An alternative high yielding and highly stereoselective method for preparing an α-Neu5NAc-(2,6)-D-GalN3 building block suitable for further glycosylation

Article abstract of DOI:10.1016/j.carres.2005.05.007

This paper deals with new approaches to α-Neu5NAc-(2,6)-D-GalN ₃ building blocks, suitable as glycosylation donors. The major improvement, by comparison with the results of the literature, lies in the glycosylation step of a new D-galactosamine acceptor (tert-butyldimethylsilyl 3-O-acetyl-2-azido-2-deoxy-β-D-galactopyranoside) with O-methyl-S- [methyl(5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-α-D- galacto-non-2-ulopyranosyl)onate] dithiocarbonate as the N-acetylneuraminic acid donor. The reaction affords the expected disaccharide in high yield (85%) and a complete α-Neu5NAc stereoselectivity. A subsequent oxidation step, eliminating the glycal by-product allows an easier purification. Afterwards, the tert-butyldimethylsilyl disaccharide can be transformed into a donor, after cleavage of the anomeric group in smooth conditions.

Full text of DOI:10.1016/j.carres.2005.05.007

Carbohydrate
RESEARCH
Carbohydrate Research 340 (2005) 1885–1892
Note
An alternative high yielding and highly stereoselective method
for preparing an a-Neu5NAc-(2,6)-D-GalN3 building block
suitable for further glycosylation
Nicolas Laurent,a Dominique Lafont,a Paul Boullangera,* and Jean Maurice Malletb
a
´
Laboratoire de Chimie Organique II—Glycochimie, Unite Mixte de Recherche CNRS 5181, Universite Lyon 1,
Chimie Physique Electronique de Lyon, 43 Boulevard du 11 Novembre 1918, F-69622 Villeurbanne, France
´
b
´ ´ ´
Departement de Chimie, Unite Mixte de Recherche CNRS 8642, Ecole Normale Superieure, 24 Rue Lhomond,
F-75231 Paris Cedex 05, France
Received 28 April 2005; received in revised form 25 May 2005; accepted 26 May 2005
Available online 17 June 2005
Abstract—This paper deals with new approaches to a-Neu5NAc-(2,6)-D-GalN3 building blocks, suitable as glycosylation donors.
The major improvement, by comparison with the results of the literature, lies in the glycosylation step of a new D-galactosamine
acceptor (tert-butyldimethylsilyl 3-O-acetyl-2-azido-2-deoxy-b-D-galactopyranoside) with O-methyl-S-[methyl(5-acetamido-4,7,8,9-
tetra-O-acetyl-3,5-dideoxy-D-glycero-a-D-galacto-non-2-ulopyranosyl)onate] dithiocarbonate as the N-acetylneuraminic acid donor.
The reaction affords the expected disaccharide in high yield (85%) and a complete a-Neu5NAc stereoselectivity. A subsequent
oxidation step, eliminating the glycal by-product allows an easier purification. Afterwards, the tert-butyldimethylsilyl disaccharide
can be transformed into a donor, after cleavage of the anomeric group in smooth conditions.
ꢀ 2005 Elsevier Ltd. All rights reserved.
Keywords: D-Galactosamine; N-Acetylneuraminic acid; a-Glycosylation; Glycal oxidation
Sialic acids are endowed with fundamental biological
properties. They can be found either as glycoproteins
or glycolipids lying, most often, at the outer part of cell
membranes. They fulfil several biological functions,
either resulting in molecular recognition (e.g., cell adhe-
sion and proliferation, immunological defence, protein
survival), or induced by their negative charge (e.g., con-
formation, viscosity or solubility of glycoproteins, total
negative charge at the surface of cells).1,2 Sialic acids
constitute a family of about 40 constituents, amongst
which N-acetylneuraminic acid (Neu5Ac) 1 is the most
representative. The synthesis of Neu5Ac containing oligo-
saccharides has been extensively studied, mostly since
they were discovered as antigenic determinants of the
Thomson–Friendenrich family, over-expressed at the
surface of cancer cells.
The glycosylation with sialic acid donors is one of the
most challenging in the field for several reasons: (a) the
anomeric centre is a hindered quaternary centre, (b) it is
deactivated by the presence of the carboxylate residue,
(c) no stereo-orientation can be expected from the nat-
ure of a substituent at C-3, (d) the nucleophilic substitu-
tion at the anomeric position is in competition with a
favoured elimination reaction giving rise to a glycal.3,4
In a seek for preparing amphiphilic derivatives of
Neu5Ac(a2-6)GalNAca, in a view to embed into lipo-
some bilayers or phospholipid monolayers,5,6 we have
investigated several methods described in the literature.
Thus, donors 2 and 3 were reacted, in various condi-
tions, with a-D-GalNAc acceptors carrying hydrophobic
aglycons. None of them afforded the expected glycosides
in good yields (best yield 24%) and/or good stereocon-
trols (a/b ꢀ 1:1).7 The discordance with the results of
the literature reported for shorter aglycons,8 was attrib-
uted to phase separation and/or possible disfavourable
*
Corresponding author. Tel.: +33 04 72 43 11 62; e-mail: paul.
boullanger@univ-lyon1.fr
0008-6215/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2005.05.007

1886
N. Laurent et al. / Carbohydrate Research 340 (2005) 1885–1892
X
OR
ZN
4
OR OH
RO
O
COOR1
O
R3O
X
OR
RO
N3
R3
R4
R
R1
NZ
X
X
OH
1
2
3
4
5
6
7
OAll
OAll
β-D-Gal
H
H
H
H
H
H
H
NHAc
NHAc
NHAc
NHAc
N3
β-Cl
8
H
H
Me
Me
Me
Bn
Me
Ac
Ac
Ac
Bn
Ac
α-S(C=S)OEt
α/β-SMe
9
OTBDMS
OTBDPS
OTBDPS
OTBDPS
SEt
10
11
12
13
14
Bn
H
α-STol
α-STol
-CMe2-
N3
Ac
Ac
H
H
OR
OTBDMS
COOR1
O
OR
ZN
RO
R
R1
NZ
NHAc
N3
15a Ac Me
15b Ac Me
15c Bn Bn
NHAc
Figure 1.
conformations in the highly hydrophobic acceptor alco-
hols, mainly at low temperatures. Therefore, we decided
to attempt the glycosylation with a galactosamine accep-
tor that could allow a subsequent activation at the ano-
meric centre for a further glycosylation step (Fig. 1).
