Synthesis and co-polymerization of an unsaturated 1,5-anhydro-D-fructose derivative

Article abstract of DOI:10.1016/j.carres.2004.06.007

An unsaturated derivative, 3,6-di-O-acetyl-1,5-anhydro-4-deoxy-D-glycero- hex-3-enopyranos-2-ulose (3), was obtained via regioselective elimination and acetylation of monohydrated 1,5-anhydro-D-fructose (1) in a single step reaction. High yield (80%) was achieved without any dimeric by-products. Its co-polymerization to saccharide polymers was investigated with different commercial vinyl co-monomers. Co-polymers were obtained and characterized.

Full text of DOI:10.1016/j.carres.2004.06.007

Carbohydrate
RESEARCH
Carbohydrate Research 339 (2004) 2077–2082
Synthesis and co-polymerization of an unsaturated
1,5-anhydro-D-fructose derivative
a
b
a
Olaf Deppe,a, Anke Glumer, Shukun Yu and Klaus Buchholz
*
€
aInstitute for Technical Chemistry, Department of Carbohydrate Technology, Technical University of Braunschweig,
Langer Kamp 5, 38106 Braunschweig, Germany
bDanisco Biotechnology, Langebrogade 1, PO Box 17, DK-1001 Copenhagen K, Denmark
Received 21 January 2004; received in revised form 4 June 2004; accepted 11 June 2004
Available online 8 July 2004
Abstract—An unsaturated derivative, 3,6-di-O-acetyl-1,5-anhydro-4-deoxy-
via regioselective elimination and acetylation of monohydrated 1,5-anhydro-
D
-glycero-hex-3-enopyranos-2-ulose (3), was obtained
-fructose (1) in a single step reaction. High yield (80%)
D
was achieved without any dimeric by-products. Its co-polymerization to saccharide polymers was investigated with different
commercial vinyl co-monomers. Co-polymers were obtained and characterized.
Ó 2004 Elsevier Ltd. All rights reserved.
Keywords: 1,5-Anhydro-D-fructose; Pyranoid enolone ester; Radical polymerization; Saccharide polymers; Sugar derivatives; Unsaturated
1. Introduction
unsymmetrically linked, dimeric hemiacetals (e.g., 5 and
6),13 which undergo acetylation to give stable acetylated
dimers instead of the required enolone.
With respect to a sustainable chemistry, unsaturated
sugar monomers are useful building blocks for co-
polymers with special properties like biocompatibility,
biodegradability, hydrophilicity/hydrophobicity balance
and skin compatibility.
The saccharide monomer 3,6-di-O-acetyl-1,5-anhy-
D
dro-4-deoxy-
first synthesized in 1997 from 1,5-anhydro-
-glycero-hex-3-enopyranos-2-ulose 3 was
-fructose
D
1,14;15 which nowadays can be enzymatically produced
by degradation of a-(1 ! 4)-glucans like starch.16 The
preparation involved an acetylation–elimination reac-
tion to give 3 directly from freeze dried 1 but with low
(50%) yields.14;15
These properties are of major importance in many
fields such as pharmaceuticals, drugs and cosmetics. Up
to now several saccharide monomers have been inves-
tigated in free radical polymerization with a wide range
of commercially available co-monomers. Vinylsacchar-
ides give rise to polymers bearing sugar appendages in
the side chains. Saccharide derivatives with an exocyclic
or endocyclic double bond, like 3, build saccharide
polymers incorporating one or two ring carbon atoms in
the backbone of the polymer chain, respectively.1–12
The difficulty in synthesizing enolones, such as 3, from
hexuloses (e.g., 1) is that dimerization occurs in con-
centrated hexulose solutions leading to the formation of
The reason for this is the dimerization of dried 1 by
ketal formation between 1 and 2. The equilibrium mix-
ture contains only 30% of monomer 1 in pyridine14 and
40% in Me2SO.15 The dimers 5 and 6 react with acetic
anhydride and form stable acetylated derivatives with-
out olefinic double bond. Lichtenthaler and co-workers
synthesized acetylated 3,2-enolone from monohydrated
acetylated uloses and benzoylated 3,2-enolone.17;18
We have now investigated the hydration of 1 in order
to shift the equilibrium in favour of 1 and the a-diol 2,
which were acetylated in pyridine with acetic anhydride
followed by spontaneous elimination to give 3 in
high yields (Scheme 1). The pyranoid enolone 3 was
* Corresponding author. Tel.: +49-5312344788; fax: +49-5313917263;
e-mail: o.deppe@tu-bs.de
0008-6215/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2004.06.007

2078
O. Deppe et al. / Carbohydrate Research 339 (2004) 2077–2082
Scheme 1. Dimerization equilibrium of 1,5-anhydro-D-fructose and synthesis of 3.
investigated in radical co-polymerization reaction in
order to produce new types of polymers, based in part
on carbohydrates as renewable resources.9;10
unit at the end of the growing polymer chain. But their
electronic effects should differ, so the e-values should
have opposite signs.
Electron-donating monomers have got negative
e-values and electron-attracting monomers have got
positive ones. Former investigations of enonolactones in
co-polymerization showed low reactivity and an elec-
tron-attracting effect.7–12 The enolone should attract
electrons more than the enonolactones, because the
þM-effect of the endocyclic oxygen in allylic position is
weaker than that of the carboxylic group in an enono-
lactone (Scheme 2).
For this reason the electron-donating vinyl com-
pounds 1-vinyl-2-pyrrolidone 7, vinyl butyl ether 9 and
vinyl acetate 11 were used as co-monomers (Scheme 3).
The polymerizations were carried out in bulk with
different monomer feed composition. Two radical initi-
ators, 2,20-azoisobutyronitrile (AIBN) and benzoyl per-
oxide (BOP), with different decomposition rates were
used in every reaction to make sure that radicals are
available during the whole reaction time. The molar
ratio of radical initiators with respect to the monomers
was constant. The homopolymerization of 3 is sterically
hindered. The homopolymer was detected only by TLC,
but could not be isolated until now.11 The monomer
decomposed when the reaction time was extended. This
corresponds to former investigations of homopolymer-
izations of saccharide monomers with an endocyclic
double bond.7–12 The glass transition temperature ðTgÞ
of the homopolysaccharide should be in a range of
200–300 °C. It has been demonstrated previously in a
few experiments, that co-polymers of 3 can be obtained,
2. Results and discussion
It has already been shown14;15 that 1 in an aqueous
solution exists as the monohydrate 2. This would make
the elimination impossible, because this reaction path-
way requires an electron-attracting function like a car-
bonyl group. It is to be assumed that 1 and its acetylated
forms are present in equilibrium in a rather low con-
centration, although it cannot be detected in 1H and 13
C
NMR spectra.16 However the carbonyl form is essential
for the elimination step, which is the dominant reaction
under appropriate conditions. This is comparable to
fructose equilibrium in an aqueous solution wherein the
ketose is the reactive species with an amount of less than
1%.19
Since no acetylated dimer was formed, the yield of 3
could be increased up to 83%. The by-products and
solvents were removed by washing and evaporation. The
product obtained is used in co-polymerization.
The optimized reaction conditions are room temper-
ature (the reaction rate is too low at lower tempera-
tures), the molar ratio of 1 to water is 1–20, the reaction
time 33 h (24 h for the hydration step and 9 h for the
elimination step). Degradation occurs at high tempera-
tures (60 °C) and after longer reaction times (24 h) for
the elimination step. Further experiments with other
bases such as NaOAc in catalytic amounts and Ac2O as
solvent gave low yields only.
OAc
OAc
OAc
2.1. Co-polymerization of 3
O
O
O
The reactivity of both monomers for a co-polymeriza-
tion should be nearly the same to obtain co-polymers
with a homogenous composition. The reactivity is de-
fined as Q-values by Alfrey and Price,20 which indicate
the stabilization by resonance of the radical monomer
AcO
O
AcO
O
AcO
O
(c)
(b)
(a)
Scheme 2. Structural elements of 3: (a) acrolein-, (b) allylic ether-, (c)
vinyl ester-type.

O. Deppe et al. / Carbohydrate Research 339 (2004) 2077–2082
2079
OAc O
O
CH2
*
3 +
*
OAc
N
N
O
O
8
7
OAc
OAc
O
O
O
3
+
*
*
CH2
*
OAc
O
O
OBu
9
10
12
O
CH2
O
*
3 +
OAc
OAc
Figure 1. IR-spectra of 8 with different co-polymer compositions.
11
Scheme 3. Scheme of the co-polymers of 3.
reaction even at high conversions. For 7 as co-mono-
mer, it is a molar ratio of 46.3% of 3 in the feed. A Tg
was not detected. It would be in the range of 200–
300 °C, but the polymers decompose before showing any
DSC trace.
but no detailed information on reaction conditions and
their influence on products formed was presented.9;10
2.2. Co-polymerization of 3 with n-vinyl-pyrrolidone 7
2.3. Co-polymerization of 3 with butyl vinyl ether 9
We obtained yields of up to 58 wt % of co-polymer 8
(Scheme 3) with reference to the monomer feed. In
general the yield of the co-polymer decreases with an
increasing amount of the sugar derivative 3 in the feed.
The molar weights extend from 22,950 to 73,310 g/mol
with no linear relationship to co-polymer composition
or yield (Table 1). Up to 50 mol % of 3 in the feed, the
proportion of 3 in the co-polymer is higher than that in
the feed. Beyond 50 mol %, there is a limit of around
60 mol % of 3 in the co-polymer composition. The
change in polymer composition is indicated by IR-
spectroscopy. The increasing content of 3 in the co-
polymer is demonstrated by the decreasing peak at
1678 cmÀ1 for the amide group and the increasing peak
at 1230 cmÀ1 for the acetyl-group (Fig. 1). The most
important value is the azeotropic composition. It is of
technical interest because at this point the compositions
of the feed and co-polymer are always equal during a
Compound 9 is a more hydrophilic co-monomer and
has a lower tendency than 7 for homopolymerization. A
statistical co-polymer should be formed. The amount of
3 integrated into the co-polymer composition is rather
high even at low content of 3 in the feed (Table 2). The
highest yield is up to 41.0 wt % and the azeotropic
monomer ratio is 48.3 mol % of 3. At this ratio the
amount of both co-monomers in the feed and in the co-
polymer are equal. The average molecular weight (MW)
increases linearly with an increasing amount of 3 in the
co-polymer.
The Tg of a co-polymer is limited by the Tg’s of the
homopolymers. The Tg of poly(vinyl butyl ether) is of
about À55 °C22 and that of the homopolysaccharide
should be in a range of 200–300 °C. However the Tg of 9
does not fit a Gordon–Taylor trend. It decreases with an
increasing amount of 3 in the co-polymer composition
and also with an increasing MW. It is assumed that the
Table 1. Yield and properties of co-polymer 8 with different compo-
sition of monomer in the feed
Table 2. Yield and Properties of co-polymer 10 with different com-
positions of monomer in the feed
Copo
Compound 3
Yield
(wt %) (g/mol)
MW
Feed
(mol %)
Entry
(mol %)
Copo
Compound 3
Yield
(wt %)
MW
(g/mol)
Tg
(°C)
Feed Entry
(mol %) (mol %)
8.1
8.2
8.3
8.4
8.5
8.6
8.7
8.8
10.03
20.02
30.00
40.00
47.11
60.23
75.01
84.92
16.8
36.4
43.3
47.6
48.6
50.8
55.7
57.6
59
43
39
29
33
25
19
10
4.1 Â 104
2.7 Â 104
2.6 Â 104
2.3 Â 104
4.2 Â 104
6.0 Â 104
6.5 Â 104
7.3 Â 104
10.1
10.2
10.3
10.4
10.5
10.6
10.32
25.49
42.85
66.30
75.56
88.66
35.5
38.8
40.8
52.3
52.6
76.9
14
41
38
14
8
2.0 Â 104
2.6 Â 104
3.6 Â 104
8.3 Â 104
9.2 Â 104
18.4 Â 104
78
99
92
73
67
25
6

2080
O. Deppe et al. / Carbohydrate Research 339 (2004) 2077–2082
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Figure 2. 1H NMR-spectra of 10 with a sugar content of 35.5 mol % in the co-polymer composition (10.1).
Figure 4. IR-spectra of 12 with different co-polymer compositions.
Figure 3. IR-spectra of 10 with different co-polymer compositions.
Table 3. Yields and properties of co-polymer 12 with different com-
positions of monomer in the feed
branching fraction increase with an increasing amount
of 3 due to an increasing number of acetyl groups in the
co-polymer composition, which lowers the Tg. Figures 2
and 3 present the 1H NNR and IR-spectra, respectively.
Copo
Compound 3
Yield MW
(wt %) (g/mol)
Tg
(°C)
T
(h)
Feed Entry
(mol %) (mol %)
12.1
12.2
12.3
12.4
12.5
12.6
12.7
12.8
12.9
12.10
12.11
14.41
24.58
23.18
35.63
15.43
24.62
35.73
49.24
63.65
75.77
85.67
14.7
24.7
33.6
35.2
18.9
34.3
38.9
50.0
50.0
57.5
60.4
30
25
23
17
40
25
18
9
3.8 Â 104
89
80
5
5
4.1 Â 104
2.8 Â 104
7.4 Â 104
2.9 Â 104
2.3 Â 104
6.0 Â 104
9.2 Â 104
11.9 Â 104
39.9 Â 104
19.7 Â 104
108
106
80
5
2.4. Co-polymerization of 3 with vinyl acetate 11
5
12
12
12
12
18
18
18
Compound 11 is the least electron-donating co-mono-
mer, but also the least reactive one. The yields are rather
low. The reaction time influences the co-polymer com-
position. For a reaction time of 5 h, feed and co-polymer
composition are approximately equal. An increasing
reaction time causes an increase of 3 in the co-polymer
composition. Figure 4 presents the IR-spectra. The
azeotropic feed composition is about 50 mol % 3 to ob-
tain a statistical co-polymer with 11 as co-monomer.
Compound 11 has a higher tendency to homopolymerize
than 7 and 9. The average molecular weight (MW) de-
pends on reaction time and feed composition (Table 3).
102
105
––
5
101
110
86
2
1
The MW in general increases with an increasing amount
of 3 in the co-polymer composition for 5 h reaction time.
For 18 h the highest MW’s are obtained, but they de-
crease with an increasing amount of 3, with more than
50 mol % of 3 in the feed and the co-polymer composi-

O. Deppe et al. / Carbohydrate Research 339 (2004) 2077–2082
2081
tion. The Tg tends to increase from 80 to 110 °C with
contents of 3 above 30 up to 60 mol % in the co-polymer,
independent of the reaction time. This effect has also
been observed with other sugar derivatives as co-
monomers where Tg values in general tend to increase
with the content of sugar derivative in the co-polymer.
The Tg does not fit strongly a Gordon–Taylor trend. The
reason is that 11 undergoes cross-linking easily. The Tg
of poly(VAc) is of about 32 °C.22
Shimadzu with a refractive index detector RID-6A
coupled with a Wyatt Dawn DSP multiangle light
scattering detector. Three chromatographic columns
operating in series were used for fractionating; one from
Polymer Standard Services Gram 3000 10 lm and the
other two from Polymer Laboratories Plgel 5 lm
MIXED-C. The eluent was HPLC-grade THF with a
flow rate of 1 mL minÀ1 at a pressure of 109 bar and a
temperature of 35 °C. The glass transition temperatures
of the polymers were determined by differential scanning
calorimetry with Mettler Toledo calorimeter 12E. The
optical rotation were determined with a Dr. Kernchen
Elektronik Automation Sucromat Digital Automatic
Saccharimeter.
3. Conclusions
The yield of 3,6-di-O-acetyl-1,5-anhydro-4-deoxy-
glycero-hex-3-enopyranos-2-ulose 3 obtained by acetyl-
ation of 1,5-anhydro- -fructose has been improved
D-
D
4.2. Synthesis of 3,6-di-O-acetyl-1,5-anhydro-4-deoxy-
glycero-hex-3-enopyranos-2-ulose 3
D-
significantly (80%). The synthesis and purification is
efficient, but may be further optimized especially with
respect to a more sustainable chemistry. The potential of
3 as a building block in polymerization has been dem-
onstrated. We synthesized three new types of co-poly-
mers based on 3 and commercial vinyl compounds
according to appropriate steric and electronic properties
of 3 and the respective co-monomers. The co-polymer
composition of each co-monomer was varied to obtain
different properties such as molecular weight and glass
transition temperature. Other properties such as bio-
compatibility of the co-polymers will be investigated for
utilization in medicine and pharmacy. Besides the syn-
thesis of polymers with other co-monomers to obtain
special properties, the acetyl groups could also be re-
moved in order to enhance hydrophilicity. The present
work represents first steps in the utilization of the now
easily accessible carbohydrate synthon 3.
Freeze-dried 1 (0.600 g (0.0037 mol)) was dissolved in
1.62 g (0.09 mol) distilled water and stirred at room
temperature for 24 h. Pyridine (32.4 g, 0.41 mol) and
then Ac2O 10.8 g (0.11 mol) was added at 0 °C. The
reaction mixture was stirred at 25 °C for 9 h. The sol-
vents and by-products like acetic acid were evaporated.
The residue was dissolved in CH2Cl2, washed with 4 M
HCl, saturated aqueous Na2CO3 and water, decoloured
with charcoal, dried with Na2SO4 and evacuated under
diminished pressure. The yield is 83%. The resulting
brown syrup is stored at À8 °C under argon atmosphere.
The spectroscopic data are identical to those already
published.14;15 The optical rotation differs from former
published values. ½aꢀ À39.2 (c 1.76, CHCl3). ½aꢀ À43.7
D
D
(c 1.71, CHCl3),14 ½aꢀ À17.7 (c 0.34, CH2Cl2).15 FT-IR
D
(KBr) mmax 2958, 1743, 1711, 1652, 1431, 1370, 1201,
1147, 1047, 1012, 908, 603 cmÀ1. Anal. Calcd for
C10H12O6 (228.2 g/mol) C, 52.63; H, 5.30; O, 42.07.
Found C, 52.58; H, 5.33; O, 42.09.
4. Experimental
4.1. General methods
4.3. Co-polymerization of 3 with vinyl compounds
All experimental investigations were carried out with
€
The reaction mixtures were degassed under diminished
pressure in liquid nitrogen by two freeze-pump-thaw
cycles.21 The polymerizations were carried out in bulk
under argon atmosphere at 80 °C for 5 h with different
monomer feed composition. Benzoyl peroxide (BOP)
(1 mol %) and 1 mol % of 2,20-azobisisobutyro-nitrile
(AIBN) with respect to the sum of monomers were used
as initiators. The reactions were stopped by cooling and
supplying oxygen. The reaction mixtures were dissolved
in CH3Cl and the polymers were precipitated in less
polar solvents.
pyridine (Grussing), acetic anhydride (Fluka) and vinyl
compounds (Fluka) as received. The initiators were
dried and stored under argon atmosphere at À8 °C. The
co-polymer compositions were determined by elemental
analysis, IR- and NMR-spectroscopy. IR-spectra were
recorded with KBr pellets at Bio-Rad FTS-25 FT-IR-
spectrophotometer. NMR spectra were recorded at
1
Bruker AM 400 spectrometer at 400.1 MHz for H and
100.6 MHz for 13C-spectra. Chemical shifts are refer-
enced to Si(CH3)4 and internal CDCl3 to d ¼ 7:270 and
77.00 ppm. Elemental analysis were determined using a
Carlo Erba Instrumentazione Elemental Analyzer 1106
with a heat conductivity detector. The average mole-
cular weights and the polydispersities were obtained by
gel permeation chromatography with an apparatus of
4.3.1. Poly(acAPM-co-VPy) 8. Besides the monomer
and the initiators 30 mol % of water was added to the
reaction mixture. The polymers were precipitated in
Et2O. The feed compositions, yields and properties are

2082
O. Deppe et al. / Carbohydrate Research 339 (2004) 2077–2082
show in Table 1. FT-IR (KBr) mmax 2972, 2956, 1742,
1678, 1462, 1422, 1370, 1282, 1230, 1042, 751, 727,
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1234, 1150, 1094, 1038, 755, 667, 603 cmÀ1. H NMR
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Acknowledgements
Financial support is gratefully acknowledged from
European project No QLK3-CT-2001-02400 by the Fifth
Framework Program of the European Commission.
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