Selectively protected galactose derivatives for the synthesis of branched oligosaccharides

Article abstract of DOI:10.1016/j.tet.2004.02.054

Synthesis and characterization of several new anomerically pure galactose derivatives, based on simple and effective protective group manipulations of benzyl β-D-galactopyranoside, are reported. The monosaccharides described contain selectively protected/deprotected hydroxyl functionalities at their 1,2,3,4- and 6-positions rendering them useful as building blocks for construction of branched oligosaccharides.

Full text of DOI:10.1016/j.tet.2004.02.054

Tetrahedron 60 (2004) 3653–3661
Selectively protected galactose derivatives for the synthesis
of branched oligosaccharides
†
‡
a,b
,
‡
, ,
a,b
a
Juho O. Lehtila, Mattias U. Roslund
and Reko Leinoa,b
, ,
*
*
¨
Reko L. Lehtila,
¨
aBiotie Therapies Corp., Viikinkaari 9, FIN-00710 Helsinki, Finland
b
˚
Department of Organic Chemistry, Abo Akademi University, FIN-20500 Abo, Finland
˚
Received 14 November 2003; revised 3 February 2004; accepted 25 February 2004
Abstract—Synthesis and characterization of several new anomerically pure galactose derivatives, based on simple and effective protective
group manipulations of benzyl b-D-galactopyranoside, are reported. The monosaccharides described contain selectively protected/depro-
tected hydroxyl functionalities at their 1,2,3,4- and 6-positions rendering them useful as building blocks for construction of branched
oligosaccharides.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
In this regard, galactose is a particularly interesting
monosaccharide due to its occurrence as a building block
in various biological structures. In plants it is one of the
main constituents of galactoglucomannans6 and arabino-
galactans.7 In humans, it is one of the main constituents of
human milk oligosaccharides8 and polylactosamines.9 The
latter structures consisting of N-acetyllactosamine units
[b-D-galactopyranosyl-(1!4)-N-acetyl-D-glucosamine]
with galactose residues at their non-reducing ends have been
extensively studied as anti-inflammatory agents. Further-
more, the axial 4-OH group of galactose renders it an
optimal starting material for exploitation of various
protective group strategies. Here, we report the preparation
of some new anomerically pure galactose derivatives,
obtained by simple and efficient protective group manipula-
tions of benzyl b-D-galactopyranoside (1). The present
paper continues our recently initiated studies on the
synthesis and conformational behavior10 of galactose-
containing mono- and oligosaccharides. The galactose
derived monosaccharides described here contain selectively
protected hydroxyl functionalities in their 1,2,3,4- and/or
6-positions, thus potentially serving as useful building
blocks for the construction of branched oligosaccharide
libraries.
Carbohydrates and glycoconjugates play a central role in
various biological recognition processes.1 Recent years
have seen a rapid extension of the field of glycobiology with
carbohydrate-derived therapeutics now entering clinical
trials.2 The limited availability of pure and structurally
defined specific oligosaccharides nevertheless remains a
major impediment to the study of carbohydrates in
biological applications. Besides the traditional chemical
synthesis techniques, enzymatic3 and automated solid-phase
synthetic4 methods have been successfully applied for
constructing stereo- and regiospecific glycosidic linkages in
complex oligosaccharide structures. However, both of these
methods suffer from limitations in scale-up. An additional
concern is the inability of fermentation techniques to
produce unnatural branched oligosaccharides. Thus, in
many cases, conventional organochemical synthesis
remains the method of choice for the preparation of
multigram amounts of chemically defined oligosaccharides
and the improvement and development of efficient protec-
tive group strategies and purification methods remains an
important and actively investigated area of carbohydrate
chemistry.5 Of particular significance is the preparation of
partially protected carbohydrate building blocks, where the
protecting groups can be manipulated such that each can be
selectively removed during the course of the synthetic route.
2. Results and discussion
Benzyl b-D-galactopyranoside (1) was prepared from
b-D-galactose pentaacetate in 66% overall yield following
a slightly modified literature procedure.11 Protecting group
manipulations of 1 are summarized in Scheme 1. The
following strategy was designed in order to create
selectively deprotected hydroxyl functionalities on the
1,2,3,4- and 6-positions of a fully protected galactose
Keywords: Galactose; Protecting groups; Monosaccharides;
Oligosaccharides.
*
Corresponding authors. Tel.: þ358-2-2154132; fax: þ358-2-2154866;
e-mail addresses: reko.leino@abo.fi; reko.lehtila@csc.fi
Present address: CSC-Scientific Computing Ltd, PO Box 405, FIN-02101
†
Espoo, Finland.
Present address: Department of Organic Chemistry Abo Akademi
‡
˚
˚
University, FIN-20500 Abo, Finland.
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.02.054

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R. L. Lehtila et al. / Tetrahedron 60 (2004) 3653–3661
3654
Scheme 1. (a) TBDMSCl, DBU, CH2Cl2, 0 8C then rt, 48 h, 98% (2); or TBDPSCl, imidazole, DMF, 0 8C then rt, 24 h, 60% (3); (b) 2,2-dimethoxypropane,
TsOH, rt, 2–3 h, 93% (4) or 71% (5); (c) acetic anhydride, Et3N or pyridine, CH2Cl2, rt, 12–48 h, 74% (6) or 93% (7); or BzCl, pyridine, rt, 6 h, 99%.
backbone: in the first step, the 6-O-position of 1 was
protected as silyl ethers of varying acid lability (TBDMS or
TBDPS). Next, the 3- and 4-hydroxyls were protected using
the conventional isopropylidene ketal formation. Finally,
the 2-hydroxyl group was protected as the base labile
acetate or benzoate.
6-O-TBDPS analogue, benzyl 6-O-(tert-butyldiphenyl-
silyl)-b-D-galactopyranoside (3)14,15 was prepared as
described in the literature and isolated in 60% yield after
purification by flash chromatography. Acid catalyzed
reactions of 2 and 3 with 2,2-dimethoxypropane gave the
corresponding isopropylidene ketals 4 and 5 in 93 and 71%
yields, respectively, after purification by flash chroma-
tography. Compound 5 has been prepared and characterized
previously by Redlich and co-workers.14a Both compounds
4 and 5 were converted into the corresponding benzyl
6-O-(tert-butyldimethylsilyl)-3,4-O-isopropylidene-b-D-
galactopyranoside 2-O-acetates 6 and 7 according to
standard procedures. Compound 5 was additionally converted
Thus, reaction of 1 with TBDMSCl and DBU in
dichloromethane gave the 6-O-protected silyl ether, benzyl
6-O-(tert-butyldimethylsilyl)-b-D-galactopyranoside (2) in
98% isolated yield after purification by flash chroma-
tography. The corresponding b-D-glucopyranoside has
been described previously.12,13 The previously reported
Scheme 2. (a) Bu4NF·3H2O, THF, 0 8C then rt, 1.5 h, 84%; (b) As (a) then Dowex DR-2030, MeOH, 22 h, 65% (10) or 55% (11); (c) 10% Pd/C, cyclohexene,
EtOH, reflux, 72 h, 93%; (d) CCl3CN, DBU, CH2Cl2, 0 8C, 2 h, 78%.

