Regioselective synthesis of a glycomimetic trisaccharide of Sialyl Lewis (sLex)

Article abstract of DOI:10.1016/j.carres.2008.11.019

Sialyl Lewis (sLe^x) is the smallest naturally occurring carbohydrate ligand that binds to E-Selectin on the activated endothelium. We report here the total synthesis of acetic acid-sLe^x analog (12), for testing as a therapeutic agent

Full text of DOI:10.1016/j.carres.2008.11.019

Carbohydrate Research 344 (2009) 395–399
Contents lists available at ScienceDirect
Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
Note
Regioselective synthesis of a glycomimetic trisaccharide of Sialyl Lewis (sLex)
Sameh E. Soliman a, Rafik W. Bassily a, Ramadan I. El-Sokkary a, Joseph Banoub b, Mina A. Nashed a,
*
a Department of Chemistry, Faculty of Science, Alexandria University, Ibrahimia, PO Box 426, Alexandria 21321, Egypt
b Department of Chemistry, Memorial University of Newfoundland, St. John’s, Newfoundland, Canada A1B 3V6
a r t i c l e i n f o
a b s t r a c t
Sialyl Lewis (sLex) is the smallest naturally occurring carbohydrate ligand that binds to E-Selectin on
Article history:
the activated endothelium. We report here the total synthesis of acetic acid-sLex analog (12), for testing
Received 28 September 2008
Received in revised form 11 November 2008
Accepted 27 November 2008
Available online 10 December 2008
as a therapeutic agent. Methoxyethyl 4-O-(3,4-O-isopropylidene-b-
oside (3) was prepared starting from the methoxyethyl-b- -lactoside (2), which was selectively benzoy-
lated to give the methoxyethyl 2,6-di-O-benzoyl-4-O-(2,6-di-O-benzoyl-3,4-O-isopropylidene-b-
galactopyranosyl)-b- -glucopyranoside (4). Glycosylation of acceptor 4 with methyl 2,3,4-tri-O-ben-
zyl-1-thio-b- -fucopyranoside (5) in the presence of cupric bromide and tetrabutylammonium bromide
afforded the corresponding methoxyethyl 2,6-di-O-benzyl-3-O-(2,3,4-tri-O-benzyl- -fucopyranosyl)-
4-O-(2,6-di-O-benzyl-3,4-O-isopropylidene-b- -galactopyranosyl)-b- -glucopyranoside (6). Selective
D-galactopyranosyl)-b-D-glucopyran-
D
D
-
D
Keywords:
L
Sialyl Lewis (sLex)
Oligosaccharides
Sialic acid bioisosters
Substituted lactoside
a
-L
D
D
removal of the 400,600-O-isopropylidene group from 6 gave the deprotected trisaccharide 7. The regiose-
lective esterification of O-300 of trisaccharide 8 (obtained from the dibutylstannylene derivative of 7)
with benzyl-2-bromoacetate and tetrabutylammonium bromide afforded the 300-O-carbobenzyloxym-
ethyl trisaccharide derivative 9, which on saponification and hydrogenolysis with palladium–charcoal
afforded the target trisaccharide 12 glycomimetic of Sialyl Lewis (sLex) trisaccharide omitting the sialic
acid moiety.
Ó 2008 Elsevier Ltd. All rights reserved.
