An improved route to PUGNAc and its Galacto -configured congener

Article abstract of DOI:10.1021/jo100614b

Figure presented An efficient, scalable, and reliable synthesis of PUGNAc and its galacto-configured congener is reported.

Full text of DOI:10.1021/jo100614b

pubs.acs.org/joc
cosaminidase inhibitors.
8
,11-20
One of these inhibitors, O-(2-
An Improved Route to PUGNAc and Its
Galacto-Configured Congener
acetamido-2-deoxy-D-glucopyranosylidene)-amino N-phenyl-
carbamate 1, commonly known as PUGNAc, has demonstrated
excellent and broad inhibitory potency for exo-β-N-acetylglu-
cosaminidases, irrespective of the fact that some of these
enzymes operate via different catalytic mechanisms. PUGNAc
†
Ethan D. Goddard-Borger and Keith A. Stubbs*
Chemistry M313, School of Biomedical, Biomolecular and
Chemical Sciences, The University of Western Australia,
5 Stirling Highway, Crawley, WA 6009, Australia. Current
12
was first prepared by Vasella and co-workers, and found to be
a potent competitive inhibitor of β-N-acetyl-glucosaminidases
†
3
12
address: Department of Chemistry, The University of British
Columbia, 2036 Main Mall, Vancouver, BC V6T 1Z1,
Canada.
from Canavalia ensiformis (K =100 nM), Mucor rouxii (K =
i i
40 nM), and bovine kidney (K =110 nM).
i
It was subsequently determined to be a competitive inhibitor
12
12
21
of the human enzymes O-GlcNAcase (K =46 nM), HEXB
i
2
1
22
kstubbs@cyllene.uwa.edu.au
Received March 31, 2010
(K = 46 nM), HEXD (K ≈ 100 μM), the prokaryotic
i
i
2
3
enzyme NagZ (K =48 nM), and even an R-N-acetyl-glucos-
aminidase (K =6 μM).
i
24
i
Indeed, the inhibitory potency of PUGNAc has prompted
the suggestion that it may be a transition state analogue,
12
although this assertion has yet to be rigorously substan-
tiated. Indeed, in the case of human O-GlcNAcase, PUG-
NAc does not appear to possess all of the properties expected
2
5
of a genuine transition state analogue.
The broad-spectrum inhibitory activity of PUGNAc argu-
ably limits its utility as a tool for probing biological systems that
21,26
contain multiple β-N-acetylglucosaminidases.
For example,
PUGNAc continues to be used as a probe for studying the
mechanisms that give rise to insulin resistance in tissue
An efficient, scalable, and reliable synthesis of PUGNAc
and its galacto-configured congener is reported.
6,27
culture, despite its established off-target effects, which have
prompted questions about the mechanism by which such a
2
8
phenotype arises. As a result, several measures have been
The exo-β-N-acetylglucosaminidases, a group of glycoside
hydrolases (glycosidases) responsible for the hydrolysis of
(
11) Legler, G.; Lullau, E.; Kappes, E.; Kastenholz, F. Biochim. Biophys.
Acta 1991, 1080, 89–95.
12) Horsch, M.; Hoesch, L.; Vasella, A.; Rast, D. M. Eur. J. Biochem.
1991, 197, 815–818.
13) Liu, J.; Shikhman, A. R.; Lotz, M. K.; Wong, C. H. Chem. Biol. 2001,
2
-deoxy-2-acetamido-β-D-glucopyranosides, are essential
(
for the catabolism of a wide range of glycoproteins, glyco-
lipids, and oligosaccharides. An almost universal require-
ment to process such biomacromolecules renders these
enzymes ubiquitous in Nature. Anomalous exo-β-N-acetyl-
glucosaminidase activity is the cause of several genetic
(
8
, 701–711.
(14) Knapp, S.; Vocadlo, D.; Gao, Z. N.; Kirk, B.; Lou, J. P.; Withers, S.
G. J. Am. Chem. Soc. 1996, 118, 6804–6805.
15) Amorelli, B.; Yang, C.; Rempel, B.; Withers, S. G.; Knapp, S. Bioorg.
(
Med. Chem. Lett. 2008, 18, 2944–2947.
(16) Stubbs, K. A.; Zhang, N.; Vocadlo, D. J. Org. Biomol. Chem. 2006, 4,
839–845.
1
disorders, and appears to play a role in the propagation of
2
-8
other diseases.
rial cell-wall processing.
