De novo asymmetric synthesis of rhamno di- and tri-saccharides related to the anthrax tetrasaccharide

Article abstract of DOI:10.1016/j.tet.2013.02.073

An asymmetric synthesis of the di- and tri-saccharide portion of the naturally occurring anthrax tetrasaccharide from acetylfuran has been developed. The construction of the di- and tri-saccharide subunits is based upon our previously disclosed route to a

Full text of DOI:10.1016/j.tet.2013.02.073

Tetrahedron 69 (2013) 3432e3436
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
De novo asymmetric synthesis of rhamno di- and tri-saccharides
related to the anthrax tetrasaccharide
,
,
b,
Hua-Yu Leo Wang a b, Haibing Guo a , George A. O’Doherty
*
*
a College of Nuclear Technology, Chemistry and Biology, Hubei University of Science and Technology, Xianning, Hubei 437100, China
b Department of Chemistry and Chemical Biology, Northeastern University, 360 Huntington Avenue, Boston, MA 02115, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
An asymmetric synthesis of the di- and tri-saccharide portion of the naturally occurring anthrax tetra-
saccharide from acetylfuran has been developed. The construction of the di- and tri-saccharide subunits
is based upon our previously disclosed route to anthrax tetrasaccharide. The approach uses iterative
diastereoselective palladium-catalyzed glycosylations, Luche reductions, diastereoselective dihydrox-
ylations, and regioselective protections for the assembly of the rhamno-di- and tri-saccharide. The route
Received 13 December 2012
Received in revised form 15 February 2013
Accepted 19 February 2013
Available online 26 February 2013
was also modified for the preparation of the mixed
D-/
L
-di-saccharide analogue.
Keywords:
Anthrax
Ó 2013 Elsevier Ltd. All rights reserved.
Oligo-rhamnose
Palladium glycosylation
1. Introduction
glycoprotein found on the exosporium of B. anthracis.8 The unusual
structure of anthrax tetrasaccharide 1 consists of unique tris- -tri-
saccharide portion terminated by a never before seen -amino-
sugar, called anthrose. These unique structural features in con-
junction with the general resistance to evolutionary change of
carbohydrates, have made the anthrax tetrasaccharide 1 an excel-
lent target for anthrax detection and in turn total synthesis.9,10
L
Until late 2001, when the unfortunate event of a powdery
sample of Bacillus anthracis was sent through the U.S. Postal Ser-
vice,1 most cultural references to Anthrax were to the American
thrash metal band from New York City. The band was formed in
1981 and named after the disease caused by B. anthracis.2 The
spore-forming B. anthracis is a Gram-positive bacterium, which
when inhaled causes anthrax, a fatal infectious disease in humans
and other mammals.3 The mature endospores exhibit remarkable
resistance to extremely harsh conditions, which allow the spores to
persist for many years,4 and make them ideal for use as biological
weapon.
D
While the origin of the weaponized material is still in dispute,
the effects of having it sent through the post in 2001 are clear. As
a result, 22 people were confirmed to be infected with B. anthracis
and only 7 survived.5 In fact, all the 7 survivors are believed to have
the more easily treated cutaneous form of anthrax. In response, to
the seriousness of the threat, there have been extensive efforts
aimed at the discovery of new inexpensive treatments (e.g., vac-
cines and antibacterials) for the disease,6 as well as, methods for
the detection of the B. anthracis spores (e.g., antibodies).7 As part of
the efforts to develop methods for detecting B. anthracis, the an-
thrax tetrasaccharide 1 (Fig. 1) was isolated from BclA, a surface
* Corresponding authors. Tel.: þ1 6173734817; e-mail addresses: haibingguojj@
yahoo.com (H. Guo), g.odoherty@neu.edu, gaodoherty@gmail.com (G.A. O’Doherty).
Fig. 1. Anthrax tetrasaccharide and its tri- and di-saccharide fragments.
