Facile synthesis of a d-galactono-1,6-lactone derivative, a precursor of a copolyester

Article abstract of DOI:10.1016/j.carres.2006.10.017

2,3,4,6-Tetra-O-methyl-d-galactonic acid (5) was readily prepared from d-galactono-1,4-lactone (1) in 47% yield. The sequence involves tritylation of HO-6 of 1, followed by O-permethylation and deprotection. Lactonization of 5 led to the per-O-methyl-d-ga

Full text of DOI:10.1016/j.carres.2006.10.017

Carbohydrate Research 341 (2006) 2973–2977
Note
Facile synthesis of a D-galactono-1,6-lactone derivative, a
precursor of a copolyester
C. Lorena Romero Zaliz and Oscar Varela*
CIHIDECAR-CONICET, Departamento de Quı´mica Orga´nica, Facultad de Ciencias Exactas y Naturales, Pabello´n II,
Ciudad Universitaria, 1428-Buenos Aires, Argentina
Received 5 September 2006; accepted 18 October 2006
Available online 25 October 2006
Abstract—2,3,4,6-Tetra-O-methyl-D-galactonic acid (5) was readily prepared from D-galactono-1,4-lactone (1) in 47% yield. The
sequence involves tritylation of HO-6 of 1, followed by O-permethylation and deprotection. Lactonization of 5 led to the per-O-
methyl-D-galactono-1,6-lactone, which was copolymerized with e-caprolactone by ring-opening polymerization catalyzed by scan-
dium triflate. The incorporation of the sugar comonomer into the polyester chain was about 10%.
ꢀ 2006 Elsevier Ltd. All rights reserved.
Keywords: D-Galactono-1,4-lactone; Aldono-1,6-lactone; e-Caprolactone; Copolyester
Polyesters and copolyesters of a-, b-, and x-hydroxy
acids are presently under investigation as matrices for
controlled drug delivery and scaffolds for tissue engi-
neering.1–3 One commonly used synthetic strategy for
preparing these polymers is the ring-opening polymeri-
zation of e-caprolactone, lactide, and other cyclic esters.
This reaction has been efficiently conducted using tran-
sition metal-initiating compounds4 as well as enzymatic
catalysis.5,6
The introduction of functional groups into the mono-
mers is an important tool to tail and modulate the prop-
erties of the resulting polymers. Thus, e-caprolactone,
lactide, or glycolide have been polymerized with more
hydrophilic lactones.7 Also, dilactones with protected
functionalities yield, after polymerization, polymers with
hydrophilic pendant groups.8 A higher biodegradability
for these materials is expected as a result of the enhanced
hydration. Due to the large number of hydroxyl func-
tions in their structures, carbohydrates are employed as
precursors of hydrophilic polymers.2 Thus, carbohy-
drate-functionalized polyesters have been prepared using
enzymes as catalysts,9 and terminally carbohydrate-
modified poly(e-caprolactones) have been synthesized
by lactic acid-promoted ring-opening polymerization of
e-caprolactone with methyl b-D-glucopyranoside or su-
crose as initiators.10 Additionally, derivatives of sugars
seem to be suitable for the preparation of polyhydroxy-
polyalkanoates. For example, aldono-1,6-lactones are
analogues of e-caprolactone carrying several hydroxyl
groups. However, as far as we know, just one prepara-
tion of a D-glucono-1,6-lactone derivative has been re-
ported. Such a derivative was synthesized by Galbis
and coworkers11 by two alternative routes, both involv-
ing the oxidation of C-1 of glucose. Furthermore, the
homopolymerization of the monomeric 1,6-lactone
derivative and its copolymerization with L-lactide were
attempted.
In our recent work on the synthesis of polyamides de-
rived from D- and L-galactono-1,4-lactones,12,13 we have
succeeded in the preparation of selectively protected al-
donic acid derivatives having free the hydroxyl group at
C-6. These compounds are suitable for 1,6-lactone for-
mation. We report here the synthesis of 2,3,4,5-tetra-
O-methyl-D-galactono-1,6-lactone (6), by a short route
starting from D-galactono-1,4-lactone (1). The homo-
polymerization of 6 and its copolymerization with
e-caprolactone were studied.
