The amide group in N-acetylglucosamine glycosyl acceptors affects glycosylation outcome

Article abstract of DOI:10.1021/jo050707+

Glycosylation of a disaccharide containing N-acetylglucosamine with rhamnosyl and mannosyl trichloracetimidates under triethysilyl triflate catalysis led to the competitive formation of glycosyl imidates. While the rhamnosyl imidate could be rearranged to

Full text of DOI:10.1021/jo050707+

The Amide Group in N-Acetylglucosamine Glycosyl Acceptors
Affects Glycosylation Outcome
Liang Liao and France-Isabelle Auzanneau*
Department of Chemistry, University of Guelph, Guelph, Ontario N1G 2W1, Canada
fauzanne@uoguelph.ca
Received April 8, 2005
Glycosylation of a disaccharide containing N-acetylglucosamine with rhamnosyl and mannosyl
trichloracetimidates under triethysilyl triflate catalysis led to the competitive formation of glycosyl
imidates. While the rhamnosyl imidate could be rearranged to the thermodynamically favored
trisaccharide, the mannosyl analogue was resistant to rearrangement. Glycosylation with perben-
zylated thiorhamnosides activated with methyl triflate (MeOTf) gave the trisaccharide as well as
the methyl imidate trisaccharide. The less reactive R-thioethyl donor led to a higher relative amount
of methyl imidate trisaccharide to trisaccharide than the more reactive â-thioglycoside. When using
a more reactive thioethyl fucoside only the trisaccharide was obtained. Interestingly, the acceptor
treated with MeOTf gave the N-methyl imidate that could be easily rhamnosylated and subsequently
converted to the N-acetamido trisaccharide. This strategy to glycosylate O-4 of N-acetylglucosamine
is under further investigation. Alternatively, bis-N-acetylation of the glucosamine prevented the
formation of imidates and allowed the efficient synthesis of two Lewis A trisaccharide analogues.
Introduction
The natural occurrence of numerous glycosides of
N-acetylglucosamine in biologically important oligo- and
polysaccharides such as bacterial polysaccharides and
blood group antigens1 often necessitates the efficient
chemical synthesis of 2-amino-2-deoxyglycopyranosides.
Among all hydroxyl groups of N-acetylglucosamine, the
4-OH group is well-known to be a poor glycosyl acceptor.2
The lack of reactivity at this position often greatly
impedes efficient chemical synthesis of oligosaccharides
in which a 1 f 4 glycosidic bond to the N-acetylglu-
cosamine is essential, for example, the tumor associated
hexasaccharide LeaLex 1 and Lewis blood group antigen
trisaccharide Lea 2.
from steric hindrance at this position.2 Recently Crich
et al. proposed an alternative explanation based on the
formation of a hydrogen bond involving the glucosamine
amide group that would lower the reactivity of such
acceptors toward glycosylation.4c While engaged in the
synthesis of analogue 3 via the coupling of acceptor 4 with
trichloroacetimidate 5, we have observed7 the formation
of a kinetically favored rhamnosyl imidate that could be
rearranged to the desired trisaccharide, albeit in moder-
ate yield. Thus, we argued that the competing formation
of glycosyl imidates could provide a third explanation to
the low reactivity of N-acetylglucosamine acceptors. We
herein further investigate this explanation coupling
In fact, construction of such glycosidic bonds usually
requires a highly reactive glycosyl donor3 or sophisticated
protection and deprotection schemes of the amino group.4-6
The low reactivity of the 4-OH group of N-acetylglu-
cosamine toward glycosylation has been believed to result
(1) (a) The Amino Sugars; Balazs, E. A., Jeanloz, R. W., Eds.;
Academic Press: New York, 1969; Vol. IIA. (b) Kennedy, J. F.; White,
C. A. In Carbohydrate Chemistry; Kennedy, J. F., Ed.; Clarendon
Press: Oxford, UK, 1988; Chapter 8 and references therein. (c) Hauser,
F. M.; Ellenberger, S. R. Chem. Rev. 1986, 86, 35-67. (d) Varki, A.
Glycobiology 1993, 3, 97-130.
(2) Paulsen, H. Angew. Chem., Int. Ed. Engl. 1982, 21, 155-173.
10.1021/jo050707+ CCC: $30.25 © 2005 American Chemical Society
Published on Web 07/01/2005
J. Org. Chem. 2005, 70, 6265-6273
6265

Liao and Auzanneau
signals expected10 for such O-orthoacetates. In contrast,
1H NMR spectroscopy showed the presence of exchange-
able OH signals at C-4 of the glucosamine units and the
absence of amide NH signals. The anomeric rhamnosyl
and mannosyl H-1′′ were found at unusually low fields
(6.08 and 6.44 ppm, respectively) while the rhamnosyl
and mannosyl anomeric carbons were found at higher
fields (92 and 91 ppm, respectively) than usually observed
for anomeric carbons. The 1JC-1′′,H-1′′ coupling constants
measured for the rhamnose and mannose anomeric
carbons, 177 and 178 Hz, respectively, confirmed that
these were R-linkages.11 In our pervious communication,7
a glycosyl imidate structure was assigned to 7 based on
the observation that a methyl group signal was found at
higher field (16 ppm) than expected for an acetyl methyl
group (24 ppm) and that a quaternary signal assigned
to the imidate CdN was found at 162 ppm. While similar
signals were found for 8, these characteristics do not
unambiguously exclude the possibility that in both cases
glycosylation might have occurred at the nitrogen atom,
leading to N-rhamno- and N-mannoside, respectively. In
fact, Dauben et al. have suggested12 the formation of an
N-glucosyl product when reacting benzyl 2-acetamido-
3,6-di-O-acetyl-2-deoxy-R-D-glucopyranoside with tetra-
O-benzoyl-R-D-glucopyranosyl bromide. And subsequently
Clinch et al.13 have reported that glycosylation of 4-ni-
trophenyl 2-acetamido-3-O-benzoyl-6-O-chloroacetyl-2-
deoxy-â-D-glucopyranoside with tetra-O-benzoyl-R-D-
galactopyranosyl bromide gave a product in which the
galactose residue could be either N- or O-linked to the
glucose N-acetyl group. In our case HMBC experiments
acquired for 7 and 8 gave additional support to the
glycosyl imidate structures. Indeed, while we found long-
range correlations between Rha-H-1′′ or Man-H-1′′ and
the quaternary carbons at 162 ppm (CdN), we did not
find the correlations that would be expected for N-
rhamno- or N-mannosylated structures, i.e., between Glu-
C-2 and Rha- or Man-H-1′′ as well as between Glu-H-2
and Rha- or Man- C-1′′, in 7 or 8, respectively. Thus we
confirm that our products are indeed imidates 7 and 8
and are unlikely to be the N-rhamnosylated or N-
mannosylated isomers. While Pougny and Sinay¨14 first
reported the isolation of glycosyl imidates when treating
a fully protected N-acetylglucosamine glycoside with
glycosyl donors in Koenigs-Knorr conditions, their for-
mation during the attempted glycosylation of an OH
group has only been hypothesized by Hindsgaul et al.15
acceptor 4 with mannosyl trichloroacetimidate 6 using
various concentrations of triethylsilyl trifluoromethane-
sulfonate (TESOTf) as an activator. As an alternative to
the use of trichloroacetimidate glycosyl donors we also
report our results when acceptor 4 was allowed to react
with thioethyl glycosyl donors under methyl trifluo-
romethanesulfonate (MeOTf) activation. While no glyco-
syl imidates were formed in these conditions, we report
here that trisaccharide methyl imidates may be isolated
in amounts that will vary depending on the reactivity of
the glycosyl donor. As communicated previously7 we also
expand on the use of a di-N-acetylated disaccharide
acceptor to efficiently prepare the mannosylated trisac-
charide using the trichloracetimidate donor.
Results and Discussion
As we have communicated,7 coupling of 4 with the R-L-
rhamnopyranosyl trichloroacetimidate8 5 at low temper-
ature and with 0.1 equiv of TESOTf afforded the imidate
derivative 7 in 42% yield. In contrast, no reaction was
observed when trichloroacetimidate mannosyl donor 69
and acceptor 4 were allowed to react in the same
conditions. However, when the concentration of TESOTf
was increased to 0.5 equiv the mannosyl imidate 8 was
isolated in 86% yield, supporting the fact that the
mannosyl donor 6 was less reactive than the rhamnosyl
donor 5. Even though donors such as 5 and 6 are prone10
to give ortho esters during glycosylation, 1H and 13C NMR
spectroscopy for 7 and 8 did not show any of the typical
(3) For examples, see: (a) Lemieux, R. U.; Driguez, H. J. Am. Chem.
Soc. 1975, 97, 4063-4068. (b) Lemieux, R. U.; Bundle, D. R.; Baker,
D. A. J. Am. Chem. Soc. 1975, 97, 4076-4083. (c) Jacquinet, J.-C.;
Sinay¨, P. J. Chem. Soc., Perkin Trans. 1 1979, 319-322. (d) Manzoni,
L.; Lay, L.; Schmidt, R. R. J. Carbohydr. Res. 1998, 17, 739-758.
(4) For examples, see: (a) Boons, G.-J.; Hale, K. Organic Synthesis
with Carbohydrates; Sheffield Academic Press: Sheffield, England,
2000; Chapter 2, pp 51-53; Chapter 3, pp 76-84; Chapter 4, pp 122-
124. (b) Lindhorst, T. K. Essentials of Carbohydrate Chemistry and
Biochemistry, 2nd ed.; Wiley-VCH Verlag GmbH & Co. KGaA: Wein-
heim, Germany, 2003; Chapter 3, pp 72-74; Chapter 4, pp 97-100.