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.02.073

H.-Y.L. Wang et al. / Tetrahedron 69 (2013) 3432e3436
3433
Since its discovery of anthrax tetrasaccharide 1 in 2004, there
have been several syntheses of analogues of 1 with various alkyl
groups at the reducing end.11 The addition of functional groups at
the anomeric position was made to give the anthrax tetra-
saccharide a chemical handle for further conjugation and sub-
sequent manipulations (e.g., antibody/vaccine development). In
addition to analogue material with a chemical handle, our de novo
approach to the anthrax tetrasaccharide 1 was the only route to
prepare synthetic material identical to the isolated natural prod-
uct.10 Our synthetic 1 was prepared as part of a broad search aimed
at the development of a method for the selective detection of 1 and
thus anthrax.7 To address concern that these methods might focus
on the more common tris-rhamnose portion of the molecule, we
needed control compounds consisting of the rhamno-di- and tri-
(
a
:
b
¼4:1).15 It is worth noting that this route provides Boc-
pyranones in 60% overall yield (three steps) with only one chro-
matographic purificationandthis route is also scalableforboth
-enantiomers.
L- and
D
saccharide structural motif. Thus, we targeted the all
L-tri-saccha-
Scheme 2. Preparation of tert-butyl-Boc pyranone sugar donors.
ride 2 and the all -di-saccharide 3 as well as the mixed D/L
L
-di-
saccharide 4 for synthesis using our previously described approach
to anthrax tetrasaccharide 1.10 Herein, we describe our successful
efforts toward the de novo asymmetric synthesis of anthrax-based
rhamno-oligosaccharides 2, 3, and 4 (Fig. 1). This de novo asym-
metric strategy features iterative use of palladium-catalyzed gly-
Using our previously described route to anthrax tetrasaccharide
1, we prepared the desired protected known precursors 5, 6, and 7
(Scheme 3).10 In brief, monosaccharide 7 with the free C-2 hydroxyl
group can be glycosylated with Boc-pyranone
a-L-8 and in two
post-glycosylation transformations (NaBH4/CeCl3 then OsO4/NMO)
converted into di-saccharide 6.16 The conversion of di-saccharide 6
into tri-saccharide 5 began with the selective protection of the C-2/
C-4 hydroxyls via a one-pot orthoester/acylation/hydrolysis pro-
cedure to give 12. Once again, a three-step palladium-catalyzed
glycosylation/post-glycosylation sequence was used to install the
final rhamnose sugar in tri-saccharide 5 with excellent yield and
diastereoselectivity.
cosylation and starts from
a commercially available and
inexpensive acetylfuran.12
Our de novo approach to anthrax oligosaccharides 2e4 is out-
lined in Scheme 1. Based on our previous route to 1, we envisioned
access the unique rhamno-oligosaccharide scaffold in both anthrax
tri-saccharide analogue 2 and di-saccharide analogues 3 and 4 from
the protected intermediates 5e7. These precursors, in turn, could
be prepared in a highly divergent manner from a glycosylation of
Ley-spiroketal di-saccharide 7 with pyranone 8 or (ent)-8. The rapid
assembly of the desired rhamno sugar relies on the iterative use of
palladium-catalyzed glycosylation, Luche reduction, and Upjohn
dihydroxylation. The required pyranone sugar donor in both
D- and
L-configuration could be obtained from the achiral starting material
acetylfuran 9 through asymmetric Noyori reduction and Achma-
towicz oxidative ring expansion.
Scheme 1. Retrosynthetic approach to anthrax saccharides 1e4.
Scheme 3. Previously reported approach to oligosaccharides 5, 6, and 7.
2. Results/discussion
The preparation of the unknown
astereomer 4 the anthrax di-saccharide analogue 3 began with the
common Ley-protected rhamnose intermediate 7. In di-
LeD-di-saccharide di-
Our approach to the monosaccharide building block began with
our efforts to selectively introduce the D- or L-stereochemistry of the
a
astereomeric fashion, the C-2 hydroxyl in 7 was glycosylated with
Boc-pyranone (ent)-8 to give 14 in a nearly identical yield (85%) for
the palladium-catalyzed glycosylation (Scheme 4). Similarly, the
resulting enone in LeD-di-saccharide 14 was reduced to give 15
(90%) and dihydroxylated to give 16 (93%), in excellent yield and
rhamnose, which could be derived from the furyl alcohol (R)-10 or
(S)-10. Previously we have shown that either (R) or (S)-furyl alcohol
could be readily prepared by an asymmetric Noyori reduction of
commercially available starting material acetylfuran 9 (Scheme 2).13
Noyori reduction of acetylfuran 9 produced the enantiomerically
pure (>96%ee)14 furfuryl alcohol (R)-10 or (S)-10, whichwas exposed
in the subsequent Achmatowicz oxidative rearrangement (NBS/H2O)
stereoselectivity. Thus in a diastereomerically divergent fashion,
the Ley-protected -rhamnose 7 can be glycosylated in a three-step
L
sequence to install either a
tical yields.