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R. L. Lehtila et al. / Tetrahedron 60 (2004) 3653–3661
3655
Scheme 3. (a) 98% CF3COOH, CH2Cl2, 0 8C then rt, 30 min, 76%.
into the corresponding 2-O-benzoate 8. The 6-O-TBDMS
derivative 6 was isolated as a transparent oil in 74% yield
after purification by flash chromatography, while its
6-O-TBDPS analogue was conveniently purified by crystal-
lization from pentane to afford 7 as a bright white solid in
93% isolated yield. The benzoate 8 was obtained as a white
solid and in quantitative yield after standard work-up
procedures. Remaining trace impurities were removed by
column chromatography.
conveniently purified by precipitation from pentane to
obtain analytically pure product in 76% isolated yield.
In summary, we have prepared several new anomerically
pure b-D-galactopyranoside derivatives containing selec-
tively protected hydroxyl groups in the 1,2,3,4- and 6
positions of the galactose framework. All new compounds
have been fully characterized by elemental analysis, mass
1
spectrometry, polarimetry, as well as by H and 13C NMR
spectroscopy. A specific objective of this study was to
design a versatile and orthogonal protective group strategy
in a simple and efficient manner. First, the anomeric position
of galactose was protected as a conventional benzyl ether.
This protective group may later be easily removed by
hydrogenation under neutral conditions. The free 1-OH can
then potentially be further activated using various strategies
leaving the protected 2,3,4- and 6-positions intact. For
example, imidate,19 fluoride20 and thiophenyl21 activations
can be used for further glycosidations.
Selective deprotection sequences for the new compounds
6-8 are summarized in Schemes 2 and 3. In order to obtain a
1,2,3,4-protected galactose derivative with a free hydroxyl
group in the 6-position, the TBDMS group of 6 was cleaved
with Bu4NF in THF under standard conditions to yield
benzyl 2-O-acetyl-3,4-O-isopropylidene-b-D-galacto-
pyranoside (9) in 84% yield after purification by flash
chromatography.16 The 3,4,6-deprotected derivatives
benzyl 2-O-acetyl-b-D-galactopyranoside (10) and benzyl
2-O-benzoyl-b-D-galactopyranoside (11)17 were prepared
in 65 and 55% yields, respectively, by treating compounds 6
and 8 first with Bu4NF in THF to obtain the crude
desilylated products, which then were stirred overnight
with Dowex DR-2030 acidic ion-exchange resin in order to
cleave the 3,4-O-isopropylidene protection. Analytically
pure 10 and 11 were then conveniently obtained after
filtration of the acid catalyst, evaporation of the solvent
and crystallization from CHCl3 or pentane/EtOAc. In a
simplified approach, both 6-TBDMS and 3,4-O-isopropyl-
idene protective groups of 6 were successfully and
simultaneously cleaved by stirring 6 with Dowex
DR-2030 in MeOH overnight. Monitoring by TLC indicated
the formation of one major product after 17 h. Filtration of
the catalyst and evaporation of the solvent left an off-white
solid that was shown to consist of fairly pure 10 by 1H NMR
analysis. This batch was not purified further. The 2,3,4,6-
protected compound 2-O-acetyl-6-O-(tert-butyldimethyl-
silyl)-3,4-O-isopropylidene-D-galactopyranose (12), con-
taining a free hydroxyl group only in the anomeric
position, was prepared from 6 in 93% yield under standard
debenzylation conditions using Pd/C and cyclohexene
followed by subsequent purification by flash chroma-
tography. Compound 12 was converted to the corresponding
trichloroacetimidate 13 in 78% yield following standard
procedures.
Next, the 6-OH position was protected as a silyl ether,
removable in high yields by tetrabutylammonium fluoride.
The acid lability of the silyl ether may be tuned by choosing
properly substituted silyl chlorides as silylation reagents.
The 3,4-O-isopropylidine protection installed in the subse-
quent step may then be removed in nearly quantitative
yields with concomitant removal or retention of the
6-O-silyl ether protection. Galactose precursors containing
free 3- and 4-hydroxyl groups may be selectively glyco-
sidated in the 3-O-position using activated imidate22 or
halogenide23 donors. Likewise, selective 4-O-glycosida-
tions in the presence of free 3-OH groups have been
reported.24,25
In the final step of the strategy described herein, the 2-OH
position is protected as an acetyl or benzoyl ester. Thus,
both 2-O- and 6-O-glycosidations should be accessible with
the selectively removable 2-O-ester and 6-O-silyl ether
protection strategies.26 Compound 10, described in the
present work, containing only 2-O-acetyl protection in
addition to the 1-O-benzyl ether group, is in turn a suitable
candidate for either 3,6-O-27 or 4,6-O-diglycosidations and,
with its free 3,4,6-hydroxyl groups, a particularly interesting
model compound for intramolecular acetyl group migration
studies.28 This topic is currently under investigation in the
authors’ laboratories.
The TBDPS silyl ether group is considerably (<100 times)
more stable than the TBDMS group toward acid hydroly-
sis.18 Thus, the 3,4-O-isopropylidene protection of 7 was
successfully and selectively cleaved with CF3COOH in
CH2Cl2 leaving the protective groups in 1,2- and 6-positions
intact (Scheme 3). The desired benzyl 2-O-acetyl-6-O-(tert-
butyldiphenylsilyl)-b-D-galactopyranoside (14) containing
free hydroxyl groups in the 3,4-positions only was
3. Experimental
3.1. General remarks
All operations with air or moisture sensitive reagents and
materials were carried out under an argon atmosphere using

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R. L. Lehtila et al. / Tetrahedron 60 (2004) 3653–3661
3656
standard Schlenk and vacuum techniques. Solvents were
dried and distilled under argon prior to use when applicable
or purchased from commercial sources NMR spectra were
recorded on a JEOL JNM A 500 NMR spectrometer, unless
otherwise indicated, and referenced against tetramethyl-
silane or the solvent signal. The sample temperature was
maintained at 30 8C by a Jeol variable temperature unit. The
1H and 13C NMR spectra were recorded at 500.16 and
125.78 MHz, respectively, using a broadband 5 mm probe.
All 2D experiments were performed with an inverse 5 mm
probe with pulsed field gradient capability. For the complete
4.86, 4.68 (2H, d, J¼11.6 Hz, CH2Ph), 4.38 (1H, d, J¼
7.7 Hz, H-1), 3.84 (1H, dd, J¼0.8, 3.4 Hz, H-4), 3.73 (1H,
dd, J¼4.5, 11.7 Hz, Hb-6), 3.67 (1H, dd, J¼7.8, 11.7 Hz,
Ha-6), 3.59 (1H, ddd, J¼0.8, 4.5, 7.8 Hz, H-5), 3.53 (1H, dd,
J¼3.4, 9.9 Hz, H-3), 3.47 (1H, dd, J¼9.9, 7.7 Hz, H-2); dC
(125.78 MHz, CDCl3, 303 K); 139.3, 129.6, 129.6, 129.3
(Ph), 102.7 (C-1), 76.1 (C-3), 73.8 (C-2), 72.3 (C-5), 71.7
(CH2Ph), 69.6 (C-4), 61.9 (C-6); EIMS calcd for C13H19O6
[MþH]þ 271.1181. Found 271.1200. Anal. Calcd for
C13H18O6 (270.3): C, 57.77; H, 6.71. Found C, 56.76; H,
6.81.
