Stereoselective synthesis of a sulfated tetrasaccharide corresponding to a rare sequence in the galactofucan isolated from Sargassum polycystum

Article abstract of DOI:10.1021/jo500503r

The first chemical synthesis of a highly sulfated tetrasaccharide 1, as the rare sequence in the galactofucan isolated from the brown alga Sargassum polycystum, was achieved in a convergent and stereoselective manner. The key features of the synthetic str

Full text of DOI:10.1021/jo500503r

Note
pubs.acs.org/joc
Stereoselective Synthesis of a Sulfated Tetrasaccharide
Corresponding to a Rare Sequence in the Galactofucan Isolated from
Sargassum polycystum
Jun Zhou, Liping Yang, and Wenhao Hu*
Shanghai Engineering Research Centre of Molecular Therapeutics and New Drug Development, and Department of Chemistry, East
China Normal University, Shanghai, 200062, PR China
S
* Supporting Information
ABSTRACT: The first chemical synthesis of a highly sulfated
tetrasaccharide 1, as the rare sequence in the galactofucan
isolated from the brown alga Sargassum polycystum, was
achieved in a convergent and stereoselective manner. The key
features of the synthetic strategy include construction of
multiple contiguous 1,2-cis glycosidic bonds and [2 + 2]
assembly based on the rationally developed D-galactose
building block 6. The synthesized oligosaccharides were fully
characterized using a combination of coupled-HSQC and
other 2D NMR techniques.
which would enable the investigation of structure−activity
ucoidans, a family of complex sulfated polysaccharides
Fextracted from brown algae, have been reported to exhibit relationship and potential application to new drug discovery.
various physiological and biological functions1 such as
Several sulfated fucoidan homo-oligosaccharides have been
chemically synthesized5 and showed antitumor activity.
anticoagulant, antithrombotic, anti-inflammatory, antiviral, and
However, such a unique type of sulfated galactofucan
oligosaccharide containing 2-linked α-D-Galp unit, as reported
by Usov, has not been synthesized yet. Herein, we report the
first chemical synthesis of a highly sulfated tetrasaccharide 1
corresponding to the rare sequence in the galactofucan isolated
from the brown alga Sargassum polycystum.
antitumor activities. These polysaccharides have a common
backbone2 built up of sulfated α-L-fucopyranose (Fucp)
residues with (1 → 3)- or (1 → 4)-linkages. Nevertheless,
depending on the algal species, crude fucoidan extracts may
contain minor heteropolysaccharide3 components with a variety
of sugar residues and different linkages. Recently, from brown
alga Sargassum polycystum, Usov4 and co-workers isolated a
novel galactofucan, in which sequences of 3-linked 4-O-sulfated
α-L-Fucp residues are interspersed by discontinuous 2-linked 4-
O-sulfated α-D-galactopyranose (Galp) residue as a distinctive
structural feature (Figure 1). It is an unusual naturally occurring
[ → 2)-α-D-Galp-(1 → ] unit in the seaweed resource and
should have influence on conformation and biological activities.
Chemical synthesis is currently an efficient approach to
obtain pure fucoidan oligosaccharides with specific structures,
Sulfated tetrasaccharide 1, which contains four contiguous
1,2-cis glycosidic6 linkages (Figure 2), presents several
significant synthetic challenges. The most prominent one is
the stereoselective construction of the [ → 2)-α-D-Galp-(1 → ]
backbone with a highly crowded 1,2-cis orientation of two sugar
moieties. In this respect, the potent steric effect between the
reducing end α-L-fucp residue and the fuco-disaccharide moiety,
oriented in a 1,2-cis configuration, requires much more
attention in convergent synthesis. Moreover, highly selective
α-galactosidic7 and α-fucosidic8 bond formation without
generating inseparable anomeric mixtures is regarded to be
challenging in assembly of oligosaccharide. In addition, as in
heparin9 oligosaccharide synthesis, differentiation of hydroxyl
groups that would remain free, undergo elongation, or be
sulfated is to rely on orthogonality10 of protecting groups.
As for the construction of (1 → 2)-linked α-D-galactoside
unit in nonterminal part of oligosaccharide chain, only a few
successful examples have been reported, despite different
plausible retrosynthetic disconnections. The use of a type of
galactosyl donor,11 carrying a glycosylated hydroxyl at C-2
Figure 1. Structure of the rare sequence in the galactofucan isolated
from the brown alga Sargassum polycystum.
Received: March 3, 2014
Published: April 25, 2014
© 2014 American Chemical Society
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Note
hydroxyls to be sulfated were masked as benzoyl (Bz) or acetyl
(Ac) esters, and benzyl (Bn) ethers were employed to block
those that would be free in the target. As described above, 4-O-
Ac and 2-O-PMB of 6 were installed to possess corresponding
functions. Capping the reducing end with p-methoxyphenyl
(PMP) group14 enables easy cleavage and further conjugate
preparation if necessary.
The synthesis of fucosyl imidate donor 8 is outlined in
Scheme 1. The known β-thiofucoside 10,15 acquired from L-
a
Scheme 1. Synthesis of Imidate Donor 8
Figure 2. Synthetic plan of the target tetrasaccharide 1.
a
position, led principally to an undesired 1,2-trans outcome in
glycosylations. From a stereochemical viewpoint, the bulky 2-
O-glycosyl moiety of the donor sterically hinders incoming
acceptor from the α-face, thereby affording a β-linked
galactoside or an anomeric mixture. In contrast, 2-OH α-
galactoside derivatives12 have been reported to serve as
appropriate acceptors mainly for L-rhamnosylations. However,
in order to glycosylate the sterically congested C-2 alcohols for
building up [α-L-Rhap-(1 → 2)-α-D-Galp-(1 → ] units, multiple
equivalents12a−d of reactive L-rhamnosyl halides or imidates
were utilized as donors in combination with stoichiometric
amount of heavy metal12a,d−f salts or other Lewis acids; in some
cases, moderate or even low yields12e,f were obtained.
Nevertheless, the efficient and stereoselective formation of
[α-L-Fucp-(1 → 2)-α-D-Galp-(1 → ] disaccharide unit, as
required for our target, using 2-OH α-galactoside acceptor and
thiofucosyl donor still remains unknown, because it requires an
appropriately reactive donor and stereochemical control of 1,2-
cis fucosylation, which is more difficult than 1,2-trans
rhamnosylation in the presence of neighboring group
participation.
Our synthetic plan (Figure 2) of the sulfated tetrasaccharide
1 suggested a convergent [2 + 2] assembly of tetrasaccharide 2,
employing disaccharide acceptor 3 and thiofucosyl donor 4, to
construct the [α-L-Fucp-(1 → 2)-α-D-Galp-(1 → ] backbone
through an α-fucosidic bond. Thus, the orthogonally protected
thiogalactosyl donor 6 was developed as a crucial and ideal
donor to build up the 1,2-cis-α-galactosidic linkage of
disaccharide 3. Herein, the 4-O-acetyl group of 6 would be
expected to confer the remote neighboring group participation
effect13 during the α-galactosidic bond formation. The p-
methoxybenzyl (PMB) ether group was installed at C-2
position of 6 as a nonparticipating group to facilitate the α-
galactosylation, as well as a temporary protection in anticipation
of chain elongation. In turn, the α-linked disaccharide 4 can be
derived from 1-thio acceptor 7 and imidate donor 8 through an
orthogonal glycosylation, minimizing the number of protecting
group manipulations.
Reagents and conditions: (a) Ac2O, pyridine, DMAP; (b) p-
thiocresol, BF3·OEt2, CH2Cl2, 87% over 2 steps; (c) MeONa,
MeOH; (d) 2,2-dimethoxypropane, TsOH, acetone; (e) BnBr, NaH,
DMF, 95% over 3 steps; (f) TsOH, MeOH, 90%; (g) Bu2SnO, toluene
then BnBr, TBAI, DMF, 98%; (h) BzCl, Py, DMAP, CH2Cl2, 83%; (i)
NBS, acetone, H2O, 87%; (j) Cl3CCN, DBU, CH2Cl2, 75%.
fucose in two steps, underwent deacetylation, 3,4-O-isopropy-
lidenation, and 2-O-benzylation to provide 11 in 95% yield over
three steps. Subsequent cleavage of the acetal in the presence of
p-toluenesulfonic acid (TsOH) in methanol afforded 3,4-diol
12 in 90% yield. Regioselective 3-O-benzylation (98%) of 12
using stannylidene approach followed by 4-O-benzoylation
(83%) and oxidative hydrolysis (87%) using N-bromosuccini-
mide (NBS) provided 1-hemiacetal 15, which was converted
into the corresponding imidate donor 8 as an α-anomer in 75%
yield.
Starting from 2,3,4-triacetate 10, building block 7 containing
a free hydroxyl at C-3 position can be efficiently synthesized
through a sequential four-step procedure16 without purification
of intermediates (Scheme 2). Briefly, crude triol generated by
deacetylation of 10, was transformed into cyclic 3,4-O-
orthobenzoate 16, which was subjected to sequential 2-O-
benzylation and regioselective acidic hydrolysis to furnish C-3
alcohol 7 in 82% yield over four steps. Using the similar
a
Scheme 2. Synthesis of Building Blocks 5 and 7
a
Reagents and conditions: (a) MeONa, MeOH; (b) PhC(OMe)3,
Strategically, these synthetic precursors were decorated by a
carefully selected set of orthogonal protections that enables
transformations on selected hydroxyls (Figure 2). Herein, the
camphorsulfonic acid, acetonitrile; (c) BnBr, NaH, DMF; (d) HCl (1
M), 82% for 7; 70% for 5; over 4 steps; (e) p-methoxyphenol, BF3·
OEt2, CH2Cl2, 78%.
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approach, the reducing end building block 5 was prepared from
17 in an overall yield of 70%. Interestingly, condensation of p-
methoxyphenol with tetra-acetate 9 afforded the fucoside 17,
which was unexpectedly identified as an exclusive α-anomer.
This 1,2-cis selectivity, as distinct from typical phenolic
glycosylation with the assistance of 2-O-acyl group, was
attributed to reversible in situ anomerization17 and the
stabilizing anomeric effect.
subsequent [2 + 2] glycosylation. We were also able to isolate
15% of N-glycosyl amide 21, a side product due to fast
decomposition of the highly reactive trichloroacetimidate donor
8, even at very low temperature. To avoid this problem, we
opted to convert hemiacetal 15 into N-phenyl trifluoroaceti-
midate23 donor 8′, which would be moderately reactive and
shelf-stable. Thus, acceptor 7 was glycosylated using 8′ as
donor under aforementioned conditions, delivering disacchar-
ide 4 in an improved yield of 78%.
