Comparative solution and solid-phase glycosylations toward a disaccharide library

Article abstract of DOI:10.1016/j.carres.2009.04.001

A comparative study on solution-phase and solid-phase oligosaccharide synthesis was performed. A 16-member library containing all regioisomers of Glc-Glc, Glc-Gal, Gal-Glc, and Gal-Gal disaccharides was synthesized both in solution and on solid phase. The

Full text of DOI:10.1016/j.carres.2009.04.001

Carbohydrate Research 344 (2009) 1428–1433
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Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
Comparative solution and solid-phase glycosylations toward
a disaccharide library
Károly Ágoston a,b, , Lars Kröger a,b, Ágnes Ágoston b, Gyula Dékány a,b, Joachim Thiem a,
*
*
a Department of Chemistry, Faculty of Science, University of Hamburg, Martin-Luther-King-Platz 6, D—20146 Hamburg, Germany
b Glycom A/S, c/o DTU, Building 201, DK—2800 Kgs. Lyngby, Denmark
a r t i c l e i n f o
a b s t r a c t
Article history:
A comparative study on solution-phase and solid-phase oligosaccharide synthesis was performed. A 16-
member library containing all regioisomers of Glc–Glc, Glc–Gal, Gal–Glc, and Gal–Gal disaccharides was
synthesized both in solution and on solid phase. The various reaction conditions for different approaches
and corresponding yields are analyzed and discussed.
Received 25 February 2009
Received in revised form 1 April 2009
Accepted 1 April 2009
Available online 10 April 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Dedicated to Professor Johannis P.
Kamerling on the occasion of his 65th
birthday
Keywords:
Oligosaccharide synthesis
Disaccharide library
Solid-phase chemistry
1. Introduction
strategy has been found that gives general control over the stereo-
chemical outcome of the newly formed stereocenter. We do be-
The advantages and disadvantages of solid-phase chemistry
compared to solution-phase chemistry are generally well discussed
and described.1 Both strategies are commonly used to synthesize
biomolecules. The chemical preparation of oligo- and polypeptides
as well as oligo- and polynucleotides nowadays is almost exclu-
sively performed on solid phase, thanks to the commercial avail-
ability of building blocks and solid supports. The different
approaches to prepare these oligomers are generalized and have
become routine procedures.2 The third group of biomolecules that
exists in oligo- or polymeric form is the carbohydrates on which
organic chemists have worked for over a hundred years.3 Great
advances have been made for the preparation of carbohydrate olig-
omers in solution phase, but it still remains a challenging and
time-consuming procedure. Due to the chemical nature of carbo-
hydrates with multiple possible linkage points giving rise to differ-
ent regioisomers, the synthesis of oligomers is complicated far
beyond that encountered in the preparation of oligopeptides or oli-
gonucleotides. The lack of commercially available protected and/or
activated building blocks for oligosaccharide synthesis makes the
situation even more complicated. Besides, until now no universal
lieve that we are still a long way from finding a general approach
that would solve the problems of oligosaccharide chemistry, and
to this end numerous fundamental studies need to be performed
until a generalized approach is reached. This process started more
than 10 years ago with the first preparation of an oligosaccharide
library in solution phase.4–6 With the help of a solid support, the
first libraries were published soon after,7–9 and the effort to create
different libraries is still ongoing.10–13 In this paper a comparative
study of a disaccharide library preparation will be discussed. A glu-
cose–galactose disaccharide library has been prepared containing
all regioisomers, but only 1,2-trans stereoisomers. The synthesis
was performed both in solution phase and on solid support. For
the solid-phase study, the donors were coupled to the resin to form
an ester linkage via its 2-hydroxyl position, thus excluding forma-
tion of 1,2-cis stereoisomers. Donors for solution phase have a sim-
ilar participating group in position 2 for the same reason.
2. Results and discussion
The two most common monosaccharide residues in nature are
D-glucose and D-galactose, and consequently, these units have been
used by organic chemists most frequently. In this study a set of
disaccharides built from glucose and/or galactose have been pre-
* Corresponding authors. Tel.: +45 45252259; fax: +45 45933968 (K.A.); tel.: +49
40 428384241; fax: +49 40 428384325 (J.T.).
