Glycosylation of allyl 2-acetamido-4,6-O-benzylidene-2-deoxy-α-D- glucopyranoside with bulky substituted glycosyl donors

Article abstract of DOI:10.1016/j.carres.2005.06.016

Glycosylation of allyl 2-acetamido-4,6-O-benzylidene-2-deoxy-α-D- glucopyranoside with bulky substituted glycosyl donors leads to the formation of derivatives of the disaccharide α-D-Glc-(1→3)-D-GlcNAc with different yields.

Full text of DOI:10.1016/j.carres.2005.06.016

Carbohydrate
RESEARCH
Carbohydrate Research 340 (2005) 2048–2051
Note
Glycosylation of allyl 2-acetamido-4,6-O-benzylidene-
2-deoxy-a-D-glucopyranoside with bulky substituted glycosyl donors
Magdalena Jankowska and Janusz Madaj*
´ ´
Sugar Chemistry Group, Faculty of Chemistry, University of Gdansk Sobieskiego 18, PL-80-952 Gdansk, Poland
Received 22 December 2004; accepted 16 June 2005
Available online 14 July 2005
Abstract—Glycosylation of allyl 2-acetamido-4,6-O-benzylidene-2-deoxy-a-D-glucopyranoside with bulky substituted glycosyl
donors leads to the formation of derivatives of the disaccharide a-D-Glc-(1!3)-D-GlcNAc with different yields.
Ó 2005 Elsevier Ltd. All rights reserved.
Keywords: Bulky protecting groups; 2-Acetamido-2-deoxy-D-glucopyranose; Triflates
The disaccharide fragment, a-D-GlcpA-(1!3)-D-
GlcpNAc, of lipopolysaccharides (LPSs) was found in
the bacterial cell walls of Shigella boydii 51 and Hafnia
alvei PCM 11852 and Proteus mirabilis 010.3 Recently,
we described its synthesis.4 Here, we present the results
of the study on the influence of bulky groups at C-6 in
the glycosyl donor molecule on the glycosylation reac-
tion of the title compound.
The aim of this work was to improve the yield of the
reaction for synthesis of derivatives of the disaccharide
a-D-Glc-(1!3)-D-GlcNAc. These disaccharides, after
selective deprotection at C-6 and oxidation, are suitable
for preparation of a-D-GlcA-(1!3)-D-GlcNAc.
like tert-butyldimethylsilyl (6) or trityl (8) can sterically
hinder the anomeric centre, which results in a lowering
of the yield or even stops the reaction.
Very important for the reaction is the configuration
of the anomeric carbon atom as confirmed by the re-
sults of the glycosidation of 9 with the thioglycosides
(6 and 76) with the 6-O-TBDMS group (a and b ano-
mers). These results strongly support the proposed
explanation in the literature7 and in our publication4
the role of a b-triflate byproduct in the mechanism of
the reaction.
Results presented in Table 1 clearly indicate that the
best glycosyl donor in this reaction is trichloroacetimi-
date 1. This means that the more reactive the glycosyl
donor, the higher the yield of the reaction. On the other
hand, the type of glycosyl donor is not the only factor
influencing the reaction. Replacing an O-benzyl group
(ether type, 1) with O-acetyl (ester type, 3) causes a dis-
tinct lowering of the reaction yield. The result is in
agreement with the theory of armed and disarmed glyco-
syl donors.5 The other factor is the steric bulk of the ter-
minal protecting group. A very bulky protecting group
1. Experimental
1.1. General methods
All reactions were carried out in commercially available
dry solvents (Fluka, water <0.005%). Thin-layer chromato-
graphy was performed with E. Merck pre-coated Silica
Gel 60 F-254 plates and detection of compounds was
achieved by charring after spraying with 5% H2SO4 in
EtOH. Column chromatography was carried out with
1
Kieselgel 60 Silica Gel (E. Merck, <200 mesh). H and
13C NMR spectra were recorded at 25 °C with a Varian
Mercury spectrometer at 400 and 100 MHz, respec-
tively, with Me4Si as internal standard. Assignments
were based on homonuclear decoupling experiments
*
Corresponding author. Fax: +48 58 345 04 72; e-mail:
januszm@chem.univ.gda.pl
0008-6215/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2005.06.016

M. Jankowska, J. Madaj / Carbohydrate Research 340 (2005) 2048–2051
2049
Table 1. The results of a glycosidation of 9 with different protected at C-6 glycosyl donors 1–8 in the presence of silver or trimethylsilyltriflate
(R00 = Ag or TMS)
OR
Ph
O
OR
O
BnO
BnO
Ph
+
O
R''OTf
O
O
BnO
BnO
O
O
BnO
HO
O
R'
OBn
AcHN
OAll
9
1-8
O
AcHN
AllO
10-13
Compound
Protecting group (R)
Leaving group (R0)
Yield (10–13) (%)
1
2
3
4
5
6
7
8
Bn
Bn
a-O(C@NH)CCl3
a-SPh
a-O(C@NH)CCl3
a-Br
a-SPh
a-SPh
70
24
45
28
14
9
Ac
Ac
Ac
TBDMS
TBDMS
Tr
b-SPh
a-SPh
0
0
and homo- and heteronuclear correlations. Mass spectra
were measured using MALDITOF with a-cyano-4-
hydroxycinnamic acid (CCA) as a matrix. Optical rota-
tions were measured with a JASCO J-20 polarimeter.
