An efficient synthesis of derivatives of 2-acetamido-4-amino-2,4,6- trideoxy-D-galactopyranose

Article abstract of DOI:10.1081/CAR-120030468

Methyl 2-acetamido-4-amino-2,4,6-trideoxy-α-D-galactopyranoside (10) was synthesized from D-glucosamine hydrochloride in eight steps in an overall yield of 31%. Key steps include the selective benzoylation at O-3 of methyl 2-acetamido-2,6-dideoxy-α-D-glucopyranoside in 89% yield and the subsequent Mitsunobu reaction using diphenylphosphoryl azide as the azide source which proceeded in 92% yield. Di- and mono-benzyloxycarbonyl derivatives of 10 were also prepared. Copyright

Full text of DOI:10.1081/CAR-120030468

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An Efficient Synthesis of Derivatives of
2‐Acetamido‐4‐amino‐2,4,6‐trideoxy‐D‐galactopyranose
Hong Liang a & T. Bruce Grindley a
a Department of Chemistry, Dalhousie University, Halifax, Nova Scotia, Canada, B3H 4J3
Published online: 18 Aug 2006.
To cite this article: Hong Liang & T. Bruce Grindley (2004): An Efficient Synthesis of Derivatives of
2‐Acetamido‐4‐amino‐2,4,6‐trideoxy‐D‐galactopyranose, Journal of Carbohydrate Chemistry, 23:2-3, 71-82
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JOURNAL OF CARBOHYDRATE CHEMISTRY
Vol. 23, Nos. 2 & 3, pp. 71–82, 2004
An Efficient Synthesis of Derivatives of
2-Acetamido-4-amino-2,4,6-trideoxy-
D-galactopyranose#
*
Hong Liang and T. Bruce Grindley
Department of Chemistry, Dalhousie University,
Halifax, Nova Scotia, Canada
ABSTRACT
Methyl 2-acetamido-4-amino-2,4,6-trideoxy-a-D-galactopyranoside (10) was synthe-
sized from D-glucosamine hydrochloride in eight steps in an overall yield of
31%. Key steps include the selective benzoylation at O-3 of methyl 2-acetamido-
2,6-dideoxy-a-D-glucopyranoside in 89% yield and the subsequent Mitsunobu
reaction using diphenylphosphoryl azide as the azide source which proceeded
in 92% yield. Di- and mono-benzyloxycarbonyl derivatives of 10 were also
prepared.
Key Words: Mitsunobu reaction; 2-Acetamido-4-amino-2,4,6-trideoxy-D-galacto-
pyranose; Selective benzoylation; C-polysaccharide.
#
´
Dedicated to Professor Gerard Descotes on the occasion of his 70th birthday.
*
Correspondence: T. Bruce Grindley, Department of Chemistry, Dalhousie University, Halifax, NS,
Canada B3H 4J3; E-mail: bruce.grindley@dal.ca.
71
DOI: 10.1081/CAR-120030468
0732-8303 (Print); 1532-2327 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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Liang and Grindley
INTRODUCTION
2-Acetamido-4-amino-2,4,6-trideoxy-D-galactopyranose (1), commonly abbreviated
as AAT, is present at the cell surface of a number of bacterial polysaccharides. The
O-specific side chains of the phase I lipopolysaccharide of the Gram-negative bacteria
Shigella sonnei[1] consist of repeating units of AAT b-linked to O-4 of 2-amino-L-altruronic
acid [!3)-b-AATp-(1!4)-a-L-AltpA-(1!]. a-Linked AAT occurs in capsules of
the Gram-positive bacteriae Streptococcus pneumoniae,[2,3] Streptococcus mitis,[4] and
Bacteroides fragilis.[5,6] In S. pneumoniae, it is one of three sugars constituting the
repeating unit [!4)-a-GalpA-(1!3)-a-GalpA-(1!3)-a-AATp-(1!] of the capsular
polysaccharide of serotype 1[2,7] and it is also one of five sugars in the repeating unit of
the C-polysaccharide, which, with slight structural variations, is common to all 90 serotypes
of S. pneumoniae.[3,8,9] The C-polysaccharide is also present in some biovars of the closely
related bacterium, S. mitis.[4] The capsule of B. fragilis contains two polysaccharides, of
which the one containing AAT has the following repeating unit: [!3)-a-AATp-
(1!4)[b-D-Galf-(1!3)]-a-D-GalpNAc-(1!3)-b-D-Galp-(1!].[5]
It was recently discovered that zwitterionic polysaccharides containing ammonium
ions are potent T-cell activators.[10–13] All of the AAT-containing polysaccharides also
have acidic groups in their structures: carboxylates, phosphonates, or sulfates.[13] The
free amino group present in AAT will be present as an ammonium ion at physiological
pHs. Thus, these AAT-containing polysaccharides have potential promise as immuno-
stimulants and an efficient synthesis of AAT derivatives is highly desirable.