E-mail addresses: ka@glycom.dk (K. Ágoston), thiem@chemie.uni-hamburg.de
(J. Thiem).
pared. To avoid stereochemical problems, only b-D-glycosides were
prepared. For solution-phase chemistry the known glucose and
0008-6215/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2009.04.001

K. Ágoston et al. / Carbohydrate Research 344 (2009) 1428–1433
1429
BnO
BnO
OBn
R1O
O
BnO
O
W
SEt
RO
SEt
BnO
O
OR
O
OR
OH
1
R
R
R
O
1
2
3
4
Ac
Bn
5
6
7
Ac
Resin-OH
H
H
Bn
Resin Bn
Resin
Bn
Resin
R1O
R2O
OR
R1O
O
O
R2O
OMe
OR3
OMe
R2 R3
Bn Bn Bn
OR3
R1
R
H
R1
Bn
R2 R3
R
8
9
12
Bn Bn
Bn Bn
H
13 Bn
H
Bn
H
Bn Bn
14
15 Bn Bn
10
Bn Bn
H
Bn
H
Bn Bn
H
Bn
H
Bn
11 Bn Bn Bn
Scheme 1. Donors and acceptors utilized for syntheses.
galactose donors (114 and 5,15 respectively) were selected, and
their precursors (216 and 615) were used to attach the monosaccha-
rides to the solid support obtaining resin-bound donors (3 and 7).
Wang resin was modified with succinic anhydride as a linker, and
an ester linkage was created afterwards between the carbohydrate
and the solid support. A resin-bound donor 4 was also prepared
from its precursor (4-OH)17 in order to have a non-participating
group at position 2. A complete set of glucose (8,18 9,19 1020, and
1121) and galactose (12,22 13,23 1424, and 1525) acceptors with a
single free hydroxy function were used for both solution and so-
lid-phase synthesis (Scheme 1).
Both in solution and on solid phase, the coupling reactions were
performed in a 1:1 mixture of DCM and acetonitrile as solvent. This
mixture is sufficient both to dissolve the catalyst and to swell the
resin. Activation of the donor was achieved with the well-known
combination of NIS and AgOTf.26
2-OH function of the monosaccharide units. The efficiency of the
loading was determined by gravimetry after cleaving the donor
from the resin. Both resin-bound donors (3 and 7) showed rela-
tively high (0.65 mmol/g) loadings. The coupling reactions were
performed at room temperature with a reaction time of around
20 hours. After extensive washing of the resin, the crude resin-
bound products were cleaved and purified by column chromatog-
raphy in order to remove unreacted or decomposed donor (Scheme
3). Only a few side products were observed in the HPLC profile of
the crude cleaved mixture of compound 18 (Fig. 2). Although by
UV detection next to the product (retention time: 8.81 min) a
strong signal of a side product (retention time: 3.16 min) was vis-
ible, evaporative light-scattering (ELS) detection showed a very
clean composition of the mixture regarding nonvolatile (carbohy-
drate) type substances. Using resin-bound donors (3 and 7) there
was no sign in the NMR spectra for the formation of
a anomers
In solution phase the coupling reactions were performed at
ꢀ15 °C, and the reaction time was generally around 30 min
(Scheme 2). Since an excess of donor was used for the reaction, do-
nor decomposition was always present in the mixture as can be
seen in the HPLC chromatogram (Fig. 1, compound 30). The peak
at 4.2 min is due to donor decomposition, whereas the desired
product is eluted at 7.7 min. Aqueous workup of the crude reaction
mixtures was followed by column chromatography and removal of
the 20-acetate groups. The final products were purified again by
column chromatography to afford the pure disaccharides.
For the solid-phase reactions commercially available Wang re-
sin was modified by esterification with succinic anhydride in
DCM, thus obtaining the linker-bound resin.27 To couple the donor
to the resin, the second carboxylic acid function of the succinic acid
linker was activated with DCC to enable ester formation with the
as expected, due to neighboring group participation of the linker
moiety. The use of resin-bound donor 4 resulted in the formation
of a 2:1 mixture of anomers in favour of the b product (see 1D
and 2D NMR in Supplementary data). Steric hindrance or another
effect caused by the resin in position 6 seems to outweigh the ex-
pected formation of the
a anomer as a main product, which is the
case in having a non-participating group in position 2 in the solu-
tion-phase reactions. This donor was not used for further
experiments.
