Total synthesis of the heptasaccharide repeating unit of the iron-binding exopolysaccharide secreted by Klebsiella oxytoca BAS-10

Article abstract of DOI:10.1016/j.tetasy.2009.07.009

The first total synthesis of a heptasaccharide found in the iron-binding exopolysaccharide produced by Klebsiella oxytoca BAS-10 has been achieved in excellent yield using a block synthetic strategy. A trisaccharide glycosyl donor was stereoselectively co

Full text of DOI:10.1016/j.tetasy.2009.07.009

Tetrahedron: Asymmetry 20 (2009) 1791–1797
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Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Total synthesis of the heptasaccharide repeating unit of the iron-binding
exopolysaccharide secreted by Klebsiella oxytoca BAS-10
*
Goutam Guchhait, Anup Kumar Misra
Bose Institute, Division of Molecular Medicine, P-1/12, C.I.T. Scheme VII-M, Kolkata 700 054, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The first total synthesis of a heptasaccharide found in the iron-binding exopolysaccharide produced by
Klebsiella oxytoca BAS-10 has been achieved in excellent yield using a block synthetic strategy. A trisac-
charide glycosyl donor was stereoselectively coupled with a tetrasaccharide glycosyl acceptor using the
trichloroacetimidate activation procedure. The yields and stereo outcome were excellent in each step of
glycosylation. A late stage oxidation protocol was adopted for the oxidation of the primary hydroxyl
group to the carboxylic functionality while keeping a secondary hydroxyl group unaffected.
Ó 2009 Elsevier Ltd. All rights reserved.
Received 1 June 2009
Accepted 6 July 2009
Available online 10 August 2009
1. Introduction
K. oxytoca BAS-10 (Fig. 1). The 4-methoxyphenyl group has been
chosen as the anomeric protection because of its easy removal
Klebsiella bacteria are gram-negative opportunistic pathogens
which cause several infections such as pneumonia, septicemia,
and urinary tract infections.1 Among several species of Klebsiella,
Klebsiella oxytoca infections are the second most frequently found
in several patients after Klebsiella pneumonia infections.2 K. Oxytoca
produces exopolysaccharides with several pharmaceutical and
environmental importances.3 Very recently, the structure of an
exopolysaccharide secreted by Klebsiella oxycota BAS-10 containing
two glucuronic acids at the non-reducing terminus has been re-
ported by De Castro et al.4 This particular exopolysaccharide has
shown strong iron binding affinity5 useful in the preparation of
bacterial biopolymers. It is believed that due to the presence of
the glucuronic acid moieties it could form stable complexes with
the metal ions through strong electrostatic attractions between
metal ion and the negatively charged uronic acid moieties.6 In
addition to the pharmaceutical properties of biopolymers, they
can also be successfully applied to the selective removal of heavy
metals and radioactive metals from water and soils.7
whenever we are required to modify the synthesized heptasaccha-
ride moiety to prepare the glycoconjugate molecule.
HO
A
HO
O
O
OH
OMp
B
HO
C
O
O
O
O
HO
O
HO
O
OH
ONa
O
HO
HO
HO
O
D
F
O
O
OH
HO
OH
O
HO
Mp: 4-Methoxyphenyl
O
HO
HO
ONa
1
O
Figure 1. Structure of the synthesized heptasaccharide antigen from Klebsiella
oxytoca BAS-10 as its 4-methoxyphenyl glycoside 1.
The preparation of carbohydrate-derived molecules for their
use in therapeutics is a thrust area in medicinal chemistry re-
search. Although the oligosaccharides can be isolated from natural
sources, their bio- and pharmaceutical evaluation require reason-
ably higher quantities of materials, which cannot be managed by
the isolation from natural sources. Therefore, concise chemical
synthetic strategies are always useful in gaining access to large
quantities of oligosaccharides in pure form.8 In this report, we
describe a concise total synthesis of the iron-binding heptasaccha-
ride repeating unit found in the exopolysaccharide secreted by
2. Results and discussion
In order to synthesize the target heptasaccharide 1 as its 4-
methoxyphenyl glycoside, a block synthetic strategy has been
adopted. A trisaccharide trichloroacetimidate derivative 18 and a
tetrasaccharide derivative 15 were prepared separately starting
from a series of suitably protected monosaccharide intermediates
(Schemes 1 and 2). Stereoselective glycosylation of compound 15
with compound 18 furnished a heptasaccharide derivative 19,
which was further transformed into the target heptasaccharide 1
after selective oxidation of the primary hydroxyl groups and
removal of protecting groups (Scheme 2). For this purpose, a
* Corresponding author. Tel.: +91 33 2569 3240; fax: +91 33 2355 3886.
E-mail address: akmisra69@rediffmail.com (A.K. Misra).
0957-4166/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2009.07.009

1792
G. Guchhait, A. K. Misra / Tetrahedron: Asymmetry 20 (2009) 1791–1797
OMp
OMp
O
a
O
b
A
a
HO
2
BnO
3
HO
OAc
BnO
OH
8
16
7
b
4
OR
OAc
BnO
O
AcO
AcO
O
E
A
F
O
OMp
BnO
OR1
O
O
OAc
OAc
AcO
O
R2O
R1O
O
B
G
O
OR1
OAc
AcO
AcO
17: R = Mp
18: R = C(NH)CCl3
9: R1 = Ac; R2 = allyl
10: R1 = Bn; R2 = allyl
11: R1 = Bn; R2 = H
c
c
BnO
BnO
d
A
OMp
O
15
b
b
5
OBn
O
BnO
BnO
O
B
A
O
O
OMp
C
O
OBn
BnO
BnO
BnO
OBn
O
O
O
B
O
D
O
O
BnO
O
C
OBn
BnO
OAc
BnO
OAc
O
BnO
OR
AcO
AcO
O
E
F
O
12: R = Ac
13: R = H
e
BnO
BnO
O
19
OAc
OAc
d, e
A
AcO
OMp
O
O
b
BnO
6
OBn
G
A
OAc
O
AcO
AcO
O
OMp
B
BnO
OBn
O
O
O
O
C
OBn
BnO
BnO
O
O
B
BnO
O
O
C
OBn
O
BnO
D
O
BnO
BnO
BnO
D
O
OH
ONa
O
O
O
HO
O
14: R = Ac
15: R = H
E
BnO
F
O
f
HO
O
OH
OAc
RO
OH
HO
f
1
O
20
Scheme 1. Reagents and conditions: (a) (i) dibutyltin oxide, CH3OH, 80 °C, 2 h; (ii)
benzyl bromide, tetrabutylammonium bromide, DMF, room temperature, 12 h,
76%; (b) NIS, TMSOTf, MS 4 Å, CH2Cl2, ꢀ45 °C, 1 h, 90% for compound 9, 88% for
compound 12, 85% for compound 14; (c) benzyl bromide, NaOH, TBAB, THF, room
temperature, 6 h, 91%; (d) PdCl2, CH3OH, room temperature, 6 h, 76%; (e) CH3ONa,
CH3OH, room temperature, 3 h, 96%; (f) (i) CH3ONa, CH3OH, room temperature, 3 h;
(ii) CH3CH(OCH3)2, p-TsOH, DMF, 2 h; (iii) 80% aq AcOH, room temperature, 30 min,
91%.
