Phytoene epoxide

Fig. 2.16. HPLC profile of carotenoids in an extract of vegetable soup. An expansion of the profile from 30 to 39 is shown in the inset (A). Monitored wavelengths were 436, 440, 464, and 409 nm for peaks 9,10,11,12, and 14, respectively, in the inset (A). Peak identification 1 + 1" = all-trans-lutein and cw-lutein 2 = 5,6-dihydroxy-5,6-dihydrolycopene (lycopene-5,6-diol) 3 = j3-apo-8 -carotenal (internal standard) 4 = lycopene 1,2-epoxide 5 = lycopene 5,6-epoxide 6 = 1,2-dimethoxyproly-copene (tentative identification) 7 = 5,6-dimethoxy-5,6-dihydrolycopene 8 = lycopene 9 = pheo-phytin b 10 = neurosporene 11 = (-carotene 12 = pheophytin a 13 = (-carotene 14 = pheophytin a isomer and (-carotene 15 = a-carotene 16 and 16" = all-trans-/fcarotene, cis-/J-carotene 17 and 17" = all-trans- or cA-phytofluene 18 and 18" = all-trans- or cw-phytoene. Reprinted with permisson from L. H. Tonucci et al. [40].

An enzyme system from the yeast Saccharomyces cerevisiae is able to incorporate isoprenoid precursors into the C30 phytoene analogue (200) only in the presence of Mn and absence of NADPH. If NAD PH is present and Mn is replaced by Mg, the sterol precursor squalene (201) is produced.The substrate specificity of the chloroplast enzyme violaxanthin deepoxidase has been examined.In addition to the normal substrate violaxanthin [(35,5/ ,65,3 5,5 i ,6 5)- 5,6,5, 6 -diepoxy-5,6,5, 6 -tetrahydro-/3,j8-carotene-3,3-diol, (196)] several all-trans-monoepoxy-carotenoids, such as anthera-xanthin [5,6-epoxy-5,6-dihydro-/3,/3-carotene-3,3 -diol (197)], diadinoxanthin [5,6-epoxy-7, 8 -didehydro-5,6-dihydro-j8, 8-carotene-3,3 -diol (198)], and /3-cryptoxanthin epoxide [5,6-epoxy-5,6-dihydro-/3,/3-caroten-3-ol (199)], all with the 38,5R,6S) configuration, were utilized. Violeoxanthin (9-cis-violaxanthin) and other 9-cis-isomers were not affected. A carrot Daucus carota) tissue culture has been shown to incorporate [ C]acetate into carotenoids. ... 

In the field of carotenoids, most TLC-MS utilizations to date have been made offline and have used TLC merely for the purpose of purification or isolation of these pigments. Mass spectrometry was introduced into carotenoid analysis in 1965 [16]. In the 1970s, separations by open column chromatography on aluminum oxide were often combined with TLC separations on silica gel and MgO/Kieselguhr to achieve sufficient purification degree of carotenoids from tomato. These were analyzed afterward by direct-insertion electron impact-MS (EI-MS) [17-19]. Such isolation procedures, applied reactions (acetylation, saponification, and reduction), Rf values, absorption, and MS spectra enabled identification of phytoene 1,2-oxide, and related compounds as the first naturally occurring epoxides of acyclic carotenoids [17]. 

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