Sixteen different disaccharides were prepared separately by
both methods, and all compounds were characterized by 1D-,
and 2D NMR spectroscopy and MALDI-TOFMS (Chart 1; for 1H
and 13C data see Tables 1 and 2). The yields of the reactions in solu-
tion and on solid phase were comparable, but were slightly
favoured by solid-phase chemistry (see Table 3 for comparison of
BnO
BnO
BnO
BnO
HO
BnO
BnO
O
O
O
BnO
+
O
SEt
BnO
O
OAc
BnO
OBn
OR
1
BnO
8
OMe
OBn
OMe
R
16 (Ac) Ac
16
Deprotection
H
Scheme 2. Solution-phase glycosylation.

1430
K. Ágoston et al. / Carbohydrate Research 344 (2009) 1428–1433
Figure 1. HPLC profile of a solution phase glycosylation (exemplary compound 30).
Functionalisation
BnO
W
W
O
BnO
O
SEt
BnO
O
OH
OH
OR
O
R
H
Resin-OH
2
3
Loading
Resin
HO
BnO
BnO
O
Coupling
O
3
+
BnO
BnO
BnO
O
OBn
MeO
8
O
OR
BnO
BnO
OBn
OMe
R
16 on resin Resin
16
Cleavage
H
Scheme 3. Solid-phase glycosylation.
Figure 2. HPLC profile of a solid-phase glycosylation (exemplary compound 18).

K. Ágoston et al. / Carbohydrate Research 344 (2009) 1428–1433
1431
the two methods). The average yield in solution phase was 72% for
two steps (coupling and deprotection) while on solid phase an
average 78% was obtained. This could well be due to the additional
chromatographic steps required for the solution-phase sequence.
The significantly longer reaction time and higher temperature nec-
essary for the solid-phase reactions did not lead to increased deg-
radation of the products. Reducing the amount of activators (NIS/
AgOTf) resulted in the appearance of intermediate orthoesters in
both approaches. During the synthesis some unexpected technical
problems turned up in the solid-phase process (e.g., solubility
problems and decreased reactivities). The amount of NaOMe
seemed to be crucial for the cleavage step and resulted in the for-
mation of disaccharides having methyl succinate in position 2
(compounds 18 and 24; see NMR, MS, and HPLC in Supplementary
data). Treating these compounds with NaOMe in MeOH afforded
the desired disaccharides.
3. Summary
A 16-member library containing all regioisomers of Glc–Glc,
Glc–Gal, Gal–Glc, and Gal–Gal disaccharides has been synthesised
in solution phase and on solid support. The isolated yields were
compared, and no significant differences were found between the
two processes, although some technical difficulties turned up dur-
ing the solid-phase reactions. To avoid the formation of anomeric
mixtures, participating groups were installed at position 2 of the
donors giving rise to only b glycosides. In contrast, by having a
non-participating group in the above-mentioned position, mix-
BnO
BnO
BnO
BnO
BnO
BnO
BnO
O
BnO
BnO
O
O
BnO
O
O
BnO
O
O
BnO
BnO
O
OH
BnO
3Glc
OH
OH
BnO
O
OMe
BnO
BnO
OMe
18 Glcβ1
→
17 Glcβ1
→
4Glc
BnO
BnO
BnO
16 Glcβ1
→
6Glc
O
OMe
BnO
O
BnO
BnO
BnO
O
OMe
OH
BnO
19 Glcβ1
→
2Glc
O
BnO
BnO
BnO
BnO
O
BnO
O
O
OBn
BnO
BnO
OBn
O
OH
O
BnO
O
O
OMe
BnO
BnO
OMe
BnO
OH
O
OMe
OBn
BnO
OH
OBn
→3Gal
21 Glcβ1→4Gal
22 Glcβ1
OBn
20 Glcβ1→6Gal
OBn
OBn
O
BnO
OMe
BnO
BnO
O
O
BnO
23 Glcβ1→2Gal
OBn
O
BnO
BnO
OH
O
BnO
BnO
OMe
BnO
BnO
OBn
O
O
BnO
BnO
BnO
OBn
O
O
BnO
O
O
BnO
O
OH
BnO
BnO
BnO
BnO
BnO
O
OH
26 Galβ1
OBn
O
25 Galβ1→4Glc
OMe
OMe
OH
BnO
BnO
6Glc
→
3Glc
O
BnO
OMe
OH
27 Galβ1
24 Galβ1
→
OBn
→
2Glc
BnO
BnO
OBn
BnO
BnO
O
OBn
O
O
O
BnO
4Gal
OBn
OBn
BnO
28 Galβ1 6Gal
BnO
BnO
OH
OBn
OBn
OBn
O
O
O
OMe
OBn
OMe
HO
O
OMe
O
OBn
OBn
29 Galβ1
→
→
OH
OBn
3Gal
BnO
30 Galβ1
→
BnO
BnO
O
OBn
OMe
BnO
O
O
OH
31 Galβ→12Gal
Chart 1. The disaccharide library.