1
assignment of the H and 13C NMR spectra of compounds
1-14, a combination of two-dimensional COSY, TOCSY,
HMBC and HMQC experiments were carried out. Inverse
detected 1H–13C 2D chemical shift correlation spectra were
acquired using the pulsed field gradient versions of HMBC
and HMQC. In the cases of severe signal overlapping, the
500.16 MHz 1H NMR spectra were finally analyzed by
PERCH software29 to perform complete spectral analyses.
Electron impact high resolution mass spectra (EIMS) were
obtained with Fisons ZabSpec mass spectrometer at 70 eV.
Polarimetric measurements were carried out using a Perkin
Elmer 241 Polarimeter with a cell volume of 1 mL and a cell
length of 10 cm. TLC analyses were performed using silica
gel F254 precoated aluminum sheets or glass plates and
visualized by charring with 25% H2SO4 in methanol or
methanol/orcinol and/or UV. Column chromatography was
performed using silica gel 60 optionally enriched with 0.1%
Ca to minimize hydrolysis of acid-labile protecting groups.
Microanalyses were conducted at the Department of
Microanalytics, University of Groningen, the Netherlands.
3.2.2. Benzyl 6-O-(tert-butyldimethylsilyl)-b-D-galacto-
pyranoside (2). To a solution of 1 (2.30 g, 8.52 mmol) in
CH2Cl2 (60 mL) was added tert-butyldimethylchlorosilane
(1.41 g, 9.35 mmol). The reaction mixture was stirred
for 30 min at ambient temperature and cooled to 0 8C. A
solution of DBU (1.40 mL, 9.37 mmol) in CH2Cl2 (10 mL)
was added during a period of 30 min and the reaction
mixture was stirred for 48 h at ambient temperature. Silica
gel was added to the reaction mixture and the solvents were
removed in vacuo. Flash column chromatography (silica gel
containing 0.1% Ca, CH2Cl2/MeOH, gradient elution) gave
pure 2 (3.22 g, 98%) as a white solid: [a]D22¼238.6 (c¼0.05
in CHCl3); dH (500.16 MHz, CDCl3, 303 K); 7.28–7.14
(5H, m, Ph), 4.80, 4.50 (2H, d, J¼11.6 Hz, CH2Ph), 4.18
(1H, d, J¼7.8 Hz, H-1), 3.85 (1H, ddd, J¼1.1, 3.3, 4.0 Hz,
H-4), 3.80 (1H, dd, J¼5.4, 10.5 Hz, Hb-6), 3.76 (1H, dd,
J¼6.9, 10.5 Hz, Ha-6), 3.61 (1H, ddd, J¼2.7, 7.8, 9.5 Hz,
H-2), 3.40 (1H, ddd, J¼3.3, 5.9, 9.5 Hz, H-3), 3.32 (1H,
ddd, J¼1.1, 5.4, 6.9 Hz, H-5), 3.25 (1H, d, J¼5.9 Hz,
OH-3), 3.06 (1H, d, J¼2.7 Hz, OH-2), 2.99 (1H, d, J¼
4.0 Hz, OH-4), 0.81 (9H, s, CMe3), 0.00 (6H, s, SiMe2); dC
(125.78 MHz, CDCl3, 303 K); 137.3, 128.6, 128.5, 128.2
(Ph), 102.1 (C-1), 75.2 (C-5), 73.9 (C-3), 71.7 (C-2),
70.9 (CH2Ph), 69.1 (C-4), 62.7 (C-6), 26.0 (CMe3), 18.5
(CMe3), 25.2, 25.5 (SiMe2); EIMS calcd for C15H23O6Si
[M2C(CH3)3]þ 327.1263. Found 327.1240. Anal. Calcd for
C19H32O6Si (384.5): C, 59.34; H, 8.39. Found C, 59.18; H,
8.42.
3.2. Synthesis and characterization of the
monosaccharides
3.2.1. Benzyl b-D-galactopyranoside (1). To a solution
of b-D-galactose pentaacetate (29.87 g, 76.52 mmol) in
˚
CH2Cl2 (300 mL) was added molecular sieves 4 A (30 g)
and benzyl alcohol (10.34 mL, 99.48 mmol). The reaction
mixture was cooled on an ice-bath and BF3·Et2O (19.39 mL,
153.04 mmol) was added dropwise during a period of
15 min. The reaction mixture was slowly warmed up to
ambient temperature and stirred for 20 h. The mixture was
cooled to 0 8C, neutralized with triethylamine, extracted
with CH2Cl2 and washed with water (3£200 mL). The
organic layer was filtered through paper, the solvents were
evaporated and the crude product was dried in vacuo. The
obtained benzyl 2,3,4,6-tetra-O-acetyl-b-D-galactopyrano-
side (42.05 g) was used in the subsequent step without
further purification. This product was dissolved in a mixture
of MeOH (1000 mL) and 1,4-dioxane (160 mL) and treated
with sodium methoxide (4.0 g, 74 mmol). The reaction
mixture was stirred at ambient temperature and monitored
by TLC indicating completion of the reaction after 22 h
(MeOH/CH2Cl2 1:5, Rf¼0.33 for the product). The reaction
mixture was neutralized with Dowex 50 W (Hþ form),
filtered and concentrated in a rotary evaporator. Solvents
were co-evaporated with toluene and the product obtained
was dried in vacuo. Column chromatography (silica gel,
MeOH/CH2Cl2, gradient elution) gave pure 1 (13.53 g,
overall yield 66% based on b-D-galactose pentaacetate) as
a white solid: [a]2D2¼231.4 (c¼0.14 in MeOH); dH
(500.16 MHz, CDCl3, 303 K); 7.44–7.30 (5H, m, Ph),
3.2.3. Benzyl 6-O-(tert-butyldiphenylsilyl)-b-D-galacto-
pyranoside (3). To an ice-cooled solution of 1 (5.10 g,
18.87 mmol) and imidazole (2.57 g, 37.74 mmol) in DMF
(50 mL) was added dropwise a solution of tert-butyldi-
phenylchlorosilane (5.19 g, 18.88 mmol) in DMF (25 mL).
The reaction mixture was stirred overnight at ambient
temperature. Monitoring by TLC indicated the disappear-
ance of nearly all starting material after 23 h. The reaction
was quenched by addition of saturated aqueous NaHCO3
(100 mL) and extracted with Et2O (3£80 mL). The com-
bined organics were washed with H2O (100 mL) and dried
over sodium sulphate. Evaporation of the solvents left a
yellowish oily foam (7.87 g) that was analyzed by 1H NMR
(250 MHz) in CDCl3 indicating the presence of the desired
product and tert-butyldiphenylsilanol in a 1:1 mixture.
