The galactosamine residue in mycobacterial arabinogalactan is α-linked

Article abstract of DOI:10.1021/jo301393s

Previous studies have demonstrated that cell wall arabinogalactan from mycobacteria possesses a single galactosamine (GalN) residue. This moiety, which is one of the rare natural occurrences of galactosamine lacking an acetyl group on the nitrogen, has be

Full text of DOI:10.1021/jo301393s

Note
pubs.acs.org/joc
The Galactosamine Residue in Mycobacterial Arabinogalactan Is
α‑Linked
Wenjie Peng,† Lu Zou,† Suresh Bhamidi,‡ Michael R. McNeil,‡ and Todd L. Lowary*,†
†Alberta Glycomics Centre and Department of Chemistry, The University of Alberta, Edmonton, Alberta T6G 2G2, Canada
‡Mycobacteria Research Laboratories, Department of Microbiology, Immunology and Pathology, Colorado State University, Fort
Collins, Colorado 80523, United States
S
* Supporting Information
ABSTRACT: Previous studies have demonstrated that cell wall arabinogalactan from
mycobacteria possesses a single galactosamine (GalN) residue. This moiety, which is one of
the rare natural occurrences of galactosamine lacking an acetyl group on the nitrogen, has
been identified as a pendant substituent attached to a highly branched arabinofuranose
residue in the arabinan core. However, the stereochemistry by which the GalN residue is
linked to the polysaccharide remains unknown. We report here the synthesis of two
tetrasaccharides, 1 and 2, consisting of GalN attached through either an α- or β-linkage to a
trisaccharide fragment of mycobacterial arabinan. These molecules represent the first
synthetic GalN-containing oligosaccharides, and the preparation of both targets was achieved
from a single donor species by modulation of the reaction solvent. Comparison of the NMR
spectra of 1 and 2 with those obtained from a sample derived from the natural glycan
revealed that the GalN residue in the polysaccharide is attached via an α-linkage.
uberculosis remains a public health concern, with
(as well as the succinate modification) are attached to the
Testimates that a third of the world’s population harbors arabinan domain of the MAG through O-2 on arabinofuranose
(Araf) residues that are further branched at both O-3 and O-5
with additional Araf motifs (Figure 1A). Although glycans
containing 2-acetamido-2-deoxy-galactose (GalNAc) are wide-
spread in nature, GalN, which lacks the acetyl group, is rare. To
date, this monosaccharide has been identified as a component
of the lipopolysaccharide in Francisella tularensis,8,9 Legionella
hackeliae,10 Campylobacter jejuni,11 Campylobacter coli,11 as well
as a glycoprotein from Bacillus thuringiensis.12
The biosynthesis of GalN in mycobacteria has been studied
and a lipid-linker GalNAc-pyrophosphate species was isolated
and characterized.13 In addition, the genes encoding for the
synthase and transferase that assemble and use this
glycosylating agent were identified. Subsequent deacetylation
(either before or after glycosylation) by a to date unidentified
amidase was proposed to complete the biosynthetic pathway.
On the basis of similarities with an intermediate isolated from
F. tularensis14,15 and the sequence of the transferase, which
predicts it to be an inverting enzyme, the stereochemistry of the
GalN moiety was proposed to be α. However, unequivocal
evidence is not available to support this stereochemical
assignment. To address this issue, we report here the synthesis
of both the α- and β-GalN stereoisomers of this tetrasaccharide
motif (1 and 2, Figure 1B) and the establishment of the linkage
stereochemistry by comparison of the NMR data for these
compounds with that for a fragment of the natural
polysaccharide.
Mycobacterium tuberculosis, the organism that causes the
disease.1 Although only a few of those infected will develop
active disease, fears about even more widespread dissemination
of tuberculosis have been heightened in recent years by the
emergence of M. tuberculosis strains with varying degrees of
drug resistance.2 These public health issues have led to
increased interest in understanding mycobacterial physiology
and the organism’s cell wall, a complex and intricate structure
that is essential to its survival, has received particular
attention.3,4
The major structural component of the mycobacterial cell
wall is a glycolipid, the mycolyl−arabinogalactan (MAG)
complex, which is covalently bound to peptidoglycan.3 The
predominant components of the MAG complex are the
monosaccharides galactose and arabinose, both in their
furanose ring form, and mycolic acids, which are C70−C90
branched chain lipids characteristic to mycobacteria and related
organisms (e.g., corynebacteria, nocardia). Also present is a
single rhamnose and a single N-acetylglucosamine phosphate
residue, which together form the linker that connects the MAG
to the peptidoglycan. More recently, two additional compo-
nents, succinic acid and 2-amino-2-deoxy-galactose (GalN),
have been identified in the MAG of some mycobacterial strains,
both of which are present at substoichiometric levels.5,6
The presence of GalN in some mycobacterial strains was
proposed more than 40 years ago.7 However, its presence was
only unequivocally established more recently due to improve-
ments in polysaccharide degradation methods and mass
spectrometry.5,6 These studies revealed that the GalN moiety
Received: July 3, 2012
Published: October 8, 2012
© 2012 American Chemical Society
9826
dx.doi.org/10.1021/jo301393s | J. Org. Chem. 2012, 77, 9826−9832

The Journal of Organic Chemistry
Note
Figure 1. (A) Proposed location of succinate and GalN residues in mycobacterial arabinogalactan. (B) Tetrasaccharide targets 1 and 2.
Scheme 1. Synthesis of 1 and 2
To the best of our knowledge, there are no previous
syntheses of oligosaccharides containing GalN residues, which
is perhaps not surprising given the rarity of this structural motif
in nature. In addition, there are no previous syntheses of
oligofuranosides containing a residue in which every hydroxyl
group is glycosylated. We anticipated the synthesis of 1 and 2
could prove challenging given steric crowding that could
prevent efficient reaction between hydroxyl groups and
activated glycosyl donors as the substitution pattern on the
core Araf ring increases. Because we wanted to synthesize both
GalN anomers attached to the triarabinofuranoside motif (1
and 2), we adopted a route involving the use of a 2-azido-2-
deoxy-galactopyranosyl donor combined with modification of
the reaction conditions to provide increased amounts of either
the α- or β-glycoside.
9827
dx.doi.org/10.1021/jo301393s | J. Org. Chem. 2012, 77, 9826−9832

The Journal of Organic Chemistry
Note
1
1
Figure 2. Comparison of the H NMR spectrum of AG containing a GalN moiety (A) with the H NMR spectra of 1 (C) and 2 (B).
