Synthesis of quercetin 3-O-β-d-apiofuranosyl-(1→2)-[α-l- rhamnopyranosyl-(1→6)]-β-d-glucopyranoside

Article abstract of DOI:10.1016/j.tetlet.2011.04.040

A concise method to construct a unique 2,6-branched trisaccharide was established by regioselective glycosylation of three free hydroxyl groups on a 3-O-protected glucose moiety, and successfully used in the synthesis of quercetin 3-O-β-d-apiofuranosyl-(1→2)-[α-l-rhamnopyranosyl- (1→6)]-β-d-glucopyranoside, a flavonol O-glycoside isolated from glandless cotton seeds which showed notable antidepressant activities.

Full text of DOI:10.1016/j.tetlet.2011.04.040

Tetrahedron Letters 52 (2011) 3154–3157
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Synthesis of quercetin 3-O-b-D-apiofuranosyl-(1?2)-[
(1?6)]-b-D-glucopyranoside
a-L-rhamnopyranosyl-
⇑
Yang Zhang, Kejun Wang, Zhilai Zhan, Yu Yang, Yimin Zhao
Beijing Institute of Pharmacology and Toxicology, Beijing 100850, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A concise method to construct a unique 2,6-branched trisaccharide was established by regioselective gly-
Received 21 January 2011
Revised 27 March 2011
Accepted 11 April 2011
Available online 16 April 2011
cosylation of three free hydroxyl groups on a 3-O-protected glucose moiety, and successfully used in the
synthesis of quercetin 3-O-b-D-apiofuranosyl-(1?2)-[a-L-rhamnopyranosyl-(1?6)]-b-D-glucopyrano-
side, a flavonol O-glycoside isolated from glandless cotton seeds which showed notable antidepressant
activities.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Flavonol glycoside
Antidepressant
Regioselective glycosylation
2,6-Branched oligosaccharides
10b–f,h,i
Quercetin 3-O-b-
D
-apiofuranosyl-(1?2)-[
a
-
L
-rhamnopyrano-
phase-transfer catalysis (PTC) or the action of silver salts.
These methods are not applicable when the glycosyl donor is a
bulky trisaccharide.10d Thus, a stepwise glycosylation approach
will be a favorable choice for the synthesis of compound 1. The
syl-(1?6)]-b- -glucopyranoside (1) is a flavonol O-glycoside iso-
D
lated from the seeds of glandless cotton (a variant of cotton plant
resulting from selective breeding).1 It showed notable antidepres-
sant effects in forced swimming experiments on mice.2 It also
exhibited the ability to promote the proliferation of hippocampal
cells in chronically stressed mice in vivo and cultured hippocampal
neural progenitor cells in vitro.3 Moreover, its intact form could be
detected in brain dialysate samples from rats after oral administra-
tion.4 Its structure is characterized by the unique 2,6-branched tri-
central b-D-glucopyranose should be linked to the 3-OH of querce-
tin first, and suitably protected to avoid tedious protection–depro-
tection steps in the process of constructing the 2,6-branched
trisaccharide moiety. Such steps often lead to low yield of the tar-
get product.
Previous studies gave examples of selectively glycosylating the
6-OH in a glucose moiety in the presence of an unprotected 2-OH
or glycosylating the 2-OH without protecting 4-OH.11 These results
showed that it might be possible to sequentially glycosylate these
three hydroxyl groups by just protecting the hydroxyl group at C-3.
Taking this into consideration, compound 4 shown in the retrosyn-
thetic analysis (Scheme 1) was designed as a key intermediate for
the synthesis of the target molecule. The intermediate 4 can be
built by conjugating the bromide 6 with the partially protected
quercetin 5. The acetyl protecting groups on 6 will ensure the for-
mation of a b-glucosyl linkage in 4 through the neighboring group
participating effect of the acetyl at C-2, and can be removed with-
out affecting the other protecting groups in the molecule. The cou-
pling of 5 and 6 will occur at C-3 of 5, since the free hydroxyl at C-5
is less reactive in this reaction because of the chelating effect of the
carbonyl at C-4.
saccharide moiety: a b-
group of the aglycone, a rare b-
D
-glucopyranose attached to the 3-hydroxyl
-apiofuranose and an -rhamno-
D
a-L
pyranose as the terminal sugars attached to the 2-hydroxyl and 6-
hydroxyl groups of the glucose, respectively. Flavonol O-glycosides
are a large group of natural products with over 1500 known struc-
tures.5 Many of them are found to have beneficial biological ef-
fects.6–9 Several flavonol O-glycosides have been synthesized in
the last decade,10 but the synthesis of flavonol O-glycosides carry-
ing complex oligosaccharide moieties is still a challenging task, be-
cause regioselective construction of multiple glycosidic linkages
requires delicate protective manipulation of the hydroxyl groups
on the aglycone and sugars. The unique structure and interesting
biological effects of compound 1 inspired us to develop a synthetic
route to it.
