5- N,4- O -carbonyl-7,8,9-tri- O -chloroacetyl-protected sialyl donor for the stereoselective synthesis of α-(2→9)-tetrasialic acid

Article abstract of DOI:10.1021/jo100824s

(Figure presented) An efficient stereoselective synthesis of α-(2→9)-tetrasialic acid was achieved using tri-O-chloroacetyl- derivatized sialyl donor and a triol sialyl acceptor. Both the acceptor and the donor were also protected with a cyclic 5-N-4-O-carbonyl protecting group. The donor is highly reactive and enabled α-selective sialylation with various primary, secondary, and tertiary acceptors under in situ activation conditions (NIS/TfOH, -78 °C, acetonitrile/dichloromethane). The trans-fused oxazolidinone ring and O-chloroacetyl protecting groups were easily removed under mild reaction conditions to provide the fully deprotected α(2→9)-tetrasialic acid.

Full text of DOI:10.1021/jo100824s

pubs.acs.org/joc
5-N,4-O-Carbonyl-7,8,9-tri-O-chloroacetyl-Protected Sialyl Donor for
the Stereoselective Synthesis of r-(2f9)-Tetrasialic Acid
Chang-Ching Lin, Nai-Pin Lin, L. Sk Sahabuddin, Vijaya Raghava Reddy, Li-De Huang,
Kuo Chu Hwang, and Chun-Cheng Lin*
Department of Chemistry, National Tsing Hua University, 101, Sec. 2, Kuang Fu Rd, Hsinchu 30013, Taiwan
cclin66@mx.nthu.edu.tw
Received April 27, 2010
An efficient stereoselective synthesis of R-(2f9)-tetrasialic acid was achieved using tri-O-chloroa-
cetyl-derivatized sialyl donor and a triol sialyl acceptor. Both the acceptor and the donor were also
protected with a cyclic 5-N-4-O-carbonyl protecting group. The donor is highly reactive and enabled
R-selective sialylation with various primary, secondary, and tertiary acceptors under in situ acti-
vation conditions (NIS/TfOH, -78 °C, acetonitrile/dichloromethane). The trans-fused oxazolidi-
none ring and O-chloroacetyl protecting groups were easily removed under mild reaction conditions
to provide the fully deprotected R(2f9)-tetrasialic acid.
Introduction
antibacterial vaccines.4,5 More than two decades ago, an R-
linked (2f9)-disialic acid unit was found to be attached to
lactosaminoglycan in human teratocarcinoma cells (PA1),6
but only recently, the linear R-(2f9)-polysialic acids were
found in C-1300 mouse neuroblastoma cells (NB41A3).7
Additionally, a glycoprotein carrying R-(2f9)-polysialic
acids has been identified in sea urchin sperm flagella.8 The
polysaccharides used in vaccines are typically isolated from
their natural sources, and thus, they are sometimes hetero-
geneous and/or contaminated with other antigenic compo-
nents. Therefore, a straightforward chemical synthesis for
preparing pure oligosaccharides for carbohydrate-based
vaccines would be of great value.
Sialic acid is the generic term for N- or O-substituted
derivatives of neuraminic acid, which is the most complex
nine-carbon carboxylated monosaccharide. The sialic acids
possess diverse substitution patterns and are typically found
at the nonreducing terminus of N- and O-glycoproteins and
glycosphingolipids.1,2 Due to their domination at the termini
of glycoproteins and glycolipids, sialic acids act either as
masks or recognition sites for the ligand-receptor and cell-
cell recognitions in many important biological events.1-3
Recent studies in glycobiology revealed that linear homo-
polymers of sialic acids are linked either internally via conti-
guous R-(2f8) and R-(2f9) linkages, respectively, or via
alternating R-(2f8) and R-(2f9) linkages. These polysialic
acids were observed as capsular polysaccharides on the sur-
face of bacteria such as Escherichia coli K1 and K92 and Neis-
seria meningitides Gps B and C. They function as virulence
factors and have the potential to be used as antigens in
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DOI: 10.1021/jo100824s
r
Published on Web 06/28/2010
J. Org. Chem. 2010, 75, 4921–4928 4921
2010 American Chemical Society

Lin et al.
JOCFeatured Article
One of the most difficult and challenging tasks in the synthesis
of oligosialic acids is the formation of R-glycosidic bond during
the coupling step with sialic acid. The presence of a destabilizing
electron-withdrawing carboxyl group at the anomeric center
and the lack of a participating auxiliary at the C-3 of sialyl donor
often result in low to moderate yields of sialylation products
with poor R-stereoselectivities. In addition, an undesirable
β-elimination sometimes occurs, giving a glycal side product.
Due to the interaction with the C5-NH group, the hydroxyl
groups at the C8/C9 positions of the sialic acid have low
reactivity toward sialylation, further impeding the synthesis
of homo-oligosialic acids.9 A variety of strategies have been
developed to address these problems, and these strategies focus
primarily on the anomeric leaving groups, the solvents, and the
promoters.10 The N-acetyl group at the C5 position of the sialyl
donor has been replaced with N,N-diacetyl,11a 2,2,2-trichlor-
oethoxycarbonyl (N-Troc),11c,d trifluoroacetyl (N-TFA),11b
azido (N3),11e,f N-Fmoc,11g N-phthalimide,11h and Boc11i
groups, and these approaches have improved the reactivity
and the R-selectivity of the sialylation reaction.10e Further-
more, 1,5-lactamized-sialyl acceptors have been developed
as alternative strategies for enhancing the reactivity of the C8
hydroxyl groups toward glycosylation.12
Previously, we reported the development of C5 N-TFA-
protected phosphite-based sialyl donors and demonstrated
their R-selectivity in the sialylation reaction to achieve the
synthesis of R-(2f9) pentasialic acid by iterative sialylation
from the nonreducing end to the reducing end.13 We also des-
cribed a convergent [2 þ 2] strategy for the construction of
tetrasialoside by coupling a disialyl phosphite donor with a
disialyl acceptor.14 In the synthesis of oligosialic acids, these
sialyl donors displayed higher reactivity compared to con-
ventional donors and underwent an R-selective sialylation to
form the glycosidic bond with improved yields. However,
when the sugar chain is elongated, the R-selectivity in sialy-
lation decreases. Thus, it remains a challenge in the synthesis
of homo-oligosialic acid.
FIGURE 1. Structure of the R(2f9)-sialoside 1, the 5-N,4-O-car-
bonyl-protected sialyl donor 2a, and the acceptor 3.
Another attractive approach involves the use of a non-
participating oxazolidinone protecting group for thiosialosyl
donors.15-20 Reactions were performed in acetonitrile using
NIS/TfOH as the promoter at -78 °C, and these donors
showed improved reactivities and R-selectivities.16b,17 Recently,
Takahashi and co-workers used a 5-N,4-O-carbonyl-protected
sialyl donor for the synthesis of R-(2f8)-18 and R-(2f9)-tetr-
asialic19 acids and obtained the sialylation products with
exclusive R-selectivity, without the need for a participating
solvent like acetonitrile. Similar results were also reported by
Wong and co-workers in the synthesis of the protected R-
(2f9)-tetrasialic20 acids by using 5-N,4-O-carbonyl-protected
phosphate-based sialyl donors. The influence of other protect-
ing groups on the oxazolidinone-based sialyl donor, however,
was not fully investigated. Herein, we describe the use of the
5-N,4-O-carbonyl-protected sialyl donor 2a as an effective
R-selective sialylation donor and its application on the stereo-
selective synthesis of R-(2f9)-tetrasialic acid 1 (Figure 1).
Results and Discussion
We envisaged that a 7,8,9-tri-O-chloroacetyl-derivatized
sialyl donor 2a and an acceptor 3 would be an ideal pair for
improving the yield and the R-selectivity of the sialylation
reaction. Both compounds are protected with a cyclic 5-N,4-
O-carbonyl protection (Figure 1), and the strong electron-
withdrawing nature of the chloroacetyl protecting groups is
expected both to exert an influence upon the activation of the
thioaryl leaving group and to enhance the solvent participa-
tion, forming the sialyl nitrilium intermediate.21 Moreover,
the reactivity of the primary hydroxyl group toward the sugar
donor is higher than that of a secondary hydroxyl group. Thus,
there is no need to protect the C7- and C8-OH during the
glycosylation reaction between the C9-OH with the sugar
donor.13,14 In addition, the O-chloroacetyl groups can be
introduced efficiently and can be removed selectively under
mild reaction conditions (Et3N in MeOH) in the presence of
other acyl protecting groups.22
(9) Castro-Palomino, J. C.; Tsvetkov, Y. E.; Schneider, R.; Schmidt,
R. R. Tetrahedron Lett. 1997, 38, 6837–6840.
(10) For recent reviews of glycosidations of sialic acid, see: (a) Boons,
G. J.; Demchenko, A. V. Chem. Rev. 2000, 100, 4539–4565. (b) Lin, C.-H.; Lin,
C.-C. In The Molecular Immunology of Complex Carbohydrates 2; Kluwer-
Plenum: New York, 2001. (c) Halcomb, R. L.; Cappell, M. D. J. Carbohydr.
Chem. 2002, 21, 723–768. (d) Ress, D. K.; Linhardt, R. J. Curr. Org. Synth.
2004, 1, 31–46. (e) De Meo, C.; Priyadarshani, U. Carbohydr. Res. 2008, 343,
1540–1552.
(11) (a) Demchenko, A. V.; Boons, G. J. Chem.;Eur. J. 1999, 5, 1278–
1283. (b) De, Meo, C.; Demchenko, A. V.; Boons, G. J. J. Org. Chem. 2001,
66, 5490–5498. (c) Ren, C.-T.; Chen, C.-S.; Wu, S.-H. J. Org. Chem. 2002, 67,
1376–1379. (d) Ando, H.; Koike, Y.; Ishida, H.; Kiso, M. Tetrahedron Lett.