Cell-surface glycoconjugates are known to act as cell–cell recog-
nition molecules via the specific binding between carbohydrates
on one cell and the protein receptors on the opposing cell.1 The
selectin biomolecules are a family of carbohydrate binding pro-
teins that mediate the tethering and rolling of the leukocytes in
the blood vessel endothelium at the sites of inflammation.2,3 They
are also implicated in the hematogenous metastasis of some cancer
2,20,6,60 having free hydroxyl groups at O-3 and potentially free
at O-30, but the structure of the resulting tetrabenzoate 4 was not
fully characterized.23,24
In the initial stage of the synthesis (Scheme 1), the catalytic O-
deacetylation of the hepta-acetate (1)25 afforded methoxyethyl 4-
O-(b-D-galactopyranosyl)-b-D-glucopyranoside (2), which on treat-
ment with 2,2-dimethoxypropane in the presence of camphorsul-
cells.4,5 The sialyl Lewis X (sLex) tetrasaccharide,6–8
(2?3)-b-Galp-(1?4)- -Fucp-(1?3)-GlcpNAc, has been generally
a
-Neup5Ac-
fonic acid26 gave the methoxyethyl 4-O-(3,4-O-isopropylidene-b-
a
D-galactopyranosyl)-b-D-glucopyranoside (3). Regioselective ben-
recognized as a common ligand for all selectin biomolecules.9,10
Numerous analogs and mimetics of the Lex and sLex have been
designed and synthesized previously11–17 to elucidate the mecha-
nism of selectin recognition and to afford novel therapeutic agents
for the treatment of allergy, microbial infection, and inflammatory
and autoimmune diseases.18–20 Recently, Asnani and Auzan-
neau21,22 used our strategy, which was reported for the synthesis
zoylation of the 30,40-O-isopropylidene derivative (3) at low tem-
perature produced mainly, methoxyethyl 2,6-di-O-benzoyl-4-O-
(2,6-di-O-benzoyl-3,4-O-isopropylidene-b-
-glucopyranoside (4) as fine needles in excellent yield.
The structural elucidation of the methoxyethyl-b-
D-galactopyranosyl)-b-
D
D-lactoside
acceptor (4) was accomplished using a two dimensional 1H–1H
COSY experiment beginning with resonances of H-20 and H-2.
The chemical shifts of the other 1H resonances were established
by tracing the connectivity of the cross-peaks on the COSY contour
map. Additional support for the proposed structure 4 was achieved
through a close examination of the 13C NMR spectrum, 13C–1H cor-
relation, and DEPT experiments.
of partially benzoylated 30,40-O-isopropylidene-b-
D-lactosides, to
prepare key intermediates for the assembly of sialyl Lewis X (sLex)
analogs.23,24 The aim of our work is to synthesize the glycomimetic
trisaccharide of sLex, lacking the sialic acid moiety, for testing as a
therapeutic agent.
In a previous work, we have shown that 30,40-O-isopropylidene-
Fucosylation of the disaccharide acceptor 4 with the glycosyl
b-D
-lactosides could be selectively benzoylated at positions
donor methyl 2,3,4-tri-O-benzyl-1-thio-b-L-fucopyranoside (5) in
the presence of the glycosyl promoter cupric bromide, tetra-n-
butylammonium bromide, and activated powdered molecular
sieves 4 Å, in methylene chloride, gave the expected trisacccharide
* Corresponding author.
E-mail address: mina4nashed@yahoo.com (M.A. Nashed).
0008-6215/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2008.11.019

396
S. E. Soliman et al. / Carbohydrate Research 344 (2009) 395–399
SMe
OBn
O
OBn
5
BnO
OR1
O
OR1
R3O
R4O
OR1
O
OBz
O
OBz
O
O
O
O
R2O
HO
HO
OBz
OBz
O
OR1
O
O
e
O
O
O
O
O
O
O
OBz
O
O
d
OBz
OBz
OBz
R1 = R2 = R3 = R4 = Ac
R1 = R2 = R3 = R4 = H
O
1
2
OBn
O
a
OBn
OBn
BnO
OBn
BnO
b
c
3
4
R1 = R2 = H , R3-R4 = C(CH3)2
R1 = Bz , R2 = H , R3-R4 = C(CH3)2
6
7
f
HO
OH
O
OH
O
OBz
O
i
RO
OBz
O
OBz
O
OBz
O
O
Bu
Sn
Bu
O
O
O
O
O
O
g
O
HO
O
O
OH
O
O
O
O
OH
O
O
O
BnO
O
OBz
OBz
O
OBz
OBz
OR
O
O
OR
OBn
OBn
RO
OBn
OBn
BnO
BnO
11
12
R = Bn
R = H
j
9
R = H
8
h
10
R = Ac
Scheme 1. Reagents and conditions: (a) (1) CH3OH, Na-metal, 2 h rt; (2) Amberlite IR-120 (H+) resin; (b) (1) camphorsulfonic acid, 2,2-dimethoxypropane, 48 h rt; (2) 10:1
CH3OH–H2O, reflux 3 h; (c) BzCl, C5H5N, –45 °C, 3–4 h; (d) (1) acceptor 4, 5:1 CH2Cl2–DMF, CuBr2, n-Bu4NBr, MS 4 Å; (2) donor 5, CH2Cl2, 48 h; (e) 80% aq AcOH, 80 °C, 4 h; (f)
Bu2SnO, CH3OH, reflux 1 h; (g) C6H6, BrCH2COOBn, n-Bu4NBr, MS 4 Å, 70 °C, 3 h; (h) Ac2O, C5H5N; (i) = (a); (j) 10% Pd–C, H2 (g), 1 atm.
