A one-pot strategy for synthesis of 5-O-(α-D-Arabinofuranosyl)-6-O-(β-D-galactofuranosyl)-D- galactofuranose present in motif E of the Mycobacterium tuberculosis cell wall

Article abstract of DOI:10.1021/jo026325a

5-O-(α-D-Arabinofuranosyl)-6-O-(β-D-galactofuranosyl)-D- galactofuranose 6 present in motif E of the Macobacterium tuberculosis cell wall has been regio- and stereospecifically synthesized using 3-O-benzoyl-1,2-O-isopropylidine-α-D-galactofuranose (10) as the glycosyl acceptor by the trichloroacetamidate method in a one-pot manner. The diol glycosyl acceptor 10 was smoothly derived from 1,2:5,6-di-O-isopropylidene-α-D-galactofuranose (8) by 3-O-benzoylation and then selective 5,6-O-deacetonation. The preparation of 8 was greatly improved by increasing the ratio of DMF to acetone and using a solid-supported catalyst.

Full text of DOI:10.1021/jo026325a

A On e-P ot Str a tegy for Syn th esis of
5-O-(r-D-Ar a bin ofu r a n osyl)-6-O-(â-D-
ga la ctofu r a n osyl)-D-ga la ctofu r a n ose
P r esen t in Motif E of th e Mycoba cter iu m
tu ber cu losis Cell Wa ll
Hairong Wang† and J un Ning*,‡
Research Center for Eco-Environmental Sciences, Chinese
Academy of Sciences, Beijing 100085, China, and
Department of Chemistry, Tsinghua University,
Beijing 100084, China
jning@mail.rcees.ac.cn
Received August 15, 2002
Abstr a ct: 5-O-(R-D-Arabinofuranosyl)-6-O-(â-D-galactofura-
nosyl)-D-galactofuranose 6 present in motif E of the Maco-
bacterium tuberculosis cell wall has been regio- and ste-
reospecifically synthesized using 3-O-benzoyl-1,2-O-isopro-
pylidine-R-D-galactofuranose (10) as the glycosyl acceptor by
the trichloroacetamidate method in a one-pot manner. The
diol glycosyl acceptor 10 was smoothly derived from 1,2:5,6-
di-O-isopropylidene-R-D-galactofuranose (8) by 3-O-benzoy-
lation and then selective 5,6-O-deacetonation. The prepa-
ration of 8 was greatly improved by increasing the ratio of
DMF to acetone and using a solid-supported catalyst.
F IGURE 1. Structures of motifs A, B, C, D, and E and the
synthesized trisaccharide 6 present in motif E.
tuberculosis (ethambutol) for the last 35 yeas actually
acts by inhibiting the biosynthesis of arabinan portions
of LAM and AG.6
Five major motifs called A, B, C, D, and E, which are
linked to the terminal ends of AG and/or LAM, have been
isolated and characterized7 as shown in Figure 1. These
oligosaccharides may play an important role in the
survival and pathogenicity of the organism. Since these
oligosaccharides are not present in humans, they tend
to be highly antigenic in the human immune system.
Motif E is expected to play a more special biological role
in M. tuberculosis and may be found to be more useful
in the development of applications for the treatment of
lethal tuberculosis, because among the motifs A-E, motif
E is structurally more distinct. Motifs A-C contain only
arabinofuranose residures, motif D has exclusively ga-
lactofuranose, while motif E contains the both arabino-
furanose and galactofuranose residues in its structural
framework. Moreover, the oligosaccharide structure of
motif E is more sterically complex because both the 5-
and 6-positions of the reducing galactofuranose compo-
nent are linked with arabinofuranosyl and galactofura-
nosyl residues, respectively.7
Although enormous efforts have been dedicated to
developing anti-infective drug molecules, tuberculosis
still constitutes the leading killer disease in the world.1
Over one third of the world’s population is estimated to
be infected with Macobacterium (M.) tuberculosis, and
more than three million deaths occur every year due to
tuberculosis.2 With the tuberculosis strains becoming
drug-resistant,3 the situation is bound to get more
serious.