The synthesis of 1 and 2 is illustrated in Scheme 1 and began
from the methyl glycoside 3. This monosaccharide, prepared as
previously reported,16 was converted into the silyl acetal
protected derivative 4 in two steps first by debenzoylation and
then treatment with di-t-butylsilyl bis(trifluoromethane-
sulfonate). The product was obtained in 84% yield over the
two steps.
yield. All of the 1H NMR resonances for the Araf linkages in 10
and 11 appeared as singlets or as small doublets (J < 2 Hz)
consistent with the α-stereochemistry.23 Contrary to our
expectation, the synthesis of the fully substituted central Araf
ring in 1 and 2 proved straightforward. We attribute this to the
enhanced flexibility of the five-membered ring, which possesses
sufficient mobility to allow efficient glycosylation of all hydroxyl
groups.
Subsequent glycosylation of this alcohol using trichloroace-
timidate 517 was carried out employing activation with
trimethylsilyl trifluoromethanesulfonate using two different
solvents to influence product stereochemistry. In one case,
the reaction was performed using diethyl ether as the solvent,18
which led to the product 6 in 90% yield as an inseparable 11:1
α:β mixture of isomers. In the other case, the reaction was
carried out in acetonitrile,19 resulting in a 71% yield of the
product 6 as a 1:5 α:β mixture of glycosides. Thus, by using
well-established solvent effects, it was possible to obtain
mixtures of 6 enriched in each of the two stereoisomers.
Although separation was not possible at this stage, each
mixture was carried through to the next step, treatment with
HF·pyridine to remove the silyl acetal. This reaction led to the
formation of 7 and 8, which could be separated by
chromatography, in a combined 77% yield.20 Determining the
stereochemistry of the pyranose residue in 7 and 8 could be
done unequivocally using 1H NMR spectroscopy. The
anomeric hydrogen in the pyranose residue in 7 appeared as
a doublet with J = 3.5 Hz, clearly supporting the α-
stereochemistry. In 8, the resonance for this hydrogen appears
as a doublet with J = 8.0 Hz, consistent with the β-
stereochemistry. The diol moiety in both 7 and 8 could then
be glycosylated independently using an excess of known
thioglycoside 9,21 promoted by N-iodosuccinimide and silver
triflate22 to afford tetrasaccharides 10 and 11, both in 94%
Deprotection of 10 and 11 proceeded in two steps. First,
each was deacylated with sodium methoxide to provide the
azido-tetrasaccharides 12 and 13, in 78 and 98% yields,
respectively. The azido groups in these materials were reduced
to the corresponding amines upon reaction of an aqueous
solution of 12 or 13 with hydrogen and palladium on carbon.
The final target compounds 1 and 2 were obtained in >97%
yield in both cases.
With both tetrasaccharide targets in hand, a comparison of
their NMR spectra with those obtained from the natural
glycans6 was carried out. The 1H NMR spectrum of the natural
glycan was expectedly complex (Figure 2A), but nevertheless it
was possible to identify characteristic resonances. In particular,
we focused our attention on a signal at 3.18 ppm, which
appears at a chemical shift anticipated for a hydrogen on a
carbon bearing a primary amine, and which integrated ∼1:1
with a signal at 4.92 ppm. The latter resonance has been
unequivocally assigned previously6 to arise from a proton on a
secondary ring carbon bearing a succinate moiety, which was
present in a 1:1 ratio with the GalN moiety. In addition,
previous studies on intact AG indicate that none of the
resonances for the other monosaccharides (arabinofuranose
and galactofuranose) appear below 3.5 ppm.24 Taking this data
into consideration, we conclude that the signal at 3.18 ppm
arises from the hydrogen on H-2 in the GalN ring in the
9828
dx.doi.org/10.1021/jo301393s | J. Org. Chem. 2012, 77, 9826−9832

The Journal of Organic Chemistry
Note
recorded on samples suspended in THF or CH3OH and with added
NaCl. Optical rotations were measured at 22 2 °C at the sodium D
line (589 nm) and are in units of deg·mL (dm·g)−1.
polysaccharide. This signal matched well with the signal for H-
2′ in the α-GalN-containing tetrasaccharide 2 (3.21 ppm,
Figure 2B). In contrast, the H-2′ resonance in the spectrum for
in β-GalN tetrasaccharide 1 was found at significantly lower
chemical shift (2.90 ppm, Figure 2C). It proved impossible to
identify the anomeric hydrogen on the GalN residue in the
polysaccharide due to spectral overlap. However, the
Methyl 2-O-(2-amino-2-deoxy-β-D-galactopyranosyl)-3,5-di-
O-(α-D-arabinofuranosyl)-α-D-arabinofuranoside (1). Tetrasac-
charide 12 (57 mg, 0.09 mmol) was dissolved in H2O (5 mL), and
hydrogenolyzed over 10% Pd−C (15 mg) under 1 atm H2 at room
temperature for 2 h. The mixture was filtered through Celite,
concentrated. The residue was dissolved in CH3OH and passed
through a polytetrafluoroethene (PTFE) syringe filter (diameter 25
mm, pore size 0.2 mm). After concentration, lyophilization of the
compound from water afforded 1 (49 mg, 98%): [α]D +109.6 (c = 0.8,
1
resonances present in the H NMR spectra of tetrasaccharide
1 (Figure 2C) provided further evidence that the naturally
occurring GalN residue is α-linked. The H-1 resonance for the
β-GalN residue in 1 is found at 4.48 ppm, a region that is
completely lacking in signals in the polysaccharide spectrum.
Finally, further evidence came from the signal for C-2′ in the
polysaccharide, 49.9 ppm,6 obtained from an HSQC experi-
ment (see Supporting Information). This chemical shift
corresponds better with this signal in tetrasaccharide 2 (51.4
ppm) than in 1 (52.9 ppm). Taken together, these data allow us
to conclude that the GalN residue in the natural glycan is α-
linked. It should be noted that this is consistent with previous
studies on the biosynthesis of this moiety,13 which have
suggested that the biochemical precursor is a β-linked
phospholipid sugar donor and that the enzyme that adds this
moiety to the arabinan is an inverting glycosyltransferase.
