Efficient synthesis of analogs of safflower yellow B, carthamin, and its precursor: Two yellow and one red dimeric pigments in safflower petals

Article abstract of DOI:10.1016/j.tet.2005.07.080

The synthesis of analogs (8, 12, 14) of two yellow pigments, safflower yellow B and the precursor of carthamin, and carthamin itself, a red pigment, which are produced in safflower (Carthamus tinctrious L.) petals and, which have a common dimeric quinocha

Full text of DOI:10.1016/j.tet.2005.07.080

Tetrahedron 61 (2005) 9630–9636
Efficient synthesis of analogs of safflower yellow B, carthamin, and
its precursor: two yellow and one red dimeric pigments in
safflower petals
*
Shingo Sato, Takashi Kusakari, Tohru Suda, Takaharu Kasai, Toshihiro Kumazawa,
Jun-ichi Onodera and Heitaro Obara
Department of Chemistry and Chemical Engineering, Faculty of Engineering, Yamagata University, 4-3-16 Jonan, Yonezawa-shi, Yamagata
992-8510, Japan
Received 16 May 2005; accepted 7 July 2005
Available online 19 August 2005
Abstract—The synthesis of analogs (8, 12, 14) of two yellow pigments, safflower yellow B and the precursor of carthamin, and carthamin
itself, a red pigment, which are produced in safflower (Carthamus tinctrious L.) petals and, which have a common dimeric quinochalcone
structure, is reported. The key compound for the synthesis of these analogs, (p-hydroxycinnamoyl)filicinic acid (7) was synthesized in six
steps from phloroglucinol in a total yield of 39%, which was reacted with 2,3,4,5,6-penta-O-acetyl-aldehydo-D-glucose, glyoxylic acid, and
ethyl orthoformate in the presence of base to afford the corresponding analog, 8, 12, 14, in good yields, respectively. Precursor analog 12 was
then converted to carthamin analog 14 by oxidative decarboxylation by treatment with potassium permanganate as well as the natural
specimen.
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
or 3. Because 4 is unstable, it readily undergoes oxidative
decarboxylation to the red pigment 5. The biosynthesis of
1 has not been reported, but it is assumed that 1 is formed
by the condensation of 2 equiv of reactive 6 and 1 equiv of
D-glucose. The unstable 6 can be formed by the oxidation
of C-glucosylchalcone or the glycosylation of
pentahydroxychalcone.8b
Carthamin (5),1 a brilliant-red component of the flower
petals of the safflower has long been used as a dye, rouge,
and Chinese medicine. Currently, 5 and the water-soluble
yellow components of safflower petals are used as a natural
food colorant. The major yellow components of safflower
petals, safflomin-A (2),1b,2 safflower yellow B (1),3
safflomin-C (3),4 and carthamin precursor (4)5 were isolated
and their structures were elucidated. In addition, recently
the N-containing yellow pigments, tinctromin6 and cartor-
min7 have also been isolated from safflower petals and their
structures were elucidated. The above pigments share a
unique C-glycosylquinochalcone, which has not been found
in any other naturally occurring products to date.
In the total synthesis of these pigments, asymmetric
synthesis of 5 (as the acetate) has been achieved,9 and the
stereochemistry of its chiral carbon was determined to be
S.10 The total synthesis of the other yellow pigments have
not yet been carried out, but the synthesis of analogs (9, 10,
11, 12, 13, and 14) in which the glucosyl group, or the
glucosyl and hydroxyl groups on the chiral carbon were
replaced by one or two methyl groups has been achieved for
2,11a 3,11b 4,11e, and 5.11c,d Since the C-glucopyranosylqui-
nochalcone structure is unique and is present as a complex
mixture of keto–enol tautomers, we have synthesized
analogs of these pigments as model compounds, and
explored the characteristics and behavior of these unique
quinochalcone pigments, and further proved the proposed
structure. However, the yield was unsatisfactory, and the
synthesis of an analog (8) of safflower yellow B (1), which
has the characteristic dimeric structure cross-linked with a
1-deoxyglucitol, has not yet been reported.
The recently proposed8 biosynthetic pathway of the main
pigments, starting from 1, is shown in Figure 1; the
hydrolysis of 1 forms 2 and an unstable C-glycosylquino-
chalcone (6),8 which rapidly reacts with glyoxylic acid
or p-hydroxycinnamic acid to form the yellow pigments, 4
Keywords: Safflower petals; Yellow and red pigments; Safflower yellow B;
Carthamin; Carthamin precursor; Analog; (p-Hydroxycinnamoyl)filicinic
acid.
Corresponding author. Tel./fax: C81 238 26 3121;
e-mail: shingo-s@yz.yamagata-u.ac.jp
*
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.07.080

S. Sato et al. / Tetrahedron 61 (2005) 9630–9636
9631
Figure 1. Proposed biosynthetic pathway for the yellow and red pigments from safflower yellow B in safflower petals and their analogs.
Herein, we wish to report on the efficient synthesis of
analogs (8, 12, and 14) of the above three dimeric pigments
(1, 4, and 5), in which both the C-glucosyl and hydroxyl
group on the chiral carbon are replaced by methyl groups.
The key compound in the synthesis of the analog of these
dimeric pigments, (p-hydroxycinnamoyl)filicinic acid (7),
which is also a stable analog of the reactive and unstable
C-glucopyranosylquinochalcone (6), was able to be syn-
thesized in six steps from phloroglucinol in a total yield of
39%, via the improvement of the yield.