Galactose building block 6 was synthesized from the reported
1818 in three steps (Scheme 3). For the purpose of making the
Disaccharide precursor 22 was assembled (Scheme 5) from
galactosyl donor 6 and the reducing end acceptor 5 in the
a
Scheme 3. Synthesis of Building Block 6
Scheme 5. Synthesis of Disaccharide 3
a
Reagents and conditions: (a) TsOH, MeOH; (b) BnBr, NaOH,
Bu4NHSO4, H2O, CH2Cl2, 61% over 2 steps; (c) Ac2O, Et3N, DMAP,
CH2Cl2, 88%.
presence of N-iodosuccinimide (NIS) and silver triflate
(AgOTf) at −20 °C in 79% yield with complete α-selectivity,
which may be credited to the remote neighboring group
participation13 by the acetyl group situated at C-4 position of 6.
The 1JC1/H1 one-bond heteronuclear coupling constant of 175.5
Hz, measured by coupled-HSQC, on the D-Gal residue was
characteristic24,6b for the newly formed α-galactosidic bond,
which could also be determined by the corresponding 3J1,2 value
of 3.2 Hz. Next, the temporary 2-O-PMB protection was
removed by treating with DDQ to obtain disaccharide acceptor
3 in 75% yield.
In general, side reaction of a highly reactive donor due to its
fast promotion, especially when coupled with a sterically
hindered or an unreactive acceptor, would be a significant issue
for glycosylation. Therefore, we decided to carry out the [2 +
2] glycosylation of acceptor 3 with thiofucosyl donor 4 using
NIS/AgOTf in a mixed solvent of CH2Cl2−Et2O (Scheme 6).
Under this somewhat mild condition, the highly reactive and
precious fucosyl donor would be promoted more slowly25 to
suppress its degradation pathways. In addition, α-selectivity
would be enhanced by ether solvent effect.8a,26 As expected, the
reaction proceeded smoothly at −10 °C over about 3 h using
1.1 equiv of donor 4 and furnished tetrasaccharide 2 in 78%
yield with exclusive α-selectivity. The 1JC1/H1 coupling constant
of 174.4 Hz on the third sugar residue of 2 confirmed the
orientation of the newly generated α-fucosidic bond.
C-4 alcohol 20 from 18, we initially attempted reductive
opening of the benzylidene ring on 18 using Et3SiH−
trifluoroacetic acid (TFA), Et3SiH−trimethylsilyl triflate
(TMSOTf), NaBH3CN−HCl and NaBH3CN−cyanuric chlor-
ide19 combinations, respectively. Unfortunately, the use of
these conditions failed to provide 20 and led to degradation of
the instable PMB20 ether in acidic media. To circumvent this
difficulty, we resorted to a stepwise approach. The benzylidene
acetal on 18 was removed to provide diol 19, which was
selectively benzylated21 at the primary alcohol under the phase
transfer condition to produce 4-OH 20 (61%, over two steps).
Acetylation of the resulting alcohol delivered building block 6
in 88% yield.
With all of the building blocks in hand, the assembly of target
oligosaccharide was continued, commencing from the synthesis
of the nonreducing end disaccharide 4 (Scheme 4). Orthogonal
glycosylation22 of donor 8 and 1-thio acceptor 7 promoted by
TMSOTf at −78 °C afforded the α-linked disaccharide 4 in a
moderate yield of 67%, which could directly serve as donor in
Scheme 4. Synthesis of Disaccharide 4
Finally, the fully protected tetrasaccharide 2 was subjected to
the cleavage of the benzoyl and acetyl ester groups under
Zemplen condition to afford the corresponding tetra-alcohol 23
́
in 82% yield (Scheme 6). O-Sulfation of 23 using SO3·Me3N in
DMF at 50 °C and subsequent hydrogenolysis over Pd(OH)2/
C afforded the crude product, which was subjected to ion-
exchange on a Dowex 50WX8 (Na+ form) column and size-
exclusion chromatography on a Sephadex G-25 column to
provide target tetrasaccharide 1 as its sodium salt in 80% yield
over two steps.
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turned off during acquisition. To designate resonances, the sugar
residues were numbered with Roman numerals I, II, III, etc., beginning
at the reducing end.
Scheme 6. Synthesis of Target Tetrasaccharide 1
p-Tolyl 2,3,4-tri-O-acetyl-1-thio-β-L-fucopyranoside (10). To
a solution of L-fucose (1.4 g, 7.73 mmol) and DMAP (134 mg, 1.10
mmol) in pyridine (30 mL) at 0 °C was added Ac2O (15 mL). The
mixture was warmed to room temperature, stirred for 12 h and then
concentrated. The residue was diluted with EtOAc, washed with 5%
citric acid (aq.), NaHCO3 (sat. aq.) and brine. The organic layer was
dried over MgSO4, filtered and concentrated to give crude 9 (2.62 g)
as a syrup, which was used without further purification. BF3·OEt2 (1.96
mL, 15.47 mmol) was added dropwise to a solution of crude 9 and p-
thiocresol (1.15 g, 9.28 mmol) in CH2Cl2 (30 mL) under nitrogen at 0
°C. After stirring at 0 °C for 2 h, the mixture was warmed to room
temperature, stirred for 12 h and quenched with NaHCO3 (sat. aq.).
The organic layer was washed with 5% NaOH (aq.) and brine, dried
over MgSO4, filtered and concentrated. Crystallization from a mixture
of i-PrOH and hexanes provided 10 (2.49 g, 81% over 2 steps) as a
white solid: [α]2D0 −4.6 (c 0.503, CH2Cl2); 1H NMR (400 MHz,
CDCl3) δ 7.44−7.38 (m, 2H, ArH), 7.13 (d, J = 7.9 Hz, 2H, ArH),
5.25 (dd, J = 3.3, 0.9 Hz, 1H, H-4), 5.20 (dd, J = 9.9, 9.9 Hz, 1H, H-2),
5.04 (dd, J = 9.9, 3.4 Hz, 1H, H-3), 4.63 (d, J = 9.9 Hz, 1H, H-1), 3.80
(qd, J = 6.3, 0.8 Hz, 1H, H-5), 2.34 (s, 3H, ArCH3), 2.14 (s, 3H,
COCH3), 2.09 (s, 3H, COCH3), 1.97 (s, 3H, COCH3), 1.23 (d, J =
6.4 Hz, 3H, H-6); 13C NMR (100 MHz, CDCl3) δ 170.6, 170.1, 169.5
(COCH3), 138.2, 133.0, 129.6, 129.1 (ArC), 86.9 (C-1), 73.1 (C-5),
72.5 (C-3), 70.4 (C-4), 67.4 (C-2), 21.2 (ArCH3), 20.9, 20.7, 20.6
(COCH3), 16.5 (C-6); HRMS (ESI-TOF) m/z Calcd for
C19H24O7NaS [M + Na]+ 419.1140, found 419.1126.
p-Tolyl 2-O-benzyl-3,4-O-isopropylidene-1-thio-β-L-fucopyr-
anoside (11). Compound 10 (1.18 g, 2.97 mmol) was dissolved in
methanol (20 mL), and MeONa (16 mg, 0.30 mmol) was added. After
12 h, Dowex 50WX8 acidic resin was added to neutralize MeONa. The
resin was removed, and the solution was concentrated in vacuo to
afford crude triol as a residue. The residue was coevaporated with
toluene and dissolved in acetone (20 mL). 2,2-Dimethoxypropane
(0.73 mL, 5.932 mmol) and p-TsOH (56 mg, 0.30 mmol) were added.
After stirring at room temperature for 4 h, triethylamine (5 mL) was
added, and the solvent was evaporated. The resulting crude alcohol
was dissolved in DMF (10 mL), and NaH (60%, 237 mg, 5.93 mmol)
was added in portions at 0 °C. After 30 min, BnBr (0.71 mL, 5.93
mmol) was added, and the mixture was stirred at room temperature
for 5 h. The mixture was poured slowly to water and extracted with
EtOAc. The organics were dried over MgSO4, filtered and
concentrated. Crystallization from hexanes afforded 11 (1.12 g,
NMR signal assignments of 1 including the identification of
anomeric configurations were carried out using a combination
of COSY, TOCSY, HSQC, HSQC-TOCSY, HMBC, ROESY,
and coupled-HSQC 2D NMR techniques. Herein, HSQC
spectrum showed four cross peaks in anomeric region. The
1
appearance of JC1/H1 values (173.8, 176.3, 175.5, 173.0 Hz) in
coupled-HSQC proved the presences of four α-glycosidic
bonds in FucI, GalII, FucIII and FucIV residues, respectively.
Furthermore, one (1 → 2)- and two (1 → 3)- linkages were
revealed through inter-residue NOEs observed in ROESY
experiment and three-bond correlations in HMBC spectrum as
well.
In summary, we have accomplished the first chemical
synthesis of a highly sulfated tetrasaccharide 1 as the rare
sequence in the galactofucan isolated from the brown alga
Sargassum polycystum in an efficient and stereoselective way.
The orthogonally protected galactose building block 6 was
proved to be a crucial and ideal donor to build up the 1,2-cis-α-
galactosidic bond, and also could enable the convergent [2 + 2]
assembly of tetrasaccharide backbone. The construction of the
multiple contiguous 1,2-cis glycosidic linkages was achieved
with exclusive stereoselectivities. In addition, 1H and 13C signals
of the synthesized oligosaccharides were fully assigned on the
basis of 2D NMR techniques.
