Removal of acid-labile protecting groups on carbohydrates using water-tolerant and recoverable vanadyl triflate catalyst

Article abstract of DOI:10.1021/jo061881g

Acetal, trityl, and TBDMS protecting groups on saccharides were subjected to alcoholysis using a catalytic amount of vanadyl triflate in an MeOH-CH ₂Cl₂ solvent system. The configuration at the anomeric positions of saccharides was retained, and no glycosidic bond cleavage and oxidation of sulfides were observed. The presented method was easily implemented, compatible with diverse functional groups, and regioselective in some cases.

Full text of DOI:10.1021/jo061881g

and AcOH are satisfactory reagents1,7 for selectively deprotect-
ing the acetonide and benzylidene on primary/secondary hy-
droxyl groups, the strong acidity and free protons can also
hydrolyze acid-sensitive groups.8
Removal of Acid-Labile Protecting Groups on
Carbohydrates Using Water-Tolerant and
Recoverable Vanadyl Triflate Catalyst
The synthetic use of vanadium-containing complexes has been
extensively investigated. They are utilized as reagents or
catalysts for redox-type C-C bond formation9,10 in the presence
of suitable co-oxidants.11 Over the past years, many water-
tolerant vanadyl and other oxometallic species have been
developed as recoverable, amphoteric catalysis and used in
nucleophilic acyl substitution,12 benzylidenation,13 and isopro-
pylidenation.14 This paper describes the use of vanadyl triflate
as a Lewis acid catalyst in the deprotection of various acid-
labile protecting groups on saccharides. The advantage of using
vanadyl triflate is that this catalyst can be recovered by
extraction with water and is reusable and, thus, more environ-
mentally friendly.
Ming-Chung Yan,†,‡ Yeng-Nan Chen,† Huan-Ting Wu,†
Chang-Ching Lin,†,‡ Chien-Tien Chen,§ and
Chun-Cheng Lin*,†,‡
Department of Chemistry, National Tsing Hua UniVersity,
Hsinchu, Taiwan, Institute of Chemistry and Genomic Research
Center, Academia Sinica, Taipei, Taiwan, and Department of
Chemistry, National Taiwan Normal UniVersity, Taipei, Taiwan
cclin66@mx.nthu.edu.tw
ReceiVed September 12, 2006
The 4,6-O-benzylidene-protected monosaccharides and the
corresponding debenzylidenation products are important precur-
sors in the synthesis of complex carbohydrates.15 Therefore, 4,6-
O-benzylideneglucose derivative 1 was selected as an example
(Table 1) to investigate the catalytic alcoholysis by vanadyl
triflate (VO(OTf)2) in the presence of MeOH. As shown in Table
1, increasing the amount of VO(OTf)2 and the reaction tem-
perature enhanced the reaction rate in methanol/dichloromethane
cosolvent system (entries 1-4). Our earlier work demonstrated
that the reactivity of vanadyl triflate in catalyzing benzylide-
nation13 and isopropylidenation14 was enhanced using acetoni-
trile as the solvent. Thus, the methanol/acetonitrile cosolvent
was tested. Although the de-benzylidenation rate was increased,
the benzoyl migration product was also observed (entries 5 and
Acetal, trityl, and TBDMS protecting groups on saccharides
were subjected to alcoholysis using a catalytic amount of
vanadyl triflate in an MeOH-CH2Cl2 solvent system. The
configuration at the anomeric positions of saccharides was
retained, and no glycosidic bond cleavage and oxidation of
sulfides were observed. The presented method was easily
implemented, compatible with diverse functional groups, and
regioselective in some cases.
(5) (a) Bessodes, M.; Komiotis, D.; Antonakis, K. Tetrahedron Lett. 1986,
27, 579-580. (b) Blickenstaff, R. T. J. Am. Chem. Soc. 1960, 82, 3673-
3676. (c) Choy, Y. M.; Unrau, A. M. Carbohydr. Res. 1971, 17, 439-443.
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1090-1092.
