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Archives of Biochemistry and Biophysics 483 (2009) 191–195

Contents lists available at ScienceDirect

Archives of Biochemistry and Biophysics
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Review

Recent progress in structural studies of carotenoids in animals and plants
Takashi Maoka *Research Institute for Production Development, Food Function and Chemistry, 15 Shimogamo-morimoto-cho, Sakyo-ku, Kyoto 606-0805, Japana r t i c l e

i n f oArticle history:
Received 28 August 2008
and in revised form 7 October 2008
Available online 1 November 2008
Keywords:
Carotenoids
New structures
Structural elucidation
Aquatic animals
Higher plants

a b s t r a c t
About 750 naturally occurring carotenoids had been reported as of 2004. Furthermore, annually, morethan 20 new structures of carotenoids are reported. Improvements of analytical instruments such as
NMR, MS, HPLC, etc., have made it possible to perform the structural elucidation of very minor carotenoids in nature. Interesting new structural carotenoids can still be identiﬁed in aquatic animals andhigher plants. The present paper provides a review of new structural carotenoids isolated from aquatic
animals and higher plants by our group over the last ﬁve years.
Ó 2008 Elsevier Inc. All rights reserved.

Since the ﬁrst structural elucidation of b-carotene by Kuhn andKarrer in 1928–1930, about 750 naturally occurring carotenoids
had been reported as of 2004 [1]. Improvements of analytical
instruments such as NMR1, MS, HPLC, etc., have made it possible
to perform the structural elucidation of very minor carotenoids innature [2,3]. Annually, more than 20 new structures of carotenoids
are being reported.
Our research group has developed structural analysis of naturally occurring carotenoids [3] using NMR, MS, MS/MS [4], LC/MS[5], etc., over the last decade. Herein, I describe the progress in
structural studies of naturally occurring carotenoids of our group.
Carotenoids in aquatic animals
Marine animals, especially bivalves (oysters, clams, scallops,etc.) contain various carotenoids, which show structural diversity[6–9]. Bivalves accumulate carotenoids from their dietary algae
and modify them through metabolic reactions. Many of the carotenoids present in bivalves are metabolites of fucoxanthin, peridinin,and diatoxanthin [6–9].
In 1992, our group isolated two unique carotenoids, named
crassestreaxanthin A (1) and B (2), from the Japanese oyster Crassostrea gigas [10]. These two carotenoids have unique structuralend groups, which have not been previously reported. These struc-* Fax: +81 75 781 1118.
E-mail address: maoka@mbox.kyoto-inet.or.jp.
1
Abbreviations used: NMR, nuclear magnetic resonance; MS, mass spectrometry;
HPLC, high performance liquid chromatography; MS/MS, mass spectrometry/mass
spectrometry; LC/MS, Liquid chromatography mass spectrometry; CD circulardichroism spectrometry, LC/NMR Liquid chromatography nuclear magnetic
resonance.
0003-9861/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved.
doi:10.1016/j.abb.2008.10.019