(c) Crich, D.; Dudkin, V. J. Am. Chem. Soc. 2001, 123, 6819-6825. (d)
Crich, D.; Vinod, A. U. Org. Lett. 2003, 5, 1297-1300. For a review on
synthesis of oligosaccharides of 2-amino-2-deoxy sugars, see: (e)
Banoub, J.; Boullanger, P.; Lafont, D. Chem. Rev. 1992, 92, 1167-
1195. Herzner, H.; Reipen, T.; Schultz, M.; Kunz, H. Chem. Rev. 2000,
100, 4495-4537. For a review on N-protection for amino sugars, see:
(f) Debenham, J.; Rodebaugh, R.; Fraser-Reid, B. Liebigs Ann. 1997,
791-802.
(5) Yan, L.; Kahne, D. J. Am. Chem. Soc. 1996, 118, 9239-9248.
(6) Crich, D.; Vinod, A. U. J. Org. Chem. 2005, 70, 1291-1296.
(7) Liao, L.; Auzanneau, F.-I. Org. Lett. 2003, 5, 2607-2610.
(8) Van Steijn, A. M. P.; Kamerling, J. P.; Vliegenthart, J. F. G.
Carbohydr. Res. 1991, 211, 261-277.
(9) (a) Kerekgyarto, J.; Kamerling, J. P.; Bouwstra, J. B.; Vliegent-
hart, J. F. G.; Lipta´k, A. Carbohydr. Res. 1989, 186, 51-62. (b) Masato,
M.; Ito, Y.; Ogawa, T. Carbohydr. Res. 1990, 195, 199-224.
(10) (a) Perlin, A. S. Can. J. Chem. 1963, 41, 399-406. (b) Auzan-
neau, F.-I.; Bundle, D. R. Can. J. Chem. 1993, 71, 534-548.
(11) Bock, K.; Pedersen, C. J. J. Chem. Soc., Perkin Trans. 2 1974,
293-297.
(12) Dauben, W.; Kohler, P. Carbohydr. Res. 1990, 203, 47-56.
(13) Clinch, K.; Evans, G.; Furneaux, R. H.; Rendle, P. M.; Rhodes,
P. L.; Roberton, A. M.; Rosendale, D. I.; Tyler, P. C.; Wright, D. P.
Carbohydr. Res. 2002, 337, 1095-1111.
(14) Pougny, J.-R.; Sinay¨, P. Carbohydr. Res. 1976, 47, 69-79.
(15) Hindsgaul, O.; Norberg, T.; Le Pendu, J.; Lemieux, R. U.
Carbohydr. Res. 1982, 109, 109-142.
6266 J. Org. Chem., Vol. 70, No. 16, 2005

Glycosylation of a Disaccharide
SCHEME 1a
fore investigated the reaction of thioglycosides 10-14
with acceptor 4 under activation with an excess (5 to 8
equiv) of MeOTf at room temperature (Table 1, entries
1-6).
Overall the activation of the known17 peracetylated
thioglycoside donors 10 and 11 with MeOTf proved to be
very difficult and led in both cases to the formation of
multiple compounds that were observed by TLC but could
be neither purified nor identified. However, while no
product could be isolated when using the R-thioglycoside
10 as a donor, coupling of the more reactive peracetylated
â-thiorhamnoside gave trisaccharide 9 in 20% yield. As
expected, the known18,19 perbenzylated thiorhamnosides
12 and 13 were more easily activated (Table 1, entries 3
and 4). In the latter case, TLC showed that the starting
materials had disappeared within 1 h of adding MeOTf
giving two new products whose relative ratio assessed
by TLC did not change overnight. In contrast, the
reaction with use of the R-donor 12 proceeded more slowly
but nevertheless gave the same two new products as 13.
These two new products were identified by NMR spec-
troscopy as being the methyl imidate trisaccharide 15 and
the desired trisaccharide 16. Signals corresponding to the
anomeric H-1′′ of the rhamnosyl unit were found at 5.00
and 4.90 ppm, for 15 and 16, respectively, while signals
at 98.7 and 97.7 ppm were assigned to the rhamnosyl
C-1′′ in 15 and 16, respectively. In both products the
R-configuration of the rhamnosidic bond was confirmed11
a Reagents and conditions: (i) TESOTf (0.5 equiv), rt; (ii)
TESOTf (0.1 equiv), -78 °C to rt.
In the latter work the suspected fucosyl imidate was seen
to be highly sensitive to hydrolysis and degraded during
chromatography. In our work while the rhamnosyl imi-
date 7 did partially degrade during purification, we
observed that the mannosyl imidate 8 was fully stable
to workup and purification leading to a much higher yield
of 8 when compared to that of the rhamnosyl imidate 7.
Since glycosyl imidates are known to be efficient
glycosyl donors,16 we investigated the ability of imidates
7 and 8 to behave as such and react via an inter- or
intramolecular delivery of the rhamnosyl or mannosyl
unit onto the free 4-OH group of the N-acetylglucosamine
residue to give the corresponding trisaccharides. How-
ever, while we had observed7 that imidate 7 could be
rearranged to trisaccharide 9 in 50% yield upon stirring
at room temperature in the presence of 0.5 equiv of
TESOTf (Scheme 1), the mannosyl imidate 8 was found
to be totally resistant to rearrangement even under harsh
conditions (e.g. 1.2 equiv of TESOTf at 35 °C). With
respect to the rhamnosyl imidate, we further report that
it could be formed when coupling 5 and 4 at -78 °C (0.1
equiv of TESOTf) and subsequently rearranged in situ
to trisaccharide 9 by adding more catalyst (up to 0.5
equiv) and raising the temperature (Scheme 1). Thus we
conclude that imidates such as 7 may be formed kineti-
cally when glycosylations of N-acetylglucosamine glycosyl
acceptors are conducted at low temperature and in
slightly basic,12,15 neutral,13 or mildly acidic reaction
conditions. In these reactions, the formation of the
desired glycosides at O-4 of the glucosamine residue
appears to be under thermodynamic control and requires
higher concentrations of Lewis acid and higher temper-
atures. However, in cases such as that of mannosyl
imidate 8 the kinetically favored intermediates may not
be able to rearrange to the glycosides and their competi-
tive formation thus constitutes a third explanation for
the poor results commonly observed when attempting to
glycosylate the 4-OH group in N-acetylglucosamine de-
rivatives.
1
by the value measured for the JC-1′′,H-1′′ coupling con-
stant of 169 and 168 Hz for 15 and 16, respectively.
However, while typical signals corresponding to the NH
and acetamido groups were found at 5.74 (NH), 170 (Cd
O), and 20 ppm (CH3) for trisaccharide 16, it was not so
for trisaccharide 15. In fact, NMR spectroscopy of trisac-
charide 15 showed analogous signals to the glycosyl
imidates 7 and 8, i.e., no NH but a quaternary CdN and
a methyl carbon that were both shifted to 165 and 16.6
ppm, respectively. The HMBC showed a long-range
correlation between the CdN signal and a new OCH3
signal found at 3.66 ppm in the 1H NMR spectrum
supporting that this compound was methyl imidate 15.
Once again, N-methylation was excluded based on the
absence of long-range correlations between the glu-
cosamine C-2 signal at 65.8 ppm and the new CH3
mentioned above as well as between the new carbon CH3
found at 52.5 ppm and H-2 of the glucosamine residue
at 3.69 ppm.
The syntheses of ethyl acetimidium fluoroborate salts20
and alkyl acetimidates21,22 by treating N-acetylglu-
cosamine derivatives with triethyloxonium fluoroborate,20
methyl perchlorate,21 methyl iodide,21a or benzyl trichlo-
roacetimidate22 have been described. These are indeed
useful intermediates to remove the acetamido group of
N-acetylglucosamine with mild conditions.20-22 In con-
As demonstrated above, the formation of glycosyl
imidates and their rearrangement to the desired glyco-
sides is highly dependent on the structure of the glycosyl
donor and the reaction conditions. It is reasonable to
expect that conditions employing an excess of Lewis acid
could prevent the formation of glycosyl imidates through
the neutralization of the N-acetamido group. We there-
(17) Auzanneau, F.-I.; Bundle, D. R. Carbohydr. Res. 1991, 212, 13-
24.
(18) Ray, A. K.; Maddali, U. B.; Roy, A.; Roy, N. Carbohydr. Res.
1990, 197, 93-100.
(19) Yu, H.; Yu, B.; Wu, X.; Hui, Y.; Han, X. J. Chem. Soc., Perkin
Trans. 1 2000, 9, 1445-1453.
(20) Hanessian, S. Tetrahedron Lett. 1967, 16, 1549-1552.
(21) (a) Kraska, U.; Pougny, J.-R.; Sinay¨, P. Carbohydr. Res. 1976,
50, 181-190. (b) Pougny, J.-R.; Kraska, U.; Sinay¨, P. Carbohydr. Res.
1978, 60, 383-388.
(16) (a) Pougny, J.-R.; Jacquinet, J.-C.; Nassr, M.; Duchet, D.; Milat,
M.-L.; Sinay¨, P. J. Am. Chem. Soc. 1977, 99, 6762-6763. (b). Schmidt,
R. R.; Kinzy, W. Adv. Carbohydr. Chem. Biochem. 1994, 50, 21-123.
(22) Kusumoto, S.; Yamamoto, M.; Shiba, T. Tetrahedron Lett. 1984,
25, 3727-3730.