Flash column chromatography (silica gel, dichloromethane/
methanol, gradient elution) gave pure 3 (5.75 g, 60%) as
1
confirmed by H and 13C NMR analysis. dH (500.16 MHz,
CDCl3, 303 K); 7.65–7.14 (15H, m, Ph), 4.78, 4.47 (2H, d,
J¼11.6 Hz, CH2Ph), 4.18 (1H, d, J¼7.8 Hz, H-1), 3.83,
(1H, dd, J¼0.8, 3.4 Hz, H-4), 3.82, (1H, dd, J¼5.7, 10.6 Hz,
Hb-6), 3.80 (1H, dd, J¼6.0, 10.6 Hz, Ha-6), 3.61 (1H, dd,

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R. L. Lehtila et al. / Tetrahedron 60 (2004) 3653–3661
3657
J¼7.8, 9.5 Hz, H-2), 3.40 (1H, dd, J¼3.4, 9.5 Hz, H-3), 3.38
(1H, ddd, J¼0.8, 5.7, 6.0 Hz, H-5), 0.99 (9H, s, CMe3); dC
(125.78 MHz, CDCl3, 303 K); 137.2–127.9 (Ph), 101.9
(C-1), 74.9 (C-5), 73.8 (C-3), 72.1 (C-2), 70.9 (CH2Ph), 69.2
(C-4), 63.4 (C-6), 27.0 (CMe3), 19.4 (CMe3). The
500.16 MHz NMR spectral data for 3 are consistent with
those reported previously for this compound.14
(548.7): C, 70.04; H, 7.35. Found C, 70.11; H, 7.26.
Residual fractions from the flash chromatography were
combined, evaporated to dryness and dried in vacuo to leave
a viscous off-yellow oil (1.43 g) consisting of three major
components as shown by TLC. Refluxing of this mixture for
24 h in MeOH/H2O (50:5 mL) and monitoring by TLC
indicated the conversion of one unidentified compound to 5.
The solvents were evaporated and the residual transparent
oil (1.26 g) purified by flash chromatography according to
the procedure described for the initial crude product (vide
supra) to afford an additional crop of 5 (0.98 g, 16%)
containing trace impurities, as confirmed by NMR, and
an off-yellow oil (165 mg, 3%) identified as benzyl 6-O-
(tert-butyldiphenylsilyl)-2,3-O-isopropylidene-b-D-galacto-
pyranoside by 1H and 13C NMR analyses: dH (500.16 MHz,
CDCl3, 303 K); 7.73–7.26 (15H, m, Ph), 4.90, 4.66 (2H,
d, J¼11.7 Hz, CH2Ph), 4.67 (1H, d, J¼7.9 Hz, H-1), 4.42
(1H, ddd, J¼1.2, 2.6, 3.3 Hz, H-4), 3.99 (1H, dd, J¼5.4,
10.5 Hz, Hb-6), 3.96 (1H, dd, J¼6.5, 10.5 Hz, Ha-6), 3.94
(1H, dd, J¼7.9, 9.5 Hz, H-2), 3.56 (1H, ddd, J¼1.2, 5.4,
6.5 Hz, H-5), 3.52 (1H, dd, J¼2.6, 9.5 Hz, H-3), 2.41 (1H, d,
J¼3.3 Hz, OH-4), 1.48, 1.46 (6H, s, CMe2), 1.08 (9H, s,
CMe3); dC (125.78 MHz, CDCl3, 303 K); 137.08–127.8
(Ph), 110.3 (CMe2), 101.1 (C-1), 79.2 (C-3), 76.0 (C-5),
73.1 (C-2), 69.9 (CH2Ph), 67.2 (C-4), 62.9 (C-6), 26.8
(CMe3), 26.8, 26.5 (CMe2), 19.2 (CMe3).
3.2.4. Benzyl 6-O-(tert-butyldimethylsilyl)-3,4-O-iso-
propylidene-b-D-galactopyranoside (4). To a solution of
compound 2 (5.20 g, 13.54 mmol) in 2,2-dimethoxypropane
(100 ml) was added in one portion p-TsOH·H2O (50 mg,
0.26 mmol). The reaction mixture was stirred at ambient
temperature under argon. The reaction was quenched after
3 h by neutralizing the solution with a mixture of Et3N and
dichloromethane (1:1). The solvents were evaporated and
the remaining transparent oil was dried in vacuo. Flash
column chromatography (silica gel containing 0.1% Ca,
EtOAc/toluene 5:100) gave pure 4 (5.34 g, 93%) as a white
solid: [a]D23¼217.9 (c¼0.12 in CHCl3); dH (500.16 MHz,
CDCl3, 303 K); 7.34–7.15 (5H, m, Ph), 4.80, 4.49 (2H, d,
J¼11.6 Hz, CH2Ph), 4.11 (1H, d, J¼8.3 Hz, H-1), 4.05 (1H,
dd, J¼2.2, 5.4 Hz, H-4), 3.91 (1H, dd, J¼5.4, 7.3 Hz, H-3),
3.82 (1H, dd, J¼7.2, 9.9 Hz, Hb-6), 3.79 (1H, dd, J¼5.8,
9.9 Hz, Ha-6), 3.66 (1H, ddd, J¼2.2, 5.8, 7.2 Hz, H-5), 3.49
(1H, dd, J¼7.3, 8.3 Hz, H-2), 1.40, 1.21 (6H, s, CMe2), 0.82
(9H, s, CMe3), 0.00 (6H, s, SiMe2); dC (125.78 MHz,
CDCl3, 303 K); 137.0, 128.6, 128.4, 128.0 (Ph), 110.0
(CMe2), 101.1 (C-1), 78.9 (C-3), 73.9 (C-5), 73.8 (C-2),
73.3 (C-4), 70.6 (CH2Ph), 62.2 (C-6), 28.3, 26.4 (CMe2),
26.0 (CMe3), 18.3 (CMe3), 25.2, 25.5 (SiMe2); EIMS
calcd for C21H33O6Si [M2CH3]þ 409.2046. Found
409.2049.
3.2.5. Benzyl 6-O-(tert-butyldiphenylsilyl)-3,4-O-isopro-
pylidene-b-D-galactopyranoside (5). To a solution of 3
(5.65 g, 11.1 mmol) in 2,2-dimethoxypropane (100 mL)
was added p-TsOH·H2O (50 mg). The reaction mixture
was stirred at ambient temperature. Monitoring by TLC
indicated the formation of three products. The reaction was
quenched after 2 h by neutralizing with Et3N in CH2Cl2 and
evaporated to dryness. The remaining off-white/yellow
foamy solid (7.61 g) was flash chromatographed (silica gel,
toluene/ethyl acetate, gradient elution) to afford the desired
product as a highly viscous colorless oil (4.55 g) in a
mixture with toluene, as confirmed by NMR. The residual
toluene was removed by co-evaporation with EtOH to leave,
after drying in vacuo, pure 5 (4.34 g, 71%) as an off-white
solid: [a]D24¼212.9 (c¼0.14 in CHCl3); dH (500.16 MHz,
CDCl3, 303 K); 7.68–7.21 (15H, m, Ph), 4.83, 4.52 (2H, d,
J¼11.6 Hz, CH2Ph,), 4.18 (1H, dd, J¼2.2, 5.4 Hz, H-4),
4.15 (1H, d, J¼8.3 Hz, H-1), 3.97 (1H, dd, J¼5.4, 7.4 Hz,
H-3), 3.95 (1H, dd, J¼5.2, 10.0 Hz, Hb-6), 3.85 (1H, dd,
J¼6.4, 10.0 Hz, Ha-6), 3.79 (1H, ddd, J¼2.2, 5.2, 6.4 Hz,
H-5), 3.54 (1H, ddd, J¼1.9, 7.4, 8.3 Hz, H-2), 2.25 (1H, d,
J¼1.9 Hz, OH-2), 1.44, 1.27 (6H, s, CMe2), 1.00 (9H, s,
CMe3); dC (125.78 MHz, CDCl3, 303 K); 137.08–127.8
(Ph), 110.3 (CMe2), 101.1 (C-1), 78.9 (C-3), 74.1 (C-2),
74.0 (C-5), 73.5 (C-4), 70.9 (CH2Ph), 63.0 (C-6), 27.0
(CMe3), 28.4, 26.5 (CMe2), 19.5 (CMe3). The NMR spectral
data for 5 are consistent with those reported previously for
this compound.14a EIMS calcd for C31H37O6Si [M2CH3]þ
533.2359. Found 533.2359. Anal. Calcd for C32H40O6Si
3.2.6. Benzyl 2-O-acetyl-6-O-(tert-butyldimethylsilyl)-
3,4-O-isopropylidene-b-D-galactopyranoside (6). To a
solution of 4 (1.14 g, 2.69 mmol) in CH2Cl2 (50 mL) was
added acetic anhydride (10 mL, 0.11 mol) and Et3N (3 mL,
21.6 mmol). The reaction mixture was stirred for 48 h at
ambient temperature, cooled to 0 8C and treated with MeOH
(100 mL). The solvents were evaporated and the remaining
oil was dissolved in CH2Cl2 (50 mL) and washed with
saturated aqueous NaHCO3 (2£50 mL) and water (50 mL).
