Neoxanthin acetate

A survey10 of several dinoflagellates has revealed the presence of some interesting new carotenoids in addition to the main carotenoid peridinin [3 -acetoxy-5,6-epoxy-3,5 -dihydroxy-6, 7 -didehydro-5,6,5, 6 -tetrahydro-12, 13, 20 -trinor-/3,/ -caroten-19,11-olide (19)]. Pyrrhoxanthin was assigned the trinor structure 3 -acetoxy-5,6-epoxy-3-hydroxy-7, 8 -didehydro-5,6-dihydro-12, 13, 20 -trinor-/3,/3-caroten-19,11-olide (20) from a consideration of its spectroscopic properties and by chemical correlation with peridinin, and dinoxanthin was shown to be an acetate of neoxanthin, i.e. 3 -acetoxy-5,6-epoxy-6, 7 -didehydro-5,6,5, 6 -tetrahydro-/3,j8-carotene-3,5 -diol (11). Small amounts were also obtained of pyrrhoxanthinol and peridininol which were shown to be the deacetylated analogues (21) and (22) of pyrrhoxanthin and peridinin respectively. 

The characteristic pigment of Pytrophyta is peridinin (XXI), but smaller amounts of diadinoxanthin (5,6-epoxy-7, 8 -didehydro-5,6-dihydro-j8,/3-carotene-3,3 -diol), dinoxanthin (neoxanthin 3-acetate), and )8-carotene, (VI) are also synthesized. In Cryptophyta, a-carotene (XXV) is found in greater amounts than /3-carotene. An acetylenic carotenoid, alloxan thin (7,8,7, 8 -tetradehydro-/8,/3-carotene-3,3 -diol), is also found. In Eugleno-phyta, pigments are found in both the chloroplasts and the eye spot of these organisms. Traces of keto carotenoids such as echinenone (/3,/8-caroten-... 

In principle the conversion of carotenoids with an allenic end group of the type present in neoxanthin (1) acetate to carotenoids with acetylenic end groups by HCI/CHCI3 or by POCI3 in pyridine (41, 105) or to products with chlorinated P-type end groups by HCI/CHCI3 (41, 105) could be useful for stereochemical considerations. 

A smaller set of eight xanthophyll pigments (e.g., chlorophylls, -carotene, neoxanthin, lutein, zeaxanthin) were baseline resolved in <15 min using a C g column (2 = 440 nm) and a step gradient fiom 94.75/1.75/1.75/1.75 acetonitrile/ water/dichloromethane/methanol to 50/50 ethyl acetate/acetonitrile at the 5 min mark after injection [879]. Peak shapes were excellent. Concentrations ranging from 0.1 to lOnmol/mL were used as standards. 

The first online coupling of TLC and MS for the analysis of carotenoids was applied for detection of neoxanthin, violaxanthin, lutein, and P-carotene in spinach extract. Separation on Cjg RP HPTLC plate was followed by extraction of the carotenoids by means of CAMAG TLC-MS interface. After the elution of compounds from the sorbent with methanol, 1% acetic acid was added to the effluent to augment the ionization in the atmospheric pressure chemical ionization (APCI) source, which operated in positive mode [25]. 

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