Creation of a flavonol 3-O-glycosyl linkage is commonly carried
out by reaction of the aglycone with glycosyl bromides under
In practice, the synthetic work was started with commercially
available rutin. Following our previous successful synthesis of 3-
O-methylquercetin,12 rutin was converted into 7,30,40-tri-O-ben-
zylquercetin 5 by benzylation and subsequent acid hydrolysis in
⇑
Corresponding author. Tel.: +86 10 66931648; fax: +86 10 68211656.
E-mail address: zhaoym@nic.bmi.ac.cn (Y. Zhao).
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.04.040

Y. Zhang et al. / Tetrahedron Letters 52 (2011) 3154–3157
3155
Scheme 1. Retrosynthetic analysis of target molecule 1.
Scheme 2. Reagents and conditions: (a) BnCl, K2CO3, DMF, 40 °C, rt, 3 h; (b) 36% HCl, EtOH, 90 °C, rt, 2 h, 91% for two steps; (c) BzCl, py, CH2Cl2, rt,12 h; (d) IR-120 (H+), H2O,
80 °C, rt, 6 h, 90% for two steps; (e) Ac2O, py, reflux 4 h, 83%; (f) HBr-HOAc, CH2Cl2, 0 °C, rt, 89%; (g) TBAB, CHCl3ꢀ0.15 M K2CO3, 50 °C, 12 h, 90%; (h) BnBr, K2CO3, DMF, rt, 12 h,
93%; (i) 5% CH3COCl, CH3OH-CH2Cl2, rt, 24 h, 82%.
excellent yield (Scheme 2). To prepare 2,4,6-tri-O-acetyl-3-O-ben-
zoyl- -glucopyranosyl bromide 6, 1,2:5,6-di-O-isopropylidene-
-glucofuranose 813 was subjected to benzoylation with BzCl in
CH2Cl2 in the presence of pyridine, followed by removal of the iso-
propylidene groups with Amberlite IR-120 (H+) resin to form 9.
Subsequent acetylation of 9 in boiling pyridine and acetic anhy-
our work, benzoyl was chosen as the protecting group with a view
to simplifying the final deprotection process as well as ensuring
a-D
a-
D
the formation of a b-
furanosyl donor 2,3,5-tri-O-benzoyl-
2, 2,3-O-isopropylidene-b- -apiofuranose 13 (Scheme 3) was
synthesized from mannose.19 Benzoylation of 13 with BzCl affor-
ded 1,5-di-O-benzoyl-2,3-O-isopropylidene-b- -apiofuranose 14
D-apiofuranosyl linkage. To prepare the apio-
a
/b- -apiofuranosyl bromide
D
D
dride afforded 1,2,4,6-tetra-O-acetyl-3-O-benzoyl-b-
nose 10. Bromination of 10 with 40% HBr in HOAc gave 6 with
an overall yield of 66% starting from 8.14 The glucopyranosyl
-bro-
D
-glucopyra-
D
(72%). The isopropylidene protecting group of 14 was cleaved with
a
mide 6 was condensed with quercetin derivative 5 in 0.15 M
K2CO3/CHCl3 in the presence of Bu4NBr at 50 °C, giving the desired
3-O-b-D
-glycoside 11 in 90% purified yield.15,10b,d The observed J1,2
value (8.0 Hz) for the anomeric proton in the 1H NMR spectrum of
11 confirmed that the glucoside had the expected b configuration.
The cross peak from glucose H-1 (d 5.69 ppm) to quercetin C-3 (d
137.73 ppm) in the HMBC spectrum clearly indicated that the glu-
cosyl moiety was linked to C-3 of the quercetin moiety. No a-ano-
mer or 5-O-glycoside was found under these glycosylation
conditions. Benzylation of the quercetin 5-hydroxyl group of 11
with BnBr and K2CO3 in DMF gave 12. Deacetylation of 12 with
5% acetyl chloride in 1:1 (v/v) CH3OH–CH2Cl216 afforded the selec-
tively protected quercetin glycoside 4.
Scheme 3. Reagents and conditions: (a) BzCl, py, CH2Cl2, rt, 6 h, 72%; (b) 80%
HCOOH, rt, 2 h, 60 °C; (c) BzCl, py, CH2Cl2, 12 h, 80% for two steps; (d) HBr-HOAc,
CH2Cl2, 0 °C, rt.