The results of the literature concerning glycosylations
with neuraminic acid donors and 2-azido galactosamine
acceptors that could be reactivated easily at the ano-
meric position are reported in Table 1.
As can be seen from Table 1 (entries 1–7), either the gly-
cosylation yields or the a/b stereoselectivities are unsatis-
factory for preparing the expected disaccharides. The best
glycosylation yield (entry 1) is obtained with a low stereo-
selectivity, whereas the best stereoselectivities (entries 5–
7) are observed for glycosylations in modest yields.
Concerning the donors, it can be mentioned that: (a)
lengthy multistep preparations of azido sialic acid deriv-
atives (entries 5–7) do not result in drastic yield
increases, though they afford excellent a-stereoselectiv-
ities, (b) whatever the leaving group is, the glycosylation
yields stay in the range of 40–60% with one exception
(entry 1) that could be explained by the use of a large
excess of donor (5 equiv) with regard to the acceptor,
(c) a competitive elimination reaction most often affords
glycals 15a–c, whatever the donor is.7,14
Concerning the acceptors, it can be pointed out that:
(a) protection at C-4 is not necessary since this position
is very unreactive (the yield reported in entry 7 is in same
the range as others), (b) protection at C-3 is of interest,
affording better yields without affecting the stereoselec-
tivity to a great extent (compare the results of entries 5
and 6), furthermore diglycosylation at C-3 and C-6
was reported for unprotected acceptors,8a (c) the azido
function at C-2 affords better results than the 2-acetam-
ido counterpart.15 Also, it should be pointed out that a
non-participating group at C-2 is necessary in a view to
performing an a-glycosylation, after reactivation at the
anomeric position. It is aforementioned that most of
these comments are also valid for other galactosamine
acceptors, not dealt with, in the present paper.
Table 1. Glycosylation of 2-azido-2-deoxy-D-galactopyranoside accep-
tors (7–14) with neuraminic acid donors (2–6)
Entry
Acceptor
Donor
(equiv)
Yield
(%)
a/b Ratio
Ref.
1
2
3
4
5
6
7
8
9
7
8
2 (5)
2 (1)
3 (2)
4 (nd)
5 (2)
5 (2)
6 (nd)
2 (2)
3 (2)
85
49
61
50
61
43
53
45
85
1.1/1
5/1
9
10
9
6.7/1
3.6/1
9/1
11
11
9
10
11
12
13
14
12
12
As a result of the above observations, we decided to
attempt the glycosylation of acceptors 13 and 14, which
have not been reported previously to our knowledge.
Both are O-acetylated at OH-3, unprotected at OH-6
a Only
10/1
3/1
13
This work
This work
a Only

N. Laurent et al. / Carbohydrate Research 340 (2005) 1885–1892
1887
OR6
PivO
HO
OPiv
R4O
R3O
O
c
O
18
X
SEt
NHAloc
NHAloc
19
16. R3=R4=R6=Ac, X= OAc
17. R3=R4=R6=Ac, X= SEt
18. R3=R6=Piv, R4=H, X= SEt
Ph
O
a
b
d
O
O
R3O
SEt
NZ
20. R3=H, NZ=NHAloc
21. R3=H, NZ=NH2
22. R3=H, NZ=N3
e
f
g
23. R3=Ac, NZ=N3
Scheme 1. Reagents and conditions: (a) EtSH, BF3ÆEt2O–CH2Cl2, 0 ꢁC; (b) MeONa, MeOH, rt, then (CH3)3CCOCl, pyridine–CH2Cl2, rt; (c) Tf2O,
CH2Cl2–pyridine, ꢁ15 ꢁC, then H2O, 80 ꢁC; (d) MeONa, MeOH, rt, then PhCH–(OMe)2, TsOH, rt; (e) 2.5 M NaOH, reflux; (f) TfN3, DMAP,
CH3CN, rt; (g) Ac2O, pyridine.
and OH-4; they carry an azido function at C-2 and a
group at anomeric position that can be either directly
used for a further glycosylation (13), or selectively
cleaved in smooth conditions (14) for a subsequent
activation.
Acceptor 13 was prepared following the reaction
pathway depicted in Scheme 1. The N-allyloxycarbonyl
derivative 1616 was treated with ethanethiol and boron-
hydrolyzed with 2.5 M, NaOH at reflux since Pd(0)
complexes reported earlier16 were shown to be less satis-
factory, in this instance. Thus, the free amino compound
21 was obtained in 96% yield. The latter was treated
with triflyl azide18 (in situ formed by reaction of triflic
anhydride and sodium azide) to afford compound 22
(96% yield). This reaction pathway to 22 (40% overall
yield from compound 16) could constitute an interesting
alternative to the usual azidonitration of D-galactal.19
Compound 22 was finally acetylated at OH-3 to afford
23 (95% yield) and the benzylidene group was cleaved
in usual conditions (69% yield) to afford the acceptor
diol 13.
´
trifluoride etherate to afford 17 (80% yield). Zemplen de-
O-acetylation and treatment with pivaloyl chloride in
CH2Cl2/pyridine gave rise to 3,6-di-O-pivaloyl com-
pound 18 in 88% overall yield. The latter was treated
with triflic anhydride and the C-4 position was inverted
by hydrolysis at 80 ꢁC to afford compound 19 (90%
overall yield) resulting in a concomitant migration of
pivaloyl ester from C-3 to C-4, as already reported by
Lay et al.17
Acceptor 14 was prepared in 59% yield by acidic
cleavage (60% trifluoroacetic acid) of the known tert-
butyldimethylsilyl 3-O-acetyl-2-azido-4,6-O-benzylidene-
2-deoxy-b-D-galactopyranoside.20
After cleavage of the pivaloyl esters and re-protection
as a 4,6-O-benzylidene derivative 20 in usual conditions
(78% overall yield), the N-allyloxycarbonyl group was
The glycosylations of acceptors 13 and 14 were
attempted with the easily accessible donors 2 and 3 in
various conditions (Scheme 2). The best results are
COOMe
OAc
COOMe
OAc
AcO
AcO
O
O
O
O
AcHN
AcHN
RO
RO
OAc
OAc
AcO
AcO
O
O
OR1
SEt
AcO
AcO
N3
N3
a
c
15 a + 26. R=H, R1= OTBDMS
27. R=Ac, R1= OTBDMS
28. R=Ac, R1= α,β-OH
13 + 2
15 a + 24. R=H, X= SEt
25. R=Ac, X= SEt
14 + 3
b
b
d
Scheme 2. Reagents and conditions: (a) AgOTf, THF, ꢁ15 ꢁC to rt; (b) Ac2O, pyridine, rt; (c) MeSOTf, CH2Cl2–CH3CN, ꢁ63 ꢁC; (d) TBAF, THF–
AcOH, rt.

