Synthesis of kaempferol 3- O -(3″,6″-Di- O - E - p -coumaroyl)-β- D -glucopyranoside, efficient glycosylation of flavonol 3-OH with glycosyl o -alkynylbenzoates as donors

Article abstract of DOI:10.1021/jo1014189

Kaempferol 3-O-(3″,6″-di-O-E-p-coumaroyl)-β-d- glucopyranoside (1), an optimal metabolite of Scots pine seedlings for protection of deep-lying tissue against damaging UV-B, represents a typical acylated flavonol 3-O-glycoside. This compound was synthesized for the first time via two approaches. The first approach, starting with kaempferol, featured formation of the flavonol 3-O-glycosidic linkage with a glycosyl bromide under conventional PTC conditions. In the second approach, 5,7,4′-tri-O-benzyl- kaempferol was readily prepared from 2′,4′,6′- trihydroxyacetophenone and p-hydroxybenzoic acid, which was coupled with a glucopyranosyl o-hexynylbenzoate under the catalysis of a gold(I) complex to provide the desired 3-O-glycoside in excellent yield. A variety of the glycosyl o-hexanylbenzoates equipped with the 2-O-benzoyl group were also proven to be highly efficient donors for construction of the flavonol 3-O-glycosidic linkages.

Full text of DOI:10.1021/jo1014189

pubs.acs.org/joc
Synthesis of Kaempferol 3-O-(300,600-Di-O-E-p-coumaroyl)-β-D-
glucopyranoside, Efficient Glycosylation of Flavonol 3-OH with
Glycosyl o-Alkynylbenzoates as Donors
Weizhun Yang,†,§ Jiansong Sun,† Wenxiang Lu,† Yan Li,† Lei Shan,‡ Wei Han,§
Wei-Dong Zhang,*,‡ and Biao Yu*,†
†State Key Laboratory of Bio-organic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, China, ‡Department of Phytochemistry,
School of Pharmacy, Second Military Medical University, Shanghai 200433, China, and §School of
Pharmacy, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, China
wdzhangy@hotmail.com; byu@mail.sioc.ac.cn
Received July 19, 2010
Kaempferol 3-O-(300,600-di-O-E-p-coumaroyl)-β-D-glucopyranoside (1), an optimal metabolite of
Scots pine seedlings for protection of deep-lying tissue against damaging UV-B, represents a typical
acylated flavonol 3-O-glycoside. This compound was synthesized for the first time via two
approaches. The first approach, starting with kaempferol, featured formation of the flavonol 3-O-
glycosidic linkage with a glycosyl bromide under conventional PTC conditions. In the second
approach, 5,7,40-tri-O-benzyl-kaempferol was readily prepared from 20,40,60-trihydroxyacetophe-
none and p-hydroxybenzoic acid, which was coupled with a glucopyranosyl o-hexynylbenzoate under
the catalysis of a gold(I) complex to provide the desired 3-O-glycoside in excellent yield. A variety of
the glycosyl o-hexanylbenzoates equipped with the 2-O-benzoyl group were also proven to be highly
efficient donors for construction of the flavonol 3-O-glycosidic linkages.
Introduction
beneficial to humans, such as antimicrobial, anticancer,
and radical-scavenging activities.1,2 Kaempferol 3-O-(300,600-di-
O-E-p-coumaroyl)-β-D-glucopyranoside (1), or 300,600-di-O-(p-
coumaroyl)astragalin, is a representative acylated flavonol
3-O-glycoside,3 which has been isolated from the needles of
Picea obovata Ledeb.4a and the leaves of Stenochlaena palustris.4b
In the seedlings of Scots pine (Pinus sylvestris L.), this compound
was found to provide optimal protection for deep-lying tissue
against damaging UV-B radiation.4c
More than 1500 flavonol O-glycosides have so far been
isolated, mostly from higher plants.1 The majority of these
compounds (∼80%) have a sugar linkage at the 3-OH, and
over 20% possess one or more acyl groups attached through
the sugar residues, which further enhances the structural
diversity of flavonol O-glycosides.1 These ubiquitous meta-
bolites play a variety of important roles in the growth and
development of plants, e.g., as interspecies signaling mole-
cules.1,2 They also demonstrate a wide spectrum of activities
(3) For some natural congeners of compound 1, see: (a) Slimestad, R.;
Andersen, Ø. M.; Francis, G. W.; Marston, F. A.; Hostettmann, K.
Phytochemistry 1995, 40, 1537. (b) Imperato, F.; Minutiello, P. Phytochem-
istry 1997, 45, 199. (c) Park, S.-H.; Oh, S. R.; Jung, K. Y.; Lee, I. S.; Ahn,
K. S.; Kim, J. H.; Kim, Y. S.; Lee, J. J.; Lee, H.-K. Chem. Pharm. Bull. 1999,
47, 1484. (d) Ercil, D.; Kaloga, M.; Radtke, O. A.; Sakar, M. K.; Kiderlen,
A. F.; Kolodziej, H. Turk. J. Chem. 2005, 29, 437. (e) Hussein, A. A.;
Barberena, I.; Correa, M.; Coley, P. D.; Solis, P. N.; Gupta, M. P. J. Nat.
Prod. 2005, 68, 231.
(1) (a) Harborne, J. B.; Williams, C. A. Nat. Prod. Rep. 1995, 12, 639.
(b) Harborne, J. B.; Williams, C. A. Nat. Prod. Rep. 1998, 15, 631.
(c) Harborne, J. B.; Williams, C. A. Nat. Prod. Rep. 2001, 18, 310. (d) Veitch,
N. C.; Grayer, R. J. Nat. Prod. Rep. 2008, 25, 555.
(2) Harborne, J. B.; Baxter, H. The Handbook of Natural Flavonoids; John
Wiley & Sons: Chichester, UK, 1999; Vol. 1.
DOI: 10.1021/jo1014189
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Published on Web 09/14/2010
J. Org. Chem. 2010, 75, 6879–6888 6879
2010 American Chemical Society

Yang et al.
JOCArticle
The wide occurrence and importance of the flavonol
glycosides have attracted attention on the synthetic studies
toward this group of natural products.5,6 In that, the forma-
tion of the flavonol 3-O-glycosidic linkages resort mostly to
the glycosylation protocol with glycosyl bromides as donors
under phase-transfer catalysis (PTC) conditions or under the
action of silver salts. Here we report two approaches to the
synthesis of kaempferol 3-O-glycoside 1, with the second one
highlighted by an efficient alternative to the synthesis of
flavonol 3-O-glycosidic linkages with the newly developed
glycosyl o-alkynylbenzoates as donors and gold(I) as a
catalyst.7
rt led to 3,7,40-tri-O-silyl ether 4 in an excellent 90% yield,8
leaving only the 5-OH intact, which forms a hydrogen bond
with the 4-carbonyl group. Selective removal of the 3-O-silyl
group, which is vicinal to the 4-carbonyl group, was effected
with I2 in MeOH (reflux for 6 h), providing 3,5-diol 5 in
moderate yield (51%).9 Protection of the 3,5-OH with the
benzoyl group gave 6 (90%). Direct conversion of the 7,40-O-
silyl group into benzyl protection was realized with BnBr in
the presence of CsF and TBAI (tetrabutylammonium iodide)
in DMF at rt,10 leading to 40,7-di-O-benzyl-3,5-di-O-benzoyl-
kaempferol 7 in good yield (72%). Subsequent removal of the
3,5-O-benzoyl group (NaOMe, MeOH, rt) provided 2(91%).5a
SCHEME 2. Preparation of 3,6-Di-O-acetyl-2,4-di-O-benzyl-
R-D-glucopyranosyl Bromide (3)
Results and Discussion
First Generation Synthesis. In line with the previous syn-
thesis of kaempferol 3-O-glycosides,5 coupling of 7,40-di-O-
benzyl-kaempferol 2 with glucopyranosyl R-bromide 3 would
serve as the key step for the synthesis of target molecule 1
(Figure 1).
The required 3,6-di-O-acetyl-2,4-di-O-benzyl-R-D-gluco-
pyranosyl bromide (3) was prepared as shown in Scheme 2.
5,6-Anhydro-3-O-allyl-1,2-O-isopropylidene-R-D-glucofur-
anose 8, which was easily obtained from D-glucose (4 steps,
54% overall yield),11 was chosen as a key precursor. Thus,
treatment of epoxide 8 with AllOH in the presence of NaH in
DME (1,2-dimethoxyethane) at reflux afforded 3,6-di-O-
allyl-1,2-O-isopropylidene-R-D-glucofuranose 9 in a good
FIGURE 1. 3-O-(300,600-Di-O-E-p-coumaroyl)-β-D-glucopyranoside
(1) and its retro-synthetic perspective.
The preparation of kaempferol derivative 2 commenced
with commercially available kaempferol (Scheme 1). Thus,
treatment of kaempferol with TBSCl and DBU in CH2Cl2 at
SCHEME 1. Preparation of 7,40-Di-O-benzyl-Kaempferol (2)
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Yang et al.