J. Org. Chem, Vol. 70, No. 16, 2005 6267

Liao and Auzanneau
TABLE 1. Methyl Triflate-Catalyzed Glycosylations
imidate
(yielda)
trisaccharide
(yielda)
recovered
entry
donor (M)
acceptor (M)
MeOTf (M)
time (h)
acceptor (yielda)
1
2
3
4
5
6
7
8
9
10 (0.05)
11 (0.05)
12 (0.05)
13 (0.05)
14 (0.05)
14 (0.09)
none
4 (0.02)
4 (0.02)
4 (0.02)
4 (0.02)
4 (0.02)
4 (0.03)
4 (0.02)
4 (0.02)
18 (0.02)
0.15
48
42
18
18d
1
6-24
18
18
1
b
b
c
0.10-0.15
0.10
b
9 (20%)
16 (24%)
16 (36%)
17 (77%)
17 (71%)
e
c
15 (58%)
15 (49%)
b
b
0.10
b
0.10
b
0.15
b
b
0.10
18 (47%)
18 (76%)
15 (85%)
48%
b
none
0.50
e
e
13 (0.05)
0.10
b
a Isolated yields. b Note detected. c Not recovered. d After 1 h, no more acceptor 4 was detected by TLC. e Not applicable.
trast, the formation of such methyl imidates during a
methyl triflate promoted O-glycosylation of N-acetylglu-
cosamine acceptors has, to our knowledge, not been
reported. In fact, only one similar methyl imidate deriva-
tive of sialic acid has been reported by Allen and
Danishefsky23 while attempting a difficult [3 + 3] cou-
pling that involved a trisaccharide acceptor carrying an
N-acetylated sialic acid residue.
Interestingly, no such imidate was isolated or even
detected by TLC when the â-thioethyl fucopyranoside24
14 was reacted with acceptor 4 (Table 1, entries 5 and 6)
and after only 1 h of reaction (Table 1, entry 5) the
trisaccharide 17 was isolated in 77% yield. Increasing the
concentration of MeOTf and maintaining stirring at room
temperature for either 6 or 24 h (Table 1, entry 6) did
not lead to the formation of any detectable trisaccharide
methyl imidate but only to the isolation of trisaccharide
17. In contrast, disaccharide acceptor 4 treated with the
same concentration of MeOTf in the absence of glycosyl
donor (Table 1, entry 7) gave the disaccharide methyl
imidate 18 in 47% yield while unreacted acceptor was
also recovered in 48% yield. These observations prompted
us to investigate if this reaction could be used as a
temporary protection of the N-acetyl group in acceptor 4
and thus increase reactivity at O-4 of the glucosamine.
Indeed, acceptor 4 was converted to the methyl imidate
18 in good yields by increasing the MeOTf concentration
(Table 1, entry 8). In turn, coupling of methyl imidate
18 with donor 13 gave trisaccharide methyl imidate 15
in 85% isolated yield after only 1 h of reaction (Table 1,
entry 9). Finally, we established simple yet efficient
reaction conditions to convert the methyl imidate trisac-
charide 15 to trisaccharide 16 in 91% yield using 23%
AcOH in Ac2O at 55 °C. Additional work on the ap-
plicability of this strategy with various combinations of
donors, acceptors, and glycosylation methods is beyond
the scope of this paper but ongoing in our laboratory.
Since the glycosylations with peracetylated glycosyl
donors gave only mediocre results, we report here the
results that we obtained when we investigated a syn-
thetic strategy established for the glycosylation of the
poorly reactive 8-OH group in sialic acid-containing
glycosyl25 acceptors and later applied to that of the 4-OH
group of an N-acetylated glucosamine acceptor.4c In these
syntheses the C-5 and C-2 amino groups in the sialic acid
and glucosamine residues, respectively, were bis-acety-
lated prior to glycosylation. As communicated previously7
the known26 disaccharide 19 was easily converted in two
steps to the desired glycosyl acceptor 21 (Scheme 2).
Glycosylation of 21 with trichloroacetimidate donor 5 was
conducted at low temperature with 0.15 equiv of TESOTf
and gave trisaccharide 22 (91%). In contrast, coupling of
the mannosyl donor 6 with disaccharide 21 did not
(25) (a) Demchenko, A. V.; Boons, G.-J. Chem. Eur. J. 1999, 5, 1278-
1282. (b) De Meo, C.; Demchenko, A. V.; Boons, G.-J. J. Org. Chem.
2001, 66, 5490-5497.
(26) Khare, D. P.; Hindsgaul, O.; Lemieux, R. U. Carbohydr. Res.
1985, 136, 285-308.
(23) Allen, J. R.; Danishefsky, S. J. J. Am. Chem. Soc. 1999, 121,
10875-10882.
(24) Lonn, H. Carbohydr. Res. 1985, 139, 105-113.
6268 J. Org. Chem., Vol. 70, No. 16, 2005

Glycosylation of a Disaccharide
SCHEME 2
donors. Upon activation with MeOTf, coupling of the
donor 14 with acceptor 21 gave trisaccharide 24 in 82%
yield only modestly improving the yield over the fucosy-
lation of N-acetylated acceptor 4 (Table 1, entries 5 and
6). However, when using the trichloroacetimidates 5 and
6, these results show that bis-acetylation of the nitrogen
in the glucosamine unit led to efficient glycosylations at
OH-4 while preventing the formation of glycosyl imidates.
Since the D-mannosylated analogue 23 is not relevant
to our overall research program it was not further
deprotected. However, since our research program re-
quires the synthesis of the Lea trisaccharide 2 as well as
that of the rhamnosylated analogue 3, trisaccharides 9
or 22 and 24 were deprotected. Zemple`n deacetylation
of 9 or 22 gave quantitatively in both cases the benzy-
lated trisaccharide 26 which was easily converted to
proceed when only 0.15 equiv of TESOTf was added, once
again further supporting that mannosyl glycosyl donors
are less reactive than the analogous rhamnosyl donors.
However, increasing the concentration of TESOTf to 0.5
equiv led to the efficient coupling of donor 6 with acceptor
21 and gave mannosylated trisaccharide 23 in excellent
yield (95%).
rhamnosylated analogue 3. Similarly, Zemple`n deacety-
lation of 24 gave quantitative yield of the benzylated
trisaccharide 27, which was converted to the trisaccha-
ride Lea (2) by hydrogenolysis (H2-Pd/C). We therefore
report here a new synthesis of the Lea trisaccharide 2
that is overall simpler than that described previously by
Yan and Kahne.5
We first attempted to couple disaccharide 21 and
fucosyl donor 14 using very mild activation conditions:
N-iodosuccinimide and trifluoromethanesulfonic acid
(TfOH) at low temperature. However, under these condi-
tions donor 14 was promptly converted to the N-succin-
imide glycoside 25 and the unreacted acceptor 21 was
recovered (Scheme 3). It is likely that formation of 25
Conclusions
Following our initial observation,7 we have now clearly
established that the formation of glycosyl imidates could
be the predominant reaction during the glycosylation of
N-acetylglucosamine glycosyl acceptors. Depending on
their stability and the reaction conditions, these imidates
formed kinetically may or may not rearrange to the
desired thermodynamically favored glycosides. The for-
mation of such imidates provides an explanation for the
difficulties encountered when attempting to glycosylate
poorly reactive hydroxyl groups in acceptors containing
N-acetylglucosamine residues. Depending on the nature
of the glycosyl donor we have shown that the glycosyation
of such acceptors could be difficult or even impossible as
was also observed but not explained recently by Lucas
et al.28 In contrast, coupling of such acceptor with
thioglycosides activated by methyl triflate may lead to
the formation of the N-methyl imidate trisaccharide. In
fact, protection of the amido function through N-methyl
imidate formation prior to glycosylation is currently
under further investigation in our group since it led in
SCHEME 3
resulted from the greater nucleophilicity of the succin-
imide nitrogen over that of the 4-OH in glycosyl acceptor
21 and, in fact, 25 was formed readily at low temperature
in the presence of aglycon 21 and before the addition of
TfOH. Similar formations of N-succinimide glycosides27
have been reported when using highly reactive glycosyl
(27) (a) Zhang, Z.; Ollmann, I. R.; Ye, X.-S.; Wischnat, R.; Baasov,
T.; Wong, C.-H. J. Am. Chem. Soc. 1999, 121, 734-753. (b) Oscarson,
S.; Tedebark, U.; Turek, D. Carbohydr. Res. 1997, 299, 159-164. (c)
Krog-Jensen, C.; Oscarson, S. J. Org. Chem. 1996, 61, 1234-1238.
(28) Lucas, R.; Hamza, D.; Lubineau, A.; Bonnaffe´, D. Eur. J. Org.
Chem. 2004, 2107-2117.
J. Org. Chem, Vol. 70, No. 16, 2005 6269

Liao and Auzanneau
δ 7.35-7.26 (m, 5H, Ar); 6.44 (d, 1H, J ) 1.7 Hz, H-1′′); 5.39-
5.36 (m, 3H, H-3′, H-4′, H-3′′); 5.30 (bd, 1H, J ) 1.0 Hz, H-2′′);
5.21-5.11 (m, 2H, H-2′, H-5′); 4.76 (d, 1H, J ) 7.8 Hz, H-1′);
4.63 (2d, 2H, J ) 12.3 Hz, OCH2Ph); 4.29 (dd, 1H, J ) 12.9,
5.0 Hz, H-6a′′); 4.19-4.08 (m, 6H, H-6b′′, H-6a′, H-6b′, H-5′′,
H-4′′, H-1); 3.9 (dd, 1H, J ) 11.0, 1.6 Hz, H-6a); 3.67 (dd, 1H,
J ) 10.9, 5.9 Hz, H-6b); 3.57 (bs, 1H, OH); 3.54-3.46 (m, 3H,
H-3, H-4, H-5); 3.44 (s, 3H, OCH3); 3.26 (dd, 1H, J ) 9.0, 7.7
Hz, H-2); 2.23-1.94 (9s, 9 × 3H, N-acetyl and O-acetyl). 13C
NMR (100.6 MHz, CDCl3) δ 170.2, 169.9, 169.9, 169.6, 169.5
(CdO); 161.4 (CdN); 138.4, 128.3, 127.5, 127.5 (Ar); 103.3 (C-
the present study to a highly reactive glycosyl acceptor
and excellent yields of the protected rhamnosylated
trisaccharide 15 that was easily converted to trisaccha-
ride 16. Similarly to the formation of the methyl imidate,
we have also prepared the corresponding bis-N-acetylated
acceptor that was glycosylated with trichloroacetimidate
glycosyl donors. This alternative strategy gave, as
expected,25,4c the desired trisaccharides in excellent yields
and we have efficiently prepared the Lea trisaccharide 2
as well as analogue 3. Thus these results shed some light
on the particular behavior of N-acetylglucosamine and
its derivatives in synthetic carbohydrate chemistry.