In conclusion, we describe here the first synthesis of GalN-
containing oligosaccharides related to those found in nature. In
particular, we have synthesized, for the first time, a highly
branched fragment of mycobacterial AG containing the GalN
substituent, consisting of an α-Araf motif glycosylated at every
hydroxyl group with either GalN (O-2) or α-Araf (O-3 and
O5). The key glycosylation reaction involved the reaction of a
2-azido-sugar glycosyl trichloroacetimidate; judicious choice of
the solvent enabled the preparation of products enriched in
either the α or β-anomer. Comparison of the NMR spectra of
these compounds with those obtained from a fragment of the
naturally occurring polysaccharide established that the GalN
residue in the natural glycan is linked to the arabinan via an α-
linkage. Now that the stereochemistry of the GalN linkage has
been established, future syntheses of this motif should be
facilitated by recently developed methodology for the
preparation of 1,2-cis-2-amino-glycosides.25−33
1
CH3OH); IR (film) 3353, 2929, 1082, 1047 cm−1; H NMR (500
MHz, D2O) δ = 5.22 (br. s, 1 H, H-1″), 5.10 (s, 1 H, H-1), 5.07 (br. s,
1 H, H-1‴), 4.48 (d, J = 8.0 Hz, 1 H, H-1′), 4.40 (br. s, 1 H, H-2), 4.31
(dd, J = 1.5, 5.5 Hz, 1 H, H-3), 4.25−4.22 (m, 1 H, H-4), 4.12−4.08
(m, 3 H, H-2″, H-2‴, H-4‴), 4.03−4.00 (m, 1 H, H-4″), 3.94−3.91
(m, 3 H, H-3″, H-3‴, H-5a), 3.87 (d, J = 3.0 Hz, 1 H, H-4′), 3.86−3.66
(m, 8 H, H-5b, H-5a″, H-5a‴, H-6a′, H-6b′, H-5b‴, H-5b″, H-5′), 3.56
(dd, J = 3.3, 10.5 Hz, 1 H, H-3′), 3.41 (s, 3 H, OCH3), 2.90 (dd, J =
8.0, 10.3 Hz, 1 H, H-2′); 13C NMR (125 MHz, D2O) δ = 107.4 (C-
1‴), 107.0(4), 107.0(3) (C-1, C-1″), 103.1 (C-1′), 86.0 (C-2), 84.1
(C-4″), 83.9 (C-4‴), 81.5 (C-4), 81.2, 81.1, 81.0 (C-2″, C-2‴, C-3),
76.7 (C-3″, C-3‴), 75.5 (C-5′), 72.3 (C-3′), 67.8 (C-4′), 66.2 (C-5),
61.2(0), 61.1(5), 61.0(6) (C-5″, C-5‴, C-6′), 54.7 (OCH3), 52.9 (C-
2′); HRESI-MS m/z [M + H+] calcd for C22H40NO17 590.2291, found
590.2288.
Methyl 2-O-(2-amino-2-deoxy-α-D-galactopyranosyl)-3,5-di-
O-(α-D-arabinofuranosyl)-α-D-arabinofuranoside (2). Compound
13 (74 mg, 0.12 mmol) was dissolved in H2O (4 mL) and
hydrogenolyzed over 10% Pd−C (20 mg) under 1 atm H2 at room
temperature for 2 h. Purification of the compound as described for 1
gave 2 (69 mg, 97%): [α]D +181.5 (c = 0.7, CH3OH); 1H NMR (600
MHz, D2O) δ = 5.20 (s, 1 H, H-1), 5.18 (d, J = 3.6 Hz, 1 H, H-1′),
5.12 (d, J = 1.2 Hz, 1 H, H-1″), 5.08 (d, J = 1.2 Hz, 1 H, H-1‴), 4.27−
4.25 (m, 1 H, H-4), 4.23−4.21 (m, 2 H, H-2, H-3), 4.12−4.07 (m, 3
H, H-2″, H-2‴, H-4‴), 4.04−4.01 (m, 1 H, H-4″), 3.96−3.91 (m, 5 H,
H-3″, H-3‴, H-4′, H-5′, H-5a), 3.85−3.80 (m, 3 H, H-5b, H-5a″, H-
5a‴), 3.75−3.68 (m, 5H, H-6a′, H-6b′, H-5b″, H-5b‴, H-3′), 3.40 (s, 3
H, OCH3), 3.21 (dd, J = 3.6, 10.5 Hz, 1 H, H-2′); 13C NMR (150
MHz, D2O) δ = 108.2 (C-1‴), 107.7, 107.6 (C-1″, C-1), 98.4 (C-1′),
86.1 (C-2), 85.0, 84.9(C-4″, C-4‴), 82.0(7) (C-4), 82.0(6), 81.9 (C-
2″, C-2‴), 81.3 (C-3), 77.5(1), 77.4(6) (C-3″, C-3‴), 72.9 (C-4′),
69.7 (C-3′), 69.2 (C-5′), 66.9 (C-5), 62.0(9), 62.0(7), 62.0(1) (C-5″,
C-5‴, C-6′), 55.5 (OCH3), 51.4 (C-2′); HRESI-MS m/z [M + Na+]
calcd for C22H39NO17Na 612.2110, found 612.2114.
Methyl 3,5-O-di-t-butylsilylene-α-D-arabinofuranoside (4).
To a solution of methyl glycoside 316 (1.49 g, 3.13 mmol) in a
mixture of CH2Cl2 (3 mL) and CH3OH (20 mL) was added a catalytic
amount of NaOCH3 (0.1 mL 10% in CH3OH). The reaction was
stirred for 4 h at room temperature and then neutralized by the
addition of Amberlite IR-120 (H+) resin. The resin was removed by
filtration through Celite, and the filtrate was concentrated. The
resulting residue was then dissolved in a mixture of CH2Cl2 (5 mL)
and DMF (22 mL) at 0 °C before 2,6-lutidine (1.45 mL, 4 equiv) and
di-t-butylsilyl bis(trifluoromethanesulfonate) (1.01 mL, 1.0 equiv)
were added. The mixture was stirred for 4 h at room temperature
before being diluted with CH2Cl2. The organic solution was washed
successively with water and brine and then dried (Na2SO4) and
concentrated. The residue was purified by chromatography on silica
gel (Hexane−EtOAc, 7:1 → 6:1) to afford 4 (800 mg, 84% over two
steps) as a white solid: Rf = 0.39 (Hexane−EtOAc, 4:1); [α]D +57.7 (c
= 0.7, CHCl3); 1H NMR (400 MHz, CDCl3) δ = 4.81 (d, J = 3.6 Hz, 1
H, H-1), 4.30−4.38 (m, 1 H, H-5a), 4.12 (dd, J = 3.6, 7.2 Hz, 1 H, H-
2), 4.00−3.89 (m, 3 H, H-3, H-4, H-5b), 3.42 (s, 3 H, OCH3), 1.06 (s,
9 H, C(CH3)3), 1.00 (s, 3 H, C(CH3)3); 13C NMR (100 MHz,
CDCl3) δ = 109.0 (C-1), 81.6 (C-2, C-3), 73.7 (C-4), 67.5 (C-5), 56.1
(OCH3), 27.4 (C(CH3)3), 27.1 (C(CH3)3), 22.6 (C(CH3)3), 20.1
(C(CH3)3); HRESI-MS m/z [M + Na+] calcd for C14H28O5SiNa
327.1598, found 327.1598.
