Synthesis of double C-glycoside analogue of sTn

Full text of DOI:10.1021/jo050691n

Synthesis of Double C-Glycoside Analogue
of sTn
Dino K. Ress,† Sultan N. Baytas,‡ Qun Wang,†
Eva M. Mun˜oz,‡ Kazuo Tokuzoki,§
Hiroshi Tomiyama,§ and Robert J. Linhardt*,†,‡
Department of Chemistry and Chemical Biology,
Department of Biology and Department of Chemical and
Biological Engineering, Rensselaer Polytechnic Institute,
Troy, New York 12180, Division of Medicinal and Natural
Product Chemistry, The University of Iowa, Iowa City, Iowa
52242, and Kotobuki Pharmaceutical Co., Ltd.,
Nagano, Japan
FIGURE 1. Tumor-associated antigens and the double C-
glycoside analogue.
of hydrolase-type enzymes called neuraminidases. A non-
hydrolyzable glycosidic linkage to neuraminic acid rep-
resents is an attractive approach to design reagents for
glycobiology and immunology. The replacement of the
interglycosidic oxygen atom with a hydroxymethylene
group using SmI2 chemistry4 affords a class of hydrolyti-
cally and metabolically inert C-glycoside analogues of
natural glycoconjugates.5 This stable linkage is being
studied to improve our understanding of biological rec-
ognition and to enhance or suppress biological events at
the molecular level.
linhar@rpi.edu
Received April 7, 2005
The development of vaccines against carbohydrates is
of crucial importance in the fields of therapeutic glyco-
biology and immunology.6 A significant portion of the
antitumor response against cancers involves carbohy-
drate tumor antigens.7 Microorganisms often express
carbohydrate antigens and the immune response of the
host to these antigens is an important mechanism of
defense.8 One approach for improving carbohydrate
antigens that has not been thoroughly explored is vac-
cination over an extended length of time using a cata-
bolically stable C-glycoside vaccine.9 These agents might
be useful in preparing immunogens for active immuniza-
tion against neuraminic acid containing glycoconjugates
in the design and preparation of antiviral,10 antibacte-
rial,11 and anticancer vaccines.12
Sialyl-Tn, [R-D-Neu5Ac-(2f6)R-D-GalNAc-(1fO)-Ser/
Thr] (sTn 1a, Figure 1) is found on the HIV envelope
glycoprotein gp12013 and in tumor-associated antigens
present in the glycoproteins on the surface of cancer cells,
including those associated with carcinomas of the breast,
prostate, pancreas, colon, ovary, lung, and stomach.14 The
sTn antigen is well-known as a prognostic indicator and
A sTn double C-glycoside, sTn analogue 2, was synthesized
using samarium chemistry developed in our laboratory.
Complications in the oxidation reaction affording aldehyde
acceptor were overcome by double protection of amide and
the use of a room-temperature ionic liquid as solvent. Studies
are underway to conjugate the sTn double C-glycoside
hapten 2 to KLH carrier protein for biological evaluation as
a vaccine.
Neuraminic acids are biologically important since they
occupy the terminal position of the glycans on macro-
molecules outside cells and cell membranes and are
involved in recognition, cell interactions, neuronal trans-
mission, ion transport, reproduction, differentiation,
epitope masking, and protection. Neuraminic acids are
also involved in pathological processes including infec-
tion, inflammations, cancer, and neurological, cardiovas-
cular, endocrinological, and autoimmune diseases.1,2 Cell
surfaces containing these terminal neuraminic acids
interact with receptors, hormones, enzymes, toxins, and
viruses and other pathogens that use Neu5Ac to localize
on the surface of cells they infect.3 The linkage of
neuraminic acid to glycoconjugates is among the most
labile glycosidic linkages and is cleaved in vitro under
mildly acidic conditions. In vivo, neuraminic acid-
containing glycoconjugates are catabolized through the
removal of the terminal sialic acid residue by the action
(4) (a) Vlahov, I. R.; Vlahova, P. I.; Linhardt, R. J. J. Am. Chem.
Soc. 1997, 119, 1480. (b) Bazin, H. G.; Du, Y.; Polat, T.; Linhardt, R.
J. J. Org. Chem. 1999, 64, 7254. (c) Du, Y.; Polat, T.; Linhardt, R. J.
Tetrahedron Lett. 1998, 39, 5007
(5) Du, Y.; Linhardt, R. J.; Vlahov, I. R. Tetrahedron 1998, 54, 9913.