methoxyethyl 2,6-di-O-benzyl-3-O-(2,3,4-tri-O-benzyl-
pyranosyl)-4-O-(2,6-di-O-benzyl-3,4-O-isopropylidene-b-
topyranosyl)-b-
-glucopyranoside (6) in excellent yield.27 The 1H
a
D
-
L
-fuco-
was similar to that of 9 except for a broad doublet (J = 2.9 Hz)
observed which was shifted to a lower field resonance of d
5.74 ppm for H-400, a singlet at d 1.80 for the methyl protons of
the acetyl group, and the absence of the OH signal.
-galac-
D
NMR spectrum gave the expected three proton doublet signal for
the fucosyl moiety at d 1.02 (J5,6 = 6.3 Hz, CH–CH3) and one proton
The Zemplén O-debenzoylation in methanolic sodium
methoxide converted the tetrabenzoate (9) quantitatively into
doublet signal at d 5.74 (J1 ,2 = 3.0 Hz, H-10), hence confirming the
assigned structure. The 13C NMR spectrum showed three anomeric
carbons at d 102.2, 100.9 (C-1 and C-100), and 98.0 (C-10) and an
additional signal at d 17.8 corresponding to the CH3 group of the
fucose moiety.
0
0
methoxyethyl 3-O-(2,3,4-tri-O-benzyl-a-L-fucopyranosyl)-4-O-(3-
O-carbobenzyloxymethyl-b- -galactopyranosyl)-b-
D
D
-glucopyran-
oside (11), which was then de-ionized with Amberlite IR-120 (H+)
resin. After filtration and concentration, the residual methyl benzo-
ate was removed by the addition and decantation of several portions
of n-hexane. The crude syrup was used for the hydrogenolysis step
without further purification.
Removal of the isopropylidene group was carried out by warm-
ing the fucosylated trisaccharide (6) in 80% aqueous acetic acid to
give the methoxyethyl 2,6-di-O-benzyl-3-O-(2,3,4-tri-O-benzyl-a-
L
-fucopyranosyl)-4-O-(2,6-di-O-benzyl-b-
D
-galactopyranosyl)-b-
D
-
The hydrogenolysis of the benzyl protecting group was carried
out with 10% Pd–charcoal in CH3OH to afford the free trisaccharide
glucomimetic of sLex (12) lacking the sialic acid moiety. The 1H
NMR spectrum of trisaccharide 12 confirmed the loss of all the
low-field Ph–H signals, and showed the three diagnostic doublets
glucopyranoside (7) in good yield. The 1H and 13C NMR spectra
confirmed the disappearance of the isopropylidene signals and per-
mitted the complete elucidation of the proposed structure.
The fucosylated trisaccharide
7 possessing a free diol at
positions 300,400 was heated at reflux with an equimolar amount of
di-n-butyltin oxide in absolute CH3OH according to the conditions
of Nashed and Anderson,28 followed by evaporation of the CH3OH
to give a syrupy solution of 300,400-O-dibutylstannylene derivative 8,
which was used immediately as such for the following regioselec-
tive etherification.
for the anomeric protons at d 5.26 (J1 ,2 = 3.8 Hz) assigned to the
-fucose moiety, d 4.31 (J = 8.4 Hz) and d 4.27 (J = 7.7 Hz) for
the b- -galactose and b- -glucose moieties.
0
0
a-L
D
D
Further versatility results from the use of methoxyethyl group
as an aglycon because it can be derivatized to the bromide,25 which
is useful as a donor to attach a lipid tail.
