A new set of orthogonal-protecting groups for oligosaccharide synthesis on a polymeric support

Article abstract of DOI:10.1016/S0957-4166(99)00569-8

The hydroxyl-protecting groups, levulinoyl (Lev) and 9-fluorenylmethoxycarbonyl (Fmoc), and the amino-protecting group 2,2,2-trichloroethoxycarbonyl (Troc), offer an ideal set of orthogonal-protecting groups which are compatible with oligosaccharide synthesis on a methylpolyethyleneglycol (MPEG) support using a p-alkyloxybenzyl-type linker. Copyright (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0957-4166(99)00569-8

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 11 (2000) 199–205
A new set of orthogonal-protecting groups for oligosaccharide
synthesis on a polymeric support
Tong Zhu and Geert-Jan Boons ∗
Complex Carbohydrate Research Center, 220 Riverbend Road, Athens, GA 30602, USA
Received 1 November 1999; accepted 8 December 1999
Abstract
The hydroxyl-protecting groups, levulinoyl (Lev) and 9-fluorenylmethoxycarbonyl (Fmoc), and the amino-
protecting group 2,2,2-trichloroethoxycarbonyl (Troc), offer an ideal set of orthogonal-protecting groups which
are compatible with oligosaccharide synthesis on a methylpolyethyleneglycol (MPEG) support using a p-
alkyloxybenzyl-type linker. © 2000 Elsevier Science Ltd. All rights reserved.
1. Introduction
The development of new protecting groups and efficient glycosylation protocols and strategies make
it possible to efficiently execute multi-step synthetic sequences leading to complex oligosaccharides.1
Despite these important developments, oligosaccharide synthesis is still a time consuming process, and
even in the hands of an experienced researcher, the preparation of di-, tri-, and tetrasaccharides may take
between several months to a year.
A number of research groups are attempting to increase the efficiency and convenience of oligo-
saccharide synthesis by employing polymer-supported procedures in combination with combinatorial
approaches.2 In addition, the use of a set of orthogonal-protecting groups and linkers enables common
building blocks to be used for the synthesis of a wide range of oligosaccharides. For example, Wong
and co-workers proposed that the chloroacetyl (ClAc), p-methoxybenzyl (PMB), levulinoyl (Lev), and
tert-butyldiphenylsilyl (TBDPS) offer an attractive set of orthogonal-protecting groups.3 It was shown
that a monosaccharide substituted with these four protecting groups can be used for the synthesis of a
large number of trisaccharides.
As part of a project to prepare combinatorial saccharide libraries on polymeric support, we required a
set of orthogonal hydroxyl- and amino-protecting groups. In addition, this set of protecting groups has to
be compatible with a linker, which enables easy attachment and cleavage from a polymeric support.
∗
Corresponding author. Tel: (+) 706-5429161; fax: (+) 706-5424412; e-mail: gjboons@ccrc.uga.edu
0957-4166/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(99)00569-8
tetasy 3203

200
T. Zhu, G.-J. Boons / Tetrahedron: Asymmetry 11 (2000) 199–205
Here, we report that the hydroxyl-protecting groups, levulinoyl (Lev) and 9-fluorenylmethoxycarbonyl
(Fmoc), and the amino-protecting group 2,2,2-trichloroethoxycarbonyl (Troc), offer an ideal set of
orthogonal protecting groups. It is also shown that these functionalities are compatible with a p-
alkoxybenzyl-type linker for immobilization to a methylpolyethyleneglycol (MPEG) support.
2. Result and discussion
In carbohydrate chemistry, the phthalimido group is the most commonly used amino-protecting group.