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83% yield. Alternatively, treatment of 3-O-allyl-1,2-O-iso-
propylidene-R-D-glucofuranose with AllBr under PTC con-
ditions (NaOH, Bu4NBr, CH2Cl2, H2O) led to 9 in only
moderate yield (<50%).11a Compound 9 was then converted
into ethyl 1-thio-β-D-glucopyranoside 10 via three conve-
nient steps (50% overall yield), i.e., deacetonidation (80%
HOAc), acetylation (Ac2O, pyridine), and ethyl thioglyco-
side formation (EtSH, BF3OEt2, CH2Cl2). The 2,4-O-acetyl
group in 10 was converted into benzyl protection (2 steps,
95% yield) to provide 11. The 3,6-O-allyl group in thioglyco-
side 11 could not survive during conversion into the corre-
sponding glycosyl bromide, thus were replaced with acetyl
protection via deallylation (t-BuOK, DMSO, 100 °C; and
then 1 N HCl, acetone, reflux; 75%) and acetylation, leading
to 13. Thioglycoside 13 was then transformed smoothly into
the desired R-bromide 3 with Br2 in CH2Cl2 at 0 °C. Bromide
3 was found unstable, thus was used directly without further
purification.
SCHEME 3. Completion of the Synthesis of Target Molecule 1
Under the previously optimized PTC conditions (TBAB,
0.1 N K2CO3, CHCl3, rt),6 glycosylation of kaempferol 3,5-
diol 2 with the crude glucopyranosyl R-bromide 3 led to the
desired 3-O-β-glucoside 14 (H-100:5.53ppm,J= 7.5 Hz) in 50%
yield, with 40% of the starting 2 being recovered (Scheme 3).
Although the yield was moderate, the stereo- and regioselec-
tivity were perfect, with no R-glycoside or 5-O-glycoside
being detected. Subsequent removal of the 300,600-O-acetyl
group (K2CO3, MeOH, THF, rt) provided 15 (85%). Intro-
duction of the E-4-benzyloxycinnamyl group onto the 300,600-
OH on 15 was found to be problematic. Under mild conditions
(2.0 equiv of E-4-benzyloxycinnamic acid, DCC, DMAP,
CH2Cl2, rt), only monoacylated product was detected (pre-
sumably at the 600-OH). Either increasing the equivalents of
the acid or prolonging the reaction time did not result in
satisfactory results. When 15 was treated with 6.0 equiv of
the acid under reflux, a mixture of the 5,300,600-tri-O-acyl and
300,600-di-O-acyl products was obtained, which could not be
separated by silica gel column chromatography due to their
similar polarity and poor solubility. Thus, the mixture was
subjected to selective removal of the phenolic 5-O-acyl
group, and under the action of 4-MePhSH in the presence
of DBU in DMF at 40 °C, the desired 300,600-di-O-acyl
product 16 was obtained in 60% yield (based on 15).12
Finally, global debenzylation was effected with BBr3 in
CH2Cl2 at low temperature (-78 °C), furnishing the target
(4) (a) Zapesochnaya, G. G.; Stepanov, A. N.; Petrow, A. A.; Ivanova,
S. Z. Khim. Prir. Soedin. 1983, 582. (b) Liu, H.; Orjala, J.; Sticher, O.; Rali, T.
J. Nat. Prod. 1999, 62, 70. (c) Jungblut, T. P.; Schnitzler, J.-P.; Heller, W.;
Hertkorn, N.; Metzger, J. M.; Szymczak, W.; Sandermann, H. Angew.
Chem., Int. Ed. Engl. 1995, 34, 312.
(5) For selected examples of kaempferol O-glycosides synthesis, see:
(a) Wagner, H.; Danninger, H.; Seligmann, O.; Nogradi, M.; Farkas, L.;
Farnsworth, N. Chem. Ber. 1970, 103, 3678. (b) Vermes, B.; Farkas, L.;
1
molecule 1 in 60% yield. The H and 13C NMR data of the
synthetic sample are identical with those reported for the
natural product.4,23
Second Generation Synthesis. In the preceding synthetic
approach, two steps are especially unsatisfactory: (1) Gly-
cosylation of kaempferol 2 with glycosyl bromide 3 under
PTC conditions gave the desired product 14 in 50% yield, in
that the bromide 3 was unstable and thus had to be used
immediately after preparation. For the preparation of bro-
mide 3, additional steps were required to replace the 300,600-O-
allyl protection (11f13). (2) Introduction of the coumaroyl
group onto the 300,600-OH of triol 15 led to a mixture of the
inseparable 300,600-di-O-acyl and 5,300,600-tri-O-acyl deriva-
tives, which required an additional step to remove selectively
the phenolic 5-O-acyl group. To avoid this impediment, we
decided to investigate the glycosylation of 5,7,40-tri-O-benzyl-
kaempferol (i.e., 22) with a glycosyl o-alkynylbenzoate as
donor toward the synthesis of target 1. The glycosyl o-alky-
nylbenzoates are shelf stable and could be activated by a
catalytic amount of gold(I) complexes for glycosidation. This
mild protocol should be advantageous in the glycosylation
of flavonols, considering many conventional glycosylation
protocols involve acidic conditions or strongly electrophilic
promoters, which might be detrimental to the flavonol substrates.
ꢀ
ꢀ
Nogradi, M. Phytochemistry 1976, 15, 1320. (c) Farkas, L.; Vermes, B.;
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Nogradi, M.; Kalman, A. Phytochemistry 1976, 15, 215. (d) Vermes, B.;
Chari, V. M.; Wagner, H. Helv. Chim. Acta 1981, 64, 1964. (e) Maloney,
D. J.; Hecht, S. M. Org. Lett. 2005, 7, 1097. (f) Shan, M.; O’Doherty, G. A.
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J. A.; Maloney, D. J.; Hecht, S. M.; Lannigan, D. A. Bioorg. Med. Chem.
2007, 15, 5018. (j) Oyama, K-i.; Kawaguchi, S.; Yoshida, K.; Kondo, T.
Tetrahedron Lett. 2007, 48, 6005.
(6) For selected examples of quercetin O-glycosides synthesis, see: (a) Li,
M.; Han, X.; Yu, B. Tetrahedron Lett. 2002, 43, 9467 and references cited
therein. (b) Du, Y.; Wei, G.; Linhardt, R. J. Tetrahedron Lett. 2003, 44, 6887.
(c) Du, Y.; Wei, G.; Linhardt, R. J. J. Org. Chem. 2004, 69, 2206. (d) Peng,
W.; Li, Y.; Zhu, C.; Han, X.; Yu, B. Carbohydr. Res. 2005, 340, 1682. (e) Zhu,
C.; Peng, W.; Li, Y.; Han, X.; Yu, B. Carbohydr. Res. 2006, 341, 1047. (f) Li,
Z.; Ngojih, G.; DeWitt, P.; Zheng, Z.; Chen, M.; Lainhart, B.; Li, V.; Felpo,
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(7) (a) Li, Y.; Yang, Y.; Yu, B. Tetrahedron Lett. 2008, 49, 3604. (b) Yang,
Y.; Li, Y.; Yu, B. J. Am. Chem. Soc. 2009, 131, 12076. (c) Yang, Y.; Li, Y.;
Yu, B. Tetrahedron Lett. 2010, 51, 1504. (d) Li, Y.; Yang, X.; Liu, Y.; Zhu, C.;
Yang, Y.; Yu, B. Chem.;Eur. J. 2010, 16, 1871.
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(8) De Groot, A. H.; Dommisse, R. A.; Lemiere, G. L. Tetrahedron 2000,
56, 1541.
(9) (a) Vaino, A. R.; Szarek, W. A. Chem. Commun. 1996, 2351. (b) Keith,
J. M. Tetrahedron Lett. 2004, 45, 2739.
(10) Oriyama, T.; Noda, K.; Yatabe, K. Synlett 1997, 701.
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SCHEME 4. Synthesis of 5,7,40-Tri-O-benzyl-Kaempferol (22)
The previous preparation of flavonol derivatives (such as
22) mostly employed Baker-Venkataraman rearrangement13
and subsequent oxidation of the resulting flavone. The oxi-
dation step required such oxidants as dimethyldioxirane
(DMDO) and hypervalent iodine derivatives5,14-16 that
has discouraged scale-up synthesis. Brouillard et al. devel-
oped an alternative approach, in that the flavonol 3-OH was
introduced by a sequence of bromination of an acetophe-
none derivative followed by substitution of the bromide with
a benzoate group.17a The feasibility of this approach to the
synthesis of 5,7,40-tri-O-benzyl-kaempferol (22) was exam-
ined (Scheme 4). Thus, condensation of hydroxyacetophe-
none 1718 and 4-benzyloxybenzoic acid 1819 was effected
under EDCI in CH2Cl2, providing ester 19 (75%). Bromina-
tion of methyl ketone 19 with phenyltrimethylammonium
tribromide (PTT) in THF afforded bromide 20 in a moderate
yield of 49%; the corresponding dibromomethyl ketone was
found to be the major byproduct. Substitution of the bro-
mide in 20 with benzoate took place in refluxing acetonitrile,
leading to 21 in 68% yield. The Baker-Venkataraman
rearrangement on 21 proceeded smoothly under the action
of sodium hydride in THF under reflux. However, the re-
ported conditions (H2SO4/HOAc, 60 °C)17 for the subsequent
cyclization/dehydration led to a complex mixture, due to
partial cleavage of the phenolic benzyl groups under the
strong acidic conditions. After trying a variety of conditions,17
we finally found that sodium acetate in acetic acid at 100 °C
could effect this transformation smoothly.20 Subsequent
saponification of the 3-O-benzoate furnished 22 in a high
yield of 70% (for 3 steps).