The protection and deprotection steps are critical to many
synthetic schemes,1 such as the synthesis of complex carbohy-
drate. Acetal,2 trityl,3 and tert-butyldimethylsilyl (TBDMS)
groups4 are effective protecting groups in organic and carbo-
hydrate chemistry and are acid-labile protecting groups. The
most extensively adopted methods for deprotecting these
protecting groups involve the use of protic acids5 and Lewis
acids.6 Although normal acidic catalysts such as HCl, HBr, TFA,
(7) (a) Barone, G.; Bedini, E.; Iadonisi, A.; Manzo, E.; Parrilli, M. Synlett
2002, 1645-1648. (b) Ramalingam, T.; Srinivas, R.; Reddy, B. V. S.;
Yadav, J. S. Synth. Commun. 2001, 31, 1091-1095. (c) Chen, M.-Y.; Lu,
K.-C.; Lee, Adam S.-Y.; Lin, C.-C. Tetrahedron Lett. 2002, 43, 2777-
2780. (d) Chen, M.-Y.; Patkar, L. N.; Lu, K.-C.; Adam, S.-Y.; Lin, C.-C.
Tetrahedron 2004, 60, 11465-11475.
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(9) (a) Togni, A. Organometallics 1990, 9, 3106-3133. (b) Chen, C.-
T.; Hon, S.-W.; Weng, S.-S. Synlett 1999, 816-818.
* To whom correspondence should be addressed. Fax: +886-3-5711082.
† National Tsing Hua University.
‡ Academia Sinica.
§ National Taiwan Normal University.
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(b) Jorgensen, K. A. Chem. ReV. 1989, 89, 431-458.
(1) (a) Greene, T. W.; Wuts, P. G. M. Protecting Groups in Organic
Synthesis, 3rd ed.; Wiley & Sons: New York, 1999. (b) Kocienski, P. J.
Protecting Groups; Georg Thieme Verlag: New York, 2004.
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(b) Crich, D.; Li, W.; Li, H. J. Am. Chem. Soc. 2004, 126, 15081-15086.
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Rodebaugh, R.; Frase-Reid, B. J. Org. Chem. 1996, 61, 5280-5289. (e)
Russell, R. N.; Weigel, T. M.; Han, O.; Liu, H.-W. Carbohydr. Res. 1990,
201, 95-114.
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95-98. (b) Hirama, M.; Node, T.; Yasuda, S.; Ito, S. J. Am. Chem. Soc.
1991, 113, 1830-1832.
(4) (a) Corey, E. J.; Venkateswarlu, A. J. Am. Chem. Soc. 1972, 94,
6190-6191. (b) Corey, E. J.; Cho, H.; Ru¨cker, C.; Hua, D. H. Tetrahedron
Lett. 1981, 22, 3455-3458. (c) Clark, J. H. Chem. ReV. 1980, 80, 429-
452.
(11) (a) Hon, S.-W.; Li, C.-H.; Kuo, J.-H.; Barhate, N. B.; Liu, Y.-H.;
Wang, Y.; Chen, C.-T. Org. Lett. 2001, 3, 869-872. (b) Barhate, N. B.;
Chen, C.-T. Org. Lett. 2002, 4, 2529-2532.
(12) (a) Chen, C.-T.; Kuo, J.-H.; Li, C.-H., Barhate, N. B.; Hon, S.-W.;
Li, T.-W.; Chao, S.-D.; Liu, C.-C.; Li, Y.-C.; Chang, I.-H.; Lin, J.-S.; Lin,
C.-J.; Chou, Y.-C. Org. Lett. 2001, 3, 3729-3732. (b) Chen, C.-T.; Kuo,
J.-H.; Pawar, V. D.; Munot, Y. S.; Weng, S.-S.; Ku, C.-H.; Liu, C.-Y. J.
Org. Chem. 2005, 70, 1188-1197. (c) Chen, C.-T.; Kuo, J.-H.; Ku, C.-H.;
Weng, S.-S.; Liu, C.-Y. J. Org. Chem. 2005, 70, 1328-1339.
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Lett. 2005, 7, 3343-3346.
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Carbohydr. Res. 2006, 341, 1948-1953.