However, this functionality can only be cleaved under relatively harsh conditions, making it incompatible
with many hydroxyl-protecting functionalities. Also, a C-2 phthalimido group significantly reduces the
glycosyl accepting properties of a neighboring 3-hydroxyl.4 Therefore, the Troc was selected as an
alternative amino-protecting group. It can be removed under relatively mild conditions5 with activated
Zn and, furthermore, glycosyl donors protected with an N-Troc functionality are generally more reactive
than similar derivatives substituted with a phthalimido group.6 The Lev and Fmoc were selected as
temporary hydroxyl-protecting groups. The Fmoc group is a well-established amino-protecting group
often used in peptide synthesis. It is exceptionally stable under acidic conditions, but sensitive towards
mild bases (ammonia, piperidine, morpholine). Surprisingly few reports7 deal with the Fmoc as a
hydroxyl-protecting group. It is to be expected that a mild and hindered base will cleave the Fmoc group
without affecting the Lev functionality. On the other hand, the Lev group can be cleaved with bidentate
nucleophiles such as hydrazine buffered with acetic acid. It was anticipated that this almost neutral
reagent would not affect the Fmoc group. Several other hydroxyl-protecting groups were considered
but dismissed. For example, the ClAc is not compatible with the removal of the N-Troc functionality.
To demonstrate the versatility of a proposed set of orthogonal protecting groups, compound 5
was prepared and the Troc, Fmoc and Lev groups were selectively removed (Scheme 1). Thus, the
readily available N-Troc-protected thioglycoside 18 was treated with benzaldehyde dimethyl acetal and
a catalytic amount of camphorsulfonic acid (CSA) in acetonitrile to give 4,6-O-benzylidene-protected
derivative 2 in 87% yield.9 The Fmoc group was introduced by reaction 2 with FmocCl in pyridine and
the desired compound 3 was afforded in 94% yield. Regioselective cleavage of the benzylidene acetal of
3 using NaCNBH3 and 1 M solution of HCl(g) in diethyl ether10 almost exclusively gave thioglycoside
4 in a yield of 94%. Treatment of compound 4 with levulinic acid and DCC in the presence of catalytic
amount of DMAP provided the fully protected compound 5 in a quantitative yield (98%).11
With key compound 5 in hand, attention was turned to examining the orthogonality of three chosen
protecting groups (Fmoc, Lev, and N-Troc). It was anticipated that treatment with hydrazine acetate11 in
MeOH/CH2Cl2 would cleave the Lev without affecting the Fmoc group. Indeed, compound 5 was cleanly
converted into 4 within 30 min and no loss of the Fmoc group was observed. The Fmoc group proved to
be stable even after prolonged reaction times (up to 24 h). It was expected that triethylamine as a non-
nucleophilic base would remove the Fmoc group without affecting the other functionalities. Treatment
of 5 with 20% Et3N in CH2Cl2 cleaved the Fmoc group and gave compound 6 in a quantitative yield.
Finally, reductive cleavage of the N-Troc with zinc in acetic acid, followed by N-acetylation with acetic
anhydride in pyridine, afforded the N-acetylated thioglycoside 7 in a yield of 86% (Scheme 1). Under
these reaction conditions, both the Lev and Fmoc group remained intact.
The above-described experiments demonstrate that the Lev, Fmoc, and Troc groups can be selectively
cleaved in the presence of each other to give the expected products in high yields. Encouraged by these
results, the orthogonally protected 5 was used for immobilization to a soluble polymeric support (Scheme
2). N-Iodosuccinimide/trimethylsilyl trifluoromethanesulfonate (NIS/TMSOTf)12 mediated coupling of

T. Zhu, G.-J. Boons / Tetrahedron: Asymmetry 11 (2000) 199–205
201
Scheme 1. Reagents and conditions: (i) dimethyl benzaldehyde acetal, CSA, MeCN, 87%; (ii) FmocCl, Py, 94%; (iii)
NaCNBH3, HCl/Et2O, TMF, MS 3 Å, 94%; (iv) LevOH, DCC, DMAP (cat.), DCM, 98%; (v) NH2NH2·HOAc, MeOH:DCM
(1:10, v/v), 99%; (vi) Et3N (20%), DCM, 99%; (vii) Zn, HOAc then Ac2O, Py, 86%
thioglycosyl donor 5 with the p-alkyloxybenzyl-type linker 813 gave compound 9 in a 75% yield. Only
the β-anomer was formed due to the presence of N-Troc as a neighboring participating group. The allyl
ester 9 was converted into the carboxylic acid 10 by heating in a mixture of THF:ethanol:water in the
presence of a catalytic amount of Pd(PPh3)4.14 The success of this reaction demonstrates that the three
protecting groups are compatible with transition metal-catalyzed cleavage of an allyl ester. Derivative 10
with immobilized onto MPEG (M.W. 5000) by ester bond formation using a standard procedure15 to give
polymer bound 11. The oligosaccharide attached to 11 could be released from the polymeric support by
cleavage of the p-alkyloxybenzyl-type linker with 10% TFA to give hemiacetal 12 in a high yield.13 As
expected, the Lev, Fmoc, and Troc groups were stable under this reaction condition.