2003, 44, 6883–6886. (e) Lu, K.-C.; Tseng, S.-Y.; Lin, C.-C. Carbohydr. Res.
2002, 337, 755–760. (f) Yu, C.-S.; Niikura, K.; Lin, C.-C.; Wong, C.-H.
Angew. Chem., Int. Ed. 2001, 40, 2900–2903. (g) Tanaka, H.; Adachi, M.;
Takahashi, T. Chem.;Eur. J. 2005, 11, 849–862. (h) Tanaka, K.; Goi, T.;
Fukase, K. Synlett 2005, 2958–2962. (i) Sherman, A. A.; Yudina, O. N.;
Shashkov, A. S.; Menshov, V. M.; Nifantiev, N. E. Carbohydr. Res. 2001,
330, 445–458.
(12) Ando, H.; Koike, Y.; Koizumi, S.; Ishida, H.; Kiso, M. Angew.
Chem., Int. Ed. 2005, 44, 6759–6763.
(13) Lin, C.-C.; Huang, K.-T.; Lin, C.-C. Org. Lett. 2005, 7, 4169–4172.
(14) Lin, C.-C.; Adak, A. K.; Horng, J.-C.; Lin, C.-C. Tetrahedron 2009,
65, 4714–4725.
(15) (a) Farris, M. D.; De Meo, C. Tetrahedron Lett. 2007, 48, 1225–1227.
(b) De Meo, C.; Farris, M.; Ginder, N.; Gulley, B.; Priyadarshani, U.;
Woods, M. Eur. J. Org. Chem. 2008, 21, 3637–3677.
(16) (a) Crich, D.; Li, W. J. Org. Chem. 2007, 72, 2387–2391. (b) Crich,
D.; Li, W. J. Org. Chem. 2007, 72, 7794–7797.
(17) Liang, F.-F.; Chen, L.; Xing, G.-W. Synlett 2009, 425–428.
(18) (a) Tanaka, H.; Nishiura, Y.; Takahashi, T. J. Am. Chem. Soc. 2006,
128, 7124–7125. (b) Tanaka, H.; Nishiura, Y.; Takahashi, T. J. Am. Chem.
Soc. 2008, 130, 17244–17245.
(19) (a) Tanaka, H.; Tateno, Y.; Nishiura, Y.; Takahashi, T. Org. Lett.
2008, 10, 5597–5600. (b) Tanaka, H.; Nishiura, Y.; Takahashi, T. J. Org,
Chem. 2009, 74, 4383–4386.
(20) Hsu, C.-H.; Chu, K.-C.; Lin, Y.-S.; Han, J.-L.; Peng, Y.-S.; Ren,
C.-T.; Wu, C.-Y.; Wong, C.-H. Chem.;Eur. J. 2010, 16, 1754–1760.
(21) Tsvetkov, Y. E.; Nifantiev, N. E. Synlett 2005, 1375–1380.
(22) Nicolaou, K. C.; Mitchell, H. J.; Fylaktakidou, K. C.; Rodrı
R. M.; Suzuki, H. Chem.;Eur. J. 2000, 6, 3116–3148.
´
guez,
4922 J. Org. Chem. Vol. 75, No. 15, 2010

Lin et al.
JOCFeatured Article
SCHEME 1. Preparation of the 5-N,4-O-Carbonyl-Protected Sialyl Donors 2a and 2b
TABLE 1. Sialylations of Donors 2a and 2b with Acceptors 6-12a
entry
donor
acceptor
product
yield (%)
R/β
1
2
3
4
5
6
7
8
9
2a
2b
2a
2a
2b
2b
2a
2b
2a
2a
2a
6
6
7
8
7
8
9
9
13
14
15
16
17
18
19
20
21
22
23
85
83
93
92
95
94
75
73
80
60
75
R
R
R
R
R
R
10/1
3/1
1/1
R
10
11
12
10
11
R
aTol = p-methylphenyl.
(compounds 7 and 8) were examined under the above reac-
tion conditions. Surprisingly, all the sialylations proceeded
with high yields and stereoselectivities (entries 3-6). On the
basis of the above observation, both donors provide similar
yield and exclusive R-stereoselectivity when they are coupled
with primary alcohols. To further evaluate the protecting
group effect on glycosyl donor 2a in the synthesis of R-(2f3)
linkage, such as GM3 antigen, acceptor 10 was prepared, and
the R-selectivity of donor 2a with 10 was significantly improved
in comparison with the use of corresponding O-acetylated
sialyl donor 2b (entries 7 vs 8). Furthermore, when 2a was
coupled with secondary and tertiary hydroxyl groups (methyl
2,3-O-isopropylidene-R-L-rhamnopyranoside 10 and 1-ada-
mantanol 11), the results also showed better R-selectivity
(entries 9 and 10) than those using an acetyl protecting group
of the N-acetyl- 5-N,7-O-oxazinanone sialyl donors.16a,17 Sia-
lylation of 2a with lactosyl acceptor 12 afforded the trisaccha-
ride 23 as a single R anomer (entry 11). It should be noted that
the anomeric configurations of compounds 13-23 were as-
signed based on the chemical shifts of the H-3eq of sialic acid.
The chemical shift of R-glycoside is more downfield than that
of β-glycoside. The H-3eq chemical shifts of the synthesized
R-anomers were located around δ 2.70-3.02 ppm, agreeing
with the reported regions.15,16 These model studies demon-
strated that 7,8,9-tri-O-chloroacetyl-protected sialyl donor 2a
is a highly efficient and R-selective donor in sialylations.
The donor 2a was then applied in the synthesis of oligo-
sialic acid. We adopted a strategy in which the chain was elo-
ngated from the reducing end toward the nonreducing end.
Removal of chloroacetyl protecting groups from 13 was
accomplished with triethylamine (Et3N) in MeOH and gave
the triol acceptor 3 in 83% yield. With the triol acceptor 3 in
FIGURE 2. Structure of sialyl donors (2a and 2b) and acceptors
(6-12).
To probe the above-described assembly strategy, donor 2a
was prepared by a straightforward sequence starting from the
known thioglycoside derivative 4,23 as shown in Scheme 1. The
acetyl protecting groups in 4 were removed under acidic con-
ditions (MsOH in MeOH), followed by selective protection
of the C4-OH and the C5-NH2 (4-nitrophenyl chloroformate
(NPCC) and NaHCO3 in CH3CN/H2O at 0 °C) to give the
5-N,4-O-carbonyl-protected derivative 5 in 82% yield over
two steps. The remaining three hydroxyl groups on the exo-
cyclic chain in 5 were O-acylated with ClCH2COCl to afford
the fully protected donor 2a in 84% yield. Its acetylated ana-
logue 2b was obtained from 5 by reaction with acetic anhyd-
ride in the presence of pyridine and was chosen as a reference
compound for R-selectivity studies.
As shown in Figure 2, donors 2a and 2b were tested with
regard to their R-selectivities in sialylation with various accep-
tors, ranging from simple alcohol to primary and secondary
hydroxyl groups of sugar acceptors. The thiosialoside donors
2a and 2b were then coupled with 3-azido-1-propanol using
NIS and a catalytic amount of TfOH as promoters (CH2Cl2/
MeCN (2/1) at -78 °C)16b to give 13 and 14 in 85% and 83%
yield with exclusive R-selectivity, respectively (Table 1, en-
tries 1 and 2). Encouraged by these preliminary results, we
then decided to study the influence of the protecting groups
of the glycosyl acceptors. Thus, armed and disarmed acceptors
(23) Izumi, M.; Shen, G.-J.; Wacowich-Sgarbi, S.; Nakatani, T.; Plettenburg,
O.; Wong, C.-H. J. Am. Chem. Soc. 2001, 123, 10909–10918.
J. Org. Chem. Vol. 75, No. 15, 2010 4923

Lin et al.
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SCHEME 2. Synthesis of the Protected R-(2f9)-Linked Di-, Tri-, and Tetrasialic Acids 24, 26, and 28
hand, we then turned our attention to the synthesis of the
R-(2f9) disialyl dimer (Scheme 2). Because the primary
hydroxyl group is more reactive than the secondary hydroxyl
group,9,13,14 the (2f9) glycosidic bond was expected to be
formed by the reaction between the donor 2a and the accep-
tor 3. Thus, coupling of the sialyl donor 2a and the acceptor 3
using the in situ activation conditions (NIS/TfOH, CH2Cl2/
MeCN(2/1), -78 °C followed by gradually warming to -50 °C)
yielded the disialoside, which was acetylated to give the di-O-
acetylated derivative 24 (83% yield over two steps). The
serves as an acceptor in the next sialylation reaction. Repeat-
ing the sialylation, acetylation, and dechloroacetylation re-
actions produced the higher order sialosides. This three-step
sequence provided the tri- and tetrasialic acids in 74% and
51% yields, respectively. Because the chloroacetyl groups on
the tetrasaccharide were unstable, these protecting groups
were transformed to the more stable acetyl protecting groups.
