Mild and efficient method for the cleavage of benzylidene acetals using HClO4-SiO2 and direct conversion of acetals to acetates

Article abstract of DOI:10.1016/j.tetlet.2006.03.133

HClO₄-SiO₂ has been used successfully for the deprotection of benzylidene acetals and the direct conversion of benzylidene acetals to the corresponding di-O-acetates. The reactions are very fast and yields are excellent.

Full text of DOI:10.1016/j.tetlet.2006.03.133

Tetrahedron Letters 47 (2006) 3653–3658
Mild and efficient method for the cleavage
of benzylidene acetals using HClO4–SiO2 and
direct conversion of acetals to acetates I
Geetanjali Agnihotri and Anup Kumar Misra*
Medicinal and Process Chemistry Division, Central Drug Research Institute, Chattar Manzil Palace, Lucknow 226001, UP, India
Received 6 February 2006; revised 13 March 2006; accepted 22 March 2006
Available online 12 April 2006
Abstract—HClO4–SiO2 has been used successfully for the deprotection of benzylidene acetals and the direct conversion of benzyl-
idene acetals to the corresponding di-O-acetates. The reactions are very fast and yields are excellent.
Ó 2006 Elsevier Ltd. All rights reserved.
Selective protection and deprotection of polyhydroxyl-
ated substrates is often of decisive importance for the
successful outcome of a chemical synthesis. Numerous
methods and reagents are available for this purpose,
particularly for carbohydrate and natural product syn-
thesis.1 Conversion of the assembled carbohydrates into
functional derivatives is a necessary prerequisite for the
synthesis of complex oligosaccharides.
ity with other functional groups and relatively harsh
reaction conditions. Therefore, the development of mild,
efficient and metal-free reaction conditions would ex-
tend the scope of this conversion. Use of a catalytic
quantity of cheap solid supported acid, which could be
removed from the reaction mixture by simple filtration
avoiding expensive and toxic reagents, could be useful
for this purpose.
A benzylidene acetal, a widely used functional group for
the protection of 1,2- and 1,3-diols, has an advantage
that it can be used to protect two hydroxyl groups
simultaneously and can be removed by hydrogenation
or hydrolysis under acidic conditions.1,2 Furthermore,
one of the two C–O bonds of the benzylidene acetal
can be regioselectively opened for application in oligo-
saccharide synthesis.2,3 Besides the selective opening of
benzylidene acetals, there are a plethora of methods
available for the complete removal of benzylidene ace-
tals, which include strong acidic media1 (H2SO4, AcOH,
Zn(OTf)2, FeCl3, BCl3, SnCl2, camphorsulfonic acid) or
other demanding conditions4 (H2/Pd–C, hydrazine,
EtSH, I2, Na/NH3, Er(OTf)3, etc.). However, in spite
of their potential utility, many of these methods suffer
from drawbacks such as relatively low yields, formation
of by-products, use of expensive reagents, incompatibil-
Recently, we have devoted considerable effort towards
the development of a more environmentally benign cata-
lyst for several important organic transformations.5
During our study on the acetylation of carbohydrate
derivatives containing acid-labile functionalities, (such
as benzylidene acetals) using perchloric acid supported
on silica5b (HClO4–SiO2), a non-toxic cheaper alterna-
tive of triflate salts and solid acids and acetic anhydride,
we observed that a clean deprotection of benzylidene
acetals was taking place with exclusive formation of
the corresponding acetylated products. Prompted by
this observation, we set out to explore the use of
HClO4–SiO2 for the removal of benzylidene acetals in
carbohydrate derivatives and for the direct conversion
of benzylidene acetals to the corresponding acetates.
6
Although HClO4–SiO2 is not commercially available,
it can be easily prepared in the laboratory and the free
flowing powder obtained can be stored for years without
any loss of catalytic activity. We herein disclose a conve-
nient methodology for the rapid deprotection of benzyl-
idene acetals and direct conversion of benzylidene
acetals to the acetylated carbohydrate derivatives using
HClO4–SiO2 (Schemes 1 and 2).