The CH2Cl2 extracts were dried over MgSO4 and evapo-
rated to dryness. Flash column chromatography (silica gel
containing 0.1% Ca, ethyl acetate/toluene, gradient elution)
gave pure 6 (0.92 g, 74%) as a transparent oil: [a]D23¼216.3
(c¼0.12 in CHCl3); dH (500.16 MHz, CDCl3, 303 K);
7.25–7.16 (5H, m, Ph), 4.95 (1H, dd, J¼7.6, 8.3 Hz, H-2),
4.77, 4.50 (2H, d, J¼12.4 Hz, CH2Ph), 4.23 (1H, d, J¼
8.3 Hz, H-1), 4.09 (1H, dd, J¼2.1, 5.4 Hz, H-4), 4.01 (1H,
dd, J¼5.4, 7.6 Hz, H-3), 3.83 (1H, dd, J¼7.0, 10.0 Hz,
Hb-6), 3.81 (1H, dd, J¼6.1, 10.0 Hz, Ha-6), 3.68 (1H, ddd,
J¼2.1, 6.1, 7.0 Hz, H-5), 1.97 (3H, s, Me), 1.47, 1.22 (6H, s,
CMe2), 0.82 (9H, s, CMe3), 0.00 (6H, s, SiMe2); dC
(125.78 MHz, CDCl3, 303 K); 169.8 (CvO), 137.5, 128.6,
128.0, 127.9 (Ph), 110.6 (CMe2), 99.1 (C-1), 77.3 (C-3),
73.9 (C-5), 73.6 (C-4), 73.5 (C-2), 70.1 (CH2Ph), 62.3 (C-6),
28.0, 26.6 (CMe2), 26.0 (CMe3), 21.2 (Me), 18.5 (CMe3),
25.1, 25.2 (SiMe2); EIMS calcd for C23H35O7Si
[M2CH3]þ 451.2152. Found 451.2147.

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3658
3.2.7. Benzyl 2-O-acetyl-6-O-(tert-butyldiphenylsilyl)-
3,4-O-isopropylidene-b-D-galactopyranoside (7). To a
solution of 5 (3.41 g, 6.21 mmol) in pyridine (40 mL) was
added acetic anhydride (20 mL) and the reaction mixture
was stirred overnight at ambient temperature. Monitoring by
TLC indicated the formation of one major product after 2 h.
The reaction mixture was cooled using an ice-bath and
quenched by addition of MeOH (100 mL). The solvents
were evaporated and the remaining oil extracted with
CH2Cl2 (100 mL), washed with H2O (100 mL) and evapo-
rated to dryness. The residual pyridine was co-evaporated
with toluene after which the remaining toluene traces were
co-evaporated with EtOH. The resulting oil (3.73 g) was
dried in vacuo and crystallized from pentane at 220 8C
to afford pure 7 (3.42 g, 93%) as a bright white solid:
[a]D24¼214.5 (c¼0.05 in CHCl3); dH (500.16 MHz, CDCl3,
303 K); 7.72–7.22 (15H, m, Ph), 5.02 (1H, dd, J¼8.0,
8.3 Hz, H-2), 4.83, 4.57 (2H, d, J¼12.5 Hz, CH2Ph), 4.32
(1H, d, J¼8.3 Hz, H-1), 4.25 (1H, dd, J¼2.1, 5.4 Hz, H-4),
4.11 (1H, dd, J¼5.4, 8.0 Hz, H-3), 3.99 (1H, dd, J¼7.0,
10.1 Hz, Hb-6), 3.95 (1H, dd, J¼6.2, 10.1 Hz, Ha-6), 3.83
(1H, ddd, J¼2.1, 6.2, 7.0 Hz, H-5), 2.05 (3H, s, Me), 1.54,
1.32 (6H, s, CMe2), 1.05 (9H, s, CMe3); dC (125.78 MHz,
CDCl3, 303 K); 169.8 (CvO), 137.5–127.9 (Ph), 110.6
(CMe2), 99.1 (C-1), 77.0 (C-3), 73.8 (C-4), 73.7 (C-2),
73.5 (C-5), 70.2 (CH2Ph), 63.0 (C-6), 28.0, 26.8 (CMe2),
27.0 (CMe3), 21.2 (Me), 19.5 (CMe3); EIMS calcd for
C33H39O7Si [M2CH3]þ 575.2465. Found 575.2463. Anal.
Calcd for C34H42O7Si (590.8): C, 69.12; H, 7.17. Found C,
69.58; H, 7.19.
3.2.9. Benzyl 2-O-acetyl-3,4-O-isopropylidene-b-D-
galactopyranoside (9). To an ice-cooled solution of 6
(681 mg, 1.46 mmol) in THF (15 mL) was added in one
portion a solution of Bu4NF·3H2O (920 mg, 2.92 mmol) in
THF (10 mL). The ice-bath was removed after 15 min and
the reaction mixture was stirred at ambient temperature.
