Neoxanthin derivatives

Most of this amount is in the form of fucoxanthin in various algae and in the three main carotenoids of green leaves lutein, violaxanthin, and neoxanthin. Others produced in much smaller amounts but found widely are p-carotene and zeaxanthin. The other pigments found in certain plants are lycopene and capsanthin (Figure 2.2.1). Colorant preparations have been made from all of these compounds and obviously the composition of a colorant extract reflects the profile of the starting material. Carotenoids are probably the best known of the food colorants derived from natural sources. ... 

The defensive excretion of the grasshopper Romalea microptera contains the allenic ketone (10). This structure is clearly related to neoxanthin (57). Racemic samples of (10) were synthesised by two routes (Scheme 5) and, although there were some differences between the two products, their n.m.r. spectra show that they belong to the natural series and that they are clearly different from the photochemically synthesised isomer (3-OH, 90, R = Ac). The stereochemistry of the synthetic racemate was shown by X-ray crystallography to be the same as an optically active sample derived from the degradation of fucoxanthin. The absolute stereochemistry of the latter sample presumably also applies to the grasshopper ketone itself. 

Lutein is the predominant xanthophyll in all LHCs and ranges between a low of <40% of total carotenoids in LHClla to >65% in LHCllb. Other carotenoids, particularly the )3-carotene derived xanthophylls, violaxanthin and neoxanthin, vary much more widely in concentration. Neoxanthin is present at similar proportions in LHClla, b and c but is virtually absent from LHClld (Bassi et al, 1993). Interestingly, LHCllb is nearly devoid of/3-carotene but the minor complexes contain 5-10% of their total carotenoids as /3-carotene (Bassi et al, 1993 Ruban et al., 1994). Violaxanthin is also proportionally enriched in the minor LHCs accounting for 30-40% of the total minor LHC carotenoids and in aggregate up to 80%... 

Chlamydomonas reinhardtii double mutant npq2/lorl lacks the P,e-carotenoids lutein and loroxanthin as well as all P,P-epoxycarotenoids derived from zeaxanthin (e g. violaxanthin and neoxanthin). Thus, the only carotenoids present in the thylakoid membranes of the npq2/lorl cells are P-carotene and zeaxanthin. The effect of these mutations and the lack of specific xanthophylls on the Chi antenna size of the photosystems was investigated [16]. In cells of the mutant strain, the Chi antenna size of PSII was substantially smaller than that of the wild type (Table 1). In contrast, the Chi antenna size of PSI was not truncated in the mutant. This analysis showed that absence of lutein, violaxanthin and neoxanthin specifically caused a smaller functional Chi antenna size for PSII but not for that of PSI. Thus, xanthophyll-bios5mthesis genes, such as lycopene e-cyclase and zeaxanthin epoxidase may be targets for a truncated Chi antenna size in PSII. 

The Ci5-building block 118 and the acetylenic Cio-diphosphonate 94 have also been used for the synthesis of neoxanthin (234). With BuLi as base the Cis-phosphonate 127 was prepared. The Horner-Emmons reaction with the Cis-allenic building block 128 (see Chapter 3 Part IV) gave, in 74% yield, the 15,15-didehydro derivative of neoxanthin which, after partial hydrogenation and isomerization, gave (all- )-neoxanthin (234) [31] (Scheme 28). 

Epoxidation of zeaxanthin by zeaxanthin epoxidase (ZE) would result in the production of violaxanthin via antheraxanthin. From that substrate, the enzyme neoxanthin synthase (NXS) would yield neoxanthin opening the cyclohexenyl 5-6 epoxide ring in violaxanthin [38]. Neoxanthin would be the last product of carotenoid biosynthesis in green parts of the plant, and it would derive in the abscisic acid (ABA) synthesis pathway. The accumulation of neoxanthin and violaxanthin in flowers results in wildtype yellow petals. A defective mutation in the gene encoding CRTR-B2 prevents formation of these xanthophylls, resulting in the white-flower phenotype [18]. 

Cano and Marin (1992) studied differences in pigment profiles between fresh (uiuipe and ripe), frozen and canned kiwi fruit shces, using thin-layer chromatography (TLC), HPLC, UV-visible spectroscopy, and chemical tests. Pigments present in fresh and frozen kiwi fruit shces were xanthophyUs (9 -cis-neoxanthin, trans-violaxanthin, cw-violaxanthin, auroxanthin, lutein epoxide, and lutein), chlorophylls and their derivatives, and one hydrocarbon carotenoid... 

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