Scheme 2. Reagents and conditions: (i) NIS/TMSOTf, MS 4 Å, DCM, 0°C, 75%; (ii) 10% Pd(PPh3)4, THF:EtOH:H2O (9:9:1,
v/v/v), 60°C, 93%; (iii) MPEG (M.W. 5000), DCC, DMAP (cat.), DCM; (iv) 10% TFA, DCM, 85%
In conclusion, we have described an orthogonal set of protecting groups for amino-sugars. The Lev,
Fmoc, and N-Troc groups can each be readily introduced using standard procedures and selectively and
rapidly be removed without affecting the others. Furthermore, the three protecting groups are compatible

202
T. Zhu, G.-J. Boons / Tetrahedron: Asymmetry 11 (2000) 199–205
with glycosylations and cleavage of allyl esters and a p-alkyloxybenzyl-type linker. The new set of
orthogonal-protecting groups will be an important tool for the rapid synthesis of large collections of
oligosaccharides.
3. Experimental
3.1. General methods
Chemicals were purchased from Aldrich and Fluka, and used without further purification. Molecular
sieves were activated at 350°C in vacuo for 3 h. All solvents were distilled from the appropriate drying
agents; dichloromethane and toluene were distilled from P2O5 and stored over 4 Å molecular sieves.
Diethyl ether and THF were distilled from CaH2, redistilled from LiAlH4, and stored over sodium wire.
Pyridine and acetonitrile were distilled from CaH2 and stored over 4 Å molecular sieves. Methanol
was distilled from sodium and stored over 4 Å molecular sieves. All the reactions were performed
under anhydrous conditions and monitored by TLC on Kieselgel 60 F254 (Merck). Detection was by
examination under UV light (254 nm) and by charring with 10% sulfuric acid in methanol. Column
chromatography was performed on silica gel (Merck, mesh 70–230). Extracts were concentrated under
reduced pressure at <40°C (bath). 1H NMR and 13C NMR spectra were recorded on a Varian Merc300
1
spectrometer and a Varian Inova500 spectrometer equipped with Sun workstations. H and 13C NMR
spectra were recorded in CDCl3; chemical shifts (δ) are given in ppm relative to solvent peaks (1H,
δ=7.26; 13C, δ=77.3) as internal standard. Negative ion matrix assisted laser desorption ionization time
of flight (MALDI-TOF) mass spectra were recorded using an HP-MALDI instrument using gentisic acid
as a matrix. Optical rotations were measured on a Jasco P-1020 polarimeter, and [α]D-values are given
in units of deg cm3 g−1
.
