First synthesis of saponarin, 6-C- and 7-O-di-β-D-glucosylapigenin

Article abstract of DOI:10.1248/cpb.c13-00264

Saponarin, apigenin 6-C- and 7-O-bis-β-D-glucoside, was synthesized in an overall yield of 37% via 11 steps, which included the C-glycosylation of 2,4-O-dibenzylphloroacetophenone, the introduction of a cinnamoyl residue by aldol condensation, the formati

Full text of DOI:10.1248/cpb.c13-00264

776
Note
Chem. Pharm. Bull. 61(7) 776–780 (2013)
Vol. 61, No. 7
First Synthesis of Saponarin, 6-C- and 7-O-Di-β-d-glucosylapigenin
Kazufumi Misawa, Yasuko Takahashi, and Shingo Sato*
Graduate School of Science and Engineering, Yamagata University; 4–3–16 Jonan, Yonezawa, Yamagata 992–8510,
Japan.
Received April 5, 2013; accepted April 17, 2013
Saponarin, apigenin 6-C- and 7-O-bis-β-d-glucoside, was synthesized in an overall yield of 37% via 11
steps, which included the C-glycosylation of 2,4-O-dibenzylphloroacetophenone, the introduction of a cin-
namoyl residue by aldol condensation, the formation of a flavone by regioselective deprotection, and oxidative
ring-closure to the final regioselective deprotection and stereoselective O-glycosylation.
Key words C,O-diglycosylflavone; regioselective deprotection; glycosylation; phloroacetophenone; hypogly-
cemic activity
By the year 2004, there had been 188 C,O-diglycosylfla- the need for the tedious regioselective introduction of a dif-
vonoides isolated from plants, and their structures had been ferent protecting group for phenol-hydroxyls was avoided.
elucidated.1) Now, a new one has been found. C,O-Diglycosyl- The synthesis of 1 was examined according to the synthetic
flavonoides have almost a flavon-skeleton with a C-glycoside plan shown in Chart 1, as follows: 1) regio- and stereoselec-
at the 6- or 8-position of the A-ring and an O-glycoside at tive C-glycosylation to 2,4-O-dibenzylphloroacetophenone;
either the 7-position of the A-ring or at the 4-position of 2) introduction of a cinnamoyl group by aldol condensa-
the B-ring. C,O-Diglycosylflavonoides also show various tion with p-methoxymethoxybenzaldehyde; 3) regioselective
bioactivities. Among them, saponarin, 6-C- and 7-O-di-β-d- 6′-O-debenzylation of C-glycosylchalcone with BF3·OEt2; 4)
glucopyranosyl-4′,5,7-trihydroxyflavone has shown potent an- formation of 6-C-glycosylflavone via an oxidative cyclization
tioxidant,2,3) hematoprotective,4) and hypoglycemic5) activities. with I2; 5) conversion of the hydroxyl-protecting group to an
In the synthesis of C,O-diglycosylflavonoides, that of acetyl group from a benzyl group followed by regioselective
flavocommelin, 6-C- and 4′-O-di-β-d-glucopyranosyl-7-O- 7-O-deacetylation with tetramethylguanidine (TMG); and, 6)
methyl-4′,5,7-trihydroxyflavone has been reported only by
Oyama and Kondo.6) Those researchers synthesized one in
12-steps for an overall yield of 6.2% via C-glycosylation to the
flavan prepared by the reduction of the 4-carbonyl group of an
available naringenin, followed by oxidation to the flavone and
O-glycosylation.
Herein, we disclose the first synthesis of saponarin, 6-C-
and 7-O-di-β-d-glucopyranosyl-4′,5,7-trihydroxyflavone (1),
which is more complex than the afore-mentioned compounds
due to the adjacent 6-C- and 7-O-bis glucosides. We achieved
the synthesis of flavone and isoflavone C-glycosides by using
phloroacetophenone C-glycoside as the key-compound.7–9)
Herein, we include our proposal for a synthetic plan for the
total synthesis of 1 employing phloroacetophenone C-glyco-
side as the key-compound (Chart 1). We used a benzyl group
as the protecting group for the glucose- and phenol-hydroxyls.