Elemental analyses were carried out with a Carlo Erba
apparatus.
The residue was dissolved in CH2Cl2, washed with aq
NaHCO3 and water, dried with MgSO4 and concen-
trated. For details of specific compounds, see Section
1.6.2, which follows.
1.2.3. Procedure C for thioglycosides. Allyl 2-acetamido-
4,6-O-benzylidene-2-deoxy-a-D-glucopyranoside (9) in
dry DMF was stirred at 0 °C under dry nitrogen. After
10 min a thioglycoside in dry CH2Cl2 and NIS were
added. After 0.5 h trimethylsilyl triflate was added and
the mixture was stirred for 1 h at 0 °C and then 16 h at
rt. Next Pr2EtN (0.1 mL) was added. The solution was
concentrated and co-concentrated with toluene to dry-
ness. The residue was dissolved in CH2Cl2, washed with
aq NaHCO3 and water, dried with MgSO4 and concen-
trated. For details of specific compounds, see Sections
1.5.2, 1.6.1 and 1.7.1, which follow.
1.2. General procedures for a glycosidation of allyl
2-acetamido-4,6-O-benzylidene-2-deoxy-a-D-gluco-
pyranoside (9)
1.2.1. Procedure
A
for glycosyl trichloroacetimi-
dates. Allyl 2-acetamido-4,6-O-benzylidene-2-deoxy-
a-D-glucopyranoside (9, prepared per the Warren and
Jeanloz procedure9) in dry DMF was stirred at ꢀ60 °C
under dry nitrogen and trimethylsilyl triflate was added.
After 10 min a glycosyl trichloroacetimidate in dry
CH2Cl2 was added dropwise and the mixture was stirred
for 1 h at ꢀ60 °C and then 16 h at rt. Next Pr2EtN
(0.1 mL) was added. The solution was concentrated
and co-concentrated with toluene to dryness. The resi-
due was dissolved in CH2Cl2, washed with aq NaHCO3
and water, dried with MgSO4 and concentrated. For
details of specific compounds, see Sections 1.5.1 and
1.6.1, which follow.
1.3. Phenyl 2,3,4-tri-O-benzyl-6-O-tert-butyldimethyl-
silyl-1-thio-a-D-glucopyranoside (6)
To a mixture of phenyl 2,3,4-tri-O-benzyl-a-D-glucopyr-
anoside8 (60 mg, 0.11 mM) and imidazole in dry DMF
stirred at 0 °C tert-butylchlorodimethylsilane was added
(45 mg, 0.27 mM). After 1 h the mixture was diluted
with EtOAc (25 mL) and washed with aq NaHCO3
(20 mL), water (20 mL), dried with MgSO4 and concen-
trated. The residue was eluted from a column of silica
gel with 3:7 acetone–hexanes to give 6 (30 mg, 42%) as
1.2.2. Procedure B for glycosyl bromides. Allyl 2-acet-
amido-4,6-O-benzylidene-2-deoxy-a-D-glucopyranoside
(9) in dry DMF was stirred at 0 °C under dry nitrogen
and silver triflate was added. After 10 min a glycosyl
bromide in dry CH2Cl2 was added, and the mixture
was stirred for 1 h at 0 °C and then for 16 h at rt. Next
Pr2EtN (0.1 mL) was added. The solution was concen-
trated and co-concentrated with toluene to dryness.
