Efficient glycosylation of unprotected sugars using sulfamic acid: A mild eco-friendly catalyst

Article abstract of DOI:10.1016/j.catcom.2011.07.016

Sulfamic acid, a mild and environmentally benign catalyst has been successfully used in the Fischer glycosylation of unprotected sugars for the preparation alkyl glycosides. A diverse range of aliphatic alcohols have been used to prepare a series of alkyl glycosides in good to excellent yield.

Full text of DOI:10.1016/j.catcom.2011.07.016

Catalysis Communications 14 (2011) 52–57
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Efficient glycosylation of unprotected sugars using sulfamic acid:
A mild eco-friendly catalyst
⁎
Goutam Guchhait, Anup Kumar Misra
Bose Institute, Division of Molecular Medicine, P-1/12, C.I.T. Scheme VII-M, Kolkata-700054, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Sulfamic acid, a mild and environmentally benign catalyst has been successfully used in the Fischer
glycosylation of unprotected sugars for the preparation alkyl glycosides. A diverse range of aliphatic alcohols
have been used to prepare a series of alkyl glycosides in good to excellent yield.
© 2011 Elsevier B.V. All rights reserved.
Received 14 March 2011
Received in revised form 7 July 2011
Accepted 15 July 2011
Available online 22 July 2011
Keywords:
Fischer glycosylation
Glycosides
Sulfamic acid
Unprotected sugars
Eco-friendly
1. Introduction
(e.g. microwave, ultrasonication) etc. Therefore, there is a constant
need to develop a mild, eco-friendly reaction condition for the Fischer
Carbohydrates in the form of glycosides and glycoconjugates play
important roles in many biological processes [1]. As a consequence,
the chemistry of glycosides and glycoconjugates has gained much
attention for many years [2,3]. Alkyl glycosides are useful interme-
diates in the synthesis of complex oligosaccharides and natural
products. Starting from the pioneering work of Koenigs and Knorr [4]
for the glycoside formation, several glycosylation techniques have
appeared in the literature [5,6], which often require judicious
protecting group manipulations. Glycoside bond formation without
involving tedious protection–deprotection techniques is always
welcome in the synthetic carbohydrate chemistry. Fischer glycosyl-
ation offers a useful method for the preparation of simple alkyl or aryl
glycosides from the unprotected, unactivated reducing sugars [7].
Conventionally, Fischer glycosylation involves the treatment of a
reducing sugar with an alcohol at an elevated temperature in the
presence of a protic or Lewis acid [8,9] to furnish an alkyl glycoside.
The conventional Fischer glycosylation reaction has been improved
using heterogeneous solid acid catalysts [10,11], microwave irradia-
tion [12], ultrasonication [13], reduced pressure [14] and room
temperature ionic liquids [15,16] etc. Despite of their usefulness, the
reaction conditions suffer from a number of serious shortcomings
such as use of large excess of alcohols (important concern for
expensive alcohols), strong mineral acids or Lewis acids, preparation
of catalysts in some cases, longer reaction time, decomposition of the
product under reaction condition, requirement of special techniques
glycosylation for the preparation of alkyl glycosides. In this context, it
was envisioned that application of a mild catalyst/condition could be
beneficial to access a diverse range of unprotected alkyl glycosides
under Fischer glycosylation. In the recent past, we noted the
application of sulfamic acid (SA) as a mild eco-friendly catalyst in
several organic transformations [17–19]. Sulfamic acid has unique
structural properties such as zwitterionic form (H3N+SO3−), moderate
acidity (pKa=1.0), non-volatile, non-corrosive, and inexpensive. We
sought to explore the catalytic activity of SA in the Fischer
glycosylation of unprotected and unactivated reducing sugars under
neat reaction condition. We report herein our findings on SA catalyzed
Fischer glycosylation of unprotected reducing sugars with a diverse
range of alcohols to furnish alkyl glycosides (Scheme 1).
2. Results and discussion
In the initial set of reactions, D-glucose (1) was allowed to react
with a varied quantity of benzyl alcohol (3–10 equiv.) in the presence
of SA (0.2 equiv. to 0.5 equiv.) at 60 °C to 100 °C in a neat reaction
condition. After a series of experimentation it was observed that
⁎
Corresponding author. Tel.: +91 33 2569 3240; fax: +91 33 2355 3886.
Scheme 1. Sulfamic acid (SA) catalyzed Fischer glycosylation of unprotected reducing
E-mail address: akmisra69@gmail.com (A.K. Misra).
sugars for the preparation of alkyl glycosides.