Extensive spectroscopic investigations were performed on the
fully protected tetrasialoside 28 to identify the diagnostic R-
linkages, which would thereby confirm the stereochemistry of
the compound. The anomeric configurations of the resulting R-
sialosides 26 and 28 were determined by analyzing the 1H NMR
spectra. The chemical shifts of the H-3eq (δ = 2.83-2.88) and
H-4 (δ = 3.85-4.07) signals and the coupling constant J7,8
(9.9-10.0 Hz) were in accordance with the empirical rules24 for
defining the anomeric configuration of 5-N,4-O-carbonyl-pro-
tected oligosialic acids. In addition, all of the H-3eq chemical
shifts on fully protected derivatives 24, 26, and 28 and fully
deprotected tetrasialic acid 1are located at the position, 2.85 and
2.73 ppm, respectively. Interestingly, the chemical shifts of
H-3eq on partially deprotected nonreducing end sialic acid of
3, 25, and 27 are more downfield (2.93 ppm) than those of fully
protected sialic acids (2.85 ppm). Notably, the sialylation yield
decreased gradually with increasing length of the sugar chain,
but no β-anomeric product was obtained in any of the sialyla-
tion reactions.
long-range coupling constants of C1 with axial H3 (3JC-1,H-3ax
)
are 5.4 Hz (δ = 167.91 ppm) and 5.3 Hz (δ = 168.47 ppm),
indicating that both anomeric centers of 24 are in the R-
configuration.14,24 These results further demonstrate that the
donor 2a exhibits good R-selectivity in the sialylation reac-
tion with primary hydroxyl acceptors. To extend the sialic
acid chain from the reducing end toward the nonreducing
end, the O-chloroacetyl protecting groups of 24 were re-
moved selectively with Et3N to afford triol 25 (83%), which
(24) Hori, H.; Nakajima, T.; Nishida, Y.; Ohrui, H.; Meguro, H. Tetra-
hedron Lett. 1988, 29, 6317–6320. and references cited therein. For 5-N,4-O-
carbonyl-protected oligosialic acids, the chemical shift of H-3eq were located
in the region of δ = 2.86-3.12 for the R anomer and δ = 2.55-2.66 for the
β anomer; H-4 are located in the region of δ = 3.86-4.06 for the R anomer
and δ = 4.43-4.66 for the β anomer. The coupling constants between H-7
and H-8 were 9.2-10.6 Hz for the R anomer and 7.7-8.7 for the β anomer
(see ref 19). In this paper, the chemical shift of H-3eq, H-4, and J7,8 values
were all located in the R anomer regions of the literature, and no β signals
were found..
Deprotection of the protected R-(2f9)-tetrasialoside 28
was then examined, as shown in Scheme 3. Upon exposure to
4924 J. Org. Chem. Vol. 75, No. 15, 2010

Lin et al.
JOCFeatured Article
SCHEME 3. Synthesis of the Fully Deprotected R-(2f9)-Tetrasialic Acid 1
basic conditions (aqueous ethanolic lithium hydroxide) at
80 °C, both the 5-N,4-O-carbonyl-protecting groups and the
ester groups were removed. The resulting amines were N-ace-
tylated (Ac2O, NaHCO3), and then exposure to base under
CH2Cl2 (19.4 mL) was added dropwise through an addition
funnel to the vigorously stirred mixture. After being stirred at rt
for 3 h, the reaction mixture was poured into a 10% aqueous
HCl solution at 0 °C (50 mL). The aqueous layer was extracted
three times with EtOAc. The combined extracts were washed
with brine and were dried over MgSO4. The solution was
concentrated under reduced pressure and then was subjected
to silica gel flash column chromatography (hexanes/EtOAc,
from 4/1 to 2/1) to afford 2a (6.27 g, 9.76 mmol, 84%): 1H
NMR (400 MHz, CDCl3) δ 2.26 (dd, J = 12.4, 12.4 Hz, 1H),
2.35 (s, 3H), 2.81 (dd, J = 3.8, 12.4 Hz, 1H), 3.21 (dd, J = 12.4,
12.4 Hz, 1H), 3.66 (s, 3H), 3.97 (AB quartet, J = 15.0 Hz, 2H),
4.07 (AB quartet, J = 15.0 Hz, 2H), 4.13 (AB quartet, J = 15.0 Hz,
2H), 4.33 (dd, J = 6.4, 12.5 Hz, 1H), 4.52 (dd, J = 2.4, 12.5 Hz,
1H), 4.59 (dd, J = 2.5, 12.4 Hz, 1H), 4.70 (ddd, J = 3.8, 12.4,
12.4 Hz, 1H), 5.26-5.29 (m, 2H), 5.54 (s, 1H), 7.17 (d, J = 8.1 Hz,
2H), 7.26 (d, J = 8.1 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ
21.4, 36.4, 40.5, 40.7, 53.0, 58.3, 63.2, 72.0, 72.5, 73.1, 77.2, 88.8,
124.9, 130.2, 136.3, 140.9, 159.5, 166.8, 167.8; HRMS (FAB)
calcd for C24H27O11Cl3NS (M þ H)þ 642.0370, found 642.0362.
Methyl (4-Methylphenyl 5-amino-7,8,9-tri-O-acetyl-5-N,4-O-
carbonyl-3,5-dideoxy-2-thio-D-glycero-β-D-galacto-non-2-ulopy-
ranoside)onate (2b). To a solution of 5 (308 mg, 0.64 mmol) in
pyridine (4 mL) was added acetic anhydride (2 mL) at 0 °C. The
reaction was stirred for 12 h at room temperature and then con-
centrated in vacuo. The residue was diluted with EtOAc, and the
resulting solution was washed with 10% HCl, saturated NaH-
CO3, and saturated NaCl in sequence. The organic phase was
dried (MgSO4) and filtered, and the filtrate was evaporated. The
residue was purified by silica gel column chromatography (EtOAc/
hexane = 1/4) to afford 2b (301 mg, 98%): 1H NMR (400 MHz,
CDCl3) δ 2.00 (s, 3H), 2.07 (s, 3H), 2.13 (s, 3H), 2.22 (dd, J =
12.5, 12.8 Hz, 1H), 2.33 (s, 3H), 2.78 (dd, J = 3.7, 12.8 Hz, 1H),
3.05 (dd, J = 9.7, 11.2 Hz, 1H), 3.60 (s, 3H), 4.22 (dd, J = 5.9,
12.5 Hz, 1H), 4.39 (dd, J = 2.0, 12.5 Hz, 1H), 4.56 (dd, J = 2.4,
9.7 Hz, 1H), 4.68 (ddd, J = 3.7, 11.2, 12.5 Hz, 1H), 5.14 (ddd,
J = 2.0, 5.2, 5.9 Hz, 1H), 5.19 (dd, J = 2.4, 5.2 Hz, 1H), 5.40 (s,
1H), 7.13 (d, J = 8.0 Hz, 2H), 7.25 (d, J = 8.0 Hz, 2H); 13C
NMR (100 MHz, CDCl3) δ 20.7, 20.8, 21.0, 21.4, 36.4, 52.8,
58.5, 61.9, 70.4, 70.9, 73.3, 76.9, 89.0, 125.3, 130.1, 136.2, 140.5,
159.3, 167.9, 170.2, 170.4, 171.4; HRMS (FAB) calcd for
C24H30NO11S (M þ H)þ 540.1540, found 540.1550.
ꢀ
Zemplen conditions (NaOMe in MeOH) ensured complete
removal of the partially regenerated O-acetyl groups. The
fully deprotected R-(2f9)-tetrasialic acid 1 was obtained in
43% overall yield (three steps).
In conclusion, we have presented an efficient and highly
R-selective method for the synthesis of R-(2f9)-tetrasialic acid
using iterative dechloroacetylation, sialylation, and acetylation
reactions. The 5-N,4-O-carbonyl-7,8,9-tri-O-chloroacetyl-pro-
tected sialyl donor 2a was also demonstrated to be a highly
reactive R-selective donor in sialylation reactions with various
acceptors. Under in situ activation conditions (NIS/TfOH,
-78 °C), the sialylation was complete within 1 h (based on
TLC analysis).
Experimental Section
Methyl (4-Methylphenyl 5-amino-5-N,4-O-carbonyl-3,5-dideoxy-
2-thio-D-glycero-β-D-galacto-non-2-ulopyranoside)onate (5). A
stirred solution of compound 4 (8.5 g, 14.22 mmol) in MeOH
(142 mL) was treated with methanesulfonic acid (2.43 mL, 42.67
mmol) at rt under N2 and then was refluxed for 24 h. After being
cooled to rt, the reaction mixture was quenched with an excess of
Et3N and then was concentrated under reduced pressure. The
residue was dissolved in MeCN/H2O (1/2, 140 mL) in the presence
of NaHCO3 (5.97 g, 71.11 mmol), and the mixture was cooled to
0 °C. 4-Nitrophenyl chloroformate (7.17 g, 35.56 mmol) in MeCN
(47.4 mL) was added to the vigorously stirred mixture over 20 min
through an addition funnel, and the resulting solution was
allowed to stir for an additional 3 h at 0 °C. After being warmed
to rt, the reaction mixture was quenched with a 10% aqueous
HCl solution, and the suspended solid was dissolved with EtOAc.
The aqueous layer was extracted with CH2Cl2 (3 ꢀ 100 mL), and
the combined extracts were washed with brine, dried over
MgSO4, and concentrated. The residue was purified by silica
gel flash column chromatography, eluting first with EtOAc and
then changing to EtOAc/MeOH (10/1 to 5/1) to give compound
1
5 as white foam (4.81 g, 11.64 mmol, 82% over two steps): H
NMR (400 MHz, CD3OD) δ 2.34 (s, 3H), 2.41 (dd, J = 12.6,
12.6 Hz, 1H), 2.87 (dd, J = 3.9, 12.6 Hz, 1H), 3.59 (dd, J = 1.8,
8.7 Hz, 1H), 3.59 (dd, J = 12.6, 9.9 Hz, 1H), 3.63 (s, 3H),
3.67-3.76 (m, 2H), 3.83 (dd, J = 2.4, 10.8 Hz, 1H), 4.63 (ddd,
J = 3.9, 12.6, 12.6 Hz, 1H), 4.68 (dd, J = 1.8, 9.9 Hz, 1H), 7.19
(d, J = 8.0 Hz, 2H), 7.47 (d, J = 8.0 Hz, 2H); 13C NMR (100
MHz, CD3OD) δ 21.4, 38.4, 53.5, 59.6, 65.1, 71.4, 72.4, 75.9,
79.4, 91.1, 127.4, 130.9, 137.9, 141.7, 162.6, 170.8; HRMS (ESI)
calcd for C18H23NNaO8S (M þ Na)þ 436.1042, found 436.1042.
