Synthesis of the antigenic tetrasaccharide side chain from the major glycoprotein of Bacillus anthracis exosporium

Article abstract of DOI:10.1021/jo070750s

(Chemical Equation Presented) A synthesis of the pentenyl glycoside of the tetrasaccharide side chain from the major glycoprotein of Bacillus anthracis by a [3 + 1] approach is described. The construction of the 1,2-trans-glycosidic linkage in the termina

Full text of DOI:10.1021/jo070750s

Synthesis of the Antigenic Tetrasaccharide Side Chain from the
Major Glycoprotein of Bacillus anthracis Exosporium
David Crich* and Olga Vinogradova
Department of Chemistry, UniVersity of Illinois at Chicago, 845 West Taylor Street,
Chicago, Illinois 60607-7061
dcrich@chem.wayne.edu
ReceiVed April 10, 2007
A synthesis of the pentenyl glycoside of the tetrasaccharide side chain from the major glycoprotein of
Bacillus anthracis by a [3 + 1] approach is described. The construction of the 1,2-trans-glycosidic linkage
in the terminal anthrose moiety was achieved through the application of known R-nitrilium ion-mediated
â-selective glycosylation methodology. An iterative glycosylation strategy was used for the assembly of
the trirhamnan building block. A new route to the anthrose saccharide was developed from D-galactose.
Introduction
contains the previously unknown terminal substituent, 2-O-
methyl-4-(3-hydroxy-3-methylbutylamino)-4,6-dideoxy-D-glu-
cose. This sugar, which is also referred to as anthrose, appears
to be specific for the spores of this bacteria, as it was not found
in spores of either Bacillus cereus or Bacillus thuringiensis, the
most phylogenetically similar species.5 Thus, tetrasacchride 1
is a very attractive tool for the development of species-specific
biomarkers, as well as of novel vaccines which target anthrax
spores. In view of the fact that pure cell surface oligosaccharides
are often difficult to obtain by isolation, effective synthetic
approaches to the tetrasaccharide and its analogues are highly
desirable.
Because of the recent uses of Bacillus anthracis, a Gram
positive bacteria and the etiological agent of anthrax,1,2 as a
biological weapon, inexpensive, effective methods of detection
and vaccination against this organism are highly desired. The
similarity of the B. anthracis spore-cell-surface antigens with
those of the opportunistic human pathogen B. cereus and other
bacteria of this group complicates the design of reliable selective
antibody-based detection systems. The spores of Bacillus
anthracis are enclosed by a prominent loose fitting layer called
the exosporium, which is the primary barrier of the spore and
the source of the spore antigens,3,4 and which interacts with the
environment, detection devices, and spore-binding cells in the
mammalian host and host defenses. The exosporium therefore
plays an important role in the spore survival and/or pathogenesis.
A highly immunogenic glycoprotein BclA, an important con-
stituent of the exosporium, was found to be substituted with
multiple copies of an O-linked oligosaccharide 1,5 which
Since its isolation in 2004,5 the preparation of several
synthetic tri-6 and tetrasaccharide7-10,11 analogues of 1 has been
(5) Daubenspeck, J. M.; Zeng, H.; Chen, P.; Dong, S.; Steichen, C. T.;
Krishna, N. R.; Pritchard, D. G.; Turnbough, C. L., Jr. J. Biol. Chem. 2004,
279, 30945-30953.
(6) Mehta, A. S.; Saile, E.; Zhong, W.; Buskas, T.; Carlson, R.;
Kannenberg, E.; Reed, Y.; Quinn, C. P.; Boons, G.-J. Chem. Eur. J. 2006,
12, 9136-9149.
* Author to whom correspondence should be addressed. Current address:
Chemistry Department, Wayne State University, 5101 Cass Avenue, Detroit,
MI 48202. Phone: 313-577-1915.
(1) Mock, M.; Fouet, A. Annu. ReV. Microbiol. 2001, 55, 647-671.
(2) Sylvestre, P.; Couture-Tosi, E.; Mock, M. Mol. Microbiol. 2002, 45,
169-178.
(3) Gerhardt, P. Fed. Proc. 1967, 26, 1504-1517.
(4) Steichen, C.; Chen, P.; Kearney, J. F.; Turnbough, C. L., Jr. J.
Bacteriol. 2003, 185, 1903-1910.
(7) Werz, D. B.; Seeberger, P. H. Angew. Chem., Int. Ed. 2005, 44,
6315-6318.
(8) Adamo, R.; Saksena, R.; Kovacˇ, P. Carbohydr. Res. 2005, 340,
2579-2582.
(9) Adamo, R.; Saksena, R.; Kovacˇ, P. HelV. Chim. Acta 2006, 89, 1075-
1089.
(10) Saksena, R.; Adamo, R.; Kovacˇ, P. Bioorg. Med. Chem. Lett. 2006,
16, 615-617.
10.1021/jo070750s CCC: $37.00 © 2007 American Chemical Society
Published on Web 07/28/2007
J. Org. Chem. 2007, 72, 6513-6520
6513