Keywords: Carbohydrate; Debenzylidenation; Acetylation; Acetates;
HClO4–SiO2; 1,3-diol.
q CDRI communication No. 6936.
*
Corresponding author. Tel.: +91 522 2612411 18; fax: +91 522
2623938; e-mail: akmisra69@rediffmail.com
0040-4039/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.03.133

3654
G. Agnihotri, A. K. Misra / Tetrahedron Letters 47 (2006) 3653–3658
OH
anoside in commercial CH3CN at room temperature
Ph
O
O
O
HClO4-SiO2
CH3CN, rt
gave clean deprotection of the benzylidene acetal in a
few minutes. In order to test the reaction protocol, a ser-
ies of protected mono-, di- and trisaccharide derivatives
containing benzylidene acetals were treated with
HClO4–SiO2 in CH3CN and the results are presented
in Table 1. Following similar reaction conditions, 4-
methoxybenzylidene acetals were also deprotected suc-
cessfully. A series of anomeric protecting groups and
interglycosidic linkages remained intact under the reac-
tion conditions. Pure products were obtained by
removal of the catalyst by simple filtration and
evaporation of the solvent. CH3CN was found to be
HO
R1O
O
R1O
R1O
R1O
OR2
OR2
Scheme 1.
As a model, methyl 2,3-di-O-acetyl-4,6-O-benzylidene-
a-D-glucopyranoside was treated with HClO4–SiO2 in
a variety of solvents and reaction conditions. After a ser-
ies of experiments, it was observed that the use of 50 mg
of HClO4–SiO2 (0.025 mmol of HClO4) per millimole of
methyl 2,3-di-O-acetyl-4,6-O-benzylidene-a-D-glucopyr-
Table 1. Cleavage of benzylidene acetals using HClO4–SiO2 in CH3CN at room temperature
Entry
Substrate
Ph
Product
Time (min)
20
Yield (%)
95
Ref.
7
OH
O
O
O
1
O
HO
AcO
AcO
AcO
AcO
OH
OMe
OMe
OMe
OMe
pMeOPh
O
O
O
O
HO
AcO
2
20
96
7
AcO
AcO
AcO
OH
OMe
Ph
Ph
O
O
O
O
HO
BzO
3
4
5
20
20
20
95
92
96
—
8
BzO
BzO
BzO
OH
OMe
OMe
O
O
BnO
O
O
HO
BnO
OMe
BnO
BnO
Ph
OH
HO
O
O
O
9
O
OMe
BzO
OMe
BzO
p-MeOPh
OBz
OH
OBz
HO
O
O
O
6
7
20
20
95
95
9
9
O
OMe
BzO
OMe
BzO
OBz
OBz
Ph
O
HO
OH
O
O
O
BnO
BnO
BnO
OMe
BnO
OMe
OH
Ph
O
O
O
O
HO
8
9
30
15
96
90
—
10
OC8H17
AcO
OC8H17
AcO
NPhth
NPhth
OH
O
Ph
Ph
O
O
O
HO
HO
HO
OH
O
O
AcO
O
O
HO
O
AcO
O
NPhth
AcO
10
11
30
30
95
92
—
—
NPhth
AcO
O
O
AcO
AcO
OH
AcO
Ph
AcO
O
OMe
O
OMe
O
O
HO
O
BzO
O
BzO
BzO
BzO
O
AcO
AcO
O
AcO
AcO
AcO
O
AcO
O
OAc
OAc
OAc
OAc
O
AcO
OAc
OAc
O
AcO

G. Agnihotri, A. K. Misra / Tetrahedron Letters 47 (2006) 3653–3658
3655
the best solvent in comparison to other commonly used
apolar solvents (e.g. CH2Cl2, CHCl3, THF) in which
lower yields were obtained (Table 2).