(6) (a) Livingston, P. Cancer Biol. 1995, 6, 357. (b) Deng, S.-J.;
Mackenzie, C. R.; Hirama, T.; Brousseau, R.; Lowary, T. L.; N. M., Y.;
Bundle, D. R.; Narang, S. A. Proc. Nat. Acad. Sci. U.S.A. 1995, 92,
4992. (c) Kuberan, B.; Linhardt, R. J. Curr. Org. Chem. 2000, 4, 653.
(7) Mouritsen, S.; Meldal, M.; Christiansen-Brams, I.; Elsner, H.;
Werdelin, O. Eur. J. Immunol. 1994, 24, 1066.
(8) Kenne L, L. B. Bacterial polysaccharides; Academic Press: New
York, 1983.
(9) Livingston, P. O. Ann. N. Y. Acad. Sci. 1993, 690, 204.
(10) Herrler, G.; Gross, H. J.; Brossmer, R. Biochem. Biophys. Res.
Commun. 1995, 216, 821.
(11) Kaijser, B.; Jodal, U. J. Clin. Microbiol. 1984, 19, 264.
(12) (a) Toyokuni, T.; Singhal, A. Chem. Soc. Rev. 1995, 231. (b)
Maclean, G.; Longenecker, B. Can. J. Oncol. 1994, 4, 249. (c) Living-
ston, P. O. Curr. Opin. Immunol. 1992, 4, 624.
* To whom correspondence should be addressed. Phone: 518-276-
3404. Fax: 518-276-3405.
† The University of Iowa.
‡ Rensselaer Polytechnic Institute.
§ Kotobuki Pharmaceutical Co., Ltd.
(1) Schauer, R. Adv. Carbohydr. Chem. Biochem. 1982, 40, 131.
(2) Varki, A. Glycobiology 1992, 2, 25.
(3) Swartley, J. S.; Marfin, A. A.; Edupugantis, D.; Liu, L. J.; Cieslak,
P.; Perkins, B.; Wenger, J. D.; Stephans, D. S. Proc. Nat. Acad. Sci.
U.S.A. 1997, 94, 271.
10.1021/jo050691n CCC: $30.25 © 2005 American Chemical Society
Published on Web 09/08/2005
J. Org. Chem. 2005, 70, 8197-8200
8197

SCHEME 1. Synthesis of 6-Formyl Galactoside 6
with Unexpected Product Hemiaminal 5a
tallography analysis had been performed to establish the
absolute stereochemistry of 4b and provide an unam-
biguous assignment of its stereogenic centers. The result-
ing crystal structure that the configuration of C-5 had
instead been inverted. We rationalized that under slightly
basic conditions in the presence of triethylamine aldehyde
6 undergoes enolization and the enolate intermediate
epimerizes at C-5. A change in ring conformation from
4C1 to 4B1 would place the weakly nucleophilic N-
acetamido functional group in close proximity to the
5-formyl electrophile. Intramolecular attack of the nitro-
gen ion pair on the adjacent aldehyde leads to the bicyclic
zwitterionic hemiaminal that on proton transfer affords
the cyclic hemiaminal product 5. Various oxidants such
as PCC and TPAP also failed to give the desired 6-formyl
derivative 6. Hypervalent iodine reagents are known to
accomplish chemoselective oxidations under neutral con-
ditions. 6-Hydroxy analogue 4a was treated with 1.5
equiv of the Dess-Martin periodinane reagent in the
presence of molecular sieves in CH2Cl2. A number of
different workup procedures were examined, but in the
best case, the desired compound 6 was isolated in less
than 10% yield. Exposure to even the most mildly basic
conditions appears to catalyze C-5 epimerization leading
to the cyclic hemiaminal product 6. We theorized that
derivatizing the N-acetamido group as a diamide would
deter the cyclization. In addition, to sterically hindering
attack of the aldehyde by the N-acetamide, a second acyl
protecting group would further reduce the nucleophilicity
of the nitrogen, preventing epimerization and subsequent
cyclization. One concern about the approach was whether
it would be possible to selectively remove the benzoyl
substituent while leaving the N-acetyl group in place.
