Chemistry Reference
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these compounds are discussed later in this chapter, in both
in vitro
and
in vivo
proof-of-concept
studies performed in most cases by the authors and their collaborators.
No stability problems were encountered when hydroxycarotenoids were combined with the
hydrophilic antioxidant resveratrol,
3.24
(Lockwood et al. 2005), Scheme 3.9. New glyco compounds
were added to the register of synthesized carotenoid sugars and carotenoid sugar alcohols, this time
intentionally prepared for use in water: astaxanthin combinations with maltose, mannitol, and sor-
bitol,
3.25
(Lockwood et al. 2005). Further, the combination of astaxanthin-citric acid,
3.26
, and
astaxanthin-glutathione,
3.27
, were obtained. The hydrophilic norcarotenoid diketones of violeryth-
rin type (i ve-membered ring),
3.28
, could become interesting compounds as blue food colorants;
their antioxidant ability is also very powerful (Lockwood et al. 2007), Scheme 3.10. Carotenoids
with hydroxybenzene rings were i rst obtained in Düsseldorf; later, in Hawaii, the renieratene type
carotenoid,
3.29
, was used as a parent compound for attaching hydrophilic groups (Korger 2005,
Lockwood et al. 2007). Unfortunately, except for minor exceptions, the available amounts of these
new hydrophilic carotenoids did not reach the necessary level for surface and aggregation stud-
ies. The phosphocholine,
3.30
, was again synthesized for self-aggregation; (Foss 2005) whereas
the intention for the synthesis of the carotenoid-selenium-lipid,
3.31
, was rather for self-assembly
studies, Scheme 3.11 (Foss et al. 2006b). Likewise, carotenoid phospholipids with saturated fatty
acids of different chain lengths,
3.32-3.34
, and the carotenoid cholinester,
3.35
, were prepared
predominantly as DNA protecting and delivery agents, although aggregation was thoroughly stud-
ied (C.L. Øpstad, Trondheim, unpublished). An intuitive approach to hydrophilic, surface active
carotenoids would be the preparation of “orange soaps,” alkali salts of carotenoid acids. Some
potassium and sodium salts of carotenoid acids with variable chain lengths are now under investiga-
tion (e.g., potassium C30-carotenoate,
3.36
, potassium C20-C35 carotenoate, Scheme 3.11) (Foss
et al. 2006b) (I.L. Alsvik, Trondheim, unpublished). Another straightforward method to introduce a
hydrophilic group would be the oximation of ketocarotenoids; oximation is one of the few reactions
of carotenoids with full conversion, and the oxime hydroxy group is expected to increase hydrophi-
licity. However, the hydrophilicity of the echinenon oxime,
3.37
, was disappointingly low, and its
aggregation behavior could only be studied in acetone-water mixtures, Scheme 3.12 (Benade 2001).
Improved hydrophilicity can easily be acquired when carotenoid oximes are reacted with HCl gas to
oximium salts. Alas, even the oximium salt,
3.38
, was not hydrophilic enough to be used for study-
ing surface properties in water (Willibald et al. 2009).
-
O
Na
+
O
-
Na
+
P
O
O
O
OH
HO
O
O
HO
OH
O
O
O
3.28
P
-
O
Na
+
Na
+
O
-
OH
OH
HO
OH
OH
HO
3.29
SCHEME 3.10
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