2. Results and discussion
The synthesis of 7, a key-compound in the synthesis of the
three dimeric analogs 8, 12, and 14, was carried out by
modifying the previous method11c,e,12 as follows (see
Scheme 1); phloroglucinol was diacetylated by heating at
100 8C in the presence of boron trifluoride acetic acid
complex (BF3$2AcOH) to give diacetylphloroglucinol (15)
in 84% yield. Diacetylphloroglucinol (15) was then
methylated by reaction with iodomethane in the presence
Scheme 1. Efficient synthesis of the key-compound (7) in the synthesis of analogs of pigments in safflower petals. Reagents and conditions: (a) BF3$2AcOH,
100 8C, 2 h, Y: 84%; (b) MeI/NaOme, Y: 78%; (c) 80% H2SO4 aqueous solution, 80 8C, 50 min, Y: 89%; (d) CH2N2, Y: 99%; (e) p-hydroxybenzaldehyde
(4 equiv)/piperidine, 80 8C, 1 h, Y: 79%; (f) 28% HBr–AcOH, 70 8C, 0.5 h, Y: 68% for 7, 15% for 20; (g) NaOMe, Y: 60%.

9632
S. Sato et al. / Tetrahedron 61 (2005) 9630–9636
of sodium methoxide (NaOMe) to give 2,4-diacetyl-6,6-
dimethylcyclohexa-1,3,5-trione (16) in 78% yield, which
was then mono-deacetylated by heating at 80 8C for 50 min
in an 80% H2SO4 aqueous solution to give acetylfilicinic
acid (17) in 89% yield. In the previous paper,11c after
benzoylphloroglucinol was acetylated, 7 was synthesized by
aldol reaction followed by debenzoylation. However, the
yield of final debenzoylation was low. Furthermore, 7 has
been synthesized by mono-aldol condensation of diacetylfi-
licininc acid followed by selective deacetylation, however,
the yield by this method was also low due to the poor
selectivity.11e To prevent side-reactions at the 6-position of
17 in the next aldol reaction, the enol-hydroxyl group of 17
was selectively methylated by treatment with diazomethane
to give 2-acetyl-3-hydroxy-5-methoxy-4,4-dimethylcyclo-
hexa-2,5-dienone (18) as colorless prisms in quantitative
yield. Aldol condensation of cyclohexadienone 18 with
p-hydroxybenzaldehyde (4 equiv) in piperidine at 80 8C for
1 h afforded the desired 2-cinnamoyl-5-O-methylfilicinic
acid (19) in 79% yield. Since the yield of de-O-methylation
reaction of 19 by refluxing in concd HCl–methanol was poor
due to its low solubility,12 de-O-methylation by heating at
70 8C for 0.5 h in a 28% HBr acetic acid solution was
carried out to give the desired cinnamoylfilicinic acid 7 and
its ring-closed flavanone 20 in 68 and 15% yield,
respectively. Flavanone 20 was then partially ring-opened
by treatment with NaOMe to give 7 in 60% yield.
dehydration and ring-closure between two enol-hydroxyl
groups. However, removal of the acetate groups under
alkaline conditions gave the desired compound 8, as
follows; 2 equiv of 7 were condensed with 1 equiv of
2,3,4,5,6-penta-O-acetyl-aldehydo-D-glucose17,18 prepared
from D-glucose via three steps in a 78% yield in the
presence of catalytic amount of NaOMe in dry methanol at
room temperature for 5 h, followed by de-O-acetylation
with a 28% NaOMe methanol solution. Although the de-O-
acetylation partially proceeded under these condensation
reaction conditions, the desired dimer 21 and its partial
de-O-acetates were obtained in a total yield of 75–85%.
Purification of their de-O-acetylation products by silica gel
and Sephadex column chromatography gave an analog 8 of
safflower yellow B (1) as a yellow powder in a yield of 71%
from 7 (Scheme 2).
The synthesis of an analog 12 of carthamin precursor (4)
was achieved by a coupling reaction of 2 equiv of 7 with
1 equiv of glyoxylic acid employing the same alkaline
conditions as for the synthesis of 21. The reaction proceeded
smoothly to afford 12 as the sole product, in an excellent
99% yield.11d In the 1H NMR spectrum of 12 in pyridine-d5,
the methine proton of the central acetic acid moiety
appeared at a low field of d 7.15 ppm, which was confirmed
by C–H COSY between the methine carbon (dC 34.8 ppm).