Glycosyl o-hexynylbenzoates 23a-g were readily pre-
pared via condensation of the corresponding lactols with
o-hexynylbenzoic acid (DCC, DMAP, CH2Cl2, >90%).7
These compounds are shelf stable. Under the standard gly-
˚
cosylation conditions (0.2 equiv of Ph3PAuNTf2, 4 A MS,
CH2Cl2, rt),7 glycosylation of 5,7,40 -tri-O-benzyl-kaempfer-
ol (22) with glycosyl o-hexynylbenzoates 23a-g was exam-
ined (Table 1). The glycosylation reaction with 2,4-di-O-acetyl-
3,6-di-O-allyl-D-glucopyranosyl o-hexynylbenzoate 23a23 led
to poor yield (14% when 3 equiv of 23a was used) of the
coupled β-O-glycoside 24a (entry 1). Similarly, glycosylation
with 2,3,4,6-tetra-O-acetyl-D-glucopyranosyl o-hexynylben-
zoate 23c7 did not provide the β-O-glycoside at all (entry 3).
These results were in accordance with our previous findings
that glucopyranosyl o-hexynylbenzoates bearing a 2-O-acetyl
group easily underwent ortho-ester formation and decom-
position under the glycosylation conditions. Evidently, the
corresponding 2-O-benzoyl counterparts 23b and 23d7 be-
haved as excellent donors, providing the expected β-O-glyco-
sides 24b and 24d in 90% and 82% yield, respectively (entries
2 and 4). It was noted that an excess amount of donors (3.0
equiv) and prolonged reaction time (12 h) were required to
achieve the good yields of kaempferol 3-O-β-glycosides,
testifying that 5,7,40-tri-O-benzyl-kaempferol (22) is a poorly
nucleophilic acceptor. In comparison, when 2-O-benzoyl-3,-
4,6-tri-O-benzyl-D-glucopyranosyl o-hexynylbenzoate 23e,7
which was equipped with a superarmed protecting pattern,21
was used as donor, the glycosylation with kaempferol deriv-
ative 22 proceeded more smoothly: 1.5 equiv of 23e and 1 h
reaction time ensured completion of the reaction to afford
the desired O-β-glycoside 24e in 95% yield (entry 5).
(13) (a) Baker, W. J. Chem. Soc. 1933, 1381. (b) Mahal, H. S.; Venkataraman,
K. Curr. Sci. 1933, 4, 214. (c) Mahal, H. S.; Venkataraman, K. J. Chem. Soc.
1934, 1767.
(14) Adam, W.; Hadjiarapoglou, L.; Levai, A. Synthesis 1992, 436.
(15) (a) Horie, T.; Kawamura, Y.; Yamamoto, H.; Yamashita, K. Chem.
Pharm. Bull. 1995, 43, 2054. (b) Horie, T.; Kitou, T.; Kawamura, Y.;
Yamashita, K. Bull. Chem. Soc. Jpn. 1996, 69, 1033. (c) Horie, T.; Shibata,
K.; Yamashita, K.; Kawamura, Y.; Tsukayama, M. Chem. Pharm. Bull.
1997, 45, 446.
(16) (a) Prakash, O.; Pahuja, S.; Tanwar, M. P. Indian J. Chem., Sect. B:
Org. Chem. Incl. Med. Chem. 1994, 33, 372. (b) Burke, A. J.; O’Sulliva, W. I.
Tetrahedron 1997, 53, 8491.
(17) (a) Fougerousse, A.; Gonzalez, E.; Brouillard, R. J. Org. Chem. 2000,
65, 583. (b) Furuta, T.; Nakayama, M.; Suzuki, H.; Tajimi, H.; Inai, M.;
Nukaya, H.; Wakimoto, T.; Kan, T. Org. Lett. 2009, 11, 2233.
(18) Huang, C.; Zhang, Z.; Li, S.; Li, Y. J. Chem. Res. 1999, 148.
(19) Samosorn, S.; Bremner, J. B.; Ball, A.; Lewis, K. Bioorg. Med. Chem.
2006, 14, 857.
R-L-Rhamnosyl residue is also frequently found at the 3-OH
of natural flavonol glycosides. However, the conventional
(20) Gerard, B.; Cencic, R.; Pelletier, J.; Porco, J. A. Angew. Chem., Int.
Ed. 2007, 46, 7831.
(21) Mydock, L. K.; Demchenko, A. V. Org. Lett. 2008, 10, 2107.
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TABLE 1. Glycosylation of Kaempferol 3-OH 22 with Glycosyl o-Hexynylbenzoates 23a-g As Donors and Ph3PAuNTf2 As a Catalyst
aIsolated yield. b12 h was required. c1 h was required.
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SCHEME 5. Completion of the Synthesis of 1 from 24b
PTC conditions could not be applied to make this linkage
with L-rhamnosyl bromides (because the R-bromide always
prevails, which would lead to β-O-rhamnoside predomi-
nantly if glycosylation did take place).22 Alternatively, Hecht
and Maloney employed silver oxide to promote the glyco-
sylation of 22 with 3,4-di-O-acetyl-2-O-benzyl-R-L-rhamno-
pyranosyl bromide to provide the corresponding kaempferol
3-O-R-L-rhamnoside in 60% yield.5e Gratifyingly, under
the present conditions, 2,4-di-O-benzoyl-3-O-benzyl-L-
rhamnopyranosyl o-hexynylbenzoate 23f coupled with
22 fluently, providing the desired O-R-L-rhamnoside 24f
in 91% yield within 1 h (entry 6). Similarly, 2,3,4-tri-O-
benzoyl-D-ribofuranosyl o-hexynylbenzoate 23g reacted
with 22 to provide O-β-D-furanoside 24g in 93% yield
within 1 h (entry 7).
droxyacetophenone and p-hydroxybenzoic acid (6 steps,
17% overall yield), which was coupled with 3,6-di-O-allyl-
2,4-di-O-benzoyl-β-D-glucopyranosyl o-hexynylbenzoate 23b
to provide the desired 3-O-glycoside 24b in a high yield of
90%. Thus, the latter approach achieved a total of 21 steps
with 6% overall yield from cheap starting materials. The gly-
cosylation of flavonol 3-OH (i.e., 22) with a variety of the
glycosyl o-hexynylbenzoates has been examined; the results
have demonstrated that glycosyl o-hexynylbenzoates bear-
ing the 2-O-benzoyl group are excellent donors under the
catalysis of Ph3PAuNTf2 complex for the glycosylation of
flavonol 3-OH. Thus, a new and highly efficient alternative
has been established for the synthesis of the widely occurring
flavonol 3-O-glycosides.
To continue the synthesis of target molecule 1, the high
yielding 5,7,40-tri-O-benzyl-3-O-(300,600-di-O-allyl-200,400-di-
O-benzoyl-β-D-glucopyranosyl)-kaempferol (24b) was used
as an advanced precursor (Scheme 5). Removal of the 200,400-
di-O-benzoyl group (NaOMe, MeOH, rt) followed by ben-
zylation (BnBr, NaH, DMF, 0 °C-rt) provided compound
25 (72%). Subsequent cleavage of the 300,600-di-O-allyl group
on 25 (PdCl2, MeOH, CH2Cl2, rt) followed by acylation of
the resulting 300,600-OH with E-4-benzyloxycinnamic acid
(DCC, DMAP, CH2Cl2, reflux) afforded 26 in 66% yield.
Finally, removal of the seven O-benzyl groups on 26 was
achieved with BBr3 in CH2Cl2 at -78 °C, furnishing the
target molecule 1 in a satisfactory 60% yield.
Experimental Section23
3,7,40-Tri-O-tert-butyldimethylsilyl-Kaempferol (4). To a sus-
pension of kaempferol (423 mg, 1.5 mmol) and TBSCl (1.4 g,
9 mmol) in dry CH2Cl2 was added DBU (1.5 mL). The reaction
mixture was stirred at room temperature for 15 min, then was
diluted with CH2Cl2 and washed with water. After drying over
Na2SO4, the solvent was evaporated to give a yellow oil, which
was further purified by flash column chromatography on silica
gel (EtOAc-petroleum ether, l:150) to provide 4 (988 mg, 90%)
as a yellow oil: 1H NMR (300 MHz, CDCl3) δ 12.68 (s, 1 H), 7.86
(d, J = 9.0 Hz, 2 H), 6.94 (d, J = 8.4 Hz, 2 H), 6.36 (s, 1 H), 6.27
(d, J = 1.8 Hz, 1 H), 1.00 (s, 9 H), 0.98 (s, 9 H), 0.84 (s, 9 H), 0.26
(s, 6 H), 0.23 (s, 6 H), 0.14 (s, 6 H); 13C NMR (75 MHz, CDCl3) δ
178.1, 161.7, 157.6, 156.4, 153.1, 135.6, 130.5, 124.2, 120.0,
106.1, 103.0, 98.3, 25.7 (2 C), 25.5, 18.6, 18.3, 18.2, -4.0, -4.4
(2 C); HRMS (MALDI) calcd for C33H53O6Si3 [M þ H]þ
629.3150, found 629.3145.