1432
K. Ágoston et al. / Carbohydrate Research 344 (2009) 1428–1433
Table 1
1H NMR data: chemical shift (d) and coupling constants (Hz) for 16–31
1
2
3
4
5
6
10
20
30
40
50
60
OMe
20-OH
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
4.83, ꢂ3 Hz
3.46
3.39
3.53
3.59
3.48
3.69
3.44
3.81
3.44
3.37
3.47
3.56
3.74
3.43
3.47
3.76
3.75
3.69
4.13
3.78
3.60
3.66
3.77
3.76
3.73
3.63
4.09
3.76
3.60
3.64
3.82
3.73
3.46
3.83
3.44
3.43
4.09
4.19
3.90
3.98
3.61
3.76
3.37
3.42
4.08
4.17
3.98
3.95
3.62
3.70
3.58
3.50
3.71
3.70
3.64
3.72
3.64
3.44
3.55
3.59
3.70
3.66
3.70
3.68
3.97, 3.67
3.94, 3.74
3.61
3.66, 3.59
3.88, 3.67
3.71, 3.53
3.67, 3.38
3.54
3.55, 3.48
3.53, 3.33
3.62, 3.57
3.60, 3.57
n.d.
3.67, 3.51
3.69, 3.50
3.52
4.28, 7.88 Hz
4.36, 7.88 Hz
4.80, 7.63 Hz
4.57, ꢂ8 Hz
3.29
3.27
3.35
3.34
3.26
3.27
3.73
3.30
3.54
3.55
3.68
3.59
3.56
3.59
3.41
3.53
3.46
3.40
3.42
3.48
3.46
3.42
3.54
3.42
3.44
3.36
3.48
3.45
3.47
3.47
3.53
3.41
3.40
3.40
3.45
3.43
3.41
3.41
3.98
3.42
3.91
3.91
3.97
3.93
3.94
3.89
3.50
3.89
3.68
3.27
3.35
3.43
3.47
3.39
3.74
3.32
3.60
3.65
3.59
3.68
3.70
3.69
3.52
3.55
3.67, 3.61
3.61, 3.48
3.63, 3.51
3.51
3.62
3.61
3.65, 3.56
3.60, 3.54
3.91, 3,64
3.92, 3.72
3.43, 3.59
3.53
3.28
3.29
3.25
3.23
3.41
3.43
3.40
3.34
3.28
3.28
3.28
3.24
3.41
3.42
3.40
3.30
5.68, 5.68 Hz
5.58, 3.46 Hz
5.55, 4.06 Hz
5.72, 6.11 Hz
5.41 br s
5.03, 4.07 Hz
5.34, 5.09 Hz
5.34, 4.41 Hz
5.31, 5.34 Hz
5.33, 5.04 Hz
5.28, 4.10 Hz
5.46, 5.36 Hz
5.22, 5.05 Hz
5.31, 5.34 Hz
5.56, 5.60 Hz
5.10, 4.70 Hz
4.79, 3.47 Hz
4.74, ꢂ3 Hz
4.84, 3.56 Hz
4.29, 7.57 Hz
4.31, 7.12 Hz
4.27, 7.63 Hz
4.31, 7.25 Hz
4.79, 3.46 Hz
4.76, 3.47 Hz
4.69, 3.46 Hz
4.75, 3.78 Hz
4.36, 7.57 Hz
4.25, 7.89 Hz
4.30, 7.63 Hz
4.27, 6.68 Hz
4.36, 7.56 Hz
4.58, 7.63 Hz
4.56, ꢂ8 Hz
4.70, 6.97 Hz
4.22, 7.63 Hz
4.29, 7.57 Hz
4.74, 7.57 Hz
4.45, 7.57 Hz
4.38, 7.25 Hz
4.30, 7.63 Hz
4.60, 7.63 Hz
4.65, 7.63 Hz
n.d.