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10.1021/jo061881g CCC: $37.00 © 2007 American Chemical Society
Published on Web 12/07/2006
J. Org. Chem. 2007, 72, 299-302
299

TABLE 1. Survey of Reaction Conditions of Benzylidene
Deprotectiona
TABLE 3. Deprotection of Benzylidene or Isopropylidene Groups
from Saccharidesa
entry
substrate
time (h)
product
yield (%)
1
2
3
4
5
6
7
8
9
11
13
15
17
19
21
23
25
27
16
16
16
16
17
17
16
18
16
12
14
16
18
20
22
24
26
28
92
93
87
85
85
78
85
83
88
VO(OTf)2 reaction reaction yield
entry
solvent
(mol %)
temp (°C) time (h) (%)
1
2
3
4
5
6
MeOH/CH2Cl2 ) 3/5
MeOH/CH2Cl2 ) 3/5
MeOH/CH2Cl2 ) 3/5
MeOH/CH2Cl2 ) 3/5
MeOH/CH3CN ) 1/3
MeOH/CH3CN ) 1/3
5
20
5
20
5
25
25
55
55
25
25
144
48
60
12
24
16
62b
81
80
80
a Tol ) p-methylphenyl.
82c
84c
20
a Tol ) p-methylphenyl. b About 27% of 1 was recovered. c About 9%
of benzoyl migration product was observed.
TABLE 2. Deprotection of Benzylidene Monosaccharides by
a
VO(OTf)2
entry
substrate
R1
R2
time (h)
yield (%)
product
1
2
3
4
5
6
7
8
1
3
4
5
6
7
8
9
H
Bz
Bz
Bz
Bz
Bz
Bz
Bn
Bn
12
16
2.5
16
36
36
40
40
80
92
91
NR
76b
68c
90
2
2
2
CH3
OMe
NO2
Cl
OAc
Cl
2
2
10
10
OAc
87
a Tol ) p-methylphenyl. b 9% of the benzoyl group migration was
isopropylidene of diisopropylidene-protected furanose 21 was
regioselectively deprotected to yield product 22 (entry 6). The
protecting group of amine at the C-5 position of the neuraminic
acid (NeuAc) has been reported to affect the reactivities of both
NeuAc donor and acceptor in glycosylation16 and the rate of
desilylation.7c-d However, the C-5 protecting group of NeuAc
did not observably influence the deprotection of terminal
isopropylidene using a catalytic amount of VO(OTf)2 (entries
7-9).
Following the success of the deprotection of benzylidene and
isopropylidene, the effectiveness of the selective cleavage of
the trityl group in sugar derivatives by the developed protocol
was examined (Table 4). Detritylation of 6-trityl glucosides 29
and 33 with a benzyl or a benzoyl group as the protecting group
of other hydroxyls (entries 1 and 3) was successfully performed
to obtain the desired products 30 and 34. However, the acyl
migration product was observed when the acetyl group was used
as the protecting group of other hydroxyls (entry 2). Notably,
chemoselective deprotection of the trityl group was achieved
in the presence of acetonide (entry 5). Moreover, the VO(OTf)2-
catalyzed detritylation efficiently deprotected trityl groups of
nucleoside 41 and amino acid 39 without cleaving the glycosidic
bond17 or transesterification (entries 7 and 6). However, TBDMS
observed. c 13% of the benzoyl group migration
6). According to these results, the reaction conditions in entry
4 were employed as standard reaction conditions because the
reaction time is short and the yield of the desired product is
good.
Table 2 refers to the deprotection of benzylidene glucosyl
derivatives under the standard reaction conditions. The depro-
tection of glucosyl derivatives 3 and 4 (entries 2 and 3), which
have the electron-donating group at the para positions of the
aryl groups, proceeded at a faster deprotection rate than that of
the unsubstituted benzylidene protected glucose 1 (entry 1). The
presence of electron-withdrawing group at benzylidene reduced
the deprotection rate (entries 4-6 vs 1). As expected, the
presence of a strong electron-withdrawing group, such as NO2,
prevented the reaction. Notably, although the deprotection of
glucosides 6 and 7 (entries 5 and 6), which have weaker
electron-withdrawing groups on benzylidene, can proceed, the
migration of benzoyl groups becomes a serious side reaction.
The catalyst was recovered by extraction with water and
reactivated by heat (∼60 °C) under vacuum. In the case of
debenzylidenation of 1, more than 95% of catalyst was
recovered with activity lost less than 5% (based on the product
formation under the same reaction conditions).