Monitoring by TLC indicated the formation of one major
product. The reaction was quenched after 1 h by the addition
of CH2Cl2 (50 mL) and subsequent washing with saturated
NaHCO3 (50 mL). The aqueous phase was extracted with
an additional portion of CH2Cl2 (20 mL) and the combined
organics washed with brine (2£50 mL) and dried over
sodium sulphate. The solvents were evaporated and the
remaining off-yellow oil was dried in vacuo to leave 636 mg
1
of fairly pure 9 as an off-white solid (identified by H and
13C NMR spectroscopy). Flash column chromatography
(silica gel, toluene/ethyl acetate, gradient elution) gave pure
9 (433 mg, 84%): [a]2D4¼20.83 (c¼0.06 in CHCl3); dH
(500.16 MHz, CDCl3, 303 K); 7.38–7.05 (5H, m, Ph), 5.05
(1H, dd, J¼7.2, 8.2 Hz, H-2), 4.86, 4.66 (2H, d, J¼12.5 Hz,
CH2Ph), 4.41 (1H, d, J¼8.2 Hz, H-1), 4.17 (1H, dd, J¼5.4,
7.2 Hz, H-3), 4.15 (1H, dd, J¼2.2, 5.4 Hz, H-4), 3.99 (1H,
dd, J¼4.3, 11.9 Hz, Hb-6), 3.84 (1H, dd, J¼7.4, 11.9 Hz,
Ha-6), 3.84 (1H, ddd, J¼2.2, 4.3, 7.4 Hz, H-5), 2.07 (3H, s,
Me), 1.55, 1.32 (6H, s, CMe2); dC (125.78 MHz, CDCl3,
303 K); 169.8 (CvO), 137.4, 128.6, 128.1, 127.9 (Ph),
111.1 (CMe2), 99.5 (C-1), 77.5 (C-3), 74.2 (C-4), 73.6
(C-5), 73.1 (C-2), 70.9 (CH2Ph), 62.6 (C-6), 27.8, 26.6
(CMe2), 21.2 (Me). The 1H and 13C NMR data of 9 reported
here in CDCl3 solution deviate from those given previously
in CD3CN/D2O.16 EIMS calcd for C18H24O7 352.1522.
Found 352.1489. Anal. Calcd for C18H24O7 (352.4): C,
61.35; H, 6.86. Found C, 61.11; H, 6.91.
3.2.8. Benzyl 2-O-benzoyl-6-O-(tert-butyldiphenylsilyl)-
3,4-O-isopropylidene-b-D-galactopyranoside (8). To a
solution of 5 (0.58 g, 1.06 mmol) in pyridine (10 mL) was
added benzoyl chloride (0.18 mL, 1.58 mmol). The reaction
mixture was stirred at ambient temperature and monitored
by TLC. Quantitative conversion of the starting material to
a single product was observed after 6 h. The mixture was
cooled using an ice-bath, quenched by addition of MeOH
(100 mL) and extracted with CH2Cl2 (100 mL). The organic
phase was washed with H2O (100 mL), dried over sodium
sulphate and evaporated to dryness. The residual pyridine
was co-evaporated with toluene after which the remaining
toluene traces were co-evaporated with EtOH. Drying in
vacuo afforded 8 as a white solid containing trace impurities
3.2.10. Benzyl 2-O-acetyl-b-D-galactopyranoside (10). To
an ice-cooled solution of 6 containing a trace of the
a-anomer (171 mg, 0.37 mmol) in THF (10 mL) was added
in one portion a solution of Bu4NF·3H2O (230 mg,
0.74 mmol) in THF (10 mL). An immediate color change
to light yellow was observed. TLC analysis after 90 min
indicated the formation of one major product in accordance
with the earlier observations during the synthesis of 9 (vide
supra). The reaction was quenched by the addition of
CH2Cl2 (50 mL) and subsequent washing with saturated
NaHCO3 (50 mL). The aqueous phase was extracted with
additional portions of CH2Cl2 (2£20 mL) and the combined
organics washed with brine (50 mL) and dried over sodium
sulphate. Evaporation of the solvents and drying in vacuo
left a yellowish oily solid (183 mg) that was dissolved in
MeOH (30 mL) and stirred at ambient temperature over-
night with Dowex DR-2030 (0.5 g, Fluka, Hþ-form). The
reaction was monitored by TLC showing the disappearance
of all starting material after 21 h. The solid catalyst was
removed by filtration, solvents were evaporated and the
residue dried in vacuo to leave an off-white/yellowish solid
(113 mg). The residue was purified by repeated washing and
cooling cycles with CHCl3 to yield pure 10 (75 mg, 65%) as
a bright white crystalline solid: [a]D23¼210.4 (c¼0.02 in
MeOH); dH (500.16 MHz, CD3OD, 303 K); 7.34–7.24 (5H,
m, Ph), 5.07 (1H, dd, J¼8.1, 10.0 Hz, H-2), 4.86, 4.62 (2H,
d, J¼12.2 Hz, CH2Ph), 4.46 (1H, d, J¼8.1 Hz, H-1), 3.87
(1H, dd, J¼0.8, 3.4 Hz, H-4), 3.81 (1H, dd, J¼6.9, 11.4 Hz,
Hb-6), 3.75 (1H, dd, J¼5.2, 11.4 Hz, Ha-6), 3.62 (1H, dd,
1
as confirmed by H NMR. Flash column chromatography
(silica gel, MeOH/CH2Cl2 1:100) gave after subsequent
evaporation and drying 700 mg (99%) of pure 8 as a white
solid: [a]D24¼211.4 (c¼0.05 in CHCl3); dH (500.16 MHz,
CDCl3, 303 K); 8.04–7.14 (20H, m, Ph), 5.23 (1H, dd,
J¼7.3, 8.3 Hz, H-2), 4.76, 4.55 (2H, d, J¼12.7 Hz, CH2Ph),
4.39 (1H, d, J¼8.3 Hz, H-1), 4.23 (1H, dd, J¼5.4, 2.1 Hz,
H-4), 4.20 (1H, dd, J¼7.3, 5.4, Hz, H-3), 3.97 (1H, dd,
J¼6.7, 10.1 Hz, Hb-6), 3.94 (1H, dd, J¼6.5, 10.1 Hz, Ha-6),
3.83 (1H, ddd, J¼2.1, 6.5, 6.7 Hz, H-5), 1.51, 1.34 (6H, s,
CMe2), 1.10 (9H, s, CMe3); dC (125.78 MHz, CDCl3,
303 K); 165.6 (CvO), 137.3–127.9 (Ph), 110.7 (CMe2),
98.9 (C-1), 77.5 (C-3), 74.0 (C-2), 73.9 (C-5), 73.7
(C-4), 69.9 (CH2Ph), 63.0 (C-6), 27.0 (CMe3), 28.0,
26.5 (CMe2), 19.5 (CMe3); EIMS calcd for C38H41O7Si
[M2CH3]þ 637.2622. Found 637.2617. Anal. Calcd for
C39H44O7Si (652.8): C, 71.75; H, 6.79. Found C, 71.61; H,
6.77.

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R. L. Lehtila et al. / Tetrahedron 60 (2004) 3653–3661
3659
J¼3.4, 10.0 Hz, H-3), 3.54 (1H, ddd, J¼0.8, 5.2, 6.9 Hz,
H-5), 2.01 (3H, s, Me); dC (125.78 MHz, CD3OD, 303 K);
172.3 (CvO), 139.3, 129.5, 129.0, 128.9 (Ph), 101.8 (C-1),
77.1 (C-5), 74.1 (C-2), 73.4 (C-3), 71.7 (CH2Ph), 70.6 (C-4),
62.6 (C-6), 21.2 (Me); EIMS calcd for C14H15O5
{[M2H2O]–CH2OH}þ 263.0919. Found 263.0913. Anal.