G
ONa
HO
HO
O
Scheme 2. Reagents and conditions: (a) (i) CH3CH(OCH3)2, p-TsOH, DMF, room
temperature, 2 h; (ii) 80% aq AcOH, room temperature, 30 min, 84%; (b) TMSOTf, MS
4 Å, CH2Cl2, ꢀ10 °C, 3 h, 64% for compound 17, 68% for compound 19; (c) (i) ceric
ammonium nitrate, CH3CN–H2O (4:1), room temperature, 3 h; (ii) CCl3CN, DBU,
CH2Cl2, ꢀ10 °C, 4 h, 70%; (d) CH3ONa, CH3OH, room temperature, 5 h; (e) (i) NaBr,
CH2Cl2, H2O, TBAB, TEMPO, NaHCO3, NaOCl, 0–5 °C, 3 h; (ii) tert-butanol, 2-methyl-
but-2-ene, NaClO2, NaH2PO4, room temperature, 3 h; (f) H2, 20% Pd(OH)2–C, CH3OH,
room temperature, 24 h, overall yield 59%.
number of differentially protected monosaccharide intermediates
2,9 3,10 4,11 5,12 6,13 and 714 were prepared from commercially
available reducing sugars using earlier reported reaction condi-
tions (Fig. 2).
OMp
OMp
AcO
AllO
OAc
Selective benzylation via the formation of stannylidene acetal 310
O
O
O
HO
BnO
SEt
furnished 4-methoxyphenyl 3,4-di-O-benzyl-
a-
L-rhamnopyrano-
HO
OH
OAc
HO
OH
side8 in 76%yield. Stereoselectiveglycosylation of compound8 with
thioglycoside derivative 4,11 in the presence of N-iodosuccinimide
(NIS) and trimethylsilyl trifluoromethanesulfonate (TMSOTf)15 fur-
nished disaccharide derivative 9 in 90% yield. The exclusive forma-
tion of the 1,2-trans-glycosidic bond was achieved due to the
presence of a neighboring group O-acetoxy at the C-2 position of
compound 4. The presence of signals in the 1H NMR [d 5.50 (br s,
H-1A), 4.51 (d, J = 8.0 Hz, H-1B)] and in the 13C NMR [d 103.4 (C-1B),
97.9 (C-1A)] confirmed the formation of compound 9. Compound 9
was transformed to compound 10 using one-pot deacetylation–ben-
zylationreaction conditions16 in 91%yield. Removalof the allyl ether
protection from compound 10 was carried out using palladium
2
3
4
SEt
SEt
OAc
NH
CCl3
O
O
O
AcO
AcO
BnO
BnO
O
BnO
AcO
OAc
OAc
OAc
5
6
7
Figure 2. Suitably protected monosaccharide intermediates used in the construc-
tion of heptasaccharide 1.
chloride17 to give compound 11 in 76% yield. The stereoselective
glycosylation of the disaccharide acceptor 11 with thioglycoside

G. Guchhait, A. K. Misra / Tetrahedron: Asymmetry 20 (2009) 1791–1797
1793
derivative 512 in the presence of NIS-TMSOTf15 as the glycosylation
3. Conclusion
promoter afforded trisaccharide derivative 12 in 88% yield, which
on deacetylation furnished trisaccharide acceptor 13 in 96% yield.
The formation of compound 12 was confirmed from spectroscopic
analysis [appearance of a new signal at d 5.31 (br s, 1H, H-1C) in
the 1H NMR and signals at d 104.9 (C-1B), 100.5 (C-1C), and 98.2
(C-1A) in the 13C NMR spectra]. Glycosylation of trisaccharide deriv-
ative 13 with thioglycoside derivative 613 was carried out using NIS-
TMSOTf15 as the thiophilic activator to furnish the tetrasaccharide
derivative 14 in 85% yield. The presence of an O-acetoxy group at
the C-2 position of compound 6 directed the exclusive formation
of compound 14, which was supported by its spectroscopic analysis
[appearance of a signal at d 4.76 (br s, H-1D) in 1H NMR and signals at
d 104.9 (C-1B), 100.1 (C-1C), 98.9 (C-1D), and 98.2 (C-1A) in the 13C
NMR spectra]. Removal of the O-acetyl groups in compound 14 using
saponification followed by selective acetylation of the C-2 hydroxy
In conclusion, the total synthesis of a heptasaccharide contain-
ing two -glucuronic acid moieties found in the iron-binding exo-
D
polysaccharide produced by K. oxytoca BAS-10 was achieved in
excellent yield using a block synthetic strategy. Most of the glyco-
sylation steps are highly stereoselective and reproducible for
scale-up. A late stage selective TEMPO-mediated oxidation of the
primary hydroxyl groups was achieved using a two-step, one-pot
phase transfer oxidation protocol without affecting the secondary
hydroxyl groups present in the molecule. The 4-methoxybenzyl
group was chosen as the temporary protecting group at the reduc-
ing end for its easy removal whenever necessary.
4. Experimental
group of the terminal L-rhamnosyl moiety via formation of an ortho-
ester18 using triethyl orthoacetate resulted in tetrasaccharide accep-
tor 15 in 91% overall yield (Scheme 1).
4.1. General methods
In another experiment, compound 29 was selectively 2-O-acet-
ylated via orthoester formation18 using triethyl orthoacetate in the
presence of p-toluene sulfonic acid to give diol derivative 16 in 84%
yield. Two consecutive stereoselective 1,2-trans-glycosylations of
the diol derivative 16 with trichloroacetimidate derivative 714
using Schmidt’s glycosylation condition19 furnished trisaccharide
derivative 17 in 64% yield, which was confirmed from its spectro-
scopic analysis [signals at d 5.24 (br s, H-1E), 4.74 (d, J = 7.7 Hz,
H-1F), and 4.69 (d, J = 8.0 Hz, H-1G) in the 1H NMR and at d 101.1
(C-1F), 99.2 (C-1G), and 96.4 (C-1E) in the 13C NMR spectra]. Com-
pound 17 was treated with ceric ammonium nitrate (CAN)10 in
moist CH3CN to give the trisaccharide hemiacetal, which was trea-
ted with trichloroacetonitrile in the presence of DBU20 to give
trisaccharide trichloroacetimidate derivative 18 in 70% overall
yield. The final stereoselective glycosylation of the trisaccharide
trichloroacetimidate derivative 18 with the tetrasaccharide deriva-
tive 15 under Schmidt’s glycosylation conditions19 furnished hep-
tasaccharide derivative 19 in 68% yield, which was confirmed
from its spectroscopic analysis [presence of signals at d 104.9
(C-1B), 100.6 (C-1F), 100.0 (C-1C), 98.8 (C-1G), 98.6 (C-1D), 98.4
(C-1E), and 98.1 (C-1A) in the 13C NMR spectrum]. Saponification
of the heptasaccharide derivative 19 using sodium methoxide
followed by TEMPO-mediated selective oxidation21 of the poly-
hydroxylated product in phase transfer reaction conditions fur-
All reactions were monitored by thin layer chromatography over
silica gel-coated TLC plates. The spots on TLC were visualized by
warming ceric sulfate (2% Ce(SO4)2 in 2 N H2SO4) sprayed plates
on a hot plate. Silica gel 230–400 mesh was used for column chroma-
tography. 1H and 13C NMR, 2D COSY, and HMQC spectra were
recorded on a Brucker 500 MHz NMR spectrometer (DRX-500) using
CDCl3 and D2O as solvents and TMS as internal reference unless
stated otherwise. Chemical shift value is expressed in d ppm. ESI-
MS were recorded on a MICROMASS QUTTRO II triple quadrupole
mass spectrometer. Elementary analysis was carried out on Carlo
ERBA-1108 analyzer. Optical rotations were measured at 25 °C on
a Rudolf Autopol III polarimeter. Commercially available grades of
organic solvents of adequate purity were used in many reactions.
4.1.1. 4-Methoxyphenyl 3,4-di-O-benzyl-a-L-
rhamnopyranoside 8
To a solution of compound 3 (6 g, 16.65 mmol) in anhydrous
CH3OH (120 mL) was added dibutyltin(IV) oxide (4.9 g,
19.68 mmol) and the reaction mixture was allowed to stir at
80 °C for 2 h. The solvents were removed under reduced pressure
and to a solution of the crude stannylidene acetal derivative in
anhydrous DMF (50 mL) were added benzyl bromide (4 mL,
33.63 mmol) and tetrabutylammonium bromide (3.3 g, 1 mmol).