Previous syntheses of analogs of AAT are described as follows. The first report, the
synthesis of the 4-acetamido derivative, in 1984 by Liav et al.,[14,15] proceeded from
N-acetyl-D-glucosamine via benzyl 2-acetamido-3-O-benzyl-4-O-methanesulfonyl-2,6-
dideoxy-a-D-glucopyranoside in 12 steps and 4% overall yield. Methyl 2-acetamido-4-
azido-2,4,6-trideoxy-a-D-galactopyranoside (2) was synthesized in six steps with an overall
yield of 18% starting from methyl 2-acetamido-4,6-benzylidene-a-D-glucopyranoside by
[16]
¨
¨
Lonn and Lonngren.
Medgyes et al. used 11 steps to obtain 2-acetamido-4-azido-
2,4,6-trideoxy-b-D-glucopyranoside in 11% yield starting from ethyl 3-O-acetyl-2-deoxy-
4,6-O-isopropylidene-2-phthalimido-1-thio-b-D-glucopyranoside.[17] This latter compound
can be prepared in five steps from D-glucosamine hydrochloride.[18] Van Boom’s
group[19] prepared benzyl 2,4-diacetamido-2,4,6-trideoxy-a/b-D-galactopyranoside from
1,6-anhydro-2,3-O-(4-methoxybenzylidene)-b-D-mannopyranose in 12 steps with an
overall yield of 4%.
We needed AAT for the synthesis of the pentasaccharide repeating unit of the C-poly-
saccharide of S. pneumoniae. None of the literature syntheses appeared to be scalable
to produce the large amounts required to prepare the pentasaccharide. It was therefore

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73
necessary to devise a short and efficient method from a readily available, cheap starting
material. This paper describes such a route to methyl 2-acetamido-4-amino-2,4,6-tri-
deoxy-a-D-galactopyranoside (10) and derivatives. Compound 10 was obtained here in
eight steps from D-glucosamine hydrochloride in an overall yield of 31%, considerably
better than that obtained with the previously available methods.
RESULTS AND DISCUSSION
D-Glucosamine hydrochloride (3) was converted into methyl 2-acetamido-6-bromo-
2,6-dideoxy-a-D-glucopyranoside (4) largely using the method of Galemno et al.
(Sch. 1).[20] However, it was found that the yield in the replacement of HO-6 by bromine
Scheme 1. Synthesis of methyl 2-acetamido-4-azido-2,4,6-trideoxy-a-D-galactopyranoside (2).

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Liang and Grindley
Scheme 2. Mitsunobu reaction on compound 5.
using two equivalents of triphenylphosphine and one of carbon tetrabromide was some-
what higher (60% vs. 46%) if the reaction was performed at 30–358C for 5 hr rather
than 60–658C for 30 min. It was also essential to recrystallize the carbon tetrabromide
to obtain good yields. An alternative method used triphenylphosphine and N-bromosucci-
nimide for the same transformation of 4.[21] Hydrogenolysis of the bromide to give the
6-deoxy compound 5 was conveniently performed in quantitative yield using 10% Pd/
C and atmospheric pressure hydrogen. Either wet (Degussa type) or dry 10% Pd/C was
found to be equally effective. The key step in the synthesis of 2 was the discovery that
this product (5) could be benzoylated regioselectively at O-3 at 2358C in pyridine in
excellent yield (89%). Wang and Lee had noted earlier that the main product of the
reaction of methyl 2-acetamido-2-deoxy-a-D-glucopyranoside with benzoyl chloride in
pyridine at 2608C was 3,6-di-O-benzoate,[22] similar to the excellent regioselectivity
obtained here for substitution at O-3 in preference to O-4. Introduction of the azide group
at O-4 with inversion of configuration to give the 4-azidogalactose derivative 7 in 92%
yield was conveniently performed using a Mitsunobu reaction with diphenylphosphoryl
azide[23] as the azide donor. The zinc azide–pyridine complex[24] was ineffective as an
azide donor here.
