Montmorillonite K-10 as a reusable catalyst for fischer type of glycosylation under microwave irradiation

Article abstract of DOI:10.1080/07328300802107437

Montmorillonite K-10-catalyzed Fischer type glycosylation was studied for various monosacharides with different alcohols under microwave irradiation. The method was found to be efficient, economic, simple, and time saving and the catalyst montmorillonite K-10 was reused three times without loss of catalytic activity and anomeric selectivity. With glycerol, the method gave products glycosylated at primary alcohols only.

Full text of DOI:10.1080/07328300802107437

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Montmorillonite K-10 as a Reusable
Catalyst for Fischer Type of
Glycosylation under Microwave
Irradiation
Dipak K. Roy a & Manobjyoti Bordoloi a
a Natural Products Chemistry Division, North East Institute of
Science and Technology, Jorhat, Assam, India
Published online: 03 Mar 2009.
To cite this article: Dipak K. Roy & Manobjyoti Bordoloi (2008) Montmorillonite K-10 as a Reusable
Catalyst for Fischer Type of Glycosylation under Microwave Irradiation, Journal of Carbohydrate
Chemistry, 27:5, 300-307
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Journal of Carbohydrate Chemistry, 27:300–307, 2008
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Copyright Taylor & Francis Group, LLC
ISSN: 0732-8303 print / 1532-2327 online
DOI: 10.1080/07328300802107437
Montmorillonite K-10 as a
Reusable Catalyst for Fischer
Type of Glycosylation under
Microwave Irradiation
Dipak K. Roy and Manobjyoti Bordoloi
Natural Products Chemistry Division, North East Institute of Science and Technology,
Jorhat, Assam, India
Montmorillonite K10 catalyzed Fischer type glycosylation was studied for various
monosacharides with different alcohols under microwave irradiation. The method was
found to be efficient, economic, simple and time saving and the catalyst montmorillonite
K-10 was reused three times without loss of catalytic activity and anomeric selectivity.
With glycerol, the method gave products glycosylated at primary alcohols only.
Keywords Montmorillonite K10, Glycosylation, glycerol glucoside, microwave radia-
tion
Due to immense biological importance of oligosacharides and glycoconjugates,
many glycosylation strategies have been developed.[1−3] Among all the existing
strategies for glycosylation of sugars, Fischer glycosylation procedure is the
earliest and the simplest. In the classical Fischer glycosylation methodology,
an unprotected carbohydrate is refluxed in an alcohol in presence of catalytic
acid to give the corresponding glycoside. In spite of many limitations, Fischer
glycosylation is utilized for synthesis of simple glycosides, such as, methyl,
allyl, benzyl and p-methoxybenzyl glycosides.[4−7] In carbohydrate chemistry,
methyl, allyl, benzyl and p-methoxybenzyl alcohols are used for temporary
protection of the anomeric hydroxyl group, as glycosides of these alcohols can
undergo easy deglycosylation.[8−10] Modification of Fischer glycosylation by re-
placing soluble acid with cation exchange resins, namely, Permutit Q, Duolite
Received March 20, 2008; accepted April 2, 2008.
The authors wish to thank the Director, NEIST, Jorhat for provision of facilities and
DKR is thankful to the CSIR, New Delhi, for providing research fellowship.
Address correspondence to Manobjyoti Bordoloi, Natural Products Chemistry Division,
North East Institute of Science and Technology, Jorhat-785006, Assam, India. E-mail:
mjb rrljt@yahoo.co.in
300

