Synthesis of a tetrasaccharide related to the triterpenoid saponin Bellisoside isolated from Bellis perennis (compositae)

Article abstract of DOI:10.1016/j.tetasy.2010.06.032

A concise synthesis of a tetrasaccharide related to the triterpenoid saponins Bellisoside has been accomplished from commercially available monosaccharides through rational protecting group manipulations and stereoselective glycosylations. For the glycosylation reactions, H ₂SO₄-silica has been successfully used as an alternative to conventional Lewis acids such as TfOH or TMSOTf. The target tetrasaccharide has been synthesized in the form of its p-methoxyphenyl glycoside which leaves scope for further glyco-conjugate formation through the selective deprotection of p-methoxyphenyl glycoside followed by trichloroacetimidate chemistry.

Full text of DOI:10.1016/j.tetasy.2010.06.032

Tetrahedron: Asymmetry 21 (2010) 2172–2176
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Tetrahedron: Asymmetry
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Synthesis of a tetrasaccharide related to the triterpenoid saponin
Bellisoside isolated from Bellis perennis (compositae)
*
Santanu Mandal, Nayan Sharma, Balaram Mukhopadhyay
Indian Institute of Science Education and Research-Kolkata (IISER-K), Mohanpur Campus, PO BCKV Campus Main Office, Mohanpur, Nadia 741 252, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A concise synthesis of a tetrasaccharide related to the triterpenoid saponins Bellisoside has been accom-
plished from commercially available monosaccharides through rational protecting group manipulations
and stereoselective glycosylations. For the glycosylation reactions, H2SO4–silica has been successfully
used as an alternative to conventional Lewis acids such as TfOH or TMSOTf. The target tetrasaccharide
has been synthesized in the form of its p-methoxyphenyl glycoside which leaves scope for further
glyco-conjugate formation through the selective deprotection of p-methoxyphenyl glycoside followed
by trichloroacetimidate chemistry.
Received 14 June 2010
Accepted 24 June 2010
Available online 23 July 2010
Dedicated to Professor Sisir Chandra
Rakshit, Burdwan University, West Bengal,
India
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
tetrasaccharide related to the saponins Bellisoside from commer-
cially available monosaccharides through rational protecting group
Triterpenoid saponins are plant secondary metabolites synthe-
sized routinely in the growth and development program in plants.
Due to their intense anti-fungal properties, it is believed that this
class of molecules act as a chemical barrier against fungal attacks
in plants.1 In addition to their role in the defence mechanism, tri-
terpenoid saponins are used as a source of drugs against various
diseases, mainly in the form of traditional medicines. Despite the
importance associated with triterpenoid saponins, the actual
mechanism of their biosynthesis and the actual roles in various
biological events are yet to be fully understood. A common feature
shared by all saponins is the presence of an oligosaccharide at-
tached to the aglycone moiety.2,3 Normally it is 3–4 sugars long
manipulation and stereoselective glycosylations. For the glycosyla-
tions, thioglycosides and glycosyl trichloroacetimidates are used as
glycosyl donors and are activated with H2SO4 immobilized on silica
in conjunction with N-iodosuccinimide (for thioglycosides) or
alone (for trichloroacetimidates) (see Fig. 1).
2. Results and discussion
Careful consideration of the retrosynthetic analysis revealed
that a (2+2) scheme is the best option to construct the target tetra-
saccharide 1. Therefore, a reducing end disaccharide acceptor, a-L-
Rha-(1?2)-b-
D
-Fuc and a suitably activated non-reducing end
and often branched and composed of
D-Glc, D-Gal, D-Fuc, L-Rha,
disaccharide,
a
-L
-Rha-(1?3)-b- -Xyl were planned. The acceptor
D
L-Ara,
D
-Xyl, etc.4 It is believed that the glycosylation takes place
disaccharide was further disconnected to a suitably protected
-Rha donor and a -Fuc acceptor. These two monosaccharide units
can be prepared from commercially available -Rha and -Fuc
through rational protecting group manipulations. Further discon-
nection of the donor disaccharide revealed that a suitable -Xyl
in the later stage of the biosynthesis of the saponins and is essen-
tial for the bioactivity exerted by the saponins. Therefore, a clear
understanding of the glycosylation and the elaboration of the oli-
gosaccharide is needed in order to gain an insight into the sapo-
nins’ biosynthesis and activity. Recently, Asada et al.5 reported
the isolation and characterization of six new triterpenoid saponins
(Bellisosides) from Bellis perennis (compositae), the common Daisy.