Methyl (4-Methylphenyl 5-amino-5-N,4-O-carbonyl-7,8,9-tri-
O-chloroacetyl-3,5-dideoxy-2-thio-D-glycero-β-D-galacto-non-2-
ulopyranoside)onate (2a). To compound 5 (4.8 g, 11.62 mmol)
dissolved in CH2Cl2 (58.1 mL, 0.2 M) was added pyridine (5.61 mL,
69.72 mmol) at rt under N2, and the resulting solution was then
cooled to 0 °C. Chloroacetyl chloride (3.22 mL, 40.67 mmol) in
General Glycosylation Procedure. A solution of donor (0.16
mmol), acceptor (0.19 mmol), and freshly activated 3 A pow-
dered molecular sieves (0.5 g/mmol) in anhydrous CH2Cl2/
MeCN (v/v = 2/1) was stirred for 1 h under N2. The reaction solu-
tion was cooled to -78 °C, and then NIS (0.23 mmol) and TfOH
(0.06 mmol) were added. The reaction mixture was stirred at this
temperature for 10 min and then was stirred at -50 °C for 1 h. The
reaction mixture was diluted with CH2Cl2 and was filtered through
Celite. The filtered solution was washed with saturated aqueous
Na2S2O3 solution, dried over MgSO4, and concentrated under
reduced pressure. The residue was purified by silica gel flash
column chromatography to give the target sialoside.
Methyl (3-azidopropyl-5-amino-5-N,4-O-carbonyl-7,8,9-tri-O-chlo-
roacetyl-3,5-dideoxy-D-glycero-r-D-galacto-non-2-ulopyranoside)-
1
onate (13): H NMR (400 MHz, CDCl3) δ 1.79 (m, 2H), 2.05
J. Org. Chem. Vol. 75, No. 15, 2010 4925

Lin et al.
JOCFeatured Article
(dd, J = 12.4, 12.4 Hz, 1H), 2.85 (dd, J = 3.5, 12.4 Hz, 1H), 3.09
(dd, J = 9.9, 9.9 Hz, 1H), 3.30 (dt, J = 6.2, 11.3 Hz, 1H), 3.37 (t,
J = 6.2 Hz, 2H), 3.77-3.81 (m, 1H), 3.80 (s, 3H), 3.92 (ddd, J =
3.5, 9.9, 12.4 Hz, 1H), 4.06 (s, 2H), 4.17 (d, J = 15.3 Hz, 1H),
4.18 (s, 2H), 4.28 (dd, J = 1.7, 9.9 Hz, 1H), 4.32 (d, J = 15.3 Hz,
1H), 4.37 (dd, J = 3.8, 12.8 Hz, 1H), 4.52 (dd, J = 2.0, 12.8 Hz,
1H), 5.18 (dd, J = 1.7, 9.8 Hz, 1H), 5.35 (s, 1H), 5.64 (ddd, J =
2.0, 3.8, 9.8 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 29.0, 37.3,
40.5, 40.6, 41.1, 48.1, 53.3, 57.5, 62.3, 63.2, 68.2, 70.4, 73.5, 76.8,
100.2, 159.3, 166.4, 167.1, 168.2, 168.8; HRMS (FAB) calcd for
C20H25Cl3N4NaO12 (M þ Na)þ 641.0432, found 641.0436.
Methyl (3-azidopropyl 5-amino-7,8,9-tri-O-acetyl-5-N,4-O-
carbonyl-3,5-dideoxy-D-glycero-r-D-galacto-non-2-ulopyranoside)-
onate (14): 1H NMR (400 MHz, CDCl3) δ 1.78 (m, 2H), 2.01 (dd,
J = 10.8, 12.0 Hz, 1H), 2.03 (s, 3H), 2.14 (s, 3H), 2.15 (s, 3H),
2.84 (dd, J = 3.6, 12.0 Hz, 1H), 3.02 (dd, J = 9.8, 10.9 Hz, 1H),
3.29 (m, 1H), 3.35 (m, 2H), 3.77 (s, 3H), 3.8 (m, 1H), 3.92 (ddd,
J = 3.6, 10.8, 10.9 Hz, 1H), 4.24 (dd, J = 1.9, 9.8 Hz, 1H), 4.26
(m, 2H), 5.09 (dd, J = 2.0, 9.8 Hz, 1H), 5.34 (s, 1H), 5.45 (ddd,
J = 2.7, 2.9, 9.8 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 20.8,
20.9, 21.2, 29.1, 37.6, 48.2, 53.1, 58.0, 61.9, 62.3, 67.1, 69.0, 73.7,
76.8, 100.2, 159.4, 168.6, 170.7, 171.7; HRMS (FAB) calcd for
C20H28O12N4Na (M þ Na)þ 539.1601, found 539.1600.
13C NMR (100 MHz, CD3OD) δ 20.0, 20.2, 20.6, 37.1, 52.6, 54.8,
57.4, 61.1, 66.2, 69.1, 72.9, 73.1, 74.3, 75.4, 76.3, 76.6, 79.1, 81.5,
97.8, 99.8, 127.2, 127.4, 127.5, 127.6, 127.7, 127.9, 128.0, 128.1,
137.8, 138.2, 138.4, 167.7, 169.3, 170.0, 171.0, 177.7; HRMS (FAB)
calcd for C45H53NO17Na (M þ Na)þ 902.3211, found 902.3201.
Methyl (5-amino-7,8,9-tri-O-acetyl-5,4-N,O-carbonyl-3,5-di-
deoxy-D-glycero-r-D-galacto-non-2-ulopyranoside)onate-(2f6)-
(methyl 2,3,4-tri-O-benzoyl-r-D-galactopyranoside) (18): 1H NMR
(400 MHz, CD3OD) δ 1.98 (s, 3H), 2.05 (s, 3H), 2.07 (s, 3H), 2.88
(dd, J = 3.0, 12.0 Hz, 1H), 2.96 (t, J = 11.0 Hz, 1H), 3.44 (s, 3H),
3.43-3.47 (m, 1H), 3.58 (dd, J = 2.9, 12.8 Hz, 1H), 3.74 (s, 3H),
3.79-3.90 (m, 2H), 4.05 (dd, J = 3.6, 10.8 Hz, 1H), 4.09-4.12 (m,
1H), 4.20 (dd, J = 3.1, 10.1 Hz, 1H), 4.95 (dd, J = 2.0, 10.1 Hz,
1H), 5.07 (td, J = 2.5, 10.1 Hz, 1H), 5.21-5.24 (m, 2H), 5.27 (br,
1H), 5.64 (t, J = 9.8 Hz, 1H), 6.00-6.05 (m, 2H), 7.27-7.54 (m,
9H), 7.85-7.95 (m, 6H); 13C NMR (100 MHz, CD3OD) δ 20.3,
20.3, 20.6, 36.7, 52.7, 55.3, 57.3, 60.9, 63.0, 66.3, 67.6, 67.9, 68.4,
70.6, 71.5, 73.2, 76.3, 96.7, 99.6, 127.9, 128.1, 128.7, 128.9, 129.1,
129.4, 129.4, 129.5, 132.8, 133.1, 159.0, 164.4, 165.50, 165.53, 167.6,
169.4, 170.1, 171.2, 177.7; HRMS (FAB) calcd for C45H47NO20Na
(M þ Na)þ 944.2589, found 944.2589.
6-Trifluoroacetamidohexyl O-[methyl (5-amino-5-N,4-O-car-
bonyl-7,8,9-tri-O-chloroacetyl-3,5-dideoxy-D-glycero-r-D-galacto-
non-2-ulopyranoside)onate]-(2f3)-O-(2,6-di-O-benzyl-β-D-gala-
ctopyranosyl)-(1f 4)-2,3,6-tri-O-benzyl-β-D-glucopyranoside (19):
1H NMR (400 MHz, CDCl3) for 19 R: δ 1.26-1.32 (m, 2H),
1.34-1.42 (m, 2H), 1.42-1.50 (m, 2H), 1.57-1.64 (m, 2H), 2.15
(dd, J = 12.3, 12.3 Hz, 1H), 2.55 (br, 1H), 2.84 (dd, J = 3.4,
12.3 Hz, 1H), 2.97 (dd, J = 10.8, 10.8 Hz, 1H), 3.20-3.27 (m,
2H), 3.33-3.44 (m, 3H), 3.43-3.56 (m, 4H), 3.57-3.7 (m, 4H),
3.73 (s, 3H), 3.85-3.95 (m, 4H), 3.98 (s, 2H), 4.08 (dd, J = 2.2,
12.7 Hz, 1H), 4.10 (d, J = 15.3 Hz, 1 H), 4.11 (d, J = 12.4 Hz,
1H), 4.12 (d, J = 12.4 Hz, 1H), 4.15(dd, J = 1.6, 10.8 Hz, 1H),
4.25 (d, J = 15.3 Hz, 1 H), 4.31 (d, J = 11.7 Hz, 1H), 4.32 (d, J =
7.8 Hz, 1 H), 4.34 (dd, J = 3.8, 12.7 Hz, 1H), 4.37 (d, J = 11.7 Hz,
1H), 4.46 (s, 2H), 4.61 (d, J = 7.8 Hz, 1H), 4.63 (d, J = 11.9 Hz,
1H), 4.69 (d, J = 11.1 Hz, 1H), 4.75 (d, J = 10.8 Hz, 1H), 4.78
(d,J= 11.9 Hz, 1H), 4.85 (d, J= 11.1 Hz, 1H), 4.92 (d, J=10.8Hz,
1H), 5.08 (dd, J = 1.6, 9.5 Hz, 1H), 5.20 (br, 1H), 5.61(ddd, J =
2.2, 3.8, 9.5 Hz, 1 H), 6.19 (br, 1H), 7.15-7.35 (m, 25H); 13C
NMR (100 MHz, CDCl3) δ 25.5, 26.2, 28.6, 29.3, 35.6, 39.7,
39.8, 40.3, 40.9, 53.3, 57.2, 62.8, 67.7, 68.2, 68.2, 68.6, 69.5, 70.0,
71.9, 72.9, 73.2, 73.3, 74.7, 74.8, 74.9, 75.2, 76.5, 76.5, 77.0, 78.1,
81.7, 82.7, 99.6, 102.3, 103.4, 115.7, 127.1, 127.2, 127.2, 127.3,
127.4, 127.5, 127.6, 127.7, 127.8, 128.0, 128.1, 128.20, 128.28,
138.0, 138.3, 138.5, 138.7, 138.9, 157.0, 159.0, 166.3, 166.9,
167.9, 168.3; HRMS (ESI) calcd for C72H82N2O23F3NaCl3 (M þ
Na)þ 1527.4224, found 1527.4221.