D- or L-rhamnose sugar in nearly iden-
and tert-butoxyl-carbonylation to give the desired Boc-pyranone
a-
D
-(ent)-8 or -8 with good -anomeric diastereoselectivity
a
-
L
a

3434
H.-Y.L. Wang et al. / Tetrahedron 69 (2013) 3432e3436
utilities of Noyori reduction, palladium-catalyzed glycosylation,
diastereoselective dihydroxylation, Luche reduction, and selective
acylation. Further use of these substrates for the screening of col-
orimetric assays for anthrax detection is ongoing and will be re-
ported in due course.
4. Experimental section
4.1. (2R,6S)-6-(((2R,3R,4aS,5S,7R,8R,8aR)-7-(Benzyloxy)-2,3-
dimethoxy-2,3,5-trimethylhexahydro-2H-pyrano[3,4b]-[1,4]-
dioxin-8-yl)oxy)-2-methyl-2H-pyran-3(6H)-one (14)
To a solution of Boc-pyranone (ent)-8 (846.6 mg, 3.713 mmol)
and Ley-spiroketal rhamnose 7 (171 mg, 0.464 mmol) in dry CH2Cl2
(0.9 mL) was added a solution of Pd2(dba)3$CHCl3 (12.01 mg,
0.012 mmol) and PPh3 (12.2 mg, 0.046 mmol) in 1.0 mL CH2Cl2 at
Scheme 4. Synthesis of LeD-di-saccharide anthrax precursor.
Finally, all the desired anthrax di- and tri-saccharide analogues
2, 3, and 4 were obtained after a two- or three-step deprotection
0
ꢀC. The reaction mixture was stirred at 0 ꢀC under argon gas for
4 h. The reaction mixture was quenched with 10 mL of saturated
NaHCO3 solution, followed by extraction with Et2O (10 mLꢁ3). The
organic layer was washed with 15 mL saturated brine solution,
dried over with Na2SO4, and concentrated under reduced pressure.
The compound was purified using flash chromatography eluting
sequence. Simply treating D/L-diastereomers 6 and 16 to aqueous
TFA gave di-saccharides 17 and 18, respectively. The desired fully
deprotected diastereomeric di-saccharides 3 and 4 were obtained
by hydrogenolysis (1 atm H2, Pd/C) in excellent yields (85 and 88%
over two steps). The deprotection of tri-saccharide 5 was slightly
more complicated due to concomitant acetate partial hydrolysis
and migration. Thus, the crude product from exposure of 5 to
aqueous TFA was immediately followed by the treatment with basic
methanol and hydrogenolysis to give tri-saccharide 2 in excellent
overall yield (81%) (Scheme 5).
with 25% EtOAc in hexanes to give the title compound 14 (188 mg,
25
0.39 mmol, 85%); a yellow oil; Rf 0.50 (30% EtOAc/hexanes); [a]
D
ꢂ138 (c 1.0, CH2Cl2); IR (thin film, cmꢂ1) 2995, 2940, 2909, 2836,
1698, 1459, 1374, 1114, 1035, 968; 1H NMR (600 MHz, CDCl3)
d
7.34e7.26 (m, 5H), 6.79 (dd, J¼10.2, 3.6 Hz, 1H), 6.03 (d, J¼10.2 Hz,
1H), 5.12 (d, J¼3.6 Hz, 1H), 5.02 (q, J¼6.6 Hz, 1H), 4.78 (d, J¼0.6 Hz,
1H), 4.68 (d, J¼12 Hz, 1H), 4.49 (d, J¼12 Hz, 1H), 4.06 (dd, J¼3.6,
1.8 Hz, 1H), 4.04 (dd, J¼10.2, 3.6 Hz, 1H), 3.82 (dq, J¼10.2, 6.6 Hz,
1H), 3.64 (dd, J¼10.2, 10.2 Hz, 1H), 3.25 (s, 3H), 3.17 (s, 3H), 1.31 (d,
J¼6.6 Hz, 3H), 1.24 (d, J¼6.0 Hz, 3H), 1.24 (s, 3H), 1.22 (s, 3H); 13C
NMR (150 MHz, CDCl3)
d 198.3, 143.3, 137.3, 128.6 (2C), 128.2 (2C),
128.1, 127.8, 100.0, 99.7, 98.3, 92.8, 75.2, 70.8, 69.3, 68.8, 67.5, 67.4,
48.1, 47.8, 18.0, 17.9, 16.8, 15.3; HRMS (CI): calcd for [C25H34O9Naþ]:
501.20950, found: 501.20966.