These enzymes are also involved in bacte-
9
(17) Stubbs, K. A.; Macauley, M. S.; Vocadlo, D. J. Angew. Chem., Int.
,10
Ed. 2009, 48, 1300–1303.
(18) Dorfmueller, H. C.; Borodkin, V. S.; Schimpl, M.; Shepherd, S. M.;
Shpiro, N. A.; van Aalten, D. M. F. J. Am. Chem. Soc. 2006, 128, 16484–
Thus, it is no surprise that considerable efforts have been
invested into the development of a range of exo-β-N-acetylglu-
1
6485.
19) Dorfmueller, H. C.; van Aalten, D. M. F. FEBS Lett. 2010, 584, 694–
700.
(20) Scaffidi, A.; Stubbs, K.; Dennis, R.; Taylor, E.; Davies, G.; Vocadlo,
(
(1) Triggs-Raine, B.; Mahuran, D. J.; Gravel, R. A. Adv. Genet. 2001, 44,
99–224.
1
(
(
2) Chou, T. Y.; Hart, G. W. Adv. Exp. Med. Biol. 2001, 491, 413–418.
3) Griffith, L. S.; Schmitz, B. Biochem. Biophys. Res. Commun. 1995,
D.; Stick, R. Org. Biomol. Chem. 2007, 5, 3013–3019.
(21) Macauley, M. S.; Whitworth, G. E.; Debowski, A. W.; Chin, D.;
Vocadlo, D. J. J. Biol. Chem. 2005, 280, 25313–25322.
(22) Gutternigg, M.; Rendi ꢀc , D.; Voglauer, R.; Iskratsch, T.; Wilson, I. B.
H. Biochem. J. 2009, 419, 83–90.
2
13, 424–431.
(
(
4) Yao, P. J.; Coleman, P. D. J. Neurosci. 1998, 18, 2399–411.
5) Liu, F.; Iqbal, K.; Grundke-Iqbal, I.; Hart, G. W.; Gong, C. X. Proc.
Natl. Acad. Sci. U.S.A. 2004, 101, 10804–10809.
6) Vosseller, K.; Wells, L.; Lane, M. D.; Hart, G. W. Proc. Natl. Acad.
Sci. U.S.A. 2002, 99, 5313–5318.
7) McClain, D. A.; Lubas, W. A.; Cooksey, R. C.; Hazel, M.; Parker, G.
J.; Love, D. C.; Hanover, J. A. Proc. Natl. Acad. Sci. U.S.A. 2002, 99, 10695–
0699.
8) Yuzwa, S. A.; Macauley, M. S.; Henioen, J. E.; Shan, X.; Dennis, R.
(23) Stubbs, K. A.; Balcewich, M.; Mark, B. L.; Vocadlo, D. J. J. Biol.
Chem. 2007, 282, 21382–21391.
(
(24) Ficko-Blean, E.; Stubbs, K. A.; Nemirovsky, O.; Vocadlo, D. J.;
Boraston, A. B. Proc. Natl. Acad. Sci. U.S.A. 2008, 105, 6560–6565.
(25) Whitworth, G. E.; Macauley, M. S.; Stubbs, K. A.; Dennis, R. J.;
Taylor, E. J.; Davies, G. J.; Greig, I. R.; Vocadlo, D. J. J. Am. Chem. Soc.
2007, 129, 635–644.
(
1
(
J.; He, Y.; Whitworth, G. E.; Stubbs, K. A.; McEachern, E. J.; Davies, G. J.;
Vocadlo, D. J. Nat. Chem. Biol. 2008, 4, 483–490.
(26) Macauley, M. S.; Vocadlo, D. J. Biochim. Biophys. Acta 2010, 1800,
107–121.
(
9) Cheng, Q.; Li, H.; Merdek, K.; Park, J. T. J. Bacteriol. 2000, 182,
836–4840.
10) Votsch, W.; Templin, M. F. J. Biol. Chem. 2000, 275, 39032–39038.
(27) Arias, E. B.; Kim, J.; Cartee, G. D. Diabetes 2004, 53, 921–930.
(28) Macauley, M. S.; Bubb, A. K.; Martinez-Fleites, C.; Davies, G. J.;
Vocadlo, D. J. J. Biol. Chem. 2008, 283, 34687–34695.