The reaction mixture was allowed to stir at room temperature
for 12 h and the solvents were removed under reduced pressure.
The crude product was dissolved in EtOAc (150 mL) and the organ-
ic layer was washed with 1 M HCl, satd NaHCO3, and water succes-
sively. The organic layer was dried (Na2SO4) and concentrated to
give the crude product, which was purified over SiO2 using hex-
ane–EtOAc (4:1) as eluant to give pure compound 8 (5.7 g, 76%);
nished two
D-glucuronic acids containing the heptasaccharide
derivative, which was hydrogenolized over Pearlman’s catalyst22
to give target heptasaccharide 1 as its 4-methoxyphenyl glycoside
in 59% overall yield. It is worth mentioning that late stage phase
transfer TEMPO-mediated oxidation conditions have been adopted
for the selective oxidation of two primary hydroxyl groups in
the presence of secondary hydroxyl groups, which furnished
Oil; ½a 2D5
ꢁ
¼ ꢀ43 (c 1.5, CHCl3); IR (neat): 2932, 2368, 1654, 1513,
1457, 1389, 1227, 1100, 1043, 774, 699 cmꢀ1
;
1H NMR (300 MHz,
D
-glucuronic acid containing heptasaccharide derivative 20 quite
CDCl3):d 7.58–7.19 (m, 10H, Ar-H), 6.98 (d, J = 9.0 Hz, 2H, Ar-H),
6.83 (d, J = 9.0 Hz, 2H, Ar-H), 5.44 (br s, 1H, H-1), 4.94 (d,
J = 11.0 Hz, 1H, PhCH2), 4.78 (br s, 2H, PhCH2), 4.70 (d, J = 11.0 Hz,
1H, PhCH2), 4.20 (br s, 1H, H-2), 4.05 (dd, J = 9.4, 2.9 Hz, 1H, H-3),
3.92–3.83 (m, 1H, H-5), 3.80 (s, 3H, OCH3), 3.53 (t, J = 9.4 Hz, 1H,
H-4), 1.30 (d, J = 6.0 Hz, 3H, CCH3); 13C NMR (75 MHz, CDCl3): d
154.9–114.6 (Ar-C), 96.2 (C-1), 79.9 (2C, 2PhCH2), 75.4 (C-4), 72.2
(C-2), 68.6 (C-5), 68.0 (C-3), 55.5 (OCH3), 17.9 (CCH3); ESI-MS:
473.2 [M+Na]+; Anal. Calcd for C27H30O6 (450.20): C, 71.98; H,
6.71. Found: C, 71.80; H, 6.95.
efficiently. The oxidized product 20 was directly subjected to
hydrogenation to give target heptasaccharide 1. The stereochemi-
cal assignments of the glycosyl linkages in compound 1 were con-
firmed from its 1D and 2D NMR spectra [signals at d 5.58 (br s, H-
1A), 5.14 (br s, H-1C), 4.95 (br s, H-1E), 4.85 (br s, H-1D), 4.67 (d,
J = 7.9 Hz, H-1G), 4.52 (d, J = 7.5 Hz, H-1F), and 4.43 (d, J = 7.8 Hz,
H-1B) in the 1H NMR and at d 107.5 (C-1B), 105.1 (C-1F), 104.3
(C-1G), 103.7 (C-1D), 103.4 (C-1E), 102.3 (C-1C), and 99.7 (C-1A) in
the 13C NMR spectra] and mass spectroscopic analysis (Scheme
2). The 4-methoxyphenyl group used as the anomeric-protecting
group remained unaffected under the oxidation and hydrogenation
conditions, which was confirmed from the appearance of signals in
the NMR spectra of compound 1 [d 6.88 (d, J = 9.0 Hz, 2H), 6.74 (d,
J = 9.0 Hz, 2H) in 1H NMR and at d 156.5, 151.7, 118.9 (2C), and
115.6 (2C)].
4.1.2. 4-Methoxyphenyl (2,4,6-tri-O-acetyl-3-O-allyl-b-
D-galac-
topyranosyl)-(1?2)-3,4-di-O-benzyl- -rhamnopyranoside 9
a
-L
To a solution of compound 8 (5 g, 11.1 mmol) and compound 4
(5.2 g, 13.32 mmol) in anhydrous CH2Cl2 (70 mL) was added MS

1794
G. Guchhait, A. K. Misra / Tetrahedron: Asymmetry 20 (2009) 1791–1797
4 Å (10 g) and the reaction mixture was allowed to stir at room tem-
perature for 1 h under argon. The reaction mixture was cooled to
ꢀ45 °C and N-iodosuccinimide (NIS; 3.5 g, 15.55 mmol) followed
6 h. The reaction mixture was concentrated to dryness under re-
duced pressure and the crude product was purified over SiO2 using
hexane–EtOAc (5:1) as eluant to give pure compound 11 (4.4 g,
by trimethylsilyltrifluoromethane sulfonate (TMSOTf; 30
lL) were
76%); Oil; ½a 2D5
ꢁ
¼ ꢀ5:9 (c 1.5, CHCl3); IR (neat): 3460, 3020, 2926,
added to it and the reaction mixture was allowed to stir at same tem-
perature for 1 h. The reaction mixture was quenched with Et3N
(0.1 mL), filtered through a CeliteÒ bed and washed with CH2Cl2
(200 mL). The organic layer was washed with 5% aq Na2S2O3, satd
aq NaHCO3, and water, dried (Na2SO4) and concentrated to dryness.
The crude product was purified over SiO2 using hexane–EtOAc (5:1)
2359, 1595, 1505, 1216, 1074, 927, 761 cmꢀ1 1H NMR (300 MHz,
;
CDCl3): d 7.41–7.16 (m, 25H, Ar-H), 6.90 (d, J = 9.0 Hz, 2H, Ar-H),
6.74 (d, J = 9.0 Hz, 2H, Ar-H), 5.56 (br s, 1H, H-1A), 5.25 (d,
J = 11.2 Hz, 1H, PhCH2), 4.91–4.46 (m, 8H, H-1B, PhCH2), 4.42–
4.32 (m, ABq, J = 11.9 Hz, 2H, PhCH2), 4.24–4.22 (m, 1H, H-2A),
4.07 (dd, J = 9.5, 2.3 Hz, 1H, H-3A), 3.85–3.77 (m, 2H, H-4B, H-5A),
3.74 (s, 3H, OCH3), 3.68–3.59 (m, 2H, H-2B, H-4A), 3.56–3.50 (m,
4H, H-3B, H-5B, H-6abB), 1.24 (d, J = 6.1 Hz, 3H, CCH3); 13C NMR
(75 MHz, CDCl3): d 154.7–114.5 (Ar-C), 104.8 (C-1B), 98.2 (C-1A),
80.4 (C-3B), 79.9 (C-3A), 79.3 (C-2B), 75.4 (C-2A), 75.3 (C-5A), 75.2
(PhCH2), 74.9 (PhCH2), 74.4 (PhCH2), 74.0 (C-4A), 73.8 (C-5B), 73.5
(PhCH2), 72.5 (PhCH2), 69.0 (C-6B), 68.5 (C-4B), 55.5 (OCH3), 18.0
(CCH3); ESI-MS: 905.4 [M+Na]+; Anal. Calcd for C54H58O11 (882.40):
C, 73.45; H, 6.62. Found: C, 73.20; H, 6.90.