It is reported that the extracts are already being used in traditional
medicines for the treatment of rheumatism and as expectorants.6
Moreover, these saponins have shown cytotoxicity against HL-60
human promyelocytic leukemia cells.5 In continuation of our ef-
forts toward the synthesis of oligosaccharides related to the biody-
namic saponins,7 we herein report the total synthesis of the
L
D
L
D
D
acceptor is required where the 3-OH position is free. It is difficult
to design a protocol for the synthesis of such an acceptor from
commercially available
D-Xyl. Thus, it was planned that diacetone
D-Glc could be utilized to discriminate the 3-OH by suitable protec-
tion and eventually converted to a
donor can be synthesized from commercially available
(Scheme 1).
D
-Xyl moiety. The other
L
L
-Rha
-Rha
The synthesis of the required acceptor disaccharide started with
the known p-tolyl 2,3-O-isopropylidene-1-thio-a-L-rhamnopyr-
anoside8 2. Acetylation of compound 2 using Ac2O in pyridine9
afforded the corresponding acetylated derivative 3 in 93% yield.
* Corresponding author. Tel.: +91 9748 261742; fax: +91 33 2587 3031.
E-mail address: sugarnet73@hotmail.com (B. Mukhopadhyay).
Donor
3 was then glycosylated with the known acceptor,
0957-4166/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2010.06.032

S. Mandal et al. / Tetrahedron: Asymmetry 21 (2010) 2172–2176
2173
HO
HO
Me
O
O
HO
O
OMP
O
OH
C
O
OH
O
HO
HO
Me
HO
HO
O
O
O
CH2OH
HO
O
O
HO
O
O
HO
OH
HO
Me
HO
O
O
HO
O
1
O
HO
OH
HO
OH
HO
Me
HO
O
HO
OH
Figure 1. Structure of the triterpenoid saponin and synthetic target.
HO
O
OMP
HO
O
Me
O
O
HO
O
O
O
HO
OH
HO
Me
HO
1
HO
OH
PO
PO
O
PO
O
O
O
OMP
O
PO
+
Me
PO
O
CCl3
Me
HO
O
PO
NH
OP
PO
OP
STol
STol
PO
PO
O
PO
HO
Me
PO
OP
O
Me
PO
+
O
O
+
OMP
PO
PO
OP
PO
OP
OH
O
O
O
Commercially available L-Rha and D-Fuc
Commercially available L-Rha
O
O
HO
Commercially available D-Glc
Scheme 1. Retrosynthetic analysis for the target oligosaccharides.
O
p-methoxyphenyl 3,4-O-isopropylidene-b-
D
-fucopyranoside7a
4
O
using N-iodosuccinimide in the presence of H2SO4–silica10 furnishing
OMP
O
STol
STol
OH
the disaccharide, p-methoxyphenyl 4-O-acetyl-2,3-O-isopropyli-
dene-a-L-rhamnopyranosyl-(1?2)-3,4-O-isopropylidene-b-D-
4
Me
AcO
Ac2O
Py
Me
HO
O
O
NIS, H2SO4-silica
O
O
O
fucopyranoside 5 in 87% yield. When the same glycosylation
reaction between donor 3 and acceptor 4 was carried out using
NIS and TMSOTf, only 71% yield was obtained. Moreover, some
degradation product was isolated which was proved to be due to
the hydrolysis of one of the two isopropylidene groups. Next,
Zemplén de-O-acetylation11 using NaOMe in MeOH resulted in
the required disaccharide acceptor p-methoxyphenyl 2,3-O-iso-
O
3
2
O
O
O
O
O
O
OMP
OMP
O
NaOMe
O
O
O
O
MeOH
propylidene-
b- -fucopyranoside 6 in 91% yield (Scheme 2).
The synthesis of the required -Xyl acceptor commenced with
a-L-rhamnopyranosyl-(1?2)-3,4-O-isopropylidene-
Me
AcO
Me
HO
D
O
O
D
O
the known, 3-O-benzyl-1,2-O-isopropylidene-a-D
-glucofuranose12
5
6
7. Oxidation using sodium periodate in methanol13 followed by so-
dium borohydride reduction14 afforded 3-O-benzyl-1,2-O-isopro-
Scheme 2. Synthesis of the disaccharide acceptor 6.

2174
S. Mandal et al. / Tetrahedron: Asymmetry 21 (2010) 2172–2176
HO
disaccharide acceptor 6 with the trichloroacetimidate donor 13
HO
O
O
in the presence of H2SO4–silica furnished the protected tetrasac-
charide 14 in 74% yield. When TMSOTf was used for trichloroace-
timidate activation, the yield was only 61% and again degraded
products, due to hydrolysis of the isopropylidene acetal, were ob-
served. Hydrolysis of the isopropylidene acetals using 80% acetic
acid at 80 °C18 followed by Zemplén de-O-acetylation finally gave
the target tetrasaccharide 1 in 80% overall yield (Scheme 4).