Calcd for C15H20O7 (312.3): C, 57.69; H, 6.45. Found C,
57.34; H, 6.22. Alternatively, a solution of 6 (75 mg,
0.16 mmol) in MeOH (15 mL) was stirred at ambient
temperature overnight with Dowex DR-2030 (0.31 g). TLC
showed the formation of one major product after 17 h. The
solid catalyst was removed by filtration, solvents were
evaporated and the residue dried in vacuo to leave an off-
white solid (50 mg). The crude product was analyzed by 1H
NMR (250 MHz) in MeOD showing nearly quantitative
cleavage of both isopropylidene and TBDMS protective
groups and the high yield formation of 10 evidenced by
drying in vacuo afforded a dark oil (1.45 g). Analysis of
1
the crude product by H NMR (250 MHz) indicated the
formation of the desired product as a mixture of the a- and
b-anomers. Flash column chromatography (silica gel,
toluene/ethyl acetate, gradient elution) gave pure 12
(1.04 g, 93%): (a-form) dH (500.16 MHz, CDCl3, 303 K);
5.25 (1H, dd, J¼3.5, 4.1 Hz, H-1), 4.83 (1H, ddd, J¼1.3,
3.5, 7.7 Hz, H-2), 4.28 (1H, dd, J¼5.7, 7.7 Hz, H-3), 4.21
(1H, ddd, J¼2.4, 2.6, 6.1 Hz, H-5), 4.20 (1H, dd, J¼2.4,
5.7 Hz, H-4), 3.80 (1H, dd, J¼6.1, 10.0 Hz, Hb-6), 3.71
(1H, dd, J¼2.6, 10.0 Hz, Ha-6), 2.90 (1H, dd, J¼1.3, 4.1 Hz,
OH-1), 2.02 (3H, s, Me), 1.38, 1.21 (6H, s, CMe2), 0.82 (9H,
s, CMe3), 0.00 (6H, s, SiMe2); dC (125.78 MHz, CDCl3,
303 K); 170.8 (CvO), 109.8 (CMe2), 90.6 (C-1), 73.2
(C-3), 73.1 (C-5), 72.3 (C-2), 68.3 (C-4), 62.5 (C-6), 28.1,
26.4 (CMe2), 26.1 (CMe3), 21.3 (Me), 18.6 (CMe3), 25.1,
25.2 (SiMe2); (b-form) dH (500.16 MHz, CDCl3, 303 K);
4.74 (1H, dd, J¼7.3, 7.8 Hz, H-2), 4.46 (1H, dd, J¼9.8,
7.8 Hz, H-1), 4.20 (1H, ddd, J¼2.0, 4.6, 5.4 Hz, H-5), 4.13
(1H, dd, J¼5.4, 7.3 Hz, H-3), 3.79 (1H, dd, J¼5.4, 10.3 Hz,
Hb-6), 3.77 (1H, dd, J¼2.0, 10.3 Hz, Ha-6), 3.77 (1H, dd,
J¼4.6, 5.4 Hz, H-4), 3.40 (1H, d, J¼9.8 Hz, OH-1), 2.02
(3H, s, Me), 1.53, 1.45 (6H, s, CMe2), 0.81 (9H, s, CMe3),
0.00 (6H, s, SiMe2); dC (125.78 MHz, CDCl3, 303 K); 170.8
(CvO), 109.9 (CMe2), 95.6 (C-1), 76.1 (C-3), 75.8 (C-2),
73.6 (C-4), 73.2 (C-5), 61.9 (C-6), 28.0, 26.2 (CMe2), 26.0
(CMe3), 21.3 (Me), 18.5 (CMe3), 25.2, 25.2 (SiMe2);
EIMS calcd for C16H29O7Si [M2CH3]þ 361.1683. Found
361.1691.
1
comparison of the H NMR spectrum with that of the pure
compound (vide supra). Further purification was not
performed.
3.2.11. Benzyl 2-O-benzoyl-b-D-galactopyranoside (11).
To an ice-cooled solution of 8 (332 mg, 0.51 mmol) in THF
(10 mL) was added in one portion a solution of Bu4NF·
3H2O (320 mg, 1.0 mmol) in THF (10 mL). TLC analysis
after 2 h was consistent with complete conversion of the
starting material. The reaction was quenched by addition of
CH2Cl2 (50 mL) and subsequent washing with saturated
NaHCO3 (50 mL). The organic phase was washed with H2O
(2£50 mL) and dried over sodium sulphate. Evaporation of
the solvents and drying in vacuo left a viscous yellow oil
that was dissolved in MeOH (30 mL) and stirred at ambient
temperature overnight with Dowex DR-2030 (0.5 g, Fluka,
Hþ-form). The solid catalyst was removed by filtration,
solvents were evaporated and the residue dried in vacuo to
leave an off-yellow/brown solid (300 mg). Washing with
pentane and subsequent crystallization from ethyl acetate
afforded 11 (105 mg, 55%) as an off white powder: [a]D23¼
234.0 (c¼0.02 in MeOH); dH (500.16 MHz, CD3OD,
303 K); 8.00–7.05 (10H, m, Ph), 5.33 (1H, dd, J¼8.0,
9.9 Hz, H-2), 4.83, 4.64 (2H, d, J¼12.4 Hz, CH2Ph), 4.60
(1H, d, J¼8.0 Hz, H-1), 3.92 (1H, dd, J¼1.1, 3.4 Hz, H-4),
3.85 (1H, dd, J¼7.1, 11.4 Hz, Hb-6), 3.79 (1H, dd, J¼5.0,
11.4 Hz, Ha-6), 3.79 (1H, dd, J¼3.4, 9.9 Hz, H-3), 3.61 (1H,
ddd, J¼1.1, 5.0, 7.1 Hz, H-5); dC (125.78 MHz, CD3OD,
303 K); 167.6 (CvO), 138.8–128.6 (Ph), 101.6 (C-1), 77.0
(C-5), 74.5 (C-2), 73.2 (C-3), 71.4 (CH2Ph), 70.7 (C-4), 62.5
(C-6). In the EIMS analysis of the parent compound 11
(C20H22O7) only peaks corresponding to decomposition
products were observed. A satisfactory analysis was,
however, obtained from the fully silylated 3,4,6-trimethyl-
siloxy derivative of 11, benzyl 2-O-benzoyl-tris-3,4,6-O-
(trimethylsilyl)-b-D-galactopyranoside for which EIMS
calcd for C28H43O7Si3 575.2317 gave the observed
575.2313.