Conclusion
3-O-(300,600-Di-O-E-p-coumaroyl)-β-D-glucopyranoside (1),
a typical acylated flavonol 3-O-glycoside, has been synthe-
sized for the first time via two approaches. The first ap-
proach, starting with kaempferol and glucose, employed a
total of 24 steps (in 2.4% overall yield), in that the flavonol
3-O-glycosidic linkage was built (in 50% yield) by a conven-
tional method with glycosyl bromide 3 as donor under PTC
conditions. In the second approach, 5,7,40-tri-O-benzyl-
kaempferol (22) was readily prepared from 20,40,60-trihy-
7, 40-Di-O-tert-butyldimethylsilyl-Kaempferol (5). To a solu-
tion of 4 (441 mg, 0.7 mmol) in MeOH/CHCl3 (5 mL:5 mL) was
added I2 (2 mg, 0.007 mmol) at room temperature. The reaction
mixture was refluxed for 6 h, and was then quenched with aq
Na2S2O3 at room temperature. The resulting mixture was
extracted with EtOAc (3 ꢀ 100 mL), and the combined extracts
were concentrated in vacuo. The residue was subjected to silica
gel column chromatography (EtOAc-petroleum ether, l:100) to
provide 5 (184 mg, 51% yield) as a yellow solid: 1H NMR (300
MHz, CDCl3) δ 11.66 (s, 1 H), 8.05 (d, J = 8.7 Hz, 2 H), 6.90 (d,
J = 8.7 Hz, 2 H), 6.65 (s, 1 H), 6.36 (d, J = 2.4 Hz, 1 H), 6.22 (d,
(22) Demetzos, C.; Skaltsounis, A.-L.; Tillequin, F.; Koch, M. Carbo-
hydr. Res. 1990, 207, 131.
(23) Experimental details and characterization data for compounds 23a,
23f,g, 24a, and 24d-g, and data comparison between the natural and
synthetic target molecule 1 are provided in the Supporting Information.
J = 1.8 Hz, 1 H), 0.92 (s, 18 H), 0.20 (s, 6 H), 0.17 (s, 6 H); 13
NMR (75 MHz, CDCl3) δ 175.3, 162.4, 160.7, 157.7, 156.5,
145.8, 135.7, 129.4, 123.7, 120.2, 104.4, 103.1, 98.7, 25.6, 25.5,
C
6884 J. Org. Chem. Vol. 75, No. 20, 2010

Yang et al.
JOCArticle
18.3, 18.2, 1.0, -4.4. HRMS (MALDI) calcd for C27H39O6Si2
[M þ H]þ 515.2285, found 515.2280.
(54 mL) was refluxed for 3 h. After cooling, the solvent was
removed under vacuum. The residue was dissolved in dry pyridine
(15 mL), and then Ac2O (5 mL) was added. The reaction mixture
was stirred overnight, and was then concentrated. The resulting
crude product was dissolved in dry CH2Cl2 (67 mL) and then
treated with EtSH (10 mL) at 0 °C. BF3OEt2 (1 mL) was added
dropwise to the reaction mixture, and stirring was continued for
2 h at 0 °C and then for 20 h at rt. Saturated aq NaHCO3 was
added and the mixture was stirred for 2 h. The organic layer was
separated, dried over Na2SO4, and concentrated. The residue
was purified by silica gel column chromatography (EtOAc-
3,5-Di-O-benzoyl-7,40-di-O-tert-butyldimethylsilyl-Kaempferol
(6). To a solution of 5 (158 mg, 0.3 mmol) in pyridine/CHCl3
(2.4 mL, v/v 1:3) at 0 °C was added BzCl (0.3 mL). After being
stirred for 10 h, the reaction mixture was diluted with EtOAc
and washed with water. After drying over Na2SO4, the solvent
was evaporated in vacuo. The residue was purified by silica gel
column chromatography (EtOAc-petroleum ether, 1:25) to
1
give 6 (211 mg, 95%) as a yellow solid: H NMR (300 MHz,
CDCl3) δ 8.26 (d, J = 7.5 Hz, 2 H), 8.14 (d, J = 7.2 Hz, 2 H),
7.81 (d, J = 8.7 Hz, 2 H), 7.60 (m, 2 H), 7.49 (m, 4 H), 6.90
(m, 3 H), 6.70 (d, J = 2.1 Hz, 1 H), 1.02 (s, 9 H), 0.97 (s, 9 H),
0.32 (s, 6 H), 0.20 (s, 6 H); 13C NMR (75 MHz, CDCl3) δ 169.9,
165.1, 163.7, 160.2, 158.3, 157.8, 154.9, 150.8, 133.6, 133.3,
133.0, 130.6, 130.5, 129.8, 129.5, 128.6, 128.4 (2 C), 122.7,
120.2, 113.3, 112.0, 106.0, 25.5 (2 C), 18.2 (2 C), -4.4 (2 C);
HRMS (MALDI) calcd for C41H47O8Si2 [M þ H]þ 723.2809,
found 723.2804.
3,5-Di-O-benzoyl-7,40-di-O-benzyl-Kaempferol (7). To a sus-
pension of 6 (96 mg, 0.1 mmol) and CsF (102 mg, 0.6 mmol) in
DMF (1.5 mL) was added BnBr (0.1 mL). After 10 min of
stirring at rt, TBAI (96 mg, 0.3 mmol) was added. The resulting
mixture was stirred for another 6 h, and was then filtered. The
filtrate was concentrated under reduced pressure to give a
residue, which was purified by silica gel column chromatogra-
phy (EtOAc-petroleum ether, l:3) to provide 7 (65 mg, 72%) as
a yellow solid: 1H NMR (300 MHz, CDCl3) δ 8.23 (d, J = 7.8
Hz, 2 H), 8.13 (d, J = 7.5 Hz, 2 H), 7.84 (d J = 8.7 Hz, 2 H), 7.58
(m, 2 H), 7.45-7.34 (m, 14 H), 6.99 (m, 3 H), 6.83 (d, J = 1.8 Hz,
1 H), 5.14 (s, 2 H), 5.04 (s, 2 H); 13C NMR (75 MHz, CDCl3) δ
169.7, 165.1, 163.6, 162.5, 160.8, 158.0, 154.6, 150.8, 136.1,
135.3, 133.6, 133.3, 133.0, 130.6, 130.5, 129.8, 129.4, 128.7,
128.6, 128.4, 128.3, 128.1, 127.5, 127,4, 122.2, 114.9, 111.5,
109.2, 99.9, 70.7, 70.0; HRMS (MALDI) calcd for C43H31O8
[M þ H]þ 675.2019, found 675.2014.
petroleum ether, 1:6) to yield 10 (1.4 g, 50% for 3 steps) as a
1
white solid: [R]29 -23.3 (c 1.0, CHCl3); H NMR (300 MHz,
D
CDCl3) δ 5.89 (m, 2 H), 5.26 (m, 4 H), 5.00 (m, 2 H), 4.39 (d, J =
10.2 Hz, 1 H), 4.07 (d, J = 5.7 Hz, 2 H), 3.96 (d, J = 5.4 Hz, 2 H),
3.60 (m, 4H), 2.76 (m, 2 H), 2.08 (s, 3 H), 2.05 (s, 3 H), 1.26 (t,
J = 7.8 Hz, 3 H); 13C NMR (75 MHz, CDCl3) δ 169.3, 169.1,
134.2, 134.1, 117.0, 116.6, 83.3, 81.0, 72.9, 72.2, 71.1, 70.6, 69.5,
23.8, 20.8 (2 C), 14.6; HRMS (MALDI) calcd for C18H28O7SNa
[M þ Na]þ 411.1453, found 411.1448.