1888
N. Laurent et al. / Carbohydrate Research 340 (2005) 1885–1892
reported in Table 1 (entries 8 and 9). When 13 was used
as the acceptor and 3 as the donor in glycosylation reac-
tions with usual promoters,21 only the degradation of
the acceptor was observed. Nevertheless, glycosylation
of 13 with donor 2, promoted by silver triflate, afforded
the expected glycoside 24, although in low yield (45%)
and with a low stereoselectivity (a/b, 3/1) to our disap-
pointment. On the contrary, when compound 14 was
used as the acceptor and xanthate 3 as the donor, the
expected disaccharide 26 was obtained with an excellent
yield using 2 equiv of donors only. The best stereoselec-
tivity (a-anomer only) and yield (85%) were achieved in
conditions very close to that reported by Halkes et al.
(CH2Cl2–CH3CN as solvent and MeSOTf as the
promoter).21
As already pointed out, one of the difficulties encoun-
tered in glycosylation reactions with neuraminic acid is
the competitive elimination leading to glycal 15a.
Besides the consumption of donor, the formation of
the latter requires a separation that is often difficult.
This drawback was overcome by a smooth oxidation
of the glycosylation mixture with a catalytic amount of
ruthenium tetraoxide in CCl4/CH3CN/H2O, as reported
for the oxidation of olefins.22 This oxidation (impossible
in the case of the thioethylglycoside 24) afforded highly
polar species that could be removed easily from the reac-
tion mixture.
Optical rotations were recorded on a Perkin–Elmer
1
241 polarimeter in a 1 dm cell at 21 ꢁC. H and 13C
NMR spectra were recorded with a Bruker AM-300
(working at 300 and 75 MHz, respectively) and a Bruker
AM-500 (working at 500 and 125 MHz, respectively)
spectrometers with Me4Si as internal standard. Elemen-
tal analyses were performed by the ꢀLaboratoire Central
dꢁAnalyses du CNRSꢁ (Vernaison, France). Mass spec-
tra were recorded on a Finnigan Mat 95 XL apparatus
in FAB mode.
1.2. Ethyl 3-O-acetyl-2-azido-2-deoxy-1-thio-b-D-galacto-
pyranoside (13)
Compound 2219 (1.50 g, 4.45 mmol) was stirred over-
night in a 2:1 pyridine–Ac2O mixture (30 mL). After
evaporation and co-evaporation with toluene twice, the
mixture was purified by column chromatography (1:1
EtOAc–petroleum ether). Compound 23 (1.60 g, 95%)
was obtained as white crystals identical with that already
described in the literature.19 This derivative (200 mg,
0.527 mmol) was dissolved in dry CH2Cl2 (6.6 mL) and
treated at 0 ꢁC with BF3ÆEt2O (20 lL, 0.3 equiv) and
EtSH (250 lL, 3.3 mmol) for 1 h. The mixture was then
treated with satd aq NaHCO3 (3 mL), diluted with
CH2Cl2 and washed with water. After evaporation, the
mixture was purified by column chromatography (3:1
EtOAc–petroleum ether). Compound 13 was obtained
as white crystals (106 mg, 69%): mp 107 ꢁC; [a]D ꢁ22 (c
Finally, disaccharides 24 and 26 could be O-acetylated
at C-4 to 25 and 27, respectively. The latter was depro-
tected in the usual conditions at C-1 to afford 28 that
can be, in turn, reactivated as a trichloroacetimidate
for a further glycosylation, if necessary.7,10 The use of
disaccharide 28 as a glycosylation precursor for the syn-
thesis of amphiphilic compounds is now under investiga-
tion in our laboratory.
1
1.0, CHCl3); Rf 0.27 (2:1 EtOAc–petroleum ether); H
NMR (CDCl3): d 4.80 (dd, 1H, J3,4 2.8 Hz, J3,2
10.0 Hz, H-3), 4.39 (d, 1H, J1,2 10.2 Hz, H-1), 4.23 (dd,
1H, J4,5 0.8 Hz, H-4), 3.93 (m, 2H, H-6a,6b), 3.86 (t,
1H, H-2), 3.53 (m, 1H, H-5), 2.81 (m, 2H, CH2S), 2.21
(s, 3H, CH3CO), 1.38 (t, 3H, J 7.6 Hz, CH3CH2S). 13C
NMR (CDCl3): d 170.3 (CH3CO), 84.8 (C-1), 77.4,
75.5, 67.7 (C-3,4,5), 62.8 (C-6), 60.2 (C-2), 25.3 (SCH2),
21.1 (CH3CO), 15.1 (CH3CH2S). Anal. Calcd for
C10H17N3O5S (291.33): C, 41.23; H, 5.88; N, 14.42.
Found: C, 41.06; H, 5.90; N, 14.22.
1. Experimental
1.1. General methods
Pyridine was dried by boiling with CaH2 prior to distil-
lation. Dichloromethane was washed twice with water,
dried with CaCl2 and distilled from CaH2. Tetra-
hydrofurane was distilled from sodium-benzophenone.
Methanol was distilled from magnesium. Acetonitrile
was distilled from CaH2. Pyridine, THF and CH2Cl2
1.3. tert-Butyldimethylsilyl 3-O-acetyl-2-azido-2-deoxy-
b-D-galactopyranoside (14)
A soln of tert-butyldimethylsilyl 3-O-acetyl-2-azido-4,6-
O-benzylidene-2-deoxy-b-D-galactopyranoside20 (380 mg,
0.869 mmol) in CH2Cl2 (20 mL) was treated for 18 h at
rt, with 60% aq CF3CO2H (0.7 mL). After neutralization
with satd aq NaHCO3, the mixture was extracted with
CH2Cl2 and the organic layer was dried over MgSO4,
before evaporation and purification by column chroma-
tography (1:1 EtOAc–petroleum ether).