as eluant to give pure 9 (7.8 g, 90%); Oil; ½a D25
¼ þ12:6 (c 1.5, CHCl3);
ꢁ
IR (neat): 3020, 2361, 1746, 1506, 1371, 1217, 1042, 761 cmꢀ1; 1H
NMR (300 MHz, CDCl3): d 7.41–7.27 (m, 10H, Ar-H), 6.94 (d, J =
9.0 Hz, 2H, Ar-H), 6.75 (d, J = 9.0 Hz, 2H, Ar-H), 5.85–5.75 (m, 1H,
CH@CH2), 5.50 (br s, 1H, H-1A), 5.39 (d, J = 2.9 Hz, 1H, H-4B), 5.32–
5.19 (m, 2H, CH2@CH), 5.14 (dd, J = 8.0 Hz each, 1H, H-2B), 4.87 (d,
J = 10.9 Hz, 1H, PhCH2), 4.79–4.69 (m, ABq, J = 11.5 Hz, 2H, PhCH2),
4.63 (d, J = 10.9 Hz, 1H, PhCH2), 4.51 (d, J = 8.0 Hz, 1H, H-1B), 4.17–
4.09 (m, 3H, H-6abB, OCH2a), 4.03–3.92 (m, 3H, H-2A, H-5A, OCH2b),
3.76 (s, 3H, OCH3), 3.80–3.73 (m, 2H, H-4A, H-5B), 3.53 (dd, J = 8.2,
2.0 Hz, 1H, H-3B), 3.51–3.45 (m, 1H, H-3A), 2.18, 1.92, 1.90 (3 s, 9H,
3COCH3), 1.28 (d, J = 6.1 Hz, 3H, CCH3); 13C NMR (75 MHz, CDCl3):
4.1.5. 4-Methoxyphenyl (2-O-acetyl-3,4-di-O-benzyl-
pyranosyl)-(13)-(2,4,6-tri-O-benzyl-b- -galactopyranosyl)-(12)-3,
4-di-O-benzyl- -rhamnopyranoside 12
a-L-rhamno-
D
a-L
d
170.2, 170.1, 169.2 (3 COCH3), 154.8–138.5 (Ar-C), 134.2
To a solution of compound 11 (4 g, 4.53 mmol) and compound 5
(2.3 g, 5.34 mmol) in anhydrous CH2Cl2 (30 mL) was added MS 4 Å
(3 g) and the reaction mixture was allowed to stir at room temper-
ature for 1 h under argon. The reaction mixture was cooled to
ꢀ45 °C and N-iodosuccinimide (NIS; 1.4 g, 6.22 mmol) followed
(CH2@CH), 128.4–114.6 (Ar-C), 117.2 (CH2@CH), 103.4 (C-1B), 97.9
(C-1A), 80.3 (C-3A), 79.5 (C-5A), 77.5 (C-2A), 76.3 (C-3A), 75.4 (PhCH2),
72.8 (PhCH2), 70.8 (C-4A), 70.6 (OCH2), 70.5 (C-2B), 68.7 (C-5B), 65.9
(C-4B), 61.9 (C-6B), 55.5 (OCH3), 20.8, 20.7, 20.4 (3COCH3), 17.9
(CCH3); ESI-MS: 801.3 [M+Na]+; Anal. Calcd for C42H50O14
(778.32): C, 64.77; H, 6.47. Found: C, 64.60; H, 6.72.
by trimethylsilyltrifluoromethane sulfonate (TMSOTf; 20 lL) were
added to it and the reaction mixture was allowed to stir at the
same temperature for 1 h. The reaction mixture was quenched
with Et3N (0.1 mL), filtered through a CeliteÒ bed, and washed with
CH2Cl2 (150 mL). The organic layer was washed with 5% aq
Na2S2O3, satd aq NaHCO3, and water, dried (Na2SO4) and concen-
trated to dryness. The crude product was purified over SiO2 using
hexane–EtOAc (5:1) as eluant to give pure 12 (5 g, 88%); Oil;
4.1.3. 4-Methoxyphenyl (3-O-allyl-2,4,6-tri-O-benzyl-b-
topyranosyl)-(1?2)-3,4-di-O-benzyl- -rhamnopyranoside 10
D-galac-
a
-L
To a solution of compound 9 (6 g, 7.70 mmol) in anhydrous THF
(80 mL) were added powdered NaOH (2 g, 50 mmol), benzyl bro-
mide (4.5 mL, 37.84 mmol), and tetrabutylammonium bromide
(500 mg, 1.55 mmol) and the reaction mixture was allowed to stir
briskly at room temperature for 6 h. The reaction mixture was
quenched with CH3OH (5 mL) and concentrated under reduced pres-
sure. The crude mass was dissolved in CH2Cl2 (200 mL) and the
organic layer was washed with water, dried (Na2SO4), and concen-
trated. The crude product was purified over SiO2 using hexane–
EtOAc (8:1) as eluant to give pure compound 10 (6.5 g, 91%); Oil;
½
a 2D5
ꢁ
¼ þ2:6 (c 1.5, CHCl3); IR (neat): 3019, 2925, 2360, 1739,
1594, 1369, 1216, 1073, 926, 761 cmꢀ1; 1H NMR (300 MHz, CDCl3):
d 7.46–7.15 (m, 35H, Ar-H), 6.94 (d, J = 9.0 Hz, 2H, Ar-H), 6.78 (d,
J = 9.0 Hz, 2H, Ar-H), 5.59 (br s, 1H, H-1A), 5.58–5.57 (m, 1H, H-
2C), 5.31 (br s, 1H, H-1C), 5.26 (d, J = 10.8 Hz, 1H, PhCH2), 4.92 (d,
J = 11.1 Hz, 1H, PhCH2), 4.84–4.44 (m, 10H, H-1B, PhCH2), 4.39–
4.26 (m, 3H, PhCH2), 4.22–4.20 (m, 1H, H-2A), 4.10 (dd, J = 9.4,
2.8 Hz, 1H, H-3A), 3.91 (dd, J = 8.0 Hz each, 1H, H-2B), 3.87–3.79
(m, 4H, H-3B, H-3C, H-5A, H-5C), 3.77 (s, 3H, OCH3), 3.71 (br s, 1H,
H-4B), 3.57 (dd, J = 9.5 Hz each, 1H, H-4A), 3.56–3.50 (m, 3H, H-
5B, H-6abB), 3.39 (t, J = 9.4 Hz each, 1H, H-4C), 2.12 (s, 3H, COCH3),
1.33, 1.25 (2 d, J = 6.1 Hz, 6H, 2CCH3); 13C NMR (75 MHz, CDCl3):
d 169.6 (COCH3), 154.7–114.5 (Ar-C), 104.9 (C-1B), 98.8 (C-1C),
98.3 (C-1A), 80.4 (C-4A), 79.9 (C-3A), 79.7 (C-4C), 79.2 (C-2B), 77.8
(C-3B), 76.9 (C-3C), 75.9 (C-4B), 75.4 (PhCH2), 75.3 (C-2A), 75.2
(PhCH2), 75.0 (PhCH2), 74.4 (PhCH2), 73.7 (C-5B), 73.5 (PhCH2),
72.5 (PhCH2), 71.4 (PhCH2), 68.9 (C-6B), 68.6 (C-5A), 68.5 (C-5C),
68.1 (C-2C), 55.4 (OCH3), 20.9 (COCH3), 18.2, 18.0 (2CCH3); ESI-
MS: 1273.6 [M+Na]+; Anal. Calcd for C76H82O16 (1250.56): C,
72.94; H, 6.60. Found:C, 72.75; H, 6.84.