Ethyl 3,6-Di-O-allyl-2,4-di-O-benzyl-1-thio-β-D-glucopyrano-
side (11). A mixture of 10 (42 mg, 0.1 mmol) and K2CO3 (15 mg,
0.1 mmol) in MeOH/THF (1.5 mL, v/v 1:2) was stirred for 20 h
at rt. The mixture was neutralized with Dowex 50W-X 8 (Hþ)
resin, and the resin was then filtered off. The filtrate was evapo-
rated to give ethyl 3,6-di-O-allyl-1-thio-β-D-glucopyranoside
(31 mg, 95%) as a white solid. To a solution of the above solid
(31 mg, 0.1 mmol) in dry DMF (1 mL) was add NaH (16 mg, 0.4
mmol). After 10 min of stirring at 0 °C, BnBr (0.05 mL) was
added. The reaction mixture was stirred at room temperature
for 2 h, and was then cooled to 0 °C and quenched by slow
addition of an icy saturated aq NH4Cl solution. The resulting
mixture was extracted twice with EtOAc (100 mL). The com-
bined extracts were dried over Na2SO4 and concentrated under
vacuum. The residue was purified by silica gel column chroma-
tography (EtOAc-petroleum ether, 1:18) to provide 11 (50 mg,
D
1
100%) as a white solid: [R]29 -5.0 (c 2.4, CHCl3); H NMR
7,40-Di-O-benzyl-Kaempferol (2). To a solution of 7 (2.8 g, 4.2
mmol) in MeOH/CH2Cl2 (144 mL, v/v 1:5) at room temperature
was added NaOMe (677 mg, 12.5 mmol). After being stirred for
5 h, the mixture was adjusted to neutral with Dowex 50W-X 8
(Hþ) resin. The resin was filtered off. The filtrate was evaporated
to give a residue, which was recrystallized with CH2Cl2 to afford
2 (1.8 g, 91%) as a yellow solid: 1H NMR (300 MHz, DMSO-d6)
δ 12.40 (s, 1 H), 9.64 (s, 1 H), 8.13 (d, J = 9.3 Hz, 2 H), 7.45-7.30
(m, 10 H), 7.16 (d, J = 9.0 Hz, 2 H), 6.79 (d, J = 1.8 Hz, 1 H),
6.38 (d, J = 2.1 Hz, 1 H), 5.17 (s, 2 H), 5.15 (s, 2 H); 13C NMR
(75 MHz, DMSO-d6) δ 176.1, 163.9, 160.4, 159.6, 156.0, 146.5,
136.6, 136.4, 136.1, 129.3, 128.5, 128.4, 128.1, 127.9, 127.8 (2 C),
123.3, 114.8, 104.2, 98.0, 92.8, 69.9, 69.3; HRMS (MALDI)
calcd for C29H23O6 [M þ H]þ 467.1495, found 467.1489.
3,6-Di-O-allyl-1,2-O-isopropylidene-r-D-glucofuranose(9). To a
suspension of sodium hydride (698 mg, 17.4 mmol) and allyl
alcohol (9.1 mL, 133.3 mmol) in dry DME (14.0 mL) was added a
solution of 8 (2.1 g, 8.7 mmol) in DME (14.0 mL) at 0 °C. The
mixture was stirred at 50 °C for 6 h, and was then diluted with
saturated NH4Cl (20 mL) and extracted with CH2Cl2 (100 mL)
three times. The combined organic layers were washed with water,
dried over Na2SO4, and concentrated. The resulting residue
was purified by silica gel column chromatography (EtOAc-
(300 MHz, CDCl3) δ 7.43-7.27 (m, 10 H), 6.04 (m, 2 H), 5.33
(dd, J = 6.3, 1.8 Hz, 1 H), 5.28 (m, 1 H), 5.19 (s, 1 H), 5.16 (s, 1
H), 4.90 (m, 2 H), 4.75 (d, J = 9.9 Hz, 1 H), 4.65 (d, J = 10.8 Hz,
1 H), 4.43 (m, 3 H), 4.09-3.97 (m, 2 H), 3.73 (dd, J = 10.8, 2.1
Hz, 1 H), 3.64 (dd, J = 11.1, 4.8 Hz, 1 H), 3.56 (m, 2 H), 3.42
(m, 2 H), 2.84 (m, 2 H), 1.34 (t, J = 7.5 Hz, 3 H); 13C NMR
(75 MHz, CDCl3) δ 138.1, 137.9, 135.0, 134.7, 128.4 (2 C), 128.3,
128.0, 127.8 (2 C), 116.9, 116.7, 86.2, 84.9, 81.6, 78.9, 77.8, 75.5,
75.0, 74.4, 72.3, 69.0, 24.9, 15.0; HRMS (MALDI) calcd for
C28H36O5SNa [M þ Na]þ 507.2181, found 507.2176.
Ethyl 2,4-Di-O-benzyl-1-thio-β-D-glucopyranoside (12). To a
solution of 11 (400 mg, 0.8 mmol) in DMSO (6.2 mL) at room
temperature under argon was added t-BuOK (194 mg, 1.7 mmol).
The reaction mixture was heated to 100 °C for 20 min and then
diluted with water. The resulting mixture was extracted with
EtOAc (3 ꢀ 100 mL), and the combined extracts were concen-
trated in vacuum. The crude enol ether was dissolved in acetone
(60 mL) and treated with 1 N HCl (10 mL). After 2 h of stirring
at 60 °C, the reaction was quenched with concentrated NH4OH.
The resulting mixture was extracted three times with EtOAc
(100 mL), then the combined extracts were washed with brine,
dried over Na2SO4, and concentrated. The residue was purified
by silica gel column chromatography (EtOAc-petroleum ether,
petroleum ether, 1:5) to give 9 (2.2 g, 83%) as a colorless oil:
1
[R]24 -34.3 (c 1.0, CHCl3); H NMR (300 MHz, CDCl3) δ
l:3) to provide 12 (250 mg, 75%) as a white solid: [R]29 -3.3
D
D
5.98-5.85 (m, 3 H), 5.35-5.18 (m, 4 H), 4.58 (d, J = 3.9 Hz, 1 H),
4.22-4.04 (m, 7 H), 3.73 (m, 1 H), 3.60 (m, 1 H), 1.49 (s, 3 H), 1.32
(s, 3 H); 13C NMR (75 MHz, CDCl3) δ 134.4, 133.8, 117.7, 117.2,
111.6, 105.0, 82.2, 81.7, 79.6, 72.2, 71.8, 71.2, 67.8, 26.6, 26.1;
HRMS (ESI) calcd for C15H24O6 [M] 300.1573, found 300.1576.
Ethyl 2,4-Di-O-acetyl-3,6-di-O-allyl-1-thio-β-D-glucopyrano-
side (10). A solution of 9 (2.6 g, 7.2 mmol) in 80% HOAc/H2O
(c 1.2, CHCl3); 1H NMR (300 MHz, CDCl3) δ 7.41-7.28 (m, 10
H), 4.97 (d, J = 10.8 Hz, 1 H), 4.86 (d, J = 10.8 Hz, 1 H), 4.70 (d,
J = 4.8 Hz, 1 H), 4.66 (d, J = 4.8 Hz, 1 H), 4.48 (d, J = 9.9 Hz,
1 H), 3.90 (dd, J= 12.0, 2.4Hz, 1 H), 3.79 (m, 2 H), 3.50 (t, J =9.3
Hz, 1 H), 3.37 (m, 1 H), 3.28 (t, J = 9.3 Hz, 1 H), 2.79 (m, 2 H),
1.34 (t, J = 7.2 Hz, 3 H); 13C NMR (75 MHz, CDCl3) δ 138.0,
137.9, 128.5(2 C), 128.2, 128.0, 127.9, 84.8, 81.4, 78.9, 78.3, 77.4,
J. Org. Chem. Vol. 75, No. 20, 2010 6885

Yang et al.
JOCArticle
75.2, 74.7, 62.1, 25.2, 15.1; HRMS (MALDI) calcd for
C22H28O5SNa [M þ Na]þ 427.1555, found 427.1550.
suspension of 15 (23 mg, 0.03 mmol), E-4-benzyloxycinnamic
acid (43 mg, 0.2 mmol), and DCC (29 mg, 0.1 mmol) in CH2Cl2
(2 mL) was added DMAP (3 mg). After 5 h of reflux, the sus-
pension was filtered. The filtrate was evaporated in vacuo. The
residue was purified by silica gel column chromatography to
give a mixture of products. To a solution of the above product
and 4-MeC6H4SH (30 mg, 0.244 mmol) in dry DMF (1 mL) was
added DBU (0.01 mL). After being stirred for 7 h at 40 °C, the
mixture was diluted with water, and was then extracted with
EtOAc. The organic phase was dried with Na2SO4 and concen-
trated in vacuo. The residue was purified by silica gel chroma-
tography (acetone-petroleum ether, l:4) to provide 16 (22 mg,
60%, two steps) as a yellow solid: [R]25D -56.1 (c 1.4, CHCl3);
1H NMR (300 MHz, CDCl3) δ 12.65 (s, 1 H), 8.03 (d, J = 8.4
Hz, 2 H), 7.69 (d, J = 16.2 Hz, 1 H), 7.53-7.17 (m, 35 H),
7.04-6.90 (m, 6 H), 6.45 (s, 1 H), 6.39 (s, 1 H), 6.26 (d, J = 15.6
Hz, 1 H), 6.19 (d, J = 15.9 Hz, 1 H), 5.67 (d, J = 7.5 Hz, 1 H),
5.55 (t, J = 8.7 Hz, 1 H), 5.13 (s, 2 H), 5.09 (s, 2 H), 5.00 (m, 5 H),
4.81 (d, J = 11.7 Hz, 1 H), 4.59 (d, J = 10.8 Hz, 1 H), 4.51 (d,
J = 10.8 Hz, 1 H), 4.33 (m, 2 H), 3.72 (m, 3 H); 13C NMR (75
MHz, CDCl3) δ 177.8, 166.4, 165.9, 164.3, 162.0, 160.6, 160.5,
157.4, 156.7, 144.9, 144.5, 138.1, 137.2, 136.3 (3 C), 135.7, 134.0,
130.8, 129.8 (2 C), 128.7, 128.6 (3 C), 128.5, 128.4, 128.3, 128.1 (2
C), 127.9, 127.4 (2 C), 127.3, 127.1, 123.1, 115.3, 115.2, 115.1,
115.0, 114.3, 106.0, 101.6, 98.6, 93.0, 78.7, 75.7, 75.3, 74.2, 73.2,
72.8, 70.3, 70.1, 69.9, 69.8, 62.1; HRMS (ESI) calcd for
C81H68O15Na [M þ Na]þ 1303.4456, found 1303.4450.