*
Corresponding author. Tel./fax: +54 11 4576 3352; e-mail: varela@
qo.fcen.uba.ar
0008-6215/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2006.10.017

2974
C. L. Romero Zaliz, O. Varela / Carbohydrate Research 341 (2006) 2973–2977
H
OMeOMe
O
Et2O.BF3,
O
1) KOH, MeOH
OMe
RO
Ph3CO
2) NaH, DMSO,
MeI
MeOH, CH2Cl2
HO
OMeOMeO
OH
1 R = H
HO
3
Ph3CCl,
C5H5N
2 R = Ph3C
OMe
OMeOMe
MeO
O
OR DCC, 4-DMAP,
4-DMAP.HCl
HO
O
MeO
MeO
OMeOMeO
KOH,
MeOH, H2O
4 R = Me
5 R = H
6
Scheme 1.
The x-hydroxy acid 5 was readily prepared from 1 as
depicted in Scheme 1 (47% overall yield). D-Galactono-
1,4-lactone (1) was converted into the 6-O-trityl deriva-
tive 2, as described for the analogue in the L-series.12
Treatment of 2 with methanolic solution of KOH affor-
ded the potassium salt of the aldonic acid, that was dried
and O-permethylated with methyl iodide in Me2SO, in
the presence of sodium hydride. The opening of the lac-
tone by formation of the potassium salt prevents side
reactions during O-alkylation, such as eliminations
and isomerizations.14 Removal of the trityl group with
F3BÆOEt2, followed by hydrolysis of the methyl ester
with alkali, led to crystalline 2,3,4,5-tetra-O-methyl-D-
galactonic acid (5), a direct precursor of the target 1,6-
lactone 6.
Furthermore, the Fourier-transform IR spectrum of 6
showed the stretching of the carbonyl group at
1749 cmꢁ1, similar to that observed for the e-caprolac-
tone (1740 cmꢁ1). The structure of 6 was further con-
firmed by mass spectrometry. The MALDI-TOF
spectrum of 6 presented a single peak at m/z 256.5 (theo-
retical for M+Na+: 257.2). This result excludes the
formation of dimeric or oligomeric rings, as observed
for cyclizations of related compounds.18 Lactone 6,
when subjected to GC–MS gave a chromatogram that
showed a single signal (retention time 10 min). The cor-
responding electron impact-mass spectrum (EIMS)
exhibited the peak at highest mass of m/z 203, which
was attributed to the loss of a methoxy group from
the molecular ion, and other diagnostic fragmentations
are illustrated in Scheme 2.
A number of procedures for lactonization and macro-
lactonization of hydroxy acids have been described, and
recently reviewed.15 We have followed the Keck–Boden
modification of the original Steglich procedure,16 which
employs dicyclohexylcarbodiimide-4-N,N-dimethylami-
nopyridine (DMAP) for the lactonization. Keck and
Boden have shown the crucial role of DMAP hydro-
chloride as a proton-transfer reagent that prevents the
formation of N-acyl urea as an undesired byproduct.16
This reaction when applied to 5 afforded 6 in 56% yield.
The structure of 6 was confirmed by comparison of
the NMR spectra with those of 5. Thus, the methylene
protons (H-6,60) appeared shifted downfield as expected
for the deshielding effect of the esterification of HO-6.
The remarkable changes in coupling constant values
from 5 to 6 were also indicative of ring formation. For
the hydroxy acid 5, the small values for J2,3 and J4,5
(2.5 and 2.8 Hz, respectively) and the large one for J3,4
(8.6 Hz), agree with a planar zigzag conformation for
the sugar backbone. It has been established that open-
chain derivatives of galactose adopt preferentially such
a conformation.13,17 In contrast, the lactone 6 showed
relatively large values for J2,3 and J4,5 (6.8 and 7.0 Hz,
respectively) and a small one for J3,4 (ꢀ1 Hz), as a result
of the cyclization to a seven-membered lactone ring.