4.2. (2R,3S,6R)-6-(((2R,3R,4aS,5S,7R,8R,8aR)-7-(Benzyloxy)-
2,3-dimethoxy-2,3,5-trimethylhexahydro-2H-pyrano[3,4b]-
[1,4]-dioxin-8-yl)oxy)-2-methyl-3,6-dihydro-2H-pyran-3-ol
(15)
A solution of di-saccharide pyranone 14 (48 mg, 0.100 mmol) in
dry CH2Cl2 (0.1 mL) and 0.4 M CeCl3/MeOH (0.1 mL) was cooled to
ꢂ78 ꢀC. NaBH4 (5 mg, 0.120 mmol) was added and the reaction
mixture was stirred for 2 h. The reaction mixture was then diluted
with Et2O (5 mL) and quenched with saturated solution of NaHCO3
(2 mL), then extracted with Et2O (5 mLꢁ3). The organic layer was
dried over with Na2SO4, concentrated under reduced pressure, and
purified using flash chromatography with 35% EtOAc in hexanes
elution to give the title compound 15 (43 mg, 0.09 mmol, 90%);
Scheme 5. Preparation of anthrax saccharides 1e4.
colorless oil; Rf 0.29 (40% EtOAc/hexanes); [
a
]
D
25 ꢂ92 (c 1.0, CH2Cl2);
IR (thin film, cmꢂ1) 3454, 2983, 2940, 2936, 2902, 2836, 1454, 1378,
3. Conclusion
1138, 1118, 1040, 999, 734; 1H NMR (600 MHz, CDCl3)
d 7.33e7.25
(m, 5H), 5.92 (d, J¼10.2 Hz, 1H), 5.74 (ddd, J¼10.2, 2.4, 1.8 Hz, 1H),
4.87 (d, J¼2.4 Hz, 1H), 4.75 (s, 1H), 4.67 (d, J¼12.0 Hz, 1H), 4.57 (d,
J¼12.0 Hz, 1H), 4.04 (dd, J¼3.6, 1.8 Hz, 1H), 4.02 (dq, J¼9.0, 6.0 Hz,
1H), 3.99 (dd, J¼10.2, 3.6 Hz, 1H), 3.80 (dq, J¼10.2, 6.0 Hz, 1H), 3.63
(dd, J¼10.2, 9.6 Hz, 1H), 3.25 (s, 3H), 3.21 (s, 3H), 1.26 (d, J¼6.0 Hz,
3H), 1.26 (s, 3H), 1.25 (s, 3H), 1.24 (d, J¼6.0 Hz, 3H); 13C NMR
In conclusion, a highly enantio- and diastereo-controlled ap-
proach to the anthrax analogues has been developed in a divergent
manner using a Ley-protected rhamno-monosaccharide 7 as the
common intermediate for the assembly of rhamno-di- and tri-
saccharides (i.e., 2 and 3) and the incorporation of
DeL-bis-
rhamno-di-saccharide diastereomer (i.e., 4). The feasibility of this
was evident in that both the di- and tri-saccharide fragments were
readily assembled from achiral starting materials by use of asym-
metric catalysis. This de novo asymmetric route illustrates the
(150 MHz, CDCl3) d 137.5, 133.9, 128.6 (2C), 128.2 (2C), 128.0, 126.8,
100.0, 99.8, 98.3, 93.1, 73.7, 70.1, 69.3, 68.9, 68.1, 67.2, 67.1, 48.0, 47.9,
18.3, 18.1, 17.9, 16.9; HRMS(CI): calcd for [C25H36O9Naþ]: 503.22515,
found: 503.22531.