1
an oil: H NMR (CDCl3): d 7.51–7.23 (m, 20H, Ph),
5.62 (d, 1H, J1,2 4.8, H-1), 4.99 (d, 1H, OCH2Ph), 4.86
(d, 1H, OCH2Ph), 4.81 (d, 1H, OCH2Ph), 4.76 (d, 1H,
OCH2Ph), 4.67 (d, 2H, OCH2Ph), 4.12 (m, 1H, H-5),
3.92–3.82 (m, 3H, H-2, H-3, H-60), 3.75 (dd, 1H, J5,6

2050
M. Jankowska, J. Madaj / Carbohydrate Research 340 (2005) 2048–2051
0
11.2, J6,6 2.0, H-6), 3.59 (t, 1H, J3,4 8.8, J4,5 10.0, H-4),
0.87 (s, 9H, Si–C–(CH3)3) 0.01 (s, 3H, Si(CH3)2), 0.01 (s,
3H, Si(CH3)2). 13C NMR d 138.89–127.14 (Ph), 87.05
(C-1), 82.76 (C-3), 80.30 (C-2), 77.64 (C-4), 76.07
(OCH2Ph), 75.30 (OCH2Ph), 72.87 (C-5), 72.67
(OCH2Ph), 62.48 (C-6), 26.16 (Si–C–(CH3)3), 18.57
(Si–C–(CH3)3), ꢀ4.96 (Si(CH3)2), ꢀ5.20 (Si(CH3)2).
This compound was used directly in synthesis as
described in Sections 1.5.1, 1.5.2, 1.6.1, 1.6.2, 1.6.3 and
1.7.1, which follow.
(C-6II), 70.31 (C-5I), 69.26 (C-6I), 68.7 (OCH2), 62.92
(C-5II), 52.27 (C-2I), 23.26 (NHCOCH3). Anal. Calcd
for C52H57NO11: C, 71.64; H, 6.54; N, 1.6. Found: C,
70.95; H, 6.87; N, 1.01.
1.5.2. Procedure C. The mixture after the reaction of 9
(0.12 g, 0.34 mM) with 211 (0.26 g, 0.41 mM) in DMF
(10 mL) and CH2Cl2 (10 mL) in the presence of NIS
(0.1 g) and TMSOTf (30 lL) was eluted from a column
of silica gel with 1:2 EtOAc–toluene to give 10 (0.07 g,
24%) as an oil. The compound was identical to that from
Procedure A, above.
1.4. Phenyl 2,3,4-tri-O-benzyl-1-thio-6-O-trityl-a-D-
glucopyranoside (8)
1.6. Allyl 6-O-acetyl-2,3,4-tri-O-benzyl-a-D-gluco-
pyranosyl-(1!3)-2-acetamido-4,6-O-benzylidene-
2-deoxy-a-D-glucopyranoside (11)
Sodium hydride (65 mg, 2.71 mM) was added to a
cooled solution of phenyl 1-thio-6-O-trityl-a-D-gluco-
pyranoside4 (0.12 g, 0.23 mM) in dry DMF (4 mL) and
the mixture was stirred for 1 h at 0 °C. Next BnBr
(0.14 mL; 1.4 mM) was added dropwise and the mixture
was stirred. After 2 h, excess of sodium hydride was
decomposed with MeOH and the mixture was concen-
trated. The residue was eluted from a column of silica
gel with 3:7 acetone–hexanes to give 8 (0.14 g, 78%) as
1.6.1. Procedure A. The mixture after the reaction of 9
(0.17 g, 0.49 mM) with 312 (0.39 g, 0.61 mM) in DMF
(15 mL) and CH2Cl2 (15 mL) in the presence of
TMSOTf (0.16 mL; 0.89 mM) was eluted from a column
of silica gel with 2:3 EtOAc–toluene to give 11 (0.18 g,
20
D
45%) as an oil: ½aꢁ +66 (c 1.4, CHCl3); 1H NMR
1
an oil: H NMR (CDCl3): d 7.61–6.95 (m, 35H, Ph),
(CDCl3): d 7.40–6.90 (m, 20H, Ph), 6.0 (d, 1H, NH),
5.89 (m, 1H, @CH), 5.49 (d, 1H, J1,2 3.6 H-1II), 5.44
(s, 1H, CHPh), 5.32 (m, 2H, @CH2), 4.97 (d, 1H,
OCH2Ph), 4.89 (d, 1H, J1,2 4.0, H-1I), 4.87 (d, 1H,
OCH2Ph), 4.77 (d, 1H, OCH2Ph), 4.53 (m, 2H,
OCH2Ph), 4.48 (m, 1H, H-2I), 4.3 (d, 1H, OCH2Ph),
4.74 (s, 1H, J1,2 4.8, H-1), 4.97–4.77 (m, 4H, OCH2Ph),
4.71–4.65 (m, 2H, OCH2Ph), 3.80–3.43 (m, 6H, H-5,
H-2, H-3, H-60, H-6, H-4). 13C NMR d 144.72–126.52
(Ph), 87.62 (C-1), 86.94 (C(C6H5)3), 81.01 (C-3), 79.27
(C-2), 77.99 (C-4), 76.03 (OCH2Ph), 75.62 (OCH2Ph),
75.25 (OCH2Ph), 73.60 (C-5), 69.20 (C-6).