3.2. Ethyl 6-O-benzyl-3-O-(9-fluorenylmethoxycarbonyl)-2-deoxy-2-[[(2,2,2-trichloroethoxy)carbonyl]
amino]-1-thio-α-D-glucopyranoside 4
A solution of hydrogen chloride in diethyl ether (1 M, 23 ml) was added to a solution of benzylidene
acetal 3 (1.3 g, 1.84 mmol) and sodium cyanoborohydride (1.45 g, 23.0 mmol) in THF (20 ml) containing
3 Å molecular sieves (500 mg). The mixture was stirred until the evolution of gas had ceased. The
reaction mixture was filtered and the filtrate was co-evaporated with methanol (3×15 ml). The residue
was diluted with dichloromethane (50 ml) and washed successively with water (2×20 ml) and brine (15
ml). The organic layer was dried (MgSO4) and concentrated under reduced pressure. The resulting syrup
was applied to a column of silica gel which was eluted with ethyl acetate:hexane (1:3, v/v) to give 4
1
as a white foam (1.22 g, 94%). H NMR (500 MHz, CDCl3): δ 7.78–7.31 (m, 13H, Ar-H), 5.42 (2d,
2H, H-1, NH, J1,2=5.1 Hz, JNH,2=9.8 Hz), 4.87 (dd, 1H, H-3, J2,3=11.1 Hz, J3,4=9.4 Hz), 4.62 (2AB q,
PhCH2, JAB=12.0 Hz, OCH2CCl3, JAB=12.0 Hz), 4.43 (dd, 1H, CHaO (Fmoc), J=7.3 Hz, 10.3 Hz), 4.37
(dd, 1H, CHbO (Fmoc), J=7.7, 10.3 Hz), 4.31 (ddd, 1H, H-2), 4.27–4.23 (m, 2H, H-5, H-9), 3.93 (t, 1H,
H-4, J4,5=9.4 Hz), 3.85 (dd, 1H, H-6a, J5,6a=4.3 Hz, J6a,6b=10.7 Hz), 3.74 (dd, 1H, H-6b, J5,6b=4.3 Hz),
2.83 (br s, 1H, OH), 2.72-2.60 (m, 2H, SCH2), 1.30 (t, 3H, SCH2CH3, J=7.3 Hz). 13C NMR (75 MHz,
CDCl3): δ 156.0, 154.2, 143.4, 143.2, 141.5, 128.7, 128.1, 127.9, 127.4, 125,4, 120.3, 95.8, 84.9, 78.2,
25
74.9, 74.0, 71.1, 70.9, 70.5, 69.9, 54.5, 46.9, 26.1, 15.5. [α]D +51.5 (c 0.3, CH2Cl2). MALDI-TOF
MS: m/z 732 [M+Na]+. Anal. calcd for C33H34Cl3NO8S: C, 55.74; H, 4.82; N, 1.97; found: C, 55.60; H,
4.84; N, 1.91.

T. Zhu, G.-J. Boons / Tetrahedron: Asymmetry 11 (2000) 199–205
203
3.3. Ethyl 6-O-benzyl-3-O-(9-fluorenylmethoxycarbonyl)-4-O-levulinoyl-2-deoxy-2-[[(2,2,2-trichloro-
ethoxy)carbonyl]amino]-1-thio-α-D-glucopyranoside 5
DCC (1.78 g, 8.65 mmol) and DMAP (3 mg) in dichloromethane (2 ml) were added to a stirred
solution of compound 4 (1.22 g, 1.73 mmol) and levulinic acid (1.78 ml, 17.3 mmol) in dichloromethane
(20 ml). The reaction mixture became instantaneously cloudy. After stirring for 1 h, TLC analysis (ethyl
acetate:hexane, 1:2, v/v) indicated a complete conversion of the starting material. The precipitated urea
was removed by filtration and the filtrate was diluted with dichloromethane (30 ml), which was washed
with water (2×20 ml) and brine (20 ml), and dried (MgSO4). The organic layer was concentrated
under reduced pressure and the residue was purified by silica gel column chromatography (eluent:
1
ethyl acetate:hexane, 1:3, v/v) to give 5 (1.37g, 98%) as a white foam. H NMR (500 MHz, CDCl3):
δ 7.78–7.28 (m, 13H, Ar-H), 5.48 (d, 1H, H-1, J1,2=5.1 Hz), 5.35 (d, 1H, NH, JNH,2=9.8 Hz), 5.33 (t, 1H,
H-4, J3,4= J4,5=9.8 Hz), 5.01 (dd, 1H, H-3, J2,3=9.4 Hz,), 4.61 (AB q, PhCH2, JAB=12.0 Hz), 4.56 (AB q,
OCH2CCl3, JAB=12.0 Hz), 4.45–4.37 (m, 4H, H-2, H-5, CH2O (Fmoc)), 4.26 (t, 1H, H-9 (Fmoc), J=7.7
Hz), 3.66 (dd, 1H, H-6a, J5,6a=3.0 Hz, J6a,6b=11.1 Hz), 3.62 (dd, 1H, H-6b, J5,6b=4.3 Hz), 2.72–2.58
(m, 4H, COCH2CH2, SCH2), 2.41 (t, 2H, COCH2CH2, J=6.9 Hz), 2.05 (s, 3H, CH3CO), 1.31 (t, 3H,
SCH2CH3, J=7.3 Hz). 13C NMR (75 MHz, CDCl3): δ 206.0, 171.3, 155.4, 154.0, 143.5, 143.3, 141.4,
138.0, 128.5, 128.1, 127.8, 127.4, 127.5, 120.2, 95.9, 84.6, 75.8, 74.9, 73.9, 71.0, 70.9, 69.1, 68.7, 54.7,
25
46.8, 38.1, 29.9, 28.2, 26.0, 15.4. [α]D +24.3 (c 0.4, CH2Cl2). MALDI-TOF MS: m/z 830 [M+Na]+.