Compound 14 (186 mg, 59%) was obtained as an
amorphous solid: [a]D +6 (c 1.0, CHCl3); Rf 0.38 (1:1
EtOAc–petroleum ether); 1H NMR (CDCl3): d 4.51
(dd, 1H, J3,4 3.2 Hz, J3,2 10.9 Hz, H-3), 4.42 (d, 1H,
˚
were stored over 4 A molecular sieves; CH3CN and
˚
MeOH over 3 A molecular sieves. Melting points were
determined on a Buchi apparatus and were uncorrected.
¨
Thin layer chromatography was performed on alumin-
ium sheets coated with Silica gel 60 F254 (E. Merck).
Compounds were visualized by spraying the TLC plates
with dilute 15% aq H2SO4, followed by charring at
150 ꢁC for a few minutes. Column chromatography
was performed on silica gel Geduran Si 60 (E. Merck).

N. Laurent et al. / Carbohydrate Research 340 (2005) 1885–1892
1889
J1,2 7.5 Hz, H-1), 3.93 (d, 1H, J4,5 0.8Hz, H-4), 3.75 (dd,
1H, J6a,5 5.5 Hz, J6a,6b 11.9 Hz, H-6a), 3.68 (dd, 1H,
J6b,5 4.5 Hz, H-6b), 3.53 (ddd, 1H, H-2), 3.35 (ddd,
1H, J4,5 0.7 Hz, H-5), 2.20 (s, 3H, CH3CO), 0.96 (s,
9H, SiC(CH3)3), 0.18 (s, 6H, Si(CH3)2). 13C NMR
(CDCl3): d 170.5 (CH3CO), 97.5 (C-1), 73.8, 73.4,
67.2, 63.33 (C-2, 3, 4, 5), 62.1 (C-6), 25.6 (SiC(CH3)3),
21.0 (CH3CO), 18.0 (SiC(CH3)3), ꢁ4.2, ꢁ5.1 (Si(CH3)2).
Anal. Calcd for C14H27N3O6Si (361.46): C, 46.52; H,
7.53; N, 11.62. Found: C, 46.24; H, 7.62; N, 11.60.
18 (4.35 g, 88%) was obtained as white crystals: mp
105 ꢁC; [a]D ꢁ37 (c 1.0, CHCl3); Rf 0.64 (1:2 EtOAc–
1
petroleum ether); H NMR (CD3COCD3): d 6.34 (d,
1H, JNH,H-2 9.9 Hz, NH), 5.93 (m, 1H, CH2@CH–),
5.32–5.11 (m, 2H, CH2@CH–), 5.04 (dd, 1H, J2,3
10.1 Hz, J3,4 9.0 Hz, H-3), 4.76 (d, 1H, J1,2 10.4 Hz,
H-1), 4.69 (d, 1H, JOH,H-4 3.0 Hz, OH), 4.48 (m, 2H,
CH2@CH–CH2–), 4.48 (dd, 1H, J5,6a 1.3 Hz, J6a,6b
11.8 Hz, H-6a), 4.18 (dd, 1H, J5,6b 5.8 Hz, H-6b), 3.74
(ddd, 1H, H-2), 3.63 (m, 2H, H-4,5), 2.71 (m, 2H,
CH2S), 1.28 (t, 3H, J 7.4 Hz, CH3CH2S), 1.21, 1.16
(m, 18H, 2 (CH3)3CO). 13C NMR (CDCl3): d 179.8,
179.1 (CO(CH3)3), 155.9 (NHCOO), 132.7 (CH2@CH–),
117.6 (CH2@CH–), 84.3 (C-1), 77.3, 76.3 (C-3,5), 69.6
(C-4), 65.6 (CH2@CH–CH2–), 63.8 (C-6), 54.7 (C-2),
39.0, 38.9 (C(CH3)3), 27.2, 27.0 (C(CH3)3), 24.1
(SCH2), 15.0 (CH3CH2S). Anal. Calcd for C22H37
NO8S (475.59): C, 55.56; H, 7.84; N, 2.95. Found: C,
55.22; H, 7.80; N, 2.98.
1.4. Ethyl 3,4,6-tri-O-acetyl-2-allyloxycarbonylamino-
2-deoxy-1-thio-b-D-glucopyranoside (17)
A soln of compound 1616 (7.50 g, 16.92 mmol) in
CH2Cl2 (75 mL) was treated at 0 ꢁC with EtSH
(2.5 mL) and BF3ÆEt2O (4 mL) for 3 h under argon.
The mixture was then washed with satd aq NaHCO3
and dried over Na2SO4. After evaporation, the mixture
was purified by column chromatography (1:1 EtOAc–
petroleum ether). Compound 17 (6.0 g, 80%) was ob-
tained as white crystals: mp 133–134 ꢁC (EtOH);
[a]D ꢁ18 (c 1.0, CHCl3); Rf 0.66 (1:1 EtOAc–petroleum
1.6. Ethyl 2-allyloxycarbonylamino-2-deoxy-4,6-di-O-
pivaloyl-1-thio-b-D-galactopyranoside (19)
1
ether); H NMR (CDCl3): d 5.91 (m, 1H, CH2@CH–),
Tf2O (2 mL, 11.8 mmol) was added dropwise to a soln
of 18 (4.28 g, 9.00 mmol) in 1,2-dichloroethane
(70 mL) and pyridine (4.7 mL), cooled at ꢁ15 ꢁC. After
4 h stirring at ꢁ15 ꢁC, water (4.3 mL) was added and the
mixture was heated to 80 ꢁC for 2 h. After cooling, the
mixture was diluted with CH2Cl2 and successively
washed with 5% aq HCl, satd aq NaHCO3 and water.