(16) (a) Demchenko, A. V.; Boons, G. -J. Chem. Eur. J. 1999, 5, 1278-
1283. (b) Demchenko, A. V.; Boons, G. -J. Tetrahedron Lett. 1998, 39,
3065-3068. (c) Yu, C.-S.; Niikura, K.; Lin, C.-C.; Wong, C.-H. Angew.
Chem., Int. Ed. 2001, 40, 2900-2903. (d) Tanaka, H.; Adachi, M.;
Takahashi, T. Chem. Eur. J. 2005, 11, 849-862. (e) Adachi, M.; Tanaka,
H.; Takahashi, T. Synlett 2004, 609-614. (f) Ando, H.; Koike, Y.; Ishida,
H.; Kiso, M. Tetrahedron Lett. 2003, 44, 6883-6886. (g) Pan,Y.; Chefalo,
P.; Nagy, N.; Harding, C.; Guo, Z. J. Med. Chem. 2005, 48, 875-883. (h)
Meijer, A.; Ellervik, U. J. Org. Chem. 2004, 69, 6249-6256. (i) De, Meo,
C.; Demchenko, A. V.; Boons, G.-J. J. Org. Chem. 2001, 66, 5490-5497.
The successful deprotection of glucosyl benzylidenes moti-
vated a study of the generality of the developed method on other
benzylidene- or isopropylidene-protected carbohydrates, as
presented in Table 3. The deprotection of the benzylidene group
on various saccharides was achieved with good product yields
(entries 1-4). The developed method also performed very well
in the deprotection of isopropylidene (entries 5-9). The terminal
300 J. Org. Chem., Vol. 72, No. 1, 2007

TABLE 4. Deprotection of Trityl or TBDMS Groups from
Saccharidesa
General Procedure for the Deprotection of Benzylidene,
Isopropylidene, Trityl, and TBDMS Groups on Saccharides and
the Recovery of Catalyst. In a dry 25-mL round-bottomed flask
was placed the protected carbohydrate (1 mmol), and then 10 mL
of MeOH/CH2Cl2 (ratio 3:5) was added. To the above solution was
added vanadyl triflate (0.2 mmol) at ambient temperature, and the
resulting mixture was stirred at 55 °C for the indicated time period.
After completion of the reaction as monitored by TLC, the reaction
mixture was cooled to ambient temperature, and then ice-cold water
(10 mL) and CH2Cl2 (50 mL) were added. The separated organic
layer was dried (MgSO4), filtered, and evaporated. The crude
product was purified by column chromatography on silica gel. The
product obtained was characterized by spectroscopic methods. The
separated aqueous layer was concentrated by rotatory evaporator
at 40 °C. Subsequently, the recovered catalyst was dried in vacuo
at 60 °C for 24 h to give blue solid (0.19 mmol, 95% recovery).
entry
substrate
time (h)
product
yield (%)
1
2
3
4
5
6
7
8
9
29
31
33
35
37
39
41
43
45
16
18
16
38
16
16
16
16
40
30
32
34
46
38
40
42
44
46
92
34b
96
91
88
85
92
96
88
a Tol ) p-methylphenyl. b 45% of the acyl group migration product was
observed.
4-Methyl phenyl 2,3-O-dibenzyl-1-thio-â-D-galactopyranoside
1
(12): syrup; H NMR (500 MHz, CDCl3) 7.44 (d, J ) 8.0 Hz,
2H), 7.40 (d, J ) 7.0 Hz, 2H), 7.35-7.27 (m, 8H), 7.08 (d, J )
7.8 Hz, 2H), 4.82 (d, J ) 10.3 Hz, 1H), 4.73 (d, J ) 10.3 Hz, 1H),
4.68 (s, 2H), 4.56 (d, J ) 9.2 Hz, 1H), 4.02 (d, J ) 3.1 Hz, 1H),
3.95 (dd, J ) 11.8, 6.8 Hz, 1H), 3.76 (dd, J ) 11.8, 4.2 Hz, 1H),
3.70 (t, J ) 9.2 Hz, 1H), 3.56 (dd, J ) 9.2, 3.1 Hz, 1H), 3.45 (dd,
J ) 6.8, 4.2 Hz, 1H), 2.30 (s, 3H), 1.94 (br, 2H); 13C NMR (100
MHz, CDCl3) 138.1, 137.8, 137.5, 132.6, 129.7, 129.6, 128.6, 128.4,
128.2, 128.1, 127.9, 127.8, 87.9, 82.4, 77.9, 77.0, 75.3, 72.3, 67.4,
62.8, 21.1; HRMS (FAB) calcd for C27H31O5S [M + H]+ 467.1892,
found 467.1895.