1566-7367/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2011.07.016

G. Guchhait, A.K. Misra / Catalysis Communications 14 (2011) 52–57
53
Table 1
Sulfamic acid (SA) catalyzed Fischer glycosylation of unprotected reducing sugars for the preparation of alkyl glycosidesa.
Sl. No.
1
Unprotected sugar
Alcohol
Product
Time (h)
5.0
Yield (%)
81
α/β
Ref
D-Glucose (1)
Benzyl alcohol
6
[20]
[21]
[10]
6
7
8
2
3
Allyl alcohol
1-Octanol
4.0
5.0
82
80
5.5
11
4
1-Butanol
4.0
85
4
[22]
9
5
6
7
2-Chloro ethanol
4-Pentenol
5.0
4.0
4.0
82
80
78
9
8
9
[23]
[24]
[10]
10
11
Propargyl alcohol
12
13
8
9
1-Dodecanol
Cyclohexanol
5.0
4.0
72
76
8
6
[10]
[25]
14
15
10
11
Cyclopentanol
2-Butanol
4.0
4.0
72
75
4
4
[26]
[27]
16
17
12
13
2-Propanol
3-Pentanol
3.5
4.0
80
78
3
5
[28]
–
18
(continued on next page)

54
G. Guchhait, A.K. Misra / Catalysis Communications 14 (2011) 52–57
Table 1 (continued)
Sl. No.
14
Unprotected sugar
Alcohol
Product
Time (h)
Yield (%)
70
α/β
Ref
2-Octanol
7.0
5
–
19
15
16
17
Tert-butanol
2-Methyl-2-butanol
Propargyl alcohol
No Product
No Product
9.0
9.0
3.0
–
–
–
–
–
–
D-Mannose (2)
76
α
[10]
20
18
1-Octanol
4.0
80
6
[29]
21
19
20
21
22
1-Dodecanol
Benzyl alcohol
Allyl alcohol
Cyclopentanol
6.0
3.0
3.0
4.0
70
73
78
75
α
7
[29]
[21]
[21]
–
22
23
24
α
5
25
26
27
28
23
24
Cyclohexanol
2-Propanol
4.0
3.0
72
82
8
9
[30]
[31]
25
2-Butanol
3.0
76
8
[32]
26
27
28
3-pentanol
4.0
7.0
4.0
75
72
78
6
5
8
–
29
30
2-Octanol
–
D-Galactose (3)
Propargyl alcohol
[10]
31

G. Guchhait, A.K. Misra / Catalysis Communications 14 (2011) 52–57
55
Table 1 (continued)
Sl. No.
29
Unprotected sugar
Alcohol
Product
Time (h)
Yield (%)
76
α/β
Ref
1-Octanol
4.0
2.5
2.5
2.5
6
[33]
[34]
[34]
[10]
32
33
34
30
31
32
L-Rhamnose (4)
Benzyl alcohol
Allyl alcohol
Propargyl alcohol
82
85
80
α
α
α
35
36
33
N-Acetyl-D-
glucosamine (5)
Allyl alcohol
3.0
74
4
[35]
a
All reactions were carried out at 80 °C. All: Allyl; Bn: benzyl.
reaction of D-glucose (1) with benzyl alcohol (4.0 equiv.) in the presence
of SA (0.2 equiv.) at 80 °C led to the formation of benzyl D-glucoside (6)
in 81% yield in 5 h as anomeric mixture (α:β=6:1). The reaction
condition has been generalized by treating a set of aliphatic alcohols
with D-glucose (1) under similar reaction condition to furnish a
series of alkyl glucosides in excellent yield. Apart from the prepara-
tion of different glucosides, other unprotected monosaccharides (e.g.
D-mannose, D-galactose, N-acetyl-D-glucosamine, L-rhamnose etc.)
were also allowed to react with different alcohols under similar reaction
condition to furnish corresponding glycosides in satisfactory yield.
Reaction of a series of primary and secondary alcohols with free sugars
gave satisfactory yield of alkyl glycosides. However, treatment of
tertiary alcohols with free sugars under the similar reaction conditions
resulted in the decomposition of the reagents and did not furnish any
product may be due to the polymerization of tertiary alcohols in the
presence of acid under the reaction conditions. The findings of the
treatment of various 1°, 2° and 3° alcohols with different unprotected
sugars in the presence of SA at 80 °C are presented in Table 1. For
detailed characterization of the products, after completion of the
reaction the crude products were acetylated by adding acetic anhydride
to the reaction mixture in the presence of SA already present in the
reaction mixture. In this case, SA can act simultaneously as an acidic
catalyst for Fischer glycosylation and acetylation. It is worth mentioning
that because of the mild acidity of SA, the products were not
decomposed with time as in the case of some strong acidic catalysts.