The benzyl group was easy to deprotect under the neutral con-
ditions of hydrogenolysis. For the regioselective deprotection
of the flavone-ring formation, we employed a 2-ethylbenzyl
group that is less deprotectable than a benzyl group.7) Kan
and co-workers employed a tert-butyldiphenylsilyl group so
it could be distinguished from a benzyl group.10) Although
Schmidt and co-workers first used a methyl group for phe-
nol protection, because of the difficulty of deprotection, they
later selected a tert-butyldimethylsilyl group.11) Both of these
silyl-protecting reagents are expensive. In the present study,
we applied the deprotectability of the phenol-hydroxyls at
the 2′,6′-positions of the A-ring of the chalcone due to the
acidity of the intramolecular hydrogen-bonding between the
phenol-hydroxyl and acyl-carbonyl groups, using 2,4-O-
dibenzylphloroacetophenone as a starting material. Therefore,
The authors declare no conflict of interest.
Chart 1. Synthetic Plan of Saponarin 1
© 2013 The Pharmaceutical Society of Japan
*To whom correspondence should be addressed. e-mail: shingo-s@yz.yamagata-u.ac.jp

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Reagents and conditions: a) 2 (3eq), per-O-benzylglucosyl α-fluoride (1eq), BF3·OEt2 (2eq), MS4A in CH2Cl2, at −70°C–rt, 3h, Y: 96% or per-O-benzylglucosyl
α-trichloroimidate (1.2eq), TMS OTf (0.2eq) in CH2Cl2, at −10°C–rt, 5h, Y: 79%; b) p-MOMO-benzaldehyde (1.5eq), NaOMe (1.2eq), in dioxane, rt, 1.5h,Y: 98%; c)
2n HCl–MeOH (1:10), reflux, 2h, Y: 95%; d) BzCl in pyridine, rt, 1.5h, Y: 100%; e) BF3OEt2 (4.5eq), in CH2Cl2, –10–0°C, 4h, Y: 81%; f) I2 (0.1eq) in DMSO at 130°C,
20min, Y: 84%; g) 1. H2–10% Pd–C, in AcOEt, rt, 4h, 2. Ac2O–pyridine (1:1), rt, 2h, Y: 98% (2 steps); h) TMG (2.5eq) in CH3CN, rt, 3h, Y: 83%; i) per-O-acetylglucosyl
α-bromide (2eq), Ag2CO3 (2eq), in quinoline, at 0°C–rt, 3h, Y: 86%; j) NaOMe in MeOH, rt, for 1h, then Dowex 50W (H+), recrystallization from H2O–CH3CN, Y: 87%.
Chart 2. Total Synthesis of Saponarin 1
stereoselective 7-O-glycosylation by Koenigs–Knorr glycosyl- −15°C, and the reaction temperature was gradually raised to
ation and de-O-acylation with NaOMe.
0°C for 4h, and 6′-hydroxylchalcone 7 was afforded in an 81%
yield without deprotection of the other benzyl groups. The
oxidative cyclization of 7 proceeded smoothly in the presence
Results and Discussion
Results are shown in Chart 2. C-Glycosylation to 2,4-O- of 0.1 equiv of iodine following heating in dimethyl sulfoxide
dibenzylphloroacetophenone (2) was examined using both (DMSO) at 130°C for 20min to give 6-C-glucosylflavone 8 in
O→C glycoside rearrangement methods with per-O-ben- a good yield (84%).7,12) Since selective debenzylation of the
zylglucosyl α-fluoride/BF3·OEt2 and per-O-benzylglucosyl 7-O-benzyl group of 8 is difficult under these same condi-
α-trichloroimidate/trimethylsilyl
trifluoromethanesulfonate tions, we changed all the benzyl groups into acetyl groups
(TMSOTf) as the combination of a glycosyl donor and a for a yield of 98% (2 steps). Next, the selective 7-O-deacet-
Lewis acid promoter. Both methods gave the desired C-glu- ylation of 7-O-acetyl-4′,5-O-dibenzoyl-6-(2″,3″,4″,6″-tetra-O-
coside 3 in good yields (96, 79%, respectively). When 1.5eq acetyl-β-d-glucosyl)apigenin (9) was achieved by employing
of α-fluoride was used for 2, the yield was 84%, but, when a method established by Oyama,13) which uses TMG (2.5eq)
3eq of 2 was used for α-fluoride, the yield was increased to and produced 7-hydroxyflavone 10 in a good yield (83%).