Ethyl 3,6-Di-O-acetyl-2,4-di-O-benzyl-1-thio-β-D-glucopyra-
noside (13). To a solution of compound 12 (202 mg, 0.5 mmol)
in pyridine (3.8 mL) at room temperature was added acetic
anhydride (0.5 mL). After being stirred for 3 h, the reaction
mixture was concentrated under vacuum. The residue was puri-
fied by silica gel column chromatography (EtOAc-petroleum
ether, l:3) to provide 13 (244 mg, 100%) as a white solid: [R]29
D
þ6.8 (c 2.2, CHCl3); 1H NMR (300 MHz, CDCl3) δ 7.37-7.23
(m, 10 H), 5.33 (t, J = 8.7 Hz, 1 H), 4.88 (d, J = 11.1 Hz, 1 H),
4.58 (m, 4 H), 4.35 (dd, J = 12.0, 1.2 Hz, 1 H), 4.22 (dd, J = 12.3,
4.8 Hz, 1 H), 3.58 (m, 2 H), 3.42 (t, J = 9.3 Hz, 1 H), 2.80 (m, 2
H), 2.06 (s, 3 H), 1.88 (s, 3 H), 1.35 (t, J = 7.2 Hz, 3 H); 13C
NMR (75 MHz, CDCl3) δ 170.6, 169.8, 137.5, 137.1, 128.5,
128.3, 128.1, 128.0 (2 C), 127.8, 85.2, 79.4, 77.0, 76.0, 74.8, 74.4,
63.1, 25.4, 20.9, 20.8, 15.0; HRMS (MALDI) calcd for C26H32-
O7SNa [M þ Na]þ 511.1766, found 511.1761.
7,40-Di-O-benzyl-3-O-(300,600-di-O-acetyl-200,400-di-O-benzyl-β-
D-glucopyranosyl)-Kaempferol (14). To a solution of compound
13 (58 mg, 1.2 mmol) in dry CH2Cl2 (1.5 mL) was added liquid
bromine (0.05 mL) with stirring for 25 min at 0 °C, The solvent
was evaporated in vacuo, then the resulting residue was coeva-
porated with toluene twice (2 ꢀ 10 mL) to give glucosyl bromide
3, which was used in the glycosylation reaction without further
purification. To the above glucosyl bromide in CHCl3 (1.7 mL)
was added compound 2 (30 mg, 0.07 mmol), aqueous K2CO3
(0.1 N, 1.7 mL), and TBAB (23 mg, 0.07 mmol). The mixture
was stirred vigorously at 50 °C for 8 h, then the organic phase
was collected, dried over Na2SO4, and concentrated. The resi-
due was subject to column chromatography on silica gel
(petroleum ether-acetone, 5:1) to provide 14 (31 mg, 54%) as
a yellow solid: [R]25D -12.3 (c 2.7, CHCl3); 1H NMR (300 MHz,
CDCl3) δ 12.61 (s, 1 H), 8.02 (d, J = 8.7 Hz, 2 H), 7.47-7.21 (m,
20 H), 7.00 (d, J = 8.7 Hz, 2 H), 6.51 (d, J = 2.1 Hz, 1 H), 6.44
(d, J = 2.1 Hz, 1 H), 5.53 (d, J = 7.8 Hz, 1 H), 5.36 (t, J = 9.3
Hz, 1 H), 5.12 (s, 4 H), 5.03 (d, J = 11.7 Hz, 1 H), 4.76 (d, J =
11.7 Hz, 1 H), 4.55 (d, J = 11.4 Hz, 1 H), 4.49 (d, J = 11.1 Hz, 1
H), 4.17 (d, J = 11.4 Hz, 1 H), 4.01 (dd, J = 11.7, 3.6 Hz, 1 H),
3.60 (m, 3 H), 1.93 (s, 3 H), 1.82 (s, 3 H); 13C NMR (75 MHz,
CDCl3) δ 177.7, 170.2, 169.6, 164.4, 161.9, 160.6, 157.2, 156.6,
138.1, 137.2, 136.2, 135.6, 134.0, 130.7, 128.7, 128.6, 128.4,
128.3, 128.2, 128.1, 128.0, 127.9, 127.6, 127.4 (2 C), 123.1,
114.3, 106.0, 101.6, 98.6, 93.0, 78.9, 75.6, 75.2, 74.2, 73.4, 72.4,
70.3, 70.0, 62.1, 21.0, 20.5; HRMS (MALDI) calcd for
C53H48O13Na [M þ Na]þ 915.2993, found 915.2987.
3-O-(300,600-Di-O-E-p-coumaroyl)-β-D-glucopyranoside (1). To a
solution of 16 (14 mg, 0.01 mmol) in CH2Cl2 (1 mL) was added
BBr3 (0.03 mL) at -78 °C. After being stirred for 4 h at this
temperature, the mixture was quenched with MeOH (1 mL) and
concentrated in vacuo. The residue was purified by preparative
TLC (MeOH-CHCl3, l:7) to afford 1 (5 mg, 60%) as a yellow
solid: [R]27D -35.8(c 0.95, CHCl3); 1H NMR (300 MHz, CD3CN)
δ 12.25 (s, 1 H), 8.04 (d, J = 8.7 Hz, 2 H), 7.73 (d, J = 16.2 Hz,
1 H), 7.54 (d, J = 8.7 Hz, 2 H), 7.46 (d, J = 16.2 Hz, 1 H), 7.38 (d,
J = 8.4 Hz, 2 H), 6.87 (m, 6 H), 6.43 (s, 1 H), 6.43 (d, J = 15.9 Hz,
1 H), 6.22 (s, 1 H), 6.14 (d, J = 16.5 Hz, 1 H), 5.31 (d, J = 7.8 Hz,
1 H), 5.12 (t, J = 9.0 Hz, 1 H), 4.27 (d, J = 11.7 Hz, 1 H), 4.21 (dd,
J = 13.2, 3.9Hz, 1 H), 3.68 (m, 1 H), 3.58 (m, 2 H); 13C NMR (125
MHz, CD3OD) δ 179.6, 169.3, 169.0, 166.2, 163.2, 161.8, 161.5 (2
C), 159.6, 158.7, 147.1, 146.9, 135.5, 132.5, 131.5, 127.6, 127.4,
123.0, 117.1 (2 C), 116.4, 115.7, 115.0, 105.9, 104.1, 100.3, 95.2,
79.0, 76.0, 74.4, 70.5, 64.4; LRMS (ESI) calcd for C39H31O15 [M -
H]þ 739.2, found 739.1.
20-(400-(Benzyloxy)benzoyloxy)-40,60-dibenzyloxyacetophenone
(19). To a suspension of 17 (348 mg, 1.0 mmol), 18 (342 mg, 1.5
mmol), and EDCI (576 mg, 3.0 mmol) in CH2Cl2 (8 mL) was
added DMAP (122 mg). After being stirred for 4 h at rt, the
mixture was diluted with EtOAc, and then washed with NaH-
CO3 (aq) and brine successively. The organic phase was dried
and concentrated in vacuo. The residue was purified by silica gel
column chromatography (EtOAc-petroleum ether, l:8) to give
19 (419 mg, 75%) as a white solid: 1H NMR (300 MHz, CDCl3)
δ 8.14 (d, J = 8.7 Hz, 2 H), 7.47-7.34 (m, 15 H), 7.07 (d, J = 9.0
Hz, 2 H), 6.56 (d, J = 2.1 Hz, 1 H), 6.50 (d, J = 1.8 Hz, 1 H), 5.16
(s, 2 H), 5.09 (s, 2 H), 5.05 (s, 2 H), 2.50 (s, 3 H); 13C NMR (75
MHz, CDCl3) δ 199.3, 164.6, 163.0, 161.1, 158.0, 149.7, 136.1,
135.9, 135.8, 132.4, 128.6, 128.2 (2 C), 127.6, 127.4 (2 C), 121.6,
118.0, 114.7, 101.3, 98.3, 70.8, 70.3, 70.1, 32.0; HRMS
(MALDI) calcd for C36H30O6Na [M þ Na]þ 581.1940, found
581.1935.
7,40-Di-O-benzyl-3-O-(200,400-di-O-benzyl-β-D-glucopyranosyl)-
Kaempferol (15). A solution of 14 (30 mg, 0.03 mmol) and
K2CO3 (5 mg, 0.04 mmol) in MeOH/THF (1.5 mL, v/v 1:2)
was stirred for 10 h at rt. The mixture was neutralized with
Dowex 50W-X 8 (Hþ) resin, and the resin was then filtered off.
