Carotenoids epoxide-containing

Seventy naturally occurring carotenoid epoxides have been referenced and 43 of them have been fully characterized. These compounds can be formally considered oxidation products as defined above, but they first have the status of carotenoids. They are indeed found in vivo and are possibly biosynthesized from the corresponding non-oxidized carotenoids. If carotenoids containing epoxide functions have been found in humans, the epoxidation reaction has not yet been proven to occur in humans. 

Similarly, Karrer and oo-workers discovered that the carotenoid flower pigment trollixanthin (XV),103 as veil aa the related substances anthoroxsnthin, M, i4 violaxanthin, 1 and epoxylutein, 10-(1 all contain epoxide units. The. subject of naturally-occurring carotenoid epoxides ha been reviewed recently.1. 8 8 and attention called to the possible need for revision in certain of the structural assignments made by Karrer and hie associates.885... 

In order to obtain nearly absolute purity of the spectra of these xanthophylls, it was necessary to calculate the difference Raman spectra. Therefore, for zeaxanthin, two spectra of samples, one containing violaxanthin and the other enriched in zeaxanthin, were measured at 514.5 nm excitation. After their normalization using chlorophyll a bands at 1354 or 1389 cm-1, a deepoxidized-minus-epoxidized difference spectrum has for the first time been calculated to produce a pure resonance Raman spectrum of zeaxanthin in vivo (Figure 7.10b). A similar procedure was used for the calculation of the pure spectrum for violaxanthin. The only difference is that the 488.0nm excitation wavelength and epoxidized-minus-deepoxidized order of spectra have been applied in the calculation. The spectra produced using this approach have remarkable similarity to the spectra of xanthophyll cycle carotenoids in pure solvents (Ruban et al., 2001). The v, peaks of violaxanthin and zeaxanthin spectra are 7 cm 1 apart and in correspondence to the maxima of this band for isolated zeaxanthin and violaxanthin, respectively. The v3 band for zeaxanthin is positioned at 1003 cm-1, while the one for violaxanthin is upshifted toward 1006 cm-1. 

Absorption and Raman analysis of LHCII complexes from xanthophyll biosynthesis mutants and plants containing unusual carotenoids (e.g., lactucoxanthin and lutein-epoxide) should also be interesting, since the role of these pigments and their binding properties are unknown. Understanding the specificity of binding can help to understand the reasons for xanthophyll variety in photosynthetic antennae and aid in the discovery of yet unknown functions for these molecules. 

The HPLC analysis of milkweed, the food-plant source for Monarch butterflies, demonstrates that it contains a complex mixture of carotenoids including lutein, several other xanthophylls, xanthophyll epoxides, and (3-carotene, Figure 25.3b. There is a component in the leaf extract that is observed to elute near 8min, which has a typical carotenoid spectrum but is not identical to that of the lutein metabolite observed at near the same retention time in the extracts from larval tissue. 

Fig. 5 RP-HPLC separation of (A) paprika extract and (B) saponified paprika extract on a Zorbax C l8 column at 460 nm. The solid peaks represent carotenoids containing a ketone group, and the hash-marked peaks represent carotenoids containing an epoxide group. (From Ref. 74a.)...

Light-harvesting Chi a/b complexes contain carotenoids of the /3-/3 type (/8-carotene, violaxanthin, antheraxanthin, zeaxanthin, neoxanthin) and of the /3-e type (lutein). Some higher plants like lettuce contain an , -carotenoid, lactucaxanthin, both in the major and in minor Chi a/b complexes which may replace either lutein or other xanthophylls (Phillip and Young, 1995). Among /3,/3-carotenoids, violaxanthin, antheraxanthin, and neoxanthin contain epoxides whereas the others do not. In order to... 

Fucoxanthin (Fig. 22-5) is the characteristic brown pigment of diatoms. One end of the molecule has an epoxide, also formed by the action of O2, while the other end contains an allene structure rare in nature. Even so, fucoxanthin may be the most abundant carotenoid of all. The structure of the allene-containing end of the fucoxanthin molecule (turned over from that shown in Fig. 22-5) is also given in Eq. 

Figure 22-5 does not indicate the stereochemistry of the allene group correctly the carotenoid chain protrudes behind the ring as drawn in the equation. Violaxanthin contains epoxide groups in the rings at... 

Capsanthin a carotenoid, M, 584.85, m.p. 176 °C, [a]cd + 36° (CHQj). It possesses a terminal 5-mem-bered ring. The secondary OH-groups have R configuration on C3, and S configuration on C3. C is the main red pigment of paprika (Capsicum annum), where it is accompanied by Capsorubin (see), crypto-capsin and capsanthin-5,6-epoxide. Ripe fiiiits contain 9-10 mg C. per 100 g fresh weight. 

Cuscuta. Since the end of the nineteenth century it was known that the normal yellow-orange coloration of the holoparasitic genus Cuscuta is due to a high content of carotenoids (Tamne 1883). About live decades later a considerable level of y-carotene, some a- and P-carotene as well as traces of lycopene and rubixanthin [(31 )-p, /-caroten-3-ol] could be detected in C. subinclusa Durand Hilg. and C. salina Engelm. (Mackinney 1935). C. australis was found to contain P- and y-carotene, a-carotene 5,6-epoxide, lutein, and taraxanthin (= lutein 5,6-epoxide) (Baccarini et al. 1965). 

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