95%) as a white solid: [α]2D0 −2.0 (c 0.353, CH2Cl2); H NMR (400
1
MHz, CDCl3) δ 7.47−7.40 (m, 4H, ArH), 7.36−7.26 (m, 3H, ArH),
7.09 (d, J = 7.9 Hz, 2H, ArH), 4.82 and 4.67 (ABq, JAB = 11.3 Hz, 2H,
CH2Ar), 4.52 (d, J = 9.7 Hz, 1H, H-1), 4.21 (dd, J = 5.9, 5.9 Hz, 1H,
H-3), 4.03 (dd, J = 5.6, 2.1 Hz, 1H, H-4), 3.79 (qd, J = 6.5, 2.1 Hz, 1H,
H-5), 3.48 (dd, J = 9.7, 6.5 Hz, 1H, H-2), 2.32 (s, 3H, ArCH3), 1.41 (s,
3H, CCH3), 1.39 (d, J = 6.6 Hz, 3H, H-6), 1.35 (s, 3H, CCH3); 13C
NMR (100 MHz, CDCl3) δ 138.1, 137.6, 132.8, 129.9, 129.5, 128.3,
128.2, 127.7 (ArC), 109.7 (CMe2), 86.5 (C-1), 79.9 (C-3), 78.3 (C-2),
76.5 (C-4), 73.5 (CH2Ar), 72.4 (C-5), 27.9 (CCH3Me), 26.4
(CMeCH3), 21.1 (ArCH3), 16.9 (C-6); HRMS (ESI-TOF) m/z
Calcd for C23H28O4NaS [M + Na]+ 423.1606, found 423.1599.
p-Tolyl 2-O-benzyl-1-thio-β-L-fucopyranoside (12). A solution
of 11 (1.11 g, 2.77 mmol) in methanol (25 mL) was treated with p-
toluenesulfonic acid (53 mg, 0.28 mmol). After stirring at room
temperature for 24 h, the mixture was neutralized by triethylamine (5
mL) and concentrated. Flash chromatography on silica gel (EtOAc/
hexanes/CH2Cl2 1:2:1) afforded 12 (895 mg, 90%) as a white solid:
[α]2D0 −3.9 (c 0.233, CH2Cl2); 1H NMR (400 MHz, CDCl3) δ 7.47 (d,
J = 8.1 Hz, 2H, ArH), 7.42−7.27 (m, 5H, ArH), 7.12 (d, J = 7.9 Hz,
2H, ArH), 4.96 and 4.69 (ABq, JAB= 11.0 Hz, 2H, CH2Ar), 4.53 (d, J =
9.6 Hz, 1H, H-1), 3.72 (dd, J = 5.1, 3.4 Hz, 1H, H-4), 3.66−3.56 (m,
2H, H-3, H-5), 3.50 (dd, J = 9.3, 9.3 Hz, 1H, H-2), 2.48 (d, J = 5.3 Hz,
1H, OH), 2.34 (s, 3H, ArCH3), 2.11 (d, J = 5.3 Hz, 1H, OH), 1.34 (d,
J = 6.5 Hz, 3H, H-6); 13C NMR (100 MHz, CDCl3) δ 138.2, 137.8,
EXPERIMENTAL SECTION
General Methods. NMR spectra were recorded on a 400 MHz
■
1
spectrometer (operating frequencies of 400.13 MHz for H, 100.61
MHz for 13C), while probe temperature was kept at 300 K during all
experiments. Chemical shifts are in ppm calibrated using TMS, CDCl3
1
or HOD as internal standards. H and 13C signals on carbohydrate
rings were fully assigned on the basis of 2D NMR techniques. Gradient
COSY, multiplicity-edited HSQC and HMBC were acquired using
standard pulse programs. TOCSY and HSQC-TOCSY were measured
with a spin lock time of 120 ms. Mixing time in ROESY experiment
was set to 400 ms. In coupled-HSQC experiment, 13C decoupler was
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Note
132.5, 130.0, 129.7, 128.6, 128.3, 128.1 (ArC), 87.7 (C-1), 78.2 (C-2),
75.3 (C-3), 75.3 (CH2Ar), 74.4 (C-5), 71.8 (C-4), 21.1 (ArCH3), 16.6
(C-6); HRMS (ESI-TOF) m/z Calcd for C20H24O4NaS [M + Na]+
383.1293, found 383.1294.
73.8 (CH2Ar), 71.6 (CH2Ar), 71.1 (C-4), 65.3 (C-5), 16.4 (C-6);
Coupled HSQC anomeric cross peak (400 MHz, CDCl3) δ 5.32/92.2
(JC1/H1 = 170.6 Hz). NMR data for 15β: 1H NMR (400 MHz, CDCl3)
δ 8.15−8.10 (m, 2H, ArH), 7.61−7.58 (m, 1H, ArH), 7.46−7.42 (m,
2H, ArH), 7.28−7.22 (m, 10H, ArH), 5.58 (dd, J = 3.3, 1.0 Hz, 1H, H-
4), 4.90−4.79 (m, 3H, CH2Ar, CHHAr), 4.74 (dd, J = 7.4, 3.0 Hz, 1H,
H-1), 4.57 (B of ABq, JAB = 11.6 Hz, 1H, CHHAr), 3.81 (qd, J = 6.3,
0.8 Hz, 1H, H-5), 3.71 (dd, J = 9.6, 3.4 Hz, 1H, H-3), 3.63 (dd, J = 9.6,
7.4 Hz, 1H, H-2), 3.16 (d, J = 4.5 Hz, 1H, OH), 1.27 (d, J = 6.4 Hz,
3H, H-6); 13C NMR (100 MHz, CDCl3) δ 166.3 (CO), 137.8,
133.2, 130.0, 129.8, 128.4, 128.2, 128.0, 127.7, 127.7, 127.6 (Ar C),
97.3 (C-1), 79.8 (C-2), 79.5 (C-3), 75.2 (CH2Ar), 71.8 (CH2Ar), 70.3
(C-4), 69.6 (C-5), 16.6 (C-6); Coupled HSQC anomeric cross peak
(400 MHz, CDCl3) δ 4.74/97.3 (JC1/H1 = 163.2 Hz).
p-Tolyl 2,3-di-O-benzyl-1-thio-β-L-fucopyranoside (13). A
mixture of 12 (884 mg, 2.45 mmol) and Bu2SnO (763 mg, 3.07
mmol) in toluene (40 mL) was heated at 130 °C for 4 h with
azeotropic removal of water. The mixture was concentrated to 1/4 of
the original volume by continued evaporation and then cooled to 60
°C. DMF (15 mL), BnBr (0.44 mL, 3.68 mmol), CsF (745 mg, 4.90
mmol) and TBAI (272 mg, 0.74 mmol) were added. The reaction was
stirred at 60 °C for 12 h and quenched with water. The mixture was
portioned between EtOAc and water. The organic layer was washed
with brine, dried over MgSO4, filtered and concentrated in vacuo.
Flash chromatography on silica gel (EtOAc/hexanes/CH2Cl2 1:5:1)
provided 13 (1.09 g, 98%) as a white solid: [α]2D0 −5.8 (c 0.243,
4-O-Benzoyl-2,3-di-O-benzyl-α-L-fucopyranosyl trichloroa-
cetimidate (8). Compound 15 (140 mg, 0.31 mmol) was dissolved
in dry CH2Cl2 (5 mL). To this solution Cl3CCN (0.26 mL, 3.0 mmol)
and DBU (15 μL, 0.11 mmol) were added at room temperature. After
stirring for 5 h, the mixture was concentrated in vacuo. Flash
chromatography on triethylamine deactivated silica gel (EtOAc/
1
CH2Cl2); H NMR (400 MHz, CDCl3) δ 7.49−7.45 (m, 2H, ArH),
7.44−7.39 (m, 2H, ArH), 7.37−7.26 (m, 8H, ArH), 7.10 (d, J = 7.9
Hz, 2H, ArH), 4.84 and 4.74 (ABq, JAB = 10.3 Hz, 2H, CH2Ar), 4.71
and 4.68 (ABq, JAB = 11.6 Hz, 2H, CH2Ar), 4.53 (d, J = 9.6 Hz, 1H, H-
1), 3.81 (ddd, J = 3.4, 3.4, 0.9 Hz, 1H, H-4), 3.65 (dd, J = 9.3, 9.3 Hz,
1H, H-2), 3.58−3.51 (m, 2H, H-3, H-5), 2.32 (s, 3H, ArCH3), 2.23
(dd, J = 3.4, 0.7 Hz, 1H, OH), 1.36 (d, J = 6.5 Hz, 3H, H-6); 13C
NMR (100 MHz, CDCl3) δ 138.3, 137.7, 137.6, 132.7, 123.0, 129.6,
128.6, 128.4, 128.3, 128.0, 127.9, 127.8 (ArC), 87.8 (C-1), 83.0 (C-3),
76.9 (C-2), 75.7 (CH2Ar), 74.2 (C-5), 72.1 (CH2Ar), 69.4 (C-4), 21.1
(ArCH3), 16.8 (C-6); HRMS (ESI-TOF) m/z Calcd for C27H30O4NaS
[M + Na]+ 473.1763, found 473.1777.
1
hexanes 1:20) afforded 8 (138.4 mg, 75%) as a syrup: H NMR (400
MHz, CDCl3) δ 8.58 (s, 1H, NH), 8.09−8.02 (m, 2H, ArH), 7.62−
7.57 (m, 1H, ArH), 7.50−7.43 (m, 2H, ArH), 7.34−7.27 (m, 7H,
ArH), 7.25−7.20 (m, 3H, ArH), 6.55 (d, J = 3.3 Hz, 1H, H-1), 5.69
(dd, J = 3.0, 1.1 Hz, 1H, H-4), 4.82 and 4.63 (ABq, JAB= 11.7 Hz, 2H,
CH2Ar), 4.78 and 4.74 (ABq, JAB= 11.9 Hz, 2H, CH2Ar), 4.34 (qd, J =
6.5, 0.7 Hz, 1H, H-5), 4.15 (dd, J = 10.0, 3.1 Hz, 1H, H-2), 4.09 (dd, J
= 10.0, 3.3 Hz, 1H, H-3), 1.22 (d, J = 6.5 Hz, 3H, H-6); 13C NMR
(100 MHz, CDCl3) δ 166.2 (COPh), 161.3 (CN), 138.3, 137.9,
133.2, 129.9, 129.8, 128.5, 128.2, 128.2, 127.9, 127.52, 127.51 (ArC),
95.2 (C-1), 91.4 (CCl3), 75.3 (C-2), 74.7 (C-3), 73.1 (CH2Ar), 71.7
(CH2Ar), 70.9 (C-4), 68.0 (C-5), 16.4 (C-6); Coupled HSQC
anomeric cross peak (400 MHz, CDCl3) δ 6.55/95.2 (JC1/H1 = 177.4
Hz); HRMS (ESI-TOF) m/z Calcd for C29H28NO6NaCl3 [M + Na]+
614.0880, found 614.0880.