After drying over Na2SO4 and evaporation, the mixture
was purified by column chromatography (1:1 EtOAc–
petroleum ether). Compound 19 (3.85 g, 90%) was ob-
tained as a colourless oil: [a]D ꢁ21 (c 1.0, CHCl3); Rf
5.34–5.15 (m, 3H, CH2@CH–, H-3), 5.08 (dd, 1H, J3,4
9.5 Hz, J4,5 9.5 Hz, H-4), 4.86 (m, 1H, JNH,H-2 8.8 Hz,
NH), 4.62 (d, 1H, J1,2 10.2 Hz, H-1), 4.58 (m, 2H,
CH2@CH–CH2–), 4.26 (dd, 1H, J5,6a 5.0 Hz, J6a,6b
12.3 Hz, H-6a), 4.13 (dd, 1H, J5,6b 2.3 Hz, H-6b), 3.75
(ddd, 1H, J2,3 9.5 Hz, H-2), 3.70 (m, 1H, H-5), 2.74
(m, 2H, CH2S), 2.08, 2.04, 2.03 (3 s, 9H, 3 CH3CO),
1.26 (t, 3H, J 7.4 Hz, CH3CH2S). 13C NMR (CDCl3):
d 170.7, 169.5 (CH3CO), 155.7 (NHCOO), 132.6
(CH2@CH–), 117.5 (CH2@CH–), 84.6 (C-1), 75.7 (C-
3), 73.7 (C-5), 68.8 (C-4), 65.8 (CH2@CH–CH2–), 62.5
(C-6), 55.0 (C-2), 24.3 (CH2S), 20.8, 20.7, 20.6
(CH3CO), 14.8 (CH3CH2S). Anal. Calcd for
C18H27NO9S (433.47): C, 49.87; H, 6.28; N, 3.23.
Found: C, 49.66; H, 6.35; N, 3.28.
1
0.50 (1:1 EtOAc–petroleum ether); H NMR (CDCl3):
d
5.92 (m, 1H, CH2@CH–), 5.37–5.20 (m, 2H,
CH2@CH–), 5.37 (dd, 1H, J3,4 3.2 Hz, J4,5 0.7 Hz, H-
4), 5.01 (br d, 1H, JNH, H-2 7.3 Hz, NH), 4.61–4.58 (m,
3H, H-1, CH2@CH–CH2–), 4.16 (dd, 1H, J5,6a 7.2 Hz,
J6a,6b 11.2 Hz, H-6a), 4.07 (dd, 1H, J5,6b 6.2 Hz, H-
6b), 3.95 (m, 1H, H-3), 3.90 (m, 1H, H-5), 3.68 (ddd,
1H, J1,2 9.4 Hz, J2,3 10.4 Hz, H-2), 2.72 (m, 2H,
SCH2), 1.30 (t, 3H, J 7.4 Hz, CH3CH2S). 13C NMR
(CDCl3): d 178.3, 178.0 (CO(CH3)3), 157.0 (NHCOO),
132.5 (CH2@CH–), 117.8 (CH2@CH–), 83.9 (C-1),
74.8 (C-5), 72.1 (C-3), 68.9 (C-4), 66.0 (CH2@CH–
CH2–), 62.1 (C-6), 53.9 (C-2), 39.3, 38.7 (C(CH3)3),
27.2, 27.1 (C(CH3)3), 24.0 (SCH2), 14.9 (CH3CH2S).
Anal. Calcd for C22H37NO8S (463.58): C, 55.56; H,
7.84; N, 2.95. Found: C, 55.57; H, 8.09; N, 2.85.
1.5. Ethyl 2-allyloxycarbonylamino-2-deoxy-3,6-di-O-
pivaloyl-1-thio-b-D-glucopyranoside (18)
The thioethylglucoside 17 (4.50 g, 10.38 mmol) was trea-
ted overnight with a chip of sodium in MeOH (100 mL)
at rt. After neutralization with Amberlite IR 120 H+, fil-
tration and evaporation, the crude product was solubi-
lized in a mixture of pyridine (31 mL) and CH2Cl2
(15 mL). After cooling to 0 ꢁC, pivaloyl chloride
(4.1 mL, 33.3 mmol) was added dropwise for 1 h. After
2 h at 0 ꢁC, the reaction was quenched with MeOH
(4 mL). The mixture was diluted with CH2Cl2 and
washed successively at 0 ꢁC with 10% aq HCl, satd aq
NaHCO3 and water. After drying over Na2SO4 and
evaporation, the mixture was purified by column chro-
matography (1:2 EtOAc–petroleum ether). Compound
1.7. Ethyl 2-allyloxycarbonylamino-4,6-O-benzylidene-
2-deoxy-1-thio-b-D-galactopyranoside (20)
Compound 19 (3.60 g, 7.57 mmol) was O-deacetylated
as already described for 17 and then solubilized in

1890
N. Laurent et al. / Carbohydrate Research 340 (2005) 1885–1892
CH3CN
(50 mL).
Benzaldehyde
dimethylacetal
mixture of compound 21 (1.55 g, 4.98 mmol) and
(2.20 mL, 14.66 mmol) and TsOH (150 mg) were then
added and the mixture was stirred at rt for 18 h. After
addition of Et3N (1 mL), the mixture was diluted with
CH2Cl2 and washed with satd aq NaHCO3, then with
water. After drying over Na2SO4, the solvent was evap-
orated to dryness and the product was recrystallized
twice from EtOH. Compound 20 (2.44 g, 78%) was ob-
tained as white crystals: mp 193–194 ꢁC (EtOH);
[a]D ꢁ38 (c 1.0, CHCl3); 1H NMR (CD3COCD3): d
7.58–7.35 (m, 5H, C6H5), 6.32 (d, 1H, JNH,H-2 8.1 Hz,
NH), 5.93 (m, 1H, CH2@CH–), 5.66 (s, 1H, CHPh),
5.30, 5.14 (m, 2H, CH2@CH–), 4.63 (d, 1H, J1,2
9.3 Hz, H-1), 4.51 (m, 2H, CH2@CH–CH2–), 4.32 (m,
1H, H-4), 4.20 (d, 1H, J5,6a 1.5 Hz, J6a,6b 12.3 Hz, H-
6a), 4.14 (dd, 1H, J5,6b 1.6 Hz, H-6b), 3.94 (ddd, 1H,
J2,3 9.0 Hz, H-2), 3.90–3.82 (m, 2H, H-3, OH), 3.63
(m, 1H, H-5), 2.80 (m, 2H, CH2S), 1.25 (t, 3H, J
7.4 Hz, CH3CH2S). Anal. Calcd for C19H25NO6S, H2O
(413.477): C, 55.19; H, 6.58; N, 3.38. Found: C, 55.17;
H, 6.70; N, 3.37.
