Novel and efficient synthesis of cyanidin 3-O-β-D-glucoside from (+)-catechin via a flav-3-en-3-ol as a key intermediate

Article abstract of DOI:10.1021/ol0614976

A novel and efficient synthesis of cyanidin 3-O-β-D-glucoside (1) was accomplished the first time by a biomimetic oxidation route. From (+)-catechin, 3-OH was glucosylated, and the 4-position of the nucleus was then oxidized and dehydrated to give the 5,7

Full text of DOI:10.1021/ol0614976

ORGANIC
LETTERS
2006
Vol. 8, No. 16
3609-3612
Novel and Efficient Synthesis of
Cyanidin 3-O- -Glucoside from
)-Catechin via a Flav-3-en-3-ol as a
Key Intermediate
â
-D
(+
Tadao Kondo,*,† Kin-ichi Oyama,‡ Saki Nakamura,† Daisuke Yamakawa,§
|
Kazunari Tokuno, and Kumi Yoshida*,†
Graduate School of Information Science, Chemical Instrument Room, Research Center
for Materials Science, Graduate School of Bioagricultural Sciences, and Graduate
School of Human Informatics, Nagoya UniVersity, Chikusa, Nagoya 464-8601, Japan
kondot@info.human.nagoya-u.ac.jp; yoshidak@is.nagoya-u.ac.jp
Received June 19, 2006
ABSTRACT
A novel and efficient synthesis of cyanidin 3-O-
â
-
D
-glucoside (1) was accomplished the first time by a biomimetic oxidation route. From
,4 -tetra-O-(tert-
MeOH
(
+
)-catechin, 3-OH was glucosylated, and the 4-position of the nucleus was then oxidized and dehydrated to give the 5,7,3′ ′
butyldimethylsilyl)flav-3-en-3-ol 3-O-glucoside (8) as a key intermediate. 8 was deprotected and oxidized under air in hydrogen chloride
−
to give 1.
Anthocyanin is a pigment widespread in flowers, leaves,
fruits, and the roots of higher plants, which shows red
through purple to blue colors.1 Nowadays, anthocyanins are
attracting attention not only as a food colorant but also for
nutritional and medicinal reasons.2 Furthermore, the pigments
are also expected to be used in solar-cell devices.3 Despite
the amount of structural and color development research, only
few synthetic methods have been reported until now.4-6 One
is the pioneering work of Robinson and his group in the early
period of the 20th century.5 They synthesized many antho-
cyanidin mono- and diglucosides using an aldol condensation
method. However, the yield was sometimes low because of
(4) For a review of the chemical synthesis of anthocyanins: Iacobucci,
G. A.; Sweeny, J. G. Tetrahedron 1983, 39, 3005-3038.
(5) (a) Robertson, A.; Robinson, R. J. Chem. Soc. 1927, 242-247. (b)
Murakami, S.; Robertson, A.; Robinson, R. J. Chem. Soc. 1931, 2665-
2671. (c) Robinson, R. Ber. 1934, 67A, 85-105.
† Graduate School of Information Science.
‡ Chemical Instrument Room, Research Center for Materials Science.
§ Graduate School of Bioagricultural Sciences.
| Graduate School of Human Informatics.
(1) (a) Goto, T.; Kondo, T. Angew. Chem., Int. Ed. Engl. 1991, 30, 17-
33. (b) Brouillard, R. In The FlaVonoids AdVances in Research since 1986;
Harborne, J. B., Ed.; Chapman & Hall: London, 1994; pp 565-588. (c)
Anderson, O. M.; Jordheim, M. In FlaVonoids Chemistry, Biochemistry and
Applications; Anderson, O. M., Markham, K. R., Eds.; CRC Press: Boca
Raton, 2006; pp 471-551.
(6) (a) Shibata, K.; Shibata, Y.; Kasiwagi, I. J. Am. Chem. Soc. 1919,
41, 208-220. (b) Krishnamurty, H. G.; Krishnamoorthy, V.; Seshadri, T.
R. Phytochemistry 1963, 2, 47-60. (c) Elhabiri, M.; Figueiredo, P.;
Fougerousse, A.; Brouillard, R. Tetrahedron Lett. 1995, 36, 4611-4614.
Elhabiri et al. reported the yield was 60%. However, we reexamined the
reduction of rutin under HCl-MeOH with zinc amalgam, zinc powder, or
magnesium powder to obtain cyanidin 3-O-rutinoside in less than 30% yield
at the optimized condition. This might be due to the fact that the value of
the molar absorption coefficients for cyanidin 3-O-rutinoside reported by
Elhabiri et al. (7000 at 510 nm) is too low compared to the theoretical
value (around 20 000 in our results); therefore, they miscalculated the yield.
(2) Lila, M. A. In Plant Pigments and their Manipulation; Davis, K.,
Ed.; Annual Plant Reviews; CRC Press: Boca Raton, 2004; Vol 14., pp
248-274.
(3) Cherepy, N. J.; Smestad, G. P.; Gra¨tzel, M.; Zhang, J. Z. J. Phys.
Chem. B 1997, 101, 9342-9351.
10.1021/ol0614976 CCC: $33.50
© 2006 American Chemical Society
Published on Web 07/12/2006