p-Tolyl 4-O-benzoyl-2,3-di-O-benzyl-1-thio-β-L-fucopyrano-
side (14). Benzyol chloride (0.83 mL, 7.20 mmol) was added
dropwise to a solution of 13 (1.08 g, 2.40 mmol), pyridine (1.4 mL,
16.79 mmol) and DMAP (59 mg, 0.48 mmol) in CH2Cl2 (20 mL)
under nitrogen at room temperature. After stirring for 18 h, the
mixture was treated with NaHCO3 (sat. aq.). The organic phase was
washed with 5% citric acid (aq.), NaHCO3 (sat. aq.) then brine, dried
over MgSO4, filtered and concentrated in vacuo. Crystallization from
methanol afforded 14 (1.1 g, 83%) as a white solid: [α]2D0 −8.5 (c
N-Phenyl-O-(4-O-benzoyl-2,3-di-O-benzyl-α/β-L-fucopyrano-
syl) trifluoroacetimidate (8′). To a solution of compound 15 (331
mg, 0.74 mmol) in CH2Cl2 (10 mL) were added N-phenyl
trifluoroacetimidoyl chloride (184 mg, 0.89 mmol) and Cs2CO3
(481 mg, 1.48 mmol). After stirring for 2 h at room temperature,
the mixture was filtered and concentrated. Flash chromatography on
triethylamine deactivated silica gel (EtOAc/hexanes 1:15) provided a
mixture of 8′β and 8′α (4.3/1.0) (396 mg, 87%) as a syrup. Pure
anomers were isolated for analysis. Data for 8′β: [α]2D0 −94.0 (c 0.350,
1
0.303, CH2Cl2); H NMR (400 MHz, CDCl3) δ 8.06−8.01 (m, 2H,
ArH), 7.63−7.54 (m, 3H, ArH), 7.48−7.43 (m, 2H, ArH), 7.42−7.37
(m, 2H, ArH), 7.36−7.24 (m, 5H, ArH), 7.24−7.19 (m, 3H, ArH),
7.15 (d, J = 7.9 Hz, 2H, ArH), 5.61 (dd, J = 3.2, 0.7 Hz, 1H, H-4), 4.79
and 4.52 (ABq, JAB = 11.3 Hz, 2H, CH2Ar), 4.74 and 4.72 (ABq, JAB
=
10.4 Hz, 2H, CH2Ar), 4.60 (d, J = 9.4 Hz, 1H, H-1), 3.81 (qd, J = 6.4,
0.8 Hz, 1H, H-5), 3.75 (dd, J = 9.1, 3.2 Hz, 1H, H-3), 3.67 (dd, J = 9.3,
9.3 Hz, 1H, H-2), 2.38 (s, 3H, ArCH3), 1.30 (d, J = 6.4 Hz, 3H, H-6);
13C NMR (100 MHz, CDCl3) δ 166.2 (CO), 138.5, 137.9, 137.6,
133.6, 133.2, 130.1, 129.8, 129.6, 129.1, 128.3, 128.2, 128.1, 127.73,
127.70 (ArC), 87.1 (C-1), 81.5 (C-3), 76.2 (C-2), 75.5 (CH2Ar), 73.4
(C-5), 71.7 (CH2Ar), 70.3 (C-4), 21.3 (ArCH3), 17.0 (C-6); HRMS
(ESI-TOF) m/z Calcd for C34H34O5NaS [M + Na]+ 577.2025, found
577.2019.
4-O-Benzoyl-2,3-di-O-benzyl-α/β-L-fucopyranoside (15). To a
solution of 14 (208 mg, 0.38 mmol) in acetone/H2O (9:1, 5 mL) at 0
°C was added NBS (133 mg, 0.75 mmol) in portions. After stirring at
0 °C for 5 h, the mixture was poured into CH2Cl2. The organic phase
was washed with NaHCO3 (sat. aq.), Na2S2O3 (sat. aq.) and then
brine, dried over MgSO4, filtered and concentrated in vacuo. Flash
chromatography on silica gel (EtOAc/hexanes/CH2Cl2 1:3:1)
provided a mixture of 15α and 15β (5/3) (146 mg, 87%) as a
foam: [α]2D0 −126.4 (c 0.140, CH2Cl2); HRMS (ESI-TOF) m/z Calcd
for C27H28O6Na [M + Na]+ 471.1784, found 471.1805. NMR data for
15α: 1H NMR (400 MHz, CDCl3) δ 8.09−8.04 (m, 2H, ArH), 7.59−
7.56 (m, 1H, ArH), 7.49−7.45 (m, 2H, ArH), 7.34−7.24 (m, 10H,
ArH), 5.64 (dd, J = 3.2, 1.0 Hz, 1H, H-4), 5.32 (d, J = 3.6 Hz, 1H, H-
1), 4.85 and 4.70 (ABq, JAB = 11.6 Hz, 2H, CH2Ar), 4.83 and 4.59
(ABq, JAB = 11.5 Hz, 2H, CH2Ar), 4.38 (qd, J = 6.6, 0.5 Hz, 1H, H-5),
4.04 (dd, J = 9.8, 3.3 Hz, 1H, H-3), 3.90 (dd, J = 9.8, 3.6 Hz, 1H, H-2),
2.96 (s, 1H, OH), 1.20 (d, J = 6.5 Hz, 3H, H-6); 13C NMR (100 MHz,
CDCl3) δ 166.3 (CO), 138.1, 138.0, 133.1, 130.0, 129.9, 128.42,
128.41, 128.3, 128.1, 127.9 (Ar C), 92.2 (C-1), 76.1 (C-3), 75.4 (C-2),
1
CH2Cl2); H NMR (400 MHz, CDCl3) δ 8.13 (d, J = 7.7 Hz, 2H,
ArH), 7.64−7.58 (m, 1H, ArH), 7.49 (t, J = 7.7 Hz, 2H, ArH), 7.35−
7.22 (m, 12H, ArH), 7.14−7.07 (m, 1H, ArH), 6.83 (d, J = 7.6 Hz, 2H,
ArH), 5.67 (brs, 1H, H-1), 5.58 (s, 1H, H-4), 4.85−4.78 (m, 3H,
CH2Ar, CHHAr), 4.57 (B of ABq, JAB = 11.6 Hz, 1H, CHHAr), 3.90
(dd, J = 8.3, 8.3 Hz, 1H, H-2), 3.82−3.55 (m, 2H, H-5, H-3), 1.26 (d, J
= 6.3 Hz, 3H, H-6); 13C NMR (100 MHz, CDCl3) δ 166.2 (COPh),
143.5, 137.9, 137.6, 133.3, 130.0, 129.7, 128.7, 128.5, 128.38, 128.35,
128.2, 128.0, 127.9, 127.8, 124.2, 119.3 (ArC), 116.2 (q, 1JC−F = 281.8
Hz, CF3), 97.21 (C-1), 79.44 (C-3), 77.57 (C-2), 75.63 (CH2Ar),
71.98 (CH2Ar), 70.56 (C-5), 69.91 (C-4), 16.33 (C-6); HRMS (ESI-
TOF) m/z Calcd for C35H32F3NO6Na [M + Na]+ 642.2079, found
642.2093. Data for 8′α: [α]2D0 −114.3 (c 0.675, CH2Cl2); H NMR
1
(400 MHz, CDCl3) δ 8.04 (d, J = 7.7 Hz, 2H, ArH), 7.58 (t, J = 7.4
Hz, 1H, ArH), 7.45 (t, J = 7.7 Hz, 2H, ArH), 7.35−7.21 (m, 12H,
ArH), 7.09 (t, J = 7.4 Hz, 1H, ArH), 6.77 (d, J = 6.6 Hz, 2H, ArH),
6.53 (brs, 1H, H-1), 5.68 (s, 1H, H-4), 4.83 and 4.63 (ABq, JAB = 11.4
Hz, 2H, CH2Ar), 4.82 and 4.73 (ABq, JAB = 11.9 Hz, 2H, CH2Ar), 4.27
(brs, 1H, H-5), 4.11 (d, J = 9.6 Hz, 1H, H-3), 4.06 (d, J = 9.6 Hz, 1H,
H-2), 1.22 (d, J = 6.3 Hz, 3H, H-6); 13C NMR (100 MHz, CDCl3) δ
166.1 (COPh), 143.7, 138.1, 137.9, 133.2, 129.9, 129.8, 128.7, 128.5,
128.4, 128.3, 127.9, 127.7, 127.7, 127.6, 124.2, 119.6 (ArC), 116.3 (q,
1JC−F = 286.7 Hz, CF3), 94.5 (C-1), 75.8 (C-3), 74.5 (C-2), 73.6
(CH2Ar), 71.9 (CH2Ar), 70.8 (C-4), 68.1 (C-5), 16.4 (C-6); HRMS
(ESI-TOF) m/z Calcd for C35H32F3NO6Na [M + Na]+ 642.2079,
found 642.2098.
4722
dx.doi.org/10.1021/jo500503r | J. Org. Chem. 2014, 79, 4718−4726

The Journal of Organic Chemistry
Note
p-Tolyl 4-O-benzoyl-2-O-benzyl-1-thio-β-L-fucopyranoside
(7). Deacetylation of 10 (337 mg, 0.85 mmol) provided the crude
triol as described in the synthesis of 11. The crude triol was
coevaporated with toluene and dissolved in acetonitrile (10 mL).