Montmorillonite K-10 as a Reusable Catalyst
301
C-3 and C-3 Zeokarb H, has simplified the removal of the catalyst.[11] In one
report, microwave was used for acceleration of Fischer glycosylation pro-
cess catalyzed by Amberlite resin IRN 120 H+.[12] Recently, sulfuric acid
immobilized on silica was reported as
a catalyst for Fischer type
glycosylation.[13] In search of an inexpensive and environmentally benign
and time saving method as part of our ongoing programme, we have devel-
oped an efficient and economic method of Fischer glycosylation catalysed by
montmorillonite K-10 under microwave irradiation (Scheme 1).
Scheme 1.
In the initial experiments for testing the feasibility of montmorilloniteK1O
as catalysts for Fischer glycosylation, a mixture of D-glucose (500 mg) and the
clay (250 mg) was refluxed in anhydrous methanol (10 mL). The reaction was
monitored by thin layer chromatography. The conversion was found to be al-
most complete in 5 hours. The reaction mixture was then cooled, filtered and
the product was recrystallized from isopropanol. A mixture of both α and β
anomer was obtained. To get the best α/β ratio, the reaction was studied in
different reaction times (Table 1). Anomeric ratio was derived from the com-
1
parison of H NMR peak at δ 4.70 (J1,2 ≈ 4.0 Hz) and δ 4.27 J1,2 ≈ 8.5 Hz).
Improved α/β ratio was obtained in 10 hrs. Increase in reaction time beyond 10
hours improved α/β ratio slightly with increase in decomposition of the product.
We then studied the conversion under microwave radiation. D-glucose
(500 mg) and montmorillonite K10 (250 mg) were mixed thoroughly in a
mortar and the mixture was placed in a quartz reaction vessel of Prolabo
Synthwave Microwave reactor. To it, 5 mL of methyl alcohol was added and
Table 1: Montmorillonite K10 catalyzed glycosylation of methanol with D-glucose
under conventional reflux condition
Entry
Reaction time, hours
Yield,a %
α/β Ratiob
1
2
3
4
6
7
8
5
6
83
84
84
84
81
79
75
8.6/1
9.2/1
12.4/1
13.3/1
13.6/1
13.8/1
14.5/1
8
10
12
14
24
aIsolated yield. bThe α/β ratio was determined by 300 MHz 1H NMR spectroscopy.

D. K. Roy
302
Table 2: Montmorillonite K10 catalyzed glycosylation of methanol with D-glucose
under microwave radiation
Entry
Reaction time, min
Yield,a %
α/β Ratiob
1
2
3
4
6
7
8
9
2
4
79
82
85
86
86
83
78
72
4.7/1
6.2/1
6
8.6/1
8
11.3/1
14.6/1
14.7/1
14.8/1
15.1/1
10
12
14
20
aIsolated yield. bThe α/β ratio was determined by 300 MHz 1H NMR spectroscopy.
the mixture was allowed to react under microwave irradiation at a temper-
ature of 90◦C for 10 minutes. During the reaction, the temperature was not
allowed to rise above 90◦C by setting the programmer. The mixture was then
allowed to cool, filtered and the product was recrystallized from isopropanol.
To get improved α/β ratio, reaction was carried out for different time periods
(Table 2). Optimum anomeric selectivity was found in 10 minutes. Further
increase in reaction time increased the α/β ratio only slightly with increased
decomposition.
After getting good result in microwave-assisted reaction between D-glucose
and methanol, we generalized the reaction with a number of monosacharides
and alcohols (Table 3). Very good yields and anomeric selectivity were obtained.
After the reaction, the catalyst could be separated by filtration. After washing
and activation at 110◦C, the recycled catalyst was used again for glycosylation
of D-glucose by benzyl alcohol. Over three times of recycle, comparable yields
with same anomeric selectivity were obtained (Table 4).
To study the utility of the method for alcohol containing both primary
and secondary hydroxyl groups, we treated D-glucopyranose with glycerol in
presence of montmorillonite K-10. In situ formed product was acetylated with
acetic anhydride. Purification of the product by column chromatography gave
l-(2,3,4,6-Tetraacetyl-α-D-glucopyranosyl)-2,3-diacetylglycerol 3a (yield 45%),
l-(2,3,4,6-Tetraacetyl-(β-D-glucopyranosyl)-2,3-diacetylglycerol 3b (yield 15%)
and 1,3-Bis (2,3,4,6-tetraacetyl-D-glucopyranosyl)-2-acetylglycerol 3c (yield
6%) with mono- and di-glycosylated product in 5:1 ratio (Scheme 2). Anomeric
ratio of the monoglycosylated products was determined to be 3:1. However, as
in the glucosidase mediated method of glucosylation of glycerol[14] or similar
to the glycerol glucoside isolated from marine blue-green alga,[15] and Lilium
japonicum[16] no product glycosylated at secondary hydroxyl of glycerol was
found to form in our reaction.
Thus, the use of montmorillonite K-10 for this Fischer type glycosylation
method, has simplified its work up procedure. Only filtration was required to
remove the catalyst. In addition, montmorillonite K-10 is stable, inexpensive,