6-Trifluoroacetamidohexyl O-[methyl (5-amino-7,8,9-tri-O-
acetyl-5-N,4-O-carbonyl-3,5-dideoxy-D-glycero-r-D-galacto-non-
2-ulopyranoside)onate]-(2f3)-O-(2,6-di-O-benzyl-β-D-galacto-
pyranosyl)-(1f 4)-2,3,6-tri-O-benzyl-β-D-glucopyranoside (20):
1H NMR (400 MHz, CDCl3) for 20R δ 1.26-1.33 (m, 2H),
1.34-1.41 (m, 2H), 1.41-1.50 (m, 2H), 1.56-1.64 (m, 2H), 2.00
(s, 3H), 2.02 (dd, J = 9.8, 12.2 Hz, 1H), 2.09 (s, 3H), 2.14 (s, 3H),
2.60 (br, 1H), 2.80 (dd, J = 3.5, 12.2 Hz, 1H), 2.94 (dd, J = 9.8,
10.9 Hz, 1H), 3.32-3.42 (m, 3H), 3.44-3.57 (m, 4H), 3.58-3.68
(m, 2H), 3.70-3.78 (m, 2H), 3.72 (s, 3H), 3.85-3.93 (m, 4H),
4.07 (dd, J = 3.9, 12.7 Hz, 1H), 4.13 (dd, J = 1.8, 9.7 Hz, 1H),
4.20 (dd, J = 2.0, 12.7 Hz, 1H), 4.31 (d, J = 7.8 Hz, 1H), 4.32 (d,
J = 12.3 Hz, 1H), 4.40 (d, J = 11.8 Hz, 1H), 4.44 (d, J = 12.3 Hz,
1H), 4.56 (d, J = 7.8 Hz, 1H), 4.64 (d, J = 11.8 Hz, 1H), 4.70 (d,
J = 11.1 Hz, 1H), 4.72 (d, J = 11.8 Hz, 1H), 4.73 (d, J = 11.8 Hz,
1H), 4.74 (d, J = 10.8 Hz, 1H), 4.84 (d, J = 11.1 Hz, 1H), 4.93
(d, J = 10.8 Hz, 1H), 5.04 (dd, J = 1.8, 9.3 Hz, 1H), 5.27 (s, 1H),
5.46 (ddd, J = 2.0, 3.9, 9.3 Hz, 1H), 6.19 (br, 1H), 7.16-7.36
(m, 25H); 13C NMR (100 MHz, CDCl3) δ 20.2, 20.6, 21.0, 25.6,
26.2, 28.7, 29.4, 35.7, 39.7, 53.1, 57.8, 61.7, 67.2, 67.8, 68.2, 68.6,
Methyl (5-amino-5,4-N,O-carbonyl-7,8,9-tri-O-chloroacetyl-
3,5-dideoxy-D-glycero-r-D-galacto-non-2-ulopyranoside)onate-
(2f6)-(methyl 2,3,4-tri-O-benzyl-r-D-galactopyranoside) (15):
1H NMR (400 MHz, CD3OD) δ 2.05-2.08 (m, 1H), 2.93-
3.02 (m, 2H), 3.34-3.36 (m, 1H), 3.36 (s, 3H), 3.48 (dd, J = 3.5,
9.7 Hz, 1H), 3.56 (t, J = 9.8 Hz, 1H), 3.68-3.71 (m, 2H),
3.71-3.77 (m, 2H), 3.74 (s, 3H), 3.83-3.96 (m, 2H), 3.99 (br,
2H), 4.07-4.17 (m, 4H), 4.20 (dd, J = 1.8, 9.8 Hz, 1H), 4.33 (d,
J = 15.5 Hz, 1H), 4.60 (d, J = 3.4 Hz, 1H), 4.64 (d, J = 12.3 Hz,
1H), 4.69 (d, J = 10.8 Hz, 1H), 4.76-4.82 (m, 3H), 4.90 (d, J =
10.8 Hz, 1H), 5.04 (dd, J = 1.8, 10.3 Hz, 1H), 5.23 (br, 1H),
5.42-5.46 (m, 1H), 7.27-7.34 (m, 15H); 13C NMR (100 MHz,
CD3OD): δ 37.2, 39.8, 40.3, 40.9, 53.1, 55.2, 57.2, 62.4, 63.7, 67.4,
69.1, 69.6, 73.1, 73.2, 74.2, 75.7, 76.5, 79.2, 81.7, 98.1, 100.1, 127.2,
127.5, 127.6, 127.81, 127.87, 127.9, 128.2, 128.34, 128.36, 138.0,
138.5, 138.6, 158.9, 166.1, 167.8, 168.1; HRMS (FAB) calcd for
C45H49Cl3NO17 (M - H)þ 980.2066, found 980.2070.
Methyl (5-amino-5,4-N,O-carbonyl-7,8,9-tri-O-chloroacetyl-
3,5-dideoxy-D-glycero-r-D-galacto-non-2-ulopyranoside)onate-
(2f6)-(methyl 2,3,4-tri-O-benzoyl-r-D-galactopyranoside) (16):
1H NMR (400 MHz, CD3OD): δ 2.14 (t, J = 12.5 Hz, 1H), 2.93
(dd, J = 3.4, 12.2 Hz, 1H), 3.01 (t, J = 10.7 Hz, 1H), 3.44-3.50
(m, 2H), 3.45 (s, 3H), 3.77 (s, 3H), 3.82-3.89 (m, 1H), 3.92 (dd,
J = 1.9, 13.1 Hz, 1H), 3.98-4.04 (m, 4H), 4.08-4.16 (m, 3H),
4.21 (dd, J = 2.7, 10.1 Hz, 1H), 4.28 (d, J = 15.4 Hz, 1H), 5.00
(dd, J = 1.8, 10.2 Hz, 1H), 5.14 (dd, J = 2.5, 9.6 Hz, 1H),
5.22-5.28 (m, 3H), 5.63 (t, J = 9.8 Hz, 1H), 6.01 (t, J = 9.4 Hz,
1H), 7.29-7.54 (m, 9H), 7.86-7.95 (m, 6H); 13C NMR (100
MHz, CD3OD): δ 37.0, 40.1, 40.3, 40.9, 53.2, 55.7, 57.3, 62.2,
62.9, 67.5, 67.7, 68.5, 69.5, 70.9, 71.6, 73.2, 76.5, 97.0, 99.8,
128.1, 128.3, 128.5, 128.9, 129.2, 129.4, 129.5, 129.6, 129.8,
133.0, 133.3, 133.4, 158.9, 164.6, 165.7, 166.2, 166.8, 168.0;
HRMS (FAB) calcd for C45H45Cl3NO20 (M - H)þ 1024.1601,
found 1024.1620.
Methyl (5-amino-7,8,9-tri-O-acetyl-5,4-N,O-carbonyl-3,5-di-
deoxy-D-glycero-r-D-galacto-non-2-ulopyranoside)onate-(2f6)-
(methyl 2,3,4-tri-O-benzyl-r-D-galactopyranoside) (17): 1H NMR
(400MHz, CD3OD): δ1.84(s, 3H),1.99(s, 3H), 2.04(t,J=6.0Hz,
1H), 2.13 (s, 3H), 2.92-297 (m, 2H), 3.34 (s, 3H), 3.37 (dd, J = 1.8,
10.5 Hz, 1H), 3.48 (dd, J = 3.5, 9.7 Hz, 1H), 3.56 (t, J = 9.5 Hz,
1H), 3.71 (s, 3H), 3.71-3.72 (m, 1H), 3.77 (dd, J = 3.0, 12.8 Hz,
1H), 3.86-3.95 (m, 2H), 3.98 (dd, J = 1.9, 12.8 Hz, 1H), 4.17 (dd,
J = 3.8, 10.4 Hz, 1H), 4.21 (dd, J = 1.9, 9.9 Hz, 1H), 4.59 (d, J =
3.5 Hz, 1H), 4.63 (d, J = 12.3 Hz, 1H), 4.71 (d, J = 10.9 Hz, 1H),
4.73 (d, J = 11.2 Hz, 1H), 4.77-4.79 (m, 2H), 7.24-7.34 (m, 15H);
4926 J. Org. Chem. Vol. 75, No. 15, 2010

Lin et al.