Scheme 1. Biosynthetic Pathway of Anthocyanin
the drastic reaction conditions at the final step.5 The other
Scheme 2. Key Steps of Our Synthetic Strategy for 1
is the reduction of flavone and flavonol by metals, which
was first described by Shibata et al.6a Although several
experiments using commercially available rutin6b,c have been
reported, these methods possess the inherent defect that it is
difficult to prepare a wide variety of flavonol glycosides and
that the reaction yield of the reduction to anthocyanin is low.6
Anthocyanin is biosynthesized from chalcone via leucoan-
thocyanidin (Scheme 1).7 The last and key step from a
colorless compound to a colored anthocyanidin is catalyzed
by anthocyanidin synthase (ANS), a family of 2-oxoglutarate-
dependent oxygenases, requiring molecular O2 and a ferrous
ion in oxidation.7 After this, anthocyanidin 3-O-glucosyl-
transferase (3GT) works to give anthocyanin. However,
leucoanthocyanidin is very unstable. Therefore, the chemical
mechanism and mode of action of ANS are still the subject
of argument.7 Furthermore, no one has yet attempted this
oxidation route to synthesize anthocyanins. Only red col-
oration of the reaction mixture and detection of the antho-
cyanidin nucleus without glycosyl residue have been previ-
ously described.8 Here, we report on the first chemical
synthesis of cyanidin 3-O-â-D-glucoside (1),9 which is one
of the most popular anthocyanidin monoglucosides, using a
biomimetic oxidative reaction of a leucoanthocyanidin
compound via the flav-3-en-3-ol derivative.
an anthocyanidin nucleus (aromatization) could proceed
under mild conditions using molecular oxygen from our
preliminary experiments (Scheme 2).
As shown in Scheme 3, the 3-hydroxyl group of 5,7,3′,4′-
tetra-O-benzylcatechin (2), prepared from (+)-catechin ac-
cording to Kawamoto’s procedure,10 was glucosylated with
peracetylglucosyl trichloroacetimidate in the presence of
catalytic amounts of TMSOTf.11 The desired â-glucoside 3
was obtained (71%) with the 3-O-acetylcatechin (15%). The
benzyl groups of 3 were replaced with TBS or acetyl groups
because the benzyl protecting groups were inappropriate for
the following reactions. After removal of the benzyl groups
of 3 by hydrogenation, the resulting product was treated with
TBSCl or AcCl to give 4 (84%, two steps) and 5 (86%, two
steps), respectively. TBS-protected 4 was oxidized with
DDQ12 in a suspension of CH2Cl2 and H2O to give the 3,4-
cis-leucoanthocyanin (6) in 74% yield as a single isomer
accompanying the corresponding flavanone 7 (9%), and the
acetylated catechin 5 did not give any 4-oxidized product
under the same oxidative conditions. The configuration of 6
was determined to be 3,4-cis, which was the same as the
biosynthetic intermediate, by NMR analysis.13
In planning the synthetic strategy, we designed 5,7,3′,4′-
tetra-O-(tert-butyldimethylsilyl)flav-3-en-3-ol 3-O-glucoside
(8) as an equivalent of the cis-leuco compound (Scheme 2).
We decided to oxidize this enol compound to anthocyanin
at the final step because the key oxidation reaction of 8 to
(7) (a) Heller, W.; Forkmann, G. In The FlaVonoids AdVances in
Research since 1986; Harborne, J. B., Ed.; Chapman & Hall: London, 1994;
pp 499-535. (b) Schwinn, K. E.; Davies, K. M. In Plant Pigments and
their Manipulation; Davis, K., Ed.; Annual Plant Reviews, CRC Press: Boca
Raton, 2004; Vol 14. pp 92-149. (c) Davies, K. M.; Schwinn, K. E. In
FlaVonoids Chemistry, Biochemistry and Applications; Anderson, O. M.,
Markham, K. R., Eds.; CRC Press: Boca Raton, 2006; pp 143-218. (d)
Nakajima, J.; Tanaka, Y.; Yamazaki, M.; Saito, K. J. Biol. Chem. 2001,
276, 25797-25803. (e) Turnbull, J. J.; Nakajima, J.; Welford, R. W. D.;
Yamazaki, M.; Saito, K.; Schofield, C. J. J. Biol. Chem. 2004, 279, 1206-
1216.
(8) In previous studies, the authors did not isolate anthocyanidins but
reported the observation of red coloration or identification of visible
absorption spectra using a reaction mixture. All the experiments were
conducted with leucoanthocyanidin or flaven-3-ol without any glycosyl
residues: (a) Sweeny, J. G.; Iacobucci, G. A. Tetrahedron 1977, 33, 2923-
2926. (b) Sweeny, J. G.; Iacobucci, G. A. Tetrahedron 1977, 33, 2927-
2932. (c) Zanarotti, A. Tetrahedron Lett. 1982, 23, 3963-3964.
(9) (a) Kuroda, C.; Wada, M. Proc. Imp. Acad. 1933, 9, 17-18. (b)
Hayashi, K.; Abe, Y. Bot. Mag., Tokyo 1955, 68, 299-308. (c) Yoshida,
K.; Sato, Y.; Okuno, R.; Kameda, K.; Isobe, M.; Kodo, T. Biosci. Biotechnol.
Biochem., 1996, 60, 589-593.
The compound 6 was dissolved in MeOH containing 5%
(w/w) hydrogen chloride, and the mixture was allowed to
stand at room temperature. The solution gradually became
(10) Kawamoto, H.; Nakatsubo, F.; Murakami, K. Mokuzai Gakkaishi
1991, 37, 488-493.
(11) (a) Schmidt, R. R.; Michel, J. Angew. Chem., Int. Ed. Engl. 1980,
19, 731-732. (b) Schmidt, R. R. Angew. Chem., Int. Ed. Engl. 1986, 25,
212-235.
(12) (a) Steenkamp, J. A.; Ferreira, D.; Roux, D. G. Tetrahedron Lett.
1985, 26, 3045-3048. (b) Steenkamp, J. A.; Mouton, C. H. L.; Ferreira,
D. Tetrahedron 1991, 47, 6705-6716. (c) Tu¨ckmantel, W.; Kozikowski,
A. P.; Romanczyk, L. J., Jr. J. Am. Chem. Soc. 1999, 121, 12073-12081.
(d) Ohmori, K.; Ohrui, H.; Suzuki, K. Tetrahedron Lett. 2000, 41, 5537-
5541.
(13) The 3,4-cis configuration of 6 was determined from J2,3 ) 10.0 Hz
and J3,4 ) 3.5 Hz.
3610
Org. Lett., Vol. 8, No. 16, 2006

