Facile synthesis of α-D-Araf-(1→5)-D-Galf, the linker unit of the arabinan to the galactan in Mycobacterium tuberculosis

Article abstract of DOI:10.1139/V06-025

The arabinogalactan is a crucial constituent of the cell wall of mycobacteria. Both monosaccharides (arabinose and galactose) are found in the furanose configuration, absent in mammals. An efficient synthesis of α-D-Araf-(1→5)-D-Galf, the linker unit of t

Full text of DOI:10.1139/V06-025

486
Facile synthesis of ␣-D-Araf-(1→5)-D-Galf, the
linker unit of the arabinan to the galactan in
Mycobacterium tuberculosis1
Lucía Gandolfi-Donadío, Carola Gallo-Rodriguez, and Rosa M. de Lederkremer
Abstract: The arabinogalactan is a crucial constituent of the cell wall of mycobacteria. Both monosaccharides
(arabinose and galactose) are found in the furanose configuration, absent in mammals. An efficient synthesis of α-D-
Araf-(1→5)-D-Galf, the linker unit of the arabinan to the galactan, is described. The strategy relies on the use of a con-
veniently substituted D-galactono-1,4-lactone as a precursor of the reducing furanose ring. The glycosylation step was
performed by the tin(IV) chloride promoted method using 1,2,3,5-tetra-O-benzoyl-α,β-D-arabinofuranose. The arabinose
donor was obtained in a crystalline state in one step by benzoylation of arabinose in hot pyridine. Selective
glycosylation of the exocyclic OH-5 was obtained in 75% yield to give 2,3,5-tri-O-benzoyl-α-D-arabinofuranosyl-
(1→5)-2,6-di-O-pivaloyl-D-galactono-1,4-lactone. Reduction with disiamylborane gave the disaccharide synthon, useful
for further glycosylations. Dec-9-enyl α-D-Araf-(1→5)-β-D-Galf, a convenient substrate for arabinofuranosyl transferases
studies, was obtained by the trichloroacetimidate method of glycosylation.
Key words: arabinofuranose, galactofuranose, Mycobacterium arabinogalactan, trichloroacetimidate, tin(IV) chloride.
Résumé : L’arabinogalactane est un constituant crucial de la paroi de la cellule des mycobactéries. Les deux monosac-
charides, arabinose et galactose, se retrouvent dans la configuration furanose qu’on ne retrouve pas chez les mammifè-
res. On décrit une synthèse efficace du α-D-Araf-(1→5)-D-Galf, l’unité de liaison de l’arabinane au galactane. La
stratégie repose sur l’utilisation d’une D-galactono-1,4-lactone substituée d’une façon appropriée comme précurseur du
cycle réducteur du furanose. L’étape de glycosylation a été réalisée par la méthode de catalyse à l’aide de chlorure
d’étain(IV) en utilisant le 1,2,3,5-tétra-O-benzoyl-α,β-D-arabinofuranose. Le donneur arabinose a été obtenu à l’état cris-
tallin en une étape benzoylation de l’arabinose dans de la pyridine à chaud. La glycosylation sélective de OH-5 exocy-
clique a été réalisée avec un rendement de 75 % pour conduire à la formation de la 2,3,5-tri-O-benzoyl-α-D-
arabinofuranosyl-(1→5)-2,6-di-O-pivaloyl-D-galactono-1,4-lactone. Sa réduction par du disiamylborane fournit le syn-
thon disaccharide utile dans des glycosylations subséquentes. Par ailleurs, le dec-9-enyl α-D-Araf-(1→5)-β-D-Galf, un
substrat approprié pour les études de transférases d’arabinofuranosyle a été préparé par la méthode de glycosylation au
trichloroacétimidate.
Mots clés : arabinofuranose, galactofuranose, arabinogalactane Mycobacterium, trichloroacétimidate, chlorure d’étain(IV).
[Traduit par la Rédaction] Gandolfi-Donadío et al. 491
Introduction
The galactan region consists of alternating β(1→5)- and
β(1→6)-linked D-Galf residues. This linear galactofuranose
chain has branch points at OH-5 at which the arabinan
chains are α-attached. Thus, an α-D-Araf-(1→5)-D-Galf link-
age anchors the arabinan component to the galactan struc-
ture. The disaccharide has been previously synthesized as
the n-octyl (4) and the ethyl glycosides (5a, 5b). These de-
rivatives are not precursors for further elongation of the
chain. In both procedures, the trichloroacetimidate method
(6) was employed for the glycosylation step. The 2,3,5-tri-
Mycobacterial diseases have reemerged in the last years
because of the appearance of multidrug-resistant strains of
Mycobacterium and the relation of tuberculosis with AIDS
(1). The integrity of the mycobacterial cell wall is essential
for the viability of mycobacteria (2).
One of the components of this unique cell wall is arabino-
galactan (AG) (3) in which both arabinose and galactose are
found in the furanose form, which is absent in mammals.
Received 30 August 2005. Published on the NRC Research Press Web site at http://canjchem.nrc.ca on 6 April 2006.
Dedicated to Professor Walter Szarek on the occasion of his 65th birthday.
L. Gandolfi-Donadío, C. Gallo-Rodriguez,2 and R.M. de Lederkremer.3 CIHIDECAR, Departamento de Química Orgánica,
Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón II, 1428 Buenos Aires,
Argentina.
1This article is part of a Special Issue dedicated to Professor Walter A. Szarek.