In the synthesis of carthamin analog 14, the coupling of 7
with triethyl orthoformate did not proceed under alkaline
conditions using NaOMe as well as the synthesis of 21, and
12. However, in the presence of 12.5 equiv of sodium
hydride (NaH),11c the reaction proceeded smoothly,
affording 14 as the sole product. After recrystallization the
overall yield was 90%. The precursor analog 12 was then
subjected to oxidative decarboxylation by treatment with an
aqueous solution of permanganate at room temperature to
give 14 in 52% yield as well as the natural specimen.5b Both
the 1H and 13C NMR spectra of 8, 12, and 14 in DMSO-d6
gave unsymmetrical and complicated spectra due to the
complex mixture of keto–enol tautomers. However, the use
of pyridine-d5 as a solvent gave symmetrical and simple
With the key-compound 7 in hand, we initially examined
the first synthesis of 9 the condensation of 2 equiv of 7
with an aldehydo-glucose in the presence of NaOMe. Three
aldehydo-glucose derivatives were prepared by the acet-
onide-, benzyl-, or acetyl-protection of the 2,3,4,5,6-
hydroxyl groups. The results for each of the condensation
reactions of 7 and these aldehydo-glucose derivatives was
satisfactory, but the subsequent deprotection of the glucitol
moiety of the resulting dimer was difficult. Deprotection of
the acetonide by treatment with a weak acid or even
hydrogenolysis of the benzyl protecting group gave a
mixture of xanthene-type products, which were produced by
Scheme 2. Synthesis of analogs (8, 12, and 14) of the three dimeric yellow and red pigments in safflower petals via quinocalcone 7. Reagents and conditions:
(a) 2,3,4,5,6-penta-O-acetyl-aldehydo-D-glucose/NaOMe; (b) NaOMe or 10% NaOH aqueous solution-MeOH, Y: 71% (from 7); (c) HO2CCHO/NaOMe, Y:
99%; (d) HC(OEt)3/NaH, Y: 90%; (e) 0.23% KMnO4 aqueous solution in acetone, Y: 52%.

S. Sato et al. / Tetrahedron 61 (2005) 9630–9636
9633
1
spectra. H and 13C NMR spectra of the 1-deoxyglucitol
1H NMR (CDCl3) d 1.45 (6H, s, CH3!2), 2.62 and 2.75
(each 3H, s, COCH3!2), 18.87 and 19.20 (each 1H, s, OH).
moiety of 8 were very analogous to those of 1, except for the
coupling constants between H3 and H4 (8: J3,4Zw0 Hz.;
18b: J3,4Z7.0 Hz). The UV–vis spectra of 8, 12, and 14 were
also very analogous to the natural specimen and they were
liable to including a solvent such as water, alcohol, or ethyl
acetate. Yellow-colored 12 was converted to red-colored 14
by treatment of peroxidase–H2O2 solution as well as the
natural specimen. Carthamin analog 14 also dyed silk and
cotton pink-red in a similar way to the natural specimen.
4.2.3. Acetylfilicinic acid; 2-acetyl-4,4-dimethylcyclo-
hexan-1,3,5-trione (17).12 Colorless prisms. Mp 172–
174 8C (lit.15 174–176 8C). 1H NMR (DMSO-d6) d 1.28 (6H,
s, CH3!2), 2.47 (3H, s, COCH3), 5.43 (1H, s, olefinic H),
18.41 (1H, s, OM. 13C NMR (DMSO-d6) d 24.6 (CH3), 28.3
(COCH3), 48.7 (C4), 94.9 (C6), 105.2 (C2), 182.5 (C]O),
188.7, 196.7, and 200.5 (C1, 3, 5).
4.2.4. 2-Acetyl-2-hydroxy-5-methoxy-4,4-dimethyl-2,5-
cyclohexadien-1-one (18).12 Colorless prisms. Mp 108–
109 8C (lit.12,16 107–109 8C). IR (KBr) n 2989, 2945, 1651,
1614, 1508 cmK1. 1H NMR (CDCl3) d 1.36 (6H, s, CH3!
2), 2.60 (3H, s, COCH3), 3.82 (3H, s, OCH3), 5.42 (1H, s,
olefinic H), 18.44 (1H, s, OH). EI-MS (m/z) 210 (MC).
3. Conclusion
We established an efficient method for the synthesis of an
analog of the main dimeric pigments in safflower petals, by
using the key compound, (p-hydroxycinnamoyl)filicinic acid
(7). Since spectral data for each synthesized analog was quite
analogous to its natural specimen, it was supported that the
proposed structure of three dimeric pigments was appropriate.
We are currently attempting the total synthesis of the main
yellow pigments in safflower petals on the basis of this result.
4.2.5. 2-[3-(p-Hydroxyphenyl)-2-propenoyl]-3-hydroxy-
5-methoxy-6,6-dimethyl-2,4-cyclohexadien-1-one (19).12
Yellow prisms. Mp 137–138 8C (lit.16 138–140 8C). IR
1
(KBr) n 3159, 3020, 2993, 2947, 1599, 1440 cmK1. H
NMR (CDCl3 including a small amount of DMSO-d6) d
1.39 (6H, s, CH3!2), 3.83 (3H, s, OMe), 5.49 (1H, s,
olefinic H), 6.87 and 7.56 (each 2H, d, JZ8.3 Hz,
p-substituted ArH), 7.90 and 8.12 (each 1H, d, JZ
15.9 Hz, trans-vinyl H), 9.37 (1H, s, ArOH), 19.00 (1H, s,
OH). 13C NMR (DMSO-d6) d 24.4 (CH3), 57.1 (OCH3),
48.6 (C6),0095.4 (C4), 104.6 (C2), 116.1 (C300), 1190.0 (C20),
130.9 (C2 ), 144.9 (C30), 160.6 (C400), 179.9 (C1 ), 186.8
(C5), 190.5 (C3), 196.4 (C1). EI-MS (m/z) 314 (MC).