4
(
DOI: 10.1021/jo100614b
r 2010 American Chemical Society
Published on Web 05/05/2010
J. Org. Chem. 2010, 75, 3931–3934 3931

Goddard-Borger and Stubbs
JOCNote
SCHEME 1. Rationalization of the Oxidative Ring Closure
SCHEME 2
taken to confer inhibitory selectivity upon derivatives of
PUGNAc: a PUGNAc analogue with an N-butyryl group,
instead of an N-acetyl group, is selective for O-GlcNAcase16
23,29
as well as for the bacterial enzyme NagZ,
while the
D-galacto-configured congener, galacto-PUGNAc 2, only re-
cently reported, can selectively inhibit human HEXA and
HEXB in cells, owing to the ability of these enzymes to process
1
7
β-glycosides of N-acetyl-D-galactosamine.
A key step in the best syntheses of PUGNAc
16,30
is the NCS-
SCHEME 3
mediated oxidative ring closure of an oxime 3 to give the
corresponding oximinolactone 4 (Scheme 1). This reaction is
problematic, in that it provides a variable yield (at best 60%,
but often worse), is acutely temperature sensitive, and is
accompanied by the formation of another compound, the
3
0
oximinolactone 5 (a difficult to remove byproduct). A solu-
tion to this “bottleneck” in these syntheses would be most
welcome, given that large quantities of PUGNAc and its
analogues continue to be used in research. It was reasoned that
problems associated with this ring closure could be ascribed to
the amide/carbamate group at C-2, which may reversibly
capture the presumed nitrile oxide intermediate 6, delaying
ring closure and enabling acetyl migration to be a competitive
process. Thus, it seemed logical that replacement of the group
at C-2 with a nonparticipating amino group surrogate, such as
an azido group, might minimize or obviate the formation of the
troublesome byproduct 5, and invariably increase the overall
yield and operational convenience of the reaction.
Oxidative ring closure then provided the desired oximino-
lactone 16 exclusively and in high yield (87%).
Treating the oximinolactones 11 and 16 with phenyl
isocyanate, under basic conditions, yielded the correspond-
ing carbamates 17 and 18, respectively, in excellent yields
after purification by flash chromatography.
Several approaches were taken to the reductive acylation
of the azido group. To begin with, the carbamate 17 was
To explore the merits of this idea, D-glucosamine hydro-
chloride 7 was converted into the corresponding peracety-
33
treated with a slight excess of thioacetic acid to return the
3
lated azido sugar 8, then treated with benzylamine to
1
desired acetamide 19 in moderate yield (Scheme 3).
Other protocols for the reductive acylation of azides were
explored to improve upon this result. Treatment of the azide
3
2
afford the lactol 9 (Scheme 2). This product was condensed
with hydroxylamine to provide the oxime 10 as a mixture of
stereoisomers.
1
zene, followed by acetyl chloride,
7 with triphenylphosphine, to form the presumed phospha-
34,35
gave the acetamide 19
Addition of DBU to a mixture containing NCS and the oxime
in modest yield. A slightly different approach to this trans-
formation, reported by Vilarrasa and co-workers, utilizes
carboxylic acids, trimethylphosphine, and a catalytic quan-
10 in dichloromethane at -40 °C provided the desired ring-
closed material 11 exclusively, and in an excellent yield (93%).
This excellent result encouraged further investigations; the
analogous route for D-galactosamine hydrochloride 12 was
explored. The results were similarly impressive: the azidosu-
0
36
tity of 2,2 -dipyridyl diselenide. This method proved to be
3
1
gar 13 was converted to the lactol 14 and thence oxime 15.
(33) Rosen, T.; Lico, I. M.; Chu, D. T. W. J. Org. Chem. 1988, 53, 1580–
1
582.
34) Garcia, J.; Urpi, F.; Vilarrasa, J. Tetrahedron Lett. 1984, 25, 4841–
4844.
(35) Garcia, J.; Vilarrasa, J.; Bordas, X.; Banaszek, A. Tetrahedron Lett.
(
(29) Asgarali, A.; Stubbs, K. A.; Oliver, A.; Vocadlo, D. J.; Mark, B. L.
Antimicrob. Agents Chemother. 2009, 53, 2274–2282.
(30) Mohan, H.; Vasella, A. Helv. Chim. Acta 2000, 83, 114–118.
(31) Goddard-Borger, E. D.; Stick, R. V. Org. Lett. 2007, 9, 3797–3800.
(32) Grundler, G.; Schimdt, R. R. Liebigs Ann. Chem. 1984, 1826–1847.
1986, 27, 639–640.
(36) Bures, J.; Martin, M.; Urpi, F.; Vilarrasa, J. J. Org. Chem. 2009, 74,
2203–2206.