Preparation of apiofuranosyl donors carrying both acetyl and
benzyl protecting groups has been reported previously.17,18 In

3156
Y. Zhang et al. / Tetrahedron Letters 52 (2011) 3154–3157
and could be used in the synthesis of other glycoconjugates bear-
ing similar 2,6-branched trisaccharides.
Acknowledgments
This work was supported by the National Natural Science Foun-
dation of China (No.30672508), Beijing Municipal Natural Science
Foundation (No.7072061) and Ministry of Science and Technology
of the People’s Republic of China through the National Key Tech-
nologies R&D Program for New Drugs (No.2009ZX09301-002).
We sincerely acknowledge their financial support.
References and notes
1. Zhang, Q.; Yang, M.; Zhao, Y.; Luan, X.; Ke, Y. Acta Pharm. Sin. 2001, 36, 827.
2. Li, Y.; Yang, M.; Yuan, L.; Zhao, Y.; Luan, X.; Luo, Z. Chin. J. Pharmacol. Toxicol.
2000, 14, 125.
3. Zhang, L.; Zhang, Y.; Liu, Y.; Gong, Z.; Zhao, Y.; Li, Y. Eur. J. Pharmacol. 2009, 607,
110.
4. Guo, J.; Zhang, S.; Meng, F.; Zhao, Y. Chem. J. Chin. U. 2009, 30, 1528.
5. (a) Williams, C. A. In Flavonoids: Chemistry, Biochemistry, and Applications;
Anderson, Ø. M., Markham, K. R., Eds.; CRC Press: Boca Raton, 2006. pp 746–
856; (b) Veitch, N. C.; Grayer, R. J. Nat. Prod. Rep. 2008, 25, 555.
6. Harborne, J. B.; Williams, C. A. Phytochemistry 2000, 55, 481.
7. Smith, J. A.; Poteet-Smith, C. E.; Xu, Y.; Errington, T. M.; Hecht, S. M.; Lannigan,
D. A. Cancer Res. 2005, 65, 1027.
8. Butterweck, V.; Jürgenliemk, G.; Nahrstedt, A.; Winterhoff, H. Planta Med. 2000,
66, 3.
9. Emura, K.; Yokomizo, A.; Toyoshi, T.; Moriwaki, M. J. Nuti. Sci. Vitaminal. 2007,
53, 68.
Scheme 4. Reagents and conditions: (a) 3 (1.5 equiv), BF3ꢁOEt2 (0.75 equiv), 4 Å
MS, CH2Cl2, ꢀ30 °C, 2 h, 75%; (b) 2 (2.2 equiv), AgOTf (2.2 equiv), CH2Cl2, ꢀ30 °C,
2 h, 52%; (c) NaOMe, CH2Cl2-CH3OH (5:1), rt, 12 h; (d) H2, 10% Pd-C, EtOH-EtOAc
(1:1), rt, 12 h, 82% for two steps.
10. (a) Bouktaib, M.; Atmani, A.; Rolando, C. Tetrahedron Lett. 2002, 43, 6263; (b) Li,
M.; Han, X.; Yu, B. Tetrahedron Lett. 2002, 43, 9467; (c) Du, Y.; Wei, G.; Linhardt,
R. J. Tetrahedron Lett. 2003, 44, 6887; (d) Du, Y.; Wei, G.; Linhardt, R. J. Org.
Chem. 2004, 69, 2206; (e) Maloney, D. J.; Hecht, S. M. Org. Lett. 2005, 7, 1097; (f)
Peng, W.; Li, Y.; Zhu, C.; Han, X.; Yu, B. Carbohydr. Res. 2005, 340, 1682; (g)
Caldwell, S. T.; Petersson, H. M.; Farrugia, L. J.; Mullen, A. C.; Hartley, R. C.
Tetrahedron 2006, 62, 7257; (h) Zhu, C.; Peng, W.; Li, Y.; Han, X.; Yu, B.
Carbohydr. Res. 2006, 341, 1047; (i) Li, Z.; Ngojeh, G.; DeWitt, P.; Zheng, Z.;
Chen, M.; Lainhart, B.; Li, V.; Felpo, P. Tetrahedron Lett. 2008, 49, 7243; (j) Yang,
W.; Sun, J.; Lu, W.; Li, Y.; Shan, L.; Han, W.; Zhang, W.; Yu, B. J. Org. Chem. 2010,
75, 6879.