1
1); 100.8 (C-1′); 90.9 (C-1′′, JC-H) 178 Hz); 86.8 (C-3); 75.9
(C-5); 73.6 (OCH2Ph); 70.8, 70.6, 70.5, 69.0, 68.6, 68.0, 67.3,
65.9 (C-4, C-2′, C-3′, C-4′, C-5′, C-2′′, C-3′′, C-4′′, C-5′′); 69.8
(C-6); 64.0 (C-2); 62.2 (C-6′′); 61.2 (C-6′); 57.1 (OCH3); 21.1,
20.8, 20.8, 20.6, 20.5, 20.5 (O-COCH3); 16.3 (N-acetimidate
CH3). HRESIMS calcd for C44H60NO24 [M + H]+ 986.3505,
found 986.3553.
Methyl 2-Acetamido-6-O-benzyl-3-O-(â-D-tetra-O-acetyl-
â-D-galactopyranosyl)-4-O-(2,3,4-tri-O-acetyl-r-L-rham-
nopyranosyl)-2-deoxy-â-D-glucopyranoside (9). Method
A. Imidate 7 (20 mg, 22 µmol) was dissolved in anhyd CH2Cl2
(2 mL). Powdered activated 4 Å molecular sieves (200 mg) were
added and the mixture was stirred for 3 h at room tempera-
ture. A freshly prepared TESOTf solution (0.37 M) in anhyd
CH2Cl2 (29 µL, 11 µmol, 0.5 equiv) was added at room
temperature and the mixture was stirred for 30 min. TLC (15:1
CHCl3-MeOH) showed the disappearance of 7 and the forma-
tion of a new compound. The reaction was quenched with NEt3
(10 µL) and worked up as described above for the synthesis of
compound 7. Column chromatography (98:2, CH2Cl2-MeOH)
gave the pure trisaccharide 9 as a colorless glass (10 mg, 50%).
Experimental Section
Methyl 3-O-(2,3,4,6-Tetra-O-acetyl-â-D-galactopyrano-
syl)-2-N-(2,3,4-tri-O-acetyl-r-L-rhamnopyranosyl)acetim-
ido-6-O-benzyl-2-deoxy-â-D-glucopyranoside (7). The dis-
accharide glycosyl acceptor 4 (50 mg, 76 µmol) and peracetylated
R-L-rhamnopyranosyl trichloroacetimidate8 5 (66 mg, 150 µmol,
2 equiv) were dissolved in anhyd CH2Cl2 (3.3 mL). Powdered
activated 4 Å molecular sieves (300 mg) were added and the
mixture was stirred 5 h at room temperature and then cooled
to -78 °C. A freshly prepared 0.37 M solution of TESOTf in
anhyd CH2Cl2 (21 µL, 7.6 µmol, 0.1 equiv) was added and the
temperature was allowed to reach room temperature over 2
h. The reaction was quenched with NEt3 (10 µL) and the
reaction mixture diluted with CH2Cl2 (50 mL) was filtered
through Celite. The solids were washed with CH2Cl2 (3 × 10
mL) and the combined filtrate and washings was washed
sequentially with saturated NaHCO3 (50 mL) and brine (50
mL). The aqueous phases were re-extracted with CH2Cl2 (30
mL) and the combined organic layers were dried (Na2SO4) and
concentrated. A quick column chromatography (98:2 CH2Cl2-
MeOH) of the residue on silica gel (70-230 mesh) gave imidate
Method B. The glycosyl acceptor 4 (100 mg, 150 mmol) and
peracetylated R-L-rhamnopyranosyl trichloroacetimidate8
5
(330 mg, 750 µmol, 5 equiv) were dissolved in anhyd CH2Cl2
(2.5 mL). Powdered activated 4 Å molecular sieves were added
and the mixture was stirred for 5 h at room temperature. A
freshly prepared solution (0.37 M) of TESOTf in anhyd CH2-
Cl2 (216 µL, 75 µmol, 0.5 equiv) was added and the mixture
was stirred overnight at room temperature. The reaction was
quenched with NEt3 (20 µL) and worked up as described above
for the synthesis of compound 7. Chromatography as described
above in method A gave the trisaccharide 9 pure as a colorless
glass (74 mg, 52%).
1
7 pure as a colorless glass (30 mg, 42%). H NMR (600 MHz,
CDCl3) δ 7.36-7.33 (m, 5H, Ar); 6.08 (d, 1H, J ) 1.7 Hz, H-1′′);
5.48 (dd, 1H, J ) 3.3, 1.9 Hz, H-2′′); 5.35 (bd, 1H, J ) 3.4 Hz,
H-4′); 5.26 (dd, J ) 10.2, 3.5 Hz, H-3′′); 5.19 (dd, 1H, J ) 10.2,
8.4 Hz, H-2′); 5.14 (m, 1H, H-4′′); 4.95 (dd, 1H, J ) 10.4, 3.5
Hz, H-3′); 4.64, 4.60 (2d, 2H, J ) 12.3 Hz, OCH2Ph); 4.54 (d,
1H, J ) 8.0 Hz, H-1′); 4.16 (d, 1H, J ) 7.8 Hz, H-1); 4.11 (d,
2H, bd, J ) 6.6 Hz, H-6a′, H-6b′); 4.02 (dd, 1H, J ) 9.8, 6.2
Hz, H-5′′); 3.98 (m, 1H, H-5′); 3.90 (s, 1H, OH); 3.89 (bs, 1H,
H-6a); 3.69 (dd, 1H, J ) 10.8, 6.0 Hz, H-6b); 3.56 (m, 2H, H-3,
H-4); 3.47 (m, 4H, OCH3, H-5); 3.25 (m, 1H, H-2); 2.20-1.77
(8 s, 8 × 3H, N-acetyl and O-acetyl); 1.23 (d, 3H, J ) 6.0, H-6′′).
13C NMR (150.9 MHz, CDCl3) δ 170.4, 170.1, 169.9, 169.3 (Cd
O); 161.6 (CdN); 138.5, 128.3, 127.6, 127.5 (Ar); 103.4 (C-1);
Method C. The glycosyl acceptor 4 (60 mg, 90 µmol) and
peracetylated R-L-rhamnopyranosyl trichloroacetimidate8 5 (79
mg, 180 µmol, 2 equiv) were dissolved in anhyd CH2Cl2 (4 mL).
Powdered activated 4 Å molecular sieves (400 mg) were added,
the mixture was stirred at room temperature for 3 h and then
cooled to -78 °C. A freshly prepared solution (0.37 M) of
TESOTf in anhyd CH2Cl2 (25.2 µL, 9 µmol, 0.1 equiv) was
added and the temperature was allowed reach room temper-
ature over 2 h. TLC (98:2 CH2Cl2-MeOH) showed the forma-
tion of imidate 7. More TESOTf solution (0.37 M) in anhyd
CH2Cl2 (125 µL, 45 µmol, 0.5 equiv) was added at room
temperature and the mixture was stirred for 1 h until TLC
showed complete conversion of imidate 7. The reaction was
quenched with NEt3 (10 µL) and worked up as described above
for the synthesis of compound 7. Chromatography as described
above in method A gave the trisaccharide 9 pure as a colorless
glass (46 mg, 55%).
Method D. The glycosyl acceptor 4 (25 mg, 38 µmol) and
ethyl 2,3,4-tri-O-acetyl-1-thio-â-L-rhamnopyranoside 11 (38
mg, 114 µmol, 3 equiv)17 were dissolved in anhyd Et2O (2 mL).
Powdered activated 4 Å molecular sieves (200 mg) were added
and the mixture was stirred at room temperature for 3 h.
MeOTf was added (22 µL, 198 µmol, 5 equiv, 0.1 M) and the
mixture was stirred at room temperature for 18 h. More
MeOTf was added (13 µL, 114 mmol, 3 equiv, total 0.15 M)
and the mixture was stirred at room temperature for another
24 h. The reaction was quenched with Et3N (50 µL) and worked
up as described above for the synthesis of compound 7.
1
101.6 (C-1′); 92.1 (C-1′′, JC-H) 177 Hz); 88.1 (C-3); 75.6 (C-
5); 73.6 (OCH2Ph); 71.0, 70.9 (C-3′, C-5′); 70.7 (C-4′′); 69.8 (C-
6); 69.0, 68.8, 68.6 (C-3′′, C-2′, C-5′′); 68.2 (C-2′′); 66.9 (C-4′);
63.8 (C-2); 61.6 (C-6′); 57.3 (OCH3); 21.0, 20.9, 20.8, 20.7, 20.6,
20.5 (O-COCH3); 17.7 (C-6′′); 15.8 (N-acetimidate CH3) HR-
CIMS calcd for C42H58NO22 [M + H]+ 928.3450, found 928.3427.