½
a 2D5
ꢁ
¼ ꢀ38:6 (c 1.5, CHCl3); IR (neat): 3020, 2360, 1598, 1507,
1216, 1074, 928, 760 cmꢀ1; 1H NMR (300 MHz, CDCl3): d 7.43–7.15
(m, 25H, Ar-H), 6.90 (d, J = 9.0 Hz, 2H, Ar-H), 6.74 (d, J = 9.0 Hz, 2H,
Ar-H), 5.97–5.85 (m, 1H, CH@CH2), 5.54 (br s, 1H, H-1A), 5.33–5.14
(m, 3H, CH2@CH, PhCH2), 4.90 (d, J = 11.6 Hz, 1H, PhCH2), 4.80–
4.65 (m, 5H, H-1B, PhCH2), 4.58 (d, J = 11.6 Hz, 1H, PhCH2), 4.44 (d,
J = 10.9 Hz, 1H, PhCH2), 4.39–4.30 (ABq, J = 11.9 Hz, 2H, PhCH2),
4.28–4.12 (m, 3H, H-2A, OCH2), 4.05 (dd, J = 9.4, 2.8 Hz, 1H, H-3A),
3.82–3.75 (m, 3H, H-2B, H-4B, H-5A), 3.73 (s, 3H, OCH3), 3.55 (t,
J = 9.4 Hz each, 1H, H-4A), 3.51–3.42 (m, 3H, H-4A, H-5B, H-6abB),
3.35 (dd, J = 9.7, 2.8 Hz, 1H, H-3B), 1.23 (d, J = 6.1 Hz, 3H, CCH3); 13
C
NMR (75 MHz, CDCl3): d 154.9–137.9 (Ar-C), 135.2 (CH@CH2),
128.4–114.5 (Ar-C), 116.4 (CH@CH2), 104.7 (C-1B), 98.2 (C-1A),
81.7 (C-3B), 80.5 (C-4A), 79.9 (C-3A), 79.5 (C-2B), 75.3 (PhCH2), 74.8
(PhCH2), 74.7 (C-2A), 74.6 (PhCH2), 73.8 (C-5A), 73.6 (C-5B), 73.5
(PhCH2), 72.3 (PhCH2), 72.2 (OCH2), 69.1 (C-6B), 68.6 (C-4B), 55.5
(OCH3), 18.0 (CCH3); ESI-MS: 945.4 [M+Na]+; Anal. Calcd for
C57H62O11 (922.43): C, 74.16; H, 6.77. Found: C, 74.0; H, 7.98.
4.1.6. 4-Methoxyphenyl (3,4-di-O-benzyl-
syl)-(13)-(2,4,6-tri-O-benzyl-b- -galactopyranosyl)-(12)-3,4-di-
O-benzyl- -rhamnopyranoside 13
a-L-rhamnopyrano-
D
a
-L
A solution of compound 12 (4.5 g, 3.6 mmol) in 0.1 M CH3ONa in
CH3OH (100 mL) was allowed to stir at room temperature for 3 h and
neutralized with Amberlite IR-120 (H+) resin. The reaction mixture
was filtered and concentrated under reduced pressure to give a
crude product, which was passed through a short pad of SiO2 column
using hexane–EtOAc (3:1) to give pure compound 13 (4.2 g, 96%);
4.1.4. 4-Methoxyphenyl (2,4,6-tri-O-benzyl-b-
osyl)-(12)-3,4-di-O-benzyl- -rhamnopyranoside 11
To a solution of compound 10 (6 g, 6.5 mmol) in anhydrous
CH3OH (80 mL) was added PdCl2 (700 mg, 3.95 mmol) and the
reaction mixture was allowed to stir at room temperature for
D-galactopyran-
a
-L
Oil; ½a 2D5
¼ ꢀ1:7 (c 1.5, CHCl3); IR (neat): 3397, 3021, 2926, 2358,
ꢁ

G. Guchhait, A. K. Misra / Tetrahedron: Asymmetry 20 (2009) 1791–1797
1795
1595, 1216, 1044, 928, 762 cmꢀ1; 1H NMR (300 MHz, CDCl3): d 7.37–
7.15 (m, 35H, Ar-H), 6.90 (d, J = 9.0 Hz, 2H, Ar-H), 6.73 (d, J = 9.0 Hz,
2H, Ar-H), 5.55 (br s, 1H, H-1A), 5.24 (br s, 1H, H-1C), 5.16 (d, J =
11.4 Hz, 1H, PhCH2), 4.86–4.33 (m, 14H, H-1B, PhCH2), 4.22–4.21
(m, 1H, H-2A), 4.05 (dd, J = 9.4, 2.8 Hz, 1H, H-3A), 3.85–3.74 (m, 5H,
H-2B, H-2C, H-3C, H-5A, H-5C), 3.73 (s, 3H, OCH3), 3.69 (br s, 1H,
H-4B), 3.64 (dd, J = 9.1, 3.1 Hz, 1H, H-3B), 3.55–3.48 (m, 4H, H-4A,
H-5B, H-6abB), 3.41 (t, J = 9.4 Hz each, 1H, H-4C), 1.26, 1.23 (2 d,
J = 6.1 Hz each, 6H, 2CCH3); 13C NMR (75 MHz, CDCl3): d 154.7–
114.5 (Ar-C), 104.9 (C-1B), 100.5 (C-1C), 98.2 (C-1A), 80.3 (C-4A),
79.8 (C-3A), 79.7 (C-3B), 79.5 (C-2B), 79.3 (C-4C), 77.7 (C-3C), 76.1
(C-4B), 75.3 (C-2A), 75.2 (PhCH2), 75.1 (PhCH2), 74.9 (PhCH2), 74.5
(PhCH2), 73.6 (C-5B), 73.5 (PhCH2), 72.3 (PhCH2), 71.7 (PhCH2),
68.9 (C-6B), 68.5 (C-5A), 68.3 (C-5C), 68.1 (C-2C), 55.5 (OCH3), 18.1,
18.0 (2CCH3); ESI-MS: 1231.5 [M+Na]+; Anal. Calcd for C74H80O15
(1208.55): C, 73.49; H, 6.67. Found: C, 73.32; H, 6.90.
ing ortho-ester derivative was dissolved in 80% aq AcOH (50 mL)
and the reaction mixture was allowed to stir at room temperature
for 30 min. The solvents were removed under reduced pressure
and co-evaporated with toluene to give the crude product, which
was purified over SiO2 using hexane–EtOAc (5:1) as eluant to give
pure compound 15 (1.6 g, 91%); Oil; ½a D25
¼ þ6:9 (c 1.5, CHCl3); IR
ꢁ
(neat): 3018, 2926, 2361, 1737, 1594, 1503, 1368, 1216, 1074, 924,
760 cmꢀ1 1H NMR (300 MHz, CDCl3): d 7.41–7.14 (m, 40H, Ar-H),
;
6.88 (d, J = 9.0 Hz, 2H, Ar-H), 6.74 (d, J = 9.0 Hz, 2H, Ar-H), 5.52 (br
s, 1H, H-1A), 5.20 (br s, 2H, H-1C, H-2D), 5.0 (d, J = 12.1 Hz, 1H,
PhCH2), 4.88–4.56 (m, 11H, H-1B, H-1D, PhCH2), 4.48–4.32 (m,
6H, PhCH2), 4.22 (br s, 1H, H-2A), 4.08 (dd, J = 9.4, 3.0 Hz, 1H, H-
3D), 4.01 (dd, J = 9.4, 3.0 Hz, 1H, H-3A), 3.87 (br s, 1H, H-2C),
3.83–3.66 (m, 10H, H-2B, H-3B, H-4B, H-4C, H-5A, H-5C, H-5D,
OCH3), 3.50–3.40 (m, 5 H, H-3C, H-4A, H-5B, H-6abB), 3.25 (t,
J = 9.4 Hz each, 1H, H-4D), 2.12 (s, 3H, COCH3), 1.25, 1.19, 1.11 (3
d, J = 6.1 Hz each, 9H, 3 CCH3); 13C NMR (75 MHz, CDCl3): d 170.4
(COCH3), 154.7–114.5 (Ar-C), 104.9 (C-1B), 100.2 (C-1C), 98.8 (C-
1D), 98.2 (C-1A), 81.7 (C-4A), 80.4 (C-3B), 79.9 (2C, C-2B, C-3A),
79.1 (C-4D), 77.9 (C-4C), 77.7 (C-5D), 76.3 (C-3C), 75.2 (PhCH2),
75.1 (PhCH2), 75.0 (PhCH2), 74.9 (C-4B), 74.8 (PhCH2), 73.7 (C-2A),
73.5 (2C, 2 PhCH2), 72.7 (C-5B), 72.3 (PhCH2), 71.7 (PhCH2), 70.1
(C-3D), 69.0 (C-6B), 68.9 (C-2D), 68.5 (C-5A), 67.9 (2C, C-2C, C-5C),
55.5 (OCH3), 21.0 (COCH3), 18.3, 18.0, 17.9 (3CCH3); ESI-MS:
1509.6 [M+Na]+; Anal. Calcd for C89H98O20 (1486.67): C, 71.85; H,
6.64. Found: C, 71.63; H, 6.90.
4.1.7. 4-Methoxyphenyl (2,3-di-O-acetyl-4-O-benzyl-
pyranosyl)-(12)-(3,4-di-O-benzyl- -rhamnopyranosyl)-(13)-(2,4,
6-tri-O-benzyl-b- -galactopyranosyl)-(12)-3,4-di-O-benzyl-
rhamnopyranoside 14
a-L-rhamno-
a-L
D
a-L-
To a solution of compound 13 (3.5 g, 2.9 mmol) and compound 6
(1.3 g, 3.4 mmol) in anhydrous CH2Cl2 (25 mL) was added MS 4 Å
(2 g) and the reaction mixture was allowed to stir at room tempera-
ture for 1 h under argon. The reaction mixture was cooled to ꢀ45 °C
and NIS (0.9 g, 4.0 mmol) followed by TMSOTf (10 lL) were added to
it and the reaction mixture was allowed to stir at same temperature
for 1 h. The reaction mixture was quenched with Et3N (0.1 mL),
filtered through a CeliteÒ bed, and washed with CH2Cl2 (150 mL).
The organic layer was washed with 5% aq Na2S2O3, satd aq NaHCO3,
and water, dried (Na2SO4) and concentrated to dryness. The crude
product was purified over SiO2 using hexane–EtOAc (5:1) as eluant
4.1.9. 4-Methoxyphenyl 2-O-acetyl-a-L-rhamnopyranoside 16
To a solution of compound 2 (2 g, 7.4 mmol) in anhydrous DMF
(5 mL) were added CH3C(OC2H5)3 (7.5 mL, 40.9 mmol) followed by
p-TsOH (100 mg) and the reaction mixture was allowed to stir at
room temperature for 2 h. The solvents were removed under re-
duced pressure and the crude ortho-ester derivative was dissolved
in 80% aq AcOH (50 mL). The reaction mixture was allowed to stir
at room temperature for 30 min and evaporated and co-evaporated
with toluene (3 ꢂ 50 mL) to give the crude product, which was
purified over SiO2 using hexane–EtOAc (1:1) as eluant to give pure
to give pure 14 (3.8 g, 85%); Oil; ½a D25
¼ ꢀ7:5 (c 1.5, CHCl3); IR (neat):
ꢁ
3020, 2925, 2360, 1749, 1593, 1429, 1216, 1081, 929, 762 cmꢀ1; 1H
NMR (300 MHz, CDCl3): d 7.40–7.16 (m, 40H, Ar-H), 6.88 (d,
J = 9.0 Hz, 2H, Ar-H), 6.72 (d, J = 9.0 Hz, 2H, Ar-H), 5.52 (br s, 1H, H-
1A), 5.42–5.40 (m, 1H, H-2D), 5.31 (dd, J = 9.6, 3.2 Hz, 1H, H-3D),
5.21 (br s, 1H, H-1C), 5.0 (d, J = 12.1 Hz, 1H, PhCH2), 4.87–4.83 (m,
2H, PhCH2), 4.76 (br s, 1H, H-1D), 4.74–4.30 (m, 14H, H-1B, PhCH2),
4.23–4.21 (m, 1H, H-2A), 4.01 (dd, J = 9.4, 3.0 Hz, 1H, H-3A), 3.88–
3.81 (m, 2H, H-2C, H-5D), 3.80–3.60 (m, 6H, H-2B, H-3B, H-4B, H-4C,
H-5A, H-5C), 3.72 (s, 3H, OCH3), 3.58–3.45 (m, 5H, H-3C, H-4A, H-5B,
H-6abB), 3.40 (t, J = 9.4 Hz, 1H, H-4D), 2.06, 1.96 (2 s, 6H, 2COCH3),
1.27, 1.17, 1.12 (3 d, J = 6.1 Hz, 9H, 3CCH3); 13C NMR (75 MHz,
CDCl3): d 169.6 (COCH3), 154.7–114.5 (Ar-C), 104.9 (C-1B), 100.1
(C-1C), 98.9 (C-1D), 98.2 (C-1A), 80.4 (C-4A), 79.9 (C-3B), 79.8 (C-3A),
79.5 (C-2B), 78.9 (C-4D), 77.7 (C-4C), 77.6 (C-5D), 76.4 (C-3C), 75.5
(C-4B), 75.3 (PhCH2), 75.2 (PhCH2), 75.0 (PhCH2), 74.9 (C-2A), 74.8
(PhCH2), 73.7 (C-5B), 73.5 (2C, PhCH2), 72.2 (PhCH2), 71.8 (PhCH2),
71.6 (C-3D), 70.4 (C-2D), 69.2 (C-5A), 68.9 (C-6B), 68.5 (C-5C), 68.2
(C-2C), 55.5 (OCH3), 20.9 (2C, 2COCH3), 18.2, 18.0, 17.8 (3 CCH3);
ESI-MS: 1551.6 [M+Na]+; Anal. Calcd for C91H100O21 (1528.68):
C, 71.45; H, 6.59. Found: C, 71.20; H, 6.86.
compound 16 (1.9 g (84%); Oil; ½a D25
¼ þ10 (c 1.0, CHCl3);IR (neat):
ꢁ
2362, 1754, 1721, 1620, 1368, 1216, 760 cmꢀ1; 1H NMR (300 MHz,
CDCl3): d 6.99 (d, J = 9.0 Hz, 2H, Ar-H), 6.79 (d, J = 9.0 Hz, 2H, Ar-H),
5.35 (br s, 1H, H-1), 5.25–5.24 (m, 1H, H-2), 4.19–4.11 (m, 1H, H-5),
3.86–3.79 (m, 1H, H-3), 3.77 (s, 3H, OCH3), 3.51 (t, J = 9.3 Hz each,
1H, H-4), 2.16 (s, 3H, COCH3), 1.29 (d, J = 6.1 Hz, 3H, CCH3); 13C
NMR (75 MHz, CDCl3): d 170.9 (COCH3), 155.2–114.6 (Ar-C), 96.7
(C-1), 73.2 (C-4), 72.4 (C-2), 70.1 (C-5), 68.8 (C-3), 55.5 (OCH3),
20.9 (COCH3), 17.6 (CCH3); ESI-MS: 335.1 [M+Na]+; Anal. Calcd
for C15H20O7 (312.12): C, 57.69; H, 6.45. Found: C, 57.50; H, 6.70.
4.1.10. 4-Methoxyphenyl (2,3,4,6-tetra-O-acetyl-b-
anosyl)-(13)-[(2,3,4,6-tetra-O-acetyl-b- -glucopyranosyl)-(14)]-
2-O-acetyl- -rhamnopyranoside 17
D-glucopyr-
D
a-L
To a solution of compound 16 (1 g, 3.2 mmol) in anhydrous
CH2Cl2 (20 mL) were added compound 7 (6 g, 12.17 mmol) and
MS 4 Å (2 g) and the reaction mixture was cooled to ꢀ10 °C under
4.1.8. 4-Methoxyphenyl (2-O-acetyl-4-O-benzyl-
anosyl)-(12)-(3,4-di-O-benzyl- -rhamnopyranosyl)-(13)-(2,4,6-
tri-O-benzyl-b- -galactopyranosyl)-(12)-3,4-di-O-benzyl-
rhamnopyranoside 15
a
-
L
-rhamnopyr-
argon. To the cooled reaction mixture was added TMSOTf (200 lL,
a-L
1.1 mmol) and allowed to stir at same temperature for 3 h. The
reaction mixture was quenched with Et3N (0.5 mL), filtered, and
washed with CH2Cl2 (150 mL). The organic layer was washed with
aq NaHCO3, water in succession, dried (Na2SO4), and concentrated.