An initial attempt to perform the Mitsunobu reaction on 5 directly, that relied on the
axial glycosidic group to inhibit displacement at C-3,[25] gave one azide-containing pro-
duct, tentatively identified as methyl 2-acetamido-4-azido-2,4,6-trideoxy-a-D-glucopyra-
noside (8), in low yield (Sch. 2). Since Brandstetter and Zbiral had obtained methyl
4-azido-2,6-di-t-butyldimethylsilyl-4-deoxy-a-D-galactopyranoside by reaction of methyl
2,6-di-t-butyldimethylsilyl-a-D-glucopyranoside with triphenylphosphine, diethylazodi-
carboxylate, and hydrogen azide in 72% yield,[26] the result obtained here in the reaction
on 5 was surprising. Compound 8 could have come from a double inversion process, per-
haps via the 3,4-epoxide having the galacto configuration. Epoxides have been observed
as intermediates and products in Mitsunobu reactions on pyranoside diols and poly-
ols.[27,28] However, in this case, diequatorial opening of the azide is required to give the
regiochemistry observed. Alternatively, it could have arisen by nucleophilic displacement
at C-4 of a 3,4-oxyphosphonium intermediate with retention, displacement from the
b-face being hindered by the large 3-oxyphosphonium group.a
Reduction of compound 7 with hydrogen over 10% Pd/C directly followed by
N-acetylation and O-deacylation gave a mixture of the diacetamido-(9) and the 2-aceta-
mido-4-benzamido-(9a) derivatives (Sch. 3). The latter product results from O- to
N-migration of the benzoyl group after reduction but before N-acetylation. Deacylation
aWe thank a referee for discussion of this point.

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75
Scheme 3. Synthesis of 10 and derivatives thereof.
of 7 gave compound 2 that could be reduced to methyl 2-acetamido-4-amino-2,4,6-tri-
deoxy-a-D-galactopyranoside (10). Compound 10 could be differentially protected as
the 4-N-benzyloxycarbonyl derivative (11) or fully protected as the 3-O-,4-N-bisbenzylox-
ycarbonyl derivative (12).
To our knowledge, this eight-step synthesis of 10 from commercially available
D-glucosamine hydrochloride is the shortest and highest yielding to date. In addition, a
number of derivatives, such as the differentially protected 11, were prepared.
EXPERIMENTAL
General Methods
Melting points were determined with a Fisher–Johns melting point apparatus and are
1
uncorrected. H and 13C NMR spectra were recorded at 300 K in 5 mm NMR tubes on
Bruker AC-250 MHz or AMX-400 NMR spectrometers operating at 250.13 or 400.13 MHz
and 62.9 or 100.08 MHz, respectively, on solutions in chloroform-d, unless otherwise
indicated. Chemical shifts are given in parts per million (ppm) (+0.01 ppm) relative to
1
that of tetramethylsilane (TMS) (0.00 ppm) in the case of H NMR spectra, and to the
central line of chloroform-d (d 77.16) for the 13C NMR spectra. All assignments were con-

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Liang and Grindley
firmed by COSY, HETCOR, HMQC, or HMBC experiments. Exact masses measured
using electron ionization (EI) (70 eV) were done on a CEC 21-110B mass spectrometer.
Electrospray mass spectra were recorded on a Fisons Quattro mass spectrometer with a
Quattro source (cone voltage: 55 V, flow rate: 5 mL/min, complexing agent: potassium
acetate, solvent: 75 : 25 v/v acetonitrile/water). Pyridine was dried by refluxing over cal-
cium hydride for 12 hr, followed by distillation. Dichloromethane was refluxed over cal-
cium hydride for 1 hr, then distilled. Chloroform was dried with magnesium sulfate, then
˚
distilled and stored over 4 A molecular sieves. TLC was performed on aluminum-backed
plates bearing 200 mm silica gel 60 F254 (Merck) or 250 mm ultra pure silica gel (Silicycle
Inc., Quebec City, Canada). Compounds were visualized by UV where applicable and/or
were located by spraying with a solution of 2% ceric sulfate in 1 M sulfuric acid followed
by heating on a hot plate until color developed. Compounds were purified on 230–240
mesh ultra pure silica gel (Silicycle Inc., Quebec City, Canada) by flash chromatography
using specified eluents. Elemental analyses were performed by the Canadian Microana-
lytical Service, Delta, BC.
Methyl 2-acetamido-6-bromo-2,6-dideoxy-a-D-glucopyranoside (4). A suspen-
sion of 2-acetamido-2-deoxy-a-D-glucopyranose[29] (20.52 g, 92.8 mmol) and dry Amber-
lite IR-120 (Hþ form) resin (20.5 g) in dry methanol (600 mL) was refluxed for 14 hr. The
resin was removed, and washed with methanol (3 ꢀ 60 mL). The combined solutions
were concentrated to give a solid residue of methyl 2-acetamido-2-deoxy-a-D-glucopyra-
noside (19.00 g, 87%). From 13C NMR spectral peak heights, this product was an approxi-
mately 6 : 1 ratio of a to b products. 13C NMR (D2O) d: 100.9 (Cb-1), 100.3 (Ca-1),
74.4 (Ca-5), 73.9 (Ca-3), 72.8 (Ca-4), 63.4 (Ca-6), 57.9 (OCH3), 56.4 (Ca-2), 24.7
(COCH3).