Montmorillonite K-10 as a Reusable Catalyst
303
Table 3: Microwave-assisted glycosylation catalyzed by Montmorillonite K10.
Reaction
time (min.)
Yields of
Entry
Sugar
Alcohol
Productsa (%)
α/β Ratiob
01
CH3OH
10
86
15/1
02
03
n-C4H9OH
PhCH2OH
10
10
82
81
10/1
9/1
04
05
06
10
10
10
84
77
74
10/1
13/1
10/1
C2H5OH
n-C8H17OH
07
08
CH3OH
PhCH2OH
10
10
84
81
11/1
8/1
09
10
10
10
83
80
9/1
10/1
n-C4H9OH
11
12
CH3OH
PhCH2OH
10
10
85
82
14/1
9/1
13
14
10
10
84
78
9/1
C2H5OH
CH3OH
12/1
15
10
87
14/1
16
17
10
10
85
83
11/1
9/1
PhCH2OH
CH3OH
18
10
85
15/1
19
20
10
10
85
80
12/1
10/1
PhCH2OH
a. Isolated yield.
b. The α/β ratio was determined by 300 MHz 1H NMR spectroscopy.
Scheme 2.

D. K. Roy
304
Table 4: Microwave assisted Glycosylation of benzyl alcohol with D-glucose
catalysed be recycled montmorillonite K-10
Number of recycle Ratiob(%)
Yield,a
α/β
1
2
3
79
78
76
9/1
9/1
9/1
aIsolated yield. bThe α/β ratio was determined by 300 MHz 1H NMR spectroscopy.
eco-friendly and found as reusable catalyst. Another advantage of the method
is that it is very fast (only 10 minutes is required). As mentioned above,
methyl, allyl and benzyl glycosides are very useful precursor for the synthesis
of oligosacharides and other glycoconjugates.
In conclusion, we have developed an ecofriendly, inexpensive and fast
method of Fischer glycosylation catalyzed by montmorillonite K-10 under mi-
crowave radiation. One notable advantage of the method is that the catalyst is
reusable.
EXPERIMENTAL
General Methods
Melting points were recorded on a Buchi melting point apparatus with
open capillary method and are unconnected. Specific rotations were recorded
on a Perkin Elmer polarimeter model 343 at sodium light of wavelength
589 nm. IR spectra were recorded on a Perkin Elmer system 2000 FT-IR Spec-
trometer. All NMR spectra were recorded on a Bruker Avance DPX300 oper-
ated at 300 MHz. Chemical shifts are given in parts per million (ppm) and
referenced to internal 0.03% TMS. Positive Electro-Spray Ionization mass
spectra [(+)-ESIMS] were recorded on Bruker Esquire 3000 Iontrap Mass
spectrometer. Elemental analysis was done on a Perkin Elmer Series II 2400
CHNS/O Micro Elemental Analyzer. Prolabo Synthwave Microwave reactor
402 with temperature programmer was used for reactions under microwave
irradiation. Buchi rotary evaporator was used for distillation under reduced
pressure. Silica gel G was used for TLC and silica gel (60–120 mesh) was used
for column chromatography. All solvents used were distilled prior to use.
General Procedure for Glycosylation under Microwave
Irradiation
Monosacharide (500 mg) and Montmorillonite K10 (250 mg) were mixed
thoroughly in a mortar. The mixture was then placed in a quartz reaction ves-
sel of Prolabo Synthwave Microwave reactor 402. To it, 5 mL of an alcohol was
added and the mixture was allowed to react under microwave irradiation at a

