A stereoselective approach to phosphodiester-linked oligomers of the repeating unit of Escherichia coli K52 capsular polysaccharide containing β-D-fructofuranosyl moieties

Article abstract of DOI:10.1016/j.tetasy.2004.11.051

A stereoselective synthesis of a dimer, β-D-Fruf-(2→2)-α-D- Galp-(1-PO₃H-3)-[β-D-Fruf-(2→2)]-D-Galp, of the repeating unit of the K52 type CPS of E. coli is described. The β-fructofuranosyl residue was introduced in a DMTST-promoted coupling us

Full text of DOI:10.1016/j.tetasy.2004.11.051

Tetrahedron:
Asymmetry
Tetrahedron: Asymmetry 16 (2005) 121–125
A stereoselective approach to phosphodiester-linked oligomers
of the repeating unit of Escherichia coli K52
capsular polysaccharide containing b-D-fructofuranosyl moieties
Stefan Oscarson* and Fernando W. Sehgelmeble
Department of Organic Chemistry, Arrhenius Laboratory, Floor 6, Stockholm University, S-106 91 Stockholm, Sweden
Received 26 October 2004; accepted 22 November 2004
Available online 25 December 2004
Abstract—A stereoselective synthesis of a dimer, b-D-Fruf-(2!2)-a-D-Galp-(1-PO3H-3)-[b-D-Fruf-(2!2)]-D-Galp, of the repeating
unit of the K52 type CPS of E. coli is described. The b-fructofuranosyl residue was introduced in a DMTST-promoted coupling
using a 1,4-TIPS-bridged thiofructofuranoside donor and a 2-OH TMSE galactoside acceptor affording exclusively the b-linked
disaccharide. Protecting group manipulation of this disaccharide yielded both a 3-OH acceptor and a reducing disaccharide, which
were linked via a phosphate diester bridge using H-phosphonate chemistry. The hemiacetal is present only as the a-anomer, why
phosphonylation yielded stereoselectively the a-H-phosphonate monoester. Activation of the latter with pivaloyl chloride in the
presence of the 3-OH disaccharide acceptor and subsequent I2-oxidation gave the target dimer in good yield.
Ó 2004 Elsevier Ltd. All rights reserved.
1. Introduction
omitted.2 We have recently developed a method for ste-
reoselective synthesis of b-fructofuranosides.3 Herein we
show that this method is applicable also to the synthesis
of the repeating unit of E. coli K52 CPS, and that the
resulting disaccharide allows conversion both to an
acceptor and an anomeric H-phosphonate monoester
to facilitate the formation of oligomers.
Bacterial polysaccharides, even with small repeating
units, often contain substantial structural complexity
with many synthetic challenges. The capsular polysac-
charide (CPS) of E. coli serotype K52 composed of
disaccharide repeating units is no exception (Fig. 1).1
Apart from a complex acylation pattern and being con-
nected via anomeric phosphate diester linkages the
repeating unit also contains a b-fructofuranosidic link-
age, which so far has not been possible to synthesise
chemically in a stereoselective manner. Hence, when
synthesis of a dimer structure of the deacylated polysac-
charide was attempted earlier the fructose part was
2. Results and discussion
To make a convergent synthesis possible, where both the
acceptor and the elongating monomer could be obtained
from the same precursor, the trimethylsilylethyl (TMSE)
glycoside of galactose4 was chosen as starting material.
