Degraded Carotenoids

A number of terpenoids appear to be derived from carotenoids by cleavage of the polyene chain. These include retinal (C20). trisporic acids (Cig), abscisic acid (C15), a-ionone (C13), and loliolide (Cu). 

Retinal (81) forms a Schiffs base with the lysine e-amino-group of the protein opsin, when the visual pigment is generated. Some of the steric requirements 

Mousseron-Canet, J.-P. Dalle, and J.-C. Mani, Tetrahedron Letters, 1968, 6037. 

The fungal hormones trisporic acids B and C were shown to have a carotenoid origin. The absolute stereochemistry of trisporic acid C (82) was established by ozonolysis and c.d. measurements. In addition to the all-trons isomers, 9-cis trisporic acids are also present.  

Abscisic acid (83) has the absolute stereochemistry shown, which should now be specified as the S enantiomer. The correlation of abscisic acid (83) with 

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Tan, S. T., Wilkins, A. L., Holland, P. T., and McGhie, T. K. (1989). Extractives from New Zealand unifloral honeys. 2. Degraded carotenoids and other substances from heather honey. /. Agric. Food Chem. 37,1217-1221. 

Walberg, I. and A.-M. Eklund (1998). Degraded carotenoids. Carotenoids, Volume 3 Biosynthesis and Metabolism. G. Britton, S. Liaaen-Jensen and H. Pfander, eds. Basel, Switzerland Birkhauser Verlag, pp. 195-216. 

Altogether, there is strong evidence that carotenoids can exert multiple effects via modulation of signaling pathways. Because oxidative stress can easily degrade carotenoids, it is not enough to investigate the effects of intact carotenoids, but it is necessary to elucidate the effects of their degradation products as well. 

Ethylene coordinates the expression of genes responsible for enhanced respiratory metabolism, chlorophyll degradation, carotenoid synthesis, conversion of starch to sugars, increased activity of cell wall-degrading enzymes, aroma volatile production, and so on. All these events stimulate a series of biochemical, physiological, and structural changes making fruits mature and attractive to the consumer. 

Degraded Carotenoids. Several compounds have been described and characterized which are related structurally to carotenoids and may be biodegradation products of carotenoids. The structure of the vitamin A dimer kitol has been determined as... 

Other Degraded Carotenoids. A new synthesis of the fungal sex hormone ( )-(7 , 9 )-trisporic acid B methyl ester (114) utilized as the key step a Michael-aldol sequence on the /3-keto-ester (115) to yield the highly functionalized cyclo-hexenone (116). The latter underwent Wittig reaction with the phosphonium salt (117) to give (114). After basic alumina-catalysed hydrogen exchange in tritiated... 

Other Degraded Carotenoids. The acetylenic diol (115), prepared by reaction of but-3-yn-2-ol dianion with 2,6,6-trimethyl-4,4-ethylenedioxycyclohex-2-en-l-one (116), afforded 3,5,5-trimethyl-4-(2-butenylidene)-cyclohex-2-en-l-one (117), a major constituent of Burley tobacco, on LiAlH4 reduction and hydrolysis.53... 

Degraded Carotenoids. Syntheses have been reported for several compounds structurally related to carotenoids. Many of the procedures used may be relevant to the construction of carotenoid end-groups. 

Degraded Carotenoids Physical Methods Separation and Assay N.M.R. Spectroscopy Mass Spectrometry Chiroptical Methods Electronic Absorption Spectroscopy Infrared and Resonance Raman Spectroscopy Other Spectroscopic Techniques Miscellaneous Physical Chemistry Photoreceptor Pigments Biosynthesis and Metabolism Stereochemistry Enzyme Systems Inhibition and Regulation... 

Several oxidized or degraded carotenoids were isolated from the algal mat obtained from desert soil. 3-Ketoretrodehydrocarotene (28) was suggested for one component, but the enolic structures proposed for two C29H40O2 isomers seem highly unlikely. 

In this Report only the briefest consideration will be given to degraded carotenoids , i.e. those compounds that are structurally and possibly biogenetically related to fragments of the carotenoid molecule, except for particular cases where the chemistry is considered directly relevant to the chemistry of carotenoids themselves. 

Other Degraded Carotenoids. The chemistry of abscisic acid (111) has been reviewed.In a stereoselective synthesis of (111), 2-c/5-3-methylpent-2-en-4-yl-l-ol (112) was used to introduce the 2-cis,4-trans geometry (abscisic acid... 

Reviews.—Reviews published during the year include articles on the chemistry and biochemistry of carotenoids of higher plants/ algae, and citrus fruits," a detailed discussion of bacterial C30 carotenoids, and a short account of carotenoids in the food industry. A review of the chemistry of polyene compounds includes carotenoids and retinoids the chemistry of the latter group, especially of vitamin A itself, has also been reviewed. Two articles on ionones, irones, and damascones include an evaluation of these compounds as degraded carotenoids . 

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). 

Other Degraded Carotenoids. Several syntheses of ionones and related compounds have been described. Some of these may prove useful for end-group construction in carotenoid synthesis. Thus 4-keto-j8-ionone (126) and 3,4-dehydro-jS-ionone (127) have been prepared by condensation of the sulphone (128) with propylene oxide, followed by elimination of phenylsulphinic acid and either oxidation or dehydration. A novel method utilizes a thermal acetylenic oxy-Cope rearrangement process to prepare the ionone compounds (129—131 R = Me) and analogues (R = Et or Pr ) from cyclohex-2-enylprop-2rynols (132). 

Confirmation of the structures of several new degraded carotenoids [(33), (34), (37)—(49)] has been obtained by their preparation from related compounds of known structure. 

New Structures and Stereochemistry Bicyclic Carotenoids Monocyclic Carotenoids Acyclic Carotenoids Apocarotenoids Degraded Carotenoids Synthesis and Reactions Carotenoids Retinoids... 

Degraded Carotenoids.—The enzyme from rabbits which cleaves the central double bond of carotenoids has been partially purified. In the mould Blakeslea... 

The plant hormone abscisic acid (110) may be a degraded carotenoid or a sesquiterpenoid. Studies using [2/ - H,2- C,3/ ]-, [2S- H,2- C,3R]-, and [2- C,3I. 5S- H]-mevalonic acid show that either route is possible." Xanthoxin (111) may be involved also, it being formed in turn from violaxanthin (108). Two new metabolites of abscisic acid have been detected. 

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