Montmorillonite K-10 as a Reusable Catalyst
305
temperature of 90◦C for 10 minutes. During the reaction the temperature was
not allowed to rise above 90◦C by setting the programmer. The reaction mix-
ture was then cooled and filtered. The residue was washed with methanol. The
combined filtrate and washings were distilled under reduced pressure with a
rotary evaporator to get the product. Product was crystallized from isopropanol
and characterized by 1H NMR (300 MHz), 13C NMR (75 MHz), ESIMS, IR spec-
troscopy and elemental analysis and direct comparison with that of authenti-
cated compound.
Procedure for Reaction between D-Glucopyranose and Glycerol
D-glucopyranose (180 mg, 1 mmol), glycerol (920 mg, 10 mmol) and mont-
morillonite K-10 (90 mg) were mixed thoroughly in a morter and then the mix-
ture was placed in a quartz reaction vessel of Prolabo Synthwave Microwave
reactor 402. Then the mixture was allowed to react under microwave irradi-
ation at a temperature of 90◦C for 10 minutes. During the reaction, the tem-
perature was not allowed to rise above 90◦C by setting the programmer. After
cooling the reaction mixture to room temperature, 5 mL of acetic anhydride
was added to it and stirred for 3 hours. Chloroform (100 mL) was then added
to it and filtered. Solid was washed with chloroform (10 mL). The combined
filtrate and washings were washed with water (3 × 10 mL) and dried over
anhydrous sodium sulfate. Solvent was distilled under reduced pressure to ob-
tain a crude, which was chromatographed over a column of silica gel using
ethyl acetate-hexane (1:3) to get two major product 3a (227 mg, 45%) and 3b
(75 mg, 15%) and a minor product 3c (48 mg, 6%).
Spectral data of 1-(2,3,4,6-Tetraacetyl-α-D-glucopyranosyl)-2,3-
diacetylglycerol 3a
Gummy, [α]3D2+169.05◦ (CHCl3, c 0.5); IR (CHCl3)ν cm−1: 2958, 2850, 1747,
1435, 1371, 1226, 1167, 1040, 957, 889, 768, 601; 1H NMR (300 MHz) in CDCl3:
δ 5.43 (dt, 1H, J1 b,2 = J2 3 a = 9.6 Hz, J1 a,2 = 1.2 Hz, H-2ꢁ), 5.17 (dd, 1H,
J3,4 = 10 Hz, J4,5 = 8.4 Hz, H-4), 5.09 (d, 1H, J1,2 = 3.2 Hz, H-1), 5.04 (t, 1H,
J2,3 =J3,4 =10Hz, H-3), 4.84 (dd, 1H, J2,3 = 10.0Hz, J1,2 = 3.2 Hz, H-2) 4.32
(m, 1H, H-3ꢁ.a), 4.25 (m, 1H, H-3ꢁb), 4.22 (dd, 1H, J6a,6b = 11 Hz, J5,6a = 2.4
Hz, H-6a), 4.12 (dd, 1H, J6a,6b = 11 Hz, J5,6b = 4.8 Hz, H-6b), 4.02(m, 1H, H-
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
1ꢁa), 3.81(m, 1H, H-1ꢁb), 3.62 (ddd, 1H, J4,5 = 8.4 Hz, J5,6a = 2.4 Hz, J5,6b
=
4.8 Hz, H-5) 2.09(s,3H, CH3-CO), 2.08(s, 3H, CH3-CO), 2.07(s,3H, CH3-CO),
2.06(s, 3H, CH3-CO), 2.03(s, 3H, CH3-CO), 2.01(s, 3H, CH3-CO); 13C NMR (75
MHz) in CDCl3: δ 169.96 (C=O), 169.95 (C=O),169.92 (C=O), 169.81 (C=O),
169.72 (C=O), 169.59 (C=O), 94.95 (C-1), 70.53 (C-2ꢁ), 69.24 (C-2), 68.61 (C-1ꢁ),
67.25 (C-3ꢁ), 65.85 (C-3), 65.73 (C-5), 62.59 (C-4), 61.82 (C-6), 21.80 (CH3-CO),
20.75 (CH3-CO), 20.73 (CH3-CO), 20.65 (CH3-CO), 20.55 (CH3-CO), 21.41 (CH3-
CO); (+)-ESIMS for C21H30O14 (M, 506): m/z 529.13 [M+Na]+, 507.16 [M+H]+,
Anal, calcd. for C21H30O14: C, 49.80%; H, 5.97%. Found C, 49.70%; H, 5.84%.