3
932 J. Org. Chem. Vol. 75, No. 11, 2010

Goddard-Borger and Stubbs
JOCNote
2
5
1
most satisfactory; when applied to compounds 17 and 18 it
affected their smooth conversion into the amides 19 and 20,
respectively, in excellent yield.
hexanes, 1:1); [R]
þ123 (c 1.0, CHCl ); H NMR (500 MHz,
D
3
CDCl
.04 (dd, J = 2.9, 10.0 Hz, 1H), 4.46 (d, J = 10.0 Hz, 1H), 4.44
ddd, J = 1.5, 5.3, 6.6 Hz, 1H), 4.29-4.24 (m, 2H), 2.16 (s, 3H),
3
) δ 8.05-8.00 (br s, 1H), 5.55 (dd, J = 1.5, 2.9 Hz, 1H),
5
(
Deprotection of 19 and 20 with ammoniacal methanol,
1
3
3
0
3
2.06 (s, 3H), 2.05 (s, 3H); C NMR (125 MHz, CDCl ) δ 170.4,
in accordance with literature procedure, provided PUG-
NAc 1 and galacto-PUGNAc 2, respectively. These com-
pounds were spectrocopically identical with samples that
had been prepared by literature methods,
ing that both oxidative ring closures had provided the desired
Z-stereoisomers.
This alternative route to PUGNAc and its analogues
greatly simplifies the preparation of these useful molecules.
The more facile conversion of R-azido-δ-hydroxy-aldoximes
to the corresponding oximinolactones, relative to the analo-
gous transformation for R-amido-δ-hydroxy-aldoximes, is
noteworthy. Regardless of whether or not the rationalization
and original motivation for using an azido group (rather
than an amide or carbamate) in these syntheses was correct,
azidosugars are evidently useful and readily accessible syn-
thons for the preparation of PUGNAc and its analogues.
1
Anal. Calcd for C12
69.6, 169.5, 148.9, 74.9, 70.7, 65.9, 61.0, 56.0, 20.6, 20.5, 20.4.
: C, 41.86; H, 4.68. Found: C,
H
16
N
4
O
8
þ
4
1.81; H, 4.61. HRMS m/z 345.1039 [M þ H] calcd for
1
7,37
thus confirm-
C
12
H
Z)-O-(3,4,6-Tri-O-acetyl-2-azido-2-deoxy-D-glucopyranosy-
17
N
4
O
8
345.1046.
(
lidene)amino N-Phenylcarbamate (17). Phenyl isocyanate (0.35
mL, 3.2 mmol) was added to the lactone 11 (1.0 g, 2.9 mmol) and
Et N (0.81 mL, 5.8 mmol) in THF (30 mL) and the solution was
3
stirred (rt, 3 h). Concentration of the mixture and flash chro-
matography of the residue (EtOAc/hexanes, 1:4) yielded the
carbamate 17 as a colorless oil (1.2 g, 91%). R
f
0.70 (EtOAc/
); H NMR (500 MHz,
) δ 7.88 (br s, 1H), 7.47 (m, 2H), 7.34 (m, 2H), 7.12 (m,
H), 5.14 (dd, J = 4.8, 12.0 Hz, 1H), 5.06 (dd, J = 4.8 Hz, 1H),
.70 (ddd, J = 3.6, 4.8, 12.0 Hz, 1H), 4.46 (d, J = 4.8 Hz, 1H),
2
5
1
hexanes, 2:3); [R]
CDCl
D
þ30 (c 1.0, CHCl
3
3
1
4
4
1
3
.39-4.35 (m, 2H), 2.14 (s, 3H), 2.13 (s, 3H), 2.12 (s, 3H);
C
NMR (125 MHz, CDCl ) δ 170.5, 169.3, 169.2, 151.9, 151.0,
3
1
20.5. Anal. Calcd for C19
36.8, 129.2, 124.3, 119.4, 74.8, 72.0, 68.1, 60.4, 57.9, 20.7, 20.6,
Experimental Section
21
H N
5
O
9
: C, 49.25; H, 4.57. Found: C,
þ
4
C H N O 464.1418.
