Synthesis of sterically crowded derivatives of anomeric pairs of D-glucose disaccharides

Article abstract of DOI:10.1016/j.carres.2005.05.016

Derivatization of carbohydrates is of considerable interest since the derivatives can be used for structural studies in the field of mass spectrometry. We report here the synthesis of a series of sterically crowded derivatives of various linkage and stere

Full text of DOI:10.1016/j.carres.2005.05.016

Carbohydrate
RESEARCH
Carbohydrate Research 340 (2005) 2055–2059
Note
Synthesis of sterically crowded derivatives of anomeric pairs
of D-glucose disaccharides
Sanford Mendonca and Roger A. Laine*
Departments of Biological Sciences and Chemistry, Louisiana State University, Baton Rouge, LA 70803, United States
Received 15 January 2005; received in revised form 10 April 2005; accepted 28 May 2005
Available online 5 July 2005
Abstract—Derivatization of carbohydrates is of considerable interest since the derivatives can be used for structural studies in the
field of mass spectrometry. We report here the synthesis of a series of sterically crowded derivatives of various linkage and stereo-
isomeric glucose–glucose disaccharides with the impetus being to understand the effect of these derivatized groups on fragmentation
of the glycosidic bond and the development of methodology for discernment of the anomeric configuration. The synthesis of per-
alkylated (methyl, ethyl, propyl, butyl, and pentyl), per-esterified (acetyl, pivaloyl, mesitoyl), and per-silylated (tert-butyl-dimethyl
silyl) glucose–glucose disaccharide derivatives has been reported.
ꢀ 2005 Elsevier Ltd. All rights reserved.
Keywords: Derivatized disaccharides; Glucose
The synthesis of derivatized carbohydrates are of con-
siderable interest because they can serve as synthetic
intermediates in which certain functional groups can
temporarily protect those hydroxyls not planned to be
involved in a desired manipulation.1 Further, they are
very widely used in structural studies in biological mass
spectrometry.2 In the search for bio-based materials,
polysaccharide derivatives and their properties are
of continuing interest. The synthesis described in this
manuscript is mainly focused on per-etherification,
per-esterification, and per-silylation of linkage and ste-
reoisomeric glucose–glucose disaccharides.
The disaccharide ethers synthesized herein are the
methyl, ethyl, propyl, butyl, and pentyl ethers. Methyl-
ation has been used for confirming linkage evidence of
carbohydrate chemical structure.3–6 With increasing reco-
gnition of the significance of complex carbohydrates,
roles played in the determination of specificities of hor-
mones, immunity, biological transport, recognition,
developmental biology, and in various pathological pheno-
mena, it has become more urgent to find rapid and sen-
sitive methods for discerning the chemical structure. For
this purpose per-methylation on a microscale is impor-
tant. The higher ethers of carbohydrates are also impor-
tant to study since they influence the conformational
behavior, making the glycosidic linkages more sterically
crowded, hence comparative fragmentation and stereo-
isomeric information can be obtained.2,18
The disaccharide esters synthesized herein are the per-
acetylated, per-pivaloylated, and the per-mesitoylated
derivatives. Per-acetylated oligosaccharides have been
used extensively in the structural determination of oligo-
saccharides7–13 because they are of interest not only in
relation to the conformational data of fully acetylated
polymeric derivatives such as cellulose acetate,14 but
also because many naturally occurring polysaccharides
particularly those of microbial origin are partially acet-
ylated.15 Although the biological functions of these ace-
tyl groups are not well understood, it is known in some
instances, for example, gellan, their presence greatly
affects the rheological properties of aqueous solutions.
Similarly, it may be possible that pivaloylated and mesi-
toylated derivatives will have some useful physical
characteristics.
*
Corresponding author. Tel.: +1 225 268 3052; e-mail: rogerlaine@
gmail.com
0008-6215/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2005.05.016

2056
S. Mendonca, R. A. Laine / Carbohydrate Research 340 (2005) 2055–2059
Several approaches have been developed for the prep-
pivaloyl and per-mesitoyl derivatives of carbohydrates
have not been reported (to the best of our knowledge)
and were prepared in good yields. No difficulties were
encountered in the synthesis of the acetylated and piva-
loylated derivatives. For the mesitoylated derivatives a
large excess of mesitoyl chloride had to be added to
ensure complete derivatization of the disaccharides.