The NMR spectral analysis of the acetylated products revealed the
formation of the products as a mixture of α- and β-anomers. The ratio of
the anomeric mixture of the products was determined by comparingthe
integration values of the peaks in the 1H NMR and 13C NMR spectra.
Although a mixture of the anomers were formed, α-product was the
major isomer in all cases. A large scale formation of benzyl D-glucoside
from D-glucose (100 mmol) was achieved in similar yield using similar
stoichiometric reagents and reaction condition. Although furanosidic
glycosides and acyclic acetals were formed in small quantities in some of
the earlier reported reaction conditions [8], no such by products were
formed under the present reaction condition. In a control experiment, a
mixture of D-glucose and benzyl alcohol was allowed to stir at 80 °C
without SA. No trace of the formation of product was observed even
after 16 h confirming the catalytic activity of SA. A comparative study on
the catalytic potential of SA with other reported catalysts has also been
performed, which is presented in Table 2. In the comparative study,
using triflic acid as a protic acid catalyst the reaction proceeded with
almost similar yield of the product that obtained with sulfamic acid.
However, use of sulfamic acid in this purpose is beneficial because of the
fact that triflic acid is moisture sensitive and corrosive in nature. From
the comparative study it is evident that SA can be considered as a useful
alternative to the existing reaction protocols. All known compounds
gave acceptable spectral data matched with the cited references.
3. Conclusion
In conclusion, sulfamic acid (SA) has been successfully applied as a
catalyst in the Fischer glycosylation for the preparation of alkyl
glycosides from unprotected and unactivated reducing sugars. The
reaction condition is reasonably mild, high yielding, applicable for
scale-up preparation and can be considered as an attractive
alternative to the existing procedures.
4. Experimental
4.1. General methods
All reactions were monitored by thin layer chromatography over
silica gel coated TLC plates. The spots on TLC were visualized by
warming ceric sulphate (2% Ce(SO4)2 in 2 N H2SO4) sprayed plates in
Table 2
Comparisons of the catalytic potential of different catalysts in the Fischer glycosylation
of D-glucose using benzyl alcohol at 80 °C.
Sl. No.
Catalyst
Catalyst load
Time (h)
Yield (%)
1
2
3
4
5
6
BF3.OEt2
Amberlite IR 120
Sc(OTf)3
HClO4–SiO2
Sulfamic acid
TfOH
1.0 equiv.
100 mg/mmol
0.1 equiv.
50 mg/mmol
0.2 equiv.
0.2 equiv.
16
24
24
5
5
5
52
60
55
72
81
77

56
G. Guchhait, A.K. Misra / Catalysis Communications 14 (2011) 52–57
hot plate. Silica gel 230–400 mesh was used for column chromatog-
raphy. 1H and 13C NMR spectra were recorded on Brucker Advance
DPX 200 MHz using CDCl3 as solvent and TMS as internal reference
unless stated otherwise. Chemical shift value is expressed in δ ppm.
ESI-MS were recorded on a Micromass Quttro II mass spectrometer.
Commercially available grades of organic solvents of adequate purity
are used in all reactions.
4.2.5. Cyclopentyl 2,3,4,6-tetra-O-acetyl-α-D-Glucopyranoside (15)
1H NMR (200 Hz, CDCl3): δ 5.40 (t, J=9.8 Hz each, 1 H, H-3), 5.11
(d, J=3.8 Hz, 1 H, H-1), 4.94 (t, J=9.8 Hz each, 1 H, H-4), 4.74
(dd, J=9.8, 3.8 Hz, 1 H, H-2), 4.26–3.99 (m, 3 H, H-5, H-6ab), 3.67–
3.60 (m, 1 H, –CH), 2.04, 1.98, 1.97, 1.95 (4 s, 12 H, 4 COCH3), 1.70–
1.45 (m, 8 H); 13C NMR (50 MHz, CDCl3): δ 170.6, 170.1, 169.6, 169.4
(4 COCH3), 94.3 (C-1), 81.5, 71.4, 70.9, 70.3, 67.2, 62.1, 33.1, 31.8, 23.3,
22.9, 20.7 (2 C), 20.6 (2 C) (4 COCH3); ESI-MS: 439.1 [M+Na]+
.