Anal. calcd for C38H40Cl3NO10S: C, 56.41; H, 4.98; N, 1.73; found: C, 56.26; H, 4.92; N, 1.77.
3.4. Procedure to remove levulinoyl on compound 5
A solution of hydrazine acetate (18 mg, 0.2 mmol) in methanol (0.5 ml) was added to a solution of
thioglycoside 5 (162 mg, 0.2 mmol) in dichloromethane (5 ml) and the resulting reaction mixture was
stirred for 30 min. The solvents were removed under reduced pressure and the residue was purified by
silica gel column chromatography (eluent: ethyl acetate:hexanes, 1:2, v/v) to give product 4 (142 mg,
99%) as a white foam.
3.5. Ethyl 6-O-benzyl-4-O-levulinoyl-2-deoxy-2-[[(2,2,2-trichloroethoxy)carbonyl] amino]-1-thio-α-D-
glucopyranoside 6
Triethylamine (0.5 ml) was added to a solution of compound 5 (81 mg, 0.1 mmol) in dichloromethane
(2 ml). After stirring for 2 h, TLC analysis (ethyl acetate:hexanes, 1:2, v/v) indicated the completion of
the reaction. The reaction mixture was concentrated under reduced pressure and the crude product was
purified by silica gel column chromatography (eluent: ethyl acetate:hexanes, 1:2, v/v) to give 6 as a white
foam (59 mg, 99%). 1H NMR (500 MHz, CDCl3): δ 7.35–7.26 (m, 5H, Ar-H), 5.53 (d, 1H, H-1, J1,2=4.9
Hz), 5.35 (d, 1H, NH, JNH,2=7.5 Hz), 5.03 (t, 1H, H-4, J3,4= J4,5=9.3 Hz), 4.74 (AB q, PhCH2, JAB=11.9
Hz), 4.54 (AB q, OCH2CCl3, JAB=11.9 Hz), 4.31 (ddd, 1H, H-5, J5,6a=J5,6b=3.5 Hz), 4.12 (ddd, 1H, H-
2), 3.73 (t, 1H, H-3, J2,3=9.3 Hz), 3.60 (d, 2H, H-6a, H-6b), 2.78–2.73 (m, 2H, COCH2CH2), 2.71–2.59
(m, 2H, SCH2), 2.54–2.39 (m, 2H, COCH2CH2), 2.17 (s, 3H, CH3CO), 1.30 (t, 3H, SCH2CH3, J=7.5
Hz). 13C NMR (75 MHz, CDCl3): δ 207.5, 172.6, 154.7, 138.1, 128.5, 128.0, 127.8, 95.6, 84.6, 75.0,
25
73.8, 72.7, 71.9, 69.9, 68.8, 56.0, 38.6, 30.1, 28.4, 26.1, 15.5. [α]D +50.3 (c 0.3, CH2Cl2). MALDI-
TOF MS: m/z 608 [M+Na]+. Anal. calcd for C23H30Cl3NO8S: C, 47.07; H, 5.15; N, 2.39; found: C,
46.85; H, 5.01; N, 2.36.