One of the most widely used protective groups for
alcohols since its introduction by Corey and Ven-
kateswarlu is the tert-butyl-dimethyl silyl (TBDMS)
group.31 The chemical properties of these hindered silyl
ethers make them desirable intermediates for a large
number of synthetic transformations involving multi-
functional compounds. The established procedure for
the preparation of TBDMS ethers involves reaction of
an alcohol with tert-butyl dimethylchlorosilane
(1.1 equiv) in the presence of imidazole (2.2 equiv) in
N,N-dimethylformamide (DMF) at room temperature.
However, this procedure was not efficient in completely
silylating all the eight hydroxyls of the disaccharides.
The TBDMS derivatives of disaccharides have been
reported to the best of our knowledge for the first time
in this manuscript using the procedure of Corey
et al.32 in which TBDMS triflate is used as the silylating
agent.
This paper discusses the synthesis of sterically
crowded derivatives of glucose–glucose disaccharides.
The impetus for the synthesis of these carbohydrate
derivatives was to test the hypothesis that the propensity
of molecular fragmentation in mass spectrometers
depends on the inverse of the molecular flexibility.2
Further, to understand the effect of the alkyl groups
on the fragmentation of the glycosidic bond and the
development of methodology for discernment of the
anomeric configuration. The mass spectrometry results
of the per-alkyl derivatives along with the molecular
modeling of the 1–4 and 1–6 linked disaccharides
have been described elsewhere by Mendonca
et al.18,33
aration of methylated derivatives. The early methods
were those of Purdie and Irvine16 and Haworth.17 The
disadvantage of the Purdie and Haworth techniques is
that they require several re-methylations to obtain com-
plete etherification. Strong bases such as sodium hydride
or potassium tert-butoxide in dipolar aprotic organic
solvents are now used. Using methyl iodide in N,N-
dimethylformamide with silver oxide,5,19 barium
hydroxide,20 or sodium hydride21 as the basic agent,
the reaction rates increased but full methylation was
not achieved. The use of sodium hydride has a disadvan-
tage in that it requires careful handling. Corey and
Chaykovsky developed a new synthesis using the methyl
sulfinyl carbanion, the conjugate base of dimethyl sulf-
oxide.22 The Wittig type synthesis was achieved with
great ease.23,24 Hakomori adapted CoreyÕs methylsulfi-
nyl carbanion25 reagent to the methylation of even com-
plex carbohydrates. In spite of the low yields (0.3 mol of
per-methylated derivative per mol of sugar), the Hako-
mori method has been used extensively in structural
investigations of carbohydrates. The use of potassium
tert-butoxide26 instead of sodium hydride improved
the stability of the reagent but did not substantially
increase the yield of the per-methylated product.27,28
In 1984, Ciucanu and Kerek29 reported a simple and
rapid method for the per-methylation of carbohydrates
by using dimethyl sulfoxide, sodium hydroxide, and
methyl iodide. This approach has the advantage of read-
ily available starting materials, potential compatibility
with a wide range of protecting groups, and a very
straightforward experimental procedure. Thus, we envi-
sioned this as an ideal method for making the different
per-alkylated derivatives efficiently, as it avoids the
experimental difficulties of the Hakomori method (e.g.,
low yields and moisture-sensitive reagents).
Herein, we show that an adaptation of this method
works very well for the preparation of protected disac-
charides with higher alkyl groups. Additionally, to the
best of our knowledge per-ethylated, per-propylated,
per-butylated, and per-pentylated glucose–glucose
disaccharides have not been reported and can be pre-
pared in good yields with this straightforward chemis-
try. The advantage of this method is the greater
generality of protecting groups that can be used.
However, for the higher derivatives complete etherifica-
tion of the disaccharides was not obtained if the alkyl-
ating agent was added in its entirety, but only if added
in incremented amounts on a daily basis for about a
week.
The per-esterified derivatives prepared were the per-
acetylated, per-pivaloyl, and the per-mestitoyl deriva-
tives. Per-acetylated derivatives have been synthesized
previously.30 The hydroxyl groups of a carbohydrate
material react readily with acetic anhydride in the pres-
ence of a basic catalyst like pyridine. However, the per-
1. Experimental
1.1. General
The protected disaccharide derivatives were prepared
according to the methods described below. The yields
are shown in Table 1 and Rf values in Table 2. Table
3 shows exact mass measurements of the various
synthetic derivatized disaccharides. Figure 1 is the
exact mass measurement of per-butylated maltose
[D-Glc-(1!4)-a-D-Glc], which serves as a representative
spectrum. The thin-layer chromatograms of the higher
derivatives like pentyl however, revealed a number of
spots because of the formation of partially derivatized
products.