4.2. Typical procedure for the Fischer glycosylation
4.2.6. 2-Butyl 2,3,4,6-tetra-O-acetyl-α-D-Glucopyranoside (16)
To a suspension of D-glucose (0.9 g, 5.0 mmol) in benzyl alcohol
(2.0 mL, 20.0 mmol) was added sulfamic acid (100 mg, 1.0 mmol) at
room temperature and the neat reaction mixture was allowed to stir
at 80 °C for 5 h (Table 1). After completion of the reaction, the solvents
was removed under pressure and the crude product was passed
through a short pad of silica using CH2Cl2-CH3OH (20:1) to furnish
pure compound 6 (1.1 g, 81%). In order to prepare the analytical
sample for NMR spectral analysis, excess benzyl alcohol was removed
from the reaction mixture and acetic anhydride (3.0 mL) was added to
it and the reaction mixture was allowed to stir at 60 °C for 2 h. The
solvents were removed under reduced pressure and the crude
product was passed through a short pad of silica using hexane-
EtOAc (3:1) to furnish pure acetylated compound 6. Following the
similar reaction methodology a series of alkyl glycosides were
prepared in excellent yield. All products were acetylated for their
characterization by NMR spectral analysis. Selected spectral data of
compounds are presented below.
1H NMR (200 Hz, CDCl3): δ 5.47 (t, J=10.2 Hz each, 1 H, H-3), 5.18
(d, J=3.7 Hz, 1 H, H-1), 5.05 (t, J=10.2 Hz each, 1 H, H-4), 4.82
(dd, J=10.1, 3.7 Hz, 1 H, H-2), 4.24–4.22 (m, 1 H, H-6a), 4.15–4.07
(m, 2 H, H-5, H-6b), 3.69–3.60 (m, 1 H, CH), 2.08, 2.03, 2.00 (3 s, 12 H,
4 COCH3), 1.24-1.21 (m, 2 H, CH2), 1.09 (d, J=6.0 Hz, 3 H, CH3), 0.88
(t, J=7.4 Hz each, 3 H, CH3); 13C NMR (50 MHz, CDCl3): δ 170.7 (2 C),
170.2, 169.7 (4 COCH3), 95.7 (C-1), 78.2, 72.9, 71.1, 70.2, 68.7, 62.2,
24.9, 20.8 (2 C), 20.6 (2 C) (4 COCH3), 19.2, 10.3; ESI-MS: 427.1
[M+Na]+
.
4.2.7. 2-Propyl 2,3,4,6-tetra-O-acetyl-α-D-Glucopyranoside (17)
1H NMR (200 Hz, CDCl3): δ 5.46 (t, J=9.8 Hz each, 1 H, H-3), 5.17
(d, J=3.9 Hz, 1 H, H-1), 5.02 (t, J=9.8 Hz each, 1 H, H-4), 4.79
(dd, J=9.8, 3.8 Hz, 1 H, H-2), 4.25–4.21 (m, 1 H, H-5), 4.12–4.05 (m, 2
H, H-6ab), 3.92–3.83 (m, 1 H, CH), 2.08, 2.04, 2.02, 2.00 (4 s, 12 H, 4
COCH3), 1.23–1.20 (m, 3 H, CH3), 1.13–1.10 (m, 3 H, CH3); 13C NMR
(50 MHz, CDCl3): δ 170.8, 170.3, 170.2, 169.7 (4 COCH3), 94.2 (C-1),
71.5, 71.0, 70.2, 68.8, 67.1, 62.2, 23.1, 21.6, 20.7 (2 C), 20.6 (2 C)
4.2.1. 1-Butyl 2,3,4,6-tetra-O-acetyl-α-D-Glucopyranoside (9)
(4 COCH3); ESI-MS: 413.1 [M+Na]+
.