The filtrate was evaporated. The residue was subjected to silica
gel column chromatography (acetone-petroleum ether, l:3) to
give 15 (23 mg, 85%) as a yellow solid: [R]28 þ11.2 (c 1.5,
D
CHCl3); 1H NMR (300 MHz, CDCl3) δ 12.59 (s, 1 H), 8.07 (d,
J = 9.0 Hz, 2 H), 7.49-7.31 (m, 20 H), 7.07 (d, J = 8.4 Hz, 2 H),
6.54 (d, J = 1.8 Hz, 1 H), 6.47 (d, J = 1.8 Hz, 1 H), 5.29 (m, 2 H),
5.14 (s, 4 H), 4.91 (d, J = 11.4 Hz, 1 H), 4.82 (d, J = 11.1 Hz, 1
H), 4.66 (d, J = 8.1 Hz, 1 H), 3.85 (t, J = 8.7 Hz, 1 H), 3.59 (dd,
J = 12.3, 2.7 Hz, 1 H), 3.51 (m, 3 H), 3.26 (m, 1 H); 13C NMR
(75 MHz, CDCl3) δ 177.8, 164.5, 162.0, 160.8, 157.6, 156.7,
138.1 (2 C), 136.1, 135.6, 134.5, 130.6, 128.7 (2 C), 128.5, 128.4,
128.3, 128.2, 128.0, 127.9, 127.8, 127.4 (2 C), 123.2, 114.4, 106.1,
102.5, 98.7, 93.1, 81.2, 76.4, 76.1, 74.6, 74.5, 74.2, 70.4, 70.1,
61.5; HRMS (MALDI) calcd for C49H44O11Na [M þ Na]þ
831.2781, found 831.2776.
20-(400-(Benzyloxy)benzoyloxy)-40,60-dibenzyloxy-2-bromoaceto-
phenone (20). To a solution of 19 (56 mg, 0.1 mmol) in dry THF
(1 mL) was added PTT (38 mg, 0.1 mmol) in portions. The
reaction mixture was stirred at room temperature for 2 h, and was
then poured into water and extracted with CH2Cl2 (3 ꢀ 50 mL).
The combined organic phase was concentrated. The residue was
7,40-Di-O-benzyl-3-O-[300,600-di-O-(4000-O-benzyl-E-coumaroyl)-
200,400-di-O-benzyl-β-D-glucopyranosyl]-Kaempferol (16). To a
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Yang et al.
JOCArticle
purified by silica gel column chromatography (toluene-
petroleum ether, 4:1) to give 20 (31 mg, 49%) as a white solid:
1H NMR (300 MHz, CDCl3) δ 8.09 (d, J = 8.7 Hz, 2 H), 7.44
(m, 15 H), 7.04 (d, J = 8.7 Hz, 2 H), 6.54 (s, 2 H), 5.13 (s, 2 H),
5.08 (s, 2 H), 5.03 (s, 2 H), 4.35 (s, 2 H); 13C NMR (75 MHz,
CDCl3) δ 191.8, 164.5, 163.1, 162.0, 158.3, 151.1, 136.1, 135.7,
135.3, 132.5, 128.8, 128.7, 128.6, 128.5, 128.4, 128.2, 127.6,
127.5, 127.4, 121.4, 114.7, 114.1, 102.0, 98.2, 71.2, 70.5, 70.1,
36.7; HRMS (MALDI) calcd for C36H29O6BrNa [M þ Na]þ
659.1045, found 659.1040.
2-Benzoyloxy-20-(400-(benzyloxy)benzoyloxy)-40,60-dibenzyloxy-
acetophenone (21). A mixture of 20 (31 mg 0.05 mmol) and
BzOK (12 mg, 0.07 mmol) was stirred in CH3CN (1 mL) at
refluxing temperature for 36 h. The mixture was diluted with
EtOAc, and was then washed with water and brine. After
concentration in vacuo, the residue was purified by silica gel
column chromatography (EtOAc-petroleum ether, 1:5) to give
21 (22 mg, 68%) as a white solid: 1H NMR (300 MHz, CDCl3) δ
8.14 (d, J = 8.7 Hz, 2 H), 8.03 (d, J = 8.1 Hz, 2 H), 7.57 (t, J =
7.2 Hz, 1H), 7.46-7.36 (m, 17 H), 7.03 (d, J = 9.0 Hz, 2 H), 6.57
(s, 1 H), 6.55 (s, 1 H), 5.25 (s, 2 H), 5.12 (s, 2 H), 5.11 (s, 2 H), 5.05
(s, 2 H); 13C NMR (75 MHz, CDCl3) δ 193.6, 165.7, 164.6,
163.0, 162.0, 158.8, 151.2, 136.1, 135.7, 135.4, 133.0, 132.6,
129.8, 129.6, 128.7 (2 C), 128.6, 128.4, 128.3, 128.2 (2 C),
127.6, 127.5, 127.4, 121.6, 114.6, 114.1, 102.2, 98.2, 71.1, 70.4,
70.0, 69.6; HRMS (MALDI) calcd for C43H34O8Na [M þ Na]þ
701.2151, found 701.2146.
5,7,40-Tri-O-benzyl-Kaempferol (22). To a suspension of so-
dium hydride (230 mg, 5.76 mmol) in dry THF (20 mL) was
added 21 (976 mg, 1.44 mmol) in THF (10 mL). The mixture was
refluxed for 90 min with stirring. The cooled mixture was poured
into a mixture of ice containing concentrated HCl (2 mL), and
was then extracted with CH2Cl2 (3 ꢀ 100 mL). After the solvent
was removed, the resulting residue was dissolved in AcOH
(11 mL), then AcONa (181 mg) was added. After being stirred
at 100 °C for 12 h, the mixture was cooled to rt and then diluted
with CH2Cl2. The mixture was washed with water and aq
NaHCO3 successively. The organic phase was concentrated to
give a residue, which was dissolved in MeOH/CH2Cl2 (8 mL, v/v
1:1). After being stirred for 10 h in the presence of a catalytic
amount of NaOMe at rt, the mixture was neutralized with
Dowex 50W-X 8 (Hþ) resin. The resins were filtered, then the
filtrate was concentrated in vacuo. The residue was purified by
silica gel column chromatography (acetone-petroleum ether-
CH2Cl2, 1:20:8) to provide 225e (562 mg, 70%) as a yellow solid.
3,6-Di-O-allyl-2,4-di-O-benzoyl-D-glucopyranosyl o-Hexynyl-
benzoate (23b) (A Typical Procedure for the Synthesis of Glycosyl
o-Hexynylbenzoates 23a-g). A solution of 3,6-di-O-allyl-2,4-di-
O-benzoyl-D-glucopyranose [prepared from compound 9 via
three steps in 58% yield, i.e., removal of the isopropylidene
(80% HOAc, reflux), benzoylation (BzCl, pyridine, rt), and
removal of the anomeric benzoate (BnNH2, THF, rt)] (105 mg,
0.22 mmol), o-hexynylbenzoic acid (55 mg, 0.27 mmol), DMAP
(27 mg, 0.22 mmol), and DCC (68 mg, 0.33 mmol) in dry CH2Cl2
was stirred for 3 h at rt. The resulting mixture was diluted with
CH2Cl2 and was then filtered through a pad of Celite. The
filtrate was washed with saturated aq NaHCO3 solution and
then concentrated under vacuum. The residue was purified by
silica gel column chromatography (petroleum ether-EtOAc
7:1) to provide 23b (134 mg, 92%) as a colorless oil. A small
portion of the R and β anomers was separated for characteriza-
tion. 23b-r: [R]28D þ65.0 (c 1.4, CHCl3); 1H NMR (300 MHz,
CDCl3) δ 8.09 (d, J = 7.8 Hz, 2 H), 7.98 (m, 3 H), 7.63 (m, 6 H),
7.41 (m, 3 H), 6.79 (d, J = 3.9 Hz, 1 H), 5.84 (m, 1 H), 5.69 (m,
3 H), 5.20 (m, 4 H), 4.40 (m, 2 H), 4.19 (m, 2 H), 3.97 (d, J = 6.0
Hz, 2 H), 3.68 (m, 2 H), 2.42 (t, J = 6.6 Hz, 2 H), 1.60 (m, 2 H),
1.48 (m, 2 H), 0.92 (t, J = 7.2 Hz, 3 H); 13C NMR (75 MHz,
CDCl3) δ 165.1 (2 C), 164.0, 134.9, 134.3, 134.1, 133.3, 133.2,
132.1, 130.6, 130.4, 129.7, 129.6, 129.3, 128.5, 128.4, 127.2,
125.1, 117.5, 117.0, 96.8, 90.5, 79.4, 76.9, 73.3, 72.6, 72.1, 71.9,
70.7, 68.8, 30.6, 22.0, 19.6, 13.6. 23b-β: [R]28 20.0 (c 1.7,
D
CHCl3); 1H NMR (300 MHz, CDCl3) δ 8.09 (d, J = 7.2 Hz, 2
H), 8.03 (d, J = 7.2 Hz, 2 H), 7.97 (d, J = 7.8 Hz, 1 H), 7.64 (m, 5
H), 7.43 (m, 3 H), 7.30 (m, 1 H), 6.17 (d, J = 8.1 Hz, 1 H), 5.84
(m, 1 H), 5.71 (m, 3 H), 5.19 (m, 4 H), 4.10 (m, 4 H), 3.96 (d, J =
6.0 Hz, 2 H), 3.72 (dd, J = 11.1, 3.3 Hz, 1 H), 3.64 (dd, J = 10.8,
5.1 Hz, 1 H), 2.50 (t, J = 6.9 Hz, 2 H), 1.67 (m, 2 H), 1.57 (m, 2
H), 0.98 (t, J = 7.2 Hz, 3 H); 13C NMR (75 MHz, CDCl3) δ
165.0, 164.9, 163.5, 134.5, 134.2, 134.1, 133.4, 133.3, 132.3,
130.9, 129.7 (2 C), 129.5, 129.3 (2 C), 128.5, 128.4, 127.2,
125.7, 117.6, 117.4, 97.1, 92.4, 79.4, 79.0, 74.7, 73.2, 72.6, 72.1,
70.7, 68.8, 30.6, 22.0, 19.5, 13.6; HRMS (ESI) calcd for
C39H40O9Na [M þ Na]þ 675.2570, found 675.2565.