M. tuberculosis, the causative agent of tuberculosis,
belongs to the mycobacteria.4 An impressive feature of
this genus of bacteria is that they synthesize cell wall
polysaccharides containing predominantly furanose resi-
dues,4 whereas a similar phenomenon has never been
found in humans. For M. tuberculosis, the major polysac-
charides formed in its cell wall are an arabinogalactan
(AG) and a lipoarabinomannan (LAM) in which all of the
galactose and arabinose residues are present in the
furanose form.4 The organism’s ability to make these
polymers is critical to its survival; therefore, interfering
with the biosynthesis of these polysaccharides is an
approach for identifying anti-TB drugs.5 It has been
demonstrated recently that one of the drugs used to treat
Providing sufficient quantities of a sample is a basic
prerequisite for detailed studies on a compound’s funda-
mental biochemical properties and possible biological
functions. However, in the carbohydrate field, these
efforts are often frustrated by the difficulty of synthesiz-
* To whom correspondence should be addressed.
† Tsinghua University.
(6) (a) Lee, R. E.; Mikusˇova´, K.; Brennan, P. J .; Besra, G. S. J . Am.
Chem. Soc. 1995, 117, 11829. (b) Deng, L.; Mikusˇova´, K.; Robuck, K.
G.; Scherman, M.; Brennan. P. J .; McNeil, M. R. Anyimicrob. Agents
Chemother. 1995, 39, 694.
(7) (a) Besra, G. S.; Khoo, K.-H.; McNeil, M. R.; Dell. A.; Moeeis, H.
R.; Brennan, P. J . Biochemistry 1995, 34, 4257. (b) Wolika, B. A.;
McNeil, M. R.; de Hoffman, E.; Chojnacki, T.; Brennan, P. J . J . Biol.
Chem. 1994, 269, 23328. (c) McNeil, M. R.; Daffe, M.; Brennan, P. J .
J . Biol. Chem. 1990, 265, 18200. (d) Daffe, M.; Brennan, P. J .; McNeil,
M. R. J . Biol. Chem. 1990, 265, 6734. (e) McNeil, M. R.; Robuck, K.
G.; Harter, M.; Brennan, P. J . Glycobiology 1994, 4, 165.
‡ Research Center for Eco-Environmental Sciences.
(1) Lee, R. E.; Brennan, P. J .; Besra, G. S. Tuberculosis. In Current
Topics in Microbiology and Immunology; Shinnick, T. M., Ed.; Springer-
Verlag: Berlin, 1996; Chapter 1, p 215.
(2) Dolin, P. L.; Raviglione, M. C.; Kochi, A. Bull. World Health Org.
1994, 72, 213.
(3) Blanchard, J . S. Annu. Rev. Biochem. 1996, 65, 215.
(4) Brennan, P. J .; Nikaido, H. Annu. Rev. Biochem. 1995, 64, 29.
(5) Lee, R. E.; Brennan, P. J .; Besra, G. S. Glycobiology 1997, 7,
1121.
10.1021/jo026325a CCC: $25.00 © 2003 American Chemical Society
Published on Web 02/14/2003
J . Org. Chem. 2003, 68, 2521-2524
2521

SCHEME 1. Syn th esis of th e Glycosyl Accep tor 10
ing saccharides. The synthesis of complex oligosaccharide
sequences containing two to six sugar units, both in
solution and on the solid phase, presents a major chal-
lenge in organic chemistry.8-11 Unlike peptides and
nucleic acids, oligosaccharides are typically branched
rather than linear. In addition, the monosaccharide units
can be connected by R or â linkages. Furthermore,
oligosaccharide synthesis requires multiple selective
protection and deprotection steps. Although over the past
few decades considerable progress12 has been made in
this field, there still is no general solution for oligosac-
charide synthesis. Maybe, owing to this structural com-
plexity, the preparation of saccharides will never achieve
the same level of ease as the preparation of peptides and
nucleic acids. But special methods that are suitable for
specific types of oligosaccharide synthesis can be devel-
oped.