D. K. Roy
306
Spectral data of 1-(2,3,4,6-Tetraacetyl-β-D-glucopyranosyl)-2,3-
diacetylglycerol 3b
mp 106–107◦C (reported[16] 107–108◦C); [α]D32–35.1◦ (CHCl3, c 0.5); IR
(CHCl3) νcm1: 2952, 2856, 1741, 1435, 1366, 1226, 1161, 1045, 955, 888, 757,
607; 1H NMR (300 MHz) in CDCl3: δ 5.18 (m,1H, H-2ꢁ), 5.17 (dd, 1H, J2,3 = 9.9
Hz, J3,4 = 9.6 Hz, H-3), 5.07 (dd, 1H, J2,3 =9.8 Hz, J1,2 = 7.2 Hz, H-2), 4.98 (d,
1H, J4,5 =9.2 Hz, J3,4 = 9.6 Hz, H-4), 4.52 (d, 1H, J=7.2 Hz, H-1), 4.32 (m, 2H,
H-3ꢁ), 4.25 (dd, 1H, J6a,6b = 12.3 Hz, J5,6a = 4.6 Hz, H-6a), 4.12 (dd, 1H, J6a,6b
=
12.2 Hz, J5,6b = 2.6 Hz, H-6b), 3.92 (ddd, 1H, J4,5 = 9.2 Hz, J5,6a = 4.7 Hz,
J5,6b = 2.6 Hz, H-5), 3.68 (m, 2H, H-1ꢁ), 2.10(s, 3H, CH3-CO), 2.09(s, 3H, CH3-
CO), 2.085 (s, 3H, CH3-CO), 2.08(s, 3H, CH3-CO), 2.03(s, 3H, CH3-CO), 2.01(s,
3H, CH3-CO). 13C NMR (75 MHz) in CDCl3: δ170.12 (C=O), 170.0 (C=O),
169.90 (C=O), 169.83 (C=O), 169.75 (C=O), 169.59 (CO), 95.57 (C-1), 72.96
(C-2), 71.88 (C-1ꢁ), 70.53 (C-3ꢁ), 70.52 (C-2ꢁ), 68.61 (C-4), 65.73 (C-3), 62.59 (C-
5), 61.82 (C-6), 21.41 (CH3-CO), 20.80 (CH3-CO), 20.78 (CH3-CO), 20.74 (CH3-
CO), 20.67 (CH3-CO), 20.52 (CH3-CO); (+)-ESIMS for C21H30O14 (M, 506): m/z
531.15 [M+2H+Na]+, 507.16 [M+H]+, Anal, calcd. for C21H30O14: C, 49.80%;
H, 5.97%. Found C, 49.67%; H, 5.81%.
Spectral data of 1,3-Bis (2,3,4,6-tetraacetyl-D-glucopyranosyl)-2-
acetylglycerol 3c
Gummy; [α]3D2+17.1◦ (CHCl3, c 0.5); IR (CHCl3)νcm−1: 2980, 2850, 1715,
1
1410, 1250; H NMR (300 MHz) in CDCl : δ 5.46 (m, 1H, H-2ꢁ), 5.30 (m, 1H),
3
5.22–5.01 (m, 5H), 4.33–4.08 (m, 8H), 3.85–3.54 (m, 4H), 2.13 (s, 3H, CH3-
CO), 2.085 (s, 3H, CH3-CO), 2.10 (s, 3H, CH3-CO), 2.096 (s, 3H, CH3-CO),
2.08 (s, 3H, CH3-CO), 2.06 (s, 3H, CH3-CO), 2.03 (s, 3H, CH3-CO), 2.02 (s, 3H,
CH3-CO), 2.01 (s, 3H, CH3-CO); 13C NMR (75 MHz) in CDCl3: .δ 170, 169.95,
169.33, 169.50 (9 C=O), 100.10 (C-1, C-1ꢁ), 71.01 (C-1ꢁꢁ and C-3ꢁꢁ), 70.80 (C-2ꢁꢁ),
69.63, 69.15, 68.33, 68.12 (6>CHO-Ac), 64.07 (C-5, C-5.ꢁ), 61.40 (2-CH2OAc, C-
6, C-6ꢁ), 21.41, 20.85, 20.78, 20.71, 20.53 (9 CH3-CO); (+)-ESIMS for C33H46O22
(M, 794): m/z 817.24 [M+Na]+, 795.26 [M+H]+; Anal, calcd for C33H46O22: C,
49.87%; H, 5.83%. Found : C, 49.99%; H, 5.70%.
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