The crude product was purified over SiO2 using hexane–EtOAc
(3:1) as eluant to give pure compound 17 (2 g, 64%); Oil;
D
a-L-
A solution of compound 14 (1.8 g, 1.17 mmol) in 0.1 M CH3ONa
in CH3OH (50 mL) was allowed to stir at room temperature for 3 h
and neutralized with Amberlite IR-120 (H+) resin. The reaction
mixture was filtered and evaporated to dryness. To a solution of
the crude product in anhydrous DMF (10 mL) were added
CH3C(OC2H5)3 (1 mL, 5.45 mmol) followed by p-TsOH (100 mg)
and the reaction mixture was allowed to stir at room temperature
for 2 h. The solvents were removed under vacuum and the result-
½
a 2D5
ꢁ
¼ ꢀ2:3 (c 1.0, CHCl3); IR (neat): 3020, 2357, 1759, 1721,
1650, 1368, 1220, 929, 739 cmꢀ1 1H NMR (300 MHz, CDCl3): d
;
6.95 (d, J = 9.0 Hz, 2H, Ar-H), 6.77 (d, J = 9.0 Hz, 2H, Ar-H), 5.36–
5.33 (m, 1H, H-2E), 5.24 (br s, 1H, H-1E), 5.16–4.99 (m, 5H, H-2F,
H-3F, H-4F, H-3G, H-4G), 4.92 (t, J = 8.0 Hz each, 1H, H-2G), 4.74

1796
G. Guchhait, A. K. Misra / Tetrahedron: Asymmetry 20 (2009) 1791–1797
(d, J = 7.7 Hz, 1H, H-1F), 4.69 (d, J = 8.0 Hz, 1H, H-1G), 4.28–4.12 (m,
4H, H-3E, H-6abF, H-6aG), 4.10–4.05 (dd, J = 12.0, 2.9 Hz, 1H, H-6bG),
3.80–3.77 (m, 2H, H-4E, H-5E), 3.75 (s, 3H, OCH3), 3.72–3.60 (m, 2H,
H-5F, H-5G), 2.21, 2.14, 2.11, 2.09, 2.04, 2.03, 2.02, 2.01, 1.98 (9 s,
27H, 9 COCH3), 1.23 (d, J = 6.1 Hz, 3H, CCH3); 13C NMR (75 MHz,
CDCl3): d 170.2, 170.1, 169.8, 169.7 (3C), 169.1, 169.0, 168.7
(9COCH3), 155.7–114.5 (Ar-C), 101.1 (C-1F), 99.2 (C-1G), 96.4 (C-
1E), 78.6 (C-3E), 75.1 (C-4E), 73.2 (C-3F), 72.7 (C-3G), 72.1 (C-2F),
72.0 (C-2G), 71.8 (2C, C-2E, C-5F), 71.4 (C-5G), 68.5 (C-4F), 67.9 (C-
4G), 67.3 (C-5E), 61.6 (C-6F), 61.5 (C-6G), 55.4 (OCH3), 21.1, 20.9,
20.7, 20.6, 20.5 (3 C), 20.4 (2C), 17.9 (CCH3). ESI-MS: 995.3
[M+Na]+; Anal. Calcd for C43H56O25 (972.31): C, 53.09; H, 5.80.
Found: C, 52.87; H, 5.68.
C-2G, C-5F), 71.9 (C-5G), 71.5 (3C, C-2E, C-3D, PhCH2), 71.2 (C-5C),
68.9 (2C, C-2D, C-6B), 68.6 (C-5A), 68.4 (C-4F), 68.1 (C-4G), 67.6
(C-2C), 67.3 (C-5E), 61.7 (C-6G), 61.0 (C-6F), 55.5 (OCH3), 21.0,
20.9, 20.7, 20.5 (3C), 20.4 (4C) (10COCH3), 18.1, 17.9, 17.7, 17.6
(4 CCH3); MALDI-TOF MS: 2358.0 [M+Na]+; Anal. Calcd for
C125H146O43 (2334.92): C, 64.26; H, 6.30. Found: C, 64.0; H, 6.50.
4.1.12. 4-Methoxyphenyl (sodium b-
(13)-[(sodium b- -glucopyranosyl uronate)-(14)]-
rhamnopyranosyl-(13)-( -rhamnopyranosyl)-(12)-(
-galactopyranosyl)-(12)-a-L-
D-glucopyranosyl uronate)-
D
a-L-
a
-L
a-L-
rhamnopyranosyl)-(13)-(b-
D
rhamnopyranoside 1
A solution of compound 19 (1.5 g, 0.64 mmol) in 0.1 M CH3ONa
in CH3OH (100 mL) was allowed to stir at room temperature for 5 h
and neutralized with Dowex-50W X8 (H+) resin. The reaction mix-
ture was filtered and concentrated under reduced pressure. To a
solution of the crude product in CH2Cl2 (30 mL) and H2O (7 mL)
were added aq solution of NaBr (2 mL; 1 M), aq solution of TBAB
(4 mL; 1 M), TEMPO (150 mg, 0.96 mmol), satd aq solution of NaH-
CO3 (15 mL), and 4% aq NaOCl (20 mL) in succession and the reac-
tion mixture was allowed to stir at 0–5 °C for 3 h. The reaction
mixture was neutralized with the addition of 1 M aq HCl solution.