Wong and co-workers, however, had successfully dem-
onstrated p-halobenzoyl ester as suitable protecting
group in carbohydrate synthesis.19
The 6-hydroxyl group in compound 3 was protected as
the TBDPS silyl ether 7 and 3,4-isopropylidinated to
afford 8 in good yield. Treatment of 8 with p-chloroben-
zoyl chloride in a 1:1 mixture of pyridine and CH2Cl2
giving 9 in good yield (92%). Chemoselective removal of
TBDPS using tetrabutylammonium flouride (TBAF) in
the presence of an excess or equimolar amount of acetic
acid resulted in decomposition. When the milder trihy-
drofluoride triethylamine was used, the corresponding
alcohol 10 was formed quantitatively. After desilylation,
we decided to explore very mild options for Dess-Martin
oxidation to completely prevent C-5 epimerization. Hy-
pervalent iodine reagent in ionic liquids reportedly leads
to mild chemoselective and in some cases regioselective
oxidative transformations.20 Our laboratory had previ-
ously used ionic liquids in synthetic carbohydrate chem-
istry.21 Compound 10 was dissolved in 1-butyl-3-meth-
ylimidazolium tetrafluoroborate ([bmim]+BF4-) and
treated with 1.5 equiv of Dess-Martin periodinane for 3
h to afford the corresponding aldehyde 11. Extraction of
the product from the ionic liquid with diethyl ether
resulted in the isolation of a single product as a solid
a Key: (a) (i) TBDPSCl, imidazole, DMF, rt, 5 h, 58%, (ii)
Me2C(OMe)2, Amberlite IR-120 (H+) (cat.), DMF, rt, 12 h, (iii)
NEt3‚3HF, THF, rt, 7h, 88%; (b) Ac2O, Pyr, rt, overnight; (c) oxalyl
chloride, DMSO, CH2Cl2/NEt3, -78 °C, 65%; (d) Dess-Martin
periodinane, CH2Cl2, rt, 7 h.
has proven to be an effective target for therapy of cancers.
Conjugate vaccines of sTn-KLH (keyhole limpet hemocy-
anin carrier protein15) showed remarkable immunoge-
nicity, resulting in the production of both IgM- and IgG-
type antibodies.16 The sTn C-glycoside 1b has been
synthesized in our laboratory in 15 steps,17 and its KLH-
conjugate is currently under biological evaluation.
An sTn double C-glycoside analogue 2 (Figure 1) was
designed to (1) reduce the number of synthetic steps
required to synthesize 1b; (2) to facilitate its conjugation
to KLH; and (3) to further increase biological half-life and
enhance immunological response.
Starting from N-acetylglucosamine, the R-C-glycoside
derivative 3 was prepared by a literature method.18
Compound 3 was protected as the 6-TBDPS silyl ether
and 3,4-isopropylidinated, and then the TBDPS protec-
tion at 6-position was removed to afford 4a in good yield.
Swern oxidation of the 6-hydroxy group, unexpectedly
failed to afford the desired 6-formyl galactoside 6. H
NMR spectroscopy instead revealed the formation of the
bicyclic compound 5 (Scheme 1).
The formation of lactol ring in 5 would require a change
in the configuration at either C-2 or C-5 of the galacto
ring. Extensive 2D-1H NMR studies suggested that the
stereochemistry at C-2 had been altered giving the tallo
form of the sugar. Thus, the prior synthesis of 3 and its
characterization18 was brought into question. X-ray crys-
1
(13) (a) Hansen, J. E.; Clausen, H.; Nielsen, C.; Teglbjaerg, S.;
Hansen, L. H.; Nielsen, C. M.; Dabelsteen, E.; Mathiesen, L.; Hako-
mori, S. I.; Nielsen, J. O. J. Virol. 1990, 64, 2833. (b) Hansen, J. E. S.;
Jansson, B.; Gram, G. J.; Clausen, H.; Nielsen, J. O.; Olofsson, S. Arch.
Virol. 1996, 141, 291. (c) Miyajima, K.; Nekado, T.; Ikeda, K.; Achiwa,
K. Chem. Pharm. Bull. 1997, 45, 1544. (d) Miyajima, K.; Nekado, T.;
Ikeda, K.; Achiwa, K., Chem. Pharm. Bull. 1998, 46, 1676.
(14) (a) Itzkowitz, S. H.; Yuan, M.; Montgomery, C. K.; Kjeldsenen,
T.; Takahashi, H. K.; Bigbee, W. L.; Kim, Y. S. Cancer Res. 1989, 49,
197. (b) Hakomori, S. I. Cancer Res. 1989, 49, 257.