After achieving satisfactory yields in the deprotection of
benzylidene acetals, we turned our attention to the
applicability of the catalyst for a sequential deprotection
of benzylidene acetal and acetylation of the diol gener-
ated in situ following a one-pot protocol. Methyl 2,3-
di-O-acetyl-4,6-O-benzylidene-a-D-glucopyranoside was
treated with acetic anhydride (5.0 equiv) in the presence
of HClO4–SiO2 (50 mg of HClO4–SiO2 per millimole) at
room temperature (Scheme 2). The exothermic reaction
started immediately and quantitative formation of
2,3,4,6-tetra-O-acetyl-a-D-glucopyranoside was achie-
ved in 15 min. The protocol was successfully applied
to a series of mono-, di- and trisaccharide derivatives
containing benzylidene or 4-methoxybenzylidene acetals
and excellent yields were achieved in every case as pre-
sented in Table 3. A variety of anomeric protecting
groups and interglycosidic linkages remained unaffected
under the reaction conditions. Pure products were iso-
lated by removal of the catalyst and evaporation under
reduced pressure.
Table 2. Deprotection of methyl 2,3-di-O-acetyl-4,6-O-benzylidene-a-
D-glucopyranoside at room temperature in different solvents
Entry
Solvent
Time (min)
Yield (%)
1
2
3
4
5
CH3CN
CH2Cl2
CHCl3
THF
20
60
60
60
120
95
40
45
75
30
Toluene
OAc
O
Ph
O
O
HClO4-SiO2
Ac2O, rt
O
AcO
R1O
R1O
R1O
R1O
OR2
OR2
Scheme 2.
Table 3. One-pot cleavage-acetylation of benzylidene acetals using HClO4–SiO2 in Ac2O at room temperature
Entry
Substrate
Product
Time (min)
Yield (%)
98
Ref.
11
Ph
O
OAc
O
O
1
15
O
AcO
AcO
AcO
AcO
AcO
OMe
OMe
OMe
OAc
O
pMeOPh
O
O
O
AcO
AcO
2
3
4
5
15
15
15
15
96
95
92
95
11
—
—
—
AcO
AcO
AcO
OMe
OAc
O
Ph
Ph
O
O
O
AcO
BzO
BzO
BzO
BzO
OMe
OMe
OMe
OAc
O
O
O
BnO
O
AcO
BnO
BnO
BnO
OMe
Ph
AcO
BnO
OAc
O
O
O
O
BnO
BnO
BnO
OMe
OMe
p-MeOPh
AcO
BnO
OAc
O
O
O
6
8
15
15
96
95
—
12
O
BnO
BnO
OMe
BnO
O
OMe
OAc
Ph
Ph
Ph
O
O
O
AcO
AcO
OC8H17
AcO
OC8H17
NPhth
NPhth
OAc
O
O
AcO
O
O
9
AcO
AcO
20
20
95
90
13
10
OCH3
OCH3
NHAc
NHAc
OAc
O
O
O
HO
O
10
AcO
AcO
Ph
AcO
OAc
O
O
OAc
O
O
11
20
96
14
OAc
O
O
O
AcO
AcO
OAllyl
AcO
O
AcO
OAc
AcO
OAllyl
AcO
OAc
(continued on next page)

3656
G. Agnihotri, A. K. Misra / Tetrahedron Letters 47 (2006) 3653–3658
Table 3 (continued)
Entry
Substrate
Product
Time (min)
Yield (%)
92
Ref.