1H NMR (200 Hz, CDCl3): δ 5.38 (t, J=10.0 Hz each, 1 H, H-3),
5.07–4.91 (m, 2 H, H-1, H-4), 4.75 (dd, J=10.2, 3.6 Hz, 1 H, H-2),
4.24–4.15 (m, 1 H, H-5), 4.08–3.90 (m, 2 H, H-6ab), 3.68–3.57 (m, 1 H,
OCH2a), 3.42–3.31 (m, 1 H, OCH2b), 2.02, 1.99, 1.96, 1.94 (4 s, 12 H, 4
COCH3), 1.60-1.52 (m, 2 H, CH2), 1.46-1.30 (m, 2 H, CH2), 0.84
(t, J=7.2 Hz each, 3 H, CH3); 13C NMR (50 Hz, CDCl3): δ 170.5, 170.0,
169.5, 169.3 (4 COCH3), 95.7 (C-1), 71.1, 70.4, 68.8, 68.5, 67.3, 62.0,
4.2.8. 3-Pentyl 2,3,4,6-tetra-O-acetyl-α-D-Glucopyranoside (18)
1H NMR (200 Hz, CDCl3): δ 5.52 (t, J=9.8 Hz each, 1 H, H-3), 5.14
(d, J=3.8 Hz, 1 H, H-1), 4.96 (t, J=9.8 Hz each, 1 H, H-4), 4.83
(dd, J=9.8, 3.8 Hz, 1 H, H-2), 4.26–4.04 (m, 3 H, H-5, H-6ab), 3.48–
3.36 (m, 1 H, CH-), 2.09, 2.03, 2.01, 1.98 (4 s, 12 H, 4 COCH3), 1.62–1.43
(m, 4 H, 2 CH2CH3), 0.94–0.82 (m, 6 H, 2 CH2CH3); 13C NMR (50 MHz,
CDCl3): δ 170.6, 170.1, 169.7, 169.3 (4 COCH3), 95.1 (C-1), 82.5, 71.7,
71.5, 70.3, 67.4, 62.2, 26.7, 25.3, 20.7 (4 C, 4 COCH3), 9.9, 9.5; ESI-MS:
29.8, 20.8 (2 C), 20.7 (2 C), 19.3, 13.9; ESI-MS: m/z=427.1 [M+Na]+
.
4.2.2. 2-Chloroethyl 2,3,4,6-tetra-O-acetyl-α-D-Glucopyranoside (10)
441.1 [M+Na]+
.
1H NMR (200 Hz, CDCl3): δ 5.39 (dd, J=10.2 Hz each, 1 H, H-3),
5.08 (d, J=3.8 Hz, 1 H, H-1), 4.92 (t, J=10.1 Hz each, 1 H, H-4), 4.78
(dd, J=10.2, 3.8 Hz, 1 H, H-2), 4.24–3.99 (m, 3 H, H-5, H-6a,b), 3.93–
3.82 (m, 1 H, OCH2a), 3.77-3.52 (m, 3 H, OCH2), 2.02, 1.99, 1.96, 1.94
(4 s, 12 H, 4 COCH3); 13C NMR (50 Hz, CDCl3): δ 171.5, 170.1, 169.9,
169.5 (4 COCH3), 96.2 (C-1), 70.8, 70.1, 69.0, 68.5, 67.8, 61.9, 42.5, 20.7
4.2.9. 2-Octyl 2,3,4,6-tetra-O-acetyl-α-D-Glucopyranoside (19)
1H NMR (200 Hz, CDCl3): δ 5.45 (t, J=9.6 Hz each, 1 H, H-3), 5.10
(d, J=3.4 Hz, 1 H, H-1), 4.96 (t, J=9.6 Hz each, 1 H, H-4), 4.82
(dd, J=9.6, 3.4 Hz, 1 H, H-2), 4.27–4.03 (m, 3 H, H-5, H-6ab), 3.70–
3.60 (m, 1 H, CH), 2.04, 2.02, 2.00, 1.98 (4 s, 12 H, 4 COCH3), 1.54–1.15
(m, 10 H), 1.10 (d, J=6.1 Hz, 3 H, CH3), 0.84 (t, J=6.6 Hz, 3 H, CH3);
13C NMR (50 MHz, CDCl3): δ 170.8, 170.5, 169.8, 169.6 (4 COCH3), 96.1
(C-1), 73.1, 71.8, 71.5, 70.5, 68.9, 62.4, 36.9, 32.0, 25.5, 22.8, 21.7, 20.7
(4C; 4 COCH3); ESI-MS: m/z=433.1 [M+Na]+
.