tures were determined to be 30 ,60 -epoxy-3-hydroxy-60 -methyl-7,8didehydro-10 ,20 ,50 ,60 ,70 ,80 -hexahydro-160 -nor-b, w-carotene-10 ,80 dione (1) and 3,30 -dihydroxy-7,8-didehydro-10 ,20 ,70 ,80 -tetrahydro60 -methyl-160 -nor-b, w-carotene-10 ,80 -dione (2), respectively, by
the detailed analysis of MS and NMR data [10] as shown in Scheme
1. Based on the structural similarity, crassostreaxanthin A and B
were assumed to be metabolites of halocynthiaxanthin. The (3R,
30 S) conﬁgurations of crassestreaxanthin B were conﬁrmed based
on total synthesis by Tode et al. [11]. Further studies of carotenoids
in marine animals revealed that crassostreaxanthin A and B andtheir 3-acetates were widely distributed in marine bivalves. Moreover, two new carotenoids, 3 and 4, possessing a structural moietyof crassostreaxanthin A, were isolated from the oyster as minor
components [12,13].
Mytiloxanthin, which has a unique enol hydroxy group at C-80
in the polyene chain and a 30 -hydroxy-60 -oxo-j-end group, is acharacteristic carotenoid in marine mussels and oysters [9]. Furthermore, three mytiloxanthin analogs containing a 3,6-epoxyend group (5), an allenic end group (6), and a 3,4-dihydroxy-bend group (7) were isolated from the oyster [12,13]. Compound 6
was assumed to be a metabolic intermediate from fucoxanthin to
mytiloxanthin. A 3,6-epoxy derivative of diadinoxanthin, named
cycloidadinoxanthin (8), was also isolated from the oyster [12].
In addition to these C40-skeletal carotenoids described above,
two new C37-skeletal carotenoids, 9 and 10, were isolated fromthe oyster [12,13]. Compound 9, having a 6-hydroxy-3-oxo-e-end
group, was assumed to be a metabolite of peridinin (Scheme 1).
Some edible clams have a bright orange or red color due to thepresence of carotenoids. Fucoxanthin 3-ester (11) and fucoxanthinol 3-ester (12) were found to be major carotenoids in Mactra chinensis [14], Ruditapes philippinarum, and Meretrix petechialis.

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T. Maoka / Archives of Biochemistry and Biophysics 483 (2009) 191–195

O
OH

O
O
HO

O
HO

Crassostreaxanthin A (1)Crassostreaxanthin B (2)
O

O

O

O

O

O
OH

O
HO

3

4

OH
O

H

O

O

H

O

.

O

OH
OH

O

5

OH

6

HO
OH

OH
O

H

O
O

OH

HO

OH

7

OH

OH
O

O

.

O

8
O

O

OH

OH
OH

O

O

O

OH

9

10

Scheme 1.

OH

O

OR2

HO

.

O

O

.
O

RO

Fucoxanthin 3-ester R1=Acyl R2=Acetyl (11)Fucoxanthinol 3-ester R 1=Acyl R2=H (12)

R1 O

OH

Amarouciaxanthin A 3-ester R=Acyl (13)

OH

OH

OR

.
OH
HO

HO

Corbiculaxanthin (14) R=H
Corbiculaxanthin 3'-acetate (15) R=Acetyl

OHOH

6-Epiheteroxanthin (16)

OH

O
O

.
HO

O
OH

7',8'-Didehydrodeepoxyneoxanthin (17)

OH

OH
O

O

.

Cyclopyrrhoxanthin (18)

O
O

OH
HO

O

OH

Hydratoperidinin (19)
Scheme 2.

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T. Maoka / Archives of Biochemistry and Biophysics 483 (2009) 191–195