Benzylidenation to give 1 followed by regioselective
tin-mediated p-methoxybenzylation5 or acetylation
afforded 2 and 3, respectively, with a free 2-OH ready
for the introduction of the fructofuranosyl residue
(Scheme 1). Attempts to use the internal aglycon deliv-
ery approach in this coupling proved fruitless.6–8 How-
ever, employing our fructofuranosyl donor 4,3 in
which the silane bridge prevents the donor attack from
the a-side and thus the formation of a-glycosides, and
DMTST as promoter, the b-linked disaccharides 5 and
6 were obtained stereoselectively in 80% and 89% yield,
respectively. To stabilise the acid-labile fructofuranosi-
dic linkage during subsequent manipulations, the silyl
O
||
→
α
3)- -
D
-Galp-(1–O–P–O–
2
|
OH
↑
2
β-
D
-Fruf
Figure 1. Structure of the deacylated repeating unit of E. coli K 52
CPS.1
*
Corresponding author. Tel.: +46 8 162480; fax: +46 8 154908; e-mail:
s.oscarson@organ.su.se
0957-4166/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2004.11.051

122
S. Oscarson, F. W. Sehgelmeble / Tetrahedron: Asymmetry 16 (2005) 121–125
Ph
Ph
O
O
O
O
O
OTMSE
iv,v
O
iii
RO
O
RO
TMS
BnOO
O
TBDMSO
OH
BnO
O
SEt
O
TBDMSO
1 R = H
i
ii
2 R = pMBn (70%)
3 R = Ac (80%)
O
O
TIPS
O
Si
Si
5 R = pMBn (80%)
6 R = Ac (89%)
O
Ph
4
O
OAc
O
AcO
AcO
HO
OAc
O
O
O
vi,v
vii
OTMSE
pMBnO
AcO
OTMSE
OTMSE
pMBnO
AcO
BnO O
O
BnO O
O
BnO O
O
AcO
OAc
7 (85%)
OAc
8 (70%)
OAc
9 (60%)
OAc
OAc
AcO
˚
Scheme 1. Reagents and conditions: (i) Bu2SnO, p-MBnCl, Bu4NI, CH3CN; (ii) AcCl, CH2Cl2/pyridine (4:1), 0 °C; (iii) DMTST, CH2Cl2, 4 A MS;
(iv) TBAF, THF; (v) AcCl, CH2Cl2/pyridine (1:1); (vi) 60% AcOH, 70 °C; (vii) DDQ, CH2Cl2.
groups in 5 were removed by fluoride treatment and the
resulting triol acetylated (!7). The chemical shift of the
fructofuranosidic anomeric C-2 in 7 is d ꢀ 102 ppm,
clearly indicating a b-linkage.3,9 The benzylidene acetal
was also removed at this stage and substituted with acet-
yl protecting groups to give 8. Subsequently the p-meth-
oxybenzyl group was cleaved, without affecting any of
the glycosidic linkages, by DDQ treatment to afford
the key precursor 9, which can either be used directly
as an acceptor or converted into various donors.
to the 63% yield obtained in the formation of the non-
fructosylated dimer.2
3. Conclusion
In conclusion, a stereoselective synthesis of a dimer of
the repeating unit of the E. coli K52 CPS has been
accomplished using a newly developed b-directing
fructofuranosyl donor and H-phosphonate chemistry.
The pathway also includes the possibility of continued
synthesis of oligomers.
If oligomers are to be constructed an acid-stable tempo-
rary protecting groups (e.g., a chloroacetate) can be
introduced at the free 3-OH before further transforma-
tion. However, at this stage our main interest was to de-
velop a methodology for the stereoselective construction
of the phosphate diester linkage and 9 was consequently
simply acetylated and the TMSE glycoside subsequently
removed by TFA-treatment (Scheme 2). Fortunately,
the resulting hemiacetal 10, as is evident from
NMR (d 5.45 (d, J 3.4 Hz, H-10)), was found to exist
exclusively as the a-anomer, which could be phosphonyl-
ated10 without anomerisation to give the a-H-phospho-
nate monoester 11 (d 5.85 (dd, J 3.2 Hz, JH,P 8.5 Hz, H-
10)) in acceptable yield. Finally coupling of 9 and 11
using standard pivaloyl chloride activation followed by
I2/H2O oxidation10 smoothly afforded the target phos-
phate diester 12 in 55% yield, which can be compared
4. Experimental
4.1. General
CH2Cl2 was distilled from CaH2 and stored over mole-
˚
cular sieves 4 A. Organic solutions were dried over
MgSO4, before concentration under reduced pressure
and at temperature below 40 °C (water bath). TLC
was performed on silica gel F254 (E. Merck) with detec-
tion by UV-light and/or charring with 8% H2SO4 or
AMC (ammonium molybdate 10 g, cerium(IV)sulfate
2 g, dissolved in aq 10% H2SO4 2 L). Silica gel (Si-60
35–70 lm, MilliporeÒ) was used for column chromato-
graphy. NMR spectra were recorded in CDCl3 (internal
OAc
AcO
OAc
OAc
AcO
AcO
Et3N+H
AcO
AcO
HN+Et3
OAc
O
O
O
AcO
O
O
P
AcO
O
ii
O
i
O
BnO
O
iii
BnO
O
O
O
OH
OAc
BnO
OTMSE
9
O
AcO
AcO
O
P
H
O-
AcO
O-
O
O
BnO
O
AcO
OAc
10 (68%)
OAc
OAc
11 (50%)
OAc
OAc
OAc
OAc
12 (55%)
Scheme 2. Reagents and conditions: (i) (a) AcCl, CH2Cl2/pyridine (1:1); (b) TFA–CH2Cl2 (2:1), 0 °C; (ii) (a) PCl3, imidazole, Et3N, MeCN;
(b) Et4NHCO3, H2O; (iii) (a) 9, Piv-Cl, pyridine; (b) I2, H2O, ꢁ40 °C.