HO
i. NaIO4, MeOH
ii. NaBH4, MeOH
i. TFA, CH2Cl2
ii. Ac2O, Py
O
O
O
O
BnO
BnO
8
7
O
H2
AcO
BnO
O
AcO
HO
OAc
OAc
OAc
Pd-C
OAc
10
9
3. Conclusion
Scheme 3. Synthesis of the xylosyl acceptor 10.
In conclusion, the synthesis of the tetrasaccharide glycone part
of the triterpenoid saponin Bellisoside has been accomplished in
the form of its p-methoxyphenyl glycoside. The choice of the glyco-
side leaves scope for further glyco-conjugate formation by selec-
tive cleavage of the p-methoxyphenyl glycoside followed by
trichloroacetimidate chemistry. Once more, H2SO4–silica proved
to be a better alternative than the conventional Lewis acids such
as TfOH or TMSOTf for the activation of the thioglycoside and tri-
chloroacetimidates. Since the protecting group manipulation strat-
egies and glycosylation steps were selective and high-yielding, the
present synthetic strategy is capable of a reasonably large scale
preparation.
pylidene-
a
-
D
-xylofuranose 8 in 81% overall yield. The 1,2-isopro-
pylidene acetal was cleaved using 90% aqueous trifluoroacetic acid
in CH2Cl2 and the resulting compound was subsequently acety-
lated using Ac2O in pyridine to furnish 1,2,4-tri-O-acetyl-3-O-ben-
zyl-D-xylopyranose 9 in 64% yield over two steps as an anomeric
mixture. The benzyl group was selectively deprotected using H2
in the presence of palladium on activated carbon to give the re-
quired acceptor, 1,2,4-tri-O-acetyl-D-xylopyranose 10 in 75% yield
(Scheme 3). The use of TMSOTf instead of H2SO4–silica was unsuc-
cessful in producing better results (68% yield).
The xylosyl acceptor 10 was then glycosylated with the known
rhamnosyl donor, p-tolyl 2,3,4-tri-O-acetyl-1-thio-
anoside15 11 using N-iodosuccinimide in the presence of
H2SO4–silica to furnish the disaccharide, 2,3,4-tri-O-acetyl-
rhamnopyranosyl-(1?3)-1,2,4-tri-O-acetyl- -xylopyranose 12 in
a-L-rhamnopyr-
4. Experimental
4.1. General
a-L-
D
76% yield. Next, the anomeric O-acetate group was selectively
cleaved using hydrazine hydrate and acetic acid16 in dimethyl
formamide and the hemiacetal thus obtained was reacted with tri-
chloroacetonitrile in the presence of DBU17 to afford the desired
disaccharide donor 13 in 71% overall yield. Glycosylation of the
All the reagents and solvents were dried prior to use according
to standard methods.19 Commercial reagents were used without
further purification unless otherwise stated. Analytical TLC was
performed on silica gel 60-F254 (Merck or Whatman) with detec-
tion by fluorescence and/or by charring following immersion in a
10% ethanolic solution of sulfuric acid. An orcinol dip, prepared
by the careful addition of concentrated sulfuric acid (20 cm3) to
an ice-cold solution of 3,5-dihydroxytoluene (360 mg) in EtOH
(150 cm3) and water (10 cm3), was used to detect the deprotected
compounds by charring. Flash chromatography was performed
with silica gel 230–400 mesh (Merck, India). Optical rotations were
measured at the sodium D-line at ambient temperature, with a
Perkin Elmer 141 polarimeter. 1H NMR and 13C NMR spectra were
recorded on a Bruker Avance spectrometer at 500 and 125 MHz,
respectively, using Me4Si or CH3OH as the internal standards, as
appropriate.
STol
Me
AcO
O
O
AcO
O
AcO
OAc
OAc
O
11
OAc
10
Me
AcO
NIS, H2SO4-silica
12
AcO
OAc
O
AcO
O
6
.