H.-Y.L. Wang et al. / Tetrahedron 69 (2013) 3432e3436
3435
4.3. (2R,3S,4S,5S,6R)-2-(((2R,3R,4aS,5S,7R,8R,8aR)-7-(Benzy-
loxy)-2,3-dimethoxy-2,3,5-trimethylhexahydro-2H-pyrano-
[3,4-b]-[1,4]dioxin-8-yl)oxy)-6-methyltetrahydro-2H-pyran-
3,4,5-triol (16)
J¼3.6,1.8 Hz,1H), 3.81 (dd, J¼9.6, 3.6 Hz,1H), 3.80 (dq, J¼9.6, 6.0 Hz,
1H), 3.75 (dd, J¼9.6, 3.6 Hz, 1H), 3.38 (dd, J¼9.6, 9.6 Hz, 1H), 3.32
(dd, J¼9.0, 9.0 Hz, 1H), 1.25 (d, J¼6.0 Hz, 3H), 1.24 (d, J¼6.0 Hz, 3H);
13C NMR (150 MHz, CD3OD)
d 100.1, 92.7, 77.8, 74.6, 74.2, 72.6, 72.3,
71.4, 70.3, 69.8, 18.4, 18.1; HRMS (CI): calcd for [C12H22O9Naþ]:
333.11560, found: 333.11566.
To a solution of allylic alcohol 15 (30 mg, 0.063 mmol) in tert-
butanol/acetone (125
lution of N-methylmorpholine-N-oxide/water (50% w/v, 65
m
L, 1:1 (v/v), 0.5 M) at 0 ꢀC was added a so-
m
L,1 M).
4.6. (3R,4R,5R,6S)-6-Methyl-3-(((2S,3R,4R,5R,6S)-3,4,5-
trihydroxy-6-methyltetrahydro-2H-pyran-2-yl)oxy)-tetrahy-
dro-2H-pyran-2,4,5-triol (3)
Crystalline OsO4 (0.16 mg, 1 mol %) was added and the reaction
mixture was stirred for 12 h at 0 ꢀC. The reaction mixture was then
quenched with 500
mL of saturated Na2S2O3 solution, extracted
with EtOAc (5ꢁ2 mL), and dried over with Na2SO4 and concen-
trated under reduced pressure. The compound was purified by flash
chromatography eluting with 85% EtOAc in hexanes to give the title
compound 16 (29.9 mg, 0.058 mmol, 93%); colorless oil; Rf 0.56
To a solution of di-saccharide 6 (26 mg, 0.05 mmol) in CH2Cl2
(0.5 mL), was added the 0.1 mL of 10:1 TFA/H2O. The reaction
mixture was stirred at room temperature for 40 min. The reaction
mixture was quenched with saturated 5 mL NaHCO3 solution, dried
over with Na2SO4, and concentrated to remove water and solvent
under reduced pressure. The crude compound was purified by
passing through a pad of silica gel eluting with 10% MeOH in EtOAc
to give the benzyl di-saccharide 17; To a solution of the benzyl di-
saccharide 17 in 0.5 mL MeOH was added 10% Pd/C (100 mg). The
reaction suspension was degassed and replaced atmosphere with
hydrogen gas three times. The reaction suspension was stirred with
hydrogen balloon for 24 h, filtered by passing through a pad of
Celite, concentrated under reduced pressure and under vacuo to
give the title compound 3 (13 mg, 0.043 mmol, 85%); viscous oil; Rf
(10% MeOH in EtOAc); [
a]
25 ꢂ50 (c 1.0, CH2Cl2); IR (thin film, cmꢂ1
)
D
3304, 2938, 2775, 2100, 1128, 1050; 1H NMR (600 MHz, CDCl3)
d
7.35e7.25 (m, 5H), 4.75 (d, J¼0.6 Hz, 1H), 4.74 (d, J¼1.2 Hz, 1H),
4.67 (d, J¼12.0 Hz, 1H), 4.47 (d, J¼12.0 Hz, 1H), 4.26 (dq, J¼9.6,
6.0 Hz, 1H), 3.99 (dd, J¼10.2, 3.0 Hz, 1H), 3.96 (m, 1H), 3.95 (dd,
J¼3.6, 1.8 Hz, 1H), 3.81 (dq, J¼9.6, 6.0 Hz, 1H), 3.64 (dd, J¼10.2,
10.2 Hz, 1H), 3.40 (dd, J¼9.6, 9.6 Hz, 1H), 3.23 (s, 3H), 3.22 (s, 3H),
1.25 (s, 3H), 1.24 (d, J¼6.0 Hz, 3H), 1.24 (s, 3H), 1.24 (d, J¼6.0 Hz, 3H);
13C NMR (150 MHz, CDCl3)
d 137.4,128.7 (2C),128.2 (2C),128.1, 99.9,
99.7, 98.5, 97.7, 74.00, 73.95, 72.2, 71.3, 69.4, 68.8, 68.0, 67.5, 67.1,
48.2, 47.9, 18.0, 17.9, 17.5, 16.9; HRMS (CI): calcd for [C25H38O11Naþ]:
537.23063, found: 537.23074.