4. Experimental
4.1. General
The solvents used in this reaction were prepared by
distillation. The synthesized compounds were separated
and purified by flash column chromatography using silica
gel (Fuji-Silysia Co., Ltd, BW-300) and by column
chromatography using Sephadex LH-20 gel (Amersham
Pharmacia Biotech AB). Melting points were determined on
a Shibayama micro-melting point apparatus and are
uncorrected. UV–vis spectra were recorded on a Hitachi
U-2010 spectrophotometer. Optical rotations were recorded
on a JASCO DIP-370 polarimeter. Mass spectral data were
obtained by electron ionization (EI) or fast-atom bombard-
ment (FAB) using 3-nitrobenzyl alcohol (NBA), glycerol, or
thioglycerol as the matrix on a JEOL JMS-AX505HA
instrument. IR spectra were recorded on a Horiba FT-720 IR
spectrometer. NMR spectra were recorded on a Varian
Inova 500 spectrometer using Me4Si as an internal standard.
4.3. De-O-methylation of 19
Methyl enol–ether 15 (1.187 g, 3.780 mmol) was added to
24 mL of a 33% HBr–acetic acid solution, and the mixture
was stirred at 80 8C for 0.5 h. The reaction mixture was
poured into ice-cold water (100 mL). The precipitated
yellow powder was filtered and washed with water. The
filtrate was extracted twice with EtOAc. The EtOAc extract
was washed with water and brine, and then dried over
anhydrous Na2SO4. After removing the organic solvents,
the residual yellow solid and the above yellow powder were
crystallized from EtOAc to give 7 (604 mg, 53%) as a
yellow powder. The filtrate was separated by flash column
chromatography on silica gel (6:1:0.1 toluene–EtOAc–
AcOH) to give 7 (170 mg, 15%) as a yellow powder and 20
(178 mg, 15%) as a pale-yellow, solid.
4.2. Synthesis of the key-compound, (p-hydroxycinnamoyl)
filicinic acid; 2-[30-(p-hydroxyphenyl)-20-propenoyl]-3,5-
dihydroxy-6,6-dimethyl-2,4-cyclohexadien-1-one (7)
4.3.1. p-Hydroxycinnamoylfilicinic acid; 2-[30-(p-hydro-
xyphenyl)-20-propenoyl]-3,5-dihydroxy-6,6-dimethyl-2,
4-cyclohexndien-1-one (7). Yellow powder. Mp 205–206 8C
(lit.11c 204–206 8C).UV–vis (EtOH) lmax (log 3) 393 (4.39)
nm (lit.11c 405 (4.5)). IR (KBT) n 3159, 1593, 1416, 1234,
4.2.1. Diacetylphloroglucinol (15). A solution of phlroglu-
cinol (20.0 g, 158 mmol) in BF3$2AcOH (95 mL) was
stirred on an oil bath at 100 8C for 3 h. The reaction mixture
was cooled to room temperature and then poured into 1 L of
an aqueous KOAc (50.1 g/L) solution and the mixture was
stirred for 3 h. The precipitated orange prisms were
collected by filtration. The crude product was recrystallized
from hot water–methanol to give 15 (23.6 g, 71%) as pale-
yellow prisms. Colorless prisms. Mp 173–174 8C (lit.13
1
1165 cmK1. H NMR (DMSO-d6) d 1.32 (6H, s, CH3!2),
5.51 (1H, s, olefinic H), 6.87 (2H, d, JZ8.5 Hz,
p-substituted ArH!2), 7.56 (2H, d, JZ8.5 Hz, p-substi-
tuted ArH!2), 7.79 (1H, d, JZ15.9 Hz, trans-vinyl H),
8.10 (1H, d, JZ15.9 Hz, trans-vinyl H), 10.17 (1H, s, OH),
12.45 (1H, br. s, enol OH), 19.12 (1H, s, OH). 13C NMR
(DMSO-d6) d 24.4 (CH3!2), 48.6 (C6), 96.5 (C4), 104.3
(C2), 116.1 (C0300 500), 119.5 (C-20), 125.9 (C100), 130.7 (C200,
600), 144.0 (C3 ), 160.4 (C400), 181.4 (C10), 186.5 (C5), 190.4
1
168 8C). H NMR (DMSO-d6) d 2.60 (6H, s, COCH3!2),
5.87 (1H, s, ArH), 13.23 (2H, s, OH), 16.30 (1H,s,OH).
4.2.2. 2,6-Diacety1-4,4-dimethylcyclohexan-1,3,5-trione
(16).12 Colorless prisms. Mp 65–66 8C (lit.14 mp 65–66 8C).

9634
S. Sato et al. / Tetrahedron 61 (2005) 9630–9636
(C3), 197.0 (C1). 1H NMR (C5D5N) d 1.63 (6H, s, CH3!2),
5.87 (1H, s, olefinic H), 7.16 (2H, d, JZ8.6 Hz, p-substituted
ArH!2), 7.73 (2H, d, JZ8.6 Hz, p-substituted ArH!2),
8.29 (2H, d, JZ15.6 Hz, trans-vinyl H), 8.86 (2H, d, JZ
15.6 Hz, trans-vinyl H). 13C NMR (D5D5N) d 25.2 (CH3!
2), 50.1 (br. s, quaternary C), 97.2, 105.6, 117.0, 121.0,
127.2, 131.4, 144.6, 161.9, 183.7, 187.8, 192.7, 198.2. FAB-
MS (NBA, m/z) 301 (MCH)C. Anal. Calcd for C17H16O5:
C, 67.99; H, 5.37. Found: C, 68.10; H, 5.39.
nm. IR (KBr) n 3406, 2983, 1618, 1601, 1516, 1414 cmK1
.