204
T. Zhu, G.-J. Boons / Tetrahedron: Asymmetry 11 (2000) 199–205
3.6. Ethyl 2-deoxy-2-acetamido-6-O-benzyl-3-O-(9-fluorenylmethoxycarbonyl)-4-O-levulinoyl-1-thio-
α-D-glucopyranoside 7
Compound 5 (81 mg, 0.1 mmol) was dissolved in acetic acid (2 ml) and zinc (nano-size activated
powder, 99.9%, 200 mg) was added. After stirring for 1 h, TLC analysis (ethyl acetate:hexanes, 1:2, v/v)
showed that the starting material was consumed. The reaction mixture was filtered through short pad of
silica gel (eluent: ethyl acetate) and the filtrate was concentrated under reduced pressure. The residue
was dissolved in a mixture of pyridine (3 ml) and acetic anhydride (2.5 ml). After stirring the reaction
mixture for 0.5 h, it was co-concentrated with toluene (3×15 ml) and the residue purified by silica gel
column chromatography (eluent: ethyl acetate:hexanes, 2:3, v/v) to give 7 as a white foam (58 mg, 86%).
1H NMR (500 MHz, CDCl3): δ 7.78–7.28 (m, 13H, Ar-H), 5.75 (d, 1H, NH, JNH,2=8.7 Hz), 5.51 (d,
1H, H-1, J1,2=5.5 Hz), 5.29 (t, 1H, H-4, J3,4= J4,5=9.6 Hz), 4.98 (dd, 1H, H-3, J2,3=11.5 Hz,), 4.64 (ddd,
1H, H-2), 4.55 (AB q, PhCH2, JAB=11.9 Hz), 4.40–4.36 (m, 3H, H-5, CH2O (Fmoc)), 4.28 (t, 1H, H-9
(Fmoc), J=7.8 Hz), 3.64 (dd, 1H, H-6a, J5,6a=2.7 Hz, J6a,6b=11.0 Hz), 3.61 (dd, 1H, H-6b, J5,6b=5.1 Hz),
2.71–2.58 (m, 4H, COCH2CH2, SCH2), 2.42 (t, 2H, COCH2CH2, J=6.9 Hz), 2.06 (s, 3H, CH3CO), 1.90
(s, 3H, NHCOCH3), 1.31 (t, 3H, SCH2CH3, J=7.2 Hz). 13C NMR (75 MHz, CDCl3): δ 206.2, 171,3,
169.9, 155.7, 143.5, 141.4, 138.1, 128.5, 128,1, 128.0, 127.8, 127.5, 127.4, 125.4, 120.2, 84.2, 75.9,
25
73.8, 70.9, 69.9, 69.2, 68.9, 52.8, 46.8, 38.1, 30.1, 28.2, 25.7, 23.7, 15.4. [α]D +18.8 (c 0.8, CH2Cl2).
MALDI-TOF MS: m/z 698 [M+Na]+. Anal. calcd for C37H41NO9S: C, 65.76; H, 6.12; N, 2.07; found:
C, 65.58; H, 6.14; N, 2.11.