Amarouciaxanthin A 3-ester (13) was also identiﬁed as a major
carotenoid in Paphia amabills. These structures were characterizedusing 1H NMR and MS spectrometry. Fatty acids esteriﬁed withthese carotenoids were assigned as C24:6, C22:5, C22:6, C20:5,
C20:0, C20:1, C18:0, C18:1, C16:0, C16:1, and C14:0 based on
FAB-MS data.
There are many reports on carotenoids in marine shellﬁsh [6–9]. However, there are few reports on the carotenoids of shellﬁshinhabiting brackish or fresh water [6–9]. In Japan, Corbicula japonica inhabits brackish water and C. sandai and C. leana inhabit fresh
water. Therefore, we studied the carotenoids of these three speciesof Corbicula clams.
Forty-three carotenoids, including six new ones, were isolated
from the three species of Corbicula clams [15,16]. Among them,
peridinin derivatives were found only in C. japonica, which inhabits
brackish water. On the other hand, lutein and loroxanthin were
found only in C. sandai and C. leana, which inhabit fresh water.
Fucoxanthin and diatoxanthin derivatives were found in all three
species [15]. From the carotenoid patterns in Corbicula clams, it
can be concluded that the brackish water clam mainly feeds on
dinoﬂagellates and diatoms and freshwater clams mainly feed on
green algae and diatoms.
Four new carotenoids, corbiculaxanthin (14), corbiculaxanthin
30 -acetate (15), 6-epiheteroxanthin (16), and 70 ,80 -didehydrodeepoxyneoxanthin (17), were found in all the above three species ofclam but not in other clam species [15,16]. Therefore, they are assumed to be carotenoids peculiar to the genus Corbicula. 70 ,80 -Didehydrodeepoxyneoxanthin (17) has an interesting structure withboth allenic and acetylenic moieties. Two new metabolites ofperidinin, cyclopyrrhoxanthin (18), and hydratoperidinin (19),were isolated from C. japonica, which inhabits brackish water[15,16] (Scheme 2). Carotenoids found in these animals provide a
key to the food chain as well as metabolic pathways [9].
Carotenoids in higher plants
Carotenoids present in photosynthetic organs have been extensively investigated. These biosynthetic roots were revealed byenzymatic and gene level experiments [17]. On the other hand,carotenoids present in non-photosynthetic organs such as fruits,seeds, and ﬂowers, showed structural diversity. Some of the
carotenoids found in non-photosynthetic organs were formed bysecondary metabolic reactions, such as oxidation, the cleavage ofpolyene chains, (Z/E) (cis–trans) isomerization, etc. [17]. Therefore,
new structural carotenoids can still be found in fruits, seeds, andﬂowers in higher plants.
Carotenoids with 6-oxo-j-end group in paprika
Paprika, Capsicum annuum, is a good source of carotenoids. Major carotenoids in paprika are capsanthin and capsorubin, containing a 3-hydroxy-6-oxo-j-end group. These carotenoids show astrong singlet oxygen quenching activity [18] and also the inhibition of lipid peroxidation induced by free radicals [19]. They also
possess excellent anti-cancer activities [20].
Several unique structural carotenoids have been reported in paprika by the University of Pécs group in Hungary [21]. Our groupalso isolated a series of apocarotenoids derived from capsanthinfrom paprika [22]. Furthermore, two new carotenoids, named 30 deoxycapsanthin (20) and 3,4-dehydroxy-30 -deoxycapsanthin(21), were isolated from paprika as very minor components [23].
These carotenoids have a 6-oxo-j-end group. Carotenoids with a

O

O

HO

3,4-Dehydroxy-3'-deoxycapsanthin (21)3'-Deoxycapsanthin (20)
5'
6

O
5

O

5

1

Myristyl

O
6

6'

O

OH
6

.

1'

3'

5'

O
5

3

MyristylO53(9Z)-Violaxanthin 3'-ester

O

6

O

Tobiraxanthin B (23)

6'

.

6'
3'
OH
OH

OH
3'

O
5

O

5'

3

1

6

Scheme 3.

OH
HO

6

6'

O

Tobiraxanthin D (25)Tobiraxanthin C (24)OH

6-Epilatoxanthin 3'-ester
Oxidative cleavage of
epoxy end group

Myristyl
O

3

HO
O

3'
Myristyl O

OH

O

OH
3

Neoxanthin 3'-ester
Oxidative cleavage of
epoxy end group

3
OH

6

6'

6
1

1

O
O
MyristylO

O

5'Myristyl
O

6'
5'

O

Oxidative cleavage of
epoxy end group

Oxidative cleavage at between C-5 (5')
and C-6 (6') epoxy end groupTobiraxanthin A (22)3'Myristyl O

9

6'
3'
O

Violaxanthin diester

Myristyl
O
3

6'

O

3
MyristylO Myristyl
3'

O

OH
3'

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6-oxo-j-end group have not been reported previously in nature.
These carotenoids were assumed to be formed from b-cryptoxanthin 50 ,60 -epoxide by pinacolic rearrangement through capsanthin
capsorubin synthase [23].