SCHEME 2. P r ep a r a tion of th e Glycosyl Don or s
12 a n d 13
There has been much interest in the synthesis of the
components of the M. tuberculosis cell wall polysaccha-
rides.13,14 The preparation of a motif E trisaccharide
derivative has been finished recently by Gurjar and co-
workers.14 Their process is a typical example of oligasac-
charide synthesis involving tediously selective protection
and deprotection steps. In complex oligosaccharide as-
sembly, the synthetic procedures can be substantially
simplified by carefully choosing unprotected or partially
protected sugars as glycosyl acceptors coupled with use
of regio- and stereoselective glycosylation reactions.15
Also, synthetic efficiency can often be greatly improved
by carefully designing reactions to be carried out in one
pot. Herein, we report a one-pot strategy for the prepara-
tion of the trisaccharide 5-O-(R-D-arabinofuranosyl)-6-O-
(â-D-galactofuranosyl)-D-galactofuranoside 6 (Figure 1)
present in motif E of the M. tuberculosis cell wall by using
3-O-benzoyl-1,2-O-isopropylidine-R-D-galactofuranose (10)
as the glycosyl acceptor via regio- and stereospecific
trichloroacetamidate-mediated O-glycosylations.
9, obtained only in 20% yield, and this significantly
improved the preparation of 8.18 Some reports showed
that high temperature is a factor known to favor furanose
formation in solutions of reducing sugars.19 Inspired by
this, we increased the ratio of DMF to acetone to 2 in
our synthesis of 8, attempting to increase the reaction
reflux temperature in order to obtain more furanose
diketal 8. To simplify the purification procedure, an
anhydrous H+ form cation-exchange resin called Dry
Hydrogen Resin was used as the solid supported catalyst
(Scheme 1). Furthermore, 4 Å molecular sieves were used
in our reaction as the water scavenger in order to
increase the yield. As a result of our reaction conditions,
the ratio of 1,2:5,6-di-O-isopropylidene-R-D-galactofura-
nose to 1,2:3,4-di-O-isopropylidene-R-D-galactopyranose
in the reaction product can reach more than 4, and the
desired 1,2:5,6-di-O-isopropylidene-R-D-galactofuranose
can be easily crystallized from the resultant residue in
50% yield. Benzoylation of 8 in pyridine with BzCl at
room temperature followed by selective 5,6-O-deaceto-
nation with 90% AcOH at 40 °C afforded the diol glycosyl
acceptor 10.
In our synthesis, 1,2:5,6-di-O-isopropylidene-R-D-ga-
lactofuranose 8 is a key starting material. The compound
8 could been obtained from D-glucose derivatives in three
or six steps16 or from D-galactose in a maximum 22%
yield.17 Recently, Rauter’s group found that by using
zeolite HY as the catalyst, the furanose diketal 8 was
formed in 40% yield, together with the pyranose diketal
The glycosyl donor 12 was synthesized from 1-O-acetyl-
2,3,5,6-tetra-O-benzoyl-D-galactofuranose (11)20 by selec-
tive 1-O-deacetylation with ammonia in THF-CH3OH
and then trichloroacetimidation with trichloroacetonitrile
in the presence of K2CO3 (Scheme 2). The structure of
(8) Toshima, K.; Tatsuta, K. Chem. Rev. 1993, 93, 1603.
(9) Khan, S. H.; Hindsgaul, O. In Molecular Glycobiology; Fukuda,
M., Hindsgaul, O., Eds.; Oxford: New York, 1994; p 206.
(10) Barresi, F.; Hindsgaul, O. J . Carbohydr. Chem. 1995, 14, 1043.
(11) Schmidt, R. R. In Glycosciences; Gabius, H.-J ., Gabius, S., Eds.;
Chapman & Hall: Weinheim, 1997; p 31.
(12) (a) Plante, O. J .; Palmacci, E. R.; Seeberger, P. H. Science 2001,
291, 1523. (b) Sears, P.; Wong, C. H. Science 2001, 291, 2344.
(13) (a) Gurjar, M. K.; Hotha, S.; Mereyala, H. B. J . Chem. Soc.,
Chem. Commun. 1998, 685. (b) D’Souza, F. W.; Lowary, T. L. Org. Lett.