S. Mendonca, R. A. Laine / Carbohydrate Research 340 (2005) 2055–2059
Table 1. Product yields for synthetic derivatized disaccharides (%)
2057
Derivative
Maltose
Cellobiose
Isomaltose
Gentiobiose
Per-methylated
Per-ethylated
90.50
76.00
69.00
60.00
49.00
90.30
75.80
61.30
69.50
91.00
83.00
70.00
59.00
49.50
90.50
73.50
63.40
70.30
90.80
81.80
68.10
56.70
50.00
91.00
96.80
62.50
68.50
91.50
80.30
67.20
57.50
52.00
92.00
75.50
60.30
69.90
Per-propylated
Per-butylated
Per-pentylated
Per-acetylated
Per-pivoylated
Per-mesitoylated
Per-TBDMsilylated
aa-Trehalose
bb-Trehalose
Kojibiose
Sophorose
Per-methylated
Per-ethylated
Per-propylated
Per-butylated
Per-pentylated
92.40
78.50
65.21
59.10
48.50
90.90
77.29
63.51
54.78
49.27
87.80
73.60
69.60
55.60
47.00
90.90
72.70
65.50
57.39
49.27
Nigerose
Laminaribiose
Per-methylated
Per-ethylated
Per-propylated
Per-butylated
Per-pentylated
89.30
78.50
68.60
59.10
51.10
92.40
76.00
64.60
58.20
47.76
Table 2. Rf values for synthetic derivatized disaccharides
Derivative
Maltose
Cellobiose
Isomaltose
Gentiobiose
Per-methylated
Per-ethylated
0.34
0.49
0.28
0.24
0.15
0.78
0.28
0.31
0.16
0.62
0.18
0.21
0.25
0.43
0.21
0.17
0.35
0.68
0.44
0.28
0.30
0.45
0.33
0.34
0.28
0.66
0.22
0.24
0.28
0.67
0.29
0.30
Per-propylated
Per-butylated
Per-pentylated
Per-acetylated
Per-pivaloylated
Per-mesitoylated
1.2. Alkylation
extracted. Butylation was carried out over a period of
7 days in 100 lL (0.16 g, 0.87 mmol) increments. Prepa-
ration of the ethyl, propyl, and butyl derivatives were all
carried out at room temperature. The pentyl derivatives
were synthesized by first heating the reaction mixture at
55–60 ꢁC for 24 h and then for 8 days at room tempera-
ture. Two milliliters of pentyl iodide was added to the
reaction mixture in aliquots of 200 lL (0.3 g, 1.5 mmol)
for 9 days, after which the product was extracted with
chloroform.
The underivatized disaccharide (5 mg, 0.015 mmol) was
introduced into a dried tube. DMSO (2 mL) was added
and the solution stirred till it dissolved. Powdered
sodium hydroxide (200 mg, 5 mmol) was added and
the suspension was stirred for 10 min. Finally methyl
iodide (0.21 g, 1.4 mmol) was added and the solution
was stirred at room temperature for 24 h. The product
was extracted with chloroform (3 mL), washed several
times with distilled water (4 · 10 mL), and dried with
sodium sulfate and then at high vacuum to yield a yel-
lowish oil. The same reagents were used for preparation
of the higher derivatives from ethyl to pentyl with differ-
ences in the proportions of alkyl iodide added. For ethy-
lation 500 lL of ethyl iodide was added in 100 lL
(0.19 g, 1.25 mmol) aliquots over a period of 5 days after
which the products were extracted in chloroform as for
methylation. For propylation 600 lL of propyl iodide
was added in 100 lL (0.17 g, 1.03 mmol) increments
over a period of 6 days after which the product was
1.3. Acetylation
The underivatized disaccharide (10 mg, 0.02 mmol) was
introduced in a dried flask. It was dissolved in dry pyr-
idine (1 mL). To this Ac2O (1.5 mL) was added and the
reaction mixture was then stirred, heated to 60 ꢁC, and
stirred for 24 h. The product was then extracted with
ethyl acetate (5 mL) and washed with water (10 mL).