Trimethyl orthobenzoate (0.29 mL, 1.7 mmol) and DL-10-
camphorsulfonic acid (20 mg, 0.085 mmol) were added. After stirring
at room temperature for 1 h, triethylamine (5 mL) was added, and the
solvent was evaporated. The resulting alcohol was dissolved in DMF
(8 mL), and NaH (60%, 68 mg, 1.7 mmol) was added in portions at 0
°C. After 30 min, BnBr (0.2 mL, 1.7 mmol) was added, and the
mixture was stirred at room temperature for 12 h. The mixture was
treated with 1 N HCl (2.6 mL). After stirring for 1 h, EtOAc and H2O
were added successively to the mixture, and the organic layer was dried
over MgSO4, filtered and concentrated in vacuo. Flash chromatog-
raphy on silica gel (EtOAc/hexanes/CH2Cl2 1:5:1) provided 7 (390
0.05 mmol). After stirring at room temperature for 36 h, the mixture
was neutralized by triethylamine (2 mL) and concentrated in vacuo to
afford crude p-tolyl 3-O-benzyl-2-O-(4-methoxybenzyl)-1-thio-β-D-
1
galactopyranoside (19) as powder: H NMR (400 MHz, CDCl3) δ
7.49−7.43 (m, 2H, ArH), 7.40−7.26 (m, 7H, ArH), 7.10 (d, J = 8.0
Hz, 2H, ArH), 6.90−6.84 (m, 2H, ArH), 4.78 and 4.68 (ABq, JAB = 9.9
Hz, 2H, CH2Ar), 4.71 (s, 2H, CH2Ar), 4.57 (d, J = 9.7 Hz, 1H, H-1),
4.05−4.00 (m, 1H, H-4), 3.99−3.92 (m, 1H, H-6a), 3.810 (s, 3H,
OCH3), 3.80−3.73 (m, 1H, H-1b), 3.70 (dd, J = 9.3, 9.3 Hz, 1H, H-2),
3.56 (dd, J = 8.9, 3.3 Hz, 1H, H-3), 3.45 (dd, J = 6.5, 4.5 Hz, 1H, H-5),
2.57 (s, 1H, OH), 2.32 (s, 3H, ArCH3), 2.10 (dd, J = 8.6, 3.8 Hz, 1H,
OH); 13C NMR (100 MHz, CDCl3) δ 159.4, 137.8, 137.6, 132.6,
130.4, 129.9, 129.7, 128.6, 128.1, 127.9, 113.8 (ArC), 87.9 (C-1), 82.5
(C-3), 78.0 (C-5), 76.8 (C-2), 75.4 (CH2Ar), 72.3 (CH2Ar), 67.5 (C-
4), 62.8 (C-6), 55.3 (OCH3), 21.1 (ArCH3); HRMS (ESI-TOF) m/z
Calcd for C28H32O6NaS [M + Na]+ 519.1817, found 519.1837.
The crude diol 19, BnBr (122 μL, 1.03 mmol) and tetrabuty-
lammonium hydrogen sulfate (35 mg, 0.10 mmol) were dissolved in
CH2Cl2 (10 mL), and then 5% NaOH (aq., 5 mL) was added. After
stirring at 50 °C for 30 h, the mixture was diluted with CH2Cl2 and
H2O. The organic phase was washed with brine, dried over MgSO4,
filtered and concentrated in vacuo. Crystallization from methanol
afforded 20 (194 mg, 61% over 2 steps) as a white solid: [α]2D0 +3.2 (c
1
mg, 82%) as a syrup: [α]D20 −26.7 (c 1.277, CH2Cl2); H NMR (400
MHz, CDCl3) δ 8.06−8.00 (m, 2H, ArH), 7.65−7.54 (m, 3H, ArH),
7.50−7.43 (m, 2H, ArH), 7.39−7.26 (m, 5H, ArH), 7.19−7.14 (m,
2H, ArH), 5.42 (dd, J = 3.4, 0.8 Hz, 1H, H-4), 4.95 and 4.66 (ABq, JAB
= 10.8 Hz, 2H, CH2Ar), 4.61 (d, J = 9.6 Hz, 1H, H-1), 3.93 (ddd, J =
9.1, 3.6, 3.6 Hz, 1H, H-3), 3.84 (qd, J = 6.4, 0.9 Hz, 1H, H-5), 3.63
(dd, J = 9.3, 9.3 Hz, 1H, H-2), 2.39 (s, 3H, ArCH3), 2.29 (d, J = 3.7
Hz, 1H, OH), 1.28 (d, J = 6.4 Hz, 3H, H-6); 13C NMR (100 MHz,
CDCl3) δ 166.7 (CO), 138.1, 137.8, 133.3, 133.0, 130.1, 129.7,
129.6, 129.4, 128.6, 128.4, 128.2, 128.0 (ArC), 87.0 (C-1), 77.5 (C-2),
75.3 (CH2Ar), 74.3 (C-3), 73.5 (C-5), 73.4 (C-4), 21.2 (ArCH3), 16.9
(C-6); HRMS (ESI-TOF) m/z Calcd for C27H28O5NaS [M + Na]+
487.1555, found 487.1578.
1
0.353, CH2Cl2); H NMR (400 MHz, CDCl3) δ 7.50−7.44 (m, 2H,
ArH), 7.37−7.27 (m, 12H, ArH), 7.05 (d, J = 7.9 Hz, 2H, ArH), 6.89−
6.84 (m, 2H, ArH), 4.77 (A of ABq, JAB = 9.9 Hz, 1H, CHHAr), 4.74−
4.65 (m, 3H, CH2Ar, CHHAr), 4.59−4.52 (m, 3H, H-1, OCH2Ar),
4.09−4.06 (m, 1H, H-4), 3.80 (s, 3H, OCH3), 3.83−3.73 (m, 2H, H-
6a, H-6b), 3.69 (dd, J = 9.3, 9.3 Hz, 1H, H-2), 3.58−3.51 (m, 2H, H-5,
H-3), 2.48 (dd, J = 2.5, 0.6 Hz, 1H, OH), 2.30 (s, 3H, ArCH3); 13C
NMR and DEPT135 (100 MHz, CDCl3) δ 159.4, 138.0, 137.8, 137.6,
132.6, 130.5, 130.0, 129.6, 128.5, 128.4, 128.0, 127.9, 127.8, 127.7,
113.8 (ArC), 88.1 (C-1), 82.7 (C-3), 77.1 (C-5), 76.8 (C-2), 75.4
(CH2Ar), 73.7 (CH2Ar), 72.2 (CH2Ar), 69.5 (C-6), 67.0 (C-4), 55.3
(OCH3), 21.1 (ArCH3); HRMS (ESI-TOF) m/z Calcd for
C35H38O6NaS [M + Na]+ 609.2287, found 609.2280.
p-Methoxyphenyl 2,3,4-tri-O-acetyl-α-L-fucopyranoside
(17). BF3·OEt2 (0.32 mL, 2.51 mmol) was added dropwise to a
solution of crude 9 (417 mg, 1.25 mmol) and p-methoxyphenol (234
mg, 1.88 mmol) in CH2Cl2 (10 mL) under nitrogen at 0 °C. After
stirring at 0 °C for 2 h, the mixture was allowed to warm to room
temperature, stirred for 12 h and quenched with NaHCO3 (sat. aq.).
The organic layer was separated and washed with 5% NaOH (aq) and
brine, dried over MgSO4, filtered, and the solvent was removed in
vacuo. Flash chromatography on silica gel (EtOAc/hexanes/CH2Cl2
1:9:1) provided 17 (386 mg, 78%) as a syrup: [α]2D0 −162.7 (c 0.473,
p-Tolyl 4-O-acetyl-3,6-di-O-benzyl-2-O-(4-methoxybenzyl)-
1-thio-β-D-galactopyranoside (6). To a solution of 20 (137 mg,
0.23 mmol), triethylamine (0.39 mL, 2.80 mmol) and DMAP (3 mg,
0.023 mmol) in dry CH2Cl2 (5 mL) was added Ac2O (0.11 mL, 1.17
mmol) at 0 °C. The reaction was stirred at room temperature for 5 h,
and then quenched with NaHCO3 (sat. aq.). The organic layer was
washed with brine, dried over MgSO4, filtered and concentrated in
vacuo. Flash chromatography on silica gel (EtOAc/hexanes/CH2Cl2
1:10:1) provided 6 (172 mg, 88%) as a white foam: [α]2D0 +14.7 (c
1
CH2Cl2); H NMR (400 MHz, CDCl3) δ 7.01−6.93 (m, 2H, ArH),
6.86−6.78 (m, 2H, ArH), 5.62 (d, J = 3.6 Hz, 1H, H-1), 5.57 (dd, J =
10.9, 3.4 Hz, 1H, H-3), 5.37 (dd, J = 3.3, 1.1 Hz, 1H, H-4), 5.26 (dd, J
= 10.9, 3.7 Hz, 1H, H-2), 4.32 (qd, J = 6.5, 0.7 Hz, 1H, H-5), 3.77 (s,
3H, OCH3), 2.19 (s, 3H, COCH3), 2.07 (s, 3H, COCH3), 2.02 (s, 3H,
COCH3), 1.14 (d, J = 6.5 Hz, 3H, H-6); 13C NMR (100 MHz,
CDCl3) δ 170.6, 170.5, 170.1 (COCH3), 155.2, 150.7, 117.8, 114.7
(ArC), 95.7 (C-1), 71.1 (C-4), 69.0 (C-3), 68.0 (C-2), 65.2 (C-5),
55.7 (OCH3), 20.8, 20.72, 20.65 (COCH3), 15.9 (C-6); Coupled
1
0.387, CH2Cl2); H NMR (400 MHz, CDCl3) δ 7.50−7.44 (m, 2H,
ArH), 7.37−7.26 (m, 12H, ArH), 7.05 (d, J = 7.9 Hz, 2H, ArH), 6.91−
6.83 (m, 2H, ArH), 5.61 (d, J = 1.7 Hz, 1H, H-4), 4.77 and 4.49 (ABq,
JAB = 11.0 Hz, 2H, CH2Ar), 4.70 and 4.65 (ABq, JAB = 9.8 Hz, 2H,
CH2Ar), 4.64−4.57 (m, 1H, H-1), 4.54 and 4.45 (ABq, JAB = 11.7 Hz,
2H, CH2Ar), 3.80 (s, 3H, OCH3), 3.71 (dd, J = 6.3, 6.3 Hz, 1H, H-5),
3.64−3.57 (m, 3H, H-3, H-2, H-6a), 3.51 (dd, J = 9.6, 6.7 Hz, 1H, H-
6b), 2.30 (s, 3H, ArCH3), 2.08 (s, 3H, COCH3); 13C NMR (100 MHz,
CDCl3) δ 170.3 (CO), 159.4, 137.71, 137.70, 137.6, 132.5, 130.5,
129.94, 129.91, 129.6, 128.44, 128.42, 128.2, 128.0, 127.84, 127.82,
113.8 (ArC), 88.2 (C-1), 81.3 (C-3), 76.6 (C-2), 75.9 (C-5), 75.4
(CH2Ar), 73.7 (CH2Ar), 72.0 (CH2Ar), 68.3 (C-6), 67.0 (C-4), 55.3
(OCH3), 21.1 (ArCH3), 20.9 (COCH3); HRMS (ESI-TOF) m/z
Calcd for C37H40O7NaS [M + Na]+ 651.2392, found 651.2381.
p-Tolyl (4-O-benzoyl-2,3-di-O-benzyl-α-L-fucopyranosyl)-(1
→ 3)-4-O-benzoyl-2-O-benzyl-1-thio-β-L-fucopyranoside (4)
and N-(4-O-Benzoyl-2,3-di-O-benzyl-α-L-fucopyranosyl)-
trichloroacetamide (21). Trichloroacetimidate donor 8 (133 mg,
0.224 mmol) and acceptor 7 (87 mg, 0.187 mmol) were azeotroped
with toluene at 20 °C and dissolved in anhydrous CH2Cl2 (5 mL).