2000, 2, 1493. (c) D’Souza, F. W.; Ayers, J . D. McCarren, P. R.; Lowary,
T. L. J . Am. Chem. Soc. 2000, 122, 1251. (d) Sanchez, S.; Bamhoud,
T.; Prandi, J . Tetrahedron Lett. 2000, 41, 7447.
1
12 was confirmed by H NMR spectral analysis. The J 1,2
is small (0-2 Hz) for the â-anomers21 and larger (4-5
Hz) for the R-anomers.21 A second glycosyl donor 13 was
prepared from D-arabinose according to the reported
procedure.22
(14) (a) Gurjar, M. K.; Reddy, L. K.; Hotha, S. Org. Lett. 2001, 3,
321. (b) Gurjar, M. K.; Reddy, L. K.; Hotha, S. J . Org. Chem. 2001, 66,
4657.
(15) (a) Wang, W.; Kong, F. Angew. Chem., Int. Ed. 1999, 38, 1247.
(b) Wang, W.; Kong, F. J . Org. Chem. 1998, 63, 5744. (c) Wang, W.;
Kong, F. J . Org. Chem. 1999, 64, 5091. (d) Wang, W.; Kong, F.
Tetrahedron Lett. 1998, 39, 1937.
(16) (a) J arosz, S.; Krajewski, J . W.; Zamojski, A.; Duddeck, H.;
Kaiser, M. Bull. Pol. Acad. Sci. Chem. 1985, 33, 181. (b) De J ongh, D.
C.; Biemann, K. J . Am. Chem. Soc. 1964, 86, 67.
(18) Rauter, A. P.; Ramoa-Riberio, F.; Fernanders, A. C.; Figueiredo,
J . A. Tetrahedron 1995, 51, 6529.
(19) (a) Acree, T. E.; Shallenberger, R. S.; Lee, C. Y.; Einset, J . W.
Carbohydr. Res. 1969, 10, 355. (b) Acree, T. E.; Shallenberger, R. S.;
Mattick, L. R. Carbohydr. Res. 1968, 6, 498.
(20) Tsvetkov, Y. E.; Nikolaev, A. V. J . Chem. Soc., Perkin Trans. 1
2000, 889.
(21) De Lederkremer, R.; Nahmad, V. B. M.; Varela, O. J . Org.
Chem. 1994, 59, 690.
(17) Morgenlie, S. Acta Chem. Scand. 1973, 27, 3609.
(22) Du, Y.; Pan, Q.; Kong, F. Carbohydr. Res. 2000, 323, 28.
2522 J . Org. Chem., Vol. 68, No. 6, 2003

SCHEME 3. Syn th esis of th e Tr isa cch a r id e 6
P r esen t in Motif Ea
protected 3-O-benzoyl-1,2-O-isopropylidine-R-D-galacto-
furanose (10) as the glycosyl acceptor through the regio-
and stereospecific glycosylations in a one-pot reaction.
The sole use of acyl groups as protecting groups in the
synthesis further simplified the procedure. The easy
preparation of this oligosaccharide present in the M.
tuberculosis cell wall should promote studies on M.
tuberculosis and the treatment of tuberculosis.
Exp er im en ta l Section
Melting points were determined with a Mel-Temp apparatus.
Optical rotations were measured at at 25 °C in the stated
1
solvent. H NMR (400 Hz) and 13C NMR (100 Hz) spectra were
recorded in CDCl3 solutions at room temperature unless other-
wise specified. Chemical shift (δ) values are given in ppm;
coupling constants (J ) are in Hz. All assignments were supported
by 2D homonuclear chemical-shift correlation spectroscopy
(gCOSY). Mass spectra were recorded on an autospec mass
spectrometer using ESI technique to introduce the sample. Thin-
layer chromatography (TLC) was performed on silica gel HF254
with detection by charring with 30% (v/v) H2SO4 in MeOH or in
some cases by a UV detector. Column chromatography was
conducted by elution of a column (10 240 mm, 18 300 mm, 35 400
mm) of silica gel (100-200 mesh) with EtOAc-petroleum ether
(60-90 °C) as the eluent. Solutions were concentrated at <60
°C under diminished pressure. Dry solvents were distilled over
CaH2 and stored over molecular sieves.