i. NH2-NH2 H2O, DMF
ii. Cl3CCN, DBU
AcO
Me
AcO
O
CCl3
H2SO4-silica
O
AcO
NH
OAc 13
4.1.1. p-Tolyl 4-O-acetyl-2,3-O-isopropylidene-1-thio-a-L-
rhamnopyranoside 3
O
O
To a solution of compound 2 (2.5 g, 8.1 mmol) in dry pyridine
(20 mL), Ac2O (5 mL) was added and the solution was stirred at
room temperature for 3 h when TLC (n-hexane–EtOAc, 4:1)
showed complete conversion of the starting material to a faster
moving spot. The solvents were evaporated in vacuo and co-evap-
orated with toluene to remove residual pyridine. The syrupy
residue thus obtained was purified by flash chromatography using
n-hexane–EtOAc (4:1) as the eluent to afford pure compound 3
O
OMP
O
º
i. 80% AcOH, 80 C
Me
O
O
O
AcO
ii. NaOMe, MeOH
O
O
O
AcO
Me
O
AcO
14
AcO
OAc
(2.6 g, 93%) as a colorless gel. ½a D25
ꢀ
¼ þ93 (c 1.1, CHCl3). 1H NMR
HO
HO
O
(500 MHz, CDCl3) d: 7.36, 7.13 (2d, 4H, S–C6H4–CH3), 5.69 (s, 1H,
H-1), 4.93 (dd, 1H, J3,4 10.0 Hz, J4,5 8.0 Hz, H-4), 4.34 (d, 1H, J2,3
2.5 Hz, H-2), 4.22 (m, 2H, H-3, H-5), 2.34 (s, 3H, S–C6H4–CH3),
2.12 (s, 3H, COCH3), 1.57, 1.25 (2s, 6H, isopropylidene–CH3), 1.11
(d, 3H, J5,6 6.5 Hz, C–CH3). 13C NMR (125 MHz, CDCl3) d: 170.1
(COCH3), 138.1, 132.5(2), 129.9(2), 129.3 (ArC), 110.0 (isopropyli-
dene–C), 84.0 (C-1), 76.5, 75.6, 74.6, 65.5, 27.7, 26.5 (2 ꢁ isopropyl-
idene–CH3), 21.2 (S–C6H4–CH3), 21.1 (COCH3), 16.9 (C–CH3). HRMS
calcd for C18H24O5SNa (M+Na)+: 375.1242, found: 375.1239.
OMP
HO
O
Me
O
O
HO
O
O
OH
HO
Me
HO
O
1
HO
OH
Scheme 4. Synthesis of the target tetrasaccharide 1.

S. Mandal et al. / Tetrahedron: Asymmetry 21 (2010) 2172–2176
2175
4.1.2. p-Methoxyphenyl 4-O-acetyl-2,3-O-isopropylidene-
rhamnopyranosyl-(1?2)-3,4-O-isopropylidene-b-D-fucopyrano-
side 5
a
-
L
-
orated. The residue was purified by flash chromatography using n-
hexane–EtOAc (3:1) as the eluent to afford pure compound 8
(1.5 g, 81%). 1H NMR (500 MHz, CDCl3) d: 7.35–7.27 (m, 5H, ArH),
5.94 (d, 1H, J1,2 3.5 Hz, H-1), 4.66, 4.47 (2d, AB system, J 12.0 Hz,
CH2Ph), 4.61 (d, 1H, J1,2, J2,3 3.5 Hz, H-2), 4.27 (m, 1H, H-4), 3.98
(d, 1H, J2,3, J3,4 3.5 Hz, H-3), 3.90 (dd, 1H, J4,5a 6.0 Hz, J5a,5b
12.0 Hz, H-5a), 3.81 (dd, 1H, J4,5b 5.0 Hz, J5a,5b 12.0 Hz, H-5b),
2.86 (br s, 1H, OH), 1.47, 1.30 (2s, 6H, 2 ꢁ isopropylidene–CH3).
13C NMR (125 MHz, CDCl3) d: 137.3, 128.9(2), 128.1, 127.5(2)
(ArC), 111.7 (isopropylidene–C), 105.0 (C-1), 82.4, 82.3, 80.5,
71.9, 60.7 (C-5), 26.8, 26.3 (2 ꢁ isopropylidene–CH3). HRMS calcd
for C15H20O5Na (M+Na)+: 303.1208, found: 303.1205.
A mixture of donor 3 (2.0 g, 5.7 mmol), acceptor 4 (1.4 g,
4.4 mmol) and MS 4 Å (1.5 g) in dry CH2Cl2 (20 mL) was stirred un-
der nitrogen for 30 min. NIS (1.7 g, 7.4 mmol) was added followed
by H2SO4–silica (50 mg) and the mixture was allowed to stir for
45 min at 5–10 °C when TLC (n-hexane–EtOAc, 4:1) showed com-
plete conversion of the acceptor. The mixture was filtered through
a pad of CeliteÒ and the filtrate was washed successively with aq
Na2S2O7 (2 ꢁ 30 mL), aq NaHCO3 (2 ꢁ 30 mL), and brine (30 mL).