To the reaction mixture were added tert-butanol (30 mL), 2-
methyl-but-2-ene (40 mL; 2 M solution in THF), aq solution of Na-
ClO2 (2 g in 10 mL), and aq solution of NaH2PO4 (2 g in 10 mL) and
the reaction mixture was allowed to stir at room temperature for
3 h. The reaction mixture was diluted with satd aq NaH2PO4 and
extracted with CH2Cl2 (200 mL). The organic layer was washed
with water, dried (Na2SO4), and concentrated to dryness. To a solu-
tion of the crude product in 90% aq CH3OH (20 mL) was added 20%
Pd(OH)2–C (200 mg) and the reaction mixture was allowed to stir
at room temperature under a positive pressure of hydrogen for
24 h. The reaction mixture was filtered through a CeliteÒ bed and
washed with CH3OH–H2O (60 mL; 5:1 v/v). The combined filtrate
was evaporated under reduced pressure to furnish compound 1,
which was purified through a Sephadex LH-20 column using
CH3OH–H2O (6:1) as eluant to give pure compound 1 (480 mg
4.1.11. 4-Methoxyphenyl (2,3,4,6-tetra-O-acetyl-b-
osyl)-(13)-[(2,3,4,6-tetra-O-acetyl-b- -glucopyranosyl)-(14)]-2-O-
acetyl- -rhamnopyranosyl-(13)-(2-O-acetyl-4-O-benzyl-
rhamnopyranosyl)-(12)-(3,4-di-O-benzyl- -rhamnopyranosyl)-
(13)-(2,4,6-tri-O-benzyl-b- -galactopyranosyl)-(12)-3,4-di-O-
benzyl- -rhamnopyranoside 19
D-glucopyran-
D
a-L
a-L-
a-L
D
a-L
To a solution of compound 17 (1.8 g, 1.85 mmol) in 80% aq
CH3CN (40 mL) was added ceric ammonium nitrate (CAN; 1.6 g,
2.92 mmol) and the reaction mixture was allowed to stir at room
temperature for 3 h. The reaction mixture was diluted with CH2Cl2
(100 mL) and the organic layer was washed with satd NaHCO3 and
water in succession, dried (Na2SO4), and concentrated. To a solu-
tion of crude hemiacetal derivative in anhydrous CH2Cl2 (20 mL)
were added CCl3CN (1.5 mL, 14.95 mmol) and DBU (120 lL,
0.82 mmol) at 0 °C and the reaction mixture was allowed to stir
at 0 °C for 4 h. The solvents were removed under reduced pressure
and the crude trichloroacetimidate derivative was purified over
SiO2 using hexane–EtOAc (6:1) as eluant to give pure compound
18 (1.3 g, 70%), which was used immediately in the next step. To
a solution of compound 15 (1.5 g, 1.0 mmol) in anhydrous CH2Cl2
(15 mL) were added MS 4 Å (1 g) and compound 18 (1.2 g,
1.2 mmol) and the reaction mixture was cooled to ꢀ10 °C under ar-
gon. To the cooled reaction mixture was injected TMSOTf (50 lL)
and it was allowed to stir at the same temperature for 3 h. The
reaction mixture was quenched with Et3N (0.5 mL), filtered, and
washed with CH2Cl2 (100 mL). The organic layer was washed with
satd NaHCO3 and water in succession, dried (Na2SO4), and concen-
trated under reduced pressure. The crude product was purified
over SiO2 using hexane–EtOAc (3:1) to give pure compound 19
(59%); white powder; ½a D25
ꢁ
¼ ꢀ64 (c 1.0, CH3OH); IR (KBr): 3020,
2362, 1754, 1721, 1216, 929, 760 cmꢀ1
;
1H NMR (300 MHz,
CH3OD–D2O): d 6.88 (d, J = 9.0 Hz, 2H, Ar-H), 6.74 (d, J = 9.0 Hz,
2H, Ar-H), 5.58 (br s, 1H, H-1A), 5.14 (br s, 1H, H-1C), 4.95 (br s,
1H, H-1E), 4.85 (br s, 1H, H-1D), 4.67 (d, J = 7.9 Hz, 1H, H-1G), 4.52
(d, J = 7.5 Hz, 1H, H-1F), 4.43 (d, J = 7.8Hz, 1H, H-1B), 4.18–4.17
(m, 1H, H-2E), 4.02 (dd, J = 9.3, 2.8 Hz, 1H, H-3E), 4.0–3.99 (m, 1H,
H-2A), 3.97–3.96 (m, 1H, H-2D), 3.91–3.90 (m, 1H, H-2C), 3.84–
3.74 (m, 5H, H-3A, H-3C, H-4B, H-5A, H-6aB), 3.70–3.66 (m, 4H, H-
3D, H-3F, H-5F, H-5G), 3.65 (s, 3H, OCH3), 3.64–3.56 (m, 6H, H-2B,
H-3B, H-4F, H-5B, H-5C, H-6bB), 3.52–4.46 (m, 2H,H-4E, H-5D), 3.40
(t, J = 9.5 Hz each, 1H, H-4C), 3.35 (t, J = 9.5 Hz, 1H, H-4D), 3.30–
3.16 (m, 5H, H-2F, H-3G, H-4G, H-4A, H-5E), 1.26–1.14 (m, 12H, 4
CCH3); 13C NMR (75 MHz, CDCl3): d 174.4, 174.3 (2COONa), 156.5
(Ar-C), 151.7 (Ar-C), 118.9 (2C, Ar-C), 115.6 (2C, Ar-C), 107.5 (C-
1B), 105.1 (C-1F), 104.3 (C-1G), 103.7 (C-1D), 103.4 (C-1E), 102.3
(C-1C), 99.7 (C-1A), 82.7 (C-3E), 82.2 (C-2A), 81.0 (C-4E), 79.5 (C-
2C), 79.3 (C-3D), 79.1 (C-5B), 78.5 (C-4F), 78.2 (C-5A), 77.8 (C-5E),
77.7 (C-3F), 76.7 (C-5D), 75.7 (C-5F), 75.4 (C-5G), 74.4 (C-4A), 74.3
(C-4D), 73.3 (C-4C), 72.7 (C-3G), 72.3 (C-2B), 72.0 (C-2F), 71.9 (2C,
C-2D, C-4B), 71.6 (C-2E), 71.2 (C-4G), 70.6 (C-2G), 70.4 (C-3B), 70.3
(C-5C), 70.0 (C-3C), 68.9 (C-3A), 62.9 (C-6B), 56.1 (OCH3), 18.4,
18.2, 18.0, 17.9 (4 CCH3); ESI-MS: 1267.0 [M]+; Anal. Calcd for
C49H72Na2O35: C, 46.45; H, 5.73. Found: C, 46.27; H, 5.98.
(1.6 g (68%); Oil; ½a D25
¼ þ3:2 (c 1.5, CHCl3); IR (neat): 3021,
ꢁ
2971, 2928, 2360, 1750, 1624, 1428, 1216, 1045, 928, 760 cmꢀ1
;
1H NMR (300 MHz, CDCl3): d 7.35–7.13 (m, 40H, Ar-H), 6.90 (d,
J = 9.0 Hz, 2H, Ar-H), 6.74 (d, J = 9.0 Hz, 2H, Ar-H), 5.51 (br s, 1H,
H-1A), 5.19–5.16 (m, 3H, H-1C, H-2D, PhCH2), 5.15–5.0 (m, 7H, H-
2F, H-3F, H-3G, PhCH2), 4.98 (br s, 1H, H-1E), 4.94 (t, J = 8.0 Hz,
1H, H-2G), 4.85–4.80 (m, 3H, H-4F, H-4G, PhCH2), 4.79 (br s, 1H,
H-1D), 4.73 (d, J = 7.7 Hz, 1H, H-1G), 4.71–4.64 (m, 6H, H-1B,
PhCH2), 4.59–4.50 (m, 3H, H-1F, H-2E, PhCH2), 4.46–4.30 (m, 4H,
PhCH2), 4.28–4.17 (m, 4H, H-2A, H-6abF, H-6aG), 4.15–4.09 (m, 2H,
H-2C, H-3E), 4.07–3.90 (m, 3H, H-3A, H-3D, H-6bG), 3.83–3.65 (m,
12H, H-2B, H-3B, H-4B, H-5A, H-5C, H-5D, H-5E, H-6abB, OCH3),
3.48–3.30 (m, 8H, H-3C, H-4A, H-4C, H-4D, H-4E, H-5B, H-5F, H-5G),
2.18, 2.13, 2.08, 2.07, 2.06, 2.03, 2.0, 1.99 (8 s, 30 H, 10 COCH3),
1.25–1.20 (m, 6H, 2CCH3), 1.17 (d, J = 6.1 Hz, 3H, CCH3), 1.10 (d,
J = 6.1 Hz, 3H, CCH3); 13C NMR (75 MHz, CDCl3): d 170.0, 169.9,
169.7, 169.6, 169.5, 169.4, 169.3 (2C), 169.2, 168.8 (10COCH3),
154.6–114.4 (Ar-C), 104.9 (C-1B), 100.6 (C-1F), 100.0 (C-1C), 98.8
(C-1G), 98.6 (C-1D), 98.4 (C-1E), 98.1 (C-1A), 80.3 (2C, C-3B, C-4A),
79.9 (C-3A), 79.6 (C-2B), 78.8 (C-4D), 78.4 (C-3E), 77.7 (C-4C), 77.2
(C-5D), 76.4 (C-3C), 76.2 (C-4E), 75.4 (C-4B), 75.2 (PhCH2), 75.0
(3C, C-3F, 2PhCH2), 74.8 (C-3G), 74.7 (PhCH2), 73.6 (PhCH2), 73.4
(2C, 2 PhCH2), 72.9 (C-2A), 72.6 (C-2F), 72.1 (PhCH2), 72.0 (2C,
Acknowledgments
G.G. thanks CSIR, New Delhi, for providing a Junior Research Fel-
lowship. This work was supported by Ramanna Fellowship (AKM),

G. Guchhait, A. K. Misra / Tetrahedron: Asymmetry 20 (2009) 1791–1797
1797
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