96%.7) Next, an aldol condensation of 3 with methoxymethoxy O-β-Glycosylation of 10 with per-O-acetylglucosyl bromide
(MOM) benzaldehyde (1.5eq) was conducted by stirring at (2.5eq) in the presence of AgCO3 (2eq) in quinoline pro-
room temperature for 2h in the presence of 28% NaOMe in ceeded β-selectively and furnished 11 in a good yield (86%).14)
1,4-dioxane to synthesize 4 in an excellent yield (98%). The Finally, the deacylation of 11 was conducted using NaOMe,
O-demethoxymethylation of 4 was achieved by 2h of reflux- followed by neutralization with Dowex® 50W×8 (H+) resin
ing in 2n HCl–MeOH (1:10), furnishing 5 in a 95% yield. and recrystallization from MeOH, providing saponarin 1
1
Subsequently, a free 4-hydroxyl group of 5 was benzoylated in an 87% yield as a white crystal. The spectra for H- and
with benzoyl chloride (1.5eq) in pyridine to give 6 quanti- 13C-NMR were measured at room temperature and in a mix-
tatively. Next, the regioselective 6′-O-debenzylation of chal- ture of rotamers along with those of the above intermediates.
cone 6 was examined, which is an important step in the total This compound, however, enabled the measurement of NMR
synthesis. The use of BF3·OEt2 as a Lewis acid appeared to (in DMSO-d6+D2O) at 90°C overnight with no cleavage, and
1
afford easy control of this reaction, though some Lewis acids gave the H- and 13C-NMR spectra without a mixture of rota-
have been known to enable regioselective debenzylation. Fi- mers. The 13C-NMR spectrum of synthetic 1 agreed with that
nally, when 4.5eq of BF3·OEt2 was added to 6 in CH2Cl2 at of the natural sample,2) as shown in Table 1. Its melting point

778
Vol. 61, No. 7
Table 1. 13C-NMR Spectra of Saponarin 1
drying at 100°C under reduced pressure for more than 2h,
each product was subjected to elemental analysis.
Synthetic
DMSO-d6+D2O
Carbon No.
Natural1-a DMSO-d6
4′,6′-Dibenzyloxy-4-methoxymethoxy-2′-hydroxy-3′-C-
(2″,3″,4″,6″-tetra-O-benzyl-β-d-glucopyranosyl)chalcone
(4) To a solution of 3 (1.65g, 1.89mmol) and p-methoxy-
methoxybenzaldehyde (0.472g, 2.84mmol) in 1,4-dioxane
(10mL), a 28% NaOMe–MeOH solution (3.0mL) was added,
and the mixture was stirred under an Ar atmosphere at room
temperature for 2h. Ice-cold 2n HCl solution (2mL) was
added to the reaction mixture, which then was extracted
three times with AcOEt. The organic layer was washed with
water and brine, dried over anhydrous Na2SO4, and evapo-
rated to dryness. The residual solid was purified by silica-
gel column chromatography (n-hexane–AcOEt=4:1–3:1) to
afford 4 (1.51g, Y: 98%) as a yellow amorphous powder.
[α]D22 −4.75 (c=0.505, CHCl3). Silica-gel TLC: Rf=0.47 (n-
hexane–AcOEt=2:1). IR (KBr) cm−1: 3448, 2925, 2856,
1623, 1560, 1508, 1454, 1232, 1151, 1068, 831, 736, and 698.
