Chemistry Reference
In-Depth Information
The ozonolysis of carotenoids was employed in order to obtain oxygenated cleavage products
for biological tests, for example, for lycopene. In this case, among a series of products, one prod-
uct formed by a double oxidative cleavage was purii ed and characterized as (
E
,
E
,
E
)-4-methyl-8-
oxo-2,4,6-nonatrienal, and it was shown to be active in the induction of apoptosis in HL-60 cells
(Zhang et al. 2003).
Osmium tetroxide/hydrogen peroxide was used to oxidatively cleave
-carotene chemically
(Wendler and Rosenblum 1950). This reagent was later used to produce oxygenated cleavage com-
pounds from lycopene. Indeed, the acyclic analogue of retinal, i.e., acycloretinal, also named apo-
15-lycopenal, is of interest for its potential biological activity. Acycloretinal was obtained by the
oxidation of lycopene using osmium tetroxide/hydrogen peroxide; subsequent oxidation or reduc-
tion gave, respectively, acycloretinoic acid and acycloretinol (Wingerath et al. 1999). Using similar
experimental conditions to those of Wendler et al., Aust et al. obtained several oxidation products,
among which one, diapocarotenoid (2,7,11-trimethyltetradecahexaene-1,14-dial), was identii ed and
shown to stimulate gap junction communication (Aust et al. 2003).
The oxidation of
β
-carotene with potassium permanganate was described in a dichloromethane/
water reaction mixture (Rodriguez and Rodriguez-Amaya 2007). After 12 h, 20% of the carotenoid
was still present. The products of the reaction were identii ed as apocarotenals (apo-8
β
′
- to apo-15-
carotenal = retinal), semi-
-carotene-5,8-epoxide.
We have developed a biphasic oxidation protocol using the hydrophilic oxidant potassium
permanganate (Caris-Veyrat et al. 2003), which we applied to lycopene. Cetyltrimethylammonium
bromide was used as a phase transfer agent to achieve the contact of the hydrophilic oxidant with
the lipophilic carotenoid lycopene dissolved in methylene chloride/toluene (50/50, v/v). Analysis of
the reaction mixture by HPLC-DAD-MS revealed the presence of (1) apolycopenals and apolyco-
penones derived from a single oxidative cleavage and (2) diapocarotenedials derived from a double
oxidative cleavage of lycopene which had lost the two
β
-carotenone, monoepoxides, and hydroxy-
β
-end groups of lycopene (Figure 11.2). No
apolycopenoic acids were found in the reaction mixture, indicating that, in our experimental condi-
tions, there was no further oxidation of apolycopenals by potassium permanganate. This oxidation
Ψ
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
or
O
O
O
O
O
O
O
O
FIGURE 11.2
Lycopene oxygenated cleavage compounds produced by the reaction of potassium perman-
ganate on lycopene in a biphasic medium: apolycopenals and apolycopenones (left column), and diapocaro-
tendials (right column).
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