The homopolymerization of lactone 6 promoted by
aluminum isopropoxide (Al(OiPr)3) or scandium triflate
(Sc(OTf)3) was attempted. However, the polymerization
failed with both catalysts. In the case of Al(OiPr)3, the
formation of decomposition products was detected. This
fact was attributed to the instability of aldonolactone
derivatives towards strong bases, which usually induce
eliminations and isomerizations.14 However, using
Sc(OTf)3, the monomer 6 was recovered unaltered from
-H2CO
101 (63)
131 (16)
- Me.
- MeOH
146 (32)
114 (9)
MeO
OMe
88 (37)
176 (2)
MeO
O
O
MeO
58 (100)
88 (37)
Scheme 2. EIMS of compound 6. Relative intensities (%) are given in
brackets.

C. L. Romero Zaliz, O. Varela / Carbohydrate Research 341 (2006) 2973–2977
2975
the reaction mixture. From the variety of transition or
O
rare-earth metal initiators for the ring-opening polymeri-
zation,4 Sc(OTf)3 presents some advantages, as being a
commercially available compound that catalyzes poly-
merizations at rt, for short times, and that contamina-
tion by protic compounds (such as water) does not
suppress its catalytic activity.19 In order to verify that
the catalyst was active, the Sc(OTf)3-induced homopoly-
merization of e-caprolactone (7) in dry toluene was con-
ducted at rt for 16 h. As expected poly(e-caprolactone)
(8) was obtained. Polyester 8 showed NMR spectra that
were in accordance to those already reported.4 From the
integral of the triplet that appeared at 4.06 ppm (meth-
ylene group bonded to oxygen) and that at 3.65 ppm
(terminal hydroxymethyl group) the molecular weight
of the polyester was estimated (Mw 4000). Also the
Mw value (4900) was determined by size exclusion chro-
matography (SEC) of the polymer.
As homopolymerization of lactones becomes more
difficult when the substitution of the lactone ring in-
creases,11 the copolymerization of 6 and 7 initiated by
Sc(OTf)3 was studied under different conditions
(Scheme 3). Thus, the aldono-1,6-lactone 6 was stirred
in a toluene soln with the catalyst at rt for 24 h, and
then e-caprolactone 7 (identical number of molar equiv-
alents as 6) was injected to the mixture. The stirring
was continued for 48 h. The same experiment was con-
ducted but starting with e-caprolactone and injecting 6
after 24 h. In both cases, the NMR spectra of the poly-
esters that were isolated and purified were very similar,
and they revealed that about 10% of 6 had been incor-
porated to the polymeric chain. Also, the molecular
weight of the material obtained in the first polymeriza-
tion was similar to that obtained in the second one
(ꢀ3000, estimated from the 1H NMR spectra). The
13C NMR spectra of the copolymer showed the signal
of the carbons bonded to oxygen of the sugar comono-
mer between 77.1 and 81.0 ppm, and those of the
methyl groups in the range of 62.1–58.0 ppm. In these
regions, more signals appeared than those expected
for a regular repeating unit of the copolyester, which
suggests different chemical environments (acid or hy-
droxy end or incorporation into the chain) for the aldo-
nic acid derivative in the polymer.
O
Sc(OTf)3
m
O
8
O
Sc(OTf)3
O
OMeOMe
6
7
O
O
OMeOMeO
n
m
9
Scheme 3.
These results show that the copolymerization of ald-
ono-1,6-lactone derivatives with e-caprolactone can be
successfully conducted. Further efforts are needed to
achieve higher incorporation of the sugar into the
copolymer chain. Other lactones, such as L-lactide,
may be employed in order to obtain hydrophilic and
potentially biodegradable polyhydroxypolyalkanoates.