1H-NMR (CDCl3) δ: 2.46 (2H, s, 4-MOM), 3.493 (3.485) (3H,
s, 4-MOM), 3.61 (1H, m H5″), 3.68 (1H, t, J=9.8, 9.1Hz, H4″),
3.77 (1H, d, J=10.6Hz, H6″a), 3.81 (1H, dd, J=2.3, 10.6Hz,
H6″b), 3.81 (1H, t, J=9.2, 9.1Hz, H3″), 4.26 (1H, t, J=9.1,
9.8Hz, H2″), 4.29 (1H, d, J=11.4Hz, CH2Ph), 4.34 (1H, d,
J=11.3Hz, CH2Ph), 4.50 (1H, d, J=12.1Hz, CH2Ph), 4.54 (1H,
d, J=11.4Hz, CH2Ph), 4.56 (1H, d, J=11.3Hz, CH2Ph), 4.60
(1H, d, J=8.3Hz, CH2Ph), 4.65 (1H, m, CH2Ph), 4.71 (1H, d,
J=12.1Hz, CH2Ph), 4.83–5.06 (4H, m, CH2Ph×2), 5.09 (1H, d,
J=10.6Hz, H1″), 6.07 (6.01) (1H, s, H5′), 6.85–7.75 (36H, m,
ArH×36H), and 14.9 (14.6) (1H, s, 2-OH). FAB-MS m/z: 1020
2
3
4
5
6
7
8
9
164.4
103.3
182.1
159.9
110.9
162.3
94.1
156.5
105.4
121.2
128.5
116.1
161.3
116.1
128.5
73.8
101.7
71.0
73.0
79.2
76.2
70.5, 70.1
81.0
77.3
164.4
103.4
182.1
159.5
110.7
162.6
94.2
156.5
105.3
121.3
128.5
116.1
161.2
116.1
128.5
73.6
101.6
70.8
72.9
78.9
76.0
70.8, 69.9
81.0
77.3
10
1′
2′
3′
4′
5′
6′
1′
1‴
2″
2‴
3″
3‴
4″, 4‴
5″
5‴
6″, 6‴
61.1, 61.1
60.9, 60.9
and specific rotation also approximated those of the natural (M+H)+. Anal. Calcd for C65H62O11: C, 76.60; H, 6.13. Found:
samples.2)
C, 76.52; H, 6.12.
4′,6′-Dibenzyloxy-2′,4-dihydroxy-3′-C-(2″,3″,4″,6″-tetra-
O-benzyl-β-d-glucopyranosyl)chalcone (5) To a solution of
Conclusion
Saponarin 1 was efficiently synthesized via 11 steps from 2 4 (1.21g, 1.22mmol) in MeOH (100mL), 2n HCl (10mL) was
for an overall yield of 37%. A concise synthesis of the C,O- added, and the mixture was refluxed for 2h. The reaction mix-
diglycosylflavone was achieved using phloroacetophenone ture was concentrated in vacuo, and the residue was extracted
bis-benzylether as a starting material. The synthetic route pro- three times with AcOEt. The organic layer was washed with
posed here was a practical one, and it proved to be applicable water and brine, dried over anhydrous Na2SO4, and then evap-
to the synthesis of various C,O-diglycosylflavonoids.
orated to dryness. The residual solid was purified by silica-gel
column chromatography (n-hexane–AcOEt=3:1–2:1) and re-
crystallized from MeOH to afford 5 (1.80g, Y: 95%) as yellow
Experimental
General The solvents used in these reactions were puri- needles. mp=166°C. [α]D22 +7.31 (c=0.520, CHCl3). Silica-gel
fied by distillation. The reactions were monitored by TLC on TLC: Rf=0.24 (n-hexane–AcOEt=2:1). IR (KBr) cm−1: 3421,
0.25-mm silica gel F254 plates (E. Merck) using UV light, 2916, 2871, 1618, 1608, 1560, 1508, 1458, 1147, 737, and 698.
and a 7% ethanolic solution of phosphomolybdic acid with 1H-NMR (CDCl3) δ: 3.45 (1H, t, J=9.8Hz, H4″), 3.65 (1H,
heat as the coloration agent. Flash column chromatography dd, J=6.8, 11.4Hz, H6″a), 3.76 (1H, m, H5″), 3.78 (1H, brd,
was performed on silica-gel (40–50µm, Kanto Reagents Co., J=9.1Hz, H6″b), 3.83 (1H, t, J=9.1Hz, H3″), 4.28–5.08 (10H,
Ltd., silica-gel 60) to separate and purify the reaction prod- m, CH2Ph×5), 4.30 (1H, t, J=9.1, 9.9Hz, H2″), 5.16 (1H, d,
ucts. Optical rotations were recorded using a JASCO DIP-370 J=10.6Hz, H1″), 5.714 (5.710) (1H, s, H5), 6.40, 6.35 (each 1H,
polarimeter. Melting points were determined using an ASONE d, J=9.0Hz, H3″,5″), 6.59, 6.67 (each 1H, d, J=8.4Hz, H2′,6′),
micro-melting point apparatus, and uncorrected values were 6.95–7.52 (30H, m, ArH), 7.41, 7.46 (each 0.5H, d, J=15.1Hz,
reported. The IR spectra were recorded on a Horiba FT-720 trans-vinyl H), 7.61, 7.68 (each 0.5H, d, J=15.1Hz, trans-vinyl
IR spectrometer using a KBr disk. The NMR spectra were H), and 15.31 (15.21) (1H, s, 2-OH). FAB-MS m/z: 976 (M+
recorded on a JEOL ECX-500 spectrometer using Me4Si as H)+. Anal. Calcd for C63H58O10: C, 77.60; H,6.00. Found: C,
the internal standard. A chemical shift in the parenthesis 77.58; H, 6.22.