2Corresponding author (e-mail: cgallo@qo.fcen.uba.ar).
3Corresponding author (e-mail: lederk@qo.fcen.uba.ar).
Can. J. Chem. 84: 486–491 (2006)
doi:10.1139/V06-025
© 2006 NRC Canada

Gandolfi-Donadío et al.
487
Scheme 1.
OBz
OBz
BzO
C5H5N, BzCl, 60 ºC
OBz
O
BzO
O
O
OBz
OBz
+
+
D
-Arabinose
OBz
OBz
BzO
OBz
OBz
1
2
O-acyl-α-D-arabinofuranosyl trichloroacetimidate donors
were prepared from D-arabinose via the methyl
arabinofuranoside in five steps.
The synthesis of a closely related trisaccharide fragment
of the arabinogalactan was described by two groups (5). The
procedures also employed the trichloroacetimidate method
for the introduction of the Araf unit.
The synthesis and conformation of D-arabinofuranosides
from mycobacteria have been reviewed (7).
In the present work, we optimized the conditions for the
one-step preparation of crystalline tetra-O-benzoyl-α,β-D-
arabinofuranose (1) from D-arabinose. The D-arabino-
furanose derivative 1 was used for tin(IV) chloride promoted
glycosylation.
were obtained when the benzoylated analog was employed
(10–12). For that reason, we thought that 1,2,3,5-tetra-O-
benzoyl-arabinofuranose (1) could be a good precursor for
the tin(IV) chloride promoted glycosylation reaction. Com-
pound 1 was synthesized, in one step, by the benzoylation of
arabinose in hot pyridine (Scheme 1). The crude product
was a mixture of β-furanose, α-furanose, and α-pyranose
perbenzoates in a 30:27:43 ratio, respectively, as shown by
the integration of the anomeric protons in the 1H NMR spec-
trum: 6.88 (d, 0.30H, J = 4.4 Hz, H-1β furanose), 6.76 (s,
0.27H, H-1α furanose), 6.26 (d, 0.43H, J = 5.6 Hz, H-1α
pyranose). No tetra-O-benzoyl-β-D-arabinopyranose was de-
tected in the perbenzoylation reaction mixture. Crystalliza-
tion of the crude product from ethanol gave a first crop of
pure crystalline 1,2,3,4-tetra-O-benzoyl-α-D-arabinopyranose
(2, 26%). Perbenzoyl arabinofuranose (1, 29%) crystallized
from the mother liquors. On purification of a sample of the
anomeric mixture by column chromatography, pure 1,2,3,5-
tetra-O-benzoyl-α-D-arabinofuranose (1␣) was obtained and
fully characterized. Compound 1␣ was previously obtained
on reaction of 2,3,5-tri-O-benzoyl-α-D-arabinofuranosyl bro-
mide with silver benzoate (17). The anomeric mixture was
used for glycosylation. Although the furanose perbenzoate
was isolated in a modest yield, its use as a donor in the route
described in this paper has the advantage that it was ob-
tained in a crystalline state in one step from D-arabinose.
With the arabinofuranosyl donor 1, a tin(IV) chloride
promoted glycosylation reaction could be performed with a
Galf template acceptor. Crystalline 2,6-di-O-pivaloyl-D-
galactone-1,4-lactone (3) (9), obtained in one step from D-
galactone-1,4-lactone, was employed as a precursor of the
galactofuranose reducing end (Scheme 2). Compound 3 was
previously used in our laboratory for the construction of β-D-
Galf-(1→5)-β-D-Galf-(1→6)-D-Galf (9). Thus, on treatment
of 1.3 equiv. of acceptor 3 with 1 equiv. of arabinose donor
1, and tin(IV) chloride as the promoter in CH2Cl2, selective
glycosylation of the exocyclic OH-5 of 3 gave 2,3,5-tri-O-
benzoyl-α-D-arabinofuranosyl-(1→5)-2,6-di-O-pivaloyl-D-
galactono-1,4-lactone (4) in 70% yield. No product of con-
densation at the OH-3 of 3 was detected. The same
regioselectivity was found when perbenzoyl galactofuranose
or other galactofuranosyl derivatives were glycosylated with
2,6-di-O-substituted D-galactono-1,4-lactones (9, 11).
Results and discussion
The synthetic strategy relied on the use of a conveniently
substituted D-galactono-1,4-lactone as the precursor of the
reducing furanose ring (8, 9). Thus, after glycosylation, the
disaccharide–lactone is reduced, acting as a virtually pro-
tected anomeric center. Activation of the anomeric center
would allow further construction of different oligosaccha-
rides.
We have extensively used the tin(IV) chloride promoted
glycosylation method (10–12) for the activation of a per-
acylated galactofuranose. We employed α,β-perbenzoyl-
galactofuranose, which is obtained in the crystalline state in
a one step-reaction from galactose (13). This is a very sim-
ple, direct, and convenient method for the construction of
the β-D-galactofuranosyl linkage. Taking into account the
stereochemical relationship between arabinose and
galactose, we applied this glycosylation method to per-
benzoyl arabinofuranose derivatives.