Subsequently, the regioselective etherification of fucosylated
trisaccharide 8 was carried out with excess bromoacetic acid ben-
zyl ester and tetrabutylammonium bromide29 in dry benzene at
70 °C for 3 h, to produce exclusively the 300-O-benzyl acetate trisac-
charide derivative (9). The 1H NMR spectrum of compound 9
showed a new signal at d 5.08 (2d, Jgem = 12.0 Hz, OCH2–COOBn),
and loss of one of the OH signals. 13C NMR spectrum showed addi-
tional three inverted peaks at d 67.9 (OCH2–COOBn), 68.8 (OCH2–
COOCH2Ar), and the carbonyl group at d 172.1.
As expected, the regioselective alkylation occurred essentially
at the equatorial oxygen.28 This was evidenced by the acetylation
of trisaccharide 9 with acetic anhydride in pyridine at room tem-
perature to give the mono-acetylated trisaccharide derivative 10.
The 1H NMR spectrum of the mono-acetylated trisaccharide 10
1. Experimental
1.1. General methods
Optical rotations were obtained at 22 °C with a Perkin–Elmer
Model 241 Polarimeter 10 cm, 1 mL microcell. 1H NMR spectra
were recorded at Glycomed, Inc. Alameda, California, USA, with a
Varian Gemini 300 MHz spectrometer, and at Faculty of Science,
Alexandria University, Egypt, at 500 MHz (JEOL EX 500 spectrome-
ter) at ambient temperature. 13C NMR spectra were recorded with
a Varian Gemini 300 MHz instrument operating at 75.50 MHz or
125.77 MHz, and the chemical shifts were referenced to CDCl3 (d
77.7 ppm). 1H NMR and 13C NMR chemical shifts (d) are reported

S. E. Soliman et al. / Carbohydrate Research 344 (2009) 395–399
397
in parts per million (ppm). Coupling constants (J) are reported in
Hertz (Hz). Assignment of proton resonance was verified by the
two dimensional 1H–1H COSY experiments to trace connectivity.
Also, the assignment of carbon resonance was supported by
13C–1H correlation and DEPT experiments. Multiplicities are abbre-
viated as follows: singlet (s), doublet (d), triplet (t), quartet (q),
multiplet (m), and doublet of quartet (dq). Thin Layer Chromatog-
raphy (TLC) was performed on aluminum plates precoated with
silica gel (Merck, GF254). Spots were detected under ultraviolet
(UV) light and/or charred with a solution of 10% H2SO4 in ethanol.
For column chromatography, Merck Silica Gel 60 (particle size
70–230 mesh) was used.
with a conventional aqueous extraction. Evaporation of the solvent
under diminished pressure gave the crude product. Crystallization
from hot CH3OH gave the crystalline tetrabenzoate (4), with a yield
of 70% (13.6 g), in addition to a small yield of the corresponding
pentabenzoate. The obtained crude crystalline compound was used
for the next step without further purification. For identification
purpose, a portion was purified by chromatography on a column
of silica gel using 20:1 toluene–acetone as the eluent. [a] +43
D
(c 1.0, CHCl3); 1H NMR (500 MHz, CDCl3): d 8.06–7.86 (3d, 8H,
J = 7.6 Hz, ortho-Ar), 7.56–7.25 (m, 12H, meta- and para-Ar), 5.37
(t, 1H, J = 7.6 Hz, H-20), 5.23 (dd, 1H, J = 9.4, 8.2 Hz, H-2), 4.87 (dd,
1H, J = 12.5, 2.4 Hz, H-60a), 4.67 (d, 1H, J = 8.2 Hz, bH-10), 4.65 (d,
2H, J = 8.2 Hz, bH-1, OH-3), 4.47–4.36 (m, 3H, H-6a, H-60b, H-30),
4.29–4.25 (m, 2H, H-40, H-50), 4.20 (dd, 1H, J = 12.2, 3.8 Hz, H-6b),
4.01 (dd, 1H, J = 9.9, 7.7 Hz, H-3), 3.86–3.80 (m, 1H, OCHH–
CH2OCH3), 3.74 (t, 1H, J = 9.9 Hz, H-4), 3.69–3.66 (m, 1H, H-5),
3.63–3.59 (m, 1H, OCHH–CH2OCH3), 3.39–3.36 (m, 2H, –CH2–
OCH3), 3.10 (s, 3H, OCH3), 1.65–1.35 (2s, 6H, C(CH3)2); 13C NMR
(75.5 MHz, CDCl3): d 167.1–165.9 (4 ꢁ COAr), 133.9–128.8 (Ar-C),
111.8 (C(CH3)2), 102.1 (C-1), 101.6 (C-10), 82.9 (C-4), 77.6 (C-30),
74.0 (C-3, C-40), 73.6 (C-20), 73.4 (C-2), 72.6 (C-5, C-50), 72.2
(–CH2–OCH3), 69.4 (–OCH2–CH2OCH3), 64.2 (C-60), 63.2 (C-6),
59.4 (OCH3), 28.2, 26.8 (C(CH3)2). HRESIMS: m/z calcd for
[C46H48O16+Na]+, 879.2840; found, 879.2957.