EXPERIMENTAL SECTION
■
General Experimental Methods. All reagents were purchased
from commercial sources and were used without further purification
unless noted. Solvents used in reactions were purified by successive
passage through columns of alumina and copper under argon. Unless
stated otherwise, all reactions were carried out at room temperature
and under a positive pressure of argon and monitored by TLC on
Silica Gel G-25 F254 (0.25 mm). TLC spots were detected under UV
light and/or by charring with a solution of anisaldehyde in ethanol,
acetic acid and H2SO4. Column chromatography was performed on
silica gel 60 (40−60 μm). Iatrobeads refers to a beaded silica gel 6RS−
8060, which is manufactured by Iatron Laboratories (Tokyo). Organic
solutions were dried using anhydrous Na2SO4, and solvents were
evaporated under reduced pressure and below 50 °C (water bath) on a
1
rotary evaporator. H NMR were recorded at 400, 500, or 600 MHz,
and 13C NMR spectra were recorded at 100 or 125 MHz. H NMR
1
chemical shifts are referenced to CHCl3 (7.26, CDCl3) or H2O (4.79,
D2O). 13C NMR chemical shifts are referenced to CDCl3 (77.0,
CDCl3) or external acetone (31.07, D2O). 1H NMR data are reported
as though they were first order, and the peak assignments were made
on the basis of 2D-NMR (1H−1H COSY and HSQC) experiments.
Before recording the NMR spectra of 1 and 2, the pH of a D2O
solution of each compound was adjusted to pH 7.6 by the addition of a
solution of DCl in D2O. ESI-MS spectra (time-of-flight analyzer) were
9829
dx.doi.org/10.1021/jo301393s | J. Org. Chem. 2012, 77, 9826−9832

The Journal of Organic Chemistry
Note
Methyl 3,4,6-tri-O-acetyl-2-azido-2-deoxy-α/β-D-galactopyr-
anosyl-(1→2)-3,5-O-di-t-butylsilylene-α-D-arabinofuranoside
(6). Method A. A mixture of alcohol 4 (120 mg, 0.39 mmol), imidate
517 (282 mg, 1.5 equiv), and powdered 4 Å molecular sieves in
anhydrous Et2O (6 mL) was stirred at −20 °C under Ar for 30 min. A
solution of TMSOTf in Et2O (0.1 equiv) was added dropwise, the
solution was stirred at −20 °C for 2 h, and then Et3N was added. After
filtration of the mixture through Celite and concentration of the
filtrate, the residue was purified by chromatography (Hexane−EtOAc,
5:1) to give disaccharide 6 as an inseparable 11:1 α:β mixture (217 mg,
90%) as a white solid: Rf = 0.28 (Hexane−EtOAc, 4:1). A small
amount of unreacted acceptor 4 (4 mg, 3%) was also recovered. Data
(CO), 106.5 (C-1), 97.5 (C-1′), 87.1 (C-2), 85.0 (C-3), 75.5 (C-4),
68.3 (C-3′), 67.4 (C-4′), 67.3 (C-5′), 62.3 (C-5), 61.9 (C-6′), 57.4
(C-2′), 55.0 (OCH3), 20.7 (CH3CO), 20.6(2) (CH3CO), 20.5(8)
(CH3CO); HRESI-MS m/z [M + Na+] calcd for C18H27N3O12Na
500.1487, found 500.1486. Data for 8: [α]D +49.0 (c = 0.7, CHCl3);
1
IR (film) 3532, 2933, 2116, 1751, 1370, 1237, 1081, 1039 cm−1; H
NMR (500 MHz, CDCl3) δ = 5.30 (d, J = 3.0 Hz, 1 H, H-4′), 4.93
(dd, J = 2.0 Hz, 1 H, H-1), 4.75 (dd, J = 3.0, 11.0 Hz, 1 H, H-3′), 4.48
(d, J = 8.0 Hz, 1 H, H-1′), 4.26 (dd, J = 4.0, 12.5 Hz, 1 H, H-6a′),
4.10−4.20 (m, 1 H, H-3), 4.07−3.97 (m, 3 H, H-2, H-4, H-6b′), 3.92
(dd, J = 4.0, 8.5 Hz, 1 H, H-5′), 3.86 (dd, J = 2.5, 12.0 Hz, 1 H, H-5a),
3.76−3.67 (m, 2 H, H-2′, H-5b), 3.40 (s, 3 H, OCH3), 3.35 (d, J = 4.0
Hz, 1 H, OH3), 2.27 (brs, 1 H, OH5), 2.14, 2.05, 2.02 (3 s, 9 H, 3
CH3CO); 13C NMR (125 MHz, CDCl3) δ = 170.4 (CO), 170.0
(CO), 169.7 (CO), 107.0 (C-1), 102.7 (C-1′), 92.6 (C-2), 82.1
(C-4), 75.5 (C-3), 71.3 (C-5′), 70.6 (C-3′), 66.5 (C-4′), 62.3 (C-6′),
61.6 (C-5), 60.5 (C-2′), 55.6 (OCH3), 20.5(4) (CH3CO), 20.5(1)
(CH3CO); HRESI-MS m/z [M + Na+] calcd for C18H27N3O12Na
500.1487, found 500.1487.
1
for α-isomer: H NMR (600 MHz, CDCl3) δ = 5.46 (dd, J = 1.2, 3.0
Hz, 1 H, H-4′), 5.41 (d, J = 3.0 Hz, 1 H, H-1′), 5.35 (dd, J = 3.0, 11.4
Hz, 1 H, H-3′), 4.87 (d, J = 3.6 Hz, 1 H, H-1), 4.30−4.38 (m, 1 H, H-
5a), 4.24−4.28 (m, 1 H, H-5′), 4.20−4.11 (m, 3 H, H-6a′, H-2, H-3),
4.06 (dd, J = 7.2, 11.4 Hz, 1 H, H-6b′), 3.96−3.92 (m, 2 H, H-4, H-5b),
3.69 (dd, J = 3.0, 11.4 Hz, 1 H, H-2′), 3.42 (s, 3 H, OCH3), 2.14 (s, 3
H, CH3CO), 2.07 (s, 3 H, CH3CO), 2.06 (s, 3 H, CH3CO), 1.06 (s, 9
H, C(CH3)3), 0.99 (s, 9 H, C(CH3)3); 13C NMR (125 MHz, CDCl3)
δ = 170.0 (CO), 169.9 (CO), 106.9 (C-1), 97.4 (C-1′), 85.8 (C-
2), 81.0 (C-3), 73.6 (C-4), 67.9 (C-3′), 67.5 (C-4′), 67.4 (C-5), 66.9
(C-5′), 61.5 (C-6′), 57.3 (C-2′), 56.1 (OCH3), 27.3(6) (C(CH3)3),
27.3(1) (C(CH3)3), 27.0 (C(CH3)3), 22.6 (C(CH3)3), 20.6(5)
(CH3CO), 20.6(3) (CH3CO), 20.5(9) (CH3CO), 20.1 (C(CH3)3);
HRESI-MS m/z [M + Na+] calcd for C26H43N3O12SiNa 640.2508,
found 640.2507.