1H NMR (C5D5N) d 1.74 and 1.89 (each 6H, s, CH3!6),
7.09 (4H, d, JZ8.5 Hz, p-substituted ArH!4), 7.15 (1H, s,
OCH–), 7.63 (4H, d, JZ8.5 Hz, p-substituted ArH!4),
8.17 (2H, d, JZ15.8 Hz, trans-vinyl H), 8.90 (2H, d, JZ
15.8 Hz, trans-vinyl H). 13C NMR (C5D5N) d 24.6, 26.9
(CH3), 34.8 (OCH–), 52.1 (quaternary C), 105.5, 107.7,
116.8, 123.4, 127.8, 130.8, 136.0, 161.0, 175.9, 186.0,
188.4, 189.1, 199.7. FAB-MS (NBA, m/z) 657 (MCH)C.
Anal. Calcd for C36H32O12 0.1H2O: C, 65.67; H, 4.93.
Found: C, 65.44; H, 5.31.
4.3.2. 7-Hydroxy-2-(4-hydroxyphenyl)-8,8-dimethyl-3,4-
dihydro-2H-1-benzopyran-4,5(8H)-dione (20). Yellow
powder. Mp 188.5 8C (dec). UV–vis (EtOH) lmax (log 3)
229 (4.29), 283 (4.08), 357 (3.73) nm. IR (KBr) n 3300,
2981, 1670, 1627, 1616, 1533, 1520, 1456, 1414, 12591,
4.5.2.
Dehydro-3,30-bis(p-hydroxycinnamoyl)-5,50-
methylenedifilicinic acid (14). To a stirred suspension of
7 (60 mg, 0.2 mmol) in ethyl orthoformate (8.5 mL), NaH
(50w60% in oil, 60 mg (12.5 mmol) with a content of 55%)
was added at room temperature. The reaction mixture
gradually dissolved and its color changed from yellow to
red. The stirring was continued at room temperature for 4 h.
After confirming that the reaction was complete by the
disappearance of 7 by silica gel TLC (5:2:0.5 toluene–
EtOAc–AcOH), the red-colored reaction mixture was
poured into 15 mL of ice-cold 2 M HCI solution, and
extracted twice with EtOAc. The combined extract was
washed with brine and then dried over anhydrous Na2SO4.
After removing the organic solvents in vacuo, the residual
solid was recrystallized from MeOH to give 14 (55.2 mg,
91%) as a reddish orange powder.
1
1223, 1144 cmK1. H NMR (CDC13CDMSO-d6) d 1.40
and 1.43 (each 3H, s, CH3!2), 2.85 (1H, dd, JZ3.0,
18.5 Hz, OCH2), 3.11 (1H, dd, JZ18.5, 11.5 Hz, OCH2),
5.24 (1H, dd, JZ3.0, 11.5 Hz, OCH–), 5.47 (1H, s, olefinic
H), 6.91 (2H, d, JZ8.5 Hz, p-substituted ArH!2), 7.24
(2H, d, JZ8.5 Hz, p-substituted ArH!2), 9.03 (1H, s, OH),
16.0 (1H, s, OH). FAB-MS (NBA, m/z) 301 (MCH)C.
Anal. Calcd for C17H16O5: C, 67.99; H, 5.37. Found: C,
68.15; H, 5.50.
4.4. The conversion of 20 to 7
To a stirred solution of 20 (178 mg, 0.593 mmol) in dry
MeOH (1.5 mL), 28% NaOMe (60 mg) was added dropwise
at room temperature and the mixture was stirred for 1 h. The
reaction mixture was neutralized by the addition of Dowex
50W (HC) resins, and then filtered and washed with MeOH.
The filtrate was evaporated in vacuo to give a brown solid,
which was separated by column chromatography on silica
gel (6:1:0.1 toluene–EtOAc–AcOH) to give 7 (107 mg,
60%) as a yellow powder and 20 (26.5 mg, 15%) as a pale-
yellow solid.
Mp 230–240 8C (dec) (lit.11C 230 8C (dec)). Silica gel TLC:
Rf 0.56 (5:2:0.5 toluene–EtOAc–AcOH). HPLC: tR
8.82 min (8:2 MeOH–25% AcOH aqueous solution).
UV–vis (EtOH) lmax (log 3) 241 (4.37), 373 (4.57), 535
(4.95) nm; carthamin (5): lit.8b EtOH lmax (log 3) 244
(4.13), 377 (4.28), 515 (4.69) nm. IR (KBr) n 3288, 2985,
1
1622, 1599, 1581, 1513, 1412 cmK1. H NMR (C5D5N) d
1.73 (1H, s, CH3!4), 7.71 (4H, d, JZ8.7 Hz, p-substituted
ArH!4), 7.81 (4H, d, JZ8.7 Hz, p-substituted ArH!4),
8.23 (2H, d, JZ15.4 Hz, trans-vinyl H!2), 8.72 (2H, d,
JZ15.4 Hz, trans-vinyl H!2), 8.94 (1H, s, ]CH–). 13C
NMR (C5D5N, at 60 8C) d 22.8 and 23.0 (CH3,!4), 52.5
(C4), 107.5 and 115.1 (C2, 6), 117.1 (C12), 120.4 and 120.6
(C8), 127.2 (C10), 131.5 and 131.8 (C11), 145.9 (C9), 147.1
(C14), 162.3 (C13), 185.2 (C7), 187.3, 188.1, 198.7 (C1, 3,
5). FAB-MS (thioglycerol, negative ion, m/z) 609
(MKH)K. Anal. Calcd for C35H30O10 0.1H2O: C, 68.64;
H, 4.97. Found: C, 68.43; H, 4.90.