1,2:5,6-Di-O-isop r op ylid en e-r-D-ga la ctofu r a n ose (8). A
solution of D-galactose (10 g, 55.56 mmol) in dry and hot
dimethylformamide (400 mL) was added to stirred acetone (200
mL), which contained an anhydrous H+ form cation-exchange
resin called Dry Hydrogen Resin (15 g) and 4 Å molecular sieves
(8 g). The reaction mixture was stirred under reflux for 48 h.
Solid material was filtered off, and the solution was concentrated
to a syrup under vacuum. TLC (3:1 petroleum ether-EtOAc)
showed that the ratio of 1,2;5,6-di-O-isopropylidene-R-D-galacto-
furanose to 1,2:3,4-di-O-isopropylidene-R-D-galactopyranose in
the resultant residue was more than 4. After the residue was
decolored and, to some degree, purified by subjection to a flash
chromatography with 3:1 petroleum ether-EtOAC as eluent,
compound 8 (7.2 g, 50%) was crystallized from petroleum ether-
EtOAc as white crystals: mp 96.5-98 °C (lit.17 mp 97-98 °C);
[R]D -33.8 (c 0.8, CH3OH) (lit.17 [R]D -34).
a
Key: (a) 12, TMSOTf (cat.), CH2Cl2, MS 4 Å powder, -45 °C
to rt, 1.5 h, 91%; (b) 13, TMSOTf (cat.), CH2Cl2, MS 4 Å powder,
rt, 1 h, 87%; (c) (i) 12, TMSOTf (cat.), CH2Cl2, MS 4 Å powder,
-45 °C to rt, 1.5 h; (ii) 13, rt, 1 h, 71% (over the two steps); (d)
10:1 HCCl3-CF3COOH, rt, 2 h; (e) an ammonia-saturated CH3OH,
rt, 72 h, 86% (over the d and e).
Condensation of 10 and 12 with TMSOTf as catalyst
and 4 Å molecular sieves in CH2Cl2 at -45 °C regio- and
stereospecifically afforded the disaccharides 14 in excel-
lent yields (91%) (Scheme 3).23 No (1 f 5)-linked disac-
1
charide was detected both from H NMR and TLC. The
structure of 14 was unambiguously confirmed by 1H
NMR data. The characteristic resonances due to the
anomeric protons H-1 and H-1′ were located as a doublet
at 5.91 ppm with J 1,2 ) 4.1 Hz and as a singlet at 5.35
ppm, respectively. Coupling of 14 and 13 with TMSOTf
as catalyst and 4 Å molecular sieves in CH2Cl2 at room
temperature gave the desired trisaccharide 15 in 87%
yield. The three anomeric proton signals in the 1NMR
spectrum of 15 were located as a doublet at 5.89 ppm
with J 1,2 ) 4.1 Hz, and singlets at 5.87 and 5.36 ppm,
respectively, whereas the 13C NMR specrtum revealed24
anomeric carbons at 105.25, 105.70, and 106.33 ppm.
Encouraged by the smoothly coupling reaction results, a
one-pot procedure for synthesis of the trisaccharide 15
was carried out. Thus, treatment of 10 and 12 with
TMSOTf as catalyst and 4 Å molecular sieves in CH2Cl2
at -45 °C, followed by addition of 13 afforded compound
15 in 71% yield. De-isopropylidenation of 15 in 10:1
CHCl3-CF3COOH (v/v) at room temperature gave the
compound 16, which after purification was treated with
an ammonia-saturated CH3OH to afford the free trisac-
charide 6 in 86% yield (over the two steps). The signals
3-O-Ben zoyl-1,2-O-isop r op ylid en e-r-D-ga la ctofu r a n ose
(10). To a solution of 8 (4.5 g, 17.3 mmol) in pyridine (20 mL)
was added benzoyl chloride (2.9 mL, 25 mmol) at 0 °C. The
reaction mixture was slowly warmed to room temperature and
stirred for 5 h. TLC (4:1 petroleum ether-EtOAc) indicated that
the reaction was complete. The mixture was poured into ice-
cold water and extracted with CH2Cl2. The organic layer was
washed with 1 N HCl and satd NaHCO3. The solution was
concentrated, and the resultant residue was directly treated with
90% AcOH (50 mL) at 40 °C. After 4 h, the solution was diluted
with toluene, and the mixture was concentrated under vacuum.