DMAP (669 mg, 5.48 mmol) in CH3CN (25 mL), under
argon. After 16 h stirring at rt, the mixture was concen-
trated to 10 mL, diluted with EtOAc (150 mL) and
washed with satd aq NaHCO3. After drying over
Na2SO4 and evaporation, the mixture was purified by
column chromatography (3:2 EtOAc–petroleum ether).
Compound 22 (1.61 g, 96%) was obtained as a white
material, crystallizing on standing: mp 105–106 ꢁC
(lit.19 106–109 ꢁC); [a]D ꢁ 40 (c 1.0, CHCl3, lit.19 ꢁ45);
Rf 0.50 (1:1 EtOAc–petroleum ether); 1H NMR
(CDCl3): d 7.53–7.38 (m, 5H, C6H5), 5.57 (s, 1H,
CHPh), 4.35 (dd, 1H, J5,6a 1.4 Hz, J6a,6b 12.6 Hz, H-
6a), 4.31 (d, 1H, J1,2 9.8 Hz, H-1), 4.23 (dd, 1H, J3,4
3.4 Hz, J4,5 0.5 Hz, H-4), 4.04 (dd, 1H, J5,6b 1.8 Hz,
H-6b), 3.68 (dd, 1H, J2,3 10.3 Hz, H-2), 3.65 (dd, 1H,
H-3), 3.48 (m, 1H, H-5), 2.82 (m, 2H, CH2S), 1.36 (t,
3H, J 7.5 Hz, CH3CH2S). 13C NMR (CDCl3): d 137.5,
128.4, 126.5 (C6H5), 101.4 (CHPh), 83.6 (C-1), 74.7,
73.4, 69.9 (C-3,4,5), 69.2 (C-6), 63.3 (C-2), 24.1
(SCH2), 15.0 (CH3CH2S).
1.8. Ethyl 2-amino-4,6-O-benzylidene-2-deoxy-1-thio-b-
D-galactopyranoside (21)
1.10. Ethyl 3,4-di-O-acetyl-2-azido-2-deoxy-6-O-
[methyl(5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-
D-glycero-D-galacto-2-nonulopyranosyl)onate]-1-thio-b-
D-galactopyranoside (25)
Compound 20 (2.20 g, 5.32 mmol), dissolved in EtOH
(20 mL) was refluxed in the presence of 10% aq NaOH
for 10 h. After cooling to rt, the mixture was filtrated
and the filter cake was washed with water (3 · 10 mL) be-
fore drying under vacuum. Compound 21 (1.59 g, 96%)
was obtained as a white amorphous solid: [a]D ꢁ73 (c
To a mixture of acceptor 13 (113 mg, 0.388 mmol),
˚
AgOTf (200 mg, 0.778 mmol) and 4 A molecular sieves
(320 mg) in THF (1.4 mL), cooled at ꢁ15 ꢁC under
argon and protected from light, was added a soln of
donor 223 (340 mg, 0.667 mmol) in THF (1 mL) over a
2 h period. After 1 h stirring at ꢁ15 ꢁC, then 25 h at
rt, the mixture was diluted with CH2Cl2 (25 mL) and
washed with satd aq NaHCO3. After drying over
MgSO4 and evaporation, the mixture was purified by
column chromatography (EtOAc). Compound 24
(133 mg, 45%) was obtained as an a /b mixture that
could be characterized by some of the signals in 13C
NMR (CDCl3): d 171.4–170.1 (CH3CO), 169.1, 168.0
(CO2CH3), 98.9, 98.4 (C-20), 84.5 (C-1), 62.7 (C-6, C-
90), 53.4, 52.9 (CO2CH3), 49.3, 49.2 (C-50), 36.9, 36.1
(C-30), 24.8, 24.6 (SCH2CH3), 14.9, 14.2 (SCH2CH3).
A better identification could be realized after acetylation
of compound 24 (131 mg, 0.171 mmol) in a mixture of
pyridine (8 mL) and Ac2O (2.5 mL), at rt, for 16 h. After
evaporation under diminished pressure and coevapora-
tion twice from toluene, the mixture was purified by col-
umn chromatography (EtOAc). Compound 25 (105 mg,
76%) was obtained as an a/b (3:1) mixture in which the
1
1.0, CHCl3); H NMR (CDCl3): d 7.49–7.37 (m, 5H,
C6H5), 5.55 (s, 1H, CHPh), 4.34 (dd, 1H, J5,6a 1.0 Hz,
J6a,6b 12.5 Hz, H-6a), 4.27 (d, 1H, J1,2 9.8 Hz, H-1),
4.18 (m, 1H, H-4), 4.03 (dd, 1H, J5,6b 1.3 Hz, H-6b),
3.58–3.50 (m, 2H, H-3,5), 3.14 (ddd, 1H, J2,3 9.0 Hz,
H-2), 2.79 (m, 2H, CH2S), 1.90 (m, 3H, OH, NH2),
1.34 (t, 3H, J 7.4 Hz, CH3CH2S). 13C NMR (CDCl3): d
137.8, 129.3, 128.3, 126.5 (C6H5), 101.4 (CHPh), 86.5
(C-1), 75.0, 74.3 (C-3,5), 70.0 (C-4), 69.6 (C-6), 52.5 (C-
2), 23.5 (SCH2), 15.3 (CH3CH2S). Anal. Calcd for
C15H21NO4S (311.389): C, 57.85; H, 6.79; N, 4.49.
Found: C, 57.62; H, 6.87; N, 4.46.