Part of the anomeric mixture from above (11.75 g, 50 mmol) was added to a sol-
ution of triphenylphosphine (26.0 g, 100 mmol) in pyridine (250 mL). Carbon tetrabro-
mide (17.5 g, 55 mmol, recrystallized from ethanol) was added at 08C, and the solution
was stirred at 30–358C for 5 hr, then concentrated. Azeotropic removal of pyridine with
toluene gave a yellow solid that was purified by column chromatography using 30 : 1
(v/v) ethyl acetate–methanol as the eluent. Compound 4 was obtained as a colorless
powder that was recrystallized from methanol–chloroform–hexane to give colorless
needles: yield 6.65 g. Chromatographic separation of the mother liquor gave an
additional 2.30 g, total yield 8.95 g (60%); m.p. 173–1748C, lit.[20] 175–1768C; 1H
NMR d: 5.95 (d, 1H, JNH,2 ¼ 7.3 Hz, NH), 4.72 (d, 1H, J1,2 ¼ 3.7 Hz, H-1), 4.01
(m, 1H, H-2), 3.80–3.50 (complex m, 5H, H-3, H-4, H-5, H-6, H-60), 3.45 (s, 3H,
1
OCH3), 2.08 (s, 3H, COCH3); H NMR (DMSO-d6) d: 7.80 (d, 1H, JNH,2 ¼ 9.6 Hz,
NH), 5.35 (s, 1H, OH-4), 4.88 (s, 1H, OH-3), 4.56 (d, 1H, J1,2 ¼ 3.1 Hz, H-1),
3.79–3.42 (complex m, 5H, H-2, H-3, H-5, H-6, H-60), 3.28 (s, 3H, OCH3), 3.13
(m, 1H, H-4), 1.84 (s, 3H, COCH3); 13C NMR d: 177.6 (C55O), 98.1 (C-1), 74.9,
73.7, 70.4 (C-3, C-4, C-5), 55.3 (OCH3), 54.0 (C-2), 32.8 (C-6), 23.2 (COCH3);
13C NMR (DMSO-d6) d: 169.5 (C55O), 98.1 (C-1), 72.9 (C-4), 71.0 (C-3), 70.4
(C-5), 54.5 (OCH3), 53.6 (C-2), 35.1 (C-6), 22.7 (COCH3).
Methyl 2-acetamido-2,6-dideoxy-a-D-glucopyranoside (5). Compound 4 (3.09 g,
10 mmol) was dissolved in dry methanol (150 mL) and 10% palladium-on-charcoal
˚
(3.09 g) and finely ground 4 A molecular sieves (12 g) were added in portions. The flask
was evacuated and hydrogen was admitted at 1 atm. The mixture was stirred at r.t. and
monitored by TLC (chloroform : methanol, 3 : 1). After 48 hr, the reaction was complete.

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77
The reaction mixture was filtered through a bed of Celite under suction and the filtrate was
concentrated to a residue that was purified by column chromatography using 13 : 1 (v/v)
ethyl acetate–methanol as the eluent to give a colorless amorphous solid: yield 2.30 g
(100%); m.p. 173–1758C, lit.[20] 168–1708C, lit.[21] 172–1738C; 1H NMR d: 6.00
(d, 1H, JNH,2 ¼ 7.9 Hz, NH), 4.62 (d, 1H, J1,2 ¼ 3.7 Hz, H-1), 4.07 (m, 1H, H-2), 3.65
(m, 1H, H-5), 3.60 (dd, 1H, J2,3 ¼ 10.4 Hz, J3,4 ¼ 9.2 Hz, H-3), 3.38 (s, 3H, OCH3),
3.24 (dd, 1H, J4,5 ¼ 9.1 Hz, H-4), 2.06 (s, 3H, COCH3), 1.31 (d, 3H, J5,6 ¼ 6.7 Hz,
CH3-6); 13C NMR d: 172.3 (C55O), 98.2 (C-1), 76.9 (C-4), 74.7 (C-3), 67.1 (C-5), 55.0
(OCH3), 54.2 (C-2), 23.3 (COCH3), 17.4 (C-6).
Methyl 2-acetamido-4-azido-2,4,6-trideoxy-a-D-glucopyranoside (8). Compound
5 (93.2 mg, 0.43 mmol) and triphenylphosphine (674.2 mg, 2.55 mmol, 6 equiv.) were
dissolved in dry THF (6 mL). Diethyl azodicarboxylate (400 mL, 2.55 mmol, 6 equiv.)