Methyl 2-O-(3,4,6-tri-O-acetyl-2-azido-2-deoxy-β-D-galacto-
pyranosyl)-3,5-di-O-(2,3,5-tri-O-benzoyl-α-D-arabinofurano-
syl)-α-D-arabinofuranoside (10). A suspension of diol 8 (72 mg,
0.15 mmol), thioglycoside donor 921 (206 mg, 2.4 equiv), and
powdered 4 Å molecular sieves in anhydrous CH2Cl2 (5 mL) was
stirred at −20 °C under Ar for 30 min. Then NIS (85 mg, 2.5 equiv)
and AgOTf (12 mg, 0.3 equiv) were added. After stirring for another 2
h at −20 °C, Et3N was added, the mixture was filtered through Celite,
and the filtrate was concentrated. The resulting residue was purified by
chromotography (Hexane−EtOAc, 2:1) to give 10 (192 mg, 94%) as a
white solid: Rf = 0.54 (Hexane−EtOAc, 1:1); [α]D +4.1 (c = 0.6,
CHCl3); IR (film) 2936, 2115, 1751, 1725, 1452, 1316, 1269, 1178,
Method B. A mixture of alcohol 4 (95 mg, 0.31 mmol), imidate 517
(243 mg, 1.6 equiv), and powdered 4 Å molecular sieves in anhydrous
CH3CN (10 mL) was stirred at −30 °C under Ar for 30 min. A
solution of TMSOTf in CH3CN (0.15 equiv) was added dropwise.
After stirring at −30 °C for 4 h, Et3N was added, and then the solution
was then filtered through Celite and concentrated. Purification of the
residue by chromatography (Hexane−EtOAc 5:1) gave disaccharide 6
as a 1:5 α:β ratio (136 mg, 71%) as a white solid: Rf = 0.28 (Hexane−
EtOAc, 4:1). Unreacted 4 (19 mg, 20%) was also recovered. Data for
β-isomer: 1H NMR (500 MHz, CDCl3) δ = 5.34 (dd, J = 1.0, 3.5 Hz, 1
H, H-4′), 4.92 (d, J = 3.0 Hz, 1 H, H-1), 4.82 (dd, J = 3.5, 11.0 Hz, 1
H, H-3′), 4.53 (d, J = 8.0 Hz, 1 H, H-1′), 4.30−4.38 (m, 1 H, H-5a),
4.22−4.10 (m, 4 H, H-2, H-3, H-6a′, H-6b′), 3.97−3.92 (m, 2 H, H-4,
H-5b), 3.88 (dt, J = 1.0, 7.0 Hz, 1 H, H-5′), 3.69 (dd, J = 8.0, 11.0 Hz,
1 H, H-2′), 3.41 (s, 3 H, OCH3), 2.16 (s, 3 H, 3 CH3CO), 2.06 (s, 3
H, 3 CH3CO), 2.02 (s, 3 H, 3 CH3CO), 1.06 (s, 9 H, C(CH3)3), 1.00
(s, 9 H, C(CH3)3); 13C NMR (125 MHz, CDCl3) δ = 170.2, 170.1,
107.7 (C-1), 101.6 (C-1′), 88.8 (C-2), 80.2 (C-3), 74.0 (C-4), 71.0
(C-3′), 70.8 (C-5′), 67.3 (C-5), 66.0 (C-4′), 60.9 (C-2′), 60.6 (C-6′),
56.0 (OCH3), 27.3(6) (C(CH3)3), 27.3(2) (C(CH3)3), 27.1(5)
(C(CH3)3), 27.1 (C(CH3)3), 27.0 (C(CH3)3), 22.6 (C(CH3)3),
20.6(5) (CH3CO), 20.6(3) (CH3CO), 20.6 (C(CH3)3).