1.1.1. High resolution electrospray ionization mass
spectrometry (HRESIMS)
High resolution conventional electrospray ionization-mass
spectrometry for all the synthesized compounds was acquired in
the positive ion mode using an Applied Biosystems API-QSTAR XL
quadrupole orthogonal time of-flight (QqTOF)-MS/MS hybrid tan-
dem mass spectrometer (Applied Biosystems International-MDS
Sciex, Foster City, California, USA). This instrument is capable of
analyzing a mass range of m/z 5–40,000, with a resolution of
10,000 in the positive ion mode. ESI was performed with the Turbo
Ionspray source operated at 5.5 kV and a temperature varying form
60 to 100 °C. The ESI-MS were recorded with a cone voltage setting
(Declustering Potential 1) varying from 150 to 200 volts. The ion
spray voltage, Curtain Gas, ion source gas 1, ion source gas 2, focus-
ing potential and Declustering Potential 2 parameters were gener-
ally kept constant.
1.4. Methoxyethyl 2,6-di-O-benzoyl 3-O-(2,3,4-tri-O-benzyl-
-fucopyranosyl)-4-O-(2,6-di-O-benzoyl-3,4-O-isopropylidene-
b- -galactopyranosyl)-b- -glucopyranoside (6)
a-
L
D
D
The glycosyl acceptor 4 (3 g, 3.5 mmol) was dissolved in 5:1 dry
1.2. Methoxyethyl 4-O-(b-
glucopyranoside (2)
D
-galactopyranosyl)-b-
D
-
CH2Cl2–DMF (35 mL), and the glycosylation promoter cupric bro-
mide (1.4 g, 6.26 mmol), tetra-n-butylammonium bromide
(240 mg, 0.74 mmol), and molecular sieve 4 Å (3 g) were added
to the solution, which was stirred for 2 h at room temperature. A
Methoxyethyl hepta-O-acetyl-b-D
-lactoside (1)25 (10 g, 14.4 mmol)
was dissolved in anhydrous CH3OH (50 mL) and sodium metal
(0.5 g) was added. The mixture was stirred at room temperature
for 2 h and then de-ionized with Amberlite IR-120 (H+) resin. The
resin was filtered off and rinsed with CH3OH and the combined
filtrate and washings were concentrated and evaporated to dryness.
Crystallization, and re-crystallization, of the residue from CH3OH
solution of methyl 2,3,4-tri-O-benzyl-1-thio-b-L-fucopyranoside
(5) (2.4 g, 5.16 mmol) in CH2Cl2 (4 mL) was slowly added over a
period of 30 min. Stirring was continued for 48 h and the reaction
progress was monitored by TLC (20:1 toluene–acetone) until com-
plete absence of the acceptor and the formation of a major product
were observed. CH3OH (3 mL) was added to the reaction mixture
and stirred for 30 min. The precipitates were filtered through Celite
and washed with CH2Cl2. The filtrate was washed with aqueous
NaHCO3 and H2O, followed by drying over anhydrous MgSO4 and
concentrated to a syrup which was purified by chromatography
on a column of silica gel with (80:10:1, toluene–acetone–CH3OH)
furnished 2 (5.46 g, 95%) as needles. [
a
]
ꢀ5.8 (c 0.5, CH3OH); 1H
D
NMR (500 MHz, D2O): d 4.33 (d, 1H, J1 ,2 = 8.4 Hz, bH-10), 4.27 (d,
2H, J1,2 = 8.4 Hz, bH-1), 3.89–3.15 (m, 12H, CH and CH2 of sugar),
3.50–3.47 (m, 4H, OCH2CH2O), 3.22 (s, 3H, OCH3); HRESIMS: m/z
calcd for [C15H28O12+Na]+, 423.1479; found, 423.1541.