It was then washed with 10% HCl (2 · 10 mL) to remove
the pyridine. It was further washed with NaHCO3

2058
S. Mendonca, R. A. Laine / Carbohydrate Research 340 (2005) 2055–2059
Table 3. Exact measurements of derivatized disaccharides
Derivative
Maltose
Cellobiose
Isomaltose
Gentiobiose
Per-methylated
Per-ethylated
455.264
589.362
701.476
813.594
925.708
701.250
1037.241
1533.479
1277.390
455.251
589.361
701.463
813.593
925.670
701.485
1037.425
1533.453
1277.450
455.264
589.363
701.472
813.583
925.701
701.195
1037.007
1533.461
1277.658
455.264
589.355
701.476
813.596
925.699
701.350
1037.140
1533.468
1277.700
Per-propylated
Per-butylated
Per-pentylated
Per-acetylated
Per-pivaloylated
Per-mesitoylated
Per-TBDMsilylated
aa-Trehalose
bb-Trehalose
Kojibiose
Sophorose
Per-methylated
Per-ethylated
Per-propylated
Per-butylated
Per-pentylated
477.254
589.376
701.509
813.582
925.704
477.254
589.373
701.486
813.598
925.698
477.254
589.367
701.488
813.615
925.737
477.255
589.372
701.485
813.505
925.735
Nigerose
Laminaribiose
Per-methylated
Per-ethylated
Per-propylated
Per-butylated
Per-pentylated
477.257
589.366
701.483
813.600
925.718
477.254
589.377
701.489
813.599
925.738
Figure 1. Exact mass measurement (813.594) of per-butylated maltose [D-Glc-(1!4)-a-D-Glc].
(2 · 10 mL) and finally with water (10 mL). It was then
dried under Na2SO4 under high vacuum.
pyridine (230 lL). Dimethyl amino pyridine (DMAP)
(17.6 mg, 0.0049 mmol) was added to catalyze the
reaction. Finally, trimethylacetyl chloride (0.18 g,
1.46 mmol) was added to the reaction mixture. The reac-
tion mixture was then stirred at room temperature for
2 days. The product was then extracted with ethyl ace-
tate (10 mL) and washed with water (2 · 10 mL),
1.4. Pivaloylation
The underivatized disaccharide (5 mg, 0.015 mmol) was
introduced into a dry flask. It was dissolved in dry

S. Mendonca, R. A. Laine / Carbohydrate Research 340 (2005) 2055–2059
2059
2. Laine, R. A.; Pamidimukkala, K.; French, A. D.; Hall,
R. W.; Abbas, S. A.; Jain, R. K.; Matta, K. L. J. Am.
Chem. Soc. 1988, 110, 6931–6939.
3. Stoffyn, P. J.; Jeanloz, R. W. J. Biol. Chem. 1960, 235,
2507–2510.
followed by 10% HCL (2 · 10 mL), then NaHCO3
(2 · 10 mL) and finally again with water (10 mL). The
product was an oil, which was vacuum rotary evapo-
rated and then dried under high vacuum.
4. Jeanloz, R. W. In Polysaccharide in Biology; Springer, G.
F., Ed.; The Josiah Macy Jr. Foundation: New York,
1958, p 23 (fourth conference).
1.5. Mesitoylation
5. Kuhn, R.; Trischmann, H.; Lo¨w, I. Angew. Chem. 1955,
67, 32–36.
6. Yamakawa, T.; Yokoyama, S.; Handa, N. J. Biochem.
1963, 53, 28–35.
7. Leung, F.; Marchessault, R. H. Can. J. Chem. 1973, 51,
1215–1222.
The underivatized disaccharide (100 mg, 0.29 mmol)
was introduced into a dry, two-necked flask under Ar.
Dry pyridine (10 mL) was added and the solution stir-
red until it dissolved. Dimethyl amino pyridine
(350 mg, 2.9 mmol) was then added followed by tri-
methylbenzoyl chloride (5.34 g, 29.2 mmol). The solu-
tion was heated to 80 ꢁC and stirred for 3 days. The
product was then extracted with ethyl acetate (20 mL)
and washed with water (10 mL) followed by 10%
HCL (2 · 10 mL), then satd aq NaHCO3 (2 · 10 mL)
and finally by water (10 mL). The product was then
rotary evaporated and finally dried with vacuum to
yield a yellowish solid.
´
8. Leung, F.; Chanzy, D.; Perez, S.; Marchessault, R. H.
Can. J. Chem. 1976, 54, 1365–1371.
9. Takeda, H.; Kaiya, T.; Yasuoka, N.; Kasai, N. Carbohydr.
Res. 1978, 62, 27–37.