(15) Harris, J. R.; Markl, J. Micron 1999, 30, 597.
(16) Zhang, S.; Walberg, L. A.; Ogata, S.; Itzkowitz, S. H.; Koganty,
R. R.; Reddish, M.; Gandhi, S. S.; Longenecker, B. M.; Lloyd, K. O.;
Livingston, P. O. Cancer Res. 1995, 55, 3364.
(19) Yu, C.; Niikura, K.; Lin, C.; Wong, C. H. Angew. Chem., Int.
Ed. 2001, 40, 2900.
(17) Kuberan, B.; Sikkander, S. A.; Tomiyama, H.; Linhardt, R. J.
Angew. Chem., Int. Ed. 2003, 42, 2073.
(20) Yadav, J. S.; Reddy, B. V. S.; Basak, A. K.; Narsaiah, A. V.
Tetrahedron 2004, 60, 2131.
(18) Cipolla, L.; Ferla, B. L.; Lay, L.; Peri, F.; Nicotra, F. Tetrahe-
dron: Asymmetry 2000, 295
(21) Murugesan, S.; Karst, N. A.; Islam, T.; Wiencek, J. M.; Linhardt,
R. J. Synlett 2003, 9, 1283..
8198 J. Org. Chem., Vol. 70, No. 20, 2005

SCHEME 2. Synthesis of sTn Double C-Glycoside 2a
a Key: (a) TBDPSCl, imidazole, DMF, rt, 5 h, 58%; (b) Me2C(OMe)2, Amberlite IR-120 (H+) (cat), DMF, rt, 12 h, quantitative; (c)
p-chlorobenzoyl chloride, Pyr-CH2Cl2 (1:1), DMAP, rt, overnight, 91%; (d) NEt3‚3HF, THF, rt, 7h, 88%; (e) Dess-Martin periodinane,
[bmim]+BF4-, rt, 3 h; (f) SmI2, THF, 25%; (g) (i) 60% AcOH, 80 °C, 1 h, (ii) NaOMe (cat.), MeOH, rt, overnight, (iii) 0.1 KOH, rt, overnight.
which was identified with MS and 1H NMR as the desired
aldehyde 11. Because of its propensity for epimerization,
11 was used directly in the C-glycosylation reaction
without further analysis or purification. C-Glycosylation
of 11 used Neu5Ac sulfone donor 12 (1.25 equiv) in the
presence of SmI2 (6 equiv) in THF (Scheme 2). A modest
25% yield of the desired C-glycoside product 13 was
obtained.
but no such coupling was observed. Thus, we conclude
that the S isomer is formed with complete diastereocon-
trol in C-glycosylation was consistent with our previous
results on the R(2f3) C-glycosylation.4b
Fully protected sTn double C-glycoside 13 was next
deprotected in three steps, deisopropylidenation with 60%
acetic acid at 80 °C for 1 h, followed by deacylation with
NaOMe and MeOH and demethylation using 0.1 KOH
affording 2 in quantitative yield.
The HRMS of the compound 13 gave a clear m/z [M +
Na]+ base peak at 919.2883 corresponding to the chemical
formula of C41H53ClN2NaO18 consistent with structure.
The structural and conformational analysis of compound
13 was determined by NMR spectroscopy and molecular
modeling (SYBYL 6.6 on a SGI interface using a TRIPOS
Studies are underway to conjugate the sTn double
C-glycoside hapten 2 to KLH carrier protein for biological
evaluation as a vaccine.
Experimental Section
1
force field and a dielectric constant set to 4.8). H NMR
showed a disaccharide product having identifiable reso-
1-(2′-Acetamido-2′-deoxy-6-[(tert-butyl(diphenyl)silyl]-r-
D-galactopyranosyl)prop-2-ene (7). tert-Butyldiphenyl silyl
chloride (1.4 mL, 7.95 mmol) was added to a solution of 3 (1.3 g,
5.3 mmol) in DMF (5 mL) in the presence of imidazole (360 mg,
5.3 mmol). The reaction mixture was stirred at room tempera-
ture for 5 h and evaporated under reduced pressure. Purification
of the residue by flash chromatography (hexane/EtOAc 4:1)
yielded 7 (1.48 g, 58%): 1H NMR (400 MHz, CDCl3) δ 7.69-
7.65 (m, 4H), 7.44-7.37 (m, 6H), 5.78-5.66 (m, 2H), 5.08-5.03
(m, 2H), 4.33-4.22 (m, 2H), 4.09 (bs, 1H), 3.94-3.83 (m, 2H),
3.70 (bs, 2H), 3.14 (d, 1H, J ) 8 Hz), 2.89 (d, 1H, J ) 5.2 Hz),
2.32-2.17 (m, 2H), 2.01 (s, 3H), 1.06 (s, 9H); ESI-MS 484 [M +
H]+, 482 [M - H]-.