showed another of the rotamers, since the NMR spectra of
2′,4-Dibenzoyloxy-4′,6′-dibenzyloxy-3′-C-(2″,3″,4″,6″-
the C-glucosides were observed as a mixture of rotamers. The tetra-O-benzyl-β-d-glucopyranosyl)chalcone (6) To a so-
mass spectral data were obtained by fast-atom bombardment lution of 5 (1.80g, 1.85mmol) in pyridine (6mL), benzoyl
(FAB) using 3-nitrobenzyl alcohol (NBA) as a matrix on a chloride (1.5mL) was dropwise added at 0°C. The reaction
JEOL JMS-AX505HA instrument. Elemental analyses were mixture was stirred at room temperature for 1.5h under an
performed with a Perkin-Elmer PE 2400 II instrument. After Ar atmosphere. Ice-cold 2n HCl (40mL) was added to the

July 2013
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1
mixture, which then was extracted three times with AcOEt. 1209, 1170, 1061, 735, and 696. H-NMR (CDCl3) δ: 3.04 (1H,
The organic layer was washed with water and brine, and dried dd, J=6.0, 11.3Hz, H6″a), 3.19 (1H, t, J=9.1, 9.9Hz, H4″),
over anhydrous Na2SO4, and then evaporated to dryness. The 3.41 (1H, dd, J=2.2, 11.3Hz, H6″b), 3.47 (1H, m, H5″), 3.74
residual solid was purified by silica-gel column chromatogra- (1H, t, J=9.1Hz, H3″), 4.20, 4.27 (each 1H, d, J=12.9Hz,
phy (n-hexane–AcOEt=4:1–2:1) to afford 5 (2.22g, Y: 100%) CH2Ph), 4.25 (1H, t, J=9.0, 9.9Hz, H2″), 4.27, 4.68 (each
as a pale-yellow amorphous powder. [α]D23 −32.8 (c=0.525, 1H, d, J=10.6Hz, CH2Ph), 4.31, 4.72 (each 1H, d, J=12.1Hz,
CHCl3). Silica-gel TLC: Rf=0.46 (n-hexane–AcOEt=2:1). IR CH2Ph), 4.87, 4.93 (each 1H, d, J=10.6Hz, CH2Ph), 5.07 (1H,
(KBr) cm−1: 3062, 3029, 2860, 1743, 1647, 1612, 1452, 1346, d, J=9.9Hz, H1″), 5.10, 5.18 (each 1H, d, J=11.4Hz, CH2Ph),
1
1261, 1170, 1061, 735, and 696. H-NMR (CDCl3) δ: 3.02 (1H, 6.56 (1H, s, H3), 6.88 (1H, s, H8), and 7.00–8.24 (35H, m,
t, J=9.1, 9.8Hz, H4″), 3.10 (1H, dd, J=5.3, 9.8Hz, H6″a), 3.37 ArH). FAB-MS m/z: 1092 (M+H)+. Anal. Calcd for C70H58O12:
(1H, 1H, brd, J=9.8Hz, H6″b), 3.44 (1H, m, H5″), 3.68 (1H, C, 77.05; H, 5.36. Found: C, 77.04; H, 5.26.