Tin(IV) chloride has been previously employed to achieve
1,2-trans α-arabinofuranosidic linkages. Tetra-O-acetyl-α-D-
arabinofuranose, which was obtained in four steps as a syrup
from arabinose, was used to give the expected 1,2-trans α-
glycosidic linkage provided by the acetyl assistance in O-2
(14). On the other hand, it was described (15) that tetra-O-
acetyl-α,β-D-arabinofuranose, obtained by ozonolysis of tri-
O-acetyl-D-glucal, was employed as a glycosyl donor. How-
ever, the reaction gave low diastereoselectivity leading to a
2:1α:β ratio in the glycosylation of methyl 2,3,4-tri-O-
benzyl-α-D-glucopyranoside (15). Similar results were ob-
tained using the L-enantiomer (16).
In the galactofuranose series, we have also noticed that
glycosylation yields diminished when employing the per-
acetylated analog, which could be attributed to the lability of
the acetyl compared with the benzoyl group in the presence
of the strong Lewis acid tin(IV) chloride. Excellent yields
The diastereoselectivity of the glycosylation was deter-
1
mined from the coupling constants. In fact, the H NMR
spectrum of 4 showed a singlet at 5.44 ppm for the H-1′ and
a doublet at 5.43 ppm (J = 1.7 Hz) for the H-2′, in agree-
ment with an α-D-Araf linkage. The 13C NMR spectrum
showed the resonance of the anomeric carbon at 107.6 ppm
confirming the α-D-arabinofuranosyl linkage. The β linkage
was not observed.
© 2006 NRC Canada

488
Can. J. Chem. Vol. 84, 2006
Scheme 2.
BzO
O
OBz
O
OBz
BzO
BzO
OBz
OBz
O
O
O
OH
O
OR
O
OAc
O
OH
OBz
1
DSB
OBz
OBz
OPiv
OPiv
OPiv
SnCl , CH Cl
(86%)
OH
4
2
2
O
O
OPiv
(70%)
OPiv
OPiv
3
4
5
R = H
6
Ac O/ C H N
2
5 5
(99%)
R = Ac
BzO
R O
1
OBz
OR
1
O
O
O
OAc
O
O
(CH )
2 7
O
CCl
3
OR
TMSOTf, 4 Å MS,
Cl2CH2, -10 ºC
Cl CCN, DBU,
2
3
CH Cl
2
2
NH
OBz
OR
1
OPiv
OR
3
9-decen-1-ol
(80%)
O
O
(70%)
OPiv
OR
3
7
8
9
R = Bz, R = Ac, R = Piv
1 2 3
-
MeO /MeOH
(90%)
R = R = R = H
1
2
3
Previous to reducing the lactone function, acetylation of 4
was performed carefully to avoid β-elimination by-products.
in the synthesis of oligosaccharide units, useful for studies
on its biosynthesis. The decenyl glycoside was also synthe-
sized allowing further functionalization of the double bond.
1
In this case, the H NMR signal of H-3 in 5 was shifted
0.97 ppm downfield compared with H-3 in 4, confirming
that glycosylation had taken place regioselectively at OH-5.
Further reduction of the lactone derivative 5 with disiamyl-
borane gave 2,3,5-tri-O-benzoyl-α-D-arabinofuranosyl-(1→5)-
3-O-acetyl-2,6-di-O-pivaloyl-D-galactofuranose (6); the tar-
get disaccharide showed both anomers in a 1:1 α:β ratio as
indicated by the integration of the anomeric protons in the
1H NMR spectrum at 5.53 ppm (d, J = 4.8 Hz, H-1α) and
5.33 (s, H-1β).
To synthesize the decenyl glycoside, the trichloroaceti-
midate method was chosen. This method has been success-
fully used for β-D-galactofuranosyl glycosylation (8, 9, 18–
20). Thus, activation of the anomeric center of 6 with
Cl3CCN and DBU gave a mixture of β- and α-trichloro-
acetimidates (7) in 88% yield. Disaccharide imidate 7 was
stable for 1 day at –20 °C. On reaction of 7 with 1.3 equiv.
of 9-decen-1-ol in CH2Cl2 with TMSOTf as the catalyst,
decenyl β-glycoside (8) was obtained diastereoselectively
(80%). In the 1H NMR spectrum, the galactofuranosyl
anomeric proton of 8 gave a signal at 4.94 (s, H-1) indicat-
ing the β-configuration. This assignment was confirmed by
the 13C NMR spectrum, which showed the signal of C-1 at
Experimental section
General
TLC was performed on 0.2 mm silica gel 60 F254 alu-
minium-supported plates. Detection was effected by expo-
sure to UV light or by spraying with 5% (v/v) sulfuric acid
in EtOH and charring. Column chromatography was per-
formed on silica gel 60 (230–400 mesh). Melting points are
uncorrected. Optical rotations were measured at 25 °C.
High-resolution mass spectra (HRMS) were recorded on a
VG ZAB2SE (1996) high-resolution mass spectrometer,
with Opus V3.1 and DEC 3000 Alpha Station. NMR spectra
were recorded at 500 MHz (1H) and 125.8 MHz (13C), or as
indicated. Homo- and hetero-nuclear correlation spectros-
copy experiments were performed when indicated.