0
0
to afford pure 6 as a syrup (3.4 g, 77%). [
a] +14.6 (c 0.6, CHCl3);
D
1.3. Methoxyethyl 2,6-di-O-benzoyl 4-O-(2,6-di-O-benzoyl-3,4-
1H NMR (300 MHz, CDCl3): d 8.20–7.90 (4d, 8H, J = 7.6 Hz, ortho-
0
0
O-isopropylidene-b-
(4)
D
-galactopyranosyl)-b-
D
-glucopyranoside
H of 4 ꢁ Bz), 7.57–6.91 (m, 27H, Ph-H), 5.46 (d, 1H, J1 ,2 = 3.7 Hz,
a
H-10), 5.42 (t, 1H, J = 8.0 Hz, H-200), 5.24 (t, 1H, J = 8.5 Hz, H-2),
4.95 (d, 1H, J = 11.5 Hz, CHHPh), 4.92–4.86 (m, 1H, H-50), 4.82–
Dry camphorsulfonic acid26 (143 mg, 0.6 mmol) was added to a
solution of 2 (5 g, 12.5 mmol) in 2,2-dimethoxypropane (300 mL).
The mixture was stirred for 48 h at room temperature. Following
addition of triethylamine (0.85 mL, 6.2 mmol), the mixture was
stirred for 15 min and concentrated to dryness and coevaporated
with toluene to remove all traces of triethylamine. A solution of
the crude product in 10:1 CH3OH–H2O (300 mL) was heated at
reflux for 3 h. The solvents were evaporated and the residue was
purified by flash chromatography (20:1, CH3Cl–CH3OH) to afford
4.72 (m, 3H, H-600, CH2Ph), 4.66 (d, 1H, J = 11.3 Hz, CHHPh), 4.56–
a
4.48 (m, 4H, H-100, H-1, H-6a, H-6b), 4.37 (d, 1H, J = 11.5 Hz, CHHPh),
4.33–4.20 (m, 5H, H-3, H-30, H-300, H-60b0, CHHPh), 4.23 (br d, 1H, H-
400), 4.08 (t, 1H, J = 9.3 Hz, H-4), 3.94 (dd, 1H, J
= 3.7 Hz,
10,20
20,30
J
= 10.3 Hz, H-20), 3.85–3.74 (m, 3H, H-40, H-500, OCHH–
CH2OCH3), 3.58–3.46 (m, 2H, H-5, OCHH–CH2OCH3), 3.34–3.24
(m, 2H, –CH2–OCH3), 3.00 (s, 3H, OCH3), 1.62–1.33 (2s, 6H,
C(CH3)2), 1.35 (d, 3H, J = 7.3 Hz, CH3 of fucose moiety); 13C NMR
(75.5 MHz, CDCl3): d 167.3–165.0 (4 ꢁ COAr), 134.0–126.0 (Ar-C),
111.5 (C(CH3)2), 102.2, 101.0 (C-1 and C-100), 98.0 (C-10), 79.7–
72.0 (11 CH of sugar, C-2, C-3, C-4, C-5, C-20, C-30, C-40, C-200, C-300,
C-400, C-500), 75.5 (CH2Ph), 73.2, 73.1 (2 ꢁ CH2Ph), 72.4 (–CH2–
OCH3), 69.4 (–OCH2–CH2OCH3), 67.0 (C-50), 63.2 (C-600), 63.1
(C-6), 59.3 (OCH3), 28.4, 26.5 (C(CH3)2), 17.8 (CH3 of fucose moi-
ety); HRESIMS: m/z calcd for [C73H76O20+Na]+, 1295.4828; found,
1295.4865.
methoxyethyl 4-O-(3,4-O-isopropylidene-b-
D
-galactopyranosyl)-b-
D-
glucopyranoside (3) (4.9 g, 89%).
