain types of chronic diseases such as cancer and heart disease. Carotenoids are also important natural sources of orange, yellow, and red food coloring for the food and beverage industries. ... 

Detailed information about carotenoids found in food or extracted from food and evaluated for their potential as food colorants appeared in Sections 4.2 and 6.2. We would like to mention some new data about the utilization of pure carotenoid molecules or extracts as allowed food additives. Looking to the list of E-coded natural colorants (Table 7.2.1), we can identify standardized colorants E160a through f, E 161a, and E161b as natural or semi-synthetic derivatives of carotenoids provided from carrots, annatto, tomatoes, paprika, and marigold. In addition, the extracts (powders or oleoresins) of saffron, - paprika, and marigold are considered more economical variants in the United States and European Union. 

The reaction of CARs with free radicals is much more complex and depends mostly on the nature of the free radical [RO ] rather than on the CAR. Certainly, at least four processes have been reported. Of course, in all four processes, the unpaired electron of the free radical is transferred to the CAR so that a new, carotenoid radical (or CAR adduct radical) is produced. ... 

Carotenoids are highly lipophilic an active area of research concerns how carotenoids interact with and affect membrane systems (see Chapters 2 and 10). Also, the lipid solubility of these compounds has important implications for carotenoid intestinal absorption (see Chapter 17) models such as the Caco-2 cell model are being used to conduct detailed studies of carotenoid absorption/ competition for absorption (Chapter 18). The lipid solubility of these carotenoids also leads to the aggregation of carotenoids (see Chapter 3). Carotenoids aggregate both in natural and artificial systems, with implications for carotenoid excited states (see Chapter 8). This has implications for a new indication for carotenoids, namely, serving as potential materials for harnessing solar energy. 

New Structures.—The Key to Carotenoids lists all carotenoids found in Nature up to the middle of 1975, and gives extensive references to occurrence and physical, chemical, and spectroscopic properties. An outline of work on the eluci-... 

Egeland, E.S., and Liaaen-Jensen, S. (1992) Eight new carotenoids from a chemosystem-atic evaluation of Prasinophyceae. Proceedings of 7th International Symposium on Marine Natural Products, Capri. 

Liaaen-Jensen, S. (1978) Marine carotenoids. In Marine Natural Products Chemical and Biological Perspectives, Vol. 2 (Scheuer, P.J., ed.), pp. 1-73, Academic Press, New York. 

A new type of end-group was detected in a carotenoid from the fungus Calo-scypha fulgens Using the provional lUPAC systematic nomenclature this compound is called /i,y-carotene, (19). Its structure was proved" by synthesis from y-ionone using standard methods. y,y-Carotene was also synthesized, though as yet it has not been found in nature. 

Thus, ethanol-water (7 3 v/v) and methanol-water in various ratios for flavonoids, methanol-25 % HCl (9 1 v/v), methanol-acetic acid (5%), methanol-tri-fluoroacetic acid (3%) for unstable anthocyanins, acetone, methanol-acetone mixtures for carotenoids, acetone and petroleum ether for chlorophylls, and so forth. The pigments are fairly stable in their natural environment, but they generally become unstable in extracts this has to be taken into consideration in the development of new, more efficaceous extraction procedures. 

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