1,2,3,5-Tetra-O-benzoyl-␣,␤-D-arabinofuranose (1␣␤),
1,2,3,5-tetra-O-benzoyl-␣-D-arabinofuranose (1␣), and
1,2,3,4-tetra-O-benzoyl-␣-D-arabinopyranose (2)
Arabinose (3.05 g, 20.3 mmol) in dry pyridine (63.9 mL)
was heated in a boiling water bath for 45 min with the ex-
clusion of moisture. The water bath was rapidly cooled to
60–65 °C and freshly distilled benzoyl chloride (11.3 mL,
97.4 mmol) was slowly added to the reaction mixture. After
stirring at 60 °C for 1.3 h, water (6 mL) was added, and the
stirring was continued for 30 min at room temperature. The
solution was slowly poured into ice water (400 g) with
vigorous stirring, affording an amorphous solid. After
decantation, the remaining solid was washed five times with
106.5 ppm. Full assignments for compound
8 were
supported by COSY and HETCOR experiments. Sodium
methoxide deprotection of 8 afforded 1-decenyl α-D-Araf-
1
(1→5)-β-D-Galf (9) in 90% yield. The H NMR spectrum of
9 is shown in Fig. 1.
Conclusion
A facile synthesis of a synthon for the α-D-Araf-(1→5)-D-
Galf (4) unit of M. tuberculosis arabinogalactan was
achieved in 70% yield from 1 and 3. The aldonolactone ap-
proach followed by DSB reduction produced the
disaccharide 6, conveniently protected for further coupling
1
water. The H NMR spectrum (CDCl3) of the solid showed
the anomeric signals with the following integrations: δ 6.88
(d, 0.30H, J = 4.4 Hz, H-1β furanosic), 6.76 (s, 0.27H, H-1α
furanosic), 6.26 (d, 0.43H, J = 5.6 Hz, H-1α pyranosic). The
© 2006 NRC Canada

Gandolfi-Donadío et al.
489
solid was dissolved in boiling EtOH (400 mL) and slow
crystallization took place. After 1 day, crystals of 1,2,3,4-
tetra-O-benzoyl-α-D-arabinopyranose (2, 3.02 g, 26%, Rf
0.46, hexane–EtOAc (3:1), twice developed) were obtained;
mp 161 to 162 °C. [α]D –113.8° (c 1, CHCl3) (lit. value (21)
mp 164 to 165 °C, MeOH–AcOH, 80:5.7; [α]D –114.4° (c
(m, 15H), 5.68 (dd, 1H, J = 1.7, 4.8 Hz, H-3′), 5.44 (bs, 1H,
H-1′), 5.43 (d, 1H, J = 1.7 Hz, H-2′), 5.37 (d, 1H, J = 8.0 Hz,
H-2), 4.80 (dd, 1H, J = 2.6, 11.2 Hz, H5a′), 4.79 (dt, 1H, J =
3.0, 8.0 Hz, H-3), 4.70 (m, 1H, H-4′), 4.67 (dd, 1H, J = 5.0,
11.2 Hz, H-5b′), 4.46 (dd, 1H, J = 5.5, 11.5 Hz, H-6a), 4.44
(dd, 1H, J = 3.5, 8.0 Hz, H-4), 4.34 (dd, 1H, J = 6.7,
11.5 Hz, H-6b), 4.20 (ddd, 1H, J = 3.5, 5.5, 6.7 Hz, H-5),
3.87 (d, 1H, J = 3.0, OH), 1.26, 1.19 (2s, 18H, (CH3)3CCO).
13C NMR (CDCl3) δ: 179.1, 177.0 ((CH3)3CCO), 168.7 (C-
1), 166.1–165.8 (COPh), 137.8–128.2 (aromatic), 107.6 (C-1′),
83.0 (C-2′), 81.2 (C-4′), 79.8 (C-4), 77.0 (C-3′), 76.4 (C-2),
74.8 (C-5), 72.4 (C-3), 63.4 (C-5′), 62.6 (C-6), 38.9, 38.7
((CH3)3CCO), 27.1, 26.9 ((CH3)3CCO). These assignments
were supported by COSY and HETCOR experiments. Anal.
calcd. for C42H46O15: C 63.79, H 5.86; found: C 63.72, H
6.13.
1
0.848, CHCl3)). H NMR (CDCl3) δ: 8.08–7.33 (m, 20H),
6.26 (d, 1H, J = 5.6 Hz, H-1), 5.95 (dd, 1H, J = 5.6, 7.3 Hz,
H-2), 5.80 (ddd, 1H, J = 2.9, 3.6, 5.2 Hz, H-4), 5.78 (dd, 1H,
J = 3.6, 7.3 Hz, H-3), 4.43 (dd, 1H, J = 5.2, 12.6 Hz, H-5a),
1
4.14 (dd, 1H, J = 2.9, 12.6 Hz, H-5b) (lit. value (22) H
NMR (acetone-d6, 100 MHz)). 13C NMR (CDCl3) δ: 164.5–
164.7 (COPh), 133.7–128.5 (aromatic), 92.4 (C-1), 69.9 (C-
3), 68.9 (C-2), 67.5 (C-4), 62.7 (C-5).