4-Methyl phenyl 2,3-O-dibenzyl-1-thio-R-D-mannopyranoside
(14): syrup; 1H NMR (400 MHz, CDCl3) 7.39-7.27 (m, 12H), 7.11
(d, J ) 8.0 Hz, 2H), 5.48 (d, J ) 1.3 Hz, 1H), 4.65 (d, J ) 12.2
Hz, 1H), 4.58 (d, J ) 7.2 Hz, 1H), 4.54 (d, J ) 7.2 Hz, 1H), 4.46
(d, J ) 12.2 Hz, 1H), 4.15-4.06 (m, 2H), 4.00 (dd, J ) 3.0, 1.3
Hz, 1H), 3.87 (dd, J ) 11.6, 3.1 Hz, 1H), 3.80 (dd, J ) 11.6, 4.7
Hz, 1H), 3.69 (dd, J ) 8.9, 3.0 Hz, 1H), 2.33 (s, 3H), 2.04 (br,
2H); 13C NMR (125 MHz, CDCl3) 137.9, 137.7, 137.6, 132.4,
123.0, 129.9, 128.5, 128.4, 127.9, 127.9, 127.9, 127.8, 86.3, 79.5,
75.5, 73.2, 72.1, 71.7, 67.2, 62.5, 21.1; HRMS (FAB) calcd for
C27H30O5SNa [M + Na]+ 489.1712, found 489.1721.
Methyl 2,3-O-dibenzyl-R-D-galactopyranoside (16): syrup; 1H
NMR (400 MHz, CDCl3) 7.36-7.25 (m, 10H), 4.79 (d, J ) 12.0
Hz, 2H), 4.68 (d, J ) 12.0 Hz, 1H), 4.68 (d, J ) 3.5 Hz, 1H), 4.65
(d, J ) 12.0 Hz, 1H), 4.03 (d, J ) 1.5 Hz, 1H), 3.91-3.82 (m,
3H), 3.77-3.73 (m, 2H), 3.37 (s, 3H), 2.45 (br, 2H); 13C NMR
(125 MHz, CDCl3) 138.2, 138.0, 128.5, 128.4, 128.0, 128.0, 127.8,
127.8, 98.6, 77.3, 75.6, 73.5, 72.9, 69.1, 68.9, 63.0, 55.3; HRMS
(FAB) calcd for C21H26O6Na [M + Na]+ 397.1627, found 397.1622.
4-Methyl phenyl 2-deoxy-3-O-levulinoyl-2-(2,2,2-trichloroet-
hoxycarbonylamino)-1-thio-â-d-glucopyranoside (18): syrup; 1H
NMR (500 MHz, CDCl3) 7.45-7.41 (m, 2H), 7.30-7.26 (m, 3H),
5.55 (d, J ) 9.6 Hz, 1H), 5.08 (t, J ) 9.6 Hz, 1H), 4.80 (d, J ) 9.6
Hz, 1H), 4.75 (s, 2H), 3.91 (dd, J ) 12.0, 3.0 Hz, 1H), 3.80 (dd,
J ) 12.0, 4.6 Hz, 1H), 3.72 (t, J ) 9.6 Hz, 2H), 3.49 (ddd, J )
9.6, 4.6, 3.0 Hz, 1H), 2.81 (ddd, J ) 18.5, 8.3, 4.7 Hz, 1H), 2.71
(ddd, J ) 18.5, 6.2, 4.7 Hz, 1H), 2.58 (br, 2H), 2.55 (ddd, J )
16.6, 8.3, 4.7 Hz, 1H), 2.45 (ddd, J ) 16.6, 6.2, 4.7 Hz, 1H), 2.13
(s, 3H); 13C NMR (125 MHz, CDCl3) 208.3, 173.4, 154.3, 132.8,
132.0, 129.1, 127.9, 95.5, 86.8, 79.3, 76.8, 74.5, 69.4, 62.4, 54.7,
38.3, 29.7, 28.2; HRMS (FAB) calcd for C20H24O8NCl3SNa [M +
Na]+ 566.0186, found 566.0181.
group did not survive, resulting in full deprotection under the
standard VO(OTf)2 conditions, as indicated in entries 4 and 9.