Methyl 3,4,6-tri-O-acetyl-2-azido-2-deoxy-α-D-galactopyra-
nosyl-(1→2)-α-D-arabinofuranoside (7) and Methyl 3,4,6-tri-
O-acetyl-2-azido-2-deoxy-β-D-galactopyranosyl-(1→2)-α-D-ara-
binofuranoside (8). To a stirred solution of 6 (366 mg, 0.59 mmol,
synthesized via method A) in THF (10 mL) and pyridine (2 mL) was
added HF·pyridine (0.05 mL). After stirring overnight at room
temperature, a saturated aq solution of NaHCO3 was added, and the
mixture was extracted with EtOAc. The organic layer was washed with
HCl (1 N) and saturated aq NaHCO3 and then dried (Na2SO4). The
organic layer was filtered through filter funnel, and the filtrate was
concentrated to give a residue that was purified by chromatography
(toluene−CH3OH, 25:1) to afford 7 (200 mg, 71%) and 8 (18 mg,
6%) both as white foams. Data for 7: [α]D +135.0 (c = 0.9, CHCl3); IR
(film) 3468, 2937, 2113, 1751, 1373, 1231, 1080, 1034 cm−1; 1H NMR
(500 MHz, CDCl3) δ = 5.45 (d, J = 3.0 Hz, 1 H, H-4′), 5.28 (dd, J =
3.0, 11.0 Hz, 1 H, H-3′), 5.19 (d, J = 3.5 Hz, 1 H, H-1′), 5.03 (s, 1 H,
H-1), 4.15−4.40 (m, 1 H, H-5′), 4.14 (dd, J = 6.0, 11.5 Hz, 1 H, H-
6a′), 4.13−4.03 (m, 4 H, H-2, H-3, H-4, H-6b′), 3.84 (dd, J = 4.0, 12.0
Hz, 1 H, H-5a), 3.78−3.72 (m, 2 H, H-2′, H-5b), 3.42 (s, 3 H, OCH3),
2.15 (s, 3 H, 3 CH3CO), 2.08 (s, 3 H, 3 CH3CO), 2.06 (s, 3 H, 3
CH3CO); 13C NMR (125 MHz, CDCl3) δ = 170.7 (CO), 170.0
1
1111, 1071, 1027, 757, 712 cm−1. H NMR (600 MHz, CDCl3) δ =
8.10−7.94 (m, 12 H), 7.62−7.35 (m, 14 H), 7.31−7.21 (m, 4 H),
5.59−5.55 (m, 3 H, H-3″, H-3‴, H-2‴), 5.52 (d, J = 1.2 Hz, 1 H, H-
2″), 5.49 (s, 1 H, H-1″), 5.37 (s, 1 H, H-1‴), 5.26 (dd, J = 0.6, 3.0 Hz,
1 H, H-4′), 5.04 (s, 1 H, H-1), 4.82 (dd, J = 3.0, 12.0 Hz, 1 H, H-5a″),
4.80 (dd, J = 3.0, 11.4 Hz, 1 H, H-3′), 4.75 (dd, J = 3.6, 11.4 Hz, 1 H,
H-5a‴), 3.70−3.60 (m, 4 H, H-5b″, H-5b‴, H-4″, H-4‴), 4.57 (d, J =
8.4 Hz, 1 H, H-1′), 4.51−4.48 (m, 2 H, H-2, H-3), 4.28−4.32 (m, 1 H,
H-4), 4.08−4.02 (m, 2 H, H-5a, H-6a′), 3.99 (dd, J = 6.0, 11.4 Hz, 1 H,
H-6b′), 3.92 (dd, J = 2.4, 11.4 Hz, 1 H, H-5b), 3.88 (dt, J = 1.2, 6.0 Hz,
1 H, H-5′), 3.67 (dd, J = 8.4, 11.4 Hz, 1 H, H-2′), 3.38 (s, 3 H,
OCH3), 2.13, 2.02 (s, 3 H, CH3CO), 2.00 (s, 3 H, CH3CO), 1.89 (s, 3
H, CH3CO); 13C NMR (100 MHz, CDCl3) δ = 170.0 (CO), 169.7
(CO), 166.2 (CO), 166.0 (CO), 165.7 (CO), 165.6 (C
O), 165.3 (CO), 133.6(2) (Ar), 133.5(6) (Ar), 133.4(4) (Ar),
133.3(7) (Ar), 133.0(7) (Ar), 129.9(5) (Ar), 129.8(5) (Ar), 129.7(8)
(Ar), 129.7(5) (Ar), 129.7(1) (Ar), 129.6(9) (Ar), 129.6 (Ar), 129.2,
129.1 (Ar), 129.0 (Ar), 128.8 (Ar), 128.6 (Ar), 128.5 (Ar), 128.4 (Ar),
128.3 (Ar), 128.2 (Ar), 107.2 (C-1), 105.6, 105.4 (C-1″, C-1‴), 102.1
(C-1′), 88.9 (C-2), 81.9, 81.8 (C-2″, C-3), 81.5(3), 81.4(6) (C-4, C-
4″, C-4‴), 80.7 (C-2‴), 77.8, 77.5 (C-3″, C-3‴), 70.8(4), 70.8(0) (C-
3′, C-5′), 66.1 (C-4′), 66.0 (C-5), 63.7, 63.6 (C-5″, C-5‴), 60.9 (C-
6′), 60.7 (C-2′), 54.9 (OCH3), 20.6 (CH3CO), 20.4 (CH3CO);
HRESI-MS m/z [M + Na+] calcd for C70H67N3O26Na 1388.3905,
found 1388.3906.
Methyl 2-O-(3,4,6-tri-O-acetyl-2-azido-2-deoxy-α-D-galacto-
pyranosyl)-3,5-di-O-(2,3,5-tri-O-benzoyl-α-D-arabinofurano-
syl)-α-D-arabinofuranoside (11). A suspension of diol 7 (48.6 mg,
0.1 mmol), thioglycoside donor 921 (133 mg, 2.3 equiv), and
powdered 4 Å molecular sieves in anhydrous CH2Cl2 (3 mL) was
stirred at −25 °C under Ar for 30 min. Then, NIS (55 mg, 2.4 equiv)
and AgOTf (8 mg, 0.3 equiv) were added, and the mixture was stirred
for another 2 h at −25 °C. The addition of Et3N was followed by
filtration through Celite, and the filtrate was concentrated. The
resulting residue was purified by chromatography (Hexane−EtOAc,
2:1) to give 11 (130 mg, 94%) as a white solid: Rf = 0.47 (Hexane−
EtOAc, 1:1); [α]D +44.9 (c = 0.8, CHCl3); IR (film) 2938, 2112, 1724,
1
1269, 1111, 1071, 1028, 712 cm−1. H NMR (600 MHz, CDCl3) δ =
8.10−7.94 (m, 12 H), 7.64−7.34 (m, 14 H), 7.31−7.22 (m, 4 H),
9830
dx.doi.org/10.1021/jo301393s | J. Org. Chem. 2012, 77, 9826−9832

The Journal of Organic Chemistry
Note
5.62−5.57 (m, 3 H, H-3″, H-3‴, H-2‴), 5.53 (s, 1 H, H-2″), 5.51 (s, 1
H, H-1‴), 5.46 (d, J = 3.0 Hz, 1 H, H-4′), 5.37−5.28 (m, 3 H, H-1″,
H-3′, H-1′), 5.01 (d, J = 1.2 Hz, 1 H, H-1), 4.80 (dd, J = 3.0, 12.0 Hz,
1 H, H-5a‴), 4.72−4.76 (m, 1 H, H-5a″), 4.68−4.62 (m, 4 H, H-4″, H-
4‴, H-5b″, H-5b‴), 4.37 (dd, J = 3.6, 6.6 Hz, 1 H, H-3), 4.32−4.34 (m,
1 H, H-2), 4.28−4.32 (m, 1 H, H-5′), 4.24−4.27 (m, 1 H, H-4), 4.13
(dd, J = 6.0, 11.4 Hz, 1 H, H-6a′), 4.10−4.02 (m, 2 H, H-5a, H-6b′),
3.90 (dd, J = 2.4, 11.4 Hz, 1 H, H-5b), 3.73 (dd, J = 2.4, 10.8 Hz, 1 H,
H-2′), 3.38 (s, 3 H, OCH3), 2.13 (s, 3 H, 3 CH3CO), 2.02 (s, 3 H, 3
CH3CO), 1.96 (s, 3 H, 3 CH3CO); 13C NMR (125 MHz, CDCl3) δ =
170.0 (CO), 169.5 (CO), 166.2 (CO), 166.0 (CO), 165.7
(CO), 165.6 (CO), 165.4 (CO), 165.3 (CO), 133.6 (Ar),
133.4 (Ar), 133.3 (Ar), 133.0(4 (Ar), 132.9(6) (Ar), 129.9 (Ar), 129.8
(Ar), 129.7(6) (Ar), 129.7(2) (Ar), 129.6(8) (Ar), 129.6 (Ar), 129.2
(Ar), 129.1 (Ar), 129.0 (Ar), 128.9 (Ar), 128.5(4) (Ar), 128.4(9)
(Ar), 128.4(6) (Ar), 128.3(5) (Ar), 128.2(9) (Ar), 128.2 (Ar), 106.3
(C-1), 105.9, 105.8 (C-1″, C-1‴), 97.8 (C-1′), 87.6 (C-2), 82.2, 81.9
(C-2″, C-2‴), 81.4, 81.3(2), 81.2(9) (C-3, C-4″, C-4‴), 79.6 (C-4),
77.7, 77.5 (C-3″, C-3‴), 68.6 (C-3′), 67.5 (C-4′), 67.2 (C-5′), 66.1
(C-5), 63.7 (C-5″, C-5‴), 61.7 (C-6′), 57.5 (C-2′), 55.1 (OCH3), 20.6
(CH3CO), 20.5 (CH3CO); HRESI-MS m/z [M + Na+] calcd for
C70H67N3O26Na 1388.3905, found 1388.3894.