5,7,40-Tri-O-benzyl-3-O-(300,600-di-O-allyl-200,400-di-O-benzoyl-
β-D-glucopyranosyl)-Kaempferol (24b) (A Typical Procedure for
the Glycosylation of 22 with Glycosyl o-Hexynylbenzoates 23a-g).
To a stirred mixture of glycosyl o-hexynylbenzoate 23b (70 mg,
˚
0.1 mmol), 22 (20mg, 0.036mmol), and4AMS in CH2Cl2 (1.5mL)
was added Ph3PAuNTf2 (5 mg, 0.007 mmol). After being stirred
at rt overnight, the mixture was filtered through a pad of Celite.
The filtrate was concentrated. The residue was purified by silica
gel column chromatography (petroleum ether-EtOAc-CH2Cl2,
5:1:1) to provide 24b (32 mg, 90%) as a yellowish oil: [R]25D -55
(c 0.8, CHCl3); 1H NMR (300 MHz, CDCl3) δ 8.30 (d, J = 7.5
Hz, 2 H), 8.13 (d, J = 6.6 Hz, 2 H), 8.05 (d, J = 7.8 Hz, 2 H),
7.61-7.34 (m, 21 H), 7.10 (d, J = 8.4 Hz, 2 H), 6.56 (s, 1 H), 6.44
(s, 1 H), 5.98 (d, J = 7.2 Hz, 1 H), 5.61 (m, 3 H), 5.35 (m, 3 H),
5.18 (s, 2 H), 5.07 (m, 6 H), 4.06 (m, 3 H), 3.74 (m, 1 H), 3.66 (m, 2
H), 3.50 (d, J =11.1Hz, 1 H), 3.39 (m, 1 H); 13C NMR (100 MHz,
CDCl3) δ 173.0, 165.9, 165.4, 163.0, 160.7, 160.0, 158.9, 154.6,
136.8, 136.2, 135.9, 134.7, 134.6, 133.5, 133.2, 130.9, 130.5, 130.0,
129.9, 128.9, 128.7, 128.6, 128.4, 128.0, 127.9, 127.0, 123.5, 117.7,
116.7, 114.7, 110.2, 99.0, 98.6, 94.2, 79.9, 74.7, 74.1, 73.5, 72.7,
71.5, 71.1, 70.7, 70.3, 69.4; HRMS (MALDI) calcd for
C62H54O13Na [M þ Na]þ 1029.3462, found 1029.3457.
5,7,40-Tri-O-benzyl-3-O-(300,600-di-O-allyl-200,400-di-O-benzyl-
β-D-glucopyranosyl)-Kaempferol (25). To a solution of 24b (23
mg, 0.023 mmol) in MeOH/CH2Cl2 (1.6 mL, v/v 1:3) at room
temperature was added NaOMe (7 mg, 0.13 mmol). After being
stirred overnight, the mixture was adjusted to neutral with
Dowex 50W-X 8 (Hþ) resin. The resin was then filtered off.
The filtrate was concentrated and the residue was dissolved in
dry DMF (1.5 mL). To the mixture was added NaH (4 mg, 0.08
mmol) and BnBr (0.01 mL) at 0 °C. After being stirred overnight
at rt, the mixture was poured into ice water and extracted with
EtOAc. The organic phase was washed with water and brine,
and then dried and concentrated. The residue was purified by
silica gel column chromatography (petroleum ether-EtOAc,
6:1) to give 25 (16 mg, 72%) as a yellow solid: [R]28D -6.8 (c 0.5,
CHCl3); 1H NMR (300 MHz, CDCl3) δ 8.08 (d, J = 9.0 Hz, 2
H), 7.62 (d, J = 7.5 Hz, 2 H), 7.49-7.26 (m, 23 H), 7.00 (d, J =
8.4 Hz, 2 H), 6.58 (s, 1 H), 6.46 (s, 1 H), 6.03 (m, 1 H), 5.70 (m,
2 H), 5.31 (m, 3 H), 5.18-4.95 (m, 8 H), 4.85 (d, J = 10.5 Hz,
2 H), 4.64 (d, J = 10.8 Hz, 1 H), 4.48 (dd, J = 11.1, 4.8 Hz, 1 H),
4.32 (dd, J= 12.3, 5.1 Hz, 1 H), 3.70 (m, 6 H), 3.48 (d, J= 11.4Hz,
1 H), 3.34 (m, 1 H); 13C NMR (100 MHz, CDCl3) δ 173.3, 162.9,
160.5, 160.1, 159.0, 154.3, 139.2, 138.7, 136.8, 136.7, 136.5, 136.0,
135.5, 135.3, 130.8, 129.0, 128.6, 128.4, 128.3, 128.0, 127.9, 127.8,
127.6, 127.0, 124.0, 116.9, 116.1, 114.6, 110.3, 101.4, 98.4, 94.1,
84.3, 82.5, 77.8, 75.4, 75.2, 74.8, 74.2, 72.5, 71.1, 70.7, 70.3, 68.8;
HRMS (MALDI) calcd for C62H58O11Na [M þ Na]þ 1001.3877,
found 1001.3871.
5,7,40-Tri-O-benzyl-3-O-[300,600-di-O-(4000-O-benzyl-E-coumaroyl)-
200,400-di-O-benzyl-β-D-glucopyranosyl]-Kaempferol (26). To a solu-
tion of 25 (16 mg, 0.016) in MeOH/CH2Cl2 (1.8 mL, v/v 1:2) was
added PdCl2 (3 mg, 0.017 mmol). After being stirred for 5 h, the
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mixture was filtered. The filtrate was concentrated. The residue was
purified by silica gel column chromatography (EtOAc-petroleum
ether, 2:5) to provide the corresponding 300,600-diol, which was
dissolved in dry CH2Cl2 (2 mL). To the mixture was added E-4-
benzyloxycinnamic acid (25 mg, 0.1 mmol), DCC (10 mg, 0.05
mmol), and DMAP (2 mg). After 5 h of reflux, the suspension was
filtered. The filtrate was concentrated in vacuo. The residue was
purified by silica gel column chromatography (petroleum ether-
acetone, 4:1) to provide 26 (15 mg, 66% for two steps) as a yellow
solid: [R]28D -37.5 (c 0.9, CHCl3); 1H NMR (300 MHz, CDCl3)
δ8.02 (d, J= 8.7 Hz, 2 H), 7.69 (m, 3 H), 7.51-7.19 (m, 38 H), 7.04
(m, 4 H), 6.88 (d, J = 7.8 Hz, 2 H), 6.51 (s, 1 H), 6.43 (m, 1 H), 6.27
(d, J = 15.6 Hz, 1 H), 6.17 (d, J = 15.9 Hz, 1 H), 5.90 (d, J = 7.2
Hz, 1 H), 5.52 (m, 1 H), 5.25 (s, 2 H), 5.13 (s, 2 H), 5.02 (m, 8 H),
4.58 (d, J=10.5Hz, 1H), 4.50(d, J= 10.5 Hz, 1 H), 4.31 (m, 2 H),
3.67 (m, 3 H); 13C NMR (75 MHz, CDCl3) δ 172.9, 166.4, 166.0,
162.6, 160.6, 160.5, 160.1, 159.7, 158.7, 154.5, 144.8, 144.3, 138.4,
137.3, 136.4 (2 C), 136.3, 135.9, 135.6, 130.5, 129.8, 129.7, 128.7,
128.6 (2 C), 128.5, 128.3 (2 C), 128.1, 128.0, 127.8, 127.6 (2 C),
127.4 (2 C), 127.3, 127.2, 127.1, 126.5, 123.7, 115.4, 115.2, 115.0,
114.2, 109.9, 100.7, 98.0, 93.8, 78.4, 75.8, 75.2, 74.2, 72.6, 72.5,
70.7, 70.4, 70.0, 69.9, 69.8, 62.3; HRMS (MALDI) calcd for
C88H74O15Na [M þ Na]þ 1393.4925, found 1393.4920.
Acknowledgment. Financial support from the National
Natural Science Foundation of China (20932009, 20621062,
and 30725045) and the Ministry of Science and Technology
of China (2009ZX09311-001) are gratefully acknowledged.
Supporting Information Available: Experimental details and
characterization data for compounds 23a, 23f,g, 24a, 24d-g, and
the 1Hand13C NMR spectra for all new compounds. This material
is available free of charge via the Internet at http://pubs.acs.org.
6888 J. Org. Chem. Vol. 75, No. 20, 2010