15
Ph
AcO
OAc
O
OAc
O
O
O
12
20
O
O
AcO
OAc
O
AcO
OMP
OSE
AcO
O
OAc
O
AcO
Ph
AcO
OMP
OSE
AcO
OAc
AcO
AcO
OAc
O
OAc
O
O
13
14
20
20
96
95
16
17
OAc
O
O
O
AcO
AcO
O
AcO
OAc
AcO
AcO
OAc
BnO
BnO
OBn
O
BnO
BnO
OBn
O
NPhth
OAllyl
NPhth
OAllyl
O
BnO
AcO
BnO
O
Ph
O
O
O
O
OAc
OAc
Ph
O
O
O
O
AcO
AcO
AcO
O
O
NPhth
AcO
15
16
20
20
95
98
—
5b
NPhth
AcO
O
O
AcO
AcO
AcO
AcO
OMe
OMe
Ph
OAc
O
O
AcO
O
O
AcO
AcO
AcO
AcO
O
O
OAc
OAc
OAc
OAc
OAc
O
O
AcO
O
O
Ph
OAc
O
Ph
O
O
AcO
O
AcO
AcO
AcO
AcO
17
20
18
O
O
OAc
O
O
OAc
OAc
OAc
AcO
AcO
OAc
OAc
MP: p-Methoxyphenyl; SE: trimethylsilyl ethyl; Phth: phthalimido.
Furthermore, the catalyst can be reused several times
without significant loss of activity. After filtering the cat-
alyst from the reaction mixture, it could be recycled after
drying under vacuum. The recovered catalyst was used
three times in the direct deprotection and acetylation
of methyl 2,3-di-O-acetyl-4,6-O-benzylidene-a-D-gluco-
pyranoside and the yields were higher than 90% in each
case.
carbohydrate derivatives were prepared (Table 1). All
the products are known compounds and gave acceptable
NMR spectra19 that matched data reported in the
literature.
A typical experimental protocol for the direct conversion
of benzylidene acetals to the corresponding di-O-acetates
is as follows: to a solution of methyl 2,3-di-O-acetyl-4,6-
O-benzylidene-a-D-glucopyranoside (366 mg, 1.0 mmol)
in acetic anhydride (0.5 mL) was added HClO4–SiO2
(50 mg) and the reaction mixture was stirred at room
temperature for 15 min. After completion (TLC), the
reaction mixture was filtered with ethyl acetate through
a Celite bed and concentrated to dryness to give methyl
2,3,4,6-tetra-O-acetyl-a-D-glucopyranoside (355 mg, 98%).
Although the product was pure enough, analytical
samples were prepared by passing the crude reaction
product through a short column of SiO2 using hexane–
EtOAc (1:1) as eluant. Following similar reaction condi-
tions, a series of acetylated carbohydrate derivatives
were prepared directly from carbohydrate benzylidene
acetals (Table 1). All the products are known com-
pounds and gave acceptable NMR spectra19 that
A typical experimental protocol for the deprotection of
benzylidene acetal is as follows: to a solution of methyl
2,3-di-O-acetyl-4,6-O-benzylidene-a-D-glucopyranoside
(366 mg, 1.0 mmol) in commercial grade CH3CN (5 mL)
was added HClO4–SiO2 (50 mg) and the reaction mix-
ture was stirred at room temperature for 20 min. After
completion (TLC), the reaction mixture was filtered with
ethyl acetate through a Celite bed and concentrated to
dryness to give methyl 2,3-di-O-acetyl-a-D-glucopyrano-
side (265 mg, 95%). Although the product was pure
enough, analytical samples were prepared by passing
the crude reaction product through a short column of
SiO2 using toluene–EtOAc (1:1) as eluant. Following
similar reaction conditions, a series of di-hydroxylated

G. Agnihotri, A. K. Misra / Tetrahedron Letters 47 (2006) 3653–3658
3657
9. Kiss, von J.; Burkhardt, F. Helv. Chim. Acta 1970, 53,
1000–1011.
10. Roth, W.; Pigman, W. Methods Carbohydr. Chem. 1963, 2,
405–408.
11. Bollenback, G. N. Methods Carbohydr. Chem. 1963, 2,
326–328.
matched data reported in the literature. Caution:
Although no explosions occured under these conditions,
extreme care has to be applied for large-scale reactions.