4.5. Synthesis of the analogs (14, and 12) of carthamin
and its precursor
4.5.1. 2,2-Bis[3-(p-hydroxycinnamoyl)filicinic acid-5-yl]
acetic acid (12). To a stirred suspension of 7 (52.4 mg,
0.175 mmol) in dry methanol (1 mL), a 25% solution of
NaOMe in methanol was added dropwise until 7 dissolved
completely. To the stirred mixture, glyoxylic acid mono-
hydrate (8.5 mg, 0.092 mmol) was added and the reaction
mixture was further stirred at room temperature for 4 h until
7 disappeared by TLC monitoring (6:1:0.2 or 5:2:0.5
toluene–EtOAc–AcOH). The reaction mixture was poured
into 15 mL of ice-cold 2 M HCI and extracted three times
with EtOAc, The organic layer was washed with brine, dried
over anhydrous Na2SO4, and evaporated in vacuo. The
residue was separated by flash column chromatography on
silica gel (6:1:0.1 toluene–EtOAc–AcOH) to give 12
(56.6 mg, 99%) as a yellow powder.
4.6. Conversion reaction of 12 to 14 via oxidative
decarboxylation using an aqueous permanganate
solution.5b
To a stirred solution of 12 (45 mg, 0.0686 mmol) in acetone
(1.5 mL), a 0.23% aqueous solution of potassium per-
manganate (1.8 mL) was added in small portions over a
period of 1.5 h at room temperature, and the stirring was
continued for an additional 0.5 h. After confirming the
disappearance of 12, the reaction mixture was added to a
1 M HCI solution (10 mL) and then extracted twice with
EtOAc. Theorganiclayer waswashedwithwaterand brine, dried
over anhydrous Na2SO4, and then evaporated in vacuo. The
residue was purified by flash column chromatography on silica
Mp 195–198 8C (lit.11e 195 8C (dec)). Silica gel TLC: Rf
0.43 (5:2:0.5 toluene–EtOAc–AcOH). HPLC: tR 7.28 min
(80:20 MeOH–25% AcOH aqueous solution). UV–vis
(EtOH) lmax (log 3) 221 (4.55), 397 (4.74) nm; carthamin
precursor (4): lit.5b MeOH lmax (log 3) 238 (4.37), 406
(4.67) nm; lit.5a EtOH lmax (log 3) 343 (4.25), 423 (4.56)

S. Sato et al. / Tetrahedron 61 (2005) 9630–9636
9635
gel (6:1:0.1 toluene–EtOAc–AcOH) to give 14 (21.8 mg,
52%) as a reddish orange powder.
(67 mg), and its mono- and di-de-O-acetates (71 mg) in
dry MeOH (2 mL) was added dropwise 0.44 mL of a 28%
NaOMe methanol solution followed by stirring at room
temperature for 1 h. After confirming the completion of the
de-O-acetylation by silica get TLC (5:4:1 toluene–ethyl
formate–formic acid), the reaction mixture was neutralized
by the addition of Dowex 50 W (HC) resin, and then filtered
and washed with methanol. The filtrate was evaporated in
vacuo and then purified by column chromatography on
silica get (5:4:1 toluene–ethyl formate–formic acid) and
then Sephadex LH-20 gel (MeOH) to give 9 (193 mg, 71%
from 7) as an orange powder.
4.7. Synthesis of the analog (8) of safflower yellow B (1)
4.7.1. 1-Deoxy-1,1-bis[30-(p-hydroxycinnamoyl)filicinic
acid-50-yl]-2,3,4,5,6-penta-O-acetyl-D-glucitol (21). To a
stirred suspension of 7 (107 mg, 0.356 mmol) in dry
methanol (1.5 mL), a 28% NaOMe methanol solution was
added dropwise until 7 dissolved. To the stirred mixture,
2,3,4,5,6-penta-O-acetyl-D-aldehydo-glucose (161 mg,
0.356 mmol) was added in small portions over a period of
3 h and then stirred at room temperature for 8 h. The
progress of the reaction was monitored by silica gel TLC
(5:2:0.5 toluene–EtOAc–AcOH). The reaction mixture was
poured into 20 mL of ice-cold 2 M HCl and extracted three
times with EtOAc. The combined organic layer was washed
with brine and dried over anhydrous Na2SO4, and the
solution evaporated in vacuo. The residue was purified by
flash column chromatography on silica gel (6:1:0.1 and
5:2:0.2 toluene–EtOAc–AcOH) to give 7 (14.5 mg, 14%),
21 (67 mg, 39%), and its mono- and di-de-O-acetates
(71 mg, 42–45%) as a yellow powder, respectively.
Mp 173–176 8C. [a]D22 C101 (c 0.55, MeOH). HPLC: tR
5.03 min (80:20 MeOH–25% AcOH aqueous solution).
UV–vis (EtOH) lmax (log 3) 218 (4.53), 403 (4.67) nm;
safflower yellow B (1): lit.8b MeOH Amax (log 3) 239 (4.43),
410 (4.77) nm. IR (KBr) n 3392, 2981, 2939, 1622, 1601,
1516, 1471, 1437, 1277, 1244, 1167 cmK1 1H NMR
.