3.2.13. 2-O-Acetyl-6-O-(tert-butyldimethylsilyl)-3,4-O-
isopropylidene-D-galactopyranosyl trichloroacetimidate
(13). To an ice-cooled solution of 12 (1.04 g, 2.88 mmol) in
CH2Cl2 (50 mL) was subsequently added trichloroaceto-
nitrile (4.16 g, 2.9 mL, 28.8 mmol) and DBU (0.52 mL,
3.46 mmol). The reaction mixture was monitored by TLC
showing consumption of all starting material after 2 h. The
solvents were evaporated to leave a thick brown oil that was
dissolved in a small amount of a solvent mixture containing
toluene, ethyl acetate and CH2Cl2. Flash column chroma-
tography (silica gel, with toluene/ethyl acetate/Et3N,
gradient elution) gave 13 in two fractions (1.07þ0.1 g,
total yield 78%) as a thick yellow oil. 1H NMR (600 MHz)
analysis revealed the first fraction to consist of fairly pure 13
enriched in single anomer, whereas the second fraction
consisted of the anomeric mixture. (a-form) dH (600.13 MHz,
CDCl3, 298 K); 8.55 (s, 1H, NH), 6.36 (1H, d, J¼3.6 Hz,
H-1), 5.09 (1H, dd, J¼3.6, 7.6 Hz, H-2), 4.41 (1H, dd,
J¼5.5, 7.6 Hz, H-3), 4.35 (1H, dd, J¼2.3, 5.5 Hz, H-4), 4.22
(1H, ddd, J¼2.3, 6.1, 7.3 Hz, H-5), 3.87 (1H, dd, J¼7.3,
10.0 Hz, Hb-6), 3.79 (1H, dd, J¼6.1, 10.0 Hz, Ha-6), 2.04
(3H, s, Me), 1.51, 1.31 (6H, s, CMe2), 0.85 (9H, s, CMe3),
0.00 (6H, s, SiMe2); dC (150.90 MHz, CDCl3, 298 K); 170.5
(CvO), 161.0 (CvNH), 110.1 (CMe2), 93.8 (C-1), 91.2
(CCl3), 73.0 (C-3), 72.7 (C-4), 70.9 (C-5), 70.6 (C-2), 62.0
(C-6), 28.0, 26.4 (CMe2), 26.0 (CMe3), 21.0 (Me), 18.5
(CMe3), 25.1, 25.2 (SiMe2); EIMS calcd for C18H29Cl3-
NO7Si [M2CH3]þ 504.0779. Found 504.0792.
3.2.12. 2-O-Acetyl-6-O-(tert-butyldimethylsilyl)-3,4-O-
isopropylidene-D-galactopyranose (12). To a solution of
6 (1.45 g, 3.11 mmol) in EtOH (100 mL) was added
activated 10% Pd/C (250 mg) and cyclohexene (5 mL).
The reaction mixture was refluxed for 72 h. The solids were
separated by filtration through Celite and subsequent
washing with CH2Cl2. Evaporation of the solvents and
3.2.14. Benzyl 2-O-acetyl-6-O-(tert-butyldiphenylsilyl)-
b-D-galactopyranoside (14). To an ice-cooled solution of
7 (105 mg, 0.18 mmol) in freshly distilled CH2Cl2 (15 mL)
was added via syringe CF3COOH (1 mL) containing 2%

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R. L. Lehtila et al. / Tetrahedron 60 (2004) 3653–3661
3660
structures also serve as branching points in human blood group
deionized H2O. The reaction mixture was stirred for 10 min
at 0 8C followed by 20 min at ambient temperature. Next,
the reaction mixture was cooled on an ice-bath followed by
addition of saturated aqueous NaHCO3 (5 mL) and stirred
for 20 min. Ice-cold saturated aqueous NaHCO3 (30 mL)
was added and the mixture extracted with CH2Cl2
(2£50 mL). The combined organics were washed with
NaHCO3 (30 mL), H2O (50 mL) and dried over sodium
sulphate. Evaporation of the solvents and drying in vacuo
´
antigens, see for example: (b) Martın, M. J.; Feizi, T.; Lateux,
C.; Pavlovic, D.; Piskarev, V. E.; Chai, W. Glycobiology 2002,
12, 829–835.
9. (a) Renkonen, O. Cell. Mol. Life Sci. 2000, 57, 1423–1439.
(b) Miller-Podraza, H. Chem. Rev. 2000, 100, 4663–4681.
(c) Biet, T.; Peters, T. Angew. Chem., Int. Ed. 2001, 40,
4189–4192.
¨ ¨
10. Roslund, M. U.; Klika, K. D.; Lehtila, R. L.; Tahtinen, P.;
¨¨
Sillanpaa, R.; Leino, R. J. Org. Chem. 2004, 69, 18–25.
1
left an off-yellow solid (122 mg) that was analyzed by H
11. Clausen, M. H.; Jørgensen, M. R.; Thorsen, J.; Madsen, R.
J. Chem. Soc., Perkin Trans. 1 2001, 543–551.
´ ´ ´
12. Francisco, C. G.; Gonzalez Martın, C.; Suarez, E. J. Org.
NMR (250 MHz) in CDCl3. The spectral data indicated
nearly quantitative conversion of the starting material to the
desired product. Precipitation from pentane gave an isolated
yield of 75 mg (76%) of pure 14 as a white solid: [a]D24¼
227.9 (c¼0.02 in CHCl3); dH (500.16 MHz, CDCl3,
303 K); 7.74–7.24 (15H, m, Ph), 5.07 (1H, dd, J¼7.9,
9.7 Hz, H-2), 4.89, 4.62 (2H, d, J¼12.4 Hz, CH2Ph), 4.43
(1H, d, J¼7.9 Hz, H-1), 4.09 (1H, ddd, J¼1.1, 3.3, 4.4 Hz,
H-4), 4.00 (1H, dd, J¼5.9, 10.6 Hz, Hb-6), 3.97 (1H, dd,
J¼5.0, 10.6 Hz, Ha-6), 3.60 (1H, ddd, J¼3.3, 8.5, 9.7 Hz,
H-3), 3.51 (1H, ddd, J¼1.1, 5.0, 5.9 Hz, H-5), 2.92 (1H,
d, J¼8.5 Hz, OH-3), 2.88 (1H, d, J¼4.4 Hz, OH-4), 2.11
(3H, s, Me), 1.10 (9H, s, CMe3); dC (125.78 MHz, CDCl3,
303 K); 171.5 (CvO), 137.4–127.8 (Ph), 99.7 (C-1), 74.3
(C-5), 73.7 (C-2), 73.2 (C-3), 70.3 (CH2Ph), 69.7 (C-4), 63.6
(C-6), 27.0 (CMe3), 21.2 (Me), 19.4 (CMe3). Anal. Calcd for
C31H38O7Si (550.7): C, 67.61; H, 6.95. Found C, 67.72; H,
6.86.
Chem. 1998, 63, 2099–2109.
´
´
13. Francisco, C. G.; Leon, E. I.; Martın, A.; Moreno, P.;
´
´
Rodrıguez, M. S.; Suarez, E. J. Org. Chem. 2001, 66,
6967–6976.
14. (a) Redlich, H.; Sudau, W.; Szardenings, A. K.; Vollerthun, R.
Carbohydr. Res. 1992, 226, 57–78. (b) Lin, C.-C.; Shimzaki,
`
M.; Heck, M.-P.; Aoki, S.; Wang, R.; Kimura, T.; Ritzen, H.;
Takayama, S.; Wu, S.-H.; Weitz-Schmidt, G.; Wong, C.-H.
J. Am. Chem. Soc. 1996, 118, 6826–6840.
15. For the b-D-glucopyranoside analogue of 3, see, for example:
Berkowitz, D. B.; Bose, M.; Pfannenstiel, T. J.; Doukov, T.
J. Org. Chem. 2000, 65, 4498–4508.
16. Compound 9 has been prepared previously by a combination
of chemical synthesis and enzymatic methods, see: Barili,
P. L.; Catelani, G.; D’Andrea, F.; Mastrorilli, E. J. Carbohydr.
Chem. 1997, 16, 1001–1010.
17. Compound 11 has been described previously, see: Levy, A.;
Flowers, H. M.; Sharon, N. Carbohydr. Res. 1967, 4,
305–311.
Acknowledgements
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The authors wish to thank Markku Reunanen for the EIMS-
measurements.
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