The organic layer was separated, dried (Na2SO4), filtered, and evap-
orated in vacuo. The residue was purified by flash chromatography
using n-hexane–EtOAc (4:1) as the eluent to give pure disaccharide
4.1.5. 1,2,4-Tri-O-acetyl-3-O-benzyl-D-xylopyranose 9
5 (2.1 g, 87%) as a white foam. ½a D25
ꢀ
¼ þ83 (c 1.2, CHCl3). 1H NMR
To a solution of compound 8 (1.3 g, 4.6 mmol) in CH2Cl2 (20 mL)
was added 90% aq TFA (4 mL) and the solution was stirred at room
temperature for 30 min when TLC (n-hexane–EtOAc, 2:1) showed
complete conversion of the starting material to a slower running
spot. The solution was neutralized carefully by adding solid NaH-
CO3 till the effervescence ceases and was then filtered. The solvents
were evaporated in vacuo and the residue was dissolved in pyri-
dine (15 mL). Ac2O (3 mL) was added and the solution was stirred
for 6 h at 10 °C. After removing the solvents by co-evaporating
with toluene, the residue was dissolved in CH2Cl2 (20 mL) and
washed with H2O (30 mL) and brine (30 mL). The organic layer
was separated, dried (Na2SO4), filtered, and evaporated. The resi-
due thus obtained was purified by flash chromatography to afford
compound 9 (1.1 g, 64%) as an anomeric mixture. 1H NMR
(500 MHz, CDCl3) d: 6.92, 6.83 (2d, 4H, OC6H4OCH3), 5.58 (s, 1H,
H-10), 4.88 (dd, 1H, J3,4 10.0 Hz, J4,5 8.0 Hz, H-40), 4.71 (d, 1H, J1,2
8.0 Hz, H-1), 4.23 (dd, 1H, J2,3 7.0 Hz, J3,4 4.4 Hz, H-3), 4.16 (d, 1H,
J2,3 4.4 Hz, H-20), 4.10 (m, 2H, H-30, H-50), 4.03 (dd, 1H, J3,4 4.4 Hz,
J4,5 2.5 Hz, H-4), 4.02 (dd, 1H, J1,2 8.0 Hz, J2,3 7.0 Hz, H-2), 3.95
(m, 1H, H-5), 3.77 (s, 3H, OC6H4OCH3), 2.08 (s, 3H, COCH3), 1.57,
1.56, 1.35, 1.34 (4s, 12H, 4 ꢁ isopropylidene–CH3), 1.43 (d, 3H,
J5,6 6.5 Hz, H-6), 1.16 (d, 3H, J5 ,6 6.0 Hz, H-60). 13C NMR
(125 MHz, CDCl3) d: 170.1 (COCH3), 155.2, 151.4, 118.2(2),
114.5(2) (ArC), 110.2, 109.7 (2 ꢁ isopropylidene–C), 99.9 (C-1),
96.0 (C-10), 80.0, 76.3, 76.0, 75.8, 74.6, 74.5, 69.0, 64.0, 55.6
(OC6H4CH3), 28.0, 27.7, 26.4(2) (4 ꢁ isopropylidene–CH3), 21.0
(COCH3), 16.8, 16.6 (2 ꢁ C–CH3). HRMS calcd for C27H38O11Na
(M+Na)+: 561.2312, found: 561.2308.
0
0
a
(500 MHz, CDCl3) d: 6.22 (d, 1H, J1,2 3.0 Hz, H-1 ), 5.76 (d, 1H, J1,2
6.5 Hz, H-1b), 4.71 (2d, AB system, 2H, J 11.0 Hz, CH2Ph), 2.14,
4.1.3. p-Methoxyphenyl 2,3-O-isopropylidene-
a
-
L
-rhamnopyra
2.02, 2.01 (3s, 9H, 3 ꢁ COCH3
a), 2.10, 2.08, 2.07 (3s, 9H,
nosyl-(1?2)-3,4-O-isopropylidene-b- -fucopyranoside 6
D
3 ꢁ COCH3b). 13C NMR (125 MHz, CDCl3) d: 169.3, 168.8, 168.7
a
To a solution of disaccharide 5 (1.5 g, 2.8 mmol) in dry MeOH
(20 mL) was added NaOMe in MeOH (2 mL, 0.5 M) and the solution
was allowed to stir at room temperature for 2 h when TLC (n-hex-
ane–EtOAc, 4:1) showed complete conversion of the starting mate-
rial to a slightly slower moving spot. The solution was neutralized
by DOWEX 50 W H+ resin, filtered through cotton wool, and the fil-
trate was evaporated in vacuo. The residue was purified by flash
chromatography using n-hexane–EtOAc (3:1) to give pure com-
(3 ꢁ COCH3), 136.6, 127.7(2), 127.5(2), 127.4 (ArC), 91.0 (C-1 ),
88.7 (C-1b), 20.1, 19.9, 19.8 (3 ꢁ COCH3). HRMS calcd for
C
18H22O8Na (M+Na)+: 389.1212, found: 389.1209.
4.1.6. 1,2,4-Tri-O-acetyl-D-xylopyranose 10
A solution of compound 9 (1.0 g, 2.7 mmol) in MeOH (100 mL)
was injected with a flow rate of 1 mL/min through the Flow Hydro-
genation Assembly (H-cubeÒ, ThalesNano, Hungary) having 10%
Pd-C cartridge. The temperature was set to 70 °C. The resulting
solution thus obtained was evaporated to dryness and the residue
was purified by flash chromatography using n-hexane–EtOAc (2:1)
as the eluent to give compound 10 (565 mg, 75%) as an anomeric
pound 6 (1.3 g, 91%) as a white foam. ½a D25
¼ þ102 (c 1.0, CHCl3).