11. (a) Yamada, H.; Kato, T.; Takahashi, T. Tetrahedron Lett. 1999, 40, 4581; (b)
Zhang, M.; Du, Y.; Kong, F. Carbohydr. Res. 2001, 330, 319; (c) Li, B.; Yu, B.; Hui,
Y.; Li, M.; Han, X.; Fung, K. Carbohydr. Res. 2001, 331, 1.
12. Li, H.; Luan, X.; Zhao, Y. Chin. J. Org. Chem. 2004, 24, 1619.
13. Schmidt, O. T. In Methods in Carbohydrate Chemistry; Whistler, R. L., Wolfrom,
M. L., Eds.; Academic Press Inc.: New York and London, 1963. Vol. 2, pp 320–
324.
14. Finan, P. A.; Warren, C. D. J. Chem. Soc. 1962, 3089.
15. Demetzos, C.; Skaltsounis, A.-L.; Tillequin, F.; Koch, M. Carbohydr. Res. 1990,
207, 131.
16. Byramova, N. E.; Ovchinnikov, M. V.; Backinowsky, L. V.; Kochetkov, N. K.
Carbohydr Res. 1983, 124, C8.
17. Mbaïraroua, O.; Ton-That, T.; Tapiéro, C. Carbohydr Res. 1994, 253, 79.
18. Ezekiel, A. D.; Overend, W. G.; Williams, N. R. J. Chem. Soc.(C) 1971, 2907.
19. Ho, P. Can. J. Chem. 1979, 57, 381.
80% formic acid to provide 5-O-benzoyl-
a
/b-
D-apiofuranose 15.
The remaining 5-O-benzoyl group of 15 ensured the
D-configura-
tion of the apiose moiety. Compound 15 was subsequently benzoy-
lated with BzCl in CH2Cl2 in the presence of pyridine to form 16
(80%). The benzoyl protected intermediates 14, 15, and 16 were
easy to purify by crystallization. Bromination on the anomeric car-
bon of 16 using 40% HBr in HAc furnished the apiofuranosyl donor
2. The glycosyl donor 3, 2,3,4-tri-O-benzoyl-
trichloroacetimidate, was synthesized as described previously.11b
Reaction of 4 with the -rhamnopyranosyl donor 3 in the pres-
a-L-rhamnopyranosyl-
L
ence of BF3ꢁOEt2 in anhydrous CH2Cl2 at ꢀ30 °C (Scheme 4) pro-
vided the quercetin disaccharide derivative 17 in 75% yield after
column chromatography.11b Subsequent regioselective glycosyla-
tion of 17 with the D-apiofuranosyl donor 2 catalyzed by silver tri-
flate afforded the desired quercetin trisaccharide derivative 18 in a
moderate isolated yield (52%).11c TOCSY and NOE difference spec-
troscopy experiments were carried out to fully assign the structure
of 18. Selective irradiation of H-1II (d 5.59 ppm) showed NOE
enhancement of H-2I (d 4.18 ppm), while selective irradiation of
H-1III (d 4.89 ppm) showed NOE enhancements of H-6aI and H-
6bI (d 3.72–3.66 ppm). This NOE result confirms the 2,6-branched
structure of the trisaccharide moiety of 18. Finally, removal of
the benzoyl groups with a catalytic amount of NaOMe in CH2Cl2–
MeOH and the benzyl groups by catalytic hydrogenation over
10% Pd-C afforded the deprotected product in high yield (82%).