0.31 (20% methanol in EtOAc); [
a
]
25 ꢂ20 (c 1.0, MeOH); IR (thin film,
D
cmꢂ1) 3351, 2981, 2935, 1645, 1055, 1032; 1H NMR (600 MHz,
CD3OD)
d
5.20 (d, J¼1.8 Hz, 1H), 4.98 (d, J¼1.8 Hz, 1H), 3.89 (dd,
4.4. (2R,3S,4S,5S,6R)-2-(((2R,3R,4R,5R,6S)-2-(Benzyloxy)-4,5-
dihydroxy-6-methyltetrahydro-2H-pyran-3-yl)oxy)-6-
methyltetrahydro-2H-pyran-3,4,5-triol (18)
J¼9.6, 3.6 Hz,1H), 3.85 (dq, J¼9.6, 6.0 Hz,1H), 3.84 (dd, J¼3.6,1.8 Hz,
2H), 3.78 (dq, J¼9.6, 6.0 Hz, 1H), 3.75 (dd, J¼9.6, 3.6 Hz, 1H), 3.44
(dd, J¼9.6, 9.6 Hz, 1H), 3.39 (dd, J¼9.6, 9.6 Hz, 1H), 1.31 (d, J¼6.0 Hz,
3H), 1.29 (d, J¼6.0 Hz, 3H); 13C NMR (150 MHz, CD3OD)
d 104.2,
To a solution of di-saccharide 16 (19.3 mg, 0.0375 mmol) in
CH2Cl2 (375 mL) was added 75 mL of TFA/H2O (10:1). The reaction
94.6, 81.2, 74.7, 74.1, 72.4, 72.2, 71.9, 70.3, 69.5,18.4,18.0; HRMS (CI):
calcd for [C12H22O9Naþ]: 333.11560, found: 333.11568.
mixture was stirred at room temperature for 4 h. The reaction
mixture was then quenched with saturated NaHCO3 solution
(3.0 mL), dried over with Na2SO4 and concentrated under reduced
pressure. The crude product was purified by flash chromatography
eluting with 8% MeOH in EtOAc to give the title compound 18
4.7. (3R,4R,5R,6S)-3-(((2S,3R,4R,5S,6S)-3,5-Dihydroxy-6-
methyl-4-(((2S,3R,4R,5R,6S)-3,4,5-trihydroxy-6-
methyltetrahydro-2H-pyran-2-yl)oxy)-tetrahydro-2H-pyran-
2-yl)oxy)-6-methyltetrahydro-2H-pyran-2,4,5-triol (2)
(14.7 mg, 0.0367 mmol, 98%); colorless oil; Rf 0.48 (20% MeOH in
25
EtOAc); [
a
]
þ5.0 (c 1.0, MeOH); IR (thin film, cmꢂ1) 3372, 2071,
To a solution of tri-saccharide 5 (42 mg, 0.05 mmol) in CH2Cl2
(0.5 mL) was added 0.1 mL of 10:1 TFA/H2O. The reaction mixture
was stirred at room temperature for 40 min. The reaction mixture
was quenched with saturated 5 mL of NaHCO3 solution, dried over
with Na2SO4, and concentrated to remove water and solvent under
reduced pressure. The crude compound was purified by passing
through a pad of silica gel eluting with 10% MeOH in EtOAc to give
diacetate; to the solution of the subsequent diacetate in MeOH
(0.2 mL) was added LiOH (9.6 mg, 0.4 mmol) and stirred for 5 h. The
reaction mixture was concentrated under reduced pressure and
purified by passing through a pad of silica gel eluting with 15%
MeOH in EtOAc to give the benzyl tri-saccharide 19; the resulting
benzyl tri-saccharide 19 was dissolved in 0.5 mL MeOH and added
10% Pd/C (100 mg). The reaction suspension was degassed and