JOCFeatured Article
68.8, 69.6, 72.3, 72.9, 73.3, 73.7, 74.8, 75.0, 75.0, 75.3, 76.5, 76.6,
77.0, 78.1, 81.8, 82.8, 99.6, 102.4, 103.5, 116.1, 127.3, 127.52,
127.58, 127.8, 128.05, 128.08, 128.20, 128.21, 128.27, 128.3,
138.2, 138.4, 138.71, 138.73, 139.0, 157.1, 159.2, 168.2, 169.6,
170.5, 171.4; HRMS (ESI) calcd for C72H86N2O23F3 (M þ H)þ
1403.5573, found 1403.5571.
perature for 10 min. The mixture was then neutralized with a
10% aqueous HCl solution and was concentrated under reduced
pressure. The residue was purified by silica gel flash column
chromatography (hexanes/EtOAc/MeOH, from 1/10/0, 1/1/
0.12, 1/1/0.16 to 1/1/0.2) to afford 3 (315 mg, 83%): 1H NMR
(400 MHz, CD3OD) δ 1.80 (m, 2H), 2.10 (dd, J = 11.8, 13.1 Hz,
1H), 2.93 (dd, J = 3.7, 11.8 Hz, 1H), 3.39 (t, J = 6.4 Hz, 2H),
3.46 (dt, J = 6.4, 12.4 Hz, 1H), 3.58 (dd, J = 1.8, 8.6Hz, 1H), 3.61
(dd, J = 9.9, 11.1 Hz, 1H), 3.68 (dd, J = 5.5, 10.6 Hz, 1H),
3.79-3.86 (m, 2H), 3.86 (s, 3H), 3.89 (dt, J = 6.4, 12.4 Hz, 1H),
4.07 (ddd, J = 3.7, 11.1, 13.1 Hz, 1H), 4.12 (dd, J = 1.8, 8.6 Hz,
1H); 13C NMR (100 MHz, CD3OD) δ 30.1, 38.1, 49.3, 53.8, 58.6,
62.8, 64.7, 71.6, 72.4, 77.3, 79.1, 101.7, 162.7, 170.7; HRMS (ESI)
calcd for C14H22N4NaO9 (M þ Na)þ 413.1284, found 413.1280.
Methyl (3-Azidopropyl 7,8-di-O-acetyl-5-amino-5-N,4-O-car-
bonyl-9-O-(methyl 5-amino-5-N,4-O-carbonyl-7,8,9-tri-O-chlor-
oacetyl-3,5-dideoxy-D-glycero-r-D-galacto-non-2-ulopyranosylonate)-
3,5-dideoxy-D-glycero-r-D-galacto-non-2-ulopyranoside)onate
(24). A mixture of donor 2a (206 mg, 0.32 mmol) and acceptor 3
(100 mg, 0.26 mmol) was dried azeotropically with toluene three
times and then was dissolved in anhydrous CH2Cl2/MeCN (2/1,
4 mL) at rt under N2. The resulting solution was transferred to a
round-bottomed flask containing dry 3-A MS (160 mg, 0.5 g/
mmol) at rt under N2. The reaction mixture was stirred for
10 min and then was cooled to -78 °C. NIS (90 mg, 0.4 mmol)
and TfOH (17 μL, 0.13 mmol) were added to the reaction mix-
ture. After being stirred at -50 °C for 1 h, the reaction mixture
was warmed to 0 °C and then was quenched with a saturated
aqueous Na2S2O3 solution. The aqueous layer was extracted
with CH2Cl2 (3 ꢀ 30 mL), and the combined extracts were dried
over MgSO4 and concentrated under reduced pressure. The
residue was dissolved in CH2Cl2 (4 mL), and then Ac2O (121 μL,
1.28 mmol) was added at 0 °C under N2, followed by TfOH
(4.3 μL, 0.032 mmol). After being stirred for 15 min, the reaction
mixture was quenched with a saturated aqueous NaHCO3 solu-
tion. The aqueous layer was extracted with EtOAc (3 ꢀ 30 mL),
and the combined extracts were dried over MgSO4. After the
solution was concentrated, the residue was purified by silica gel
flash column chromatography (hexanes/EtOAc/MeOH, from
1/1/0 to 1/1/0.1) to afford 24 (211 mg, 83% over two steps): 1H
NMR (400 MHz, CDCl3) δ 1.79 (m, 2H), 1.97-2.05 (br-dd,
2H), 2.16 (s, 3H), 2.21 (s, 3H), 2.82-2.87 (br-dd, 2H), 3.05 (dd,
J = 10.8, 10.8 Hz, 1H), 3.13 (dd, J = 10.8, 10.8 Hz, 1H), 3.29
(dt, J = 6.4, 11.7 Hz, 1H), 3.35 (dd, J = 1.9, 12.7 Hz, 1H), 3.36
(t, J = 6.4 Hz, 2H), 3.78 (s, 6H), 3.78-3.93 (m, 4H), 4.05 (s, 2H),
4.16 (d, J = 15.3 Hz, 1H), 4.22 (s, 2H), 4.22-4.25 (br-dd, 2H),
4.28 (d, J = 15.3 Hz, 1H), 4.30 (dd, J = 4.2, 12.7 Hz, 1H), 4.52
(dd, J = 1.9, 12.7 Hz, 1H), 5.18 (dd, J = 1.8, 9.9 Hz, 1H), 5.22
(dd, J = 1.9, 9.9 Hz, 1H), 5.38 (br, 1H), 5.39 (s, 1H), 5.55 (ddd,
J = 1.9, 4.2, 9.9 Hz, 1H), 5.59 (s, 1H); 13C NMR (100 MHz,
CDCl3) δ 21.0, 21.1, 29.1, 37.2, 37.6, 40.5, 40.6, 41.0, 48.2, 53.1,
53.4, 57.2, 58.0, 62.2, 63.2, 63.6, 67.2, 67.9, 68.8, 70.3, 73.6, 73.7,
76.6, 76.9, 100.0, 100.1, 159.2, 159.7, 167.1, 168.3, 168.6, 169.8,
171.7, 177.8; HRMS (ESI) calcd for C35H44Cl3N5NaO22 (M þ
Na)þ 1014.1441, found 1014.1433.
Methyl (5-amido-5-N,4-O-carbonyl-7,8,9-tri-O-chloroacetyl-
3,5-dideoxy-D-glycero-r/β-D-galacto-non-2-ulopyranoside)onate-
(2f4)-methyl 2,3-O-isopropylidene-r-L-rhamnopyranoside (21):
1H NMR (400 MHz, CDCl3) δ 1.20-1.24 (m, 9H), 1.30 (s, 3H),
1.43 (s, 3H), 1.45 (s, 3H), 1.93-2.00 (m, 2H), 2.51 (t, J = 12.8 Hz,
1H), 2.79-2.85 (m, 2H), 3.00 (t, J = 10.5 Hz, 1H), 3.31 (broad s,
6H), 3.35-3.40 (m, 2H), 3.51 (dd, J = 5.8, 9.6 Hz, 1H) 3.58 (dd,
J = 6.1, 9.6 Hz, 1H), 3.61-3.68 (m, 1H), 3.73 (s, 3H), 3.75 (s,
3H), 3.88-3.95 (m, 1H), 4.02 (s, 3H), 4.03 (s, 2H), 4.05-4.10 (m,
2H), 4.12 (br, 3H), 4.13 (s, 1H), 4.15-4.16 (m, 4H), 4.17-4.19
(m, 1H), 4.27 (d, J=15.4 Hz, 1H), 4.31-4.41 (m, 2H), 4.48-
4.55 (m, 2H), 4.66 (d, J = 12.8 Hz, 1H), 4.76-4.77 (m, 2H), 5.15
(dd, J = 1.3, 9.9 Hz, 1H), 5.24 (dd, J = 2.7, 5.8 Hz, 1H), 5.47 (br,
1H), 5.53 (dd, J = 2.1, 6.0 Hz, 1H), 5.64 (d, J = 9.8 Hz, 1H), 6.00
(br, 1H); 13C NMR (100 MHz, CDCl3) δ 18.1 (2 C), 25.7, 25.9,
27.5, 27.6, 36.9, 37.7, 40.1, 40.2, 40.3, 40.4, 40.5, 40.7, 52.7, 53.1,
54.7, 54.8, 57.6, 57.7, 62.5, 63.1, 63.7, 63.9, 68.7, 69.9, 71.0 (2 C),
72.4, 73.1, 75.7, 76.0, 76.2, 76.6, 76.9, 77.0, 77.1, 77.7, 98.0, 98.1,
98.9, 100.0, 109.0, 109.1, 159.3, 159.7, 165.9, 166.2, 166.8, 166.9,
167.0, 167.1, 167.8, 167.9; ESIHRMS calcd for C27H36Cl3NO16-
Na (M þ Na)þ 758.0997, found 758.1025.