Scheme 3. Synthesis of Cyanidin 3-O-â-D-Glucoside (1) via a Flav-3-en-3-ol 3-O-Glucoside 8 as a Key Intermediate
red, and after 20 h, the color was dark red. However, the
amount of cyanidin 3-O-glucoside (1) quantified by HPLC
was very low.14 Presumably, this is due to the formation of
oligomers by self-condensation; decomposition products
might also be produced after carbocation formation at the
C-4 position.10,12c Therefore, we concluded that 6 was not a
suitable substrate for oxidation to anthocyanin. Therefore,
we designed flav-3-en-3-ol 3-O-glucoside 8 as a key
intermediate to inhibit formation of the carbocation at C-4
and to enhance radical hydrogen atom abstraction at the C-2
position.15 Accordingly, 6 was treated with MsCl and i-Pr2-
NEt in CH2ClCH2Cl at 80 °C to give 8 in 82% yield (Scheme
3). Using the combination of Tf2O and Et3N or pyridine did
not give 8 but instead caused decomposition.
Deprotection of the O-acetyl groups of 8 with NaOMe
gave 9 in 82% yield with a small amount of partially
desilylated compounds. Removal of the TBS groups and
oxidation were performed in one pot under acidic condi-
tions,16,17 which used hydrogen chloride in anhydrous MeOH.
Thus, 9 was dissolved in 1% (w/w) HCl-MeOH18 under
dried air, and the reaction mixture was allowed to stand at
room temperature. The reaction mixture gradually became
red, and after 3 h, 1 was detected by HPLC as coexisting
with colorless compounds.19 After 8 h, the colorless com-
pounds disappeared, and the reaction was complete. When
the reaction was conducted in 1% (w/w) aqueous hydro-
chloric acid-MeOH at room temperature, the oxidation
reaction was slower than that with gaseous hydrogen
chloride-MeOH, and the yield was lower. Finally, 32 mg
(51%, two steps) of cyanidin 3-O-â-D-glucoside (1) was
obtained directly from 8 (119 mg, 111 µmol) by treatment
with 2.5 equiv of NaOMe, followed by 1% hydrogen
chloride-MeOH.20
In conclusion, we established a novel and efficient
synthetic route to cyanidin 3-O-â-D-glucoside (1) from (+)-
catechin using a biomimetic oxidation reaction via flav-3-
en-3-ol 3-O-glucoside 8. This study can provide a practical
(16) In general, the phenolic TBS group is relatively stable in acidic
conditions, but we found that the TBS group of polyphenols such as
flavonoides was deprotected easily from our preliminary experiments:
Davies, J. S.; Higginbotham, C. L.; Tremeer, E. J.; Brown, C.; Treadgold,
R. C. J. Chem. Soc., Perkin Trans. 1 1992, 3043-3048.
(17) In acidic media, anthocyanins form stable flavylium ions, whose
color is usually red. However, they become colorless in neutral or basic
media due to hydration.1a
(14) Develosil ODS-HG-5 column (2.0 mm φ × 250 mm) with linear
gradient elution from 10% aqueous to 90% MeCN containing 0.5% TFA;
flow rate of 0.2 mL/min, detection with a photodiode array, and a
temperature of 40 °C.
(15) In this reaction, the oxidation to anthocyanin might proceed by a
radical process via a phenoxyl radical intermediate: (a) Jovanovic, S. V.;
Steenken, S.; Tosic, M.; Marjanovic, B.; Simic, M. G. J. Am. Chem. Soc.
1994, 116, 4846-4851. (b) Rice-Evans, C. A.; Miller, N. J.; Paganga, G.
Free Radical Biol. Med. 1996, 20, 933-956. (c) Cren-Olive´, C.; Hapiot,
P.; Pinson, J.; Rolando, C. J. Am. Chem. Soc. 2002, 124, 14027-14038.
(18) In the case of the deprotection and oxidation of 6, 5% HCl was
required. However, the reactions of 9 smoothly proceeded using 1% HCl,
and the starting material was completely consumed.
(19) The colorless peaks might be intermediates corresponding to mono-
or tetra-desilylated compounds; the spectra obtained by 3D-HPLC were
similar to those of 8 and 9 (λmax 280 nm).
Org. Lett., Vol. 8, No. 16, 2006
3611