t, J=9.1, 9.2Hz, H3″), 4.11 (1H, t, J=9.1, 9.8Hz, H2″), 4.19,
7-Acethoxy-4′,5-dibenzoyloxy-6-C-(2″,3″,4″,6″-tetra-O-
4.60 (each 1H, d, J=10.6Hz, CH2Ph), 4.24, 4.66 (each 1H, d, acetyl-β-d-glucopyranosyl)flavone (9) To a solution of 8
J=11.4Hz, CH2Ph), 4.29, 4.32 (each 1H, d, J=10.6Hz, CH2Ph), (300mg, 0.275mmol) in AcOEt (1.5mL) and EtOH (1.5mL),
4.81, 4.89 (each 1H, d, J=11.3Hz, CH2Ph), 4.94, 5.01 (each 10% Pd–C (100mg) was added, and the mixture was vigor-
1H, d, J=12.9Hz, CH2Ph), 5.02, 5.05 (each 1H, d, J=12.1Hz, ously stirred at room temperature under a H2 atmosphere
CH2Ph), 5.02 (1H, d, J=11.4Hz, H1″), 6.45 (1H, s, H5), and for 3h. The resultant mixture was filtered with a celite pad
6.94–8.21 (46H, m, ArH). FAB-MS m/z: 1184 (M+H)+. Anal. followed by washing with EtOH, and the filtrate was then
Calcd for C77H66O12: C, 78.15; H, 5.62. Found: C, 78.47; H, evaporated to dryness. The residual white powder was dis-
5.58.
solved in Ac2O (1.0mL) and pyridine (1.0mL), and stirred at
2′,4-Dibenzoyloxy-4′-benzyloxy-6′-hydroxy-3′-C- room temperature for 2h. Ice-cold water was added to the
(2″,3″,4″,6″-tetra-O-benzyl-β-d-glucopyranosyl)chalcone reaction mixture, which then was stirred for 2h. The resul-
(7) To a solution of 5 (1.10g, 0.930mmol) in CH2Cl2 (2.5mL) tant white powder was filtered to afford 9 (229mg, Y: 98%, 2
BF3·OEt2 (525 µL, 4.18mmol) was dropwise added at −10°C, steps) as a colorless amorphous powder. [α]D23 +8.14 (c=0.565,
and the mixture was stirred for 4h under an Ar atmosphere CHCl3). Silica-gel TLC: Rf=0.14 (n-hexane–AcOEt=1:1). IR
with the temperature being raised gradually to 0°C over a (KBr) cm−1: 3066, 2943, 1751, 1655, 1452, 1367, 1246, 1165,
1
priod of 4h. Ice-cold water was added to the mixture, which 1061, and 706. H-NMR (CDCl3) δ: 1.90, 2.00, 2.02, 2.09 (each
then was extracted three times with AcOEt. The organic 3H, s, OAc ×4), 2.52 (3H, s, ArOAc), 3.79 (1H, m, H5″), 4.01
layer was washed with water and brine, dried over anhydrous (1H, brd, J=11.3, 12.1Hz, H6″a), 4.44 (1H, dd, J=3.8, 12.1Hz,
Na2SO4, and evaporated to dryness. The residual solid was H6″b), 4.93 (1H, d, J=9.8Hz, H1″), 5.17 (2H, m, H3″,4″), 5.78
purified by silica-gel column chromatography (n-hexane– (1H, t, J=9.8Hz, H2″), 6.60 (1H, s, H3), 7.38 (1H, s, H8), 7.39
AcOEt=4:1–3:1) to afford 6 (824mg, Y: 81%) as a yellow (2H, d, J=8.4Hz, p-substituted ArH), 7.91 (2H, d, J=8.4Hz,
amorphous powder. [α]D23 −34.8 (c=0.535, CHCl3). Silica-gel p-substituted ArH), 7.54, 7.60 (each 2H, t, J=7.5Hz, benzoyl
TLC: Rf=0.55 (n-hexane–AcOEt=2:1). IR (KBr) cm−1: 3483, ArH), 7.69 (2H, q, J=7.5Hz, benzoyl ArH), and 8.23 (4H, m,
3062, 3030, 2917, 2856, 1743, 1635, 1560, 1508, 1452, 1213, benzoyl ArH). FAB-MS m/z: 851 (M+H)+. Anal. Calcd for
1
1061, 737, and 698. H-NMR (CDCl3) δ: 2.90 (1H, dd, J=5.3, C45H38O17: C, 63.53; H, 4.50. Found: C, 63.23; H, 4.25.