The mother liquors were kept at room temperature (20–
23 °C) for 2 days and the second crop of crystals was fil-
tered and characterized as 1,2,3,5-tetra-O-benzoyl-α,β-D-
arabinofuranose (1␣␤, 3.34 g, 29%, Rf 0.53 and 0.49, hex-
2,3,5-Tri-O-benzoyl-␣-D-arabinofuranosyl-(1→5)-3-O-
acetyl-2,6-di-O-pivaloyl-D-galactono-1,4-lactone (5)
1
ane–EtOAc (3:1), twice developed) in a 7:3 α:β ratio. H
NMR (CDCl3) δ: 8.13–7.24 (m, 20H), 6.87 (d, 0.3H, J =
4.7 Hz, H-1 β anomer), 6.76 (s, 0.7H, H-1 α anomer), 6.11
(dd, 0.3H, J = 5.2, 7.0 Hz, H-3), 5.94 (dd, 0.3H, J = 4.7,
7.0 Hz, H-2), 5.82 (d, 0.7H, J = 0.8 Hz, H-2), 5.68 (dd,
0.7H, J = 3.7, 0.8 Hz, H-3), 4.83 (dd, 0.7H, J = 3.9, 12.7 Hz,
H-5a), 4.82 (m, 0.7H, H-4), 4.81 (dd, 0.3H, J = 6.7, 14.1 Hz,
H-5a), 4.73 (dd, 0.7H, J = 6.4, 12.7 Hz, H-5b), 4.67 (m,
0.3H, H-4), 4.66 (dd, 0.3H, J = 6.1, 14.1 Hz, H-5b). 13C
NMR (CDCl3) δ: 166.2–164.6 (COPh), 133.7–128.2 (aro-
matic), 99.8 (C-1 α anomer), 94.5 (C-1 β anomer), 83.9 (C-4
α anomer), 80.9 (C-2 α anomer), 79.8, 77.5, 76.2, 75.5,
64.7, 63.7.
To a solution of 4 (1.29 g, 1.63 mmol) in dry pyridine
(13 mL), cooled at 0 °C, was added acetic anhydride
(13 mL, dropwise) and the mixture was stirred at room tem-
perature for 30 min. After cooling to 0 °C, the reaction was
quenched by a slow addition of MeOH (20 mL) and the stir-
ring continued for 30 min at room temperature. The solution
was diluted with CH2Cl2 (200 mL) and then sequentially
washed with 10% HCl (2 × 200 mL), water (200 mL), satd.
aq. NaHCO3 (200 mL), water, dried (Na2SO4), and then con-
centrated to give 5 (1.34 g, 99%) as a chromatographically
pure syrup. Rf 0.66 (toluene–EtOAc, 3:1). [α]D –21.3° (c 1,
1
CHCl3). H NMR (CDCl3) δ: 8.04–7.16 (m, 15H, aromatic),
A sample of 1␣␤ was purified by column chromatography
(toluene) to yield pure 1,2,3,5-tetra-O-benzoyl-α-D-arabino-
furanose (1␣). Crystallization from EtOH gave: mp 100 to
101 °C (EtOH). [α]D +26.7° (c 1, CHCl3) (lit. value (17) mp
117–121 °C (EtOH). [α]D +27.9° (c 2.13, CHCl3)). 1H NMR
(CDCl3) δ: 8.14–7.26 (m, 20H), 6.76 (s, 1H, H-1), 5.82 (d,
1H, J = 0.8 Hz, H-2), 5.68 (dd, 1H, J = 3.7, 0.8 Hz, H-3),
4.83 (dd, 1H, J = 3.9, 12.7 Hz, H-5a), 4.82 (m, 1H, H-4),
4.73 (dd, 1H, J = 6.4, 12.7 Hz, H-5b). 13C NMR (CDCl3) δ:
166.2–164.6 (COPh), 133.8–128.3 (aromatic), 99.8 (C-1),
83.9 (C-4), 80.9 (C-2), 77.5 (C-3), 63.7 (C-5). These assign-
ments were supported by HETCOR experiments.
5.76 (t, 1H, J = 6.6 Hz, H-3), 5.66 (d, 1H, J = 6.9 Hz, H-2),
5.63 (dd, 1H, J = 1.4, 4.6 Hz, H-3′), 5.59 (bs, 1H, H-1′),
5.56 (d, 1H, J = 1.4 Hz, H-2′), 4.80 (dd, 1H, J = 5.3,
13.5 Hz, H-5a′), 4.67 (m, 2H, H-4′, H-5b′), 4.55 (dd, 1H,
J = 3.0, 6.4 Hz, H-4), 4.48 (dd, 1H, J = 4.4, 11.0 Hz, H-6a),
4.29 (dd, 1H, J = 7.1, 11.0 Hz, H-6b), 4.25 (ddd, 1H, J =
3.0, 4.4, 7.1 Hz, H-5), 2.11 (s, 3H, CH3), 1.20, 1.18 (2s,
18H, (CH3)3CCO)). 13C NMR (CDCl3) δ: 177.6, 177.1
((CH3)3CCO), 169.9 (C-1), 168.4 (COCH3), 166.1–165.4
(COPh), 133.5–128.3 (aromatic), 107.6 (C-1′), 82.4 (C-2′),
81.7 (C-4′), 79.1 (C-4), 77.2 (C-3′), 75.4 (C-5); 72.9, 72.0
(C-2, C-3), 63.6 (C-5′), 62.4 (C-6), 38.7, 38.6 ((CH3)3CCO),
27.1, 26.8 ((CH3)3CCO), 20.5 (COCH3). These assignments
were supported by COSY and HETCOR experiments. Anal.
calcd. for C44H48O16: C 63.45, H 5.81; found: C 63.48, H
5.83.