Methyl (1-adamantanyl-5-amino-5-N,4-O-carbonyl-7,8,9-tri-
O-chloroacetyl-3,5-dideoxy-D-glycero-r-D-galacto-non-2-ulopyr-
anoside)onate (22): 1H NMR (400 MHz, CDCl3) δ 1.56 (s, 6H),
1.60 (s, 6H), 2.01-2.08 (m, 4H), 2.82 (dd J = 3.4, 12.1 Hz, 1H),
3.05 (t, J = 10.4 Hz, 1H), 3.74 (s, 3H), 3.77-3.86 (m, 1H), 4.05
(s, 2H), 4.16 (s, 2H), 4.20 (s, 1H), 4.33 (s, 1H), 4.37-4.41 (m,
2H), 4.56 (dd, J = 1.8, 12.8 Hz, 1H), 5.12 (br, 1H), 5.15 (dd, J =
1.3, 10.2 Hz, 1H), 5.32 (s, 1H), 5.51 (td, J = 2.8, 9.2 Hz, 1H); 13
C
NMR (100 MHz, CDCl3) δ 24.6, 30.9, 36.3, 40.2, 40.3, 40.4,
40.7, 43.2, 52.7, 57.6, 62.7, 68.8, 70.0, 73.5, 79.5, 99.2, 159.2,
166.3, 167.0, 167.9, 171.2; ESIHRMS calcd for C27H34Cl3NO12-
Na (M þ Na)þ 692.1044, found 692.1053.
O-(8-Azido-3,6-dioxaoctyl)-N-3,6,9-trioxaoctylcarbamoyl
O-[methyl (5-amino-5-N,4-O-carbonyl-7,8,9-tri-O-chloroacetyl-3,5-
dideoxy-D-glycero-r-D-galacto-non-2-ulopyranoside)onate]-(2f6)-
O-(2,3-di-O-benzoyl-β-D-galactopyranosyl)-(1f4)-2,3,6-tri-O-
benzoyl-β-D-glucopyranoside (23): 1H NMR (400 MHz, CDCl3)
δ 1.86 (t, J = 12.8 Hz, 1H), 2.70 (dd, J = 3.4, 12.8 Hz, 1H), 3.20
(t, J = 10.4 Hz, 1H), 3.18-3.27 (m, 6H), 3.31-3.38 (m, 6H),
3.45-3.56 (m, 3H), 3.60-3.70 (m, 9H), 3.77 (s, 3H), 3.83-3.94
(m, 3H), 3.99 (s, 2H), 4.13-4.30 (m, 9H), 4.32 (dd, J= 4.4, 12.9 Hz,
1H), 4.44 (dd, J = 5.1, 11.9 Hz, 1H), 4.48 (dd, J = 2.3, 11.9 Hz,
1H), 4.60 (dd, J = 1.8, 11.9 Hz, 1H), 4.82 (d, J = 7.8 Hz, 1H), 4.86
(d, J = 7.8 Hz, 1H), 5.11 (dd, J = 3.1, 10.4 Hz, 1H), 5.18 (dd,
J = 1.5, 9.1 Hz, 1H), 5.22 (t, J = 5.2 Hz, 1H), 5.33 (dd, J = 7.8,
9.3 Hz, 1H), 5.38 (br, 1H), 5.60 (ddd, J = 2.3, 3.8, 9.1 Hz, 1H),
5.66 (dd, J = 7.8, 10.4 Hz, 1H), 5.76 (t, J = 9.3 Hz, 1H), 7.12 (t,
J = 7.8 Hz, 2H), 7.29-7.57 (m, 13H), 7.84 (d, J = 7.3 Hz, 2H),
7.81-7.99 (m, 10H); 13C NMR (100 MHz, CDCl3) δ 36.2, 40.2,
40.3, 40.5, 40.8, 50.5, 53.3, 57.3, 62.1, 62.7, 63.1, 63.7, 65.8, 68.4,
69.1, 69.5, 69.6, 69.7, 69.9, 70.00, 70.06, 70.3, 70.40, 70.49, 72.0,
72.5, 72.9, 73.0, 73.7, 74.0, 76.30, 76.31, 77.2, 100.4, 100.5, 100.6,
128.2 (ꢀ4), 128.3 (ꢀ2), 128.6, 128.9, 129.2, 129.4, 129.5, 129.6
(ꢀ2), 129.6, 129.7, 132.9, 132.9, 133.1, 133.1, 133.3, 156.3, 158.9,
165.0, 165.1, 165.2, 165.7, 165.7, 166.3, 167.0, 167.9, 168.1; HRMS
(ESI) calcd for C77H84Cl3N5NaO33 (MþNa)þ 1734.4012, found
1734.4022.
Methyl (3-Azidopropyl-7,8-di-O-acetyl-5-amino-5-N,4-O-car-
bonyl-9-O-(methyl 5-amino-5-N,4-O-carbonyl-3,5-dideoxy-D-gly-
cero-r-D-galacto-non-2-ulopyranosylonate)-3,5-dideoxy-D-glycero-
r-D-galacto-non-2-ulopyranoside)onate (25). The disialoside triol
acceptor 25 (216 mg, 83%) was synthesized by the methods
described in the synthesis of 3: 1H NMR (400 MHz, CD3OD) δ
1.78 (m, 2H), 2.05 (dd, J = 11.8, 11.8 Hz, 1H), 2.08 (dd, J = 11.7,
11.7 Hz, 1H), 2.16 (s, 3H), 2.22 (s, 3H), 2.85 (dd, J = 3.6, 11.8 Hz,
1H), 2.93 (dd, J = 3.7, 11.7 Hz, 1H), 3.28 (dd, J = 10.1, 10.9 Hz,
1H), 3.35-3.39 (m, 1H), 3.40 (t, J = 6.2 Hz, 2H), 3.58 (dd, J =
10.1, 10.1 Hz, 1H), 3.59 (dd, J = 1.9, 8.5 Hz, 1H), 3.68 (dd, J =
2.6, 11.2 Hz, 1H), 3.69 (dd, J = 1.3, 11.4 Hz, 1H), 3.76-3.85 (m,
3H), 3.82 (s, 3H), 3.85 (s, 3H), 4.00 (dd, J = 3.7, 11.2 Hz, 1H),
Methyl (3-Azidopropyl 5-amino-5-N,4-O-carbonyl-3,5-dideoxy-
D-glycero-r-D-galacto-non-2-ulopyranoside)onate (3). A solution
of compound 13 (600 mg, 0.97 mmol) in MeOH (24 mL) was
treated with Et3N (200 μL) and then was stirred at room tem-
J. Org. Chem. Vol. 75, No. 15, 2010 4927

Lin et al.
JOCFeatured Article
4.01-4.13 (m, 2H), 4.06 (dd, J = 1.9, 10.1 Hz 1H), 4.25 (dd, J =
1.7, 10.1 Hz, 1H), 5.29 (dd, J = 1.7, 9.3 Hz, 1H), 5.36 (ddd, J =
2.6, 3.7, 9.3 Hz, 1H); 13C NMR (100 MHz, CD3OD) δ 20.9, 21.2,
30.1, 37.9, 38.1, 49.2, 53.5, 53.6, 58.6, 58.7, 63.1, 63.8, 64.7, 69.5,
70.0, 71.4, 72.1, 75.0, 77.6, 78.4, 78.9, 101.1, 101.4, 162.0, 162.5,
169.9, 170.2, 171.8, 173.1; HRMS(ESI) calcd for C29H41N5NaO19
(M þ Na) þ 786.2293, found 786.2293.
ally increased to -50 °C, and then the mixture was stirred for
1 h. After completion of the reaction (as evidenced by TLC), the
reaction mixture was diluted with CH2Cl2 and filtered through
Celite. The filtrate was washed with a saturated aqueous
Na2S2O3 solution, dried over Na2SO4, and concentrated under
reduced pressure. The residue was dissolved in MeOH (1 mL),
and then Et3N (3 μL) was added at rt under N2. After being
stirred for 5 min, the reaction mixture was neutralized with a
10% aqueous HCl solution and then was concentrated. The residue
was dissolved in pyridine (200 μL), and then Ac2O (100 μL) was
added at rt under N2. After the reaction mixture was stirred for
12 h, the solvent was removed. The residue was dissolved in
EtOAc and was washed with a 10% aqueous HCl solution, and
then the aqueous layer was extracted with EtOAc. The com-
bined extracts were dried over MgSO4. The solution was con-
centrated, and the residue was purified by silica gel flash column
chromatography (hexanes/EtOAc/MeOH, from 1/1/0 to 1/1/
0.2) to afford tetrasialoside 28 (66 mg, 51% over three steps): 1H
NMR (400 MHz, CDCl3) δ 1.77-1.83 (m, 2H), 1.93-2.04 (m,
4H), 2.04 (s, 3H), 2.13 (s, 3H), 2.14 (s, 3H), 2.15 (s, 3H), 2.16 (s,
3H), 2.17 (s, 3H), 2.22 (s, 3H), 2.23 (s, 3H), 2.24 (s, 3H),
2.83-2.88 (m, 4H), 2.98-3.07 (m, 4H), 3.25-3.35 (m, 4H),
3.37 (t, J = 6.6 Hz, 2H), 3.75 (s, 3H), 3.75 (s, 3H), 3.76 (s, 3H),
3.77 (s, 3H), 3.76-3.95 (m, 8H), 4.15-4.23 (m, 4H), 4.21-4.23
(m, 2H), 5.11 (dd, J = 1.6, 10.0 Hz, 1H), 5.22-5.28 (m, 3H),
5.26-5.37 (m, 4H); 13C NMR (100 MHz, CDCl3) δ 20.8, 20.9,
21.2, 29.2, 37.4, 37.6, 37.7, 48.3, 53.1, 53.20, 53.26, 53.3, 57.8,
57.9, 58.0, 58.1, 61.8, 62.3, 63.3, 66.6, 66.8, 66.9, 67.2, 68.7, 69.0,
73.7, 73.8, 73.9, 76.7, 76.8, 99.9, 100.01, 100.05, 100.1, 159.2,
159.3, 159.4, 159.6, 167.9, 168.1, 168.7, 169.9, 170.0, 170.7,
171.2, 171.3, 171.5; HRMS (ESI) calcd for C65H85N7NaO42
(M þ Na)þ 1658.4628, found 1658.4631.