Freshly activated 4 Å molecular sieves (500 mg) were added, and the
mixture was stirred at room temperature for 1 h under nitrogen. The
reaction mixture was cooled to −78 °C and TMSOTf (3.4 μL, 18.7
μmol) was added dropwise. After stirring for 20 min at −78 °C, the
mixture was allowed to warm to 0 °C over 0.5 h. The mixture was
HSQC anomeric cross peak (400 MHz, CDCl3) δ 5.62/95.7 (JC1/H1
=
176.4 Hz); HRMS (ESI-TOF) m/z Calcd for C19H24O9Na [M + Na]+
419.1318, found 419.1308.
p-Methoxyphenyl 4-O-benzoyl-2-O-benzyl-α-L-fucopyrano-
side (5). According to the sequential four-step procedure described
in the synthesis of 7, compound 17 (350 mg, 0.88 mmol) was
converted into 5 (298 mg, 70%) as a foam: [α]2D0 −136.4 (c 0.287,
1
CH2Cl2); H NMR (400 MHz, CDCl3) δ 8.10−8.04 (m, 2H, ArH),
7.62−7.56 (m, 1H, ArH), 7.50−7.42 (m, 2H, ArH), 7.36−7.26 (m,
5H, ArH), 7.06−7.00 (m, 2H, ArH), 6.87−6.81 (m, 2H, ArH), 5.55
(dd, J = 3.4, 1.1 Hz, 1H, H-4), 5.50 (d, J = 3.5 Hz, 1H, H-1), 4.71 (s,
2H, CH2Ar), 4.49 (dd, J = 10.0, 3.5 Hz, 1H, H-3), 4.32 (qd, J = 6.6, 0.8
Hz, 1H, H-5), 3.96 (dd, J = 10.1, 3.5 Hz, 1H, H-2), 3.79 (s, 3H,
OCH3), 2.43 (br.s, 1H, OH), 1.17 (d, J = 6.6 Hz, 3H, H-6); 13C NMR
(100 MHz, CDCl3) δ 166.5 (CO), 155.1, 151.2, 137.7, 133.2, 129.9,
129.8, 128.6, 128.5, 128.12, 128.08, 118.0, 114.7 (ArC), 96.4 (C-1),
76.4 (C-2), 73.5 (C-4), 72.7 (CH2Ar), 68.3 (C-3), 65.9 (C-5), 55.7
(OCH3), 16.2 (C-6); Coupled HSQC anomeric cross peak (400 MHz,
CDCl3) δ 5.50/96.4 (JC1/H1 = 171.0 Hz); HRMS (ESI-TOF) m/z
Calcd for C27H28O7Na [M + Na]+ 487.1733, found 487.1728.
p-Tolyl 3,6-di-O-benzyl-2-O-(4-methoxybenzyl)-1-thio-β-D-
galactopyranoside (20). A solution of 18 (300 mg, 0.51 mmol)
in methanol (5 mL) was treated with p-toluenesulfonic acid (10 mg,
4723
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The Journal of Organic Chemistry
Note
treated with NaHCO3 (sat. aq.), diluted with CH2Cl2 and filtered
through a pad of Celite. The organic layer was washed with brine,
dried over MgSO4, filtered and concentrated in vacuo. Flash
chromatography on silica gel (EtOAc/hexanes/CH2Cl2 1:10:2)
afforded disaccharide 4 (112 mg, 67%) and side product 21 (17 mg,
15%) as white foam. Glycosylation of acceptor 7 (52 mg, 0.112 mmol)
using trifluoroacetimidate 8′ (84 mg, 0.135 mmol) under the
activation of TMSOTf (2 μL, 11.2 μmol) in anhydrous CH2Cl2 (3
mL) was conducted at −78 °C over 2.5 h with the same procedure,
providing disaccharide 4 (79 mg, 78%).
CDCl3) δ 170.5 (COCH3), 166.5 (COPh), 158.8, 155.0, 151.1, 138.4,
138.3, 138.2, 133.2, 130.8, 130.1, 129.9, 128.9, 128.5, 128.32, 128.29,
128.2, 127.9, 127.7, 127.6, 127.5, 127.4, 118.1, 114.6, 113.4 (ArC),
98.9 (C-1II), 97.0 (C-1I), 76.1 (C-3II), 75.9 (C-2I), 74.6 (C-2II), 74.2
(C-4I), 73.4 (CH2Ar), 72.6 (CH2Ar), 72.4 (C-3I), 72.1 (CH2Ar), 72.0
(CH2Ar), 69.5 (C-6II), 68.9 (C-4II), 68.7 (C-5II), 65.8 (C-5I), 55.7
(OCH3), 55.2 (OCH3), 20.9 (COCH3), 16.1 (C-6I); Coupled HSQC
anomeric cross peaks (400 MHz, CDCl3) δ 5.34/97.0 (JC1/H1 = 171.0
Hz, residue I), 5.46/98.9 (JC1/H1 = 175.5 Hz, residue II); HRMS (ESI-
TOF) m/z Calcd for C57H60O14Na [M + Na]+ 991.3881, found
991.3931.
Data for 4. [α]2D0 −162.7 (c 0.117, CH2Cl2); H NMR (400 MHz,
1
CDCl3) δ 8.05−7.98 (m, 2H, ArH), 7.96−7.87 (m, 2H, ArH), 7.66−
7.59 (m, 2H, ArH), 7.59−7.49 (m, 2H, ArH), 7.45−7.28 (m, 9H,
ArH), 7.22−7.06 (m, 12H, ArH), 5.67 (d, J = 2.9 Hz, 1H, H-4I), 5.28
(d, J = 3.4 Hz, 1H, H-1II), 5.16 (dd, J = 3.0, 0.9 Hz, 1H, H-4II), 5.02
and 4.55 (ABq, JAB = 10.5 Hz, 2H, CH2Ar), 4.65 (d, J = 9.5 Hz, 1H, H-
1I), 4.63 and 4.41 (ABq, JAB = 11.1 Hz, 2H, CH2Ar), 4.52 and 4.43
(ABq, JAB = 12.1 Hz, 2H, CH2Ar), 4.12 (qd, J = 6.4, 0.8 Hz, 1H, H-
5II), 4.01 (dd, J = 9.5, 3.2 Hz, 1H, H-3I), 3.90 (dd, J = 10.1, 3.2 Hz, 1H,
H-3II), 3.86−3.77 (m, 3H, H-2I, H-2II, H-5I), 2.41 (s, 3H, ArCH3),
1.28 (d, J = 6.4 Hz, 3H, H-6I), 0.91 (d, J = 6.5 Hz, 3H, H-6II); 13C
NMR (100 MHz, CDCl3) δ 166.3 (CO), 166.2 (CO), 138.3,
138.24, 138.23, 137.9, 133.4, 133.2, 132.9, 130.2, 130.0, 129.8, 129.7,
129.6, 129.2, 128.5, 128.4, 128.3, 128.1, 128.0, 127.9, 127.7, 127.6,
127.3, 127.2 (ArC), 93.4 (C-1II), 87.3 (C-1I), 76.1 (C-3II), 75.8 (C-2I),
75.7 (C-3I), 75.5 (CH2Ar), 74.0 (C-2II), 73.6 (C-5I), 72.7 (CH2Ar),
71.5 (CH2Ar), 71.3 (C-4II), 68.8 (C-4I), 65.0 (C-5II), 21.3 (ArCH3),
17.0 (C-6II), 16.0 (C-6II); Coupled HSQC anomeric cross peaks (400
MHz, CDCl3) δ 4.65/87.3 (JC1/H1 = 153.3 Hz, residue I), 5.28/93.4
(JC1/H1 = 172.1 Hz, residue II); HRMS (ESI-TOF) m/z Calcd for
C54H54O10NaS [M + Na]+ 917.3335, found 917.3351.
p-Methoxyphenyl (4-O-acetyl-3,6-di-O-benzyl-α-D-galacto-
pyranosyl)-(1 → 3)-4-O-benzoyl-2-O-benzyl-α-L-fucopyrano-
side (3). DDQ (41 mg, 0.19 mmol) was added to a solution of
compound 22 (157 mg, 0.16 mmol) in a mixed solvent (CH2Cl2/
pH7.0 phosphate buffer = 20/1, 5 mL) at 0 °C. After stirring for 2 h at
0 °C, the reaction was quenched by adding NaHCO3 (sat. aq.) and
CH2Cl2. The organic phase was washed consecutively with NaHCO3
(sat. aq.) and brine, dried over MgSO4, filtered and concentrated.