S. Oscarson, F. W. Sehgelmeble / Tetrahedron: Asymmetry 16 (2005) 121–125
123
Me4Si, d = 0.00) at 25 °C unless otherwise stated, using
a Varian 300 MHz or 400 MHz instrument.
110.25, 123.55–146.75. 1H NMR, d 0.02 (s, 9H), 0.09 (s,
6H), 0.82–1.18 (m, 39H), 3.29 (s, 1H), 3.50 (m, 3H),
3.74–4.01 (m, 6H), 3.79 (s, 3H), 4.22–4.32 (m, 2H), 4.34
(d, 1H, J 7.6 Hz), 4.44 (m, 2H), 4.56 (m, 4H), 4.94 (d,
1H, J 12.4 Hz), 5.38 (s, 1H), 6.8–7.6 (m, 14H).
4.2. 2-(Trimethylsilyl)ethyl 4,6-O-benzylidene-3-O-p-
methoxybenzyl-b-D-galactopyranoside 2
Bu2SnO (1.06 g, 2.25 mmol) was added to a solution of
compound 1 (1.3 g, 3.53 mmol) in MeOH (40 mL). After
refluxing for 1 h the reaction mixture became clear. The
solution was allowed to attain room temperature, then
concentrated, co-evaporated three times with toluene
(20 mL) and dried in vacuum for 1 h. p-MBnCl
(0.38 mL, 2.83 mmol) and Bu4NI were added to a solu-
tion of the residue in dried MeCN (40 mL). The reaction
mixture was warmed to 100 °C and then stirred for 2 h
after which MeOH (5 mL) was added. The mixture was
concentrated and the residue re-dissolved in CH2Cl2
(50 mL), washed with H2O, dried, concentrated and the
residue purified by silica gel chromatography (toluene–
EtOAc 3:1) to afford 2 (1.2 g, 2.4 mmol, 70%). 13C
NMR, d ꢁ1.40, 18.16, 55.27, 66.63, 67.01, 69.31, 70.03,
4.5. 2-(Trimethylsilyl)ethyl [3-O-benzyl-6-O-tert-butyldi-
methylsilyl-1,4-O-(1,1,3,3-tetraisopropyldisiloxane-1,3-
diyl)-b-D-fructofuranosyl]-(2!2)-4,6-O-benzylidene-3-O-
acetyl-b-D-galactopyranoside 6
A solution of 3 (57 mg, 0.139 mmol), 4 (93 mg,
0.139 mmol) and DTBMP (28 mg, 0.139 mmol) in
CH2Cl2 (8 mL) containing powdered molecular sieves
˚
(4 A) was stirred for 15 min at room temperature under
an Ar atmosphere. DMTST (144 mg, 0.56 mmol) was
then added to the mixture and the stirring continued
for 20 min. Et3N (0.2 mL) was then added and the mix-
ture was filtered through Celite and concentrated. The
crude mixture was applied to a silica gel column and
eluted with toluene–EtOAc 18:1 to yield 6 (126 mg,
0.124 mmol, 89%). 13C NMR, d ꢁ5.27, ꢁ5.23, ꢁ1.54,
15.43–16.68, 20.10–33.03, 63.39, 64.76, 67.08, 68.95,
70.66, 70.99, 74.91, 75.05, 75.15, 80.35, 84.40, 88.71,
102.00, 104.29, 111.43, 127.63–140.22, 172.01.