was added dropwise to the mixture and the solution was stirred for 4 hr at r.t. Diphenylphos-
phoryl azide (560 mL, 2.55 mmol, 6 equiv.) was added to the clear pink reaction mixture,
which was stirred for 13.5 hr, then concentrated to an orange-red syrup. Chromatography
1
on silica gel (ethyl acetate : hexane, 1 : 1) gave a colorless syrup, yield 18 mg (18%); H
NMR d: 6.61 (d, 1H, JNH,2 ¼ 9.1 Hz, NH), 4.79 (d, 1H, J1,2 ¼ 3.7 Hz, H-1), 4.62 (dq,
1H, J2,3 ¼ 11.3 Hz, H-2), 4.34 (dd, 1H, J3,4 ¼ 10.2 Hz, H-3), 3.99 (m, 1H,
J4,5 ¼ 9.8 Hz, H-5), 3.83 (dd, 1H, H-4), 3.39 (s, 3H, OCH3), 2.04 (s, 3H, COCH3), 1.37
(d, 3H, J5,6 ¼ 6.1 Hz, CH3-6); 13C NMR d: 170.2 (C55O), 99.1 (C-1), 81.7 (C-4), 79.4
(C-3), 66.7 (C-5), 55.8 (OCH3), 51.9 (C-2), 23.1 (COCH3), 17.5 (C-6).
Methyl 2-acetamido-3-O-benzoyl-2,6-dideoxy-a-D-glucopyranoside (6). Benzoyl
chloride (70 mL, 0.60 mmol, 1.1 equiv.) was added dropwise to a solution of compound 5
(0.12 g, 0.55 mmol) in dry pyridine (4 mL) at 2358C. The resultant suspension was stirred
at that temperature for 2 hr, then was allowed to warm gradually to r.t. over 3 hr. Methanol
(1.5 mL) was added and the reaction mixture was stirred for 10 min, then concentrated.
The white residue was dissolved in chloroform (15 mL), and the solution was washed suc-
cessively with 3% hydrochloric acid (2 mL), cold saturated aqueous sodium bicarbonate
(2 mL), and water (2 mL), then dried (anhydrous sodium sulfate) and filtered. The filtrate
was concentrated to give a solid residue, that on crystallization from ethanol afforded col-
1
orless needles; yield 165 mg (89%); m.p. 158–1608C; [a]D þ 45.08 (c 0.9, CHCl3); H
NMR d: 8.00 (d, 2H, J ¼ 7.3 Hz, o-Ph), 7.56 (t, 1H, J ¼ 7.3 Hz, p-Ph), 7.42 (t, 2H,
J ¼ 7.3 Hz, m-Ph), 6.10 (d, 1H, JNH,2 ¼ 9.5 Hz, NH), 5.09 (t, 1H, J2,3 ¼ 10.4 Hz,
J3,4 ¼ 9.5 Hz, H-3), 4.44 (d, 1H, J1,2 ¼ 3.2 Hz, H-1), 4.15 (dt, 1H, H-2), 3.64 (s, 1H,
OH-4), 3.56 (m, 1H, J4,5 ¼ 10.3 Hz, H-5), 3.32 (t, 1H, H-4), 3.21 (s, 3H, OCH3), 1.61
(s, 3H, COCH3), 1.12 (d, 3H, J5,6 ¼ 5.5 Hz, CH3-6); 13C NMR d: 170.1, 168.3
(2 ꢀ C55O), 133.6, 130.0, 129.3, 128.6 (Ph), 98.2 (C-1), 74.7 (C-3), 73.9 (C-4), 67.8
(C-5), 55.0 (OCH3), 52.1 (C-2), 22.9 (COCH3), 17.7 (C-6).
HRMS (EI, m/z) Calcd for [C16H21NO6 2 CH3O]þ: 292.1185. Found: 292.1188.
Methyl 2-acetamido-4-azido-3-O-benzoyl-2,4,6-trideoxy-a-D-galactopyranoside
(7). Compound 6 (100 mg, 0.31 mmol) and triphenylphosphine (81 mg, 0.31 mmol)
were dissolved in dry THF (5 mL). Diethyl azodicarboxylate (48 mL, 0.31 mmol) was
added to the mixture, followed by diphenylphosphoryl azide (68 mL, 0.31 mmol) in
THF (0.7 mL). The mixture was stirred at r.t. for 24 hr. The reaction mixture was diluted
with chloroform (10 mL), and the resulting solution was washed with distilled water
(2 mL), dried (anhydrous sodium sulfate), and filtered. Concentration of the filtrate gave
a yellow residue. Chromatography on silica gel (ethyl acetate : hexane, 3 : 1) afforded a

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Liang and Grindley
colorless solid, yield 99 mg (92%); m.p. 177–1788C; [a]D 2 8.38 (c 0.3, CHCl3); 1H NMR
d: 8.07 (d, 2H, J ¼ 7.5 Hz, o-Ph), 7.59 (t, 1H, J ¼ 7.5 Hz, p-Ph), 7.45 (t, 2H, J ¼ 7.5 Hz,
m-Ph), 5.79 (d, 1H, JNH,2 ¼ 9.3 Hz, NH), 5.46 (dd, 1H, J2,3 ¼ 10.8 Hz, J3,4 ¼ 3.4 Hz,
H-3), 4.78 (dt, 1H, J1,2 ¼ 3.7 Hz, H-2), 4.71 (d, 1H, H-1), 4.11 (m, 1H, H-5), 3.93 (dd,
1H, J3,4 ¼ 3.4 Hz, J4,5 ¼ 2.1 Hz, H-4), 3.38 (s, 3H, OCH3), 1.87 (s, 3H, COCH3), 1.33
(d, 3H, J5,6 ¼ 7.6 Hz, CH3-6); 13C NMR d: 169.9, 166.6 (2 ꢀ C55O), 133.6, 128.61,
128.57 (Ph), 98.8 (C-1), 71.9 (C-3), 64.8 (C-4), 64.2 (C-5), 55.3 (OCH3), 47.7 (C-2),
23.3 (COCH3), 17.3 (C-6).