Methyl 3-O-(2,3,4,6-Tetra-O-acetyl-â-D-galactopyrano-
syl)-2-N-(2,3,4,6-tetra-O-acetyl-r-D-mannopyranosyl)ace-
timido-6-O-benzyl-2-deoxy-â-D-glucopyranoside (8). The
disaccharide glycosyl acceptor 4 (25 mg, 30 µmol) and per-
acetylated R-D-mannopyranosyl trichloroacetimidate9 6 (74 mg,
150 µmol, 5 equiv) were dissolved in anhyd CH2Cl2 (1 mL).
Powdered activated 4 Å molecular sieves (100 mg) were added
and the mixture was stirred for 4 h at room temperature. A
freshly prepared solution (0.37 M) of TESOTf in anhyd CH2-
Cl2 (41 µL, 15 µmol, 0.5 equiv) was added and the reaction
was stirred for 18 h at room temperature. The reaction was
then quenched with NEt3 (10 µL) and workup was carried out
as previously described for the synthesis of imidate 7. The
crude product was purified by flash chromatography (98:1 CH2-
Cl2-MeOH then 98:2 CH2Cl2-MeOH) to give imidate 8 (32.5
mg, 86%) pure as a colorless glass. 1H NMR (400 MHz, CDCl3)
6270 J. Org. Chem., Vol. 70, No. 16, 2005

Glycosylation of a Disaccharide
Chromatography as described above in method A gave the
phy (CH2Cl2-MeOH 98:2) of the dry residue gave the trisac-
charide 16 pure as a colorless glass (9 mg, 91%).
Analytical Data for Compound 15. H NMR (400 MHz,
trisaccharide 9 pure as a colorless glass (7 mg, 20%).
1
1
Analytical Data for 9. H NMR (600 MHz, CDCl3) δ 7.33
(m, 5H, Ar); 5.84 (d, 1H, J ) 7.9 Hz, NH); 5.40 (d, 1H, J ) 3.0
Hz, H-4′); 5.19-5.07 (m, 6H, H-1′, H-2′, H-3′, H-2′′, H-3′′, H-4′′);
4.87 (bs, 1H, H-1′′); 4.62 (d, 1H, J ) 4.2 Hz, H-1); 4.57, 4.54
(2d, 2H, J ) 12.3 Hz, OCH2Ph); 4.30 (m, 1H, H-5′′); 4.22 (dd,
1H, J ) 10.9, 8.2 Hz, H-6a′); 4.17 (t, 1H, J ) 6.5 Hz, H-5);
4.09 (dd, 10.9, 5.9 Hz, H-6b′); 3.99 (m, 2H, H-3, H-4); 3.81 (m,
1H, H-2); 3.71 (m, 3H, H-5′, H-6a, H-6b); 3.39 (s, 3H, OCH3);
2.11-1.97 (8s, 8 × 3H, N-acetyl and O-acetyl); 1.28 (d, 3H, J
) 6.1 Hz, H-6′′). 13C NMR (100.6 MHz, CDCl3) δ 170.2, 170.0,
CDCl3) δ 7.25 (m, 23 H, Ar); 5.28 (d, 1H, J ) 2.0 Hz, H-4′);
5.09 (dd, 1H, J ) 10.1, 8.5 Hz, H-2′); 5.00 (m, 3H, H-1′, H-1′′,
OCH2Ph); 4.79 (dd, 1H, J ) 10.3, 6.9 Hz, H-3′); 4.69-4.56 (m,
7H, OCH2Ph); 4.47 (m, 1H, H-5′′); 4.33 (m, 1H, H-6a); 4.11
(m, 2H, H-6b, H-1); 3.90-3.73 (m, 5H, H-3, H-4, H-5, H-5′,
H-2′′); 3.67-3.59 (m, 2H, H-4′′, H-6a′), 3.66 (s, 3H, NdC-
OCH3); 3.50 (m, H-6b′); 3.42 (s, 3H, OCH3); 3.38 (m, 1H, H-3′′);
3.29 (dd, 1H, J ) 9.3, 8.5 Hz, H-2); 2.04, 1.99, 1.91, 1.91 1.55
(5s, 5 × 3H, N-acetyl and O-acetyl); 1.39 (d, 1H, J ) 6.3 Hz,
H-6′′). 13C NMR (75.5 MHz, CDCl3) δ 188.2, 170.6, 170.4, 170.1,
168.9 (CdO); 165.1 (CdN); 139.2, 138.7, 138.6, 138.1 (Ar);
128.3, 128.3, 128.1, 127.7, 127.5, 127.3, 126.9, 126.1 (Ar); 103.9
170.0, 169.3 (CdO); 138.0, 128.3, 127.6 (Ar); 99.7 (C-1, 1JC-H
)
1
168 Hz); 99.0 (C-1′); 96.4 (C-1′′, JC-H) 172 Hz); 78.0 (C-3 or
C-4); 73.4 (C-5′); 73.0 (OCH2Ph); 72.8 (C-5); 70.8, 70.6, 70.0,
69.1, 68.3 (C-2′, C-2′′, C-3′′, C-4′′, C-3′); 68.8 (C-6); 67.0 (C-4′);
66.7 (C-5′′); 60.5 (C-6′); 55.6 (OCH3); 54.5 (C-2); 23.3, 20.8, 20.7,
20.6, 20.5 (O- and N-COCH3); 17.2 (C-6′′). HRCIMS calcd for
C42H58NO22 [M + H]+ 928.3450, found 928.3513.
1
1
(C-1, JC-H ) 159 Hz); 100.3 (C-1′); 98.7 (C-1′′, JC-H ) 169
Hz); 80.7 (C-4′′); 80.4, 80.1, 75.7, 74.1, 70.2 (C-3, C-4, C-5, C-5′,
C-2′′); 76.0 (C-3′′); 75.2, 73.6, 72.4, 72.3 (OCH2PH); 71.7 (C-
3′); 68.8 (C-6′); 68.6 (C-2′); 68.2 (C-5′′); 66.7 (C-4′); 65.8 (C-2);
61.0 (C-6); 57.1 (OCH3); 52.5 (NdC-OCH3); 20.7, 20.7, 20.5,
19.8 (O-COCH3); 17.8 (C-6′′); 16.6 (NdC-CH3). HRESIMS
calcd for C58H71NO19Na [M + Na]+ 1108.4518, found 1108.4473.
Methyl 3-O-(2,3,4,6-Tetra-O-acetyl-r-D-galactopyrano-
syl)-6-O-benzyl-4-O-(2,3,4-tri-O-benzyl-r-L-rhamnopyra-
nosyl)-2-N-methylacetimido-2-deoxy-r-D-glucopyrano-
side (15) and Methyl 2-Acetamido-3-O-(2,3,4,6-tetra-O-
acetyl-r-D-galactopyranosyl)-6-O-benzyl-4-O-(2,3,4-tri-
O-benzyl-r-L-rhamnopyranosyl)-2-deoxy-r-D-glucopyrano-
side (16). Method A. The glycosyl acceptor 4 (25 mg, 38 µmol)
and ethyl 2,3,4-tri-O-benzyl-1-thio-R-L-rhamnopyranoside 12
(55 mg, 114 µmol)18 were dissolved in anhyd Et2O (2 mL).
Powdered activated 4 Å molecular sieves (200 mg) were added
and the mixture was stirred for 3 h at room temperature.
MeOTf was added (22 µL, 198 µmol, 5 equiv, 0.1 M) and the
mixture was stirred for 18 h at room temperature. The reaction
was quenched with Et3N (40 µL) and worked up as described
above for the synthesis of compound 7. Chromatography (CH2-
Cl2-MeOH 100:1 then 98:2) of the dry residue first gave the
methyl imidate trisaccharide 15 pure as a colorless glass (24
mg, 58%) and then the trisaccharide 16 pure as a colorless
glass (10 mg, 24%).
Method B. The glycosyl acceptor 4 (22 mg, 34 µmol) and
ethyl 2,3,4-tri-O-benzyl-1-thio-â-L-rhamnopyranoside 13 (55
mg, 11 µmol, 3 equiv)19 were dissolved in anhyd Et2O (2 mL).
Powdered activated 4 Å molecular sieves (200 mg) were added
and the mixture was stirred for 3 h at room temperature.
MeOTf was added (22 µL, 198 µmol, 5.8 equiv, 0.1 M) and the
mixture was stirred at room temperature for 18 h. The reaction
was then quenched with Et3N (40 µL) and worked up as
described above for the synthesis of compound 7. Chromatog-
raphy (CH2Cl2-MeOH 100:1 then 98:2) of the dry residue first
gave the methyl imidate trisaccharide 15 pure as a colorless
glass (18 mg, 49%) and then the trisaccharide 16 pure as a
colorless glass (13 mg, 36%).
Glycosylation of Methyl Imidate Acceptor 18 To Give
Trisaccharide 15. Methyl imidate 18 (32 mg, 47 µmol) and
ethyl 2,3,4-tri-O-benzyl-1-thio-â-L-rhamnopyranoside19 13 (53
mg, 110 µmol) were dissolved in anhyd Et2O (2 mL). Powdered
activated 4 Å molecular sieves (200 mg) were added and the
mixture was stirred for 3 h at room temperature. MeOTf was
added (22 µL, 198 µmol, 0.1 M) and the mixture was stirred
for 1 h at room temperature. The reaction was quenched with
Et3N (40 µL) and worked up as described above for the
synthesis of compound 7. Chromatography (CH2Cl2-MeOH
100:1 then 98:2) of the dry residue gave the methyl imidate
trisaccharide 15 pure as a colorless glass (44 mg, 85%).