The residue was purified by flash chromatography (2:1 petro-
leum ether-EtOAc) to give 10 as a syrup (5.01 g, 90%): [R]D
1
of the H NMR spectrum of 6 were not distinguishable.
1
+40.2 (c 0.65, CHCl3); H NMR (400 MHz, CDCl3) δ 8.04-7.44
However, the chemical shifts of anomeric carbons of 6
were at 107.5, 107.5, and 108.6 ppm, confirming the
structure of 6. Further analysis by ESI-MS spectrometry
gave an (M + H+)+ signal at 475.4 indicating that 6 was
a trisaccharide (calcd 474.415).
(m, 5 H), 6.07 (d, 1 H, J ) 4.1 Hz), 5.34 (d, 1 H, J ) 1.6 Hz),
4.85 (d, 1 H, J ) 4.1 Hz), 4.30 (dd, 1 H, J ) 1.6, 8.2 Hz), 4.03
(m, 1 H), 3.89 (dd, 1 H, J ) 4.8, 11.9 Hz), 3.82 (dd, 1 H, J ) 4.6,
11.9 Hz), 1.59 (s, 3 H), 1.36 (s, 3 H). Anal. Calcd for C16H20O7:
C, 59.25, H, 6.22. Found: C, 59.41, H, 6.15.
In conclusion, a highly efficient and concise synthesis
of the complex trisaccharide 6 present in motif E of the
M. tuberculosis cell wall was achieved by using partially
2,3,5,6-Tetr a -O-ben zoyl-â-D-ga la ctofu r a n osyl Tr ich lor o-
a cetim id a te (12). A solution of 1-O-acetyl-2,3,5,6-tetra-O-
benzoyl-D-galactofuranose (11)20 (3.6 g, 5.64 mmol) in 1.5 N NH3
solution of 3:1 THF-CH3OH (80 mL) was kept at room tem-
peratur for 3 h, at the end of which time TLC (3:1 petroleum
ether-EtOAc) showed that the reaction was complete and the
solution was concentrated. The resultant residue without puri-
fication was dissolved in dry CH2Cl2 (50 mL), and then trichlo-
roacetonitrile (2.6 mL, 12.4 mmol) and anhydrous K2CO3 (3 g,
(23) (a) Schmidt, R. R.; Michel, J . Angew. Chem., Int. Ed. Engl. 1980,
19, 731. (b) Schmidt, R. R. Angew. Chem., Int. Ed. Engl. 1986, 25, 212.
(24) (a) Cyr, N.; Perlin, A. S. Can. J . Chem. 1979, 57, 2504. (b)
Marino, C.; Varela, O.; De Lederkremer, R. M. Carbohydr. Res. 1989,
190, 65.
J . Org. Chem, Vol. 68, No. 6, 2003 2523

21.8 mmol) were added. The reaction mixture was stirred at
room temperature for 12 h, and solid material was filtered off.
Concentration of the filtrate, followed by purification on a silica
gel column with 3:1 petroleum ether-EtOAc as eluent, gave the
monosaccharide donor 12 (3.42 g, 82%): [R]D +28.3 (c 1.0,
CHCl3); 1H NMR (400 MHz, CDCl3): δ 8.72 (s, 1 H), 8.09-7.26
(m, 20 H), 6.70 (s, 1 H), 6.13 (m, 1 H), 5.78 (d, 1 H, J ) 4.3 Hz),
5.75 (s, 1 H), 4.86 (t 1 H, J ) 4.3 Hz), 4.78-4.75 (m, 2 H). Anal.