The major carotenoids in the yellow seeds are violaxanthin,(9Z)-violaxanthin, antheraxanthin, and neoxanthin esters. On theother hand, a series of acylated seco-carotenoids having a 3-acyloxy-5,6-diseco-5,6-diketo-b-end group, named tobiraxanthin A(22), B (23), C (24), and D (25), were isolated from red seeds as major carotenoids [24]. These structures were elucidated by the detailed analysis of MS and NMR spectral data. Tobiraxanthin A, B,
C, and D are corresponding oxidative cleavage products of C5–C6(C50 –C60 ) bond(s) in the violaxanthin diester, (9Z)-violaxanthin
30 -ester, neoxanthin 30 -ester, and 6-epilatoxanthin 30 -ester, respectively as shown in Scheme 3.
These seco-carotenoids (22–25) showed on approximately 15–
30 nm longer wavelength shift than their corresponding precursor
epoxy carotenoids because of the introduction of conjugated carbonyl group(s) at C6 (C60 ) by the oxidative cleavage of C5–C6 (C50 –C60 ) bond(s). Therefore, it was revealed that the color change fromyellow to red in the seeds is due to the formation of these secocarotenoids from epoxy carotenoids. Furthermore, it was assumed
that these seco-carotenoids protected the seeds from oxidation induced by sunlight and singlet oxygen because it was reported thatthe introduction of the conjugated double bond system in carotenoids enhanced the singlet oxygen quenching activity [25,26].
Moreover, seco-carotenoids with a 3-acyloxy-5-hydroxy-5,6diseco-6-keto-b-end group were also isolated from the red seeds[27].
These seco-carotenoids showed lability in alkaline medium.
Tobiraxanthin B was converted to a carotenoid with a 3-methoxy-5-keto-5,6-seco-4,6-cyclo-b-end group (26) on treatment with
KOH/MeOH [24] as shown in Scheme 4.

Seco-carotenoids in the seeds of Pittosporum tobira
Pittosporum tobira is a small, slender, evergreen tree growing insouthern Japan. In summer, the seeds have a pale yellow color. In
autumn, the seeds are exposed to sunlight and change color fromyellow to red.

Myristyl
O

O

5

3

6
1

O
O

Tobiraxanthin B (23)
KOH/MeOH

OH

O
H 3CO
O

26

Carotenoid and a-tocopherol complexes in the seeds of P. tobira

OH

Reaction of alkaline medium with tobiraxanthin B

A series of carotenoid and a-tocopherol complexes named pittosporumxanthins were isolated from the red-colored seeds of P.

Scheme 4.

O
R1

O

12'

11' O

OH

-R1 -R2

R2

O
HO

A1 :
A2 :

H
H

H
H

Pittosporumxanthin A1 (27)
Pittosporumxanthin A2 (28)
O
R1

O

12'

11'

R2

OH

-R1 -R2

O

B1:
B2:

HO

H
H

H
H

Pittosporumxanthin B1 (29)
Pittosporumxanthin B2 (30)
O
R1

.
HO

O

12'

11'

R2

OH

Pittosporumxanthin C1 (31)Pittosporumxanthin C2 (32)
Scheme 5.

OHO-R1 -R2
C1 :
C2 :

H
H

H
H

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T. Maoka / Archives of Biochemistry and Biophysics 483 (2009) 191–195

195

NMR, MS, CD, HPLC, LC/MS, LC/NMR etc., has made it possible toperform the structural elucidation of very minor carotenoids.
Structures of new carotenoids provide information on the function,biosynthesis in plants, and a key to the food chain as well as metabolic pathways in animals.
Acknowledgments
I thank Dr. N. Akimoto of Graduate School of Pharmaceutical
Sciences, Kyoto University and collaborators at Kyoto Pharmaceutical University for supporting this work.
References

Fig. 1. UV–vis (top) and CD (bottom) spectra of 1: pittosporumxanthin A1 and 2:
pittosporumxanthin A2 in ether.

tobira [28,29]. Pittosporumxanthin A1 (27) and A2 (28) were diastereomeric pairs of the cycloaddition product of (9Z)-violaxanthin
at the C-110 and C-120 positions, with a-tocopherol showing a O–
C120 –C110 –C2800 linkage. Furthermore, (9Z)-antherxanthin and atocopherol complexes, named pittosporumxanthin B1 (29) andB2 (30) and (90 Z)-neoxanthin, and a-tocopherol complexes, named
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