Flash chromatography on silica gel (EtOAc/hexanes/CH2Cl2 1:5:1)
1
afforded 3 (103 mg, 75%) as a white foam: H NMR (400 MHz,
CDCl3) δ 8.06−8.01 (m, 2H, ArH), 7.65−7.57 (m, 1H, ArH), 7.50−
7.43 (m, 2H, ArH), 7.36−7.20 (m, 15H, ArH), 7.03−6.96 (m, 2H,
ArH), 6.87−6.79 (m, 2H, ArH), 5.57 (d, J = 2.4 Hz, 1H, H-4II), 5.53
(d, J = 2.7 Hz, 1H, H-4I), 5.43 (d, J = 3.5 Hz, 1H, H-1I), 5.39 (d, J =
3.9 Hz, 1H, H-1II), 4.71 and 4.61 (ABq, JAB = 11.6 Hz, 2H, CH2Ar),
4.66 and 4.26 (ABq, JAB = 11.3 Hz, 2H, CH2Ar), 4.59 and 4.50 (ABq,
JAB = 11.8 Hz, 2H, CH2Ar), 4.52 (dd, J = 10.1, 3.5 Hz, 1H, H-3I), 4.40
(dd, J = 6.2, 6.2 Hz, 1H, H-5II), 4.18 (q, J = 6.3 Hz, 1H, H-5I), 4.04
(dd, J = 10.2, 3.5 Hz, 1H, H-2I), 3.89 (ddd, J = 10.0, 8.1, 3.9 Hz, 1H,
II
H-2II), 3.79 (s, 3H, OCH3), 3.62−3.51 (m, 2H, H-6aII, H-6b ), 3.48
(dd, J = 10.0, 3.2 Hz, 1H, H-3II), 2.14 (d, J = 8.1 Hz, 1H, OH), 2.04 (s,
3H, COCH3), 1.07 (d, J = 6.5 Hz, 3H, H-6I); 13C NMR (100 MHz,
CDCl3) δ 170.4 (COCH3), 166.3 (COPh), 155.1, 151.1, 138.2, 137.9,
137.6, 133.4, 129.8, 128.6, 128.5, 128.33, 128.28, 128.2, 128.0, 127.9,
127.7, 127.6, 118.1, 114.6 (ArC), 100.4 (C-1II), 96.6 (C-1I), 76.7 (C-
3II), 75.9 (C-2I), 73.8 (C-3II), 73.7 (C-3I), 73.4 (CH2Ar), 72.6
(CH2Ar), 71.6 (CH2Ar), 68.9 (C-5II), 68.8 (C-6II), 68.6 (C-2II), 67.7
(C-4II), 65.8 (C-5I), 55.7 (OCH3), 20.8 (COCH3), 16.1 (C-6I);
Coupled HSQC anomeric cross peaks (400 MHz, CDCl3) δ 5.43/96.6
(JC1/H1 = 171.9 Hz, residue I), 5.39/100.4 (JC1/H1 = 174.4 Hz, residue
II); HRMS (ESI-TOF) m/z Calcd for C49H52O13Na [M + Na]+
871.3306, found 871.3295.
Data for 21. [α]2D0 −76.7 (c 0.333, CH2Cl2).1H NMR (400 MHz,
CDCl3) δ 8.10−8.05 (m, 2H, ArH), 7.63−7.58 (m, 1H, ArH), 7.51−
7.44 (m, 2H, ArH), 7.36−7.26 (m, 11H, ArH, NH), 5.67 (dd, J = 5.4,
5.4 Hz, 1H, H-1), 5.64 (dd, J = 3.3, 1.7 Hz, 1H, H-4), 4.84 and 4.59
(ABq, JAB = 11.5 Hz, 2H, CH2Ar), 4.76 and 4.61 (ABq, JAB = 11.5 Hz,
2H, CH2Ar), 4.08 (dd, J = 9.2, 5.2 Hz, 1H, H-2), 4.04 (qd, J = 6.5, 1.6
Hz, 1H, H-5), 3.79 (dd, J = 9.2, 3.3 Hz, 1H, H-3), 1.27 (d, J = 6.5 Hz,
3H, H-6); 13C NMR (100 MHz, CDCl3) δ 166.1 (COPh), 162.4
(COCCl3), 137.5, 137.2, 133.4, 129.9, 129.6, 128.6, 128.5, 128.4,
128.2, 127.96, 127.95, 127.8 (ArC), 92.5 (CCl3), 77.2 (C-1), 76.1 (C-
3), 73.49 (C-2), 73.45 (CH2Ar), 71.9 (CH2Ar), 69.9 (C-4), 66.9 (C-
5), 16.2 (C-6); Coupled HSQC anomeric cross peak (400 MHz,
CDCl3) δ 5.67/77.2 (JC1/H1 = 169.4 Hz); HRMS (ESI-TOF) m/z
Calcd for C29H28NO6NaCl3 [M + Na]+ 614.0880, found 614.0859.
p-Methoxyphenyl [4-O-acetyl-3,6-di-O-benzyl-2-O-(4-me-
thoxybenzyl)-α-D-galactopyranosyl]-(1 → 3)-4-O-benzoyl-2-O-
benzyl-α-L-fucopyranoside (22). Donor 6 (159 mg, 0.253 mmol)
and acceptor 5 (98 mg, 0.211 mmol) were azeotroped with toluene
and dissolved in anhydrous CH2Cl2 (5 mL). Freshly activated 4 Å
molecular sieves (500 mg) were added, and the mixture was stirred at
room temperature for 0.5 h. The reaction mixture was cooled to −20
°C and treated successively with NIS (57 mg, 0.253 mmol) and
AgOTf (5 mg, 21.1 μmol) under nitrogen. After stirring for 1 h at −20
°C, the mixture was treated with NaHCO3/Na2S2O3 (sat. aq.), diluted
with EtOAc and filtered through a pad of Celite. The organic layer was
washed with brine, dried over MgSO4, filtered and concentrated in
vacuo. Flash chromatography on silica gel (EtOAc/hexanes/CH2Cl2
1:5:1) afforded disaccharide 22 (162 mg, 79%) as a white foam: [α]D20
+149.4 (c 0.027, CH2Cl2); 1H NMR (400 MHz, CDCl3) δ 8.09−8.03
(m, 2H, ArH), 7.63−7.57 (m, 1H, ArH), 7.49−7.42 (m, 2H, ArH),
7.37−7.32 (m, 2H, ArH), 7.30−7.19 (m, 13H, ArH), 7.01−6.95 (m,
4H, ArH), 6.85−6.79 (m, 2H, ArH), 6.68−6.62 (m, 2H, ArH), 5.60
(dd, J = 2.8, 1.1 Hz, 1H, H-4II), 5.50 (dd, J = 3.4, 0.8 Hz, 1H, H-4I),
5.46 (d, J = 3.2 Hz, 1H, H-1II), 5.34 (d, J = 3.6 Hz, 1H, H-1I), 4.64−
p-Methoxyphenyl (4-O-benzoyl-2,3-di-O-benzyl-α-L-fuco-
pyranosyl)-(1 → 3)-(4-O-benzoyl-2-O-benzyl-α-L-fucopyrano-
syl)-(1 → 2)-(4-O-acetyl-3,6-di-O-benzyl-α-D-galactopyrano-
syl)-(1 → 3)-4-O-benzoyl-2-O-benzyl-α-L-fucopyranoside (2).
A solution of donor 4 (65.1 mg, 72.7 μmol) and acceptor 3 (55 mg,
64.8 μmol) in a mixed anhydrous solvent (CH2Cl2/ether = 1/1, 4 mL)
containing freshly activated 4 Å molecular sieves (400 mg) was stirred
at room temperature for 1 h under nitrogen. The mixture was cooled
to −10 °C and treated successively with NIS (18 mg, 78.8 μmol) and
AgOTf (2 mg, 6.5 μmol). After stirring for 3 h at −10 °C, the mixture
was treated with triethylamine and filtered through a pad of Celite.
The filtrate was concentrated in vacuo to residue. Flash chromatog-
raphy on silica gel (EtOAc/hexanes/CH2Cl2 1:10:1) provided
tetrasaccharide 2 (82 mg, 78%) as a white foam: [α]2D0 −141.6 (c
1
0.243, CH2Cl2); H NMR (400 MHz, CDCl3) δ 8.11−8.05 (m, 2H,
ArH), 8.00−7.93 (m, 2H, ArH), 7.91−7.84 (m, 2H, ArH), 7.66−7.60
(m, 1H, ArH), 7.59−7.52 (m, 1H, ArH), 7.51−7.39 (m, 7H, ArH),
7.39−7.19 (m, 10H, ArH), 7.18−7.07 (m, 14H, ArH), 7.07−7.01 (m,
2H, ArH), 7.01−6.92 (m, 4H, ArH), 6.87 (d, J = 7.2 Hz, 2H, ArH),
6.82−6.75 (m, 2H, ArH), 5.66 (d, J = 2.4 Hz, 1H, H-4II), 5.57 (d, J =
2.7 Hz, 1H, H-4I), 5.46 (d, J = 3.5 Hz, 1H, H-1I), 5.44 (d, J = 3.6 Hz,
1H, H-1II), 5.40 (d, J = 3.7 Hz, 1H, H-1III), 5.18 (d, J = 3.0 Hz, H-1IV),
5.12−5.08 (m, 2H, H-4III, H-4IV), 4.81 and 4.77 (ABq, JAB = 12.5 Hz,
2H, CH2Ar), 4.71 (A of ABq, JAB = 11.4 Hz, 1H, CHHAr), 4.68−4.59
(m, 3H, H-3I, H-5II, CHHAr), 4.53 and 4.38 (ABq, JAB = 12.2 Hz, 2H,
CH2Ar), 4.52 (B of ABq, JAB = 11.7 Hz, 1H, CHHAr), 4.47 (A of ABq,
JAB = 11.5 Hz, 1H, CHHAr), 4.36 (A of ABq, JAB = 12.0 Hz, 1H,
4.45 (m, 9H, H-5II, H-3I, CHHAr, 3 × CH2Ar), 4.28 (B of ABq, JAB
=
11.1 Hz, 1H, CHHAr), 4.12 (qd, J = 6.6, 0.7 Hz, 1H, H-5I), 4.05 (dd, J
= 10.1, 3.6 Hz, 1H, H-2I), 3.78 (s, 3H, OCH3), 3.77−3.73 (m, 2H, H-
II
3II, H-2II), 3.72 (s, 3H, OCH3), 3.62−3.57 (m, 2H, H-6aII, H-6b ), 2.03
(s, 3H, COCH3), 1.02 (d, J = 6.5 Hz, 3H, H-6I); 13C NMR (100 MHz,
4724
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The Journal of Organic Chemistry
Note
CHHAr), 4.33−4.10 (m, 8H, H-5III, H-3III, 3 × CHHAr, H-2II, H-2I,
H-5I), 3.94 (dd, J = 10.3, 3.2 Hz, 1H, H-3II), 3.88−3.73 (m, 7H, H-5IV,
tetra-O-sulfated derivative: HRMS (ESI-TOF) m/z Calcd for
C73H80O31Na3S4 [M + 3Na]− 1649.3260, found 1649.3213.