(C5D5N-CD3OD 98:2, 60 8C) d 1.47, 1.62, 1.68, 1.72
(each 3H, s, CH3!4), 4.31 (1H, dd, JZ4.6, 11.5 Hz, H-6a),
4.36 (2H, dd, JZ4.1, 5 Hz, H-6b), 4.36 (1H, m, H-5), 4.54
(1H, d, JZ8.5 Hz, H-4), 4.73 (1H, d, JZ7.0 Hz, H-3), 5.61
(1H, d, JZ7.0 Hz, H-1), 5.73 (1H, t, JZ7.0 Hz, H-2), 7.59
and 7.61 (each 2H, d, JZ8.5 Hz, p-substituted ArH!4),
7.03, 7.04 (each 2H, d, JZ8.5 Hz, p-substituted ArH!4),
8.03, 8.04 (each 1H, d, JZ15.6 Hz, trans-vinyl H!2), 8.55,
8.83 (each 2H, d, JZ15.6 Hz, trans-vinyl H!2). 13C NMR
(C5D5N-CD3OD 98:2, 80 8C) d 23.6, 23.9, 24.4, and 25.2
(CH3!4), 38.2 and 38.4 (C10), 46.2 and 53.3 (C4), 64.3
(C60), 70.8, 72.60 and 72.8 0(two peaks), 73.0 and 73.1 (two
peaks), 93.8 (C2 , 30, 40, 5 ) 104.7, 105.2, 106.7, and 111.5
(C2, 6), 116.5 and 116.6 (C12), 120.6 and 121.2 (C8), 127.6
and 128.6 (C10), 130.3 and 131.0 (C11), 139.9 and 143.8
(C9), 160.0 and 161.01 (C13), 179.3 (C7), 184.0 and 185.3,
185.8 and 187.6, 199.5 and 200.3 (C1, 3, 5). FAB-MS
(glycerol, negative ion, m/z) 761 (MKH)K. Anal. Calcd for
C40H42O15 C.62.25; 5; H, 5.62. Found: C, 62.08; H, 5.65.
Data for 21. Mp 140–143 8C. Silica gel TLC: Rf 0.47
(5:2:0.5 toluene–EtOAc–AcOH). HPLC: tR 16.92 min
(90:10 MeOH–25% AcOH aqueous solution). IR (KBr) n
3417, 2995, 2937, 2885, 1751, 1620, 1601, 1516, 1416,
1
1217 cmK1. H NMR (DMSO-d6) d 1.16, 1.17, 1.20, 1.32
(each 3H, s, CH3!4), 1.85, 1.94, 1.96, 1.96, 2.05 (each 3H,
s, OAc!5), 4.19 (2H, d, JZ4.9 Hz, H-60a,b), 4.98 (1H, d0d,
JZ4.4, 4.9 Hz, H-50), 4.98 (1H, br. d, JZ8.5 Hz, H-3 ),
5.19 (IH, dd, JZ8.5, 4.4 Hz, H-40), 5.310(1H, d, JZ10.7 Hz,
H-20), 6.28 (1H, br. d, JZ10.7 Hz,H-2 ), 6.82 (2H, d, JZ
8.8 Hz, p-substituted ArH!2), 6.83 (2H, d, JZ8.3 Hz,
p-substituted ArH!2), 7.50 (2H, d, JZ8.8 Hz, p-substi-
tuted ArH!2), 7.53 (2H, d, JZ8.3 Hz, p-substituted ArH!
2), 7.61 (1H, d, JZ15.6 Hz, trans-vinyl H), 7.71 (1H, d, JZ
15.6 Hz, trans-vinyl H), 8.06 (2H, JZ15.6 Hz, trans-vinyl
H), 10.5 (2H, br. s, OH!2), 19.4, 19.6 (each 1H, s, OH!2).
1H NMR (C5D5N) d 1.62, 1.75, 1.82, 1.92 (each 3H, s,
CH3!4), 2.02, 2.08, 2.13, 2.16, 2.23 (each 3H, s, OAc!5),
4.83 (1H, dd, JZ8.1, 11.9 Hz, H-6a) 4.94 (1H, dd, JZ2.6,
11.9 Hz, H-6b), 5.85 (1H, ddd JZ2.6, 4.3, 8.1 Hz, H-5),
5.93 (1H, dd, JZ1.3, 8.5 Hz, H-3), 6.10 (1H, dd, JZ4.3,
8.5 Hz, H-4), 6.49 (1H, d, JZ11.1 Hz, H-1), 7.06, 7.09
(each 1H, d, JZ9.0 Hz, p-substituted ArH!2), 7.32 (1H,
dd, JZ1.2, 11.1 Hz, H-2), 7.58, 7.65 (each 2H, d, JZ9.0 Hz,
p-substituted ArH!4), 8.09, 8.21 (each 1H, d, JZ15.8 Hz,
trans-vinyl H!2), 8.87, 8.88 (each 1H, trans-vinyl H!2),
17.56 (1H, br. s, chelated OH). 13C NMR (C5D5N) d 20.5,
20.7, 20.9, 21.1, 21.4 (COCH3!5), 29.4 (C10) 51.3 and 52.6
(C4), 61.7(C60), 70.7, 71.0, 71.2, 71.5(C20 30, 40, 50)105.3and
105.8 (C2), 106.0 and 106.8 (C6), 116.7 and 116.8 (C12),
122.6 and 125.6 (C8), 128.7 and 129.4 (C10), 130.7 and 130.9
(C11), 141.4 and 142.6 (C9), 160.9 and 161.2 (C13) 170.1,
170.2 170.4, 170.7, and 170.9 (COCH3!5), 173.4 (C7), 186.1
and 186.8, 189.0 and 190.1, 199.2 and 200.1 (C1, 3, 5). FAB-
MS (NBA, m/z) 973 (MCH)C. Anal. Calcd for C50H52O20: C,
61.72; H, 5.39. Found: C, 61.79; H, 5.53.