ꢀ
1H NMR (500 MHz, CDCl3) d: 6.91, 6.78 (2d, 4H, ArH), 5.52 (s, 1H,
H-10), 4.69 (d, 1H, J1,2 8.0 Hz, H-1), 4.21 (dd, 1H, J2,3 7.0 Hz, J3,4
5.5 Hz, H-3), 4.14 (d, 1H, J2 ,3 5.5 Hz, H-20), 4.02 (m, 4H, H-2, H-
0
0
a
30, H-4, H-50), 3.92 (m, 1H, H-5), 3.73 (s, 3H, OC6H4OCH3), 3.40 (t,
mixture. 1H NMR (500 MHz, CDCl3) d: 6.17 (s, 1H, H-1 ), 5.60 (d,
1H, J3 ,4 , J4 ,5 8.5 Hz, H-40), 2.82 (br s, 1H, OH), 1.56, 1.51, 1.33,
1.32 (4s, 12H, 4 ꢁ isopropylidene–CH3), 1.41 (d, 3H, J5,6 6.5 Hz, H-
1H, J1,2 7.0 Hz, H-1b), 2.27 (br s, 1H, OH), 2.17, 2.04, 2.02 (3s, 9H,
0
0
0
0
3 ꢁ COCH3
a
), 2.12, 2.09, 2.07 (3s, 9H, 3 ꢁ COCH3b). HRMS calcd
6), 1.29 (d, 3H, J5 ,6 6.5 Hz, H-60). 13C NMR (125 MHz, CDCl3) d:
155.1, 151.3, 118.0(2), 114.5(2) (ArC), 110.1, 109.3 (2 ꢁ isopropyl-
idene–C), 99.9 (C-1), 95.8 (C-10), 79.9, 78.4, 76.3, 75.8, 74.5, 74.3,
68.9, 65.9, 60.3, 55.5 (OC6H4OCH3), 27.9(2), 26.4, 26.1 (4 ꢁ isopro-
pylidene–CH3), 17.2 (C-6), 16.6 (C-60). HRMS calcd for C25H36O10Na
(M+Na)+: 519.2206, found: 519.2202.
for C11H16O8Na (M+Na)+: 299.0743, found: 299.0739.
0
0
4.1.7. 2,3,4-Tri-O-acetyl-
acetyl-b- -xylopyranosyl trichloroacetimidate 13
mixture of acceptor 10 (500 mg, 1.8 mmol), donor 11
a-L-rhamnopyranosyl-(1?3)-2,4-di-O-
D
A
(950 mg, 2.4 mmol), and MS 4 Å (1.0 g) in dry CH2Cl2 (15 mL)
was stirred under nitrogen for 30 min. Then H2SO4–silica (30 mg)
was added and the mixture was stirred at room temperature for
45 min when TLC (n-hexane–EtOAc, 3:1) showed complete conver-
sion of the acceptor. The mixture was neutralized with Et3N and fil-
tered through CeliteÒ. The filtrate was evaporated and purified by
flash chromatography to afford the disaccharide 12 (755 mg, 76%)
as an anomeric mixture. Subsequently, disaccharide 12 (750 mg,
1.4 mmol) was dissolved in dry DMF (10 mL), hydrazine hydrate
4.1.4. 3-O-Benzyl-1,2-O-isopropylidene-a-D-xylofuranose 8
To a solution of known di-ol 7 (2.0 g, 6.4 mmol) in MeOH
(25 mL) was added NaIO4 (2.7 g, 12.8 mmol) at 0 °C and the mix-
ture was allowed to stir for 3 h after which the temperature was
slowly raised to 25 °C. The mixture was filtered and the solvents
were evaporated in vacuo and the resulting syrup was dissolved
in MeOH (20 mL) followed by the addition of NaBH4 (970 mg,
25.6 mmol) at 0 °C. The mixture was stirred at 0–10 °C for 5 h.
The excess NaBH4 was neutralized by adding acetone and the sol-
vents were evaporated in vacuo. The residue was dissolved in
CH2Cl2 (20 mL) and washed with H2O (30 mL) and brine (30 mL).