1
71.06, 73.21, 78.77, 101.16, 102.44, 113.83–159.33. H
NMR, 0.01 (s, 9H), 0.95 (m, 2H), 2.42 (d, 1H, J 1.6 Hz),
3.33 (d, 1H, J 1.1 Hz), 3.44 (dd, 1H, J 3.5 Hz, J 9.6 Hz),
3.52 (m, 1H), 3.78 (s, 3H), 3.93 (m, 4H), 4.28 (d, 1H, J
7.6 Hz), 4.67 (q, 2H), 5.45 (s, 1H), 6.80–7.55 (m, 9H).
4.6. 2-(Trimethylsilyl)ethyl (1,4,6-tri-O-acetyl-3-O-benz-
yl-b-D-fructofuranosyl)-(2!2)-4,6-O-benzylidene-3-O-p-
methoxybenzyl-b-D-galactopyranoside 7
4.3. 2-(Trimethylsilyl)ethyl 4,6-O-benzylidene-3-O-acet-
yl-b-D-galactopyranoside 3
Acetyl chloride (0.22 mL, 2.27 mmol) in CH2Cl2
(0.2 mL) was added, at 0 °C and under Ar atmosphere
to a solution of compound 1 (856 mg, 2.32 mmol) in
CH2Cl2–pyridine (4:1, 5 mL). After stirring for 1 h the
reaction was diluted with CH2Cl2 (10 mL), the organic
phase was washed with H2O, NaHCO3 (saturated aq),
H2O, dried, concentrated and the product purified by
silica gel chromatography (toluene–EtOAc 3:1) to give
3 (769 mg, 1.87 mmol, 80%). 13C NMR, d ꢁ1.41,
18.11, 20.94, 66.21, 67.14, 68.25, 68.94, 73.40, 73.80,
100.71, 102.51, 126.26–137.81, 170.95. 1H NMR, d
0.01 (s, 9H), 0.95 (m, 2H), 2.14 (s, 3H), 3.51 (m, 2H),
4.00 (m, 3H), 4.37 (m, 3H), 4.83 (dd, 1H, J 3.6 Hz, J
10.4 Hz), 5.50 (s, 1H), 7.34–7.52 (m, 5H).
TBAF (1.4 mL, 1 M in THF) was added to a solution of
disaccharide 5 (0.37 g, 0.34 mmol) in THF (5 mL). After
stirring for 2 h the reaction mixture was diluted with
CH2Cl2 (30 mL), washed with H2O, dried, concentrated
and the residue was subjected to silica gel chromatogra-
phy (CHCl3–MeOH 18:1) to afford 2-(trimethylsilyl)-
ethyl
(3-O-benzyl-b-D-fructofuranosyl)-(2!2)-4,6-O-
benzylidene-3-O-p-methoxybenzyl-b-D-galactopyrano-
side, which was dissolved in pyridine–CH2Cl2 1:1
(5 mL) and acetyl chloride (0.24 mL, 3.4 mmol) in
CH2Cl2 (0.5 mL) was added at 0 °C and under an Ar
atmosphere. The reaction mixture was stirred for 2 h at
room temperature, then diluted with CH2Cl2 (20 mL)
and washed with NaHCO3 (saturated aq) and H2O,
dried, concentrated and purified by silica gel chromato-
graphy (toluene–EtOAc 6:1) to give 7 (0.25 g, 0.29 mmol,
85% after two steps). 13C NMR, d ꢁ1.51, 20.85, 20.90,
55.26, 64.62, 65.00, 66.39, 66.99, 69.25, 69.75, 70.92,
72.43, 73.30, 75.10, 77.70, 78.55, 80.03, 101.07, 101.85,
102.17, 113.74–137.90, 169.48, 170.10, 170.82. 1H
NMR, d 0.01 (s, 9H), 1.01 (m, 2H), 1.90 (s, 3H), 2.01
(s, 6H), 3.27 (s, 1H), 3.46 (dd, 1H, J 3.4 Hz, J 8.9 Hz),
3.58 (m, 1H), 3.75 (s, 3H), 3.89 (m, 4H), 4.11(d, 1H J
7.6 Hz), 4.14 (d, 1H, J 4.0 Hz), 4.25 (d, 1H, J 11.1 Hz),
4.32 (d, 1H, J 7.6 Hz), 4.37 (m, 4H), 4.52 (m, 4H), 5.34
(s, 1H), 5.67 (t, 1H, J 8.6 Hz), 6.78–7.5 (m, 14H).