II
H-2III, H-2IV, H-3IV, OCH3), 3.66−3.60 (m, 2H, H-6aII, H-6b ), 2.08
A solution of this crude product in a mixed solvent (MeOH/H2O =
1/2, 6 mL) containing 20% Pd(OH)2/C (450 mg) was degassed and
equipped with a hydrogen balloon. After stirring at room temperature
for 2 days, the mixture was filtered through Celite, and the filtrate was
concentrated in vacuo. The residue was subjected to a Dowex 50WX8
(Na+ form) column followed by size-exclusion chromatography on a
Sephadex G-25 column eluted with H2O. The appropriate fractions
were lyophilized to provide final compound 1 (17 mg, 80% as
(s, 3H, COCH3), 1.03 (d, J = 6.5 Hz, 3H, H-6I), 0.94 (d, J = 6.5 Hz,
3H, H-6III), 0.72 (d, J = 6.5 Hz, 3H, H-6IV); 13C NMR (100 MHz,
CDCl3) δ 170.3 (COCH3), 166.6 (COPh), 166.3 (COPh), 166.0
(COPh), 155.1, 151.2, 138.6, 138.38, 138.36, 138.3, 138.2, 138.0,
133.4, 132.9, 132.8, 130.2, 129.94, 129.91, 129.89, 129.84, 129.83,
128.7, 128.6, 128.3, 128.2, 128.1, 128.02, 128.01, 127.9, 127.8, 127.7,
127.6, 127.5, 127.2, 127.1, 127.0, 126.9, 126.8, 126.7, 118.0, 114.6
(ArC), 99.8 (C-1II), 97.7 (C-1III), 96.2 (C-1I), 92.8 (C-1IV), 76.2 (C-
3II), 76.1 (C-3IV), 75.9 (C-2I), 74.2 (C-2IV), 73.9 (C-4I, C-2III), 73.5
(CH2Ar), 72.3 (CH2Ar), 72.1 (C-3I), 71.6 (C-2II, C-4IV), 71.5
(CH2Ar), 71.3 (CH2Ar), 71.0 (CH2Ar), 70.9 (CH2Ar), 69.5 (C-6II),
69.4 (C-4III), 69.3 (C-3III), 69.0 (C-5II), 68.2 (C-4II), 65.8 (C-5I) 65.2
(C-5IV), 64.61 (C-5III), 55.7 (OCH3), 20.9 (COCH3), 16.3 (C-6III),
16.1 (C-6I), 15.9 (C-6IV); Coupled HSQC anomeric cross peaks (400
MHz, CDCl3) δ 5.46/96.2 (JC1/H1 = 171.9 Hz, residue I), 5.44/99.8
(JC1/H1 = 176.9 Hz, residue II), 5.40/97.7 (JC1/H1 = 174.4 Hz, residue
III), 5.18/92.8 (JC1/H1 = 171.9 Hz, residue IV); HRMS (ESI-TOF) m/
z Calcd for C96H98O23Na [M + Na]+ 1641.6397, found 1641.6345.
p-Methoxyphenyl (2,3-di-O-benzyl-α-L-fucopyranosyl)-(1 →
3)-(2-O-benzyl-α-L-fucopyranosyl)-(1 → 2)-(3,6-di-O-benzyl-α-
D-galactopyranosyl)-(1 → 3)-2-O-benzyl-α-L-fucopyranoside
(23). To a solution of tetrasaccharide 2 (74 mg, 45.4 μmol) in
methanol (5 mL) was added MeONa (12 mg, 230 μmol). The mixture
was heated at 50 °C for 3 d. Dowex 50WX8 acidic resin was added to
neutralize MeONa. The resin was removed, and the solution was
concentrated in vacuo. Flash chromatography on silica gel (MeOH/
CH2Cl2 1:100) provided tetraol 23 (47 mg, 82%) as a white powder:
[α]2D0 −100.1 (c 0.817, CH2Cl2); 1H NMR (400 MHz, CDCl3) δ
7.39−7.10 (m, 30H, ArH), 7.01−6.95 (m, 2H, ArH), 6.85−6.79 (m,
2H, ArH), 5.37 (d, J = 3.7 Hz, 1H, H-1I), 5.26 (d, J = 3.3 Hz, 1H, H-
1II), 5.02 (d, J = 3.6 Hz, 1H, H-1III), 4.92 and 4.84 (ABq, JAB = 12.8
Hz, 2H, CH2Ar), 4.76 and 4.62 (ABq, JAB = 11.8 Hz, 2H, CH2Ar),
4.74−4.67 (m, 2H, CH2Ar), 4.68 (A of ABq, JAB = 11.7 Hz, 1H,
CHHAr), 4.63 (A of ABq, JAB = 11.6 Hz, 1H, CHHAr), 4.59−4.54 (m,
1H, H-4II), 4.54−4.45 (m, 5H, H-1IV, CH2Ar, CHHAr, CHHAr), 4.28
(qd, J = 5.9, 0.8 Hz, 1H, H-5III), 4.14−4.06 (m, 2H, H-3I, H-5IV),
4.06−4.00 (m, 2H, H-4I, H-5II), 4.00−3.88 (m, 5H, H-5I, H-2II, H-2I,
H-3II, H-3III), 3.88−3.71 (m, 7H, H-6aII, H-3IV, H-2III, OCH3, H-2IV),
1
tetrasodium salt) as a white fluffy solid: H NMR and HSQC (400
MHz, D2O, 300 K) δ 7.14 (d, J = 9.1 Hz, 2H, ArH), 7.01 (d, J = 9.0
Hz, 2H, ArH), 5.51 (d, J = 3.8 Hz, 1H, H-1I), 5.37 (d, J = 3.7 Hz, 1H,
H-1II), 5.29 (d, J = 3.9 Hz, 1H, H-1III), 5.19 (d, J = 3.9 Hz, 1H, H-1IV),
4.80−4.75 (overlapped by HOD, 3H, H-4III, H-4II, H-4I), 4.64 (d, J =
2.7 Hz, 1H, H-4IV), 4.52 (dd, J = 8.5, 3.6 Hz, 1H, H-5II), 4.50−4.36
(m, 5H, H-5IV, H-5III, H-5I, H-3I, H-3II), 4.18 (dd, J = 10.5, 3.9 Hz, 1H,
H-2I), 4.14 (dd, J = 10.5, 2.7 Hz, 1H, H-3III), 4.05 (dd, J = 10.6, 3.1
Hz, 1H, H-3IV), 4.00 (dd, J = 10.5, 3.8 Hz, 1H, H-2II), 3.93 (dd, J =
10.4, 3.9 Hz, 1H, H-2III), 3.89−3.76 (m, 6H, H-6aII, OCH3, H-2IV, H-
II
6b ), 1.30 (d, J = 6.5 Hz, 6H, H-6III, H-6IV), 1.25 (d, J = 6.5 Hz, 3H, H-
6I); 13C-APT NMR (100 MHz, D2O, 300 K) δ 154.7, 150.3, 119.1,
115.2 (ArC), 100.0 (C-1III), 99.4 (C-1II), 98.4 (C-1I), 97.6 (C-1IV),
80.8 (C-4IV), 80.0 (C-4I), 78.9 (C-4III), 78.2 (C-4II), 75.4 (C-3III), 73.8
(C-2II), 73.0 (C-3I), 71.1 (C-5II), 69.0 (C-3IV), 68.6 (C-2IV), 68.1 (C-
2I), 67.9 (C-3II), 67.2 (C-2III), 67.1 (C-5I), 66.4 (C-5III), 66.3 (C-5IV),
61.5 (C-6II), 55.8 (OCH3), 15.90 (C-6III), 15.86 (C-6IV), 15.8 (C-6I);
Coupled HSQC anomeric cross peaks (400 MHz, D2O) δ 5.51/98.4
(JC1/H1= 173.8 Hz, residue I), 5.37/99.4 (JC1/H1 = 176.3 Hz, residue
II), 5.29/100.0 (JC1/H1 = 175.5 Hz, residue III), 5.19/97.6 (JC1/H1
=
173.0 Hz, residue IV); HRMS (ESI-TOF) m/z Calcd for
C31H44O31Na3S4 [M + 3Na]− 1109.0443, found 1109.0490.
ASSOCIATED CONTENT
■
S
* Supporting Information
1H, 13C, and 2D NMR spectra of synthetic compounds. This
material is available free of charge via the Internet at http://
pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: whu@chem.ecnu.edu.cn. Fax: +86-021-62221235.
■
II
3.71−3.63 (m, 2H, H-6b , H-4IV), 3.22 (br.s, 1H, OH), 3.19 (d, J = 1.7
Hz, 1H, H-4III), 2.58 (s, 1H, OH), 2.32 (s, 1H, OH), 1.62 (br.s, 1H,
OH), 1.36 (d, J = 6.5 Hz, 3H, H-6III), 0.94 (d, J = 6.6 Hz, 3H, H-6IV),
0.81 (d, J = 6.5 Hz, 3H, H-6I); 13C NMR and DEPT135 (100 MHz,
CDCl3) δ 154.7, 151.6, 138.8, 138.5, 138.3, 138.0, 137.9, 136.8,
128.61, 128.57, 128.5, 128.34, 128.25, 128.23, 128.18, 128.00, 127.98,
127.83, 127.76, 127.7, 127.6, 127.5, 127.4, 117.6, 114.6 (ArC), 101.0
(C-1III), 99.8 (C-1II), 97.3 (C-1I), 94.0 (C-1IV), 81.7 (C-3I), 80.4 (C-
2II), 78.3 (C-3IV), 75.0 (C-2IV), 75.0 (C-2III), 74.4 (C-3III), 74.12 (C-
3II), 74.10 (2 × CH2Ar), 73.53 (C-2I), 73.51 (CH2Ar), 72.7 (CH2Ar),
72.4 (CH2Ar), 72.2 (CH2Ar), 71.2 (C-6II), 70.7 (C-4I), 69.9 (C-4IV),
69.4 (C-4II), 69.3 (C-5II), 68.0 (C-4III), 66.7 (C-5I), 65.9 (C-5III), 65.6
(C-5IV), 55.7 (OCH3), 17.2 (C-6III), 15.9 (C-6I, C-6IV); Coupled
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We wish to thank the NSFC (21125209, 21332003), the
MOST of China (2011CB808600), and STCSM
(12JC1403800) for financial support.
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