The lactone 6, similar to its D-gluco analogue, seems
to be less reactive than e-caprolactone for the ring-open-
ing polymerization. The lower reactivity of 6 can be
explained taking into account the mechanism proposed
for the Sc(OTf)3-catalyzed polymerization.19 The first
step is the coordination of the metal to the lactone
carbonyl, which is activated (the ‘activated monomer
mechanism’20) for the attack of traces of water con-
tained in the Sc(OTf)3 (lanthanide salts are extremely
difficult to obtain in anhydrous state21) In the case of
6, the methoxy groups can compete with the carbonyl
for the coordination with Sc(OTf)3, thus diminishing
its catalytic activity. On the other hand, as one molecule
of reactive catalyst produces a large number of polymer
molecules,19 an increment in the lanthanide will generate
a larger number of polymeric chains, resulting in the
lowering of the molecular weight of the polyester.
1. Experimental
1.1. General methods
Melting points were determined with a Fisher–Johns
apparatus and are uncorrected. Analytical thin-layer
chromatography (TLC) was performed on Silica Gel
60 F254 (E. Merck) aluminum-supported plates (layer
thickness 0.2 mm). Visualization of the spots was
effected by exposure to UV light or by charring with a
soln of 5% (v/v) sulfuric acid in EtOH, containing
0.5% p-anisaldehyde. Column chromatography was car-
ried out with Silica Gel 60 (230–400 mesh, E. Merck).
Optical rotations were measured with a Perkin–Elmer
343 digital polarimeter at 25 ꢁC. Nuclear magnetic reso-
nance (NMR) spectra were recorded on a Bruker AC-
200 or Bruker AMX-500 spectrometers. Size exclusion
The copolymer 9 was also synthesized adding succes-
sively equimolar amounts of comonomers 6 and 7 to a
suspension of Sc(OTf)3 in toluene. The resulting copoly-
ester 9 gave NMR and IR spectra identical to those
shown by the polymers prepared previously under
different reaction conditions. We have also found that
the incorporation of aldonic acid to the polymer
could not be increased using higher concentrations of
7 during the polymerization. Polyester 9 displayed
unimodal chromatograms by SEC, using THF as
solvent, from which the molecular weight (Mw 3500)
was estimated.

2976
C. L. Romero Zaliz, O. Varela / Carbohydrate Research 341 (2006) 2973–2977
chromatography (SEC) was performed at rt with a
Waters apparatus equipped with a Waters 2414 refrac-
tive index detector and Styragel HR (7.8 · 300 mm)
Waters columns, using THF as mobile phase. The flow
rate was 1 mL minꢁ1. Calibration was based on polysty-
rene standards. IR spectra (films) were recorded with a
Nicolet 510P FTIR spectrometer. MALDIMS measure-
ments were performed using a Shimadzu Kratos, Kom-
pact MALDI 4 (pulsed extraction) laser desorption
time-of-flight mass spectrometer (Shimadzu, Kyoto,
Japan) equipped with a pulsed nitrogen laser (337 nm;
pulse width 3 ns), tunable PDE and PSD (MS/MS
device) modes. GC–EIMS analyses were made in a
GC–MS QP5050A (Shimadzu), using a ionization
potential of 70 eV. Conditions: injector temperature
240 ꢁC, interface temperature 270 ꢁC, oven temperature
from 150 ꢁC at 10 ꢁC/min to 250 ꢁC (20 min), split 90:1,
total flow 20 mL minꢁ1, column flow 0.2 mL minꢁ1. The
mass spectrometer was used in scan mode (40–500 amu).