4.4. 2-(Trimethylsilyl)ethyl [3-O-benzyl-6-O-tert-butyl-
dimethylsilyl-1,4-O-(1,1,3,3-tetraisopropyldisiloxane-1,3-
diyl)-b-D-fructofuranosyl]-(2!2)-4,6-O-benzylidene-3-O-
p-methoxybenzyl-b-D-galactopyranoside 5
A solution of 2 (327 mg, 0.67 mmol), 43 (350 mg,
0.52 mmol) and DTBMP (105 mg, 0.52 mmol) in CH2Cl2
˚
(8 mL) containing powdered molecular sieves (4 A) was
stirred for 15 min at room temperature under an Ar atmo-
sphere. DMTST (346 mg, 1.34 mmol) was added and the
stirring continued for 20 min. Et3N (0.3 mL) was then
added and the mixture was filtered through Celite and
concentrated. The residue was applied to a silica gel col-
umn and eluted with toluene–EtOAc 18:1 to yield 5
(0.46 g, 0.42 mmol, 80%). 13C NMR, d ꢁ5.28, ꢁ5.24,
ꢁ1.50, 12.29, 12.79, 13.36, 13.71, 17.01–18.01, 25.75,
36.05, 50.56, 63.08, 64.56, 65.99, 67.60, 68.39, 69.59,
71.67, 73.59, 76.61, 78.25, 82.83, 87.68, 99.94, 101.58,
4.7. 2-(Trimethylsilyl)ethyl (1,4,6-tri-O-acetyl-3-O-benz-
yl-b-D-fructofuranosyl)-(2!2)-4,6-di-O-acetyl-3-O-p-meth-
oxybenzyl-b-D-galactopyranoside 8
Compound 7 (0.25 g, 0.29 mmol) in acetic acid (60%,
5 mL) was stirred at 70 °C for 1 h. The reaction mixture

124
S. Oscarson, F. W. Sehgelmeble / Tetrahedron: Asymmetry 16 (2005) 121–125
was concentrated and co-evaporated three times with
toluene (10 mL). The concentrate was dissolved in pyr-
idine–CH2Cl2 1:1 (5 mL) and AcCl (0.2 mL 2.8 mmol)