Conversion of Methyl Imidate 15 to the N-Acetylated
Trisaccharide 16. The imidate 15 (10 mg) was dissolved in
a mixture of Ac2O (720 µL) and AcOH (220 µL) and the solution
was stirred at 55 °C for 3 h. The mixture was diluted with
CH2Cl2 (50 mL) and washed with saturated NaHCO3 (3 × 50
mL) and water (50 mL). The aqueous washings were re-
extracted with CH2Cl2 (30 mL) and the combined organic
phases were dried (Na2SO4) and concentrated. Chromatogra-
1
Analytical Data for Compound 16. H NMR (400 MHz,
CDCl3) δ 7.31 (m, 25H, Ar); 5.74 (d, 1H, J ) 8.5 Hz, NH); 5.36
(d, 1H, J ) 3.0 Hz, H-4′); 5.15 (dd, 1H, J ) 10.5, 8.0 Hz, H-2′);
4.99 (dd, 1H, J ) 10.5, 3.5 Hz, H-3′); 4.95 (d, 1H, J ) 11.0 Hz,
OCH2Ph); 4.90 (d, 1H, J ) 1.5 Hz, H-1′′); 4.79 (d, 1H, J ) 8.0
Hz, H-1′); 4.69-4.56 (m, 7 H, OCH2Ph); 4.52 (d, 1H, J ) 4.3
Hz, H-1); 4.14 (m, 2H, H-6a, H-6b); 3.96-3.88 (m, 4 H, H-4,
H-5, H-5′, H-5′′); 3.79 (m, 1H, H-2); 3.76-3.58 (m, 6H, H-3,
H-6a′, H-6b′, H-2′′, H-3′′, H-4′′); 3.39 (s, 3H, OCH3); 2.05-1.85
(5s, 5 × 3H, N-acetyl and O-acetyl); 1.33 (d, 1H, J ) 6.2 Hz,
H-6′′). 13C NMR (100.6 MHz, CDCl3) δ 170.3, 169.6 (CdO);
128.4, 128.3, 127.9, 127.9, 127.7, 127.6, 127.5 (Ar); 100.3 (C-
1
1
1, JC-H ) 166 Hz); 99.4 (C-1′); 97.7 (C-1′′, JC-H ) 168 Hz);
79.9 (C-4′′); 79.1 (C-3); 75.5, 72.7, 70.7, 68.8 (C-4, C-5, C-5′,
C-5′′); 75.3, 73.4, 72.7, 71.9 (OCH2Ph); 74.7, 74.7 (C-2′′, C-3′′);
70.9 (C-3′); 69.7 (C-6′); 68.4 (C-2′); 66.9 (C-4′); 60.9 (C-6); 56.0
(OCH3); 51.6 (C-2); 23.4, 20.8, 20.6, 20.6, 20.4 (N-COCH3 and
O-COCH3); 17.9 (C-6′′). HRESIMS calcd for C57H73N2O19 [M
+ NH4]+ 1089.4808, found 1089.4833.
Methyl 2-Acetamido-3-O-(2,3,4,6-tetra-O-acetyl-â-D-ga-
lactopyranosyl)-6-O-benzyl-4-O-(2,3,4-tri-O-benzyl-r-L-fu-
copyranosyl)-2-deoxy-â-D-glucopyranoside (17). A solu-
tion of glycosyl acceptor 4 (25 mg, 38 µmol) and glycosyl donor
ethyl 2,3,4-tri-O-benzyl-1-thio-â-L-fucopyranoside24 14 (55 mg,
114 µmol, 3 equiv) in anhyd Et2O (2 mL) containing powdered
activated 4 Å molecular sieves (200 mg) was stirred for 3 h at
room temperature. MeOTf was added (22 µL, 198 µmol, 5
equiv, 0.1 M) and the reaction mixture was stirred for 1 h at
room temperature. The reaction was quenched with Et3N (40
µL) and worked up as described above for the synthesis of
compound 7. The dry residue was submitted to chromatogra-
phy with CHCl3-MeOH (30:1 then 25:1) and gave trisaccha-
1
ride 17 pure as a colorless glass (31 mg, 77%). H NMR (600
MHz, CDCl3) δ 7.40-7.25 (m, 20 H, Ar); 6.67 (d, 1H, J ) 9.3
Hz, NH); 5.39 (d, 1H, J ) 3.4 Hz, H-4′); 5.25 (d, 1H, J ) 3.9
Hz, H-1′′); 5.15 (dd, 1H, J ) 10.5, 8.0 Hz, H-2′); 5.02-4.66 (m,
8H, H-1′, H-3′, OCH2Ph); 4.55 (d, 1H, J ) 2.7 Hz, H-1); 4.59-
4.49 (2d, 2H, J ) 11.9 Hz, OCH2Ph); 4.14 (m, 3H, H-4, H-5,
H-2′′); 4.08 (m, 2H, H-6a′, H-6b′); 4.01 (m, 2H, H-5′′, H-2); 3.97
(m, 1H, H-6a); 3.89 (m, 2H, H-3, H-5′); 3.83 (dd, 1H, J ) 10.0,
2.7 Hz, H-3′′); 3.71 (d, 1H, J ) 2.0 Hz, H-4′′); 3.67 (dd, 1H, J
) 10.3, 4.7 Hz, H-6b); 3.41 (s, 3H, OCH3); 2.07, 2.01, 1.99, 1.97
(4s, 4 × 3H, O-acetyl); 1.60 (s, 3H, N-acetyl); 1.18 (d, 3H, J )
6.5 Hz, H-6′′). 13C NMR (150.9 MHz, CDCl3) δ 169.7, 169.4 (Cd
1
O); 138.6, 138.4, 137.9,129.3-127.2 (Ar); 100.8 (C-1, JC-H
)
167 Hz); 99.5 (C-1′); 93.1 (C-1′′); 79.9 (C-3′′); 77.1 (C-4′′); 70.6,
70.8 (C-3′, C-5′); 76.2, 70.8 (C-2′′, C-5); 75.0 (C-3); 69.4, 66.9,
49.8 (C-2, C-4, C-5′′); 68.3 (C-2′); 66.9 (C-4′); 74.8, 73.8, 73.1,
72.9 (OCH2Ph); 69.8 (C-6); 60.6 (C-6′); 55.8 (OCH3); 22.8, 20.8,
J. Org. Chem, Vol. 70, No. 16, 2005 6271

Liao and Auzanneau
20.6, 20.6 (O- and N-COCH3); 16.7 (C-6′′). HRESIMS calcd for
C57H70NO19 [M + H]+ 1072.4542, found 1072.4546.
21 as a colorless glass (40 mg, 80%). 1H NMR (400 MHz,
CDCl3) δ 7.35-7.26 (m, 5H, Ar); 5.36 (d, 1H, J ) 3.3 Hz, H-4′);
5.24 (dd, 1H, J ) 10.4, 8.1 Hz, H-2′); 5.01 (d, 1H, J ) 7.7 Hz,
H-1); 4.94 (dd, 1H, J ) 10.4, 3.4 Hz, H-3′); 4.63 (bs, 2H, OCH2-
Ph); 4.45 (m, 1H, H-3); 4.41 (d, 1H, J ) 8.0 Hz, H-1′); 4.16-
4.10 (m, 3H, OH, H-6a′, H-6b′); 4.00 (m, 1H, H-5′); 3.85 (dd,
1H, J ) 10.9, 1.7 Hz, H-6a); 3.70 (dd, 1H, J ) 10.9, 5.3 Hz,
H-6b); 3.60 (m, 2H, H-2, H-4); 3.55 (m, 1H, H-5); 3.46 (s, 3H,
OCH3); 2.49-1.97 (6s, 6 × 3H, N-acetyl and O-acetyl).13C NMR
(100.6 MHz, CDCl3) δ 175.2, 174.7, 170.4, 170.0, 169.9, 169.6
(CdO); 138.3, 128.3, 127.5 (Ar); 101.4 (C-1′); 99.6 (C-1); 83.9
(C-3); 75.0 (C-5); 73.5 (OCH2Ph); 71.2, 71.0 (C-3′, C-5′); 70.3
(C-4); 69.3 (C-6); 68.7 (C-2′); 66.8 (C-4′); 62.8 (C-2); 61.7 (C-
6′); 57.1 (OCH3); 28.5, 25.4, 20.7, 20.6, 20.4, 20.4 (O- and
N-COCH3). HRCIMS calcd for C32H47N2O16 [M + NH4]+
715.2926, found 715.2998.