3.67, 3.51
3.49, 3.45
3.52
Table 2
13C NMR data: chemical shift (d) for 16–31
1
2
3
4
5
6
10
20
30
40
50
60
OMe
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
97.71
97.54
96.63
99.92
104.59
103.74
103.52
102.65
97.03
96.91
97.14
99.77
104.38
104.87
103.51
102.69
80.36
79.64
79.76
81.44
75.08
78.84
78.56
76.64
79.79
82.28
82.62
81.18
82.87
82.78
78.38
75.76
82.06
80.58
77.71
81.61
82.11
80.86
82.10
83.62
81.52
73.03
77.95
81.67
82.04
81.81
82.27
83.12
n.d.
70.07
70.41
69.79
74.80
73.26
72.55
72.49
73.32
73.09
79.56
70.09
71.21
73.41
73.40
72.61
73.38
68.98
69.24
68.63
69.87
68.22
69.78
68.88
69.33
68.70
68.37
69.43
69.23
69.68
69.70
69.12
69.49
103.87
103.27
102.59
105.26
103.68
102.52
104.92
103.47
103.88
102.94
103.19
105.66
104.38
103.54
104.51
103.98
74.58
75.29
74.63
74.75
74.80
74.53
71.13
75.01
70.69
70.70
71.47
71.21
71.24
71.59
74.54
73.58
n.d.
78.29
85.51
84.70
78.32
78.21
77.14
74.10
78.34
74.37
74.06
74.67
75.03
74.85
75.12
77.75
75.05
70.10
69.33
69.94
69.17
69.86
69.78
68.84
68.88
69.70
67.97
68.40
69.01
70.29
69.68
69.70
68.61
69.49
55.30
55.49
54.69
55.58
57.12
56.08
56.19
56.09
55.08
54.64
55.03
55.37
57.10
56.94
56.25
56.16
77.41
76.24
78.30
74.31
73.80
76.23
74.47
77.40
76.18
76.31
78.56
74.17
73.97
76.72
74.56
78.40
77.27
85.58
85.64
84.37
81.91
85.59
82.24
79.40
80.20
82.66
79.53
82.78
84.68
82.82
75.29
74.63
78.32
79.43
74.09
72.64
75.01
70.16
69.77
73.28
73.62
73.41
73.70
74.01
71.90
tures of anomers were obtained. All in all, solid-phase preparations
afforded cleaner reaction mixtures with less chromatographic
purification necessary, but still more work must be done to estab-
lish solid-phase techniques as a daily routine in the field of carbo-
hydrate chemistry.
(1H: 2.50 ppm, 13C: 39.43 ppm). Kieselgel 60 (E. Merck, Darmstadt,
Germany) was used for column chromatography. MALDI-TOFMS
measurements were carried out on a Bruker Biflex III mass spec-
trometer. 2,5-Dihydroxybenzoic acid was used as the matrix, and
100–200 laser shots were applied for each spectrum.
4.2. General protocols for solution-phase reactions
4. Experimental
4.1. General
4.2.1. Coupling
Molecular sieves (4 Å, 100 mg) were added to a solution of do-
nor (0.15 mmol) and acceptor (0.1 mmol) in anhyd DCM (3 mL),
and the mixture was stirred for 1 h. Then NIS (0.3 mmol) and
AgOTf (0.01 mmol) in CH3CN (3 mL) were added to the mixture
at ꢀ40 °C, and the mixture was stirred at ꢀ15 °C. When TLC
Commercially available starting materials were used without
further purification. Wang resin was purchased from Novabio-
chem, Darmstadt, Germany. Solvents were dried according to
standard methods. NMR spectra were recorded on a Bruker AMX-
400 (100.62 MHz for 13C) or DRX-500 (125.83 MHz for 13C) spec-
trometer in DMSO-d6 as solvent. All chemical shifts are quoted in
ppm downfield from the characteristic signals of the solvents used
showed the disappearance of the acceptor, pyridine (100 lL) was
added, and the mixture was diluted with DCM (20 mL), washed
with aq Na2S2O3 (1 ꢁ 10 mL) and aq NaHCO3 (1 ꢁ 10 mL), dried,
Table 3
Comparative table for solution and solid phase methods
Glycosylation conditions
Deprotection
conditions
Average yield
(over two steps,
calculated for
Best yield/
worst yield
(%)
Solvent
Donor/
acceptor
ratio
Promoter
Temperature
Work-up
Reaction
time
the acceptor) (%)
Solution phase reactions DCM/MeCN, 1:1 1.5:1
Solid phase reactions DCM/MeCN, 1:1 0.65:1
NIS (3 equiv)/ ꢀ40 to ꢀ15 °C Aqueous
30 min–1 h NaOMe in DCM/ 72
MeOH, 5:1
88 (16);
58 (21)
90 (16);
55 (25)
AgOTf (cat)
extractions
Wash and
drain
NIS (2 equiv)/ ꢀ50 to +20 °C
10 h
NaOMe in DCM/ 78
MeOH, 5:2
AgOTf (cat)

K. Ágoston et al. / Carbohydrate Research 344 (2009) 1428–1433
1433
filtered, and concentrated. Column chromatography (3:2 hexane–
EtOAc) of the residue gave the fully protected disaccharide.