The organic layer was separated, dried (Na2SO4), filtered, and evap-
(60 lL, 1.7 mmol) was added followed by AcOH (97 lL, 1.7 mmol)
and the solution was stirred at room temperature for 3 h. The sol-
vents were evaporated, the residue was dissolved in CH2Cl2
(20 mL), and washed with H2O (30 mL) and brine (30 mL). The
organic layer was collected, dried (Na2SO4), filtered, and evaporate

2176
S. Mandal et al. / Tetrahedron: Asymmetry 21 (2010) 2172–2176
in vacuo. The residue was further dissolved in dry CH2Cl2 (15 mL),
Cl3CCN (700 L, 7.0 mmol) was added followed by DBU (210 L,
target tetrasaccharide 1 (225 mg, 80%) as white amorphous pow-
l
l
der. ½a 2D5
ꢀ
¼ þ63 (c 0.8, CHCl3). 1H NMR (500 MHz, D2O) d: 5.00 (s,
00
0
1H, H-1000), 4.96 (d, 1H, J1 ,2 8.0 Hz, H-1 ), 4.73 (s, 1H, H-1 ), 4.62
(d, 1H, J1,2 8.5 Hz, H-1), 3.91-3.18 (m, 17H, H-2, H-20, H-200, H-2000,
H-3, H-30, H-300, H-3000, H-4, H-40, H-400, H-4000, H-5, H-50, H-5a00, H-
5b00, H-5000), 3.75 (s, 3H, OC6H4OCH3), 1.05, 1.00, 0.86 (3d, 9H,
3 ꢁ C–CH3). 13C NMR (125 MHz, D2O) d: 154.3, 150.2, 116.6(2),
113.9(2) (ArC), 101.5 (C-1), 100.8 (C-100), 99.7 (C-10), 98.4 (C-1000),
76.5, 76.3, 76.1, 75.8, 75.5, 75.1, 74.4, 71.8, 71,6, 70.3, 70.1, 68.7,
68.3, 67.6, 64.5, 60.1, 55.4 (OC6H4OCH3), 17.9, 17.7, 17.1 (3 ꢁ C–
CH3). HRMS calcd for C30H46O18Na (M+Na)+: 717.2582, found:
717.2577.
00 00
1.4 mmol), and the solution was stirred at room temperature for
2 h. After evaporation of the solvents, the residue was purified by
flash chromatography using n-hexane–EtOAc (3:1) as the eluent
to afford pure trichloroacetimidate derivative 13 (630 mg, 71%).
This trichloroacetimidate derivative was used for the final glyco-
sylation without any further characterization.
4.1.8. p-Methoxyphenyl 2,3,4-tri-O-acetyl-
(1?3)-2,4-di-O-acetyl-b- -xylopyranosyl-(1?4)-2,3-O-isopropyl-
idene- -rhamnopyranosyl-(1?2)-3,4-O-isopropylidene-b-
fucopyranoside 14
a-L-rhamnopyranosyl-
D
a
-
L
D-
A mixture of the disaccharide acceptor 6 (300 mg, 0.6 mmol),
trichloroacetimidate donor 13 (600 mg, 0.9 mmol), and MS 4 Å
(500 mg) in dry CH2Cl2 (10 mL) was stirred under nitrogen for
30 min. Next, H2SO4–silica (15 mg) was added and the mixture
was allowed stir at room temperature for 2 h when TLC (n-hex-
ane–EtOAc, 2:1) showed complete consumption of the acceptor.
The mixture was neutralized with Et3N and filtered through Cel-
iteÒ. The filtrate was evaporated in vacuo and the residue was puri-
fied by flash chromatography using n-hexane–EtOAc (4:1 to 2:1
gradient) as the eluent to afford pure tetrasaccharide 14 (440 mg,
Acknowledgments
S.M. is thankful to The Council for Scientific and Industrial
Research, New Delhi for Senior Research Fellowship and N.S. is
thankful to The Indian Institute of Science Education and
Research-Kolkata (IISER-K) for summer fellowship. The work is
funded by The Department of Science and Technology, New Delhi,
India through Grant SR/S1/OC-67/2009.
References
74%) as
a
white foam.
½
a 2D5
ꢀ
¼ þ78 (c 0.9, CHCl3). 1H NMR
(500 MHz, CDCl3) d: 6.92, 6.87 (2d, 4H, ArH), 5.52 (s, 1H, H-1000),
1. Papadopoulou, K.; Melton, R. E.; Legget, M.; Daniels, M. J.; Osbourn, A. E. Proc.
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2005, 61, 2921–2929.
6. Hansel, R.; Keller, K.; Rimpler, H.; Schneider, G. Hagers Handbuch der
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166; (b) Dasgupta, S.; Pramanik, K.; Mukhopadhyay, B. Tetrahedron 2007, 63,
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9. Hudson, C. S.; Dale, I. K. J. Am. Chem. Soc. 1915, 37, 1264.
10. Preparation of H2SO4–silica: To a slurry of silica gel (10 g, 200–400 mesh) in
dry diethyl ether (50 mL) was added commercially available conc. H2SO4
(1 mL) and the slurry was shaken for 5 min. The solvent was evaporated under
reduced pressure resulting in free flowing H2SO4–silica which was dried at
110 °C for 3 h and used for the reactions. For the use of H2SO4–silica in various
carbohydrate reactions see: (a) Mandal, S.; Sharma, N.; Mukhopadhyay, B.