3.7. 4-Alloxycarbonylpentoxybenzyl
6-O-benzyl-3-O-(9-fluorenylmethoxycarbonyl)-4-O-levulinoyl-
2-deoxy-2-[[(2,2,2-trichloroethoxy)carbonyl]amino]-β-D-glucopyranoside 9
A solution of 5 (162 mg, 0.2 mmol) and 8 (61 mg, 0.22 mmol) in dichloromethane (4 ml) was stirred
in the presence of 4 Å molecular sieves (100 mg, powdered) for 15 min. The mixture was cooled (0°C)
and NIS (50 mg, 0.22 mmol) and TMSOTf (4 µl, 22 µmol) were added. After 5 min, TLC analysis
(ethyl acetate:hexanes, 1:1, v/v) showed that compound 5 was consumed. The reaction mixture was
diluted with dichloromethane (50 ml), filtered, and the filtrate was washed successively with aqueous
sodium thiosulfate (15%, 2×25 ml), water (20 ml), and brine (15 ml). The organic phase was dried
(MgSO4), filtered, and the filtrate was concentrated in vacuo. Purification of the residue by silica gel
column chromatography (eluent: ethyl acetate:hexanes, 1:2, v/v) gave 9 as an amorphous solid (154
1
mg, 75%). H NMR (500 MHz, CDCl3): δ 7.77–6.83 (m, 17H, Ar-H), 5.98–5.90 (m, 1H, CH_CH2),
5.36–5.25 (m, 2H, CH_CH2), 5.22–5.16 (m, 2H, H-3, H-4), 5.09 (br s, 1H, NH), 4.87–4.57 (m, 9H,
H-1, PhCH2, OCH2CCl3, CH2CH_CH2, CH2O (Fmoc)), 4.27 (t, 1H, H-9 (Fmoc), J=7.6 Hz), 3.97
(t, 2H, PhOCH2CH2, J=6.4 Hz), 3.75–3.64 (m, 4H, H-2, H-5, H-6a, H-6b), 2.59 (t, 2H, COCH2CH2,
J=5.2 Hz), 2.42–2.38 (m, 4H, COCH2CH2, CH2COOAll), 2.04 (s, 3H, CH3CO), 1.85–1.50 (m, 6H,
OCH2CH2CH2CH2CH2). 13C NMR (75 MHz, CDCl3): δ 205.9, 173.4, 171.5, 159.1, 155.1, 154.0,
143.5, 141.4, 138.1, 132.4, 130.0, 128.7, 128.5, 128.1, 128.0, 127.9, 127.4, 125.5, 120.2, 118.4, 114,7,
100.3, 98.7, 95.6, 76.4, 74.7, 73.9, 73.6, 70.8, 69.8, 69.3, 67.9, 65.3, 56.8, 46.8, 38.0, 34.5, 29.9, 29.3,
25
28.1, 26.0, 25.0. [α]D −4.6 (c 0.2, CH2Cl2). MALDI-TOF MS: m/z 1046 [M+Na]+. Anal. calcd for
C52H56Cl3NO14: C, 60.91; H, 5.50; N, 1.37; found: C, 60.98; H, 5.66; N, 1.32.
3.8. 4-Hydroxylcarbonylpentoxybenzyl 6-O-benzyl-3-O-(9-fluorenylmethoxycarbonyl)-4-O-levulinoyl-
2-deoxy-2-[[(2,2,2-trichloroethoxy)carbonyl]amino]-β-D-glucopyranoside 10
Pd(PPh3)4 (12 mg, 0.01 mmol) was added to a solution of compound 9 (103 mg, 0.1 mmol) in
ethanol (2 ml), THF (2 ml), and water (0.2 ml). After stirring the reaction mixture for 2 h at 60°C,

T. Zhu, G.-J. Boons / Tetrahedron: Asymmetry 11 (2000) 199–205
205
TLC analysis (ethyl acetate:hexanes, 1:1, v/v) indicated the completion of the reaction. The reaction
was concentrated to dryness and the crude product was subjected to a column of silica gel (eluent:
MeOH:dichloromethane, 2:100, v/v) to give compound 10 as a colorless syrup (91 mg, 93%). 1H NMR
(500 MHz, CDCl3): δ 7.78–6.84 (m, 17H, Ar-H), 5.22–5.10 (m, 3H, H-3, H-4, NH), 4.86–4.56 (m, 7H,
H-1, PhCH2, OCH2CCl3, CH2O (Fmoc)), 4.26 (t, 1H, H-9 (Fmoc), J=7.6 Hz), 3.97 (t, 2H, PhOCH2CH2,
J=6.4 Hz), 3.75–3.63 (m, 4H, H-2, H-5, H-6a, H-6b), 2.58 (t, 2H, COCH2CH2, J=5.2 Hz), 2.42–2.32
(m, 4H, COCH2CH2, CH2COOH), 2.02 (s, 3H, CH3CO), 1.85–1.44 (m, 6H, OCH2CH2CH2CH2CH2).
MALDI-TOF MS: m/z 1006 [M+Na]+. Anal. calcd for C49H52Cl3NO14: C, 59.73; H, 5.32; N, 1.42;
found: C, 59.58; H, 5.36; N, 1.46.