Methyl 2-O-(2-azido-2-deoxy-β-D-galactopyranosyl)-3,5-di-
O-(α-D-arabinofuranosyl)-α-D-arabinofuranoside (12). A solu-
tion of 10 (192 mg) in CH2Cl2 (2 mL) and CH3OH (3 mL) was
treated with catalytic amount NaOCH3 solution (1 M in CH3OH, 0.1
mL) under Ar at room temperature. After stirring overnight at room
temperature, the mixture was neutralized by the addition of Amberlite
IR-120 (H+) resin. After filtration and concentration, the residue was
purified by chromatography on Iatrobeads (CH2Cl2−CH3OH 4:1) to
give 12 (67 mg, 78%) as an oil: Rf = 0.46 (CH2Cl2−CH3OH, 3:1);
[α]D +72.8 (c = 0.4, CH3OH); IR (film) 3349, 2938, 2118, 1606,
1078, 1036 cm−1; 1H NMR (500 MHz, D2O) δ = 5.23 (d, J = 1.5 Hz,
1 H, H-1″), 5.16 (s, 1 H, H-1), 5.08 (d, J = 1.5 Hz, 1 H, H-1‴), 4.64
(d, J = 7.5 Hz, 1 H, H-1′), 4.45 (d, J = 1.0 Hz, 1 H, H-2), 4.33 (dd, J =
1.0, 5.5 Hz, 1 H, H-3), 4.24−4.30 (m, 1 H, H-4), 4.13 (dd, J = 1.5, 3.5
Hz, 1 H, H-2‴), 4.12 (dd, J = 1.5, 3.0 Hz, 1 H, H-2″), 4.08−4.11 (m, 1
H, H-4‴), 4.01−4.06 (m, 1 H, H-4″), 3.97−3.90 (m, 4 H, H-3″, H-3‴,
H-4′, H-5a), 3.87−3.64 (m, 8 H, H-5b, H-5a″, H-5a‴, H-6a′, H-6b′, H-
5b‴, H-5b″, H-5′), 3.61 (dd, J = 3.5, 10.5 Hz, 1 H, H-3′), 3.54 (dd, J =
7.5, 10.5 Hz, 1 H, H-2′), 3.43 (s, 3 H, OCH3); 13C NMR (125 MHz,
D2O) δ = 108.3 (C-1‴), 108.0 (C-1″), 107.9 (C-1), 102.7 (C-1′), 87.0
(C-2), 84.9, 84.7 (C-4″, C-4‴), 82.5 (C-4), 82.0 (C-2″, C-2‴, C-3),
77.6, 77.5 (C-3″, C-3‴), 76.2 (C-5′), 72.1 (C-3′), 69.7 (C-4′), 67.2
(C-5), 64.2 (C-2′), 62.0(4), 62.0, 61.7 (C-5″, C-5‴, C-6′), 55.6
(OCH3); HRESI-MS m/z [M + Na+] calcd for C22H37N3O17Na
638.2015, found 638.2019.
60.4 (C-2′), 55.6 (OCH3); HRESI-MS m/z [M + Na+] calcd for
C22H37N3O17Na 638.2015, found 638.2018.
ASSOCIATED CONTENT
■
S
* Supporting Information
1H and 13C NMR spectra of new compounds and the HSQC
spectrum of the polysaccharide. This material is available free of
charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: tlowary@ualberta.ca.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the Alberta Glycomics Centre, the
University of Alberta and the Natural Sciences and Engineering
Research Council of Canada. We thank Dr. Christopher D.
Rithner at Colorado State University for providing the NMR
data for the GalN-containing polysaccharide. Dr. M.R. Richards
is thanked for assistance in generating Figure 2.
REFERENCES
■
(1) Tuberculosis, World Health Organization Fact Sheet Number
104, 2012. http://www.who.int/mediacentre/factsheets/fs104/en/
index.html (accessed Oct 13, 2012).
(2) Albanna, A. S.; Menzies, D. Drugs 2011, 71, 815.
(3) Kaur, D.; Guerin, M. E.; Skovierova, H.; Brennan, P. J.; Jackson,
M. Adv. Appl. Microbiol. 2009, 69, 23.
(4) Mishra, A. K.; Driessen, N. N.; Appelmelk, B. J.; Besra, G. S.
FEMS Microbiol. Rev. 2011, 35, 1126.
(5) Draper, P.; Khoo, K. H.; Chatterjee, D.; Dell, A.; Morris, H. R.
Biochem. J. 1997, 327, 519.
(6) Bhamidi, S.; Scherman, M. S.; Rithner, C. D.; Prenni, J. E.;
Chatterjee, D.; Khoo, K. H.; McNeil, M. R. J. Biol. Chem. 2008, 283,
12992.
(7) Acharya, P. V.; Goldman, D. S. J. Bacteriol. 1970, 102, 733.
(8) Wang, X.; Ribeiro, A. A.; Guan, Z.; McGrath, S. C.; Cotter, R. J.;
Raetz, C. R. H. Biochemistry 2006, 45, 14427.