Synlett 2009, 3111–3114; (b) Roy, B.; Verma, P.; Mukhopadhyay, B. Carbohydr.
Res. 2009, 344, 145–148; (c) Rajput, V. K.; Mukhopadhyay, B. Tetrahedron Lett.
2006, 47, 5939–5941; (d) Mukhopadhyay, B. Tetrahedron Lett. 2006, 47, 4337–
4341; (e) Roy, B.; Mukhopadhyay, B. Tetrahedron Lett. 2007, 48, 3783–3787.
11. Zemplén, G.; Gerecs, A.; Hadácsy, I. Ber. Dtsch. Chem. Ges. 1936, 69, 1827–1830.
12. Rajput, V. K.; Roy, B.; Mukhopadhyay, B. Tetrahedron Lett. 2006, 47, 6987–6991.
13. Bhattacharjya, A.; Pal, A. J. Org. Chem. 2001, 66, 9071–9074.
9.5 Hz, H-3000), 5.07 (m, 2H, H-20,
000,3000
000,4000
5.16 (dd, 1H, J2
2.5 Hz, J3
H-2000), 5.02 (s, 1H, H-10), 4.97 (dd, 1H, J3
000,4000
000,5000
9.5 Hz, J4 10.0 Hz,
H-4000), 4.91 (d, 1H, J1 ,2 7.0 Hz, H-100), 4.91 (m, 1H, H-400), 4.68 (d,
00 00
1H, J1,2 8.0 Hz, H-1), 4.24 (dd, 1H, J3 ,4 9.5 Hz, J4 ,5 10.0 Hz, H-40),
0
0
0
0
4.11 (dd, 1H, J4 ,5a 4.5 Hz, J5a ,5b 11.5 Hz, H-5a00), 4.05 (m, 3H, H-
00
00
00
00
2, H-3, H-20), 3.94 (m, 3H, H-30, H-4, H-5b00), 3.88 (t, 1H, J2 ,3
,
00 00
J3 ,4 8.5 Hz, H-300), 3.78 (s, 3H, OC6H4OCH3), 3.74 (m, 1H, H-5),
3.52 (m, 1H, H-50), 3.27 (m, 1H, H-5000), 2.14, 2.12, 2.09, 2.07, 2.03
(5s, 15H, 5 ꢁ COCH3), 1.56, 1.50, 1.45, 1.32 (4s, 12H, 4 ꢁ isopropyl-
idene–CH3), 1.29, 1.23, 1.17 (3d, 9H, J 6.5 Hz, 3 ꢁ C–CH3). 13C NMR
(125 MHz, CDCl3) d: 169.1, 169.0, 168.8, 168.6, 168.4 (5 ꢁ COCH3),
154.1, 150.5, 116.8(2), 113.7(2) (ArC), 109.2, 108.2 (2 ꢁ isopropyl-
idene–C), 98.9 (C-1), 98.6 (C-100), 97.2 (C-10), 94.6 (C-1000), 80.0, 78.8,
78.2, 78.0, 76.3, 76.1, 74.5, 71.6, 70.9, 70.0, 68.9, 68.7, 67.0, 64.2,
62.1, 55.7 (OC6H4OCH3), 28.6, 28.5, 27.8, 27.6 (4 ꢁ isopropyli-
dene–CH3), 21.1, 20.9, 20.8, 20.7(2) (5 ꢁ COCH3), 18.1, 17.9, 17.8
(3 ꢁ C–CH3). HRMS calcd for C46H64O23Na (M+Na)+: 1007.3736,
found: 1007.3732.
00 00
4.1.9. p-Methoxyphenyl
a
-L
-rhamnopyranosyl-(1?3)-b-
D-
xylopyranosyl-(1?4)-
a-L
-rhamnopyranosyl-(1?2)-b-
D-
fucopyranoside 1
A solution of compound 14 (400 mg, 0.4 mmol) in 80% aq AcOH
(10 mL) was stirred at 80 °C for 3 h. Then the solvents were evap-
orated and co-evaporated with toluene to remove residual AcOH.
The residue was dissolved in MeOH (10 mL), after which NaOMe
in MeOH (0.5 M, 1 mL) was added and the solution was allowed
to stir at room temperature for 6 h. The solution was neutralized
by DOWEX 50 W H+ resin, filtered and evapoarated to afford pure
14. Kishore, N.; Sinha, N.; Jain, S.; Upadhyaya, R. S.; Chandra, R.; Arora, S. K.
ARKIVOC 2005, 65–74.
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17. Kerékgyártó, J.; Szurmai, Z.; Lipták, A. Carbohydr. Res. 1993, 245, 65–80.
18. Medgyes, G.; Jerkovich, G.; Kuszmann, J. Carbohydr. Res. 1989, 186, 225–239.
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