Anal. Calcd for C16H20N4O5 (348.3616): C, 55.17; H, 5.79; N, 16.08. Found: C,
55.26; H, 5.71; N, 15.74.
Methyl 2,4-diacetamido-2,4,6-trideoxy-a-D-galactopyranoside (9). Compound 7
(49.9 mg, 0.13 mmol) in dry methanol (5 mL) containing 10% Pd/C (74.8 mg, 50%
wet) was stirred under hydrogen at atmospheric pressure. After the disappearance of 7
(19 hr) on TLC (ethyl acetate : hexane, 3 : 1), the catalyst was removed by filtration. Con-
centration yielded a colorless solid, that was taken up in pyridine (2 mL) and acetic anhy-
dride (2.0 mL, 0.2 mmol, 4 equiv.). The reaction mixture was stirred at r.t. until the amino
compound had disappeared on TLC (chloroform : methanol, 8 : 1) (0.5 hr). The reaction
mixture was quenched with methanol (5 mL), and evaporated to give the diacetamide as
a syrup. This syrup was dissolved in methanol (4 mL) and sodium methoxide was
added (0.8 mL, 30 mg sodium in 6 mL methanol). After being stirred at r.t. for 1 hr, the
reaction mixture was neutralized with Amberlite IR-120(Hþ), filtered, and concentrated
to a yellow syrup. The syrup was separated on a column of silica gel (ethyl acetate : metha-
nol, 6 : 1) into two components. The first component, compound 9 was a colorless solid,
1
yield 33.8 mg (74%); m.p. 213–2158C; [a]D þ 125.98 (c 0.5, ethanol); H NMR d: 6.10
(d, 1H, JNH,4 ¼ 7.8 Hz, NH-4), 5.82 (d, 1H, JNH,2 ¼ 9.4 Hz, NH-2), 4.69 (d, 1H,
J1,2 ¼ 4.1 Hz, H-1), 4.31 (m, 1H, H-4), 4.13–4.07 (m, 2H, H-2, H-5), 3.92 (dd, 1H,
J2,3 ¼ 10.8 Hz, J3,4 ¼ 4.0 Hz, H-3), 3.35 (s, 3H, OCH3), 2.12, 2.04 (2s, 2 ꢀ 3H,
2 ꢀ COCH3), 1.17 (d, 3H, J5,6 ¼ 6.6 Hz, CH3-6); 13C NMR (D2O) d: 178.4, 177.3
(2 ꢀ C55O), 101.0 (C-1), 69.7 (C-3), 68.0 (C-5), 58.0 (OCH3), 56.2 (C-4), 52.9 (C-2),
24.7 (2 ꢀ COCH3), 18.3 (C-6).
HRMS (EI, m/z) Calcd for [C11H20N2O5 2 CH3OH]þ: 228.1110. Found: 228.1110.
The second component, methyl 2-acetamido-4-benzamido-2,4,6-trideoxy-a-D-galac-
topyranoside (9a) was isolated as a colorless syrup, yield: 9 mg (21%); [a]D þ 140.58 (c
0.9, ethanol); 1H NMR d: 7.85–7.42 (m, 5H, Ph), 6.69 (d, JNH,4 ¼ 7.4 Hz, NH-4), 6.01 (bs,
1H, NH-2), 4.75 (d, 1H, J1,2 ¼ 3.7 Hz, H-1), 4.51 (m, 1H, H-4), 4.16–3.98 (m, 3H, H-2,
H-3, H-5), 3.36 (s, 3H, OCH3), 1.96 (s, 3H, COCH3), 1.22 (d, 3H, J5,6 ¼ 5.5 Hz, CH3-6);
13C NMR d: 171.4, 169.9 (2 ꢀ C55O), 133.9, 131.9, 128.6, 127.3 (Ph), 98.5 (C-1), 69.4(C-
3), 64.8 (C-5), 55.5 (OCH3), 54.4 (C-4), 51.0 (C-2), 23.3 (COCH3), 16.9 (C-6).