1.5. 2,3,4,5-Tetra-O-methyl-D-galactonic acid (5)
To a soln of 4 (0.72 g, 1.46 mmol) in MeOH–water (3:1,
15 mL) was added a soln of KOH (0.2 g, 3.57 mmol) in
the same solvent (1 mL). The mixture was stirred at rt
for 3 h and the MeOH evaporated. The residue was
diluted with water (80 mL), acidified with HCl (5%) to
pH 3 and extracted with CH2Cl2 (3 · 50 mL). The or-
ganic extract was dried (MgSO4) and concentrated to
give 5 (0.33 g, 90%) as a crystalline solid. Recrystallized
from hexane–EtOAc, 5 gave mp 143 ꢁC; [a]D ꢁ10.4 (c
1
0.8, CHCl3); H NMR (500 MHz, CDCl3) d: 4.06 (d,
0
1H, J2,3 2.5 Hz, H-2), 3.91 (dd, 1H, J5,6 5.5, J6,6
11.6 Hz, H-6), 3.88 (dd, 1H, J3,4 8.5 Hz, H-3), 3.86
(dd, 1H, J5,6 4.8 Hz, H-60), 3.55 (dd, 1H, J4,5 2.8 Hz,
0
H-4), 3.51 (m, 1H, H-5), 3.53, 3.51, 3.50, 3.45 (4s,
12H, OCH3); 13C NMR (125 MHz, CDCl3) d: 174.2
(C-1), 81.0, 80.0, 79.7, 79.4 (C-2,3,4,5), 61.2 (C-6),
60.4, 60.0, 58.9, 58.0 (OCH3). Anal. Calcd for
C10H20O7: C, 47.61; H, 7.99. Found: C, 47.81; H, 7.97.
1.2. 6-O-Trityl-D-galactono-1,4-lactone (2)
1.6. 2,3,4,5-Tetra-O-methyl-1,6-D-galactonolactone (6)
It was prepared by reaction of triphenylmethyl chloride
(trityl chloride, 1.87 g, 6.72 mmol) with D-galactono-1,4-
lactone (1, 1.0 g, 5.61 mmol) in anhyd pyridine (8.4 mL),
as previously described.12 Crystalline 2 (2.25 g, 95%)
gave mp 77–78 ꢁC, [a]D +20.0 (c 1.0, CHCl3). Lit.12
mp 77–78 ꢁC, [a]D ꢁ22.4 for the enantiomer.
A soln of 5 (0.25 g, 0.99 mmol) in anhyd CHCl3 (7 mL)
was added dropwise to a soln of DCC (0.47 g,
2.20 mmol), 4-DMAP (0.44 g, 3.60 mmol), and 4-
DMAP hydrochloride (0.37 g, 2.30 mmol) in anhyd
CHCl3 (30 mL). The reaction mixture was stirred at rt
for 18 h, when TLC (1:1 hexane–EtOAc) showed a
major spot having Rf 0.27. The suspension was filtered
and the solvent evaporated. The residue was purified
by column chromatography (1:1 hexane–EtOAc) to give
6 (0.13 g, 56%) as a colorless syrup that crystallized on
1.3. Methyl 2,3,4,5-tetra-O-methyl-6-O-trityl-D-galacto-
nate (3)
To a soln of 2 (1.00 g, 2.38 mmol) was slowly added 30%
KOH in MeOH with stirring. When the alkalinity of the
soln (pH ꢀ7.5) persisted for about 30 min, the solvent
was evaporated to afford the solid potassium salt. The
dried solid was dissolved in anhyd Me2SO (6.5 mL),
and a suspension of NaH (1.15 g) in Me2SO (10 mL)
was added to the cooled soln (ice bath). The mixture
was stirred at rt for 30 min, cooled to 0 ꢁC, and methyl
iodide (1.75 mL) was injected. After 2 h at rt, MeOH
was added carefully to the suspension, which was then
neutralized with acetic acid, diluted with water and
extracted with CH2Cl2 (3 · 80 mL). The extract was
dried (MgSO4) and concentrated to afford a syrup that
was subjected to column chromatography with 5:1
hexane–EtOAc. Compound 3 was isolated as a colorless
oil (0.94 g, 78%); [a]D +8.0 (c 1.0, CHCl3). Lit.12 [a]D
ꢁ5.1 for the enantiomer.
1
standing; mp 67–68 ꢁC; [a]D +10.5 (c 0.6, CHCl3); H
0
NMR (400 MHz, CDCl3) d: 4.44 (dd, 1H, J5,6 6.8, J6,6
12.9 Hz, H-6), 4.28 (d, 1H, J2,3 6.0 Hz, H-2), 4.23 (dd,
1H, J5,6 2.4 Hz, H-60), 3.79 (br s, 1H, H-3), 3.58 (ddd,
0
1H, J4,5 8.0 Hz, H-5), 3.50 (br s, 1H, H-4), 3.53, 3.52,
3.48, 3.47 (4s, 12H, OCH3); 13C NMR (50.3 MHz,
CDCl3) d: 176.3 (C-1), 80.9, 80.0, 79.6, 79.3 (C-
2,3,4,5), 61.2, 60.5, 58.9, 58.0 (OCH3). Anal. Calcd for
C10H18O6: C, 51.27; H, 7.75. Found: C, 50.92; H, 8.02.