The generation of the catalyst should be performed with
special care and in a safe environment.
12. Campos-Valdes, M. T.; Marino-Albernas, J. R.; Verez-
Bencomo, V. J. Carbohydr. Chem. 1987, 6, 509–513.
13. Conchie, J.; Levvy, G. A. Methods Carbohydr. Chem.
1963, 2, 332–335.
14. Okamoto, K.; Kondo, T.; Goto, T. Tetrahedron 1987, 43,
5919–5928.
15. Zhang, Z.; Magnusson, G. Carbohydr. Res. 1996, 295, 41–
55.
16. Jansson, K.; Ahlfors, S.; Frejd, T.; Kihlberg, J.; Magnus-
son, G. J. Org. Chem. 1988, 53, 5629–5647.
17. Misra, A. K.; Basu, S.; Roy, N. Synth. Commun. 1996, 26,
2857–2862.
In summary, we have introduced a new method for the
rapid deprotection of benzylidene acetals and direct con-
version of acid labile benzylidene acetals to the base-
labile acetate derivatives in a one-pot reaction using
HClO4–SiO2 with almost quantitative yields avoiding
the formation of by-products. HClO4–SiO2 is a non-
toxic catalyst system, which can be reused after easy
recovery from the reaction mixture. As the reaction does
not require any toxic reagents and chromatographic
purification, this environmentally benign reaction proto-
col should find application in synthetic organic
chemistry.
18. Binkley, W. W.; Horton, D.; Bhacca, N. S. Carbohydr.
Res. 1969, 10, 245–258.
19. Spectral data of selected compounds:
Methyl 2,3-di-O-benzoyl-a-D-glucopyranoside (Table 1,
entry 3): 1H NMR (200 MHz, CDCl3): d 7.97–7.25 (m,
10H, aromatic protons), 5.70 (t, J = 9.0 Hz, 1H), 5.19 (t,
J = 8.8 Hz, 1H), 5.08 (d, J = 3.6 Hz, 1H), 3.91–3.70 (m,
4H), 3.43 (s, 3H); ESI-MS: m/z 425 [M+Na]; Anal. calcd
for C21H22O8 (402): C, 62.68; H, 5.51; found: C, 62.84; H,
5.80.
Acknowledgements
Instrumentation facilities from SAIF, CDRI are grate-
fully acknowledged. G.A. thanks CSIR, New Delhi,
for providing a Senior Research Fellowship. This pro-
ject was partly funded by the Department of Science
and Technology (DST), New Delhi (SR/FTP/CSA-10/
2002), India.
Octyl 3-O-acetyl-2-deoxy-2-phthalimido-b-D-glucopyrano-
side (Table 1, entry 8): 1H NMR (200 MHz, CDCl3): d
7.88–7.71 (m, 4H, aromatic protons), 5.62 (t, J = 8.0 Hz,
1H), 5.40 (d, J = 8.4 Hz, 1H), 4.16 (dd, J = 8.5 Hz, 8.5 Hz,
1H), 4.0–3.55 (m, 5H), 3.52–3.40 (m, 1H), 1.93 (s, 3H), 1.39–
1.20 (m, 2H), 1.25–1.10 (m, 10H), 0.81 (t, J = 6.8 Hz, 3H);
ESI-MS: m/z 486 [M+Na]; Anal. calcd for C24H33NO8
(463): C, 62.19; H, 7.18; found: C, 62.40; H, 7.40.
Methyl (3-O-acetyl-2-deoxy-2-phthalimido-b-D-glucopy-
ranosyl)-(1 ! 6)-2,3,4-tri-O-acetyl-a-D-glucopyranoside
References and notes
1. (a) Greene, T. W.; Wuts, P. G. M. Protective Groups in
Organic Synthesis, 3rd ed.; John Wiley and Sons: New
York, 1999; (b) Kocienski, P. J. Protecting Groups, 1st ed.;
George Thieme Verlag: Stuttgart, 1994; (c) Kocienski, P.