10.6Hz, H6″a), 3.12 (1H, t, J=9.1, 9.8Hz, H4″), 3.28 (1H,
4′,5-Dibenzoyloxy-7-hydroxy-6-C-(2″,3″,4″,6″-tetra-O-
brd, J=10.6Hz, H6″b), 3.39 (1H, m, H5″), 3.76 (1H, t, J=9.0, acetyl-β-d-glucopyranosyl)flavone (10) To a solution of
9.1Hz, H3″), 4.03, 4.12 (each 1H, d, J=12.2Hz, CH2Ph), 4.21, 9 (290mg, 0.341mmol) in CH3CN (3.5mL), TMG (107µL,
4.99 (each 1H, d, J=10.6Hz, CH2Ph), 4.25 (1H, t, J=9.0, 0.183mmol) was dropwise added at room temperature, and
9.1Hz, H2″), 4.55, 4.74 (each 1H, d, J=11.3Hz, CH2Ph), 4.75 the mixture was stirred for 3h. A saturated NH4Cl aqueous
(1H, d, J=11.4Hz, H1″), 4.93, 4.97 (each 1H, d, J=10.6Hz, solution (10mL) was added to the reaction mixture, which
CH2Ph), 5.09, 5.15 (each 1H, d, J=12.1Hz, CH2Ph), 6.48 (1H, then was extracted three times with AcOEt. The organic layer
s, H8′), 6.94–8.20 (41H, m, ArH), and 13.50 (1H, s, 6′-OH). was washed with water and brine, and dried over anhydrous
FAB-MS m/z: 1094 (M+H)+. Anal. Calcd for C70H60O12: C, Na2SO4, and evaporated to dryness. The residual solid was pu-
76.90; H,5.53. Found: C, 77.29; H, 5.45.
rified by silica-gel column chromatography (CHCl3–MeOH=
4′,5-Dibenzoyloxy-7-benzyloxy-6-C-(2″,3″,4″,6″-tetra-O- 30:1) to afford 10 (229mg, Y: 83%) as a pale-yellow amor-
benzyl-β-d-glucopyranosyl)flavone (8) A solution of 7 phous powder. [α]D23 +35.8 (c=0.520, CHCl3). Silica-gel TLC:
(750mg, 0.686mmol) and iodine (18.8mg, 0.0686mmol) in Rf=0.42 (n-hexane–AcOEt=2:3). IR (KBr) cm−1: 3448, 2943,
1
DMSO (1.5mL) was stirred at 130°C (oil bath) for 0.5h under 1751, 1647, 1637, 1363, 1246, 1170, 1061, and 706. H-NMR
an Ar atmosphere. After cooling at room temperature, ice- (CDCl3) δ: 1.97, 2.01, 2.03, 2.04, 2.16 (12H, OAc×4), 3.89
cold water was added to the resultant mixture, which then (3.93) (1H, m, H5″), 4.17 (4.21) (1H, dd, J=10.6, 12.1Hz, H6″a),
was extracted three times with AcOEt. The organic layer 4.37 (4.35) (1H, dd, J=3.0, 12.1Hz, H6″b), 4.99 (5.15) (1H, dd,
was washed with a saturated Na2S2O3 solution and brine, and J=9.8Hz, H1″), 6.53 (1H, s, H3), 7.03 (1H, s, H8), 7.38 (2H, d,
dried over anhydrous Na2SO4, and then evaporated to dry- J=8.3Hz, p-substituted ArH), 7.91 (2H, d, J=8.3Hz, p-substi-
ness. The residual solid was purified by silica-gel column tuted ArH), 7.52–7.59 (4H, m, benzoyl ArH), 7.65–7.71 (2H,
chromatography (1st, n-hexane–AcOEt=3:1–2:1. 2nd, tolu- m, benzoyl ArH), and 8.21–8.25 (4H, m, benzoyl ArH). FAB-
ene–AcOEt–AcOH=10:1:0.1) to afford 8 (629mg, Y: 84%) as MS m/z: 810 (M+H)+. Anal. Calcd for C43H36O16: C, 63.86; H,
a colorless amorphous powder. [α]D23 +8.71 (c=0.505, CHCl3). 4.49. Found: C, 63.94; H, 4.64.