In conclusion, benzylidene, isopropylidene, trityl, and TB-
DMS protecting groups on saccharides were hydrolyzed using
a catalytic amount of vanadyl triflate in a MeOH-CH2Cl2
solvent system. The configuration at the anomeric positions was
retained and no glycosidic bond cleavage or oxidation of sulfides
was observed. This developed method was easy to implement,
compatible with diverse functional groups, and regioselective
in some cases. In combination with our previously reported
method,13,14 VO(OTf)2 can be used as a catalyst either in the
formation or cleavage of benzylidene and isopropylidene.
Remarkably, the water-tolerant catalyst was recovered easily
from the aqueous layer following the removal of water. The
catalyzes of the current and various vanadyl complexes augured
well for their potential applications in organic and carbohydrate
chemistry.
Experimental Section
4-Methyl phenyl (â-D-galactopyranosyl)-(1f4)-1-thio-â-D-
1
Compounds 2, 10, 22, 30, 32, 34, 38, 40, and 44 have been
previously characterized and their NMR spectral data were in good
agreement with the literature data. References for the reported
compounds are cited in the Supporting Information.
glucopyranoside (20): syrup; H NMR (500 MHz, MeOD) 7.46
(d, J ) 8.1 Hz, 2H), 7.13 (d, J ) 8.1 Hz, 2H), 4.57 (br, 7H), 4.53
(d, J ) 9.8 Hz, 1H), 4.36 (d, J ) 7.5 Hz, 1H), 3.89 (dd, J ) 12.3,
2.4 Hz, 1H), 3.82 (dd, J ) 12.3, 4.6 Hz, 1H), 3.81 (d, J ) 3.6 Hz,
1H), 3.77 (dd, J ) 11.5, 7.6 Hz, 1H), 3.69 (dd, J ) 11.5, 4.5 Hz,
1H), 3.59-3.52 (m, 4H), 3.49 (dd, J ) 9.7, 3.2 Hz, 1H), 3.43-
3.40 (m, 1H), 3.25 (dd, J ) 9.7, 8.8 Hz, 1H); 13C NMR (125 MHz,
(17) Krecknerhova, M.; Seela, F. Nucleosides Nucleotides 1992, 11,
1393-1396.
J. Org. Chem, Vol. 72, No. 1, 2007 301

CDCl3) 137.5, 132.3, 129.2, 129.1, 103.4, 87.9, 79.0, 78.6, 76.4,
75.6, 73.3, 71.8, 71.0, 68.8, 61.0, 60.5, 19.6; HRMS (FAB) calcd
for C19H28O10S [M + H]+ 448.1403, found 448.1408.
115.5 (q, J ) 285.6 Hz), 86.3, 75.3, 71.3, 70.2, 68.6, 63.3, 53.1,
50.8, 37.1, 21.3; HRMS (FAB) calcd for C26H29O9NF3S [M + H]+
588.1515, found 588.1512.
Methyl (4-methyl phenyl 5-acetamido-4-O-benzoyl-3,5-dideoxy-
2-thio-R-D-galacto-non-2-ulopyranosid)onate (24): syrup; 1H
NMR (500 MHz, CDCl3) 8.02 (d, J ) 7.5 Hz, 2H), 7.62 (t, J )
7.5 Hz, 1H), 7.47 (t, J ) 7.5 Hz, 2H), 7.40 (d, J ) 8.0 Hz, 2H),
7.15 (d, J ) 8.0 Hz, 2H), 6.45 (d, J ) 10.5 Hz, 1H), 5.16 (ddd, J
) 12.3, 10.5, 4.9 Hz, 1H), 4.20 (q, J ) 10.5 Hz, 1H), 3.90-3.86
(m, 2H), 3.75-3.72 (m, 1H), 3.65 (s, 3H), 3.57 (d, J ) 8.31 Hz,
1H), 3.44 (d, J ) 10.5 Hz, 1H), 3.09 (br, 3H), 3.00 (dd, J ) 12.3,
4.9 Hz, 1H), 2.35 (s, 3H), 2.27 (t, J ) 12.3 Hz, 1H), 1.93 (s, 3H);
13C NMR (125 MHz, CDCl3) 173.4, 169.4, 167.3, 140.9, 136.7,
134.0, 129.9, 129.7, 128.7, 128.7, 124.6, 86.3, 76.6, 71.0, 70.1,
69.2, 64.1, 53.2, 51.3, 37.3, 22.8, 21.4; HRMS (FAB) calcd for
C26H31O9NSNa [M + Na]+ 556.1617, found 556.1618.