preparation process for anthocyanin synthesis. The difference
in reactivity between the leuco derivative 6 and the flav-3-
en-3-ol derivative 8 indicated that the oxidation mechanism
by ANS might go through a flavenol intermediate. The
synthesis of various anthocyanins according to this procedure
is in progress.
Acknowledgment. This work was financially supported
by The Ministry of Education, Culture, Sports, Science and
Technology, Japan ((B) No. 16370021, The 21st Century
COE Program No. 14COEB01-00, Creative Scientific Re-
search No. 16GS0206, Priority Areas No. 17035041,
18032037, and Young Scientists (B) No. 18780086).
Supporting Information Available: Full experimental
details and copies of H NMR spectra. This material is
available free of charge via the Internet at http://pubs.acs.
org.
(20) To the reaction mixture was added a large amount of water, and
the mixture was then absorbed to an Amberlite XAD-7 column. The column
was eluted with 50% MeCN containing 0.5% TFA to give crude 1. The
crude fraction was purified by HPLC (Develosil ODS-HG-5 column,
stepwise elution from 0.5% TFA to 30% MeCN aqueous containing 0.5%
TFA) to give pure 1 as a dark red TFA salt. The synthetic 1 was identical
1
1
with the natural one (CD, UV/VIS, H NMR, and HPLC).9c
OL0614976
3612
Org. Lett., Vol. 8, No. 16, 2006