3.9. Immobilization of compound 10 on MPEG
A mixture of MPEG (1 g, 0.2 mmol) and compound 10 (196 mg, 0.2 mmol) was dried over P2O5 at
high vacuum for 12 h. This mixture was dissolved in dichloromethane (10 ml), and a catalytic amount of
DMAP (3 mg), followed by DCC (45 mg, 0.22 mmol), was added. The solution became cloudy within
15 min and was stirred overnight at room temperature. The precipitated urea was removed by filtration,
washed with dichloromethane, and the combined filtrates were concentrated to dryness. The residue was
dissolved in dichloromethane (8 ml), cooled (0°C), and tert-butyl methyl ether (100 ml) was added with
vigorous stirring. The precipitate was washed with diethyl ether (2×10 ml) and cold ethanol (2×10 ml),
and then further purified by recrystallization from ethanol.
References
1. (a) Toshima, K.; Tatsuta, K. Chem. Rev. 1993, 93, 1503–1531. (b) Boons, G. J. Tetrahedron 1996, 52, 1095–1121.
2. (a) For a review on recent developments in polymer supported syntheses of oligosaccharide see: Osborn, H. M. I.; Khan,
T. H. Tetrahedron, 1999, 55, 1807–1850. (b) Ling, R.; Yan, L.; Loebach, J.; Ge, M.; Uozumi, Y.; Sekanina, K.; Horan, N.;
Gildersleeve, J.; Thompson, C.; Smith, A.; Biswas, K.; Still, W. C.; Kahne, D. Science 1996, 274, 1520–1522. (c) Zhu, T.;
Boons, G. J. Angew. Chem., Int. Ed. Engl. 1998, 37, 1898–1900.
3. Wong, C. H.; Ye, X. S.; Zhang, Z. J. Am. Chem. Soc. 1998, 120, 7137–7138.
4. (a) Spijker, N. M.; van Boeckel, C. A. A. Angew. Chem., Int. Ed. Engl. 1991, 30, 180–183. (b) Ellervik, U. H.; Magnusson,
G. J. Org. Chem. 1998, 63, 9314–9322.
5. (a) Windholz, T. B.; Johnston, D. B. R. Tetrahedron Lett. 1967, 2555–2557. (b) Just, G.; Grozinger, K. Synthesis 1976,
457–458.
6. Zhang, Z.; Ollmann, I. R.; Ye, X.; Wischnat, R.; Baasov, T.; Wong, C. H. J. Am. Chem. Soc. 1999, 121, 734–753.
7. (a) Gioeli, C.; Chattopadhyaya, J. B. J. Chem. Soc., Chem. Commun. 1982, 672–674. (b) Nicolaou, K. C.; Winssinger, N.;
Pastor, J.; DeRoose, F. J. Am. Chem. Soc. 1997, 119, 449–450. (c) Nicolaou, K. C.; Watanabe, N.; Li, J.; Pator J.; Winssinger,
N. Angew. Chem., Int. Ed. Engl. 1998, 37, 1559–1561.
8. Ellervik, U.; Magnusson, G. Carbohydr. Res. 1996, 280, 251–260.
9. Ellervik, U.; Grundberg, H.; Magnusson, G. J. Org. Chem. 1998, 63, 9323–9338.
10. Garegg, P. J.; Hultberg, H.; Wallin, S. Carbohydr. Res. 1982, 108, 97–101.
11. Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic Synthesis, 3rd ed.; John Wiley & Sons: New York, 1999; p.
168, and references cited therein.
12. Veeneman, G. H.; van Leeuwen, S. H.; van Boom, J. H. Tetrahedron Lett. 1990, 31, 1331–1334.
13. (a) Shimizu, H.; Ito, Y.; Kanie, O.; Ogawa, T. Bioorg. Med. Chem. Lett. 1996, 6, 2841–2846. (b) Manabe, S.; Ito, Y.; Ogawa,
T. Synlett 1998, 628–630.
14. Waldmann, H.; Kunz, H. Liebigs Ann. Chem. 1983, 10, 1712–1725.
15. Douglas, S. P.; Whitfield, D. M.; Krepinsky, J. J. J. Am. Chem. Soc. 1991, 113, 5095–5097.