Methyl 2-acetamido-4-azido-2,4,6-trideoxy-a-D-galactopyranoside (2). Sodium
(0.02 g, 0.80 mmol) was dissolved in dry methanol (6 mL) and compound 7 (0.25 g,
0.71 mmol) was added. After 5 min, the solution was neutralized with Amberlite IR-120
(Hþ), filtered, washed with methanol (2 ꢀ 5 mL) and evaporated to a colorless solid.
Recrystallization from ethyl acetate–hexane gave colorless needles, yield: 0.15 g
1
(98%); m.p. 195.5–197.08C; [a]D þ 152.48 (c 0.6, ethanol); H NMR d: 5.92 (d, 1H,
JNH,2 ¼ 9.5 Hz, NH), 5.09 (dd, 1H, J2,3 ¼ 10.4 Hz, J3,4 ¼ 9.5 Hz, H-3), 4.64 (d, 1H,
J1,2 ¼ 4.1 Hz, H-1), 4.28 (ddd, 1H, H-2), 3.64 (s, 1H, OH-4), 3.56 (m, 1H, H-5), 3.32
(dd, J4,5 ¼ 10.3 Hz, H-4), 3.21 (s, 3H, OCH3), 1.61 (s, 3H, COCH3), 1.12 (d, 3H,

ORDER
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Efficient Synthesis of Derivatives of AAT
79
J5,6 ¼ 5.5 Hz, C-6); 13C NMR d: 170.4, 168.4, 167.4 (C55O), 98.2 (C-1), 74.7 (C-3), 73.9
(C-4), 67.8 (C-5), 55.0 (OCH3), 52.1 (C-2), 22.9 (COCH3), 17.7 (C-6).
Anal. Calcd for C9H16N4O4 (244.2506): C, 44.26; H, 6.60. Found: C, 44.00; H, 6.62.
Methyl 2-acetamido-4-amino-2,4,6-trideoxy-a-D-galactopyranoside (10). A solu-
tion of compound 2 (90.0 mg, 0.37 mmol) in dry ethanol (1.5 mL) was stirred with 10%
palladium-on-charcoal (0.24 g) under hydrogen at r.t. for 16 hr. The reaction mixture
was filtered through a bed of Celite under suction and the filtrate was concentrated to a
colorless residue. The residue was purified by flash chromatography using 4 : 1 (v/v)
dichloromethane–methanol to give the title compound (10) as a colorless solid:
1
65.0 mg (82%); m.p. 194.5–196.08C; [a]D þ 159.48 (c 1.2, ethanol); H NMR d: 6.99
(d, 1H, J2,NH ¼ 8.5 Hz, NH), 4.65 (d, 1H, J1,2 ¼ 3.8 Hz, H-1), 4.08 (ddd, 1H,
J2,3 ¼ 10.8 Hz, H-2), 3.97 (qd, 1H, J5,6 ¼ 6.6 Hz, J4,5 ¼ 1.8 Hz, H-5), 3.73 (dd, 1H,
J3,4 ¼ 4.2 Hz, H-3), 3.35 (s, 3H, OCH3), 2.96 (dd, 1H, H-4), 2.05 (s, 3H, COCH3), 1.25
(d, 3H, H-6); 13C NMR d: 171.7 (C55O), 98.5 (C-1), 69.7 (C-3), 65.4 (C-5), 55.2
(OCH3), 54.8 (C-4), 50.5 (C-2), 23.5 (COCH3), 16.8 (C-6).
HRMS (EI, m/z). Calcd for [C9H18N2O4 2 NH2CH3]þ: 187.0845. Found: 187.0878.
ESI MS (m/z). Calcd for [C9H18N2O4 þ K]þ: 257.2. Found: 257.5.