in CH2Cl2 (0.5 mL) was added at 0 °C and under an
Ar atmosphere. After stirring for 1 h at room tempera-
ture, the reaction mixture was diluted with CH2Cl2
(20 mL), washed with NaHCO3 (saturated aq), H2O,
dried and concentrated. The residue was purified by
silica gel chromatography (toluene–EtOAc 4:1) to give
8 (0.18 g, 0.20 mmol, 70%). 13C NMR, d ꢁ1.50, 18.03,
20.80, 20.80, 21.94, 55.29, 62.22, 64.55, 64.99, 66.25,
67.49, 70.11, 70.74, 71.15, 72.52, 75.06, 77.74, 77.83,
79.96, 102.09, 102.18, 113.50, 137.50, 169.59, 170.00,
(s, 3H), 2.04 (s, 3H), 2.07 (s, 3H), 2.09 (s, 3H), 2.13 (s,
3H), 4.01 (m, 5H), 4.19 (m, 3H), 4.34 (m, 1H), 4.44
(m, 1H), 4.59 (dd, 2H, J 11.8 Hz, J 22.8 Hz), 5.29 (m,
2H), 5.43 (dd, 1H, J 1.7 Hz, J 3.3 Hz), 5.45 (d, 1H, J
3.4 Hz), 7.23 (m, 5H).
4.10. Triethylammonium (1,4,6-tri-O-acetyl-3-O-benzyl-
b-D-fructofuranosyl)-(2!2)-3,4,6-tri-O-acetyl-a-D-galac-
topyranosyl hydrogenphosphonate 11
To a stirred solution of imidazole in MeCN (1 mL) at
0 °C was added PCl3 (11 lL, 0.122 mmol) and Et3N
(59 lL, 0.428 mmol). The stirring was continued for
15 min at the same temperature and a solution of com-
pound 10 (19 mg, 28 lmol) in MeCN (1 mL) was added
dropwise. After stirring at room temperature for 20 min,
the reaction was quenched by addition of 1 M TEAB
(0.163 mL), concentrated and the residue re-dissolved
in pyridine–Et3N 4:1 (5 mL) and concentrated. The res-
idue was taken up in CHCl3 and washed four times with
0.5 M TEAB, filtered through Na2SO4 (s), concentrated
and the residue was purified on a silica gel column
(CHCl3–MeOH 9:1+1% Et3N) to give 11 (12 mg,
14 lmol, 50%). 13C NMR, d 8.51, 20.67, 20.71, 20.74,
20.79, 20.90, 45.46, 61.57, 64.13, 65.03, 67.09, 67.99,
68.36, 68.72, 77.46, 80.83, 94.50 (d, JC-1,P 5.3 Hz),
103.20, 128.06–137.50, 169.79, 170.19, 170.31, 170.52,
1
170.53, 170.59, 170.73. H NMR, d 0.01 (s, 9H), 1.00
(m, 2H), 1.87 (s, 3H), 1.98 (s, 3H), 1.99 (s, 3H), 2.03
(s, 3H), 2.09 (s, 3H), 3.47 (dd, 1H, J 2.8 Hz, J 9.2 Hz),
3.61, (m, 2H), 3.73 (s, 3H), 3.87 (m, 2H), 4.06 (m,
3H), 4.27 (m, 3H), 4.56 (m, 2H), 5.48 (d, 1H, J
2.9 Hz), 5.60 (t, 1H, J 8.6 Hz), 6.79–7.31 (m, 9H).
4.8. 2-(Trimethylsilyl)ethyl (1,4,6-tri-O-acetyl-3-O-benz-
yl-b-D-fructofuranosyl)-(2!2)-4,6-di-O-acetyl-b-D-galac-
topyranoside 9
DDQ (45 mg, 0.20 mmol) and H2O (6 drops) were added
to a solution of disaccharide 8 (0.132 g, 0.15 mmol) in
CH2Cl2 (10 mL). The mixture was stirred overnight, then
diluted with CH2Cl2 (20 mL) and washed with NaHCO3
(saturated aq) and H2O, dried, concentrated and the res-
idue purified on a silica gel column (toluene–EtOAc 4:1)
to yield 9 (80 mg, 92 lmol, 60%). 13C NMR, d ꢁ1.49,
18.15, 20.72, 20.78, 20.82, 20.91, 61.97, 62.74, 65.86,
67.84, 68.88, 70.88, 72.10, 73.18, 74.50, 77.05, 78.78,
1
170.80. H NMR, d 1.29 (t, 9H), 2.00 (s, 3H), 2.02 (s,
3H), 2.03 (s, 3H), 2.05 (s, 3H), 2.08 (s, 3H), 2.14 (s,
3H), 2.96 (q, 6H), 3.82 (d, 1H, J 11.8 Hz), 3.95 (m,
8H), 4.27 (m, 2H), 4.42 (m, 7H), 5.34 (dd, 1H), 5.45
(d, 1H, J 2.7 Hz), 5.51 (t, 1H, J 7.9 Hz), 5.85 (dd, 1H,
J1,2 3.2 Hz, JH-1,P 8.5 Hz), 7.05 (d, 1H, J 640 Hz,
PO3Hꢁ), 7.24 (m, 5H). 31P NMR, d 1.36 (dd, J
640 Hz, J 8.5 Hz).
1
82.77, 101.80, 103.88, 128.19–128.61, 169.87, 170.5. H
NMR, d 0.10 (s, 9H), 1.00 (m, 2H), 1.90 (s, 3H), 1.99(s,
3H), 2.05 (s, 6H), 2.1 (s, 3H), 3.50 (m, 1H), 3.70 (m,
6H), 4.08 (m, 7H), 4.61 (s, 2H), 5.35 (d, 1H, J 3.3 Hz),
5.40 (t, 1H, J 6.8 Hz), 7.20 (m, 5H).