9.30; H, 4.61. HRMS m/z 464.1423 [M þ H] calcd for
(E)-and(Z)-3,4,6-Tri-O-acetyl-2-azido-2-deoxy-D-glucose Oxime
10). Hydroxylamine hydrochloride (1.0 g, 14 mmol) was added to
1
9
22
5
9
(
the hemiacetal 9 (3.0 g, 9.0 mmol) and pyridine (2.0 mL, 25 mmol)
(
Z)-O-(3,4,6-Tri-O-acetyl-2-azido-2-deoxy-D-galactopyrano-
sylidene)amino N-Phenylcarbamate (18). The crude oxime 16
1.1 g, 3.2 mmol) was treated in the same manner as for the
preparation of 17 to give the title compound 18 as a colorless oil
32
in MeOH (30 mL) and the resulting solution was stirred at reflux
(2 h). The solution was concentrated and coevaporated with toluene
(
(
2 ꢀ 20 mL). The residue was taken up in EtOAc and washed with
25
(
CHCl
1.3 g, 85%). R
f
0.65 (EtOAc/hexanes, 2:3); [R]
D
þ43 (c 1.0,
water (2 ꢀ 50 mL) and brine (50 mL), dried (MgSO ), filtered, and
concentrated. The residue was subjected to flash chromatography
4
1
); H NMR (500 MHz, CDCl
3 3
) δ 8.08-8.03 (br s, 1H),
7.48 (m, 2H), 7.33 (m, 2H), 7.11 (m, 1H), 5.60 (dd, J = 1.6, 3.0
Hz, 1H), 5.09 (dd, J = 3.0, 9.9 Hz, 1H), 4.64 (d, 9.9 Hz, 1H), 4.59
(
(
EtOAc/hexanes, 2:3) to give the presumed oxime 10 (3.0 g). R
EtOAc/hexanes, 1:1).
Z)-3,4,6-Tri-O-acetyl-2-azido-2-deoxy-D-glucono-hydroximo-
,5-lactone (11). DBU (1.50 mL, 10 mmol) was added to the
f
0.35
(
(
1
6
ddd, J = 1.7, 6.8 Hz, 1H), 4.32-4.26 (m, 2H), 2.18 (s, 3H), 2.10
13
(
s, 3H), 2.08 (s, 3H); C NMR (125 MHz, CDCl
3
) δ 170.2,
69.4, 169.3, 152.7, 151.0, 136.8, 129.1, 124.3, 119.3, 76.1, 69.9,
5.3, 60.6, 55.8, 20.6, 20.5, 20.4. Anal. Calcd for C H N O : C,
1
crude oxime 10 (3.0 g, 8.7 mmol) and N-chlorosuccinimide (1.3 g,
0 mmol) in CH Cl (50 mL) at -45 °C in such a way that the
1
9
21
5
9
1
2
2
49.25; H, 4.57. Found: C, 49.40; H, 4.60. HRMS m/z 464.1428
temperature did not go above -40 °C and the resulting mixture
was stirred for 60 min at this temperature, then left to warm to
room temperature over 3 h. Water was added (10 mL), and the
mixture was diluted with EtOAc (100 mL). The organic layer was
separated and washed with water (2 ꢀ 50 mL) and brine (1 ꢀ 50
þ
[
M þ H] calcd for C19
22 5 9
H N O 464.1418.
(
Z)-O-(3,4,6-Tri-O-acetyl-2-acyl-2-deoxy-D-glucopyranosyli-
dene)amino N-Phenylcarbamate (19). Procedure A: Thioacetic
acid (50 μL, 0.60 mmol) was added to the carbamate 17 (0.23 g, 0.50
mmol) in THF (5 mL) at 0 °C and the solution was stirred (2 h).
Concentration of the mixture gave a yellow residue, which was
dissolved in EtOAc (30 mL) and washed with water (2 ꢀ 20 mL)
4
mL), dried (MgSO ), filtered, and concentrated. Flash chroma-
tography of the residue (EtOAc/hexanes, 2:3) gave compound 11
as a colorless oil (2.8 g, 93%): R 0.40 (EtOAc/hexanes, 1:1);
); H NMR (500 MHz, CDCl ) δ
f
and brine (1 ꢀ 20 mL), dried (MgSO
4
), filtered, and concen-
2
5
1
[
7
R]
D
þ89 (c 1.0, CHCl
3
3
trated. Flash chromatography (EtOAc/hexanes, 7:3) of the
residue gave 19 as a colorless oil (58%), which had a H NMR
.20-7.10 (br s, 1H), 5.15 (dd, J = 6.0, 12.0 Hz, 1H), 5.06 (dd,
J = 6.0 Hz, 1H), 4.56 (ddd, J = 3.0, 4.8, 12.0 Hz, 1H), 4.38 (dd,
J = 4.8, 13.0 Hz, 1H), 4.34 (dd, J = 3.0, 13.0 Hz, 1H), 4.28 (d,
1
37
spectrum consistent with that found in the literature.