1.7. General procedure for lactone polymerization or
copolymerization initiated with Sc(OTf)3
1.7.1. Poly(e-caprolactone) (8).
A
suspension of
Sc(OTf)3 (10 mg, 20 lmol) in dry toluene (1 mL) was
placed in a sealed vial, under an argon atmosphere,
and freshly distilled caprolactone (7, 0.11 mL,
0.99 mmol) was injected slowly with a syringe. The reac-
tion mixture was stirred at rt for 16 h, when TLC
(EtOAc) showed no remaining caprolactone (Rf 0.51).
The mixture was diluted with toluene (30 mL) and
washed with water (2 · 10 mL). The organic extract
was dried (MgSO4), filtered, and concentrated, to afford
1.4. Methyl 2,3,4,5-tetra-O-methyl-D-galactonate (4)
Trityl removal12 from 3 (0.75 g, 1.48 mmol) with
F3BÆOEt2 (0.2 mL) in MeOH (0.6 mL) and CH2Cl2
(40 mL) afforded oily 4 (0.28 g, 72%); [a]D +10.0 (c
0.9, CHCl3). Lit.12 [a]D ꢁ10.5 for the enantiomer.

C. L. Romero Zaliz, O. Varela / Carbohydrate Research 341 (2006) 2973–2977
2977
poly(e-caprolactone) 8 (0.10 g, 85%) as a white solid; 1H
NMR (200 MHz, CDCl3) d: 4.06 (t, 2H, J 6.6 Hz, CH2-
a), 2.31 (t, 2H, J 7.4 Hz, CH2-e), 1.63 (m, 4H, CH2-b, d),
1.38 (m, 2H, CH2-c); 13C NMR (50.3 MHz, CDCl3) d:
173.5 (CO), 64.1 (OCH2), 34.1 (COCH2), 28.3, 25.5,
24.5 (3CH2). These spectra were similar to those already
described for poly(e-caprolactone).4
´
4. Cayuela, J.; Boor-Legare, V.; Cassagnau, P.; Michel, A.
Macromolecules 2006, 39, 1338–1346, and references cited
therein.
5. (a) Gross, R. A.; Kumar, A.; Kalra, B. Chem. Rev. 2001,
101, 2097–2124; (b) Kobayashi, S.; Uyama, H.; Kimura,
S. Chem. Rev. 2001, 101, 3793–3818.
6. Hans, M.; Gasteier, P.; Keul, H.; Moeller, M. Macromole-
cules 2006, 39, 3184–3193.
7. (a) Chen, X.; Gross, R. A. Macromolecules 1999, 32, 308–
314; (b) Kumar, R.; Gao, W.; Gross, R. A. Macromole-
cules 2002, 35, 6835–6844.
1.7.2. Poly(e-caprolactone)-co-poly(2,3,4,5-tetra-O-methyl-
1,6-D-galactonolactone) (9). The procedure described
above was applied for the copolymerization of 6 with
7. Compound 6 (0.034 mL, 0.31 mmol) and 7 (0.07 g,
0.31 mmol) were successively injected to a suspension
of Sc(OTf)3 (3.1 mg, 6.2 lmol) in dry toluene (0.7 mL).
After the work-up and washing of the residue with hex-
ane (2 · 2 mL), the polyester 9 (70 mg, 66%) was ob-
˚
8. Trollsas, M.; Lee, V. Y.; Mecerreyes, D.; Lo¨wenhielm, P.;
Mo¨ller, M.; Miller, R. D.; Hedrick, J. L. Macromolecules
2000, 33, 4619–4627.