1-{(2′-Acetamido-2′-deoxy-3,4-diisopropylidine-6-[(tert-
butyl(diphenyl)silyl]-r-D-galactopyranosyl}prop-2-ene (8).
Dimethoxypropene (1.4 mL, 7.95 mmol) was added to a solution
of 7 (1.0 g, 2.07 mmol) in DMF (5 mL) in the presence of catalytic
amount Amberlite IR-120 (H+). The reaction mixture was stirred
at room temperature for 12 h, filtered, and evaporated under
reduced pressure. Purification of the residue by flash chroma-
tography (hexane/EtOAc 4:1) yielded 8 (1.07 g, quant.). 1H NMR
(400 MHz, CDCl3) δ 7.72-7.67 (m, 4H), 7.45-7.35 (m, 6H), 5.70-
5.56 (m, 2H), 5.07-5.03 (m, 2H), 4.52-4.50 (m, 1H), 4.26-4.24
nances corresponding to -CO2Me, -OAc, -NHAc,
1
(CH3)2C-, and allyl. H-1H COSY was used to make
proton assignments. NOE spectroscopy showed strong
through-space interaction between H-6 of galactosamine
with H-4 and H-5 of galactosamine as well as H-3ax of
Neu5Ac. The H-6 GalNAcBzfH-3ax Neu5Ac interaction
was consistent with the expected R-configuration of the
anomeric center. The signal corresponding to the reso-
1
nance of H-6 in GalNAcBz in the H NMR spectrum of
13 is a doublet. H-6 is coupled with the C6-OH hydroxyl
proton, with a JH,OH of 6.4 Hz and no coupling is observed
between H-6 and H-5 of GalNAcBz. According to the
molecular models the value of the H6-C6-C5-H5
torsion angle in the S and R isomers is -59.1 and
-177.0°, respectively. The absence of coupling between
H-6 and H-5 is in agreement with the presence of the S
isomer, where the torsion angle is closer to 90 degrees.
In the 1H NMR spectrum of the R isomer the H-6
resonance signal would clearly show coupling with H-5
J. Org. Chem, Vol. 70, No. 20, 2005 8199

(m, 1H), 4.12 (m, 1H), 3.91-3.79 (m, 4H), 2.35-2.22 (m, 1H),
2.18-2.03 (m, 1H), 2.01 (s, 3H), 1.48 (s, 3H), 1.32 (s, 3H), 1.05
(s, 9H); ESI-MS 524 [M + H]+, 522 [M - H]-.
Methyl 5-Acetamido-4,7,8,9-tetra-O-acetyl-2,6-anhydro-
3,5-dideoxy-2-C-{(S)-hydroxy-[6-((2′-acetyl-2′-p-chloro-
benzoyl)amino-2′-deoxy-3,4-diisopropylidine-1-(1-prop-2-
enyl)-r-D-galactopyranosyl)]methyl}-D-erythro-L-manno-
nononate (13). A solution of compounds 11 (22 mg, 0.05 mmol)
and 12 (40 mg, 0.065 mmol) in CH2Cl2 (2 mL) was evaporated
to dryness and the resulting residue dried overnight under high
vacuum. To the dried residue placed under argon was added a
solution of freshly prepared SmI2 (0.1 M, 5 mL), and the reaction
mixture was stirred at room temperature for 20 min. The
reaction mixture was then diluted with ether, washed succes-
sively with 1 N HCl, saturated aqueous Na2S2O3, and H2O, dried
over anhydrous MgSO4, and filtered, and the solvents were
evaporated. The residue was purified by chromatography on