Methyl 3-O-(2,3,4,6-Tetra-O-acetyl-r-D-galactopyrano-
syl)-6-O-benzyl-2-N-methylacetimido-2-deoxy-â-D-glucopy-
ranoside (18). A solution of disaccharide glycosyl acceptor 4
(75 mg, 120 µmol) in anhyd Et2O (6 mL) containing 4 Å
powdered activated molecular sieves (300 mg) was stirred for
3 h at room temperature. MeOTf (330 µL, 3 mmol, 0.5 M) was
added and the mixture was stirred for 18 h at room temper-
ature. The reaction was quenched with Et3N (420 µL) and
worked up as described above for the synthesis of compound
7. Chromatography (CH2Cl2-MeOH 98:2) of the dry residue
1
gave compound 18 pure as a colorless glass (57 mg, 76%). H
NMR (400 MHz, CDCl3) δ 7.35 (m, 6H, Ar); 5.36 (d, 1H, J )
2.74, H-4′); 5.19 (dd, 1H, J ) 10.2, 8.2 Hz, H-2′); 4.96 (dd, 1H,
J ) 10.4, 3.2 Hz, H-3′); 4.64 (2d, 2H, J ) 12.3 Hz, OCH2Ph);
4.58 (d, 1H, J ) 8.2 Hz, H-1′); 4.20 (d, 1H, J ) 7.7 Hz, H-1);
4.12 (m, 2H, H-6a′, H-6b′); 3.99 (m, 1H, H-5′); 3.93 (br s, 1H,
OH); 3.91 (br s, 1H, H-6a); 3.69 (m, 1H, H-6b); 3.61 (s, 3H,
NdC-CH3); 3.55 (m, 2H, H-3, H-4); 3.46 (s, 3H, OCH3); 3.45
(m, 1H, H-5); 3.25 (t, 1H, J ) 7.8 Hz, H-2); 2.15, 2.02, 2.00,
1.99, 1.87 (N-acetyl and O-acetyl). 13C NMR (75.5 MHz, CDCl3)
δ 185.7, 175.7, 174.1, 171.4 (CdO); 164.9 (CdN); 152.1, 141.8,
138.5, 137.8 (Ar); 128.3, 127.6, 127.5 (Ar); 104.0 (C-1); 102.1
(C-1′); 89.0, 75.7, 68.8 (C-3, C-4, C-5); 73.6 (OCH2Ph); 71.1 (C-
3′); 70.9 (C-5′); 70.0 (C-6); 68.6 (C-2′); 66.8 (C-4′); 63.7 (C-2);
61.5 (C-6′); 57.2 (OCH3); 52.4 (NdC-OCH3); 20.6, 20.5, 20.5,
20.2 (O-COCH3); 16.1 (NdC-CH3). HRESIMS calcd for
C31H44NO15 [M + H]+ 670.2711, found 670.2731.
Methyl 2-(N-Acetylacetamido)-3-O-(2,3,4,6-tetra-O-ace-
tyl-â-D-galactopyranosyl)-4-O-(2,3,4-tri-O-acetyl-r-L-rhamno-
pyranosyl)-6-O-benzyl-2-deoxy-â-D-glucopyranoside (22).
Acceptor 21 (300 mg, 430 µmol) and peracetylated R-L-
rhamnopyranosyl trichloroacetimidate8 5 (930 mg, 2.14 mmol,
5 equiv) were dissolved in anhyd CH2Cl2 (7.5 mL) containing
powdered activated 4 Å molecular sieves (600 mg) and the
mixture was stirred for 5 h at room temperature. The reaction
mixture was cooled to -78 °C and a freshly prepared solution
(0.37 M) of TESOTf in anhyd CH2Cl2 (177 µL, 64.5 µmol, 0.15
equiv) was added. The reaction was then allowed to reach room
temperature slowly (over 2 h) and was quenched with NEt3
(20 µL). Workup was carried out as previously described for
the synthesis of imidate 7 and chromatography (EtOAc-
hexane 1:1) gave trisaccharide 22 as a colorless glass (378 mg,
91%). 1H NMR (400 MHz, CDCl3, 308 K) δ 7.32-7.25 (m, 5H,
Ar); 5.35 (d, 1H, J ) 3.2 Hz, H-4′); 5.24 (m, 2H, H-2′′, H-3′′);
5.16 (m, 2H, H-2′, H-4′′); 5.02 (bs, 1H, H-1′′); 4.90 (d, 1H, J )
7.7 Hz, H-1); 4.85 (dd, 1H, J ) 10.4, 3.7 Hz, H-3′); 4.80 (t, 1H,
J ) 9.3 Hz, H-3); 4.62-4.53 (m, 3H, OCH2Ph, H-5′′); 4.42 (d,
1H, J ) 8.1 Hz, H-1′); 4.37 (dd, 1H, J ) 11.2, 7.1 Hz, H-6a′);
4.17 (dd, 1H, J ) 11.2, 6.5 Hz, H-6b′); 3.90-3.70 (m, 4H, H-4,
H-5′, H-6a, H-6b); 3.64 (dd, 1H, J ) 9.8, 8.0 Hz, H-2); 3.50 (m,
1H, H-5); 3.42 (s, 3H, OCH3); 2.40-1.92 (9s, 9 × 3H, N-acetyl
and O-acetyl); 1.30 (d, 3H, J ) 6.2 Hz, H-6′′). 13C NMR (100.6
MHz, CDCl3) δ 170.1, 169.8 (CdO); 138.1, 128.3, 127.5 (Ar);
Methyl 2-(N-Acetylacetamido)-3-O-(2,3,4,6-tetra-O-ace-
tyl- â-D-galactopyranosyl)-4,6-O-benzylidene-2-deoxy-â-
D-glucopyranoside (20). N,N-Diisopropylethylamine (134 µL,
77 µmol, 10 equiv) and acetyl chloride (279 µL, 3.85 mmol, 50
equiv) were added at room temperature to a solution of methyl
2-acetamido-4,6-O-benzylidene-2-deoxy-3-O-(2,3,4,6-tetra-O-
acetyl-â-D-galactopyranosyl)-â-D-glucopyranoside26 19 (50 mg,
77 µmol) in anhyd CH2Cl2 (5 mL). The reaction mixture was
stirred overnight at room temperature, diluted with CH2Cl2
(50 mL), and washed sequentially with saturated NaHCO3 (30
mL) and brine (30 mL). The aqueous phases were re-extracted
with CH2Cl2 (30 mL) and the combined organic layers were
dried (Na2SO4) and concentrated. Chromatography (EtOAc-
hexane 40:60) gave compound 20 as a colorless glass (50 mg,
94%). 1H NMR (400 MHz, CDCl3) δ 7.48-7.37 (m, 5H, Ar);
5.53 (s, 1H, >CHPh); 5.25 (d, 1H, J ) 3.4 Hz, H-4′); 5.12 (dd,
1H, J ) 10.4, 8.2 Hz, H-2′); 5.11 (d, 1H, J ) 7.8 Hz, H-1); 4.88
(dd, 1H, J ) 10.3, 3.5 Hz, H-3′); 4.76 (dd, 1H, J ) 9.5, 8.4 Hz,
H-3); 4.54 (d, 1H, J ) 8.1 Hz, H-1′); 4.35 (dd, 1H, J ) 10.5, 4.9
Hz, H-6a′); 4.01 (dd, 1H, J ) 10.9, 8.6 Hz, H-6a); 3.87 (dd, 1H,
J ) 10.9, 8.7 Hz, H-6b′); 3.81-3.70 (m, 3H, H-2, H-4, H-6b);
3.59 (m, 1H, H-5′); 3.52 (m, 1H, H-5); 3.46 (s, 3H, OCH3); 2.48-
1.91 (6s, 6 × 3H, N-acetyl and O-acetyl). 13C NMR (100.6 MHz,
CDCl3) δ 174.9, 174.7, 170.2, 170.1, 169.2 (CdO); 136.9, 129.3,
128.4, 126.0 (Ar); 101.6 (>CHPh); 100.8 (C-1′); 100.4 (C-1′′);
81.4 (C-4); 77.4 (C-3); 71.1 (C-3′); 70.4 (C-5); 69.2 (C-2′); 68.8
(C-6′); 66.6 (C-4′); 65.4 (C-5′); 63.3 (C-2); 60.5 (C-6); 57.5
(OCH3); 28.3, 25.3, 20.7, 20.6, 20.5 (O- and N-COCH3). HR-
CIMS calcd for C32H42NO16 [M + H]+ 696.2504, found 696.2517.
Methyl 2-(N-Acetylacetamido)-3-O-(2,3,4,6-tetra-O-ace-
tyl-â-D-galactopyranosyl)-6-O-benzyl-2-deoxy-â-D-gluco-
pyranoside (21). Sodium cyanoborohydride (37 mg, 590 µmol,
8 equiv) was added to a solution of disaccharide 20 (50 mg, 72
µmol) in anhyd THF (2 mL) containing powdered activated 4
Å molecular sieves (50 mg) and the mixture was cooled to 0
°C. A 2 M solution of HCl in Et2O (650 µL) was added at 0 °C
over ∼30 min and stirring was maintained at 0 °C for an
additional 30 min. The reaction mixture was diluted with CH2-
Cl2 (50 mL) and washed sequentially with 0.5 M HCl (30 mL),
saturated aqueous NaHCO3 (30 mL), and brine (30 mL). The
aqueous phases were re-extracted with CH2Cl2 (30 mL) and
the combined organic layers were dried (Na2SO4) and concen-
trated. Chromatography (EtOAc-hexane 4:6) gave acceptor
1
1
99.9 (C-1′); 99.8 (C-1, JC-H ) 164 Hz); 97.4 (C-1′′, JC-H
)
172 Hz); 75.4 (C-3); 74.7 (C-5); 73.2 (OCH2Ph); 71.6, 71.5 (C-
4′′, C-3′, C-5′); 70.4 (C-2′′ or C-3′′); 69.4 (C-2′′ or C-3′′); 69.0
(C-2′); 68.5 (C-6); 67.3 (C-4′); 66.6 (C-5′′); 64.6 (C-2); 60.8 (C-
6′); 57.1 (OCH3); 20.8, 20.6, 20.6, 20.3 (O- and N- COCH3); 17.5
(C-6′′). HRCIMS calcd for C44H63NO23 [M + NH4]+ 987.3822,
found 987.3848.
Methyl 2-(N-Acetylacetamido)-3-O-(2,3,4,6-tetra-O-ace-
tyl-â-D-galactopyranosyl)-4-O-(2,3,4,6-tetra-O-acetyl-r-D-manno-
pyranosyl)-6-O-benzyl-2-deoxy-â-D-glucopyranoside (23).