Methyl (3-Azidopropyl-7,8-di-O-acetyl-5-amino-5-N,4-O-car-
bonyl-9-O-(methyl 7,8-di-O-acetyl-5-amino-5-N,4-O-carbonyl-
9-O-(methyl 5-amino-5-N,4-O-carbonyl-7,8,9-tri-O-chloroacetyl-
3,5-dideoxy-D-glycero-r-D-galacto-non-2-ulopyranosylonate)-
3,5-dideoxy-D-glycero-r-D-galacto-non-2-ulopyranosylonate)-
3,5-dideoxy-D-glycero-r-D-galacto-non-2-ulopyranoside)onate (26).
The trisialoside 26 (200 mg, 74%, two steps) was synthesized by
the methods described in the synthesis of 24: 1H NMR (400 MHz,
CDCl3) δ 1.79 (m, 2H), 1.94-2.06 (m, 3H), 2.14 (s, 3H), 2.15 (s,
3H), 2.22 (s, 3H), 2.22 (s, 3H), 2.83-2.87 (m, 3H), 3.00-3.07 (br-
dd, 2H), 3.14 (dd, J = 10.7, 10.7 Hz, 1H), 3.28 (dt, J = 6.7,
11.9 Hz, 1H), 3.31-3.37 (m, 2H), 3.37 (t, J = 7.7 Hz, 2H), 3.76
(s, 3H), 3.77 (s, 3H), 3.77 (s, 3H), 3.76-3.93 (m, 6H), 4.05 (s,
2H), 4.15 (d, J = 15.2 Hz, 1H), 4.17-4.27 (m, 6H), 4.28 (d, J =
15.2 Hz, 1H), 4.53 (dd, J = 1.9, 12.6 Hz, 1H), 5.17 (dd, J = 1.8,
9.9 Hz, 1H), 5.21-5.29 (m, 3H), 5.34-5.39 (m, 1H), 5.50-5.54
(m. 1H); 13C NMR (100 MHz, CDCl3) δ 20.7, 20.8, 21.1, 29.1,
37.1, 37.4, 37.6, 40.5, 40.6, 41.0, 48.2, 53.0, 53.1, 53.4, 57.2, 57.7,
58.0, 62.2, 63.3, 63.5, 67.0, 67.2, 67.8, 68.7, 68.8, 70.4, 73.6, 73.8,
73.5, 76.5, 76.6, 76.9, 99.8, 99.9, 100.1, 159.2, 159.5, 159.6, 166.4,
167.0, 168.0, 168.3, 168.6, 169.8, 169.91, 169.96, 171.5, 171.6;
HRMS (ESI) calcd for C50H63Cl3N6NaO32 (Mþ Na)þ 1387.2450,
found 1387.2456.
Methyl (3-Azidopropyl 7,8-di-O-acetyl-5-amino-5-N,4-O-car-
bonyl-9-O-(methyl 7,8-di-O-acetyl-5-amino-5-N,4-O-carbonyl-
9-O-(methyl 5-amino-5-N,4-O-carbonyl-3,5-dideoxy-D-glycero-
r-D-galacto-non-2-ulopyranosylonate)-3,5-dideoxy D-glycero-r-
D-galacto-non-2-ulopyranosylonate)-3,5-dideoxy-D-glycero-r-D-
galacto-non-2-ulopyranoside)onate (27). The trisialoside triol
acceptor 27 (133 mg, 80%) was synthesized by the methods
described in the synthesis of 3: 1H NMR (400 MHz, CD3OD) δ
1.79 (m, 2H), 1.99-2.08 (m, 3H), 2.16 (s, 3H), 2.17 (s, 3H), 2.23
(s, 3H), 2.25 (s, 3H), 2.84-2.88 (m, 2H), 2.92 (dd, J = 3.7, 11.6
Hz, 1H), 3.22-3.31 (m, 2H), 3.35-3.42 (m, 1H), 3.41 (t, J = 6.2
Hz, 2H), 3.50 (dd, J = 2.2, 11.2 Hz, 1H), 3.58 (dd, J = 10.5, 10.5
Hz, 1H), 3.59 (dd, J=1.7, 8.5 Hz, 1H), 3.67 (dd, J = 2.7, 11.2
Hz, 1H), 3.68 (dd, J = 2.7, 11.2 Hz, 1H), 3.76-3.86 (m, 3H),
3.81 (s, 3H), 3.82 (s, 3H), 3.85 (s, 3H), 3.93 (dd, J = 3.8, 11.2 Hz,
1H), 3.99 (dd, J = 3.4, 11.2 Hz, 1H), 4.01-4.13 (m, 4H),
4.21-4.25 (m, 2H), 5.25-5.40 (m, 4H); 13C NMR (100 MHz,
CD3OD) δ 21.0, 21.2, 30.1, 37.9, 38.1, 53.5, 53.6, 53.7, 58.5, 58.7,
63.1, 63.9, 64.4, 64.8, 69.2, 69.4, 70.2, 71.5, 72.2, 75.0, 75.2, 77.6,
78.3, 78.4, 79.0, 101.2, 101.4, 161.9, 162.0, 162.5, 169.4, 170.0,
170.2, 171.7, 172.6, 172.8; HRMS (APCI) calcd for C44H60-
N6NaO29 (M þ Na)þ 1159.3302, found 1159.3308.
3-Azidopropyl 5-Acetamido-9-O-(5-acetamido-9-O-(5-acetam-
ido-(5-acetamido-3,5-dideoxy-DD-glycero-r-D-galacto-non-2-ulo-
pyranosylonic acid)-3,5-dideoxy-D-glycero-r-D-galacto-non-2-ulo-
pyranosylonic acid)-3,5-dideoxy-D-glycero-r-D-galacto-non-2-ulo-
pyranosylonic acid)-3,5-dideoxy-D-glycero-r-D-galacto-non-2-ulo-
pyranosylonic Acid (1). To a solution of tetrasialoside 28 (40 mg,
0.024 mmol) in EtOH (2.5 mL) and H2O (2.5 mL) was added
LiOH (17.24 mg, 0.72 mmol) at rt under N2. After being stirred at
80 °C for 16 h, the reaction mixture was neutralized with a 10%
aqueous HCl solution and then was concentrated. The residue
was dissolved in H2O (1 mL), and then NaHCO3 (28 mg) and
Ac2O (16 μL) were added at rt under N2. After beingstirred for an
additional 3 h, the solvent was evaporated under reduced pres-
sure. The residue was dissolved in MeOH (1 mL), and then
NaOMe (30 mg) was added at rt under N2. After being stirred
for 16 h, the reaction mixture was neutralized with DOEWX
50WX8-200 resin, and the neutralized solution was concentrated.
The residue was purified by P2 biogel column chromatography,
eluting with H2O, to give tetrasialic acid 1 (13 mg, 43% yield over
three steps): 1H NMR(600 MHz, D2O) δ 1.60-1.70 (m, 4H), 1.83
(m, 2H), 2.03, 2.04 (s, 12H), 2.70-2.74 (m, 4H), 3.41 (t, J = 6.2
Methyl (3-Azidopropyl 7,8-di-O-acetyl-5-amino-5-N,4-O-car-
bonyl-9-O-(methyl 7,8-di-O-acetyl-5-amino-5-N,4-O-carbonyl-
9-O-(methyl 7,8-di-O-acetyl-5-amino-5-N,4-O-carbonyl-9-O-(methyl
5-amino-5-N,4-O-carbonyl-7,8,9-tri-O-acetyl-3,5-dideoxy-D-glycero-
r-D-galacto-non-2-ulopyranosylonate)-3,5-dideoxy-D-glycero-r-
D-galacto-non-2-ulopyranosylonate)-3,5-dideoxy-D-glycero-r-D-
galacto-non-2-ulopyranosylonate)-3,5-dideoxy-D-glycero-r-D-
galacto-non-2- ulopyranoside)onate (28). A mixture of the donor
2a (61.1 mg, 0.095 mmol) and the acceptor 27 (90 mg, 0.079 mmol)
was dried azeotropically with toluene three times and then was
dissolved in CH2Cl2/MeCN (v/v = 2/1, 1 mL) at rt under N2.
The solution was transferred to a round-bottomed flask con-
taining dry 3 A molecular sieves at rt under N2. The resulting
reaction mixture was stirred for 10 min and then was cooled to
-78 °C. NIS (32 mg, 0.143 mmol) and TfOH (5 μL, 0.038 mmol)
were added sequentially. The reaction temperature was gradu-
Hz, 2H), 3.52 (dt, J = 6.2, 10.0 Hz, 1H), 3.52-3.97 (m, 29H); 13
C
NMR (100 MHz, D2O, acetone-d6) δ 22.4, 22.4, 28.8, 40.5, 40.7,
48.4, 52.2, 52.3, 62.1, 63.0, 65.2, 65.40, 65.48, 67.9, 68.4, 68.54,
68.57, 68.6, 68.75, 68.78, 68.8, 68.9, 70.5, 70.6 (ꢀ 2), 70.7, 72.0,
72.6, 72.7, 100.5, 100.9, 173.9, 175.2; HRMS (MALDI) calcd for
C47H75N7NaO33 (M þ Na)þ 1288.4304, found 1288.4324.
Acknowledgment. We thank the National Science Council
of Taiwan (NSC 97-2752-B-007-002-PAE and 98-2119-M-007-
011), the National Tsing Hua University, and the Academia
Sinica, Taiwan, for providing financial support for this research.
Supporting Information Available: 1H and 13C NMR spec-
tra of the synthesized compounds. This material is available free
of charge via the Internet at http://pubs.acs.org.
4928 J. Org. Chem. Vol. 75, No. 15, 2010