9. (a) Bisht, K. S.; Deng, F.; Gross, R. A.; Kaplan, D. L.;
Swift, G. J. Am. Chem. Soc. 1998, 120, 1363–1367;
´
(b) Cordova, A.; Iversen, T.; Hult, K. Macromolecules
1998, 31, 1040–1045.
10. Persson, P. V.; Schro¨der, J.; Wickholm, K.; Hedenstro¨m,
E.; Iversen, T. Macromolecules 2004, 37, 5889–5893.
11. Molina Pinilla, I.; Bueno Martınez, M.; Galbis, J. A.
Carbohydr. Res. 2003, 338, 549–555.
12. Romero Zaliz, C. L.; Varela, O. Tetrahedron: Asymmetry
2003, 14, 2579–2586.
13. Romero Zaliz, C. L.; Varela, O. Tetrahedron: Asymmetry
2005, 16, 97–103.
14. Lederkremer, R. M.; Varela, O. Adv. Carbohydr. Chem.
Biochem. 1999, 50, 125–209.
1
tained as a white solid; [a]D ꢁ3.4 (c 1.1, CHCl3); H
´
NMR (200 MHz, CDCl3) d: 4.50–3.80 (m, 6H, H-galac-
tonic acid), 4.06 (t, 2H, J 6.6 Hz, OCH2), 3.55–3.30 (m,
12H, OCH3), 2.31 (t, 2H, J 7.5 Hz, COCH2), 1.75–1.25
(m, 6H, 3CH2); IR: 1735 cmꢁ1 (CO), 1100 cmꢁ1
(OCH3); Mw 3500 (SEC).
15. Parenty, A.; Moreau, X.; Campagne, J.-M. Chem. Rev.
2006, 106, 911–939.
16. Boden, E. P.; Keck, G. E. J. Org. Chem. 1985, 50, 2394–
2395.
Acknowledgments
Support of our work by the University of Buenos Aires
(project X059), the National Research Council of
Argentina (CONICET, project PIP 5011) and the Na-
tional Agency for Promotion of Science and Technology
(ANPCyT, project 13922) is gratefully acknowledged.
We thank Dr. Rosa Erra-Balsells and Dr. Hiroshi Non-
ami (Ehime University, Japan) for the MALDI-TOF
mass spectra. O.V. is a Research Member of CONICET.
17. (a) Horton, D.; Walaszek, Z.; Ekiel, I. Carbohydr. Res.
1983, 119, 263–268; (b) Blanc-Muesser, M.; Defaye, J.;
Horton, D. Carbohydr. Res. 1980, 87, 71–86; (c) Sweeting,
L. M.; Coxon, B.; Varma, R. Carbohydr. Res. 1979, 72,
43–55.
18. Mayes, B. A.; Stetz, R. J. E.; Watterson, M. P.; Edwards,
A. A.; Ansell, C. W. G.; Tranter, G. E.; Fleet, G. W. J.
Tetrahedron: Asymmetry 2004, 15, 627–638.
19. Nomura, N.; Taira, A.; Tomioka, T.; Okada, M. Macro-
molecules 2000, 33, 1497–1499.
20. (a) Okamoto, Y. Polym. Prepr., Am. Chem. Soc., Div.
Polym. Chem. 1984, 25, 264–265; (b) Brzezinska, K.;
Szymanski, R.; Kubisa, P.; Penczek, S. Makromol. Chem.,
Rapid Commun. 1986, 7, 1–5; (c) Tokar, R.; Kubisa, P.;
Penczek, S.; Dworak, A. Macromolecules 1994, 27, 320–
322.
References
1. Ha, C. S.; Gardella, J. A. Chem. Rev. 2005, 105, 4205–
4232.
21. Aspinall, H. C.; Dwyer, J. L. M.; Greeves, N.; McIver,
E. G.; Woolley, J. C. Organometallics 1998, 17, 1884–
1888.
2. Okada, M. Prog. Polym. Sci. 2002, 27, 87–133.
3. Uhrich, K. E.; Cannizzaro, S. M.; Langer, R. S.; Shake-
sheff, K. M. Chem. Rev. 1999, 99, 3181–3198.