1.9. Ethyl 2-azido-4,6-O-benzylidene-2-deoxy-1-thio-
b-D-galactopyranoside (22)
Trifluoromethane
sulfonic
anhydride
(1.82 mL,
10.77 mmol) was added dropwise over 30 min to a mix-
ture of NaN3 (3.46 g, 53.22 mmol) in water (15 mL) and
CH2Cl2 (15 mL), cooled at 0 ꢁC. After 2 h stirring at
0 ꢁC, the organic layer was separated and the aq layer
was extracted with CH2Cl2 (2 · 10 mL). The combined
organic extracts were then washed with satd aq NaH-
CO3, water and finally dried over Na2SO4. After filtra-
tion, the resulting TfN3 soln was added in 1 h to a
1
ratio of anomers could be deducted from the H NMR
signals of H-1 (a-4.51, b-4.44) and H-30eq (a-2.50,
b-2.42). A small amount of the a-anomer could be
separated by subsequent chromatographies, for identifi-
1
cation purpose: H NMR (CDCl3); d 5.42 (d, 1H, J3,4
2.8 Hz, H-4), 5.29 (m, 3H, NHAc, H-70, H-80), 4.93

N. Laurent et al. / Carbohydrate Research 340 (2005) 1885–1892
1891
(dd, 1H, J3,2 10.1 Hz, H-3), 4.82 (m, 1H, H-40), 4.51 (d,
J3 eq,3 ax 12.7 Hz, H-30eq), 2.18, 2.15, 2.05, 2.04 (5 s,
15H, 5 CH3CO), 1.89 (m, 4H, CH3CO, H-30ax), 0.95
(s, 9H, SiC(CH3)3), 0.18 (s, 6H, Si(CH3)2). 13C NMR
(CDCl3): d 171.0, 170.9, 170.4, 170.3, 170.2 (CH3CO),
167.9 (CO2CH3), 98.8 (C-20), 97.6 (C-1), 73.3, 73.0,
72.7, 69.5, 69.0, 67.4, 66.0, 63.3 (C-2, 3, 4, 5, C-40, 60,
70, 80), 62.6 (C-6, C-90), 53.1 (CO2CH3), 49.3 (C-50),
36.9 (C-30), 25.7 (SiC(CH3)3), 23.2, 21.1, 21.0, 20.8
(CH3CO), 18.0 (SiC(CH3)3), ꢁ4.1, ꢁ5.2 (Si(CH3)2);
HRMS m/z calcd for [C34H54N4O18Si + H]+: 835.3281.
Found: 835.3290.
0
0
0
0
1H, J1,2 10.4 Hz, H-1), 4.29 (dd, 1H, J9a ,8 2.2 Hz,
J9a ,9b 12.2 Hz, H-9a0), 4.04 (m, 3H, H-50, H-60,
H-9b0), 3.90 (m, 1H, H-5), 3.77 (m, 4H, CO2CH3,
H-6a), 3.65 (t, 1H, H-2), 3.34 (dd, 1H, J6b,6a 10.3 Hz,
J6b,5 7.3 Hz, H-6b), 2.79 (m, 2H, SCH2CH3), 2.50 (dd,
1H, J3 eq,4 4.1 Hz, J3 ax,3 eq, 12.6 Hz, H-30eq), 2.21–
2.00 (6 s, 18H, 6 CH3CO), 1.87 (m, 4H, CH3CO, H-
30ax), 1.34 (t, 3H, J 7.6 Hz, SCH2CH3). 13C NMR
(CDCl3): d 171.2–171.0 (CH3CO), 169.3 (CO2CH3,
0
0
0
0
0
0
JC-1 ,H-3 ax 5.7 Hz), 100.0 (C-20), 84.8 (C-1), 75.5 (C-5),
73.5 (C-30), 73.0 (C-60), 69.1 (C-40), 68.4, 67.5 (C-70,
80), 67.1 (C-4), 63.4, 63.1 (C-6, C-90), 61.0 (C-2), 53.3
(CO2CH3), 49.6 (C-50), 38.2 (C-30), 25.6 (SCH2CH3),
23.6–21.1 (CH3CO), 15.4 (SCH2CH3).
0
0
1.12. tert-Butyldimethylsilyl 3,4-di-O-acetyl-2-azido-
2-deoxy-6-O-[methyl(5-acetamido-4,7,8,9-tetra-O-
acetyl-3,5-dideoxy-D-glycero-a-D-galacto-2-nonulo-
pyranosyl)onate]-b-D-galactopyranoside (27)
1.11. tert-Butyldimethylsilyl 3-O-acetyl-2-azido-2-
deoxy-6-O-[methyl(5-acetamido-4,7,8,9-tetra-O-acetyl-
3,5-dideoxy-D-glycero-a-D-galacto-2- nonulopyrano-
syl)onate]-b-D-galactopyranoside (26)
To a soln of compound 26 (235 mg, 0.281 mmol) in pyr-
idine (13 mL) cooled at 0 ꢁC, was added dropwise Ac2O
(4.5 mL). The mixture was left reaching rt and stirring
was continued for 18 h. After evaporation and co-evap-
oration from toluene under diminished pressure, the
mixture was diluted with CH2Cl2 (25 mL) and the or-
ganic soln was washed with water and satd aq NaCl
before drying over MgSO4, evaporation and purification
was done by column chromatography (EtOAc). Com-
pound 27 (204 mg, 83%) was obtained as an amorphous
solid: [a]D ꢁ22 (c 1.0, CHCl3); Rf 0.48 (EtOAc); 1H
NMR (CDCl3): d 5.34 (m, 3H, H-4, H-70,80), 5.20 (d,
A mixture of acceptor 14 (119 mg, 0.329 mmol) and
donor 324 (390 mg, 0.658 mmol) was carefully dried by
azeotropic distillation from toluene and then kept
under diminished pressure for 2 h, before solubilization
in a mixture of CH2Cl2 (3.8 mL) and CH3CN (9 mL).