4.27–4.16 (m, 4H, H-3I, H-5II, H-6II, OCH2), 4.12
0
(m, 2H, H-4I, H-6II ), 4.04 (m, 1H, OCH2), 3.95 (m,
0
1.5. Allyl 2,3,4,6-tetra-O-benzyl-a-D-glucopyranosyl-
(1!3)-2-acetamido-4,6-O-benzylidene-2-deoxy-a-D-
glucopyranoside (10)
3H, H-3II, H-6I, H-6I ), 3.77 (m, 1H, J4,5 9.6, J5,6 10.4,
H-5I), 3.38 (dd, 1H, J2,3 9.2, H-2II), 3.25 (t, 1H, J3,4
9.2, J4,5 9.6, H-4II), 2.08 (s, 3H, COCH3), 2.02 (s, 3H,
NCOCH3). 13C NMR d 171.18 (COCH3), 170.35
(NCOCH3), 138.86 (@CH), 138.27–126.61 (Ph), 118.72
(@CH2), 102.41 (CHPh), 97.66 (C-1I), 96.09 (C-1II),
83.22 (C-3II), 81.48 (C-4I), 79.32 (C-2II), 78.64
(C-4II), 75.9 (OCH2Ph), 74.77 (OCH2Ph), 72.06
(C-5II), 71.15 (OCH2Ph), 69.20 (C-5I), 68.91 (OCH2),
68.31 (C-3I), 64.58 (C-6II), 62.99 (C-6I), 51.86 (C-2I),
23.31 (COCH3), 21.15 (NHCOCH3). MALDITOF-MS:
Calcd for C47H53NO12: 823.9 [M]. Found: 846.3
[M+Na]+.
1.5.1. Procedure A. The mixture after the reaction of 9
(0.19 g, 0.54 mM) with 110 (0.47 g, 0.68 mM) in DMF
(17 mL) and CH2Cl2 (17 mL) in the presence of
TMSOTf (0.12 mL, 0.69 mM) was eluted from a column
of silica gel with 1:2 EtOAc–toluene to give 10 (0.33 g,
20
D
70%) as an oil: ½aꢁ +50 (c 1, CHCl3); 1H NMR
(CDCl3): d 7.41–7.24 (m, 25H, Ph), 6.25 (d, 1H, NH),
5.77 (m, 1H, @CH), 5.44 (d, 1H, J1,2 4.0, H-1II), 5.42
(s, 1H, CHPh), 5.21 (m, 2H, @CH2), 4.94 (d, 1H,
OCH2Ph), 4.87 (d, 1H, J1,2 3.2, H-1I), 4.81 (d, 1H,
OCH2Ph), 4.70 (d, 1H, OCH2Ph), 4.5 (m, 3H,
OCH2Ph), 4.39 (m, 1H, H-2I), 4.24 (m, 3H, H-3I, H-
1.6.2. Procedure B. The mixture after the reaction of 9
(0.20 g, 0.57 mM) with 412 (0.25 g, 0.88 mM) in DMF
(15 mL) and CH2Cl2 (15 mL) in the presence of AgOTf
(0.40, 1.56 mM) was eluted from a column of silica gel
with 2:3 EtOAc–toluene to give 11 (0.13 g, 28%) as an
oil. The compound was identical to that from Procedure
A, above.