4.11. 2-(Trimethylsilyl)ethyl (1,4,6-tri-O-acetyl-3-O-benz-
yl-b-D-fructofuranosyl)-(2!2)-(3,4,6-tri-O-acetyl-a-D-
galactopyranosyl phosphate)-(1!3)-[(1,4,6-tri-O-acetyl-
3-O-benzyl-b-D-fructofuranosyl)-(2!2)]-4,6-di-O-acetyl-
b-D-galactopyranoside triethylammonium salt 12
4.9. (1,4,6-Tri-O-acetyl-3-O-benzyl-b-D-fructofuranosyl)-
(2!2)-3,4,6-tri-O-acetyl-a-D-galactopyranose 10
Acetyl chloride (20 lL, 0.28 mmol) in CH2Cl2 (0.2 mL)
was added, at 0 °C and under an Ar atmosphere, to a
solution of compound 9 (52 mg, 70 lmol) in pyridine–
CH2Cl2 (1:1, 2 mL). After stirring for 1 h at room tem-
perature, the reaction mixture was diluted with CH2Cl2
(20 mL), washed with NaHCO3 (saturated aq), dried,
concentrated and purified by silica gel chromatography
(toluene–EtOAc 3:1) to give 2-(trimethylsilyl)ethyl
(1,4,6-tri-O-acetyl-3-O-benzyl-b-D-fructofuranosyl)-(2!
2)-3,4,6-tri-O-acetyl-b-D-galactopyranoside (42 mg, 61
lmol, 90%). TFA (1 mL) was added, at 0 °C and under
an Ar atmosphere, to a solution of the acetylated prod-
uct (32 mg, 46 lmol) in CH2Cl2 (0.5 mL). After stirring
for 1 h at 0 °C, n-propylacetate (1 mL) and toluene
(1 mL) were added. The mixture was concentrated, co-
evaporated with toluene (2 mL) and the residue purified
on a silica gel column to afford 10 (21 mg, 30 lmol,
75%). 13C NMR, d 20.67, 20.74, 20.81, 61.81, 63.59,
63.77, 66.32, 68.35, 68.54, 68.79, 72.87, 76.14, 78.89,
81.52, 92.59, 104.34, 127.88–136.99, 169.83, 170.00,
Pivaloyl chloride (4.3 lL, 35 lmol) was added, under an
Ar atmosphere, to a solution of compounds 9 (12 mg,
16.2 lmol) and 11 (12 mg, 14.8 lmol) in pyridine
(0.4 mL). After stirring for 30 min the mixture was cooled
to ꢁ 40 °C and water (15 lL) and iodine (4 mg, 16.6 mol)
were added. The temperature was allowed to raise to
0 °C, when the reaction mixture was partitioned between
CHCl3 and 1 M Na2S2O3. The organic phase was washed
twice with 1 M TEAB, filtered through Na2SO4 (s) and
concentrated. The product was purified using silica gel
chromatography (CHCl3–MeOH 9:1+0.5% Et3N) to
yield 12 (13 mg, 8.18 lmol, 55%). 13C NMR, ꢁ1.5, 8.7,
17.79, 20.76, 20.88, 21.01, 45.32, 61.20, 63.56, 64.03,
64.78, 65.16, 65.36, 66.64, 67.00, 68.10, 68.71, 69.05,
69.85, 70.35, 71.22, 71.91, 72.56, 73.92, 74.09, 74.60,
75.64, 77.23, 80.20, 80.37, 94.70 (JCꢁ1,P 5.3 Hz), 101.55,
101.99, 103.3, 127.49–138.49, 169.40, 169.51, 170.12,
1
170.22, 170.40, 170.59, 170.75. H NMR (assorted sig-
nals), d 0.01 (s, 9H), 0.82 (m, 2H), 1.01 (t, Et3N), 1.98–
2.19 (m, 33H), 3.6–4.85 (m, 28H), 5.63 (t, 1H, J 8.6 Hz),
5.78 (d, 1H, J 2.2 Hz), 5.89 (dd, 1H, J1,2 3.2 Hz, JH,P
1
170.22, 170.54, 170.81. H NMR, d 1.94 (s, 3H), 2.01

S. Oscarson, F. W. Sehgelmeble / Tetrahedron: Asymmetry 16 (2005) 121–125
125
8 Hz). 31P NMR, d ꢁ1.49 (dd, J 6.0 Hz, J 8.0 Hz). MAL-
DI-TOF MS: Calcd for C65H88O35PSi: 1488.43; Found:
1511.43 [M+Na]; 1527.50 [M+K].
4. Jansson, K.; Ahlfors, S.; Frejd, T.; Kihlberg, J.; Magnus-
son, G. J. Org. Chem. 1988, 53, 5626–5647.
5. Reka¨ı, E.-D.; RubinStenn, G.; Mallet, J.-M.; Sinay, P.
¨
Synlett 1998, 831–834.
6. Krog-Jensen, C. Doctoral Thesis, Stockholm University
1997.
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