˚
To this soln were added 4 A molecular sieves (720 mg)
and AgOTf (171 mg, 0.665 mmol); the mixture was then
stirred overnight under argon. After cooling to ꢁ63 ꢁC,
a soln of MeSBr,25 previously prepared by mixing dim-
ethyldisulfide (1.4 mL) with bromine (0.8 mL) in
CH2Cl2 (1.8 mL) and stirred under argon overnight
(0.48 mL) was added dropwise (25 min) to the preceed-
ing soln. After 6.5 h stirring at ꢁ63 ꢁC, N,N-diisopro-
pylethylamine (0.5 mL) was added to quench the
reaction and after 30 min, the mixture was left reaching
rt. After dissolution with CH2Cl2 and filtration on Cel-
ite, the organic extract was washed with water and dried
over MgSO4. After evaporation, the mixture was puri-
fied by column chromatography (EtOAc) to afford 26
contaminated with about 9% of glycal 15a (total amount
314 mg). This mixture was diluted in CH3CN (4.5 mL)–
CCl4 (4.5 mL) and water (7.5 mL) and vigorously stirred
in the presence of RuCl3Æ6H2O (10 mg, 0.03 mmol) and
NaIO4 (435 mg, 2.03 mmol), for 30 min. After extrac-
tion with CH2Cl2 (75 mL), the organic soln was dried
over MgSO4, evaporated and purified by column chro-
mato-graphy (EtOAc). Compound 26 (235 mg, 85%)
was obtained as an amorphous solid: [a]D ꢁ8 (c 1.0,
0
0
0
1H, JNH,H-5 9.5 Hz, NHAc), 4.86 (ddd, 1H, J3 eq,4
0
4.4 Hz, J3 ax,4 9.8 Hz, J4 ,5 12.3 Hz, H-40), 4.78 (dd,
1H, J3,4 3.5 Hz, J3,2 11.1 Hz, H-3), 4.65 (d, 1H, J1,2
0
0
0
0
0
0
0
7.6 Hz, H-1), 4.29 (dd, 1H, J9a ,8 2.5 Hz, J9a ,9b
12.6 Hz, H-9a0), 4.06 (m, 3H, H-50,60,9b0), 3.81 (m,
5H, H-5,6a, CO2CH3), 3.59 (dd, 1H, H-2), 3.30 (dd,
1H, J6b,5 9.1 Hz, J6a,6b 13.9 Hz, H-6b), 2.53 (dd, 1H,
J3 ax,3 eq 12.9 Hz, H-30eq), 2.17–2.03 (m, 21H,
7
0
0
CH3CO), 1.89 (m, 1H, H-30ax), 0.97 (s, 9H, SiC(CH3)3),
0.21 (s, 6H, Si(CH3)2). 13C NMR (CDCl3): d 170.9,
170.6, 170.3, 170.2, 169.8, 169.5 (CH3CO), 167.8
(CO2CH3, JC-1 ,H-3 ax 6.5 Hz), 98.8 (C-20), 97.2 (C-1),
72.5, 71.9, 71.0, 68.9, 67.9, 67.1, 66.9, 63.3 (C-2,3,4,5,
C-40,60,70,80), 63.2 (C-6), 62.4 (C-90), 52.9 (CO2CH3),
49.4 (C-50), 37.9 (C-30), 25.7 (SiC(CH3)3), 23.2, 21.0,
20.9, 20.8, 20.7 (CH3CO), 18.1 (SiC(CH3)3), ꢁ4.2,
ꢁ5.2 (Si(CH3)2); HRMS m/z calcd for [C36H56N4O19-
Si + H]+: 877.3386. Found: 877.3373.
0
0
1.13. 3,4-Di-O-acetyl-2-azido-2-deoxy-6-O-[methyl(5-
acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-
glycero-a-D-galacto-2-nonulopyranosyl)onate]-D-galacto-
pyranose (28)
1
CHCl3); Rf 0.45 (EtOAc); H NMR (CDCl3): d 5.38
(m, 1H, H-4), 5.34 (m, 1H, H-70), 5.18 (m, 2H, NHAc,
H-80), 4.87 (m, 1H, H-40), 4.65 (dd, 1H, J3,4 3.1 Hz,
J3,2 10.8 Hz, H-3), 4.58 (d, 1H, J1,2 7.6 Hz, H-1), 4.43
(dd, 1H, J9a ,8 2.3 Hz, J9a ,9b 13.4 Hz, H-9a0), 4.06 (m,
4H, H-50, 60, 9b0, H-5), 3.82 (m, 4H, CO2CH3, H-6a),
To a soln of compound 27 (188 mg, 0.214 mmol) in
THF (2.8 mL) cooled at 0 ꢁC were added 1M Bu4NF
in THF (0.25 mL, 4.0 equiv) and AcOH (0.12 mL).
0
0
0
0
3.66 (m, 2H, H-6b, H-2), 2.56 (dd, 1H, J3 eq,4 4.6 Hz,
0

1892
N. Laurent et al. / Carbohydrate Research 340 (2005) 1885–1892
Dziadek, S.; Kunz, H. Chem. Eur. J. 2003, 9, 6018–6030;
(e) Keil, S.; Claus, C.; Dippold, W.; Kunz, H. Angew.
Chem., Int. Ed. 2001, 40, 366–369.
The mixture was left reaching rt and then stirred for a
further 8 h. The mixture was diluted with CH2Cl2
(30 mL) and successively washed with water and satd
aq NaHCO3 before evaporation and purification by col-
umn chromatography (EtOAc). Compound 28 (115 mg,
71%) was obtained as a colourless oil: [a]D ꢁ9 (c 1.0,
CHCl3, lit.10 ꢁ14.1); Rf 0.56 (EtOAc); 13C NMR
(CDCl3): d 171.5–169.8 (CH3CO), 168.2 (CO2CH3),
98.8 (C-20), 96.4 (C-1b), 92.5 (C-1a), 72.6–66.8 (C-
2,3,4,5, C-40,60,70,80), 63.2, 62.9 (C-6, C-90), 52.9
(CO2CH3), 49.4 (C-50), 37.7 (C-30), 24.7–20.7 (CH3CO).
9. Iijima, H.; Ogawa, T. Carbohydr. Res. 1989, 186, 95–
106.
10. Iijima, H.; Ogawa, T. Carbohydr. Res. 1988, 172, 183–193.
11. Liebe, B.; Kunz, H. Tetrahedron Lett. 1994, 35, 8777–
8778.
12. Lu, K.-C.; Tseng, S.-Y.; Lin, C.-C. Carbohydr. Res. 2002,
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13. Yu, C.-S.; Niikura, K.; Lin, C.-C.; Wong, C.-H. Angew.
Chem., Int. Ed. 2001, 40, 2900–2903.
14. (a) Adachi, M.; Tanaka, H.; Takahashi, T. Synlett 2004,
609–614; (b) Reipen, T.; Kunz, H. Synthesis 2003, 2487–
2502.
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