The pure 30,40-O-isopropylidene-b-
D-lactoside derivative (3)
(10 g, 22.7 mmol) was dissolved in absolute pyridine (200 mL),
the solution was cooled to ꢀ45 °C and benzoyl chloride (11.1 mL,
4.2 M equiv) was added dropwise with stirring over a period of
3–4 h. The mixture was diluted with CH2Cl2, and then processed

398
S. E. Soliman et al. / Carbohydrate Research 344 (2009) 395–399
1.5. Methoxyethyl 2,6-di-O-benzoyl 3-O-(2,3,4-tri-O-benzyl-
-fucopyranosyl)-4-O-(2,6-di-O-benzoyl-b- -galactopyranosyl)-
b- -glucopyranoside (7)
a
-
C-40, C-200, C-300, C-400, C-500), 74.7 (CH2Ph), 73.6, 73.3 (2 ꢁ CH2Ph),
72.4 (–CH2–OCH3), 69.4 (–OCH2–CH2OCH3), 67.5 (OCH2–COOBn),
68.5 (OCH2–COOCH2Ph), 66.5 (C-50), 63.1 (C-600), 61.5 (C-6), 59.4
(OCH3), 21.0 (CH3CO), 17.8 (CH3 of fucose moiety); HRESIMS: m/z
calcd for [C81H82O23+Na]+, 1445.5145; found, 1445.5275.
L
D
D
Compound 6 (3 g, 2.4 mmol) was dissolved in 80% acetic acid
(10 mL), and stirred at 80 °C for 4 h, at which time TLC (8:2 tolu-
ene–EtOAc) showed complete conversion of the starting material
into a product with lower mobility. The mixture was evaporated
and coevaporated with toluene to remove the acetic acid. The
crude diol syrup was purified on a column of silica gel (CH3Cl) to
give the title compound 7 (2.5 g, 86%). 1H NMR (300 MHz, CDCl3):
d 8.14–7.95 (m, 8H, ortho-H of 4 ꢁ Bz), 7.60–6.93 (m, 27H, Ph-H),
1.7. Methoxyethyl 3-O-(
carbobenzyloxymethyl-b-
glucopyranoside (12)
a
-
D
L
-fucopyranosyl)-4-O-(3-O-
-galactopyranosyl)-b-
D-
The tetrabenzoate 9 (330 mg, 0.24 mmol) was suspended in
CH3OH (30 mL), and sodium metal (100 mg) was added. The solu-
tion was warmed and debenzoylation was monitored by TLC (1:3
CH3OH–CH2Cl2), which indicated the disappearance of the starting
material. The solution was cooled for 1 h and neutralized with
Amberlite IR-120 (H+) resin. The resin was filtered and rinsed with
CH3OH and the combined filtrate and washings were concentrated
to afford methoxyethyl 3-O-(2,3,4-tri-O-benzyl-
4-O-(3-O-carbobenzyloxymethyl-b- -galactopyranosyl)-b-
ranoside (11) as syrup in almost quantitative yield. n-Hexane was
added and then decanted to remove methyl benzoate.
A solution of compound 11 (150 mg, 0.17 mmol) in CH3OH
(15 mL) was treated with 10% palladium–charcoal catalyst
(0.8 g), and the suspension was stirred overnight under hydrogen
at 1 atmosphere. TLC (3:3:1, EOAc–2-propanol–H2O) showed the
disappearance of the starting material and formation of one new
product, the mixture was filtered to remove the catalyst and the
filtrate was evaporated under diminished pressure to give com-
5.43 (t, 1H, J = 8.0 Hz, H-200), 5.41 (d, 1H, J 1 ,2 = 3.6 Hz,
a
H-10),
0
0
5.24 (t, 1H, J = 8.1 Hz, H-2), 4.95–4.86 (m, 2H, CHHPh, H-50),
4.82–4.66 (m, 4H, 3 ꢁ CHHPh, H-60a0), 4.64–4.54 (m, 4H, H-100, H-
10, H-6a, H-6b), 4.36 (d, 1H, J = 11.4 Hz, CHHPh), 4.28–4.12 (m, 7H,
H-3, H-4, H-30, H-300, H-400, H-60b0, CHHPh), 3.94–3.74 (m, 4H, H-20,
H-40, H-500, OCHH–CH2OCH3), 3.62–3.46 (m, 3H, H-5, OCHH–
CH2OCH3, OH), 3.30–3.14 (m, 3H, –CH2–OCH3, OH), 3.00 (s, 3H,
OCH3), 1.33 (d, 3H, J = 7.3 Hz, CH3 of fucose moiety); 13C NMR
(75.5 MHz, CDCl3): d 167.3–165.0 (4 ꢁ COAr), 134.0–126.5 (Ar-C),
102.2 (C-1), 100.6 (C-100), 98.2 (C-10), 79.6–68.4 (11 CH of sugar,
C-2, C-3, C-4, C-5, C-20, C-30, C-40, C-200, C-300, C-400, C-500), 75.8
(CH2Ph), 73.2, 73.0 (2 ꢁ CH2Ph), 72.4 (–CH2–OCH3), 69.3 (–OCH2–
CH2OCH3), 67.1 (C-50), 63.4 (C-600), 62.4 (C-6), 59.4 (OCH3), 17.2
(CH3 of fucose moiety); HRESIMS: m/z calcd for [C70H72O20+Na]+,
1255.4828; found, 1255.4893.