Calcd for C36H28O10NCl3: C, 58.35, H, 3.81. Found: C, 58.56,
H, 3.74.
6-O-(2,3,5,6-Tetr a -O-ben zoyl-â-D-ga la ctofu r a n osyl)-3-O-
ben zoyl-1,2-O-isop r op ylid en e-r-D-ga la ctofu r a n ose (14). A
solution of 10 (1.7 g, 5.25 mmol) and 12 (3.9 g, 5.25 mmol) in
dry CH2Cl2 (50 mL) was stirred with activated 4 Å molecular
sieves (2 g) at room temperature under an atmosphere of
nitrogen for 20 min. Then the reaction mixture was cooled to
-45 °C, and TMSOTf (12 µL, 0.06 mmol) was added. After 30
min, the temperature was allowed to rise to room temperature,
and the reaction mixture was stirred for further 1 h, at the end
of which time TLC (2.5:1 petroleum ether-EtOAc) indicated that
the reaction was complete. The reaction mixture was neutralized
with triethylamine and filtered, and the filtrate was concen-
trated. The resultant residue was subjected to the column
chromatography with 2.5:1 petroleum ether-EtOAc as eluent
to afford the disaccharide 14 (4.32 g, 91%): [R]D -4.2 (c 0.73,
CHCl3); 1H NMR (400 MHz, CDCl3) δ 7.99-7.17 (m, 25 H), 6.04
(m, 1 H), 5.91 (d, 1 H, J ) 4.1 Hz), 5.53 (d, 1 H, J ) 5.1 Hz),
5.45 (s, 1 H), 5.37 (d, 1 H, J ) 2.2 Hz), 5.35 (s, 1 H), 4.75-4.65
(m, 4 H), 4.24 (dd, 1 H, J ) 2.2, 6.7 Hz), 4.12 (m, 1 H), 3.93 (dd,
1 H, J ) 5.4, 10.5 Hz), 3.66 (dd, 1 H, J ) 5.4, 10.5 Hz), 1.52 (s,
3 H), 1.27 (s, 3 H). Anal. Calcd for C50H46O16: C, 66.51, H, 5.13.
Found: C, 66.29, H, 5.26.
1.31 (s, 3 H, C(CH3)2); 13C NMR (100 MHz, CDCl3) δ 166.09,
166.05, 165.76, 167.70, 165.58, 165.39, 165.23, 165.20, 113.29,
106.33, 105.70, 105.25, 86.04, 84.90, 82.24, 81.99, 81.73, 80.97,
77.96, 77.88, 77.32, 74.43, 70.44, 67.19, 63.86, 63.80, 26.68, 26.17.
Anal. Calcd for C76H66O23: C, 67.75, H, 4.94. Found: C, 67.98,
H, 5.11.
A On e-P ot p r oced u r e for P r ep a r a tion of th e Tr isa cch a -
r id e 15. A solution of 10 (0.6 g, 1.85 mmol) and 12 (1.4 g, 1.90
mmol) in dry CH2Cl2 (30 mL) was stirred with activated 4 Å
molecular sieves (2 g) at room temperature under an atmosphere
of nitrogen for 20 min. Then the reaction mixture was cooled to
-45 °C, and TMSOTf (10 µL, 0.05 mmol) was added. After 30
min, the temperature was allowed to rise to room temperature,
and the reaction mixture was stirred for a further 1 h, at the
end of which time TLC (2.5:1 petroleum ether-EtOAc) indicated
that the reaction was complete. To the stirred reaction mixture
was added 13 (1.6 g, 2.6 mmol) under an atmosphere of nitrogen
at room temperature. The reaction mixture was stirred for 1 h,
at the end of which time TLC (2.5:1 petroleum ether-EtOAc)
indicated that the reaction was complete. The reaction mixture
was neutralized with triethylamine and filtered, and the filtrate
was concentrated. Purification of the resultant residue by column
chromatography with 2.5:1 petroleum ether-EtOAc as eluent
gave 15 (1.7 g, 71%).
