- Kinetic Studies on the Thermal (Z/E)-Isomerization of C40-Carotenoids
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Rates of thermal (Z/E)-isomerization among all-E-, 9(9')Z-, 13Z-, 13'Z- and 15Z-isomers of zeaxanthin (1), natural violaxanthin (2), "semi-synthetic" violaxanthin (2a), capsorubin (3), capsanthin (4) and lutein epoxide (5) have been measured at temperatures over the range 333.4-368.4 K.From the specific rate constants calculated on the basis of four kinetic models, the Arrhenius and activation parameters have been derived.The effect of the different end groups and different solvents on the composition of the (Z/E)-equilibrium mixtures have been investigated as well.The rates of the isomerization reactions have been measured by HPLC, UV/VIS spectrophotometry and "classic" column chromatography.
- Molnar, Peter,Kortvelyesi, Tarnas,Matus, Zoltan,Szabolca, Jozsef
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p. 801 - 841
(2007/10/03)
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- Syntheses of Enantiomerically Pure Violaxanthins and Related Compounds
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The epoxides 16 and ent-16, prepared by Sharpless-Katsuki oxidation of 15 in excellent yield and very high enantiomeric purity, were used as synthons for the preparation of (+)-(S)-didehydrovomifoliol (45), (+)-(6S,7E,9E)-abscisic ester 46, (+)-(6S,7E,9Z)-abscisic ester 47, (-)-(3S,7E,9E)-xanthoxin (49), (-)-(3R,7E,9E)-xanthoxin (50), (3S,5R,6S,3'S,5'R,6'S,all-E)-violaxanthin (1), (3R,5R,6S,3'R,5'R,6'S,all-E)-violaxanthin (55) and their (9Z) (see 53, 57), (13Z) (see 54, 58), and (15Z) (see 60) isomers.The novel violadione (61) was prepared from 1 by oxidation with DMSO/Ac2O.By base treatment, 61 was converted into violadienedione (62), a potential precursor of carotenoids with phenolic end groups.
- Acemoglu, Murat,Uebelhart, Peter,Rey, Max,Eugster, Conrad Hans
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p. 931 - 956
(2007/10/02)
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