Methyl (4-methyl phenyl 4-O-benzoyl-3,5-dideoxy-5-trifluo-
roacetamido-2-thio-R-D-galacto-non-2-ulopyranosid)onate (26):
syrup; 1H NMR (500 MHz, CDCl3) 7.99 (d, J ) 7.3 Hz, 2H), 7.77
(d, J ) 10.5 Hz, 1H), 7.60 (t, J ) 7.3 Hz, 1H), 7.46 (t, J ) 7.3 Hz,
2H), 7.34 (d, J ) 8.0 Hz, 2H), 7.12 (d, J ) 8.0 Hz, 2H), 5.20
(ddd, J ) 12.2, 10.5, 4.9 Hz, 1H), 4.33 (q, J ) 10.5 Hz, 1H), 3.85-
3.77 (m, 2H), 3.74 (dd, J ) 10.7, 3.5 Hz, 1H), 3.67 (d, J ) 10.5
Hz, 1H), 3.61 (d, J ) 8.7 Hz, 1H), 3.45 (s, 3H), 3.02 (dd, J )
12.2, 4.9 Hz, 1H), 2.86 (br, 3H), 2.32 (s, 3H), 2.19 (t, J ) 12.2
Hz, 1H); 13C NMR (125 MHz, CDCl3) 169.3, 167.0, 159.2 (q, J )
38.0 Hz), 141.0, 136.6, 134.0, 129.9, 129.7, 128.7, 128.6, 124.4,
Methyl (4-methyl phenyl 5-azido-4,6-O-dibenzoyl-3,5-dideoxy-
2-thio-R-D-galacto-non-2-ulopyranosid)onate (28): syrup; 1H
NMR (500 MHz, CDCl3) 8.18 (d, J ) 7.2 Hz, 2H), 7.99 (d, J )
7.2 Hz, 2H), 7.68 (t, J ) 7.2 Hz, 1H), 7.59-7.53 (m, 3H), 7.46-
7.40 (m, 4H), 7.18 (d, J ) 7.9 Hz, 2H), 5.48 (dd, J ) 9.2, 1.8 Hz,
1H), 5.03 (ddd, J ) 11.6, 10.5, 4.9 Hz, 1H), 4.09 (ddd, J ) 9.2,
5.9, 2.4 Hz, 1H), 3.81 (s, 3H), 3.76 (dd, J ) 10.5, 1.8 Hz, 1H),
3.71 (dd, J ) 12.0, 2.4 Hz, 1H), 3.60 (dd, J ) 12.0, 5.9 Hz, 1H),
3.54 (t, J ) 10.5 Hz, 1H), 3.20 (dd, J ) 12.9, 4.9 Hz, 1H), 2.38 (s,
3H), 2.00 (dd, J ) 12.9, 11.6 Hz, 1H); 13C NMR (125 MHz, CDCl3)
169.3, 165.6, 165.3, 140.9, 136.7, 133.7, 133.6, 130.1, 129.8, 129.7,
129.1, 128.9, 128.7, 128.5, 124.4, 86.3, 74.38, 72.6, 70.5, 70.1,
63.2, 60.0, 53.6, 37.1, 21.4; HRMS (FAB) calcd for C31H31O9N3-
SNa [M + Na]+ 644.1679, found 644.1674.
Acknowledgment. We gratefully acknowledge support from
National Tsing Hua University, Academia Sinica, and National
Science Council in Taiwan.
Supporting Information Available: 1H and 13C NMR spectra
of deprotected products. This material is available free of charge
via the Internet at http://pubs.acs.org.
JO061881G
302 J. Org. Chem., Vol. 72, No. 1, 2007