Procedure B: Triphenylphosphine (0.16 g, 0.60 mmol) was
added to the carbamate 17 (0.23 g, 0.50 mmol) in CH Cl (5 mL)
at 0 °C and the solution was stirred (1 h). Acetyl chloride
(0.11 mL, 1.5 mmol) was then added and the mixture refluxed
13
J = 6.0 Hz), 2.14 (s, 3H), 2.13 (s, 3H), 2.12 (s, 3H); C NMR
125 MHz, CDCl ) δ 170.6, 169.4, 169.3, 148.5, 74.2, 72.2, 68.2,
2
2
(
3
6
1.4, 58.3, 20.7, 20.6, 20.5. Anal. Calcd for C H N O : C,
12 16 4 8
4
1.86; H, 4.68. Found: C, 41.72; H, 4.65. HRMS m/z 345.1053
(
2 2
5 h). The mixture was diluted with CH Cl (20 mL) and washed
þ
[
M þ H] calcd for C12
17 4 8
H N O 345.1046.
with water (2 ꢀ 20 mL) and brine (1 ꢀ 20 mL), dried (MgSO ),
4
(
E)- and (Z)-3,4,6-Tri-O-acetyl-2-azido-2-deoxy-D-galactose
filtered, and concentrated. Flash chromatography (EtOAc/hex-
anes, 7:3) of the residue gave 19 as a colorless oil (40%), which
3
2
Oxime (15). The hemiacetal 14 (2.5 g, 7.5 mmol) was treated in
the same manner as for the preparation of 10. The presumed
oxime 15 (2.5 g) was used in the next step without further
1
had a H NMR spectrum consistent with that found in the
literature.
37
purification. R 0.30 (EtOAc/hexanes, 1:1).
f
Procedure C: A solution of Me P (1.0 M in toluene, 0.50 mL,
3
0.50 mmol) was added to a mixture of acetic acid (30 μL, 0.5
mmol), 17 (0.23 g, 0.50 mmol), and 2,2 -dipyridyl diselenide
(
Z)-3,4,6-Tri-O-acetyl-2-azido-2-deoxy-D-galactonohydroxi-
mo-1,5-lactone (16). The crude oxime 15 (2.5 g, 7.2 mmol) was
treated in the same manner as for the preparation of 11 to give
compound 16 as a colorless oil (2.2 g, 87%). R 0.33 (EtOAc/
0
38
(
30 mg, 0.10 mmol) in toluene (5 mL) at 0 °C under nitrogen.
f
A few minutes later, after the evolution of bubbles had ceased,
the ice bath was removed and the reaction was stirred at room
(37) Beer, D.; Maloisel, J. L.; Rast, D. M.; Vasella, A. Helv. Chim. Acta
990, 73, 1918–1922.
1
(38) Bhasin, K. K.; Singh, J. J. Organomet. Chem. 2002, 658, 71–76.
J. Org. Chem. Vol. 75, No. 11, 2010 3933

Goddard-Borger and Stubbs
JOCNote
temperature (2 h). Water (1 mL) was added and the mixture
Acknowledgment. K.A.S. acknowledges the support of
the Australian Research Council.
was stirred (10 min). The mixture was diluted with CH
(
2
Cl
(2 ꢀ 20 mL), water
2
20 mL) and washed with aqueous NaHCO
3
(
and concentrated. Flash chromatography (EtOAc/hexanes, 7:3) of
2 ꢀ 20 mL), and brine (1 ꢀ 20 mL), dried (MgSO ), filtered,
4
Note Added after ASAP Publication. Configuration anno-
tations of some of the molecules were incorrect in the version
published ASAP May 5, 2010; the correct version reposted
May 7, 2010.
1
the residue gave 19 as a colorless oil (89%), which had a H NMR
37
spectrum consistent with that found in the literature.
Z)-O-(3,4,6-Tri-O-acetyl-2-acetamido-2-deoxy-D-galactopyr-
anosylidene)amino N-Phenylcarbamate (20). Using procedure C,
8 was used to prepare compound 20, which was obtained as a
(
1
13
1
Supporting Information Available: H and C NMR spec-
tra for compounds 11, 16, 17, and 18. This material is available
free of charge via the Internet at http://pubs.acs.org.
1
colorless oil (85%). The material had a H spectrum consistent
with that found in the literature.
1
7
3
934 J. Org. Chem. Vol. 75, No. 11, 2010