J. J. Chem. Soc., Perkin Trans. 1 2001, 2109–2135.
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cel Dekker: New York, 1997, pp 53–67.
3. (a) Arasappan, A.; Fraser-Reid, B. J. Org. Chem. 1996, 61,
2501–2506; (b) Kotsuki, H.; Ushio, Y.; Yoshimura, N.;
Ochi, M. J. Org. Chem. 1987, 52, 2594–2596; (c) Pohl, N.
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1
(Table 1, entry 10): H NMR (200 MHz, CDCl3): d 7.84–
7.71 (m, 4H, aromatic protons), 5.62 (t, J = 9.0 Hz, 1H),
5.42 (d, J = 8.4 Hz, 1H), 5.31 (t, J = 9.6 Hz, 1H), 4.80 (t,
J = 9.6 Hz, 1H), 4.67 (dd, J = 10.2 and 3.3 Hz, 1H), 4.53 (d,
J = 3.3 Hz, 1H), 4.20 (t, J = 8.7 Hz, 1H), 4.0–3.85 (m, 3H),
3.81–3.75 (m, 2H), 3.64–3.60 (m, 1H), 3.54–3.47 (m, 1H),
3.05 (s, 3H), 1.99 (s, 3H), 1.90 (s, 6H), 1.87 (s, 3H); 13C
NMR (50 MHz, CDCl3): d 171.5, 170.4 (2C), 170.0, 168.3
(2C), 134.5–123.7 (aromatic carbons), 98.8, 96.7, 76.3, 73.9,
71.2, 70.4, 70.1, 69.5, 69.1, 68.0, 62.3, 55.3, 54.9, 21.0, 20.9
(2C), 20.8; ESI-MS: m/z 676 [M+Na]; Anal. calcd for
C29H35NO16 (653): C, 53.29; H, 5.40; found: C, 53.10; H,
5.58.
(2,3-Di-O-benzoyl-b-D-glucopyranosyl)-(1 ! 6)-(2,3,4,6-
tetra-O-acetyl-a-D-glucopyranosyl)-(1 ! 1)-2,3,4-tri-O-
acetyl-a-D-glucopyranose (Table 1, entry 11): 1H NMR
(200 MHz, CDCl3): d 7.96–7.32 (m, 10H, aromatic pro-
tons), 5.43–5.36 (m, 3H), 5.01–4.87 (m, 5H), 4.74–4.65 (m,
4H), 4.17–4.01 (m, 2H), 3.97–3.89 (m, 5H), 3.59–3.52 (m,
2H), 2.07 (s, 3H), 2.05 (s, 3H), 2.04 (s, 6H), 1.99 (s, 6H), 1.93
(s, 3H); 13C NMR (50 MHz, CDCl3): d 171.6, 170.9, 170.6,
170.4, 170.2, 170.0, 169.9, 167.2, 165.5, 133.7–128.7 (aro-
matic carbons), 101.1, 92.5, 92.3, 76.6 (2C), 71.6, 70.6, 70.3,
70.2 (2C), 69.7, 69.4, 68.9, 68.6, 68.4, 62.2, 62.0, 60.8, 21.3,
21.1 (2C), 21.0 (2C), 20.9, 20.7; ESI-MS: m/z 1029 [M+Na];
Anal. calcd for C46H54O25 (1006): C, 54.87; H, 5.41; found:
C, 54.70; H, 5.60.
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6. Preparation of HClO4–SiO2: HClO4 (1.8 g, 12.5 mmol, as
a 70% aq solution) was added to a suspension of SiO2
(230–400 mesh, 23.7 g) in Et2O (70.0 mL). The mixture
was concentrated and the residue was heated at 100 °C for
72 h under vacuum to furnish HClO4–SiO2 (0.5 mmol/g)
as a free flowing powder.