0
0
6II , OCH2Ph), 4.20 (m, 2H, H-6I , OCH2), 3.85 (m,
4H, H-3II, H-4I, H-5II, OCH2), 3.77 (m, 2H, H-6I, H-
6II), 3.5 (m, 2H, H-2II, H-5I), 3.19 (dd, 1H, J3,4 10.0,
J4,5 10.4, H-4II), 1.86 (s, 3H, NHCOCH3). 13C NMR d
170.69 (NCOCH3), 138.89 (@CH), 138.4–126.64 (Ph),
118.07 (@CH2), 102.44 (CHPh), 97.24 (C-1I), 96.36
(C-1II), 83.10 (C-3II), 81.88 (C-4I), 78.73 (C-2II), 77.99
(C-4II), 75.97 (OCH2Ph), 7.75 (OCH2Ph), 74.17
(OCH2Ph), 72.45 (C-3I), 71.03 (OCH2Ph), 70.49
1.6.3. Procedure C. The mixture after the reaction of 9
(0.15 g, 0.42 mM) with 54 (0.30 g, 0.51 mM) in DMF
(7 mL) and CH2Cl2 (7 mL) in the presence of NIS

M. Jankowska, J. Madaj / Carbohydrate Research 340 (2005) 2048–2051
2051
(0.12 g) and TMSOTf (30 lL) was eluted from a column
of silica gel with 1:2 EtOAc–toluene to give 11 (0.049 g,
14%) as an oil. The compound was identical with that
from Procedure A, above.
Calcd for C51H65NO11: 896.1 [M]. Found: 918.2
[M+Na]+.
Acknowledgements
1.7. Allyl 2,3,4-tri-O-benzyl-6-O-tert-butyldimethylsilyl-
a-D-glucopyranosyl-(1!3)-2-acetamido-4,6-O-benzyl-
idene-2-deoxy-a-D-glucopyranoside (12)
We thank the KBN (BW/8000-5-0184-4, DS/8361-4-
0134-4) for support of this work.
1.7.1. Procedure C. The mixture after the reaction of 9
(57 mg, 0.16 mM) with 6 (0.15 g, 0.19 mM) in DMF
(7 mL) and CH2Cl2 (7 mL) in the presence of NIS
(45 mg) and TMSOTf (15 lL) was eluted from a column
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20
D
9%) as an oil: ½aꢁ +75 (c 1.4, CHCl3); 1H NMR
(CDCl3): d 7.38–6.88 (m, 20H, Ph), 6.03 (d, 1H, NH),
5.85 (m, 1H, @CH), 5.43 (s, 1H, CHPh), 5.65 (d, 1H,
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0
3.95–3.84 (m, 4H, H-4I, H-5I, H-6I, H-6I ), 3.76 (t, 1H,
J6,6 10.4, J5,6 9.6, H6II), 3.40 (m, 2H, H-5I, H-2II),
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3.25 (t, 1H, J3,4 9.2, J4,5 9.2, H-4II), 2.04 (s, 3H,
NCOCH3), 0.90 (s, 9H, Si–C–(CH3)3) 0.11 (s, 3H,
Si(CH3)2), 0.08 (s, 3H, Si(CH3)2). 13C NMR: d 170.64
(NCOCH3), 138.96 (@CH), 138.51–126.65 (Ph), 118.83
(@CH2), 102.51 (CHPh), 97.97 (C-1II), 96.41 (C-1I),
83.26 (C-3II), 82.04 (C-4I), 79.03 (C-2II), 78.18 (C-4II),
76.04 (OCH2Ph), 74.74 (OCH2Ph), 72.52 (C-3I), 71.33
(C-5II), 71.05 (OCH2Ph), 69.33 (C-6II), 68.75 (OCH2),
64.06 (C-5I), 62.80 (C-6I), 52.55 (C-2I), 26.35 (Si–C–
(CH3)3), 23.18 (NHCOCH3), 18.70 (Si–C–(CH3)3),
ꢀ4.75 (Si(CH3)2), ꢀ5.17 (Si(CH3)2). MALDITOF-MS:
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