a-
L-fucopyranosyl)-
D
D-glucopy-
1.6. Methoxyethyl 2,6-di-O-benzoyl 3-O-(2,3,4-tri-O-benzyl-
a-
pound 12 (98 mg, 95%) as an amorphous solid. [
CH3OH), 1H NMR (500 MHz, D2O): d 5.26 (d, 1H, J 1 ,2 = 3.8 Hz,
H-10), 4.31, 4.27 (2d, 2H, J = 8.4 Hz, J = 7.7 Hz, bH-100 and bH-1),
a
]
ꢀ31.3 (c 1.8,
D
L
-fucopyranosyl)-4-O-(4-O-acetyl-2,6-di-O-benzoyl-3-O-carbob-
0 0
enzyloxymethyl-b-D-galactopyranosyl)-b-D-glucopyranoside
(10)
a
(m, 22H, CH and CH2 of sugar, OCH2–CO, and OCH2–CH2O), 3.20
(s, 3H, OCH3), 1.00 (d, 3H, J = 6.9 Hz, CH3 of fucose moiety); 13C
NMR (125.77 MHz, D2O): d 102.2, 101.6 (C-1, C-100), 98.3 (C-10),
81.7-65.0 (12 CH of sugar, C-2, C-3, C-4, C-5, C-20, C-30, C-40, C-50,
C-200, C-300, C-400, C-500), 72.5–68.0 (3 CH2, OCH2–CH2OCH3, OCH2–
COOH), 61.6 (C-600), 59.6 (C-6), 58.0 (OCH3), 15.2 (CH3 of fucose
moiety); HRESIMS: m/z calcd for [C23H40O18+Na]+, 627.2112;
found, 627.2022.
A stirred mixture of compound 7 (1.5 g, 1.2 mmol) and dibutyl-
tin oxide (0.36 g, 1.2 M equiv) in CH3OH (20 mL) was heated at re-
flux for 1 h. The CH3OH was evaporated and the residual solid was
dried under vacuum for 1 h. The residue of 30,40-O-dibutylstannyl-
ene derivative
8 in benzene (15 mL), benzyl-2-bromoacetate
(0.58 mL, 3 M equiv), tetra-n-butylammonium bromide (196 mg,
0.5 M equiv), and molecular sieves 4 Å (0.5 g) were heated for 3 h
at 70 °C. Most of the solvent was removed by evaporation under
reduced pressure and the product was extracted with CH2Cl2. After
evaporation of the solvent, the residue was purified by chromatog-
raphy on a column of silica gel (CH3Cl) to give methoxyethyl
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.carres.2008.11.019.
2,6-di-O-benzoyl
(2,6-di-O-benzoyl-3-O-carbobenzyloxymethyl-b-
b- -glucopyranoside (9) (1.33 g, 79%) as a syrup.
Acetylation of compound 9 with acetic anhydride in pyridine at
3-O-(2,3,4-tri-O-benzyl-
a-
L-fucopyranosyl)-4-O-
D-galactopyranosyl)-
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room temperature afforded the title compound 10. [a]D +2.3 (c 9.1,
CHCl3); 1H NMR (500 MHz, CDCl3): d 8.14–7.92 (m, 8H, ortho-H of
4 ꢁ Bz), 7.60–7.00 (m, 27H, Ph-H), 5.47 (d, 1H, J = 2.9 Hz, H-400),
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