Methyl 4,6-di-O-acetyl-2,3-di-O-benzoyl-a-D-glucopyrano-
side (Table 3, entry 3): 1H NMR (200 MHz, CDCl3): d
7.97–7.32 (m, 10H, aromatic protons), 5.90 (br s, 2H), 5.31
(t, J = 8.8 Hz, 1H), 5.17 (br s, 1H), 4.30 (dd, J = 11.0 and
7. Whistler, R. L.; Kazeniac, S. J. J. Am. Chem. Soc. 1954,
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8. Dennison, J. C.; McGilvray, D. I. J. Chem. Soc. 1951,
1616.

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4.5 Hz, 1H), 4.16–4.09 (m, 2H), 3.45 (s, 3H), 2.13, 1.94 (2s,
1H), 4.84 (d, J = 11.0 Hz, 1H), 4.68 (dd, 11.0 and 3.8 Hz,
2H), 4.50 (d, J = 11.3 Hz, 1H), 4.24 (m, 1H), 4.14–4.10 (m,
2H), 3.74–3.70 (m, 1H), 3.56 (s, 3H), 3.53–3.50 (m, 2H),
2.14, 2.06 (2s, 6H); ESI-MS: m/z 481 [M+Na]; Anal. calcd
for C25H30O8 (458): C, 65.49; H, 6.60; found: C, 65.31; H,
6.78.
6H); ESI-MS: m/z 509 [M+Na]; Anal. calcd for
C25H26O10 (486): C, 61.72; H, 5.39; found: C, 61.50; H,
5.60.
Methyl 4,6-di-O-acetyl-2,3-di-O-benzyl-a-D-glucopyrano-
side (Table 3, entry 4): 1H NMR (200 MHz, CDCl3): d
7.27–7.13 (m, 10H, aromatic protons), 4.87 (t, J = 10.0 Hz,
1H), 4.76–4.52 (2 ABq, 4H), 4.48 (d, J = 3.5 Hz, 1H), 4.09
(dd, J = 9.9 and 3.5 Hz, 1H), 3.91 (dd, J = 12.8 and 2.2 Hz,
1H), 3.84 (t, J = 9.3 Hz, 1H), 3.75–3.70 (m, 1H), 3.51 (dd,
J = 12.8 and 3.5 Hz, 1H), 3.31 (s, 3H), 1.98, 1.81 (2s, 6H);
ESI-MS: m/z 481 [M+Na]; Anal. calcd for C25H30O8 (458):
C, 65.49; H, 6.60; found: C, 65.32; H, 6.80.
Methyl (3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-b-D-glu-
copyranosyl)-(1 ! 6)-2,3,4-tri-O-acetyl-a-D-glucopyrano-
1
side (Table 3, entry 15): H NMR (200 MHz, CDCl3): d
7.86–7.65 (m, 4H, aromatic protons), 5.75 (t, J = 10.2 Hz,
1H), 5.38 (t, J = 8.3 Hz, 1H), 5.30 (br s, 1H), 5.17 (t,
J = 9.4 Hz, 1H), 4.79–4.65 (m, 2H), 4.45 (br s, 1H), 4.38–
4.19 (m, 3H), 3.90–3.80 (m, 3H), 3.54–3.45 (m, 1H), 3.01 (s,
3H), 2.12, 2.03, 2.0, 1.92, 1.90, 1.86 (6s, 18H); ESI-MS: m/z
760 [M+Na]; Anal. calcd for C33H39NO18 (737): C, 53.73;
H, 5.33; found: C, 53.55; H, 5.52.
Methyl 4,6-Di-O-acetyl-2,3-di-O-benzyl-a-D-galacto-pyran-
oside (Table 3, entries 5 and 6): 1H NMR (200 MHz,
CDCl3): d 7.33–7.14 (m, 10H, aromatic protons), 5.44 (br s,