Silica-gel TLC: Rf=0.19 (n-hexane–AcOEt=3:1). IR (KBr)
4′,5-Dibenzoyloxy-7-hydroxy-6-C-(2″,3″,4″,6″-tetra-
cm−1: 3062, 3029, 2864, 1743, 1647, 1612, 1452, 1346, 1261, O-acetyl-β-d-glucopyranosyl)-7-O-(2‴,3‴,4‴,6‴-tetra-O-

780
Vol. 61, No. 7
acetyl-β-d-glucopyranosyl)flavone (11) To a solution of 10 AcOH=30:15:5:1). IR (KBr) cm−1: 3400, 2927, 1655, 1617,
(100mg, 0.123mmol) in quinoline (0.3mL), Ag2CO3 (67.8mg, 1508, 1489, 1458, 1354, 1188, 1091, and 1076. 1H-NMR
0.246mmol) and per-O-acetylglucosyl bromide (101mg, [DMSO-d6+D2O (2 drops), at 90°C] δ: 3.2–3.29 (5H, m), 3.36
0.246mmol) were added at 0°C, and the resultant mixture was (1H, t, J=9.1Hz), 3.38 (1H, t, J=9.0Hz), 3.48 (1H, m), 3.55
stirred at room temperature in the dark under an Ar atmo- (1H, dd, J=5.3, 11.4Hz, H6″ or 6‴), 3.66 (1H, brd, J=9.8Hz,
sphere for 3h. The reaction was quenched with MeOH, and H6″ or 6‴), 3.78 (1H, d, J=11.3Hz, H6″ or 6‴), 4.72 (1H, d,
the mixture was eluted through a short silica-gel column with J=8.4Hz, H1″), 4.97 (1H, d, J=6.8Hz, H1‴), 6.74 (1H, s, H3),
AcOEt. The eluate was evaporated to dryness. To the residue, 6.89 (1H, s, H8), 6.95, 7.89 (each 2H, d, J=8.5, 8.3Hz, H3′,5′
1n HCl (8mL) was added, and the resultant mixture was ex- and H2′,6′), 10.4 (1H, s, 4′-OH), and 13.4 (1H, brs, 6-OH).
tracted three times with AcOEt. The organic layer was washed FAB-MS m/z: 593 (M−H)−. Anal. Calcd for C27H30O15·2H2O,
with water and brine, and dried over anhydrous Na2SO4. After C, 51.43, H, 5.44. Found: C, 51.16, H, 5.48.
evaporation, the residue was purified by silica-gel column
chromatography (CHCl3–MeOH=30:1) to afford 11 (12mg, Y:
Acknowledgment We thank Mr. Masaki Yamaguchi for
86%) as colorless prisms. mp >300°C. [α]D23 −47.5 (c=0.510, his technical assistance.
CHCl3). Silica-gel TLC: Rf=0.32 (n-hexane–AcOEt=2:3). IR
(KBr) cm−1: 2945, 1751, 1653, 1508, 1458, 1375, 1226, 1063,
References
and 707. 1H-NMR (CDCl3) δ: 1.80, 1.97, 2.02, 2.06, 2.09,
2.23 (each 3H, s, OAc×6), 2.10 (6H, s, OAc×2), 3.72–3.74
(1H, m, H5‴), 3.76 (1H, dd, J=1.5, 12.2Hz, H6‴a), 3.90 (1H,
dd, J=5.3, 12.2Hz, H6‴b), 4.09 (1H, m, H5″), 4.26 (1H, dd,
J=2.3, 12.1Hz, H6″a), 4.32 (1H, dd, J=6.8, 12.1Hz, H6″b),
4.78 (1H, t, J=9.8Hz, H4‴), 5.08 (1H, d, J=10.6Hz, H1‴), 5.19
(1H, t, J=9.8Hz, H4″), 5.24 (1H, d, J=7.6Hz, H1″), 5.28 (1H,
t, J=9.1, 9.9Hz, H3‴), 5.43 (1H, m, H3″), 5.45 (1H, m, H2″),
5.79 (1H, t, J=9.8, 9.9Hz, H2‴), 6.53 (1H, s, H3), 7.03 (1H,
s, H8), 7.55, 7.59 (each 2H, t, J=7.6Hz, benzoyl ArH), 7.66
(2H, q, J=7.5Hz, benzoyl ArH), 8.22, and 8.30 (each 2H, d,
J=6.8Hz, benzoyl ArH). FAB-MS m/z: 1140 (M+H)+. Anal.
Calcd for C57H54O25: C, 60.10; H, 4.78. Found: C, 60.08; H,
4.66.
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[α]D23 −36.8 (c=0.505, DMSO) [natural2-a: [α]D25 −33 (c=0.50,
DMSO)]; Silica-gel TLC: Rf=0.39 (acetone–AcOEt–H2O–