2,3,5-Tri-O-benzoyl-␣-D-arabinofuranosyl-(1→5)-2,6-di-
O-pivaloyl-D-galactono-1,4-lactone (4)
To an externally cooled (0 °C) solution of tetra-O-
benzoyl-α,β-D-arabinofuranose (1␣␤, 1.07 g, 1.9 mmol) in
dry CH2Cl2 (50 mL) was added SnCl4 (0.22 mL, 1.9 mmol)
with stirring in an argon atmosphere. After 10 min, this solu-
tion was added to a solution of compound 3 (9) (0.86 g,
2.5 mmol) in CH2Cl2 (50 mL) over a 25 min period and then
the mixture was stirred for 3 h at 0 °C. The solution was
poured into aq. NaHCO3 and extracted with CH2Cl2 (2 ×
200 mL). The organic extract was washed with water (3 ×
100 mL), dried (Na2SO4), filtered, and concentrated under
reduced pressure. Purification of the residue by column
chromatography (toluene–EtOAc, 20:1) gave 1.05 g of 4
(70% yield) as a foamy solid. Rf 0.45 (toluene–EtOAc, 3:1).
2,3,5-Tri-O-benzoyl-␣-D-arabinofuranosyl-(1→5)-3-O-
acetyl-2,6-di-O-pivaloyl-D-galactofuranose (6)
A solution of bis(2-butyl-3methyl)borane (9.24 mmol) in
anhydr. THF (2.6 mL), cooled to 0 °C and under an argon
atmosphere, was added to a flask containing previously
dried compound 5 (1.28 g, 1.54 mmol). The resulting solu-
tion was stirred for 22 h at room temperature and then pro-
cessed as previously described (23). The organic layer was
washed with water, dried (Na2SO4), and concentrated. Boric
acid was eliminated by coevaporation with MeOH (5 ×
20 mL) at room temperature. The residue was purified by
column chromatography (toluene–EtOAc, 15:1) to give
1
[α]D –28.1° (c 1, CHCl3). H NMR (CDCl3) δ: 8.07–7.14
© 2006 NRC Canada

490
Fig. 1. H NMR spectrum of compound 9 (D2O, 500 MHz, acetone was used as internal reference).
Can. J. Chem. Vol. 84, 2006
1
6.0
5.5
5.0
4.5
4.0
3.5
3.0
(ppm)
2.5
2.0
1.5
1.0
0.5
0.0
13
1.05 g (86%) of 6 (syrup) as a 2:3 α:β anomeric mixture. Rf
0.43 (toluene–EtOAc, 3:1). [α]D –2.4° (c 1, CHCl3). 1H
NMR (CDCl3) anomeric protons δ: 5.67 (bs, 0.5H, H-1′ for
β anomer), 5.63 (bs, 0.5H, H-1′ for α anomer), 5.53 (d, 0.5H,
J = 4.7 Hz, H-1 α anomer), 5.33 (bs, 0.5H, H-1 β anomer).
13C NMR (CDCl3) δ: 178.0–177.4 ((CH3)3CCO)), 170.6,
170.1 (COCH3), 166.1–165.3 (COPh), 133.7–125.3 (aro-
matic), 107.6 (C-1′ β anomer), 106.5 (C-1′ α anomer), 100.6
(C-1 β anomer), 95.0 (C-1 α anomer), 82.8, 82.1, 82.0, 81.7,
81.2, 80.9, 80.3, 77.7, 77.2, 77.1, 76.9, 76.7, 75.5, 75.2,
63.7, 63.6, 63.5, 63.0, 38.7 ((CH3)3CCO)), 27.1, 27.0, 26.9
((CH3)3CCO), 20.7, 20.6 (CH3). These assignments were
supported by COSY and HETCOR experiments. Anal. calcd.
for C44H50O16: C 63.30, H 6.04; found: C 63.65, H 6.44.
(s, 0.8H, H-1 β anomer).
C NMR (CDCl3, 25 MHz) for
the β anomer δ: 177.8, 177.0 ((CH3)3CCO), 170.0 (CH3CO),
166.2–165.2 (COPh), 160.2 (NHCOCl3), 133.5–125.3 (aro-
matic), 106.5 (C-1′), 102.8 (C-1), 97.9 (C-1 α anomer),
84.0, 82.1, 81.3, 80.4, 77.6, 75.8, 74.3, 63.6, 63.4, 38.6
((CH3)3CCO × 2), 27.1, 26.9 ((CH3)3CCO), 20.6 (CH3CO).
A vigorously stirred suspension of the trichloroaceti-
midate 7 (241 mg, 0.25 mmol), 9-decen-1-ol (60.4 ␮L,
0.33 mmol), and powdered activated 4 Å molecular sieves
(0.5 g) in anhydr. CH2Cl2 (9 mL) was cooled to –20 °C, and
TMSOTf (13.3 µL, 0.073 mmol) was slowly added. After
30 min of stirring, the mixture was filtered into aq. NaHCO3
(15 mL) and then extracted with CH2Cl2 (2 × 25 mL). The
organic layer was washed with water (3 × 40 mL), dried
(Na2SO4), filtered, and concentrated under reduced pressure.
The residue was purified by column chromatography
(toluene–EtOAc, 45:1) affording 8 (243 mg, 80%) as a
syrup. Rf 0.60 (toluene–EtOAc, 9:1). [α]D –23.9° (c 1, CHCl3).
