A. Strand et S. Liaaen-jensen, First preparation and characterization of the allenic carotenoids (all-E,6S)- and (9 ' Z,6S)-neoxanthin, J CHEM S P1, (4), 2000, pp. 595-598
Conditions for obtaining optimum allenic photoisomerization of (6R)-neoxant
hin in benzene solution have been studied using diphenyl diselenide, diphen
yl ditelluride or iodine as catalyst with various light qualities (sunlight
, UVA irradiation or artificial, visible light) and intensities. The effect
of adding base in order to prevent furanoid rearrangement was examined. At
optimum conditions 77% conversion of (R)- to (S)-allene was observed for n
eoxanthin (UVA, 2 x molar excess diphenyl diselenide:neoxanthin, presence o
f Hunig's base). These conditions were superior to iodine catalyzed isomeri
zation.
(All-E,6S)- and (9'Z,6S)-neoxanthin were prepared for the first time and ch
aracterized by chromatographic (HPLC) and spectroscopic (VIS, MS, 2D H-1 NM
R, CD) techniques. Other geometrical isomers of the allenic (6S)-series wer
e obtained by (E)/(Z) isomerization of (6S)-neoxanthin and characterized by
HPLC and VIS data. At comparable conditions the ease of allenic (R)/(S) is
omerization was peridinin > fucoxanthin > neoxanthin.