(9) Phillips, N. J.; Schilling, B.; McLendon, M. K.; Apicella, M. A.;
Gibson, B. W. Infect. Immun. 2004, 72, 5340.
(10) Sonesson, A.; Jantzen, E.; Tangen, T.; Zahringer, U.
Microbiology 1994, 140, 2663.
Methyl 2-O-(2-azido-2-deoxy-α-D-galactopyranosyl)-3,5-di-
O-(α-D-arabinofuranosyl)-α-D-arabinofuranoside (13). A solu-
tion of 11 (178 mg, 0.13 mmol) in CH2Cl2 (2 mL) and CH3OH (10
mL) was treated with a catalytic amount of NaOCH3 solution (1 M in
CH3OH, 0.1 mL). After stirring overnight at room temperature, the
solution was neutralized by the addition of Amberlite IR-120 (H+)
resin. After filteration through Celite and concentration of the filtrate,
the resulting residue was purified by chromatography on Iatrobeads
(CH2Cl2−CH3OH, 4:1) to give 13 (77 mg, 96%) as an oil: Rf = 0.48
(CH2Cl2−CH3OH, 3:1); [α]D +186.8 (c = 0.9, CH3OH); IR (film)
3380, 2931, 2112, 1643, 1451, 1413, 1318, 1230, 1038 cm−1; 1H NMR
(600 MHz, D2O) δ = 5.27 (d, J = 3.0 Hz, 1 H, H-1′), 5.19 (s, 1 H, H-
1), 5.18 (d, J = 0.6 Hz, 1 H, H-1″), 5.09 (d, J = 1.8 Hz, 1 H, H-1‴),
4.30−4.25 (m, 3 H, H-4, H-3, H-2), 4.15−4.13 (m, 2 H, H-2″, H-2‴),
4.09−4.11 (m, 1 H, H-4‴), 4.08−4.03 (m, 3 H, H-3′, H-4′, H-4″),
3.98−3.94 (m, 4 H, H-3″, H-3‴, H-5′, H-5a), 3.88−3.82 (m, 3 H, H-
5b, H-5a″, H-5a‴), 3.78−3.71 (m, 4 H, H-5b″, H-5b‴, H-6a′, H-6b′),
3.61 (dd, J = 3.6, 10.8 Hz, 1 H, H-2′), 3.42 (s, 3 H, OCH3); 13C NMR
(100 MHz, D2O) δ = 108.2 (C-1‴), 108.0 (C-1″), 107.6 (C-1), 98.6
(C-1′), 86.3 (C-2), 84.9 (C-4″), 84.6 (C-4‴), 82.1, 82.0 (C-4, C-2″, C-
2‴), 81.4 (C-3), 77.5, 77.4 (C-3″, C-3‴), 72.7 (C-5′), 69.7 (C-4′),
68.4 (C-3′), 67.1 (C-5), 62.0, 61.9(8), 61.9(4) (C-5″, C-5‴, C-6′),
(11) Beer, W.; Adam, M.; Seltmann, G. J. Basic Microbiol. 1986, 26,
201.
(12) Pfannenstiel, M. A.; Muthukumar, G.; Couche, G. A.;
Nickerson, K. W. J. Bacteriol. 1987, 169, 796.
(13) Skovierova, H.; Larrouy-Maumus, G.; Pham, H.; Belanova, M.;
Barilone, N.; Dasgupta, A.; Mikusova, K.; Gicquel, B.; Gilleron, M.;
Brennan, P. J.; Puzo, G.; Nigou, J.; Jackson, M. J. Biol. Chem. 2010,
285, 41348.
(14) Wang, X.; Ribeiro, A. A.; Guan, Z.; Raetz, C. R. H. Biochemistry
2009, 48, 1162.
(15) Song, F.; Guan, Z.; Raetz, C. R. H. Biochemistry 2009, 48, 1173.
(16) Callam, C. S.; Lowary, T. L. J. Chem. Educ. 2001, 78, 73.
(17) Grundler, G.; Schmidt, R. R. Liebigs Ann. 1984, 1826.
(18) Demchenko, A.; Stauch, T.; Boons, G. J. Synlett 1997, 1997,
818.
(19) Braccini, I.; Derouet, C.; Esnault, J.; Herve Du Penhoat, C.;
Mallet, J. M.; Michon, V.; Sinay, P. Carbohydr. Res. 1993, 246, 23.
(20) This yield shown in Scheme 1 is that obtained starting with the
mixture of 6 enriched in the α-isomer. The products could be obtained
in comparable yield from the mixture of 6 enriched in the β-isomer.
(21) Callam, C. S.; Gadikota, R. R.; Lowary, T. L. J. Org. Chem. 2001,
66, 4549.
9831
dx.doi.org/10.1021/jo301393s | J. Org. Chem. 2012, 77, 9826−9832

The Journal of Organic Chemistry
Note
(22) Konradsson, P.; Udodong, U. E.; Fraser-Reid, B. Tetrahedron
Lett. 1990, 31, 4313.
(23) Mizutani, K.; Kasai, R.; Nakamura, M.; Tanaka, O.; Matsuura,
H. Carbohydr. Res. 1989, 185, 27.
(24) Lee, R.; Li, W.; Chatterjee, D.; Lee, R. Glycobiology 2005, 15,
139.
(25) Bongat, A. F. G.; Demchenko, A. V. Carbohydr. Res. 2007, 342,
374.
(26) Kerns, R. J.; Zha, C.; Benakli, K.; Liang, Y. Z. Tetrahedron Lett.
2003, 44, 8069.
(27) Boysen, M.; Gemma, E.; Lahmann, M.; Oscarson, S. Chem.
Commun. 2005, 3044.
(28) Geng, Y.; Zhang, L. H.; Ye, X. S. Tetrahedron 2008, 64, 4949.
(29) Manabe, S.; Ishii, K.; Ito, Y. J. Am. Chem. Soc. 2006, 128, 10666.
(30) Manabe, S.; Ishii, K.; Ito, Y. Eur. J. Org. Chem. 2011, 497.
(31) Nokami, T.; Shibuya, A.; Saigusa, Y.; Manabe, S.; Ito, Y.;
Yoshida, J. I. Beilstein J. Org. Chem. 2012, 8, 456.
(32) Mensah, E. A.; Nguyen, H. M. J. Am. Chem. Soc. 2009, 131,
8778.
(33) Mensah, E. A.; Yu, F.; Nguyen, H. M. J. Am. Chem. Soc. 2010,
132, 14288.
9832
dx.doi.org/10.1021/jo301393s | J. Org. Chem. 2012, 77, 9826−9832