1H NMR (CDCl3) δ: 8.07–7.26 (m, 15H, aromatic), 5.80
(ddt, 1H, J = 6.7, 10.2, 17.2 Hz, CH=CH2), 5.65 (s, 1H, H-1′),
5.61 (dd, 1H, J = 1.5, 5.0 Hz, H-3′), 5.57 (d, 1H, J = 1.5 Hz,
H-2′), 5.23 (dd, 1H, J = 1.7, 5.5 Hz, H-3), 5.07 (d, 1H, J =
1.7 Hz, H-2), 4.98 (ddt, 1H, J = 1.2, 1.7, 17.2 Hz,
HC=CHaH), 4.94 (bs, 1H, H-1), 4.92 (ddt, 1H, J = 1.3, 2.5,
10.2 Hz, HC=CHbH), 4.80 (dd, 1H, J = 3.2, 11.4 Hz, H-5a′),
4.71 (m, 1H, H-4′), 4.67 (dd, 1H, J = 4.8, 11.4 Hz, H-5b′),
4.36 (m, 1H, H-5), 4.24–4.30 (m, 3H, H-6a, H-6b, H-4),
3.67 (dt, 1H, J = 6.7, 9.7 Hz, CHaHO), 3.40 (dt, 1H, J = 6.5,
9.7 Hz, CHbHO), 2.07 (s, 3H, CH3), 2.04 (m, 2H, CH2), 1.58
(m, 2H, CH2), 1.27 (m, 12H, CH2), 1.17, 1.16 (2s, 18H,
9-Decenyl 2,3,5-tri-O-benzoyl-␣-D-arabinofuranosyl-
(1→5)-3-O-acetyl-2,6-di-O-pivaloyl-D-galactofuranoside (8)
To a stirred solution of 6 (314 mg, 0.40 mmol) and
trichloroacetonitrile (0.20 mL, 2.0 mmol) in dry CH2Cl2
(10 mL), cooled to 0 °C, DBU (28.4 µL, 0.18 mmol) was
slowly added. After 1 h, the solution was concentrated under
reduced pressure, and the residue was purified by column
chromatography (toluene–EtOAc–TEA, 40:1:0.4) to give
342 mg (88%) of O-(2,3,5-tri-O-benzoyl-α-D-arabinofurano-
syl-(1→5)-3-O-acetyl-2,6-di-O-pivaloyl-α,β-D-galactofuranosyl)
trichloroacetimidate (7) as an amorphous solid (Rf 0.33 and
0.47 in toluene–EtOAc–TEA (9:1:0.09) for the α and β anomers,
respectively). Compound 7 was stable for 1 day at –20 °C.
1H NMR (CDCl3, 200 MHz) δ: 8.61 (s, 0.8H, NH), 8.44 (s,
0.2H, NH), 6.55 (d, 0.2H, J = 4.6 Hz, H-1 α anomer), 6.30
© 2006 NRC Canada

Gandolfi-Donadío et al.
491
((CH3)3CCO). 13C NMR (CDCl3) δ: 177.9, 177.4
((CH3)3CCO), 170.2 (CH3CO), 166.1–165.2 (COPh), 139.1
(CH=CH2), 133.5–128.3 (aromatic), 114.1 (CH=CH2), 106.5
(C-1′), 105.3 (C-1), 82.2 (C-2′), 81.9 (C-2), 81.0 (C-4′),
80.9 (C-4), 77.7 (C-3′), 76.9 (C-3), 74.6 (C-5), 67.6 (CH2O),
63.7 (C-5′), 63.6 (C-6), 38.7, 38.6, ((CH3)3CCO), 33.8, 29.4,
29.3, 29.0, 28.9, 27.1, 26.9, 26.0 ((CH3)3CCO), 20.7 (CH3).
These assignments were supported by COSY and HETCOR
experiments. Anal. calcd. for C54H68O16: C 66.65, H 7.04;
found: C 66.48, H 7.09.
Técnicas (CONICET). L. Gandolfi-Donadio is a fellow from
CONICET.
References
1. (a) World Health Organization (WHO). In Anti-tuberculosis
drug resistance in the world. The WHO/IUATLD Global Pro-
ject on Anti-tuberculosis Resistance Surveillance. WHO,
Geneva, Switzerland. 1997. Publication WHO/TB/97.229;
(b) D. Butler. Nature, 406, 670 (2000).
2. F. Pan, M. Jackson, Y. Ma, and M. McNeil. J. Bacteriol. 183,
3991 (2001).
3. D.C. Crick, S. Mahaprata, and P.J. Brennan. Glycobiology, 11,
107 (2001).