the resin was drained and washed sequentially with DCM
(5 ꢁ 5 mL), DMF (5 ꢁ 5 mL), and DCM (5 ꢁ 5 mL).
4.2.2. Deprotection
4.3.5. Cleavage
NaOMe was added (pH ꢂ 9) to a solution of fully protected
disaccharide (0.08 mmol) in DCM (5 mL) and MeOH (2 mL). When
TLC showed complete conversion, Amberlite IR-120 (H+) was
added to neutralize the mixture, then the resin was filtered off
and the filtrate was concentrated. Column chromatography (3:2
hexane–EtOAc) of the residue gave the disaccharide.
NaOMe (50 mg) in DCM (5 mL) and MeOH (1 mL) was added to
the resin and shaken for 30 min. The resin was drained and washed
with DCM (5 ꢁ 5 mL). The combined organic phases were washed
with water (2 ꢁ 10 mL), dried, filtered, and concentrated. Column
chromatography (3:2 hexane–EtOAc) of the residue gave the disac-
charide derivative.
4.3. General protocols for solid-phase reactions
Acknowledgments
4.3.1. Functionalization of the Wang resin
Support of this work by the Deutsche Forschungsgemeinschaft
(SFB 470, A5) and Glycom A/S is gratefully acknowledged.
A mixture of succinic anhydride (10 equiv) and DMAP (100 mg)
in DCM (5 mL) and pyridine (2 mL) was added to Wang resin (1 g,
preswollen in DCM). The mixture was shaken for 10 h, then the re-
sin was drained and washed sequentially with DCM (5 ꢁ 5 mL),
DMF (5 ꢁ 5 mL), and DCM (5 ꢁ 5 mL).
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.carres.2009.04.001.
4.3.2. Loading
Monosaccharide derivative (0.2 mmol), DCC (100 mg) and
DMAP (50 mg) were added in DCM (5 mL) to the functionalized re-
sin (1 g), and the mixture was shaken for 10 h. Then the resin was
drained and washed sequentially with DCM (2 ꢁ 5 mL), DMF
(3 ꢁ 5 mL), DCM (5 ꢁ 5 mL), and MeOH (2 ꢁ 5 mL). The resin was
dried overnight under high vacuum.
References
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4.3.3. Determination of loading
To the sample of resin (ꢂ50 mg, preswollen in DCM),
NaOMe (10 mg) in DCM (2 mL) and MeOH (0.5 mL) was added,
and the mixture was shaken for 1 h. The resin was drained
and washed with DCM (5 ꢁ 3 mL). The combined filtrates were
washed with water (2 ꢁ 3 mL), dried, filtered, and concentrated.
Column chromatography of the residue gave the monosaccha-
ride derivative.
The loading was calculated using the following equation, where x
is the loading in mol/g, z is the mass of the sugar cleaved from the re-
sin in mg, y is the mass of the loaded resin in mg, and M is the molec-
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z
x ¼
y ꢃ M
Loadings obtained: 4 Glc 6-OH, 0.54 mmol/g, 3 Glc 2-OH, 0.65 mmol/
g, 7 Gal 2-OH, 0.65 mmol/g.
4.3.4. Coupling
A mixture of the sugar-loaded resin (100 mg, 0.065 mmol),
monosaccharide acceptor (0.1 mmol), and 4 Å molecular sieves
(50 mg) was stirred in DCM (3 mL) for 2 h. A mixture of NIS
(0.13 mmol) and AgOTf (0.01 mmol) in CH3CN (3 mL) was added
at ꢀ50 °C. The mixture was allowed to warm to rt and stir for
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10 h. The reaction was stopped by adding pyridine (100 lL), then