5-O-(r-D-Ar a b ifu r a n osyl)-6-O-(â-D-ga la ct ofu r a n osyl)-D-
ga la ctofu r a n ose (6). Compound 15 (1.6 g, 1.19 mmol) was
treated with 10:1 CHCl3-CF3COOH (30 mL) at room temper-
ature for 2 h, at the end of which time TLC (1:1 petroleum
ether-EtOAc) indicated that the reaction was complete, the
solution was diluted with toluene (100 mL), and the mixture
was concentrated under vacuum. The residue was purified by
flash chromatography (1:1 petroleum ether-EtOAc) to give 16
which was dissolved in an ammonia-saturated CH3OH (30 mL).
After 72 h at room temperature, the reaction mixture was
concentrated, the residue was washed with CH2Cl2 four times
and dried under high vacuum to give 6 (485 mg, 86% for over
two steps): [R]D -15.4 (c 0.8, MeOH); 13C NMR (100 MHZ, D2O)
δ 108.6, 107.5, 107.5, 83.8, 82.8, 80.9, 80.9, 80.9, 76.7, 75.9, 70.7,
70.7, 62.7, 62.7, 62.7, 61.1, 61.1; ESI-MS 475.4 (M + H+)+, calcd
for C17H30O15 474.415. Anal. Calcd for C17H30O15: C, 43.04; H,
6.37. Found: C, 43.52; H, 6.61.
5-O-(2,3,5-Tr i-O-ben zoyl-r-D-a r a bifu r a n osyl)-6-O-(2,3,5,6-
tetr a -O-ben zoyl-â-D-ga la ctofu r a n osyl)-3-O-ben zoyl-1,2-O-
isop r op ylid en e-r-D-ga la ctofu r a n ose (15). A solution of 14
(1.8 g, 1.99 mmol) and 2,3,5-tri-O-benzoyl-R-D-arabinofurano-
syltrichloroacetamidate (13)22 (1.5 g, 2.5 mmol) in anhydrous
CH2Cl2 (40 mL) was stirred with activated 4 Å molecular sieves
at room temperature for 20 min, and then TMSOTf (8 µL, 0.04
mmol) was added. The mixture was stirred for 1 h, at the end of
which time TLC (2.5:1 petroleum ether-EtOAc) indicated that
the reaction was complete. The reaction mixture was neutralized
with triethylamine and filtered, and the filtrate was concen-
trated. Purification of the resultant residue by column chroma-
tography with 2.5:1 petroleum ether-EtOAc as eluent gave 15
(2.30 g, 87%): [R]D -18.6 (c 0.4, CHCl3); 1H NMR (400 MHz,
CDCl3) δ 8.04-7.24 (m, 40 H, 8 BzH), 6.17 (m, 1 H, HB-5), 5.89
(d, 1 H, J 1,2 ) 4.1 Hz, HA-1), 5.87(s, 1 H, HC-1), 5.62 (d, 1 H, J 3,4
Ack n ow led gm en t. This work was supported by the
National Natural Science Foundation of China (59973026
and 29905004) and the Beijing Natural Science Foun-
dation (6021004).
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra of
) 2.9 Hz, HA-3), 5.60-5.58 (m, 2 H, HC-2, 3), 5.54 (d, 1 H, J 3,4
)
1
10, 12, 14, and 15, 1H-1H and H-13C 2D-correlational NMR
4.8 Hz, HB-3), 5.49 (s, 1 H, HB-2), 5.36 (s, 1H, HB-1), 4.86 (m, 1
H, HB-4), 4.78-4.69 (m, 5 H, HB-6, 6′, HC-4, 5, 5′), 4.66 (d, 1 H,
J 1,2 ) 4.1 Hz, HA-2), 4.43 (m, 1 H, HA-5), 4.33 (dd, 1 H, HA-4),
4.15 (dd, 1 H, HA-6), 3.76 (dd,1 H, HA-6′), 1.63 (s, 3 H, C(CH3)2),
spectra of 15, and 13C NMR spectra of 6 and 15. This material
is available free of charge via the Internet at http://pubs.acs.org.
J O026325A
2524 J . Org. Chem., Vol. 68, No. 6, 2003