Acceptor 21 (20 mg, 29 µmol) and trichloroacetimidate9 6 (71
mg, 140 µmol, 5 equiv) were dissolved in anhyd CH2Cl2 (2 mL)
containing powdered activated 4 Å molecular sieves (200 mg)
and the mixture was stirred for 5 h at room temperature. The
reaction mixture was cooled to -78 °C and a freshly prepared
solution (0.37 M) of TESOTf in anhyd CH2Cl2 (44 µL, 16 µmol,
0.55 equiv) was added. The reaction was allowed to reach room
temperature slowly over 2 h and was quenched with NEt3 (10
µL). Workup was carried out as previously described for the
synthesis of imidate 7 and chromatography (EtOAc-hexane
1:1) of the dry residue gave trisaccharide 23 pure as a colorless
glass (28 mg, 95%). 1H NMR (400 MHz, CDCl3, 313 K) δ 7.34-
7.26 (m, 5H, Ar); 5.43 (bs, 1H, H-2′′); 5.29 (m, 4H, H-1′′, H-3′′,
H-4′′, H-4′); 5.19 (dd, 1H, J ) 10.1, 8.2 Hz, H-2′); 4.95 (d, 1H,
J ) 7.7 Hz, H-1); 4.85 (m, 2H, H-3, H-3′); 4.67, 4.57 (2d, 2H,
J ) 12.2 Hz, OCH2Ph); 4.37 (d, 1H, J ) 8.0 Hz, H-1′); 4.26
(dd, 1H, J ) 11.3, 7.2 Hz, H-6a or H-6a′); 4.18-3.95 (m, 4H,
H-6a or H-6a′, H-6b, H-6b′, H-5′′); 3.88-3.65 (m, 5H, H-4, H-5,
H-5′, H-6a′′, H-6b′′); 3.60 (dd, 1H, J ) 10.1, 8.0 Hz, H-2); 3.44
(s, 3H, OCH3); 2.39 (bs, 6H, N-acetyl); 2.14-1.93 (8s, 8 × 3H,
6272 J. Org. Chem., Vol. 70, No. 16, 2005

Glycosylation of a Disaccharide
O-acetyl). 13C NMR (100.6 MHz, CDCl3) δ 170.2, 169.9, 169.8
(CdO); 138.1, 128.4, 127.7, 127.5 (Ar); 100.2 (C-1, 1JC-H) 165
donor24 14 (68 mg, 140 µmol, 5 equiv) in CH2Cl2 (2 mL)
containing powdered activated 4 Å molecular sieves (200 mg)
was stirred at room temperature for 3 h. The temperature was
then brought down to -40 °C and N-iodosuccinimide (37 mg,
165 µmol, 5.5 equiv) was added followed by a 0.15 M solution
of TfOH in anhyd CH2Cl2 (30 µL, 4.5 µmol, 0.15 equiv). After
the solution was stirred at -40 °C for 30 min, the reaction
was quenched with NEt3 (10 µL) and workup was carried out
as previously described for the synthesis of imidate 7. Chro-
matography (EtOAc-hexane 1:1) of the dry residue gave
compound 25 (35 mg, 48%) and unreacted gycosyl acceptor 21
(20 mg, quant).
1
Hz); 99.5 (C-1′); 99.3 (C-1′′, JC-H ) 176 Hz); 77.0, 74.3, 71.7
(C-4, C-5, C-5′); 76.2 (C-3); 71.6 (C-3′); 69.8 (C-2′′); 69.3, 69.1
(C-2′, C-5′′); 69.2, 66.8, 66.8 (C-4′, C-3′′, C-4′′); 64.1 (C-2); 73.5
(OCH2Ph); 69.8 (C-6′′); 62.5 (C-6′); 60.6 (C-6); 57.1 (OCH3);
20.9, 20.6, 20.4, 20.3 (N- and O-COCH3). HRESIMS calcd for
C46H61NO25Na [M + Na]+ 1050.3430, found 1050.3575.
Methyl 2-(N-Acetylacetamido)-3-O-(2,3,4,6-tetra-O-ace-
tyl-â-D-galactopyranosyl)- 6-O-benzyl-4-O-(2,3,4-tri-O-
benzyl-r-L-fucopyranosyl)-2-deoxy-â-D-glucopyrano-
side (24). Glycosyl acceptor 21 (100 mg, 140 µmol) and ethyl
2,3,4-tri-O-benzyl-1-thio-â-L-fucopyranoside24 14 (215 mg, 450
µmol, 3 equiv) were dissolved in anhyd Et2O (5 mL) containing
powdered activated 4 Å molecular sieves (500 mg). The mixture
was stirred at room temperature for 3 h, MeOTf (85 µL, 0.7
mmol, 5 equiv) was added, and the reaction was allowed to
proceed at room temperature for 18 h. It was then quenched
with NEt3 (200 µL) and worked up as previously described for
the synthesis of imidate 7. Chromatography (EtOAc-hexane
3:7) gave trisaccharide 24 as a colorless glass (130 mg, 82%).
1H NMR (400 MHz, CDCl3) δ 7.35-7.26 (m, 20 H, Ar); 5.32
(bd, 1H, J ) 3.5 Hz, H-4′); 5.14 (d, 1H, J ) 3.8 Hz, H-1′′); 5.08
(dd, 1H, J ) 10.4, 8.2 Hz, H-2′); 5.00 (d, 1H, OCHPh); 4.91-
4.74 (m, 7 H, H-1, H-3, H-3′, 4 OCHPh); 4.69 (m, 1H, H-5′′);
4.66 (d, 1H, OCHPh); 4.41 (bs, 2H, OCH2Ph); 4.34 (d, 1H, J )
8.2 Hz, H-1′); 4.25 (dd, 1H, J ) 10.5, 9.1 Hz, H-6a′), 4.17 (dd,
1H, J ) 8.5, 3.8 Hz, H-2′′); 4.05-3.85 (m, 4H, H-4, H-6a, H-6b′,
H-3′′); 3.77 (m, 2H, H-5′, H-4′′); 3.60 (m, 2H, H-2, H-6b); 3.50
(m, 1H, H-5); 3.41 (s, 3H, OCH3); 2.46, 2.32 (2 bs, 2 × 3H,
N-acetyl); 2.02, 2.01, 1.93, 1.77 (4s, 4 × 3H, O-acetyl); 1.31 (d,
1H, J ) 6.5 Hz, H-6′′). 13C NMR (100.6 MHz, CDCl3) δ 169.9,
169.8, 169.1 (CdO); 138.7, 138.6, 138.3, 138.0, 128.6-127.0
(Ar); 100.0 (C-1′); 99.4 (C-1); 97.6 (C-1′′); 80.7, 76.4, 75.6, 74.9,
73.7, 71.5, 70.4, 68.6 (C-3, C-4, C-5, C-3′, C-5′, C-2′′, C-3′′, C-4′′);
74.9, 74.0, 73.1, 72.2 (OCH2Ph); 67.3 (C-2′); 66.5 (C-6); 66.3,
66.3 (C-4′, C-5′′); 64.4 (C-2); 57.0 (OCH3); 20.6, 20.5, 20.4 (O-
and N-COCH3); 17.0 (C-6′′). HRESIMS calcd for C59H71N2O20-
Na [M + Na]+ 1136.4467, found 1136.4556.
Analytical Data for 25. 1H NMR (400 MHz, CDCl3) δ
7.39-7.26 (m, 15 H, Ar); 6.13 (d, 1H, J ) 7.5 Hz, H-1); 5.00-
4.74 (m, 5H, OCH2Ph); 4.67 (dd, 1H, J ) 7.8, 3.0 Hz, H-3);
4.48 (d, 1H, J ) 11.5, OCH2Ph); 4.28 (m, 1H, H-5); 3.72 (d,
1H, J ) 2.4 Hz, H-4); 2.59 (m, 4H, 2 × OCCH2); 1.09 (d, 3H,
J ) 6.4 Hz, H-6). 13C NMR (100.6 MHz, CDCl3) δ 177.9 (Cd
O), 138.9, 138.5, 138.0, 128.4-127.5 (Ar); 80.5 (C-1); 77.0 (C-
3); 76.7 (C-2); 74.8 (C-4); 72.7 (C-5); 75.0, 73.6, 73.2 (OCH2Ph);
28.2 (OCCH2); 17.4 (C-6). HRESIMS calcd for C31H34NO16 [M
+ H]+ 516.2386, found 516.2419.
Acknowledgment. We thank the Research Corpo-
ration, the National Science and Engineering Research
Council of Canada, the Canada Foundation for Innova-
tion, and the Ontario Innovation Trust for financial
support as well as Aventis Pasteur Ltd for in kind
support of this work.
Supporting Information Available: Experimental pro-
cedures and analytical data for the deprotection of 9 or 22 and
24 leading to 26 and 27, respectively, as well as those to obtain
2 and 3 from 27 and 26; 1H, Jmod, COSY, and HSQC spectra
1
for 2 and 3 in D2O; H, Jmod, COSY, HSQC, and HMBC for
1
7, 8, 15, and 18 in CDCl3; H, Jmod, COSY, and HSQC for 9,
16, 17, and 22-25 in CDCl3, and 26 and 27 in CD3OD; and
1H and Jmod for 20 and 21 in CDCl3. This material is available
free of charge via the Internet at http://pubs.acs.org.
Succinimidate 2,3,4-Tri-O-benzyl-1-N-â-L-fucopyrano-
side (25). A solution of acceptor 21 (20 mg, 30 µmol) and
JO050707+
J. Org. Chem, Vol. 70, No. 16, 2005 6273