Crich and Vinogradova
SCHEME 1. Synthesis of the Anthrose Donor
FIGURE 1. Literature approaches to the target.
reported in the literature (Figure 1). The first total synthesis
described, that of the tetrasaccharide analogue 2,7 featured a
terminal pentenyl group, which served as a convenient point of
attachment to a carrier protein in vaccine development. In this
first synthesis a convergent approach was utilized to facilitate
access to analogues and shorter sequences, and assembly of the
terminal anthrose was accomplished in a short, straightforward
way starting from D-fucose. A different [3 + 1] tack was taken
in the synthesis of 3;8-10 both a stepwise approach proceeding
from the downstream toward the upstream end of the oligosac-
charide9,10,12 as well as sequential glycosylation with different
types of glycosyl donors8 were explored in the construction of
the trirhamnan. In this second approach the terminal anthrose
building block was synthesized by a more lengthy strategy from
a 4-azido-4,6-dideoxy-D-mannose derivative.13-16 A similar,
[2 + 1] approach was taken for the synthesis of trisaccharide
analogues 4-7,6 but in this case an azido deoxy galactose
derivative17 was used as precursor of the terminal anthrose unit.
Despite the different overall strategies, these syntheses have
many points in common. First, glycosylation with neighboring
group (bromoacetyl or levulinoyl) participation was used in the
construction of the â-linkage to the terminal anthrose unit,7-10
thereby necessitating subsequent removal of the protecting group
at 2-position and then methylation.18 Second, R-selectivity in
the rhamnosylation reactions was achieved in all but one case
by anchimeric assistance.6,7 In all cases the synthesis of the
anthrose building block required extensive protective group
manipulations,13-16 or an expensive starting material.7 In
planning our synthesis of 2 in a [3 + 1] manner, we wanted to
address these problems through (a) application of known
R-nitrilium-mediated â-selective glycosylation19,20 methodology
for the construction of the 1,2-trans glycosidic linkage in the
terminal anthrose moiety; (b) the straightforward assembly of
the rhamnan building block through the recently developed
iterative glycosylation strategy21 using thiorhamnoside donors,
known to give good R-selectivity without neighboring group
participation; and (c) developing a new, shorter route to the
anthrose saccharide, utilizing inexpensive D-galactose as a
precursor.
Results and Discussion
We began our synthesis of the anthrose monosaccharide
building block with the galactose derivative 8, which is readily
available from D-galactose in four steps (Scheme 1).22 Regio-
selective installation of a 2-naphthylmethyl (Nap)23-25 group
at the 3-position through the intermediacy of a tin acetal,26,27
followed by methylation, gave 10. Deprotection in acidic media,
followed by regioselective substitution of the primary 6-OH in
(19) Braccini, I.; Derouet, C.; Esnault, J.; du Penhoat, C. H.; Mallet, J.
M.; Michon, V.; Sinay, P. Carbohydr. Res. 1993, 246, 23-41.
(20) Vankar, Y. D.; Vankar, P. S.; Behrendt, M.; Schmidt, R. R.
Tetrahedron 1991, 47, 9985-9992.
(21) Code´e, J. D. C.; Litjens, R. E. J. N.; van den Bos, L. J.; Overkleeft,
H. S.; van der Marel, G. A. Chem. Soc. ReV. 2005, 34, 769-782.
(22) Ellervik, U.; Magnusson, G. J. Org. Chem. 1998, 63, 9314-9322.
(23) Wright, J. A.; Yu, J.; Spencer, J. B. Tetrahedron Lett. 2001, 42,
4033-4036.
(24) Xia, J.; Abbas, S. A.; Locke, R. D.; Piskorz, C. F.; Alderfer, J. L.;
Matta, K. L. Tetrