Regioselective copolymerization of acryl sucrose monomers

Article abstract of DOI:10.1021/jo048957y

1′,2,3,3′,4,4′,6-Hepta-O-benzyl-sucrose has been prepared and selectively 6′-O-esterified with small α,β-unsaturated acid derivatives. New chiral copolymers containing sucrose have been synthesized by radical polymerization, and some of their physical pro

Full text of DOI:10.1021/jo048957y

D-gluconolactone, is described.10 The homopolymerization
of the vinylsugar has been conducted in both aqueous
and organic media using free-radical initiators, forming
high-molar-mass water-soluble polymers. Sugar-based
hydrogels, obtained by nonselective modification of su-
crose with the introduction of vinyl groups,11 and the
synthesis of a monomeric methacrylate ester of D-galac-
topyranose and its copolymerization with ethyl acrylate
have also been described.12
Because sucrose has eight chemically active hydroxyl
groups, regioselective derivatization is important in the
selective synthesis of sucrose-containing linear poly-
mers.13,14 The route to selective derivatization of the 6′-
position of the sucrose has been developed in our labo-
ratory.15,16 It allowed us to obtain the fully protected
sucrose with only the 6′-hydroxyl unprotected, and we
have prepared unsaturated sucrose esters from this
intermediate. This monomer could be converted into pure
linear polymers, avoiding the formation of mixtures of
di- and higher substituted unsaturated esters, which
results in cross-linked polymers.17
Regioselective Cop olym er iza tion of Acr yl
Su cr ose Mon om er s
Maria Teresa Barros,* Krasimira T. Petrova, and
Ana Maria Ramos
REQUIMTE, CQFB, Departamento de Quı´mica, Faculdade
de Cieˆncias e Tecnologia, Universidade Nova de Lisboa,
2829-516 Caparica, Portugal
mtbarros@dq.fct.unl.pt
Received J une 21, 2004
Abstr a ct: 1′,2,3,3′,4,4′,6-Hepta-O-benzyl-sucrose has been
prepared and selectively 6′-O-esterified with small R,â-
unsaturated acid derivatives. New chiral copolymers con-
taining sucrose have been synthesized by radical polymer-
ization, and some of their physical properties have been
determined.
Sugars are an important resource for the development
of new materials such as water-soluble and/or biocom-
patible polymers owing to their low price.1,2 Sucrose, as
a cheap bulk product, could play an important role for
this purpose. Some possible applications for sucrose-
based polymers are drug delivery systems, dental medi-
cine, bioimplants, contact lenses, and tissue engineer-
ing.3,4 For these and other applications, they have the
advantage of being potentially biodegradable.
Here, the synthesis of these sugar monomers is pre-
sented. A study on the copolymerization of these sugar
monomers with styrene and methyl methacrylate, as well
as some physical properties of the resulting polymeric
materials, is also reported.
The first step to our target consisted of a regioselective
silylation of the 6′-hydroxyl group (Scheme 1) of the
sucrose using tert-butyldiphenylchlorosilane (TBDPSCl)
in dry pyridine at room temperature according to the
methods described earlier.18 By closely following the
reaction by TLC and stopping the reaction when di-
TBDPS first appeared, the yield was optimized up to 85%.
The monosilylated sucrose 1 was benzylated with
benzyl bromide in DMF in the presence of NaH and
Bu4N+I- as a catalyst, leading to the compound 2.19
Because of a slight instability of the TBDPS protecting
group under the basic reaction conditions, we have
always obtained the octabenzylated sucrose as a byprod-
uct in yields of about 20% for this step. The yield was
optimized by controlling the reaction temperature; the
reagents were mixed at 0 °C, and the mixture then was
allowed to warm to room temperature (below 30 °C),
(Scheme 1).
In 1946, Haworth and co-workers5 first reported the
preparation of polymerization products from substituted
carbohydrates containing acrylate or methacrylate groups.
Since then, there has been extensive interest in the
synthesis and polymerization of monofunctionalized car-
bohydrate monomers. In 1991 Dordick et al. reported a
poly(sucrose acrylate) and poly(sucrose adipamide) syn-
thesis with the help of an enzyme (Proleather, an alkaline
protease from a Bacillus sp.).6 Deffieux et al. have pre-
pared monomethacryloyl sucrose esters by two different
routes, in aqueous media and in organic solvent,7 as well
as several ethylenic acetals of sucrose8 and have exam-
ined their homo- and copolymerization with styrene.
Akashi et al. have synthesized methacryloyl and acryloyl-
type glucose-containing vinyl monomers and have shown
that it is possible to produce them on an industrial scale.
They also prepared hydrogels from them and showed
some practical applications for these products.9 The
synthesis of a water-soluble monomer, derived from
Selective deprotection of the silyl group, with TBAF
in THF at room temperature,20 led to compound 3 in 85%
yield after column chromatography (Scheme 1).
(1) Descotes, G. In Carbohydrates as Organic Raw Materials;
Lichtenthaler, F. W., Ed.; VCH: Weinheim, New York, 1991.
(2) Dordick, J . S.; Linhardt, R. J .; Renthwish, D. Chemtech 1994,
33.
(3) Pachence, J . M.; Kohn, J . In Principles of Tissue Engineering;
Lanza, R. P., Langer, R., Vacanti, J ., Eds.; Academic Press: New York,
2000.
(4) Lanza, R.; Langer, R.; Chick, W.; Academic Press/R.G. Landes
Company: New York, 1997; Chapter 19, pp 273-285.
(5) Haworth, W. N., Gregory, H., Wiggins, K. F. J . Chem. Soc. 1946,
488.
(10) Narain, N.; J hurry, D.; Wulff, G. Eur. Polym. J . 2002, 38, 273-
280.
(11) Ferreira, L.; Vidal, M.M.; Geraldes, C. F. G. C.; Gil, M. H.
Carbohydr. Polym. 2000, 41, 15.
(12) Carneiro, M. J .; Fernandes, A.; Figueiredo, C. M.; Fortes, A.
G.; Freitas, A. M. Carbohydr. Polym. 2001, 45, 135.
(13) Fanton, E. M.; Fayet, C.; Gelas, J .; Deffieux, A.; Fontanille, M.;
J hurry, D. Carbohydr. Res. 1993, 240, 143-152.
(14) Potier, P.; Bouchou, A.; Descotes, G.; Queneau, Y. Tetrahedron
Lett. 2000, 41, 3597.
(6) Patil, D. R.; Dordick, J . S.; Rethwisch, D. Macromolecules 1991,
24, 3462.
(15) Barros, M. T.; Sin˜eriz, F. Synthesis 2002, 10, 1407-1411.
(16) Barros, M. T., Maycock, C. D., Sin˜eriz, F., Thomassigny, C.
Tetrahedron 2000, 56, 6511.
(17) Chen, J .; Park, K. Carbohydr. Polym. 2000, 41, 259.
(18) Karl, H., Lee, C. K., Khan, R. Carbohydr. Res. 1982, 101, 31-
38.
(7) J hurry, D.; Deffieux, A.; Fontanille, M.; Betremieux, I.; Mentech,
J .; Descotes, G. Makromol. Chem. 1992, 193, 2297.
(8) Fanton, E.; Fayet, C.; Gelas, J .; J hurry, D.; Deffieux, A.;
Fontanille, M. Carbohydr. Res. 1992, 226, 337.
(9) Akashi, M.; Sakamoto, N. Kagaku Kogyo 1994, 45 (6), 507-515.
(19) J arosz, S.; Kosciolowska, I. Poland 177,187, 1999.
10.1021/jo048957y CCC: $27.50 © 2004 American Chemical Society
Published on Web 10/06/2004
7772
J . Org. Chem. 2004, 69, 7772-7775

SCHEME 1. Syn th esis of Acr yl Su cr ose Mon om er sa
a
Reaction conditions: (i) TBDPSCl, py, 4-DMAP, rt, 85%; (ii) BnBr/NaH, DMF, Bu4N+I-, rt, 80%; (iii) TBAF, THF, rt, 85%; (iv)
(CH3CHdCHCO)2O, CH2Cl2, Et3N, 4-DMAP, rt, 81%; (v) (CH2dC(CH3)CO)2O, CH2Cl2, Et3N, 4-DMAP, rt, 73%.
TABLE 1. Cop olym er iza tion of 4 w ith Styr en e or Meth yl Meth a cr yla te in th e P r esen ce of Ra d ica l In itia tor AIBN in
Mild Con d ition s (Tolu en e, 70 °C) a n d in a n d Au tocla ve (Tolu en e, 150 °C)
c
d
alkene
styrene
styrene (autoclave)
methyl methacrylate
[4]0a/[C]0
[4]b/[C]
reaction time [h]
yield (%)
Mw
Mw/Mn
[R]D
Tg [°C]
0.1
1.0
0.1
0.016
0.151
0.0015
96
48
96
12.9
9.8
23.3
10777
2917
26211
1.4
1.2
1.4
+3.40 (c 1.00, CHCl3)
+8.57 (c 0.42, CHCl3)
+5.53 (c 1.00, CHCl3)
87.42
74.93
116.72
a
b
Initial mole ratio of monomers. Mole ratio of comonomer units in copolymer, determined by 1H NMR. c Determined by SEC with
d
CHCl3 as solvent using polystyrene standards. Determined by DSC.
Esterifications of the free 6′-hydroxyl of 3 were carried
out by treating it in a mixture of dichloromethane and
triethylamine, at room temperature, with the appropriate
anhydride to afford the expected compounds 4 and 5 in
good yields (Scheme 1).
150 °C under pressure in an autoclave, followed by
precipitation in cold ethanol. A study of the effect of the
reaction conditions, the monomer structure, and the
initial quantity of the comonomers on the sugar incor-
poration in the final copolymers has been carried out. As
a result we obtained a number of copolymers with diverse
contents of protected sucrose, with different chain length,
reported by the weight average molecular weight, Mw,
polidispersity, Mw/Mn (being Mn the number average
molecular weight), and different physical properties such
as optical rotations, [R]D, and glass transition tempera-
tures, Tg (Tables 1 and 2).
Copolymer composition has been determined by 1H
NMR. When the comonomer is methyl methacrylate, the
structures have been verified by comparing the peak
areas of the methylene, methyl (0.8-2.2 ppm), and
methoxy (3.6 ppm) protons of the polymer chain with the
14 sucrose unit protons.
1
The H NMR spectra of these compounds exhibit two
signals that have been attributed to the double bond: for
crotonate 4 a mutiplet at 6.90 ppm and a doublet at 5.80
ppm and for methacrylate 5 a singlet at 6.15 ppm and a
doublet at 5.60 ppm. We assigned the allylic methyl
groups of the molecules at 1.70 ppm for 4 and 1.95 ppm
for 5.
The copolymerization of monomers 4 and 5 with
styrene and methyl methacrylate has been examined in
the presence of AIBN as free-radical initiator in toluene
at 70 °C under normal pressure (mild conditions) and at
(20) Cheˆnevert, R.; Caron, D. Tetrahedron: Asymmetry 2002, 13,
339-342.
J . Org. Chem, Vol. 69, No. 22, 2004 7773

TABLE 2. Cop olym er iza tion of 5 w ith Styr en e or Meth yl Meth a cr yla te in th e P r esen ce of Ra d ica l In itia tor AIBN in
Mild Con d ition s (Tolu en e, 70 °C) a n d in a n Au tocla ve (Tolu en e, 150 °C)
reaction
time [h]
[5]b/[C]
yield (%)
Mw
Mw/Mn
[R]D
Tg [°C]
c
d
alkene
[5]0a/[C]0
styrene
styrene
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0.160
0.100
0.263
0.083
0.435
0.124
0.526
0.228
120
96
70.70
36.02
64.27
44.90
41.05
55.90
79.02
59.72
6856
30968
12575
6649
14829
18382
12149
17280
1.3
1.9
1.5
1.3
1.4
1.8
1.4
1.6
+24.86 (c 1.00, CHCl3)
+28.80 (c 1.00, CHCl3)
+27.17 (c 1.01, CHCl3)
+32.52 (c 1.07, CHCl3)
+26.80 (c 1.00, CHCl3)
+27.85 (c 0.79, CHCl3)
+20.96 (c 0.94, CHCl3)
+41.54 (c 0.78, CHCl3)
90.88
56.70
94.84
53.27
115.62
64.90
115.50
97.60
styrene (autoclave)
48
styrene (autoclave)
24
methyl methacrylate
168
120
48
methyl methacrylate
methyl methacrylate (autoclave)
methyl methacrylate (autoclave)
24
a
b
Initial mole ratio of monomers. Mole ratio of comonomer units in copolymer, determined by 1H NMR. c Determined by SEC with
d
CHCl3 as solvent using polystyrene standards. Determined by DSC.
F IGUR E 2. Glass transition temperatures versus mole
percent of incorporation of 1′,2,3,3′,4,4′,6-hepta-O-benzyl-6′-
O-methacryloyl-sucrose (5) in poly(5-co-styrene).
F IGURE 1. Molecular weights of the copolymers versus mole
percent of incorporation of 1′,2,3,3′,4,4′,6-hepta-O-benzyl-6′-
O-methacryloyl-sucrose (5) in poly(5-co-methyl methacrylate).
The analysis of the results presented in Table 1 showed
that using the same initial molar composition of the
monomers and reaction conditions, we got 10 times lower
incorporation of the sugar in the polymer in the case of
using methyl methacrylate than with styrene. Also, with
an excess of methyl methacrylate a very low incorpora-
tion of sugar was obtained at normal pressure. Therefore,
all subsequent experiments with sucrose monomer 5 were
carried out with equimolar initial ratio of comonomers.
Comparing the behavior of sucrose derivatives, the
compound with a terminal double bond (5), which is
expected to be more reactive, readily gave copolymers
with a considerable molecular weight (up to 30 000), both
under mild conditions and in the autoclave, whereas the
crotonoyl sucrose (4) failed to react under mild conditions
to give copolymers with significant sucrose content.
The majority of the results obtained for the copolym-
erization of sucrose derivative 5 show that we got
polymers with a lower incorporation of sucrose than
alkene, as it was expected. Nevertheless, two interesting
copolymers were achieved with methyl methacrylate, in
mild conditions (168 h) and under pressure (48 h), with
molar ratios [V]/[C] ) 0.435 and 0.526, respectively,
corresponding to the highest sucrose derivative content
obtained. The highest chemical yield value (79.02%) was
observed for the copolymer 5/methyl methacrylate, with
the best monomer 5 incorporation.
F IGUR E 3. Glass transition temperatures versus mole
percent of incorporation of 1′,2,3,3′,4,4′,6-hepta-O-benzyl-6′-
O-methacryloyl-sucrose (5) in poly(5-co-methyl methacrylate).
comonomer and were generally higher for the copolymers
with methacrylic moiety.
Data obtained by size exclusion chromatography (SEC)
analysis revealed monomodal molecular weight distribu-
tions. Copolymer average molecular weights (Mw), esti-
mated by the same method, were in a range of values
similar to those of similar copolymers reported in the
literature (10-20 000)2. In general, the molecular weights
of the copolymers were decreasing for the polymers with
larger incorporation of the sugar comonomer (Figure 1),
which is less reactive and also provides more possibilities
for chain transfer reactions in the reaction mixture. All
of the values of polydispersity obtained are very low,
varying between 1.2 and 1.9, which means that the
copolymers are very homogeneous.
Concerning the effect of the pressure on both reaction
systems, 5/styrene and 5/methyl methacrylate, it is not
possible to establish any correlation between this pa-
rameter and the results obtained.
As expected, optical rotations were lower in the poly-
mers with larger incorporation of the nonoptically active
All copolymers synthesized are amorphous, bearing
only glass transition temperature. Glass transition tem-
peratures were increasing exponentially with the mole
percent of sugar incorporation for the copolymers with
methacrylic moiety, both with styrene and methyl meth-
acrylate (Figures 2 and 3), probably as a result of the
7774 J . Org. Chem., Vol. 69, No. 22, 2004

by flash column chromatography (eluent hexanes-ethyl acetate,
3:1) yielded 0.3414 g (85%) of 3. 1H NMR (CDCl3): δ 7.37-
7.13(m, 35H), 5.72(d, J ) 3.7 Hz, 1H), 4.83(d, J ) 11.0 Hz, 1H),
4.79(d, J ) 11.0 Hz, 1H), 4.72-4.33(m, 14H), 4.18(d, J ) 12.0
Hz, 1H), 4.11(dd, J ) 11.2, 5.5 Hz, 1H), 4.09-4.05(m, 1H), 3.93(t,
J ) 9.2 Hz, 1H), 3.75-3.62(m, 3H), 3.55-3.47(m, 2H), 2.29(s,
1H). 13C NMR (CDCl3): δ 68.5, 66.9, 68.6, 70.3, 72.3, 72.4, 73.2,
73.5, 73.6, 75.0, 75.7, 77.8, 79.6, 79.9, 81.9, 82.5, 83.9, 89.9, 104.6,
restrained movements of the polymer molecule with more
bulky substituents.
In summary, 1′,2,3,3′,4,4′,6-hepta-O-benzyl-sucrose has
been prepared and selectively 6′-O-esterified with small
R,â-unsaturated acid derivatives. New chiral copolymers
containing sucrose have been synthesized by radical
polymerization, and some of their physical properties
were determined.
127.6-138.9. [R]20 +46.12(c 1.34, CHCl3)
D
1′,2,3,3′,4,4′,6-Hep ta -O-ben zyl-6′-O-cr oton yl-su cr ose (4)
a n d
1′,2,3,3′,4,4′,6-H ep t a -O-b en zyl-6′-O-m et h a cr yloyl-
su cr ose (5).5
To a 0.1 M solution of 3 (500 mg, 0.514 mmol) in
Exp er im en ta l Section
anhydrous CH2Cl2 were added Et3N (130 mg, 1.286 mmol) and
a catalytic amount of 4-DMAP. The mixture was cooled to 0 °C,
and then a 0.5 M solution of crotonic/methacrylic anhydride (1.2
equiv) in anhydrous CH2Cl2 was added. The reaction mixture
was allowed to warm to room temperature. When no more
starting material remained, more CH2Cl2 was added (5 × 15
mL per mmole of starting material) and washed with aqueous
1.0 N HCl (15 mL per mmole of starting material), saturated
aqueous NaHCO3, and distilled H2O. The organic layer was dried
(Na2SO4), and the solvent was evaporated. Purification by flash
column chromatography (eluent hexanes-ethyl acetate, 5:1)
yielded 0.4333 g (81%) of 4 and 0.3905 (73%) of 5.
Reagents and solvents were purified before use.21 All reactions
were carried out under a positive pressure of dry argon. Optical
rotations were measured at 20 °C on an AA-1000 polarmeter
(0.5 dm cell). NMR spectra were recorded at 400 MHz in CDCl3
with chemical shift values (δ) in ppm downfield from TMS.
Average molecular weights were determined using a size exclu-
sion chromatography (SEC) apparatus, including a solvent
delivery system composed of a pump, injector, and refractive
index detector. The operation temperature was 30 °C, chloroform
was used as eluent with a series of three columns, 103, 104, and
105 Å, and the calibration was performed with monodisperse
polystyrene standards. Glass transition temperatures were
measured at the second heating cycle with a rate of 10 °C/min.
6′-O-ter t-Bu tyld ip h en ylsilyl-su cr ose (1).18 A solution of
sucrose (5.00 g) in dry pyridine (70 mL) was stirred with
4-(dimethylamino)pyridine (0.05 g) and 1.1 molar equiv of tert-
butyldiphenylsilyl chloride (3.9 mL) at room temperature and
monitored by TLC (ethyl acetate-acetone-water, 10:10:1).
When the less polar 6,6′-di-OTBDPS-sucrose appeared (Rf 0.49,
4-5 h), the reaction mixture was concentrated and purified by
column chromatography (ethyl acetate to ethyl acetate-acetone-
Da ta for 4. 1H NMR (CDCl3): δ 7.37-7.13(m, 35H), 6.90(dq,
J ) 15.6, 6.8, 1H), 5.80(d, J ) 15.6, 1H), 5.72(d, J ) 3.7 Hz,
1H), 4.83(d, J ) 11.0 Hz, 1H), 4.79(d, J ) 11.0 Hz, 1H), 4.72-
4.33(m, 14H), 4.18(d, J ) 12.0 Hz, 1H), 4.11(dd, J ) 11.2, 5.5
Hz, 1H), 4.09-4.05(m, 1H), 3.93(t, J ) 9.2 Hz, 1H), 3.75-3.62(m,
3H), 3.55-3.47(m, 2H), 1.75 (s, 3H). [R]20D +48.12(c 1.33, CHCl3).
Anal. Calcd: C, 74.98; H, 6.58. Found: C, 74.74; H, 6.66.
1
Da ta for 5. H NMR (CDCl3): δ 7.37-7.13(m, 35H), 6.15(d,
J ) 3.6 Hz, 1H), 5.55(d, J ) 3.6 Hz, 1H), 5.72(d, J ) 3.7 Hz,
1H), 4.83(d, J ) 11.0 Hz, 1H), 4.79(d, J ) 11.0 Hz, 1H), 4.72-
4.33(m, 14H), 4.18(d, J ) 12.0 Hz, 1H), 4.11(dd, J ) 11.2, 5.5
Hz, 1H), 4.09-4.05(m, 1H), 3.93(t, J ) 9.2 Hz, 1H), 3.75-3.62(m,
3H), 3.55-3.47(m, 2H), 2.00(s, 3H). [R]20D +46.88 (c 1.23, CHCl3).
Anal. Calcd: C, 74.98; H, 6.58. Found: C, 74.69; H, 6.88.
Gen er a l P r oced u r e for Cop olym er iza tion u n d er Mild
Con d ition s. Copolymerizations of compounds 4 and 5 with
styrene or methyl methacrylate were carried out in anhydrous
toluene solutions (0.1 M) in the presence of AIBN as radical
initiator (1 wt % with respect to the monomer mixture).
Dissolved oxygen was removed from the solutions by three
freeze-thaw cycles on the vacuum pump. They were then heated
at 85 °C until the polymerizations were complete, the solutions
were then cooled to room temperature, and the product was
precipitated in cold EtOH. The white solid was filtered and
washed several times with cold EtOH. The polymers were
purified by repeated dissolution in toluene and reprecipitation
in cold EtOH and dried under vacuum. The yields and some
physical properties of thus prepared polymers are shown in
Tables 1 and 2.
1
water, 100:100:1) to yield 7.208 g (85%) of 1. H NMR (CDCl3):
δ 7.66(m, 4H), 7.41(m, 6H), 5.60(d, J ) 3.7 Hz, 1H), 5.52(t, J )
5.7 Hz, 1H), 5.40(t, J ) 9.8 Hz, 1H), 5.39(d, J ) 5.6, 1H), 5.03(t,
J ) 9.9 Hz, 1H), 4.80(dd, J ) 10.3, 3.7 Hz, 1H), 4.70(s, 1H),
4.17-3.93(m, 7H), 1.06(s, 9H). [R]20 +44°(c 1, methanol).