replaced atmosphere with hydrogen gas for three times. The re-
action suspension was stirred under the hydrogen balloon for 24 h,
filtered by passing through a pad of Celite, concentrated under
reduced pressure and under vacuo to give the title compound 2
D
1508, 1334, 1120, 973, 786; 1H NMR (600 MHz, CD3OD)
d 7.35e7.28
(m, 5H), 4.87 (d, J¼1.8 Hz, 1H), 4.74 (d, J¼1.8 Hz, 1H), 4.70 (d,
J¼12.0 Hz, 1H), 4.54 (d, J¼12.0 Hz, 1H), 3.98 (dq, J¼9.6, 6.0 Hz, 1H),
3.92 (dd, J¼3.6, 1.8 Hz, 1H), 3.81 (dd, J¼3.6, 1.8 Hz, 1H), 3.79 (dd,
J¼9.6, 3.6 Hz, 1H), 3.74 (dd, J¼9.6, 3.0 Hz, 1H), 3.62 (dq, J¼9.0,
6.0 Hz, 1H), 3.37 (dd, J¼9.6, 9.6 Hz, 1H), 3.35 (dd, J¼9.6, 9.6 Hz, 1H),
1.25 (d, J¼6.6 Hz, 3H), 1.24 (d, J¼6.6 Hz, 3H); 13C NMR (150 MHz,
CD3OD)
d 139.1, 129.6 (2C), 129.2 (2C), 129.0, 100.1, 97.9, 76.9, 74.3,
74.1, 72.6, 72.3, 71.7, 70.5, 70.4, 70.3, 18.2, 18.0; HRMS(CI): calcd for
[C19H28O9þNaþ]: 423.16255, found: 423.16269.
4.5. (3R,4R,5R,6S)-6-Methyl-3-(((2R,3S,4S,5S,6R)-3,4,5-
trihydroxy-6-methyltetrahydro-2H-pyran-2-yl)oxy)-tetrahy-
dro-2H-pyran-2,4,5-triol (4)
To a solution of benzyl di-saccharide 18 (11.4 mg, 0.030 mmol) in
MeOH (0.1 mL) was added 10% Pd/C (60 mg). The reaction sus-
pension was degassed and replaced atmosphere with hydrogen gas
three times. The reaction mixture was stirred for 24 h and filtered
through a pad of Celite. The solute was concentrated under reduced
pressure to give the title compound 4 (8.2 mg, 0.026 mmol, 90%);
(18.5 mg, 0.041 mmol, 81%); viscous oil; Rf 0.19 (20% MeOH in
25
EtOAc); [
a
]
D
ꢂ82 (c 1.2, MeOH); IR (thin film, cmꢂ1) 3356, 2981,
2934, 1572, 1416, 1059, 986; 1H NMR (600 MHz, CD3OD)
d 5.18 (d,
J¼1.8 Hz, 1H), 5.10 (d, J¼1.8 Hz, 1H), 4.98 (d, J¼1.8 Hz, 1H), 4.12 (dd,
J¼3.6, 1.8 Hz, 1H), 4.03 (dd, J¼3.6, 1.8 Hz, 1H), 3.86 (m, 7H), 3.57 (dd,
J¼9.6, 9.6 Hz, 1H), 3.45 (dd, J¼9.6, 9.6 Hz, 1H), 3.43 (dd, J¼9.6,
9.6 Hz, 1H), 1.35 (d, J¼6.0 Hz, 3H), 1.31 (d, J¼6.0 Hz, 3H), 1.29 (d,
viscous oil; Rf 0.52 (40% MeOH in EtOAc); [
a]
25 þ16 (c 1.0, MeOH); IR
D
(thin film, cmꢂ1) 3375, 2991, 2942, 1570, 1145, 995; 1H NMR
(600 MHz, CD3OD)
3.98 (dq, J¼9.6, 6.0 Hz, 1H), 3.86 (dd, J¼3.0, 1.8 Hz, 1H), 3.83 (dd,
d
5.10 (d, J¼1.8 Hz, 1H), 4.79 (d, J¼1.2 Hz, 1H),
J¼6.0 Hz, 3H); 13C NMR (150 MHz, CD3OD)
d 104.0(2C), 94.7, 80.9,

3436
H.-Y.L. Wang et al. / Tetrahedron 69 (2013) 3432e3436
8. Daubenspeck, J. M.; Zeng, H.; Chen, P.; Dong, S.; Steichen, C. T.; Krishna, N. R.;
Pritchard, D. G.; Turnbough, C. L., Jr. J. Biol. Chem. 2004, 279, 30945e30953.