Methyl 2-acetamido-4-(benzyloxylcarbonyl)amino-2,4,6-trideoxy-a-D-galacto-
pyranoside (11). Benzyl chloroformate (64 mL, 0.45 mmol, 1.5 equiv.) was added to a
solution of compound 10 (65.2 mg, 0.30 mmol) and sodium bicarbonate (75.6 mg,
0.90 mmol, 3 equiv.) in 2 : 1 (v/v) THF–water (1.5 mL) dropwise at 08C. The mixture
was stirred at 08C for 2 hr. The result two-phase mixture was diluted with ethyl acetate
(3 mL) and extracted with ethyl acetate (3 ꢀ 3 mL). The combined organic layers were
concentrated in vacuo and purified by silica gel chromatography using 20: 1 (v/v) dichloro-
methane–methanol (Rf ¼ 0.2) as eluent to give the title compound (11) as a colorless
1
solid: 81.1 mg (77%); m.p. 62.5–64.58C; [a]D þ 87.08 (c 0.7, CHCl3); H NMR d: 7.36
(bs, 5H, Ph), 5.79 (d, 1H, J2,NH ¼ 8.7 Hz, NHAc), 5.30 (d, 1H, J4,NH ¼ 9.8 Hz,
NHCbz), 5.17, 5.09 (2d, 2H, J ¼ 12.2 Hz, CH2Ph), 4.63 (d, 1H, J1,2 ¼ 3.7 Hz, H-1),
4.12–4.02 (m, 3H, H-2, H-4, H-5), 3.86 (m, 1H, H-3), 3.34 (s, 3H, OCH3), 3.22 (d, 1H,
J4,OH ¼ 6.1 Hz, OH), 2.01 (s, 3H, COCH3), 1.18 (d, 3H, J5,6 ¼ 6.4 Hz, CH3-6); 13C
NMR d: 170.1 (C55O, NHAc), 154.8 (C55O, NHCbz), 128.6, 128.2 (Ph), 98.4 (C-1), 69.8
(C-3), 67.3 (CH2Ph), 64.9 (C-5), 65.6 (C-4), 55.3 (OCH3), 50.9 (C-2), 23.4 (COCH3),
16.6 (C-6); MS (EI, m/z) 321 ([C17H24N2O6 2 CH3O]þ, 16%), 320 ([C17H24N2O6 2
CH3OH]þ, 20%), 303 (321 2 H2O, 5%), 91 (C7Hþ7 , 100%).
HRMS (EI, m/z). Calcd for [C17H24N2O6 2 CH3OH]þ: 320.1372. Found: 320.1364.
Methyl 2-acetamido-4-(benzyloxylcarbonyl)amino-3-O-benzyloxylcarbonyl-2,4,6-
trideoxy-a-D-galactopyranoside (12). Compound 10 (106.5mg, 0.49mmol) was dried
in vacuo and then dissolved in 3 : 4 (v/v) THF–water (7 mL). Addition of sodium
bicarbonate (205.8mg, 2.44mmol, 5 equiv.) to the clear solution gave a milky mixture.
Benzyl chloroformate (180mL, 1.18mmol, 2.4 equiv.) was added to the mixture dropwise
at 08C. The mixture was stirred at 08C for 0.5 hr and then at r.t. for 1 hr. The resulting
two-phase mixture was extracted with ethyl acetate (3 ꢀ 10mL). The combined organic
layers were concentrated in vacuo and the residue was purified by the column chromato-
graphy using 2 : 1 (v/v) ethyl acetate–hexane as eluent to give the title compound (12) as
1
a colorless solid: 0.18g (33%); m.p. 120.0–123.08C; [a]D þ 98.88 (c 0.5, CHCl3); H
NMR (acetone-d6) d: 7.42–7.26 (m, 10H, 2 ꢀ Ph), 7.00 (d, 1H, J2,NH ¼ 8.5 Hz, NHAc),
6.77 (d, 1H, J4,NH ¼ 10.0Hz, NHCbz), 5.17, 5.10 (2d, 2H, J ¼ 12.4Hz, 4-CH2Ph), 5.08

ORDER
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80
Liang and Grindley
(s, 2H, 3-CH2Ph), 4.89 (dd, 1H, J2,3 ¼ 11.8Hz, J3,4 ¼ 4.20Hz, H-3), 4.64 (d, 1H,
J1,2 ¼ 3.7 Hz, H-1), 4.41 (ddd, 1H, H-2), 4.30 (ddd, 1H, J4,5 ¼ 1.8 Hz, H-4), 4.08 (qd,
1H, J5,6 ¼ 6.48Hz, H-5), 3.34 (s, 3H, OCH3), 1.83 (s, 3H, COCH3), 1.18 (d, 3H, H-6);
13C NMR d: 170.2 (C55O, NHAc), 157.0 (C55O, OCbz), 154.9 (C55O, NHCbz), 136.4,
135.2 (q Ph), 128.41, 128.39, 128.37, 128.2, 127.9, 127.4 (Ph), 98.3 (C-1), 73.46 (C-3),
69.8, 66.8 (2 ꢀ CH2Ph), 64.5 (C-5), 55.3 (OCH3), 52.7 (C-4), 48.0 (C-2), 23.0 (COCH3),
16.4 (C-6).
MS (ESI, m/z). Calcd for [C25H30N2O8 þ K]þ: 525.0. Found: 525.0.
ACKNOWLEDGMENTS
The authors thank the Natural Sciences and Engineering Research Council of Canada
for support. NMR spectra were recorded at the Atlantic Region Magnetic Resonance
Centre. The authors are grateful to Dr. Mike Lumsden (NMR) and Xiao Feng and Mike
Potvin (MS) for assistance.
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Received August 11, 2003
Accepted November 21, 2003

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