Acknowledgements
We thank for Mr. Minoru Suzuki for technical assistance.
References and notes
1. (a) Obara, H.; Onodera, J.-I. Chem. Lett. 1979, 201–204. (b)
Takahashi, Y.; Miyasaka, N.; Tasaka, S.; Miura, I.; Urano, S.;
Ikura, M.; Hikichi, K.; Matsumoto, T.; Wada, M. Tetrahedron
Lett. 1982, 23, 5163–5166.
2. (a) Onodera, J.-I.; Obara, H.; Osone, M.; Maruyama, Y.; Sato,
S. Chem. Lett. 1981, 433–436. (b) Goda, Y.; Suzuki, J.;
Kametani, T. Jpn. J. Food Chem. 1997, 4, 54–58.
3. Takahashi, Y.; Saito, K.; Yanagiya, M.; Ikura, M.; Hikichi, K.;
Matsumoto, T.; Wada, M. Tetrahedron Lett. 1984, 25,
2471–2474.
4. Onodera, J.-I.; Obara, H.; Hirose, R.; Matsuba, S.; Sato, N.;
Sato, S.; Suzuki, M. Chem. Lett. 1989, 1571–1574.
5. (a) Kumazawa, T.; Sato, S.; Kanenari, D.; Kunimatsu, A.;
Hirose, R.; Matsuba, S.; Obara, H.; Suzuki, M.; Sato, M.;
4.7.2. Deoxy-1,1-bis[30-(p-hydroxycinnamoyl)filicinic
acid-50-yl]-D-glucitol (8). To a solution of acetate 21

9636
S. Sato et al. / Tetrahedron 61 (2005) 9630–9636
Onodera, J.-I. Chem. Lett. 1994, 2343–2344. (b) Kazuma, K.;
Shirai, E.; Wada, M.; Umeo, K.; Sato, A.; Matsumoto, T.;
11. (a) Obara, H.; Machida, Y.; Namai, S.; Onodera, J.-I. Chem.
Lett. 1985, 1393–1394. (b) Sato, S.; Obara, H.; Onodera, J.-I.;
Endo, A.; Matsuba, S. Bull. Chem. Soc. Jpn. 1992, 65,
452–457. (c) Obara, H.; Onodera, J.-I.; Shirasaki, F. Chem.
Lett. 1980, 1095–1098. (d) Obara, H.; Namai, S.; Machida, Y.
Chem. Lett. 1986, 495–496. (e) Kumazawa, T.; Amano, Y.;
Haga, T.; Matsuba, S.; Sato, S.; Kawamoto, K.; Onodera, J.-I.
Chem. Lett. 1995, 625–626.
Okuno, T. Biosci. Biotechol. Biochem. 1995, 59, 1588–1590.
6. Meselhy, M. R.; Kadota, S.; Momose, Y.; Hattori, M.; Namba,
T. Chem. Pharm. Bull. 1992, 40, 3355–3357.
7. Yin, H.-B.; He, Z.-S. Tetrahedron Lett. 2000, 41, 1955–1958.
8. (a) Onodera, J.-I.; Kawamoto, K.; Matsuba, S.; Sato, S.;
Kojima, H.; Kaneya, Y.; Obara, H. Chem. Lett. 1995, 901–902.
(b) Kazuma, K.; Takahashi, T.; Sato, K.; Takeuchi, H.;
Matsilmoto, T.; Okuno, T. Biosci. Biotechnol. Biochem. 2000,
64, 1588–1599. (c) Meselhy, M. R.; Kadota, S.; Hattor, M.;
Namba, T. J. Nat. Prod. 1993, 56, 39–45.
12. Sato, S.; Obara, H.; Endo, A.; Onodera, J.-I.; Matsuba, S. Bull.
Chem. Soc. Jpn. 1992, 65, 2552–2554.
13. Campbell, T. W.; Coppinger, G. M. J. Am. Chem. Soc. 1951,
73, 2708.
9. Sato, S.; Kumazawa, T.; Watanabe, H.; Takayanagi, K.;
Matsuba, S.; Onodera, J.-I.; Obara, H.; Furuhata, K. Chem.
Lett. 2001, 1318–1319.
14. Hoefer, K.; Riedl, W. Annalen 1962, 656, 127–130.
15. Riedl, W.; Risse, K. H. Annalen 1954, 585, 209–219.
16. Nilsson, M. Acta Chem. Scand. 1959, 13, 750.
17. Wolfrom, M. L. J. Am. Chem. Soc. 1929, 51, 2188–2193.
18. Fischer, E. Chem. Ber. 1894, 27, 673–679.
10. Sato, S.; Obara, H.; Kumazawa, T.; Onodera, J.-I.; Furuhata,
K. Chem. Lett. 1996, 833–834.