silica gel (petroleum ether-ethyl acetate, v/v 4:1 to 1:1) to give
13 (12 mg, 25%): 1H NMR (500 MHz, CDCl3) δ 7.69 (d, 2H, J )
8.6 Hz), 7.45 (d, 2H, J ) 8.6 Hz), 5.81 (m, 1H, H-2′′), 5.35 (ddd,
1H, J ) 2.6 Hz, J ) 6.8 Hz, J ) 7.4 Hz, H-8), 5.30 (dd, 1H, J )
2.1 Hz, J ) 7.4 Hz, H-7), 5.11-5.00 (m, 3H, H-3′′a, H-3′′b, H-3′),
4.81-4.70 (m, 2H, H-4, H-2′), 4.38 (d, 1H, J ) 3.1 Hz, H-4′),
4.35 (dd, 1H, J ) 2.6 Hz, J ) 12.6 Hz, H-9a), 4.15-4.00 (m, 5H,
H-9b, H-1′, H-6, H-5, H-5′), 3.93 (d, 1H, J ) 6.4 Hz, H-6′), 3.66
(s, 3H, COOCH3), 3.18 (d, 1H, J ) 6.4 Hz, C6′-OH), 2.84 (dd,
1H, J ) 4.4 Hz, J ) 13.2 Hz, H-3eq), 2.48 (dd, 2H, J ) 6.9 Hz,
J ) 6.9 Hz, H-1′′a, H-1′′b), 2.15, 2.12, 2.08, 2.03 (4s, 4 × 3H,
OAc), 1.86 (m, 4H, NAc, H-3ax), 1.83 (s, 3H, NAc), 1.52 and 1.35
(s, 2 × 3H, 2 ×CH3); ESI-MS 897.3 [M + H]+, 919.3 [M + Na]+;
HRMS calcd for C41H53ClN2NaO18 [M + Na]+ 919.2880, found
m/z 919.2883 [M + Na]+.
5-Acetamido-2,6-anhydro-3,5-dideoxy-2-C-{(S)-hydroxy-
[6-(2′-acetyl-2′-deoxy-1-(1-prop-2-enyl)-r-D-galactopyrano-
syl)]methyl}-D-erythro-L-manno-nononate (2). Fully pro-
tected sTn double C-glycoside 13 (9 mg, 0.01 mmol) and 60%
acetic acid (2 mL) were stirred at 80 °C for 1 h. The reaction
mixture was extracted with CHCl3, and the organic phase was
combined, dried over MgSO4, filtered, and evaporated. The dried
residue was reacted with a catalytic amount NaOMe in methanol
overnight followed by stirring with 0.1 M KOH another over-
night. The resulting mixture was neutralized with Amberlite
IR-120 (H+) exchange resin and filtered and the solvent evapo-
rated to dryness. The residue was passed through a P2 desalting
column. Fractions were collected, evaporated under high vacuum,
redissolved in water, and lyophilized to give a white powder in
quantitative yield: 1H NMR (500 MHz, D2O) δ 5.81 (m, 1H,
H-2′′), 5.09-5.02 (m, 2H, H-3′′a, H-3′′b), 4-57-3.53 (m, 12H),
2.84 (dd, 1H, J ) 4 Hz, J ) 13.5 Hz, H-3eq), 2.49 (m, 1H, H-1′′a),
2.35 (m, 1H, H-1′′b), 1.96, 1.92 (2s, 2 × 3H, NAc), 1.71 (t, 1H, J
) 12.5, H-3ax); ESI-MS 535.3 [M - H]-, 559.3 [M + Na]+; HRMS
calcd for C22H36N2NaO13 [M + Na]+ 559.2115, found m/z
559.2113 [M + Na]+.
1-{(2′-Acetyl-2′-p-chlorobenzoyl)amino-2′-deoxy-3,4-di-
isopropylidine-6-[(tert-butyl(diphenyl)silyl]-r-D-galacto-
pyranosyl}prop-2-ene (9). Compound 8 (380 mg, 0.73 mmol)
was dissolved in 2 mL of pyridine-dichloromethane (1:1)
mixture at 0 °C, and p-chlorobenzoyl chloride (184 µL, 1 mmol)
was added. After 10 min at 0 °C, reaction mixture was stirred
at room temperature overnight, poured into ice-water, and
extracted with CHCl3. The organic phase was washed with
NaHCO3 and water, dried over MgSO4, filtered, and evaporated.