9-Decenyl ␣-D-arabinofuranosyl-(1→5)-␤-D-
galactofuranoside (9)
Compound 8 (112 mg, 0.12 mmol) was suspended in
0.48 mol/L sodium methoxide in a methanol solution
(1.7 mL) and cooled at 0 °C. After stirring for 1 h at 0 °C,
the resulting solution was warmed to room temperature,
stirred for 2 h, and water (0.5 mL) was added. The solution
was passed through a column containing Amberlite IR-120
plus (H+) resin (3 mL) and the column washed with MeOH–
H2O (9:1). The combined eluates were evaporated and the
remaining methyl benzoate was eliminated by five succes-
sive coevaporations with water. The residue was dissolved in
water, further purified through a C8-Maxi-Clean cartridge,
and the solution lyophilized. Glycoside 9 (49 mg, 90%) was
obtained as a hygroscopic syrup. Rf 0.86 (n-propanol–EtOH–
H2O, 7:1:1). [α]D –4.4° (c 0.6, H2O). 1H NMR (D2O) δ: 5.79
(ddt, 1H, J = 6.7, 10.4, 17.0 Hz, CH=CH2), 5.14 (d, 1H, J =
1.9 Hz, H-1′), 4.95 (ddt, 1H, J = 1.5, 3.7, 17.0 Hz,
HC=CHaH), 4.90 (bs, 1H, H-1), 4.88 (ddt, 1H, J = 1.1, 2.2,
10.4 Hz, HC=CHbH), 4.11 (dd, 1H, J = 1.9, 3.7 Hz, H-2′),
4.07 (ddd, 1H, J = 3.3, 5.9, 6.1 Hz, H-4′), 4.01–3.98 (m, 3H,
H-2, H-3, H-4), 3.89 (dd, 1H, J = 3.7, 6.1 Hz, H-3′), 3.83
(m, 1H, H-5), 3.76 (dd, 1H, J = 3.3, 12.6 Hz, H-5a′), 3.74–
3.63 (m, 3H, H-6a, H-6b, CHaHO), 3.65 (dd, 1H, J = 5.9,
12.6 Hz, H-5b′), 3.46 (dt, 1H, J = 6.7, 10.0 Hz, CHbHO),
1.98 (m, 2H, CH2), 1.54 (m, 2H, CH2), 1.36–1.22 (m, 10H,
CH2). 13C NMR (D2O) δ: 140.3 (CH=CH2), 114.6
(CH=CH2), 109.1 (C-1′), 107.6 (C-1), 84.4 (C-4′), 82.4 (C-2′),
81.9, 81.7 (C-4, C-2), 78.4 (C-5), 77.0, 76.9 (C-3′, C-3),
69.6 (CH2O), 62.1 (C-6), 61.8 (C-5′), 34.0, 29.6, 29.5, 29.4,
29.2, 29.1, 26.1. HRMS (FAB+) m/z calcd. for
C21H38O10Na: 473.2363 (M + Na+); found: 473.2356. Anal.
calcd. for C21H38O10·0.5H2O: C 54.89, H 8.55; found: C
54.86, H 8.68.
4. A.K. Pathak, V. Pathak, W.J. Suling, S.S. Gurcha, C.B.
Morehouse, G.S. Besra, J.A. Maddry, and R.C Reynolds.
Bioorg. Med. Chem. 10, 923 (2002).
5. (a) M.K. Gurjar, L.K. Reddy, and S. Hotha. Org. Lett. 3, 321
(2001); (b) M.K. Gurjar, L.K. Reddy, and S. Hotha. J. Org.
Chem. 66, 4657 (2001); (c) H. Wang and J. Ning. J. Org.
Chem. 68, 2521 (2003).
6. R.R. Schmidt and K.-H. Jung. In Preparative carbohydrate
chemistry. Edited by S. Hanessian. Marcel Dekker Inc., New
York. 1997. pp. 283–312.
7. T.L Lowary. In Glycochemistry: Principles, synthesis, and ap-
plications. Edited by P.G Wang and C.R. Bertozzi. Marcel
Dekker Inc., New York. 2001. pp. 133–162.
8. L. Gandolfi-Donadío, C. Gallo-Rodriguez, and R.M. de
Lederkremer. J. Org. Chem. 67, 4430 (2002).
9. L. Gandolfi-Donadío, C. Gallo-Rodriguez, and R.M. de
Lederkremer. J. Org. Chem. 68, 6928 (2003).
10. C. Marino, O. Varela, and R.M. de Lederkremer. Carbohydr.
Res. 190, 65 (1989).
11. R.M. de Lederkremer, C. Marino, and O. Varela. Carbohydr.
Res. 200, 227 (1990).
12. C. Gallo-Rodriguez, O. Varela, and R.M. de Lederkremer. J.
Org. Chem. 61, 1886 (1996).
13. (a) N.B. D’Accorso, I.M.E. Thiel, and M. Schüller. Carbohydr.
Res. 124, 177 (1983); (b) C. Gallo-Rodriguez, O. Varela, and
R.M. de Lederkremer. Carbohydr. Res. 305, 163 (1998).
14. A.K. Pathak, Y.A. El-Kattan, N. Bansal, J.A. Maddry, and
R.C. Reynolds. Tetrahedron Lett. 39, 1497 (1998).
15. F.W. D’Souza, P.E. Cheshev, J.D. Ayers, and T.L. Lowary. J.
Org. Chem. 63, 9037 (1998).
16. K. Mizutani, R. Kasai, M. Nakamura, O. Tanaka, and H.
Matsuura. Carbohydr. Res. 185, 27 (1989).
17. R.K. Ness and H.G. Fletcher. J. Am. Chem. Soc. 80, 2007
(1958).
18. A.K. Choudhury and N. Roy. Carbohydr. Res. 308, 207 (1998).
19. C. Gallo-Rodriguez, L. Gandolfi, and R.M. de Lederkremer.
Org. Lett. 1, 245 (1999).
20. C. Gallo-Rodriguez, M.A. Gil-Libarona, V.M. Mendoza, and
R.M. de Lederkremer. Tetrahedron, 58, 9373 (2002).
21. H.G. Fetcher, Jr. and C.S. Hudson. J. Am. Chem. Soc. 69,
1145 (1947).
Acknowledgments
This work was supported by grants from Agencia
Nacional de Promoción Científica
Universidad de Buenos Aires, and Fundación Antorchas. C.
Gallo-Rodriguez and R.M. de Lederkremer are research
members of Consejo Nacional de Investigaciones Científicas
y
Tecnológica,
22. P.L. Durette and D. Horton. J. Org. Chem. 36, 2658 (1971).
23. L.M. Lerner. Methods Carbohydr. Chem. 6, 131 (1972).
© 2006 NRC Canada