D
1′,2,3,3′,4,4′,6-Hep ta -O-ben zyl-6′-O-ter t-bu tyld ip h en ylsi-
lyl-su cr ose (2).19 6′-O-tert-Butyldiphenylsilylsucrose (1) (0.5000
g, 0.862 mmol) was dissolved in 10 mL of DMF together with a
catalytic amount (5 mg) of (n-Bu)4N+I-. The solution was cooled
to 0 °C, and 0.463 g NaH (50% suspension in oil, 11.2 equiv)
was added carefully. After 20 min 1.46 mL of benzyl bromide
(14 equiv) was added drop by drop for 15 min. The ice bath was
removed, and the reaction was monitored by TLC (hexanes-
ethyl acetate, 5:1). When there was no more of the initial
compound (4-5 h), the reaction mixture was poured into H2O
(100 mL). The product was extracted 4 times with 40 mL of
diethyl ether, and the collected organic layers were washed twice
with 10 mL of H2O, dried with Na2SO4, and concentrated. The
residue was purified by column chromatography (eluent hex-
anes-ethyl acetate, 5:1) to yield 0.8345 g (80%) of 2. 1H NMR
(CDCl3): δ 7.37-7.13(m, 45H), 5.72(d, J ) 3.7 Hz, 1H), 4.83(d,
J ) 11.0 Hz, 1H), 4.79(d, J ) 11.0 Hz, 1H), 4.72-4.33(m, 14H),
4.18(d, J ) 12.0 Hz, 1H), 4.11(dd, J ) 11.2, 5.5 Hz, 1H), 4.09-
4.05(m, 1H), 3.93(t, J ) 9.2 Hz, 1H), 3.75-3.62(m, 3H), 3.55-
3.47(m, 2H), 3.37(dd, J ) 10.1, 2.4 Hz, 1H), 1.25(s, 9H). 13C NMR
(CDCl3): δ 19.1, 26.8, 65.0, 68.4, 70.5, 71.2, 72.1, 72.4, 73.1, 73.3,
73.4, 74.7, 75.5, 77.5, 79.9, 81.3, 82.0, 82.7, 84.2, 89.8, 104.7,
Gen er a l P r oced u r e for Cop olym er iza tion in a n Au to-
cla ve. The autoclave copolymerizations of compounds 4 and 5
with styrene or methyl methacrylate were carried out in
anhydrous toluene solution (0.1 M) in the presence of AIBN as
radical initiator (1 wt % with respect to the monomer mixture).
The solutions were placed in an autoclave vessel and kept at
150 °C for 24 h. The solutions were then cooled to room
temperature, and 0.05-mL samples were taken from the mixture
and dropped into ethanol. If there was no precipitation, the
mixture was heated for another 24 h. As soon as precipitation
appeared, the reaction was stopped by precipitating the whole
mixture in cold EtOH. The white solid was filtered and washed
several times with cold EtOH. The polymers were purified by
repeated dissolution in toluene and reprecipitation in cold EtOH
and finally dried under vacuum.
127.5-139.1. [R]20 +30.9(c 0.9, CHCl3).
D
1′,2,3,3′,4,4′,6-Hep ta -O-ben zyl-su cr ose (3).10 Compound 2
(500 mg, 0.413 mmol), dissolved in 10 mL of dry THF, was
treated with tetrabutylammonium fluoride (0.496 mL, 0.496
mmol, 1 M solution in THF) at room temperature, and the
reaction monitored by TLC (hexanes-ethyl acetate, 3:1). When
no more of the starting material remained (4-5 h), the solvent
was evaporated. The residue was dissolved in dichloromethane,
washed twice with H2O, dried, and concentrated. Purification
Ack n ow led gm en t. This work has been supported
by Fundac¸a˜o para a Cieˆncia e a Tecnologia (SFRH/BPD/
9474/2002 and POCTI/QUI/47973/2002).
(21) Purification of Laboratory Chemicals, 2nd Ed.; Perrin, D. D.,
Armarego, W. L. F., Perrin, D. R., Eds.; Pergamon Press Ltd.: New
York, 1980.
J O048957Y
J . Org. Chem, Vol. 69, No. 22, 2004 7775