The residue was purified on a silica gel column (petroleum
ether-ethyl acetate v/v 6:1) to afford 9 (456 mg, 95%): 1H NMR
(500 MHz, CDCl3) δ 7.75-7.63 (m, 6H), 7.45-7.31 (m, 8H), 5.77
(m, 1H, H-2), 5.17-4.96 (m, 3H, H-3a, H-3b, H-3′), 4.74 (dd, 1H,
J ) 8, J ) 14.5, H-2′), 4.44 (dd, 1H, J ) 4, J ) 9, H-4′), 4.14-
3.93 (m, 3H, H-1′, H-5′′, H-6′a), 3.81 (dd, 1H, J ) 10, J ) 15.5,
H-6′b), 2.53 (m, 1H, H-1a), 2.32 (m, 1H, H-1b), 1.91 (s, 3H,
NCOCH3), 1.52 and 1.29 (s, 2 × 3H, 2 ×CH3), 1.05 (s, 9H, tert-
butyl); 13C NMR (300 MHz, CDCl3) δ 173.9, 173.2, 135.8, 135.9,
134.9, 134.5, 133.8, 133.7, 130.9, 129.8, 129.6, 127.8, 127.8, 117.1,
109.3, 73.4, 73.3, 70.7, 69.1, 63.3, 60.4, 32.4, 28.5, 27.6, 26.9,
26.3, 19.4, 1.2; ESI-MS 662.2 [M + H]+, 684.2 [M + Na]+; HRMS
calcd for C37H44ClNNaO6Si [M + Na]+ 684.2524, found m/z
684.2533 [M + Na]+.
1-[(2′-Acetyl-2′-p-chlorobenzoyl)amino-2′-deoxy-3,4-di-
isopropylidine-r-D-galactopyranosyl]prop-2-ene (10). Com-
pound 9 (30 mg, 0.045 mmol) was dissolved in 1 mL of anhydrous
THF, and trihydrofluoride triethylamine (300 µL) was added.
The reaction mixture was stirred at room temperature. After 3
h, additional trihydrofluoride triethylamine (500 µL) was added
and the mixture stirred for an additional 4 h. The reaction
mixture was dropped into cold NaHCO3 and extracted with Et2O.
The combined organic phase was washed with water, dried over
MgSO4, filtered, and evaporated. The residue was purified on a
silica gel column (petroleum ether-ethyl acetate v/v 5:1) to afford
10 (17 mg, 88%): 1H NMR (500 MHz, CDCl3) δ 7.67 (d, 2H),
7.42 (d, 2H), 5.81 (m, 1H), 5.20-4.98 (m, 3H), 4.72 (bs, 1H), 4.36
(bs, 1H), 4.20-3.62 (m, 4H), 2.51 (m, 1H), 2.36 (m, 1H), 1.92 (s,
3H), 1.52 and 1.29 (s, 2 × 3H); ESI-MS 424.1 [M + H]+, 446.1
[M + Na]+; HRMS calcd for C21H26ClNO6 [M + H]+ 424.1527,
found m/z 424.1521 [M + H]+.
1-[(2′-Acetyl-2′-p-chlorobenzoyl)amino-2′-deoxy-3,4-di-
isopropylidine-5-formyl-r-D-galactopyranosyl]prop-2-
ene (11). Compound 10 (33 mg, 0.078 mmol) was placed into a
5 mL round-bottom flask along with 500 µL of butylmethylimi-
dazolium tetrafluoroborate (bmim[BF4]) under high vacuum for
2 h. Dess-Martin periodinane (1.5 equiv) was added. The
reaction mixture was stirred under argon for 3 h, poured into
water, and extracted with diethyl ether. The organic phases were
combined and suction filtered through a pad of Celite/NaHCO3
(1:1 by mass). The filtrate was dried over MgSO4 and concen-
trated under reduced pressure. A 32 mg amount of 11 was
isolated and used for the next step without any further purifica-
tion: 1H NMR (500 MHz, CDCl3) δ 9.62 (s, 1H), 7.68 (d, 2H),
7.45 (d, 2H), 5.89 (m, 1H), 5.17-5.02 (m, 3H), 4.80-4.62 (m, 2H),
4.34-3.73 (m, 4H), 2.50-2.31 (m, 2H), 1.91 (s, 3H), 1.50 and
1.30 (s, 2 × 3H); ESI-MS 422.1 [M + H]+.
Supporting Information Available: 1D and 2D H NMR
spectra for compounds 2, 4a, 5-11, and 13; 13C NMR spectra
for compound 13, and X-ray data for compound 4b. This
material is available free of charge via the Internet at
http://pubs.acs.org.
JO050691N
8200 J. Org. Chem., Vol. 70, No. 20, 2005