- Olefin metathesis in carotenoid synthesis
-
Olefin metathesis is a powerful and widely applicable synthetic method for carbon-carbon double bond formation. However, its application to the synthesis of conjugating polyene chains has been very limited because of possible undesired side reactions. We attempted to apply this method to the synthesis of symmetrical carotenoids. In this paper, the syntheses of violaxanthin and mimulaxanthin are described using the olefin metathesis protocol.
- Kajikawa, Takayuki,Iguchi, Naoko,Katsumura, Shigeo
-
-
Read Online
- NATURALLY OCURING DI-CIS-VIOLAXANTHINS FROM VIOLA TRICOLOR: ISOLATION AND IDENTIFICATION BY 1H NMR SPECTROSCOPY OF FOUR DI-CIS-ISOMERS
-
From blossoms of Viola tricolor, four new naturally occuring geometrical isomers of violaxanthin (5,6,5',6'-diepoxy-5,6,5',6'-tetrahydro-β,β-carotene-3,3'-diol) have been isolated in the crystalline state.By two-dimensional 1H NMR methods, the new pigments are shown to be the 9,9'-, 9,13'-,9,15-and 9,13-di-cis isomers.Thermal and iodine-catalysed photochemical stereomutations of the new natural pigments have also been studied.Key Word Index-Viola tricolor; Violaceae; 9,9'-, 9,13'-, 9,15- and 9,13-di-cis-violaxanthins.
- Molnar, Peter,Szabolcs, Jozsef,Radics, Lajos
-
-
Read Online
- Preparation and (E/Z)-Isomerization of the Diastereoisomers of Violaxanthin
-
Violaxanthin A (=(all-E,3S,5S,6R,3′S,5′S,6′ R)-5,6:5′,6′-diepoxy-5,6,5′,6′-tetrahydro-β, β-carotene-3,3′-diol = syn,syn-violaxanthin; 5) and violaxanthin B (=(all-E,3S,5S,6R,3′S,5′R,6′S)-5,6:5′, 6′-diepoxy-5,6,5′,6′-tetrahydro-β,β-carotene-3, 3′-diol = syn,anti-violaxanthin; 6) were prepared by epoxidation of zeaxanthin diacetate (1) with monoperphthalic acid. Violaxanthins 5 and 6 were submitted to thermal isomerization and I2-catalyzed photoisomerization. The structure of the main products, i.e., (9Z)-5, (13Z)-5, (9Z)-6, (9′Z)-6, (13Z)-6, and (13′Z)-6, was determined by their UV/VIS, CD, 1H-NMR, 13C-NMR, and mass spectra.
- Molnar, Peter,Deli, Jozsef,Zsila, Ferenc,Steck, Andrea,Pfander, Hanspeter,Toth, Gyula
-
-
- Kinetic Studies on the Thermal (Z/E)-Isomerization of C40-Carotenoids
-
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
-
p. 801 - 841
(2007/10/03)
-
- Syntheses of Enantiomerically Pure Violaxanthins and Related Compounds
-
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
-
p. 931 - 956
(2007/10/02)
-
- Isomerizing cis-carotenoids to all-trans-carotenoids
-
Cis-isomers of a carotenoid are isomerized to an all-trans-isomer of the carotenoid by heating the cis-isomers in water at above about 50° C.
- -
-
-