9. (a) Werz, D. B.; Seeberger, P. H. Angew. Chem., Int. Ed. 2005, 44, 6315e6318; (b)
Adamo, R.; Saksena, R.; Kovac, P. Carbohydr. Res. 2005, 340, 2579e2582; (c)
Saksena, R.; Adamo, R.; Kovac, P. Bioorg. Med. Chem. Lett. 2006, 16, 615e617; (d)
Adamo, R.; Saksena, R.; Kovac, P. Helv. Chim. Acta 2006, 89, 1075e1089; (e)
Mehta, A. S.; Saile, E.; Zhong, W.; Buskas, T.; Carlson, R.; Kannenberg, E.; Reed,
Y.; Quinn, C. P.; Boons, G. J. Chem.dEur. J. 2006, 12, 9136e9149; (f) Crich, D.;
Vinogradova, O. J. Org. Chem. 2007, 72, 6513e6520; (g) Werz, D. B.; Adibekian,
A.; Seeberger, P. H. Eur. J. Org. Chem. 2007, 1976e1982.
79.4, 74.7, 74.3, 73.5, 72.4, 72.3, 72.0(2C), 70.6, 70.3, 69.5, 18.4, 18.1,
18.0; HRMS (CI): calcd for [C18H32O13Naþ]: 479.17351, found:
479.17367.
Acknowledgements
We are grateful to NIH (GM090259), NSF (CHE-1213596), and
National Nature Science Foundation of China (21202136) for the
support of our research programs.
10. (a) Guo, H.; O’Doherty, G. A. Angew. Chem., Int. Ed. 2007, 46, 5206e5208; (b)
Guo, H.; O’Doherty, G. A. J. Org. Chem. 2008, 73, 5211e5220.
11. Several approaches to related tri- and penta-saccharides, see: (a) Saksena, R.;
Adamo, R.; Kovac, P. Bioorg. Med. Chem. 2007, 15, 4283e4310; (b) Wang, Y.;
Liang, X.; Wang, P. Tetrahedron Lett. 2011, 52, 3912e3915; (c) Tamborrini, M.;
Bauer, M.; Bolz, M.; Maho, A.; Oberli, M. A.; Werz, D. B.; Schelling, E.; Jakob, Z.;
Seeberger, P. H.; Frey, J.; Pluschke, G. J. Bacteriol. 2011, 193, 3506e3511; (d)
Milhomme, O.; Dhenin, S. G. Y.; Djedaini-Pilard, F.; Moreau, V.; Grandjean, C.
Carbohydr. Res. 2012, 356, 115e131.
12. (a) Babu, R. S.; O’Doherty, G. A. J. Carbohydr. Chem. 2005, 24, 169e177; (b) Zhou,
M.; O’Doherty, G. A. Org. Lett. 2006, 8, 4339e4342; (c) Zhou, M.; O’Doherty, G.
A. Org. Lett. 2008, 10, 2283e2286; (d) Yu, X.; O’Doherty, G. A. Org. Lett. 2008, 10,
4529e4532; (e) Yu, X.; Li, M.; O’Doherty, G. A. Heterocycles 2011, 82,
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Supplementary data
Copies of the spectral data 1H NMR and 13C NMR for all the new
compounds can be found in the Supplementary data. Supplemen-
tary data related to this article can be found at http://dx.doi.org/
10.1016/j.tet.2013.02.073.
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