´
10. Perez, S.; Brisse, F. Acta Crystallogr. Sect. B 1977, 33,
2578–2584.
´
11. Perez, S.; St.-Pierre, J.; Marchessault, R. H. Can. J. Chem.
1978, 56, 2866–2871.
´
12. Brisse, F.; Marchessault, R. H.; Perez, S.; Zugenmaier, P.
J. Am. Chem. Soc. 1982, 104, 7470–7476.
´
13. Perez, S.; Vergelati, C.; Tran, V. H. Acta Crystallogr.,
Sect. B 1985, 41, 262–267.
14. Marchessault, R. H.; Sundarajan, P. R. In The Poly-
saccharides; Aspinall, G. O., Ed.; Academic Press: New
York, 1979; Vol. 2.
15. Microbial Polysaccharides and Polysacharases; Berkeley,
R. C. W., Gooday, C. W., Ellwood, D. C., Eds.; Academic
Press: New York, 1979.
16. Purdie, T.; Irvine, J. C. J. Chem. Soc. 1903, 83, 1021–1037.
17. Haworth, W. N. J. Chem. Soc. 1915, 107, 8–16.
18. Mendonca, S.; Cole, R. B.; Zhu, J.; Cai, Y.; French, A. D.;
Johnson, G. P.; Laine, R. A. J. Am. Soc. Mass Spectrom.
2003, 14, 63–78.
19. Walker, H. G.; Gee, M.; Mcready, R. M. J. Org. Chem.
1962, 27, 2100–2102.
20. Kuhn, R.; Baer, H. H.; Seeliger, A. Justus Liebigs Ann.
Chem. 1958, 611, 236–241.
21. Tamura, Z.; Imanari, T. Chem. Pharm. Bull. 1964, 12,
1386–1391.
22. Corey, E. J.; Chaykovsky, M. J. Am. Chem. Soc. 1962, 84,
866–867.
1.6. Silylation
The underivatized sugar (100 mg, 0.29 mmol) was intro-
duced in a dry flask under Ar. Dry methylene chloride
(10 mL) was added and the solution stirred until most
of the sugar dissolved. Dry 2,6-lutidine (0.75 g,
6.9 mmol) was then added followed by tert-butyl-di-
methyl triflate (0.93 g, 3.5 mmol). On addition of the tri-
flate the undissolved sugar dissolved completely and the
reaction mixture became clear. The reaction mixture was
stirred at room temperature for a day. The product was
extracted with ether (20 mL) and washed with water
(20 mL). The aqueous layer was then extracted with
ether (3 · 10 mL). The product in the combined ether
extracts was rotary evaporated and dried under high
vacuum to yield a clear oil.
23. Chaykovsky, M.; Corey, E. J. J. Org. Chem. 1962, 28,
254–255.
Acknowledgments
24. Greenwald, R.; Chaykovsky, M.; Corey, E. J. J. Org.
Chem. 1962, 28, 1128–1129.
25. Hakomori, S. J. Biochem. 1964, 55, 205–208.
26. Brauman, J. J.; Bryson, A.; Kahl, D. C.; Nelson, N. J.
J. Am. Chem. Soc. 1970, 92, 6679–6680.
27. Lindberg, B. Methods Enzymol. 1972, 28, 178–195.
28. Finne, J.; Krusius, T.; Rauvala, H. Carbohydr. Res. 1980,
80, 336–339.
29. Ciucanu, I.; Kerek, F. Carbohydr. Res. 1984, 131, 209–
217.
30. Hudson, C. S.; Brauns, D. H. J. Am. Chem. Soc. 1915, 37,
1264–1270.
We would like to thank Professors Robert Hammer and
Patrick Limbach for helpful discussions regarding
synthesis and mass spectrometry of the derivatives
described herein. We would also like to acknowledge
the support from the Louisiana Educational Quality
Support Fund (LEQSF) from the Board of Regents of
Louisiana State University.
31. Corey, E. J.; Venkateswarlu, A. K. J. Am. Chem. Soc.
1972, 94, 6190–6191.
32. Corey, E. J.; Cho, H.; Rucker, C.; Rucker, D. H.
Tetrahedron Lett. 1981, 22, 3455–3458.
References
1. McOmoie, J. F. W. Protective Groups in Organic Chem-
istry; Plenum Press: London, 1973.
33. Mendonca, S.; Johnson, G. P.; French, A. D.; Laine, R.
A. J. Phys. Chem. A 2002, 106, 4115–4124.