4.2.3. 4-Pentenyl 2,3,4,6-tetra-O-acetyl-α-D-Glucopyranoside (11)
1H NMR (200 Hz, CDCl3): δ 5.88–5.71 (m, 1 H, CH=CH2), 5.47
(t, J=9.6 Hz each, 1 H), 5.15–4.99 (m, 4 H, H-1, H-4, CH=CH2), 4.84
(dd, J=10.0, 3.6 Hz, 1 H, H-2), 4.31–4.23 (m, 1 H, H-5), 4.16–3.99
(m, 2 H, H-6ab), 3.78–3.67 (m, 1 H, OCH2a), 3.56–3.40 (m, 1 H, OCH2b),
2.11, 2.06, 2.0, 1.99 (4 s, 12 H, 4 COCH3), 2.0–1.90 (m, 2 H, CH2), 1.77–
1.67 (m, 2 H, CH2); 13C NMR (50 Hz, CDCl3): δ 170.5, 170.0, 169.5,
169.3 (4 COCH3), 137.7, 115.4, 95.8 (C-1), 71.0, 70.3, 68.7, 67.9, 67.3,
(4 C, 4 COCH3), 19.9, 14.2; ESI-MS: 483.2 [M+Na]+
.
4.2.10. Cyclopentyl 2,3,4,6-tetra-O-acetyl-α-D-Mannopyranoside (25)
1H NMR (200 Hz, CDCl3): δ 5.38 (dd, J=10.0, 3.3 Hz, 1 H, H-3),
5.24 (t, J=9.9 Hz each, 1 H, H-4), 5.14–5.12 (m, 1 H, H-2), 4.85 (br s, 1
H, H-1), 4.27–4.01 (m, 3 H, H-5, H-6ab), 3.51–3.31 (m, 1 H, CH), 2.10,
2.04, 1.99, 1.94 (4 s, 12 H, 4 COCH3), 1.57–0.76 (m, 8 H); 13C NMR
(50 MHz, CDCl3): δ 170.6, 169.9, 169.8, 169.4 (4 COCH3), 96.5 (C-1),
81.7, 70.2, 68.7, 68.2, 66.3, 62.6, 26.6, 25.3, 20.9, 20.6 (2 C), 20.3
62.0, 30.2, 28.6, 20.7 (4C, 4 COCH3); ESI-MS: m/z=439.1 [M+Na]+
.
4.2.4. Cyclohexyl 2,3,4,6-tetra-O-acetyl-α-D-Glucopyranoside (14)
(4 COCH3), 9.9, 9.0; ESI-MS: 439.1 [M+Na]+
.
1H NMR (200 Hz, CDCl3): δ 5.38 (t, J=10.0 Hz each, 1 H, H-3), 5.08
(d, J=3.9 Hz, 1 H, H-1), 4.86 (t, J=10.0 Hz each, 1 H, H-4), 4.67 (dd,
J=10.0, 3.8 Hz, 1 H, H-2), 4.16–3.91 (m, 3 H, H-5, H-6ab), 3.57–3.43
(m, 1 H), 1.99, 1.93, 1.91, 1.90 (4 s, 12 H, 4 COCH3), 1.82-1.61 (m, 4 H),
1.40-1.15 (m, 6 H); 13C NMR (50 Hz, CDCl3): δ 170.5, 170.0, 169.5,
169.0 (4 COCH3), 94.0 (C-1), 76.8, 71.1, 70.3, 68.8, 67.2, 62.0, 33.2,
31.6, 25.6, 24.0, 23.7, 20.7 (4 C, 4 COCH3); ESI-MS: m/z=453.1
4.2.11. Cyclohexyl 2,3,4,6-tetra-O-acetyl-α-D-Mannopyranoside (26)
1H NMR (200 Hz, CDCl3): δ 5.36 (dd, J=10.0, 3.3 Hz, 1 H, H-3),
5.23 (t, J=9.9 Hz each, 1 H, H-4), 5.16–5.15 (m, 1 H, H-2), 4.92 (br s, 1
H, H-1), 4.26–4.21 (m, 1 H, H-6a), 4.12–4.03 (m, 2 H, H-5, H-6b), 3.59–
3.51 (m, 1 H, CH), 2.12, 2.06, 2.01, 1.96 (4 s, 12 H, 4 COCH3), 1.84–0.66
(m, 4 H), 1.50–1.18 (m, 6 H); 13C NMR (50 MHz, CDCl3): δ 170.6,
170.2, 169.9, 169.8 (4 COCH3), 95.8 (C-1), 76.7, 70.3, 69.2, 68.4, 66.5,
[M+Na]+
.

G. Guchhait, A.K. Misra / Catalysis Communications 14 (2011) 52–57
57
62.6, 33.1, 31.4, 25.4, 24.0, 23.8, 20.9, 20.7 (3C) (4 COCH3); ESI-MS:
453.1 [M+Na]+
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Acknowledgements
G. G. thanks CSIR, New Delhi for providing a Senior Research
Fellowship. This work was partly supported by Bose Institute, Kolkata.