Purification of the deprotected product on Sephadex LH20 eluted
with MeOH furnished the target molecule 1. All the spectroscopic
data recorded for 1 were in accordance with those of its natural
counterpart.1,20,21
In summary, a feasible approach to the synthesis of a flavonol
triglycoside which bears a unique 2,6-branched trisaccharide sub-
unit was established. The longest linear sequence (from 8 to 1) in
the synthetic route required eleven steps and reached an overall
yield of 14.6%. To date, this is the first synthesis of a flavonol gly-
coside carrying a 2,6-branched trisaccharide. The strategy for the
construction of the 2,6-branched trisaccharide subunit was concise
20. Wang, Q.; Li, L.; Li, M. Chin. Tradit. Herbal Drugs. 1996, 27, 518.
21. Selected data for the key compounds. 11. ½a D24
ꢂ
ꢀ116.4°(c 0.1, CH3COCH3); 1H
NMR (400 MHz, CDCl3): d 8.00–7.30 (m, 22H, H-60, H-20 and Ar), 7.01 (d, 1H, J
8.4 Hz, H-50), 6.48 (d, 1H, 2.2 Hz, H-8), 6.43 (d, 1H, J 2.2 Hz, H-6), 5.69 (d, 1H, J
8.0 Hz, H-1I), 5.53 (t, 1H, J 9.6 Hz, H-3I), 5.36–5.32 (m, 3H, H-4I and ArCH2O–),
5.27 (s, 2H, ArCH2O–), 5.25 (t, 1H, J 9.6 Hz, H-2I), 5.13 (s, 2H, ArCH2O–), 4.02–
4.00 (m, 2H, H-5I and H-6aI), 3.72 (m, 1H, H-6bI), 2.01, 1.92, 1.85 (3s, 9H, 3 Ac);
HR-MS (ESI-TOF) calcd for C55H49O16 [M+H]+ 965.3015, found 965.3013. 4. ½a 2D5
ꢂ
+9.4°(c 1.0, CHCl3); 1H NMR (400 MHz, CDCl3): d 8.13–7.26 (m, 27H, H-60, H-20
and Ar), 7.01 (d, 1H, J 8.4 Hz, H-50), 6.55 (d, 1H, 2.2 Hz, H-8), 6.49 (d, 1H, J
2.2 Hz, H-6), 5.25, 5.24, 5.20, 5.09 (4s, 8H, 4 ArCH2O–), 5.07 (t, 1H, J 10.8 Hz, H-
3I), 4.81 (d, 1H, J 8.0 Hz, H-1I), 3.88 (t, 1H, J 9.8 Hz, H-4I), 3.59–3.24 (m, 4H, H-2I,
H-5I, H-6aI and H-6bI); HR-MS (ESI-TOF) calcd for C56H49O13 [M+H]+ 929.3173,
found 929.3131. 18. ½a D24
ꢂ
ꢀ67.6°(c 0.1, CH3COCH3); 1H NMR (400 MHz, CDCl3):
d 8.12–7.13 (m, 58H, H-60, H-20, H-50 and Ar), 6.35 (m, 2H, H-8 and H-6), 6.17
(d, 1H, J 7.6 Hz, H-1I), 5.81 (s, 1H, H-2II), 5.76 (dd, 1H, J 10.0, 3.2 Hz, H-3III), 5.63
(m, 1H, H-2III), 5.59 (s, 1H, H-1II), 5.57 (t, 1H, J 10.0 Hz, H-4III), 5.47 (t, 1H, J
9.2 Hz, H-3I), 5.33–4.91 (m, 10H, H-5aII, H-5bIIand 4 ArCH2O–), 4.89 (s, 1H, H-
1III), 4.56 (d, 1H, J 10.8 Hz, H-4aII), 4.39 (d, 1H, J 10.8 Hz, H-4bII), 4.18 (t, 1H, J
8.0 Hz, H-2I), 4.08 (m, 1H, H-5III), 4.02 (d, 1H, J 10.8 Hz, H-5I), 3.84 (t, 1H, J
9.2 Hz, H-4I), 3.72–3.66 (m, 2H, H-6aI and H-6bI), 1.18 (d, 3H, J 6.0 Hz, H-6III);
HR-MS (ESI-TOF) calcd for C109H91O27 [M+H]+ 1831.5742, found 1831.5745. 1.
½
a 2D4
ꢂ
ꢀ36.0°(c 0.1, MeOH); 1H NMR (400 MHz, DMSO-d6): d 7.59 (dd, 1H, J 8.4,
2.4 Hz, H-60), 7.50 (d, 1H, J 2.4 Hz, H-20), 6.82 (d, 1H, J 8.4 Hz, H-50), 6.37 (d, 1H, J
2.0 Hz, H-8), 6.18 (d, 1H, J 2.0 Hz, H-6), 5.47 (d, 1H, J 7.6 Hz, H-1I), 5.33 (s, 1H,
H-1II), 4.32 (s, 1H, H-1III), 3.82 (d, 1H, J 9.6 Hz, H-4bII), 3.80 (d, 1H, J 3.2 Hz, H-

Y. Zhang et al. / Tetrahedron Letters 52 (2011) 3154–3157
3157
2II), 3.68 (d, 1H, J 9.6 Hz, H-4aII), 3.51–3.03 (m, 12H), 0.96 (d, 3H,J 6.4 Hz, H-
6III); 13C NMR (100 MHz, DMSO-d6): d 177.31, 163.98, 161.28, 156.30 (2C),
148.39, 144.80, 133.00, 121.84, 121.25, 116.03, 115.21, 108.63, 103.97, 100.66,
98.77, 98.61, 93.50, 79.26, 76.91, 76.90, 76.19, 75.73, 73.96, 71.82, 70.55, 70.35
(2C), 68.24, 66.88, 64.31, 17.70; HR-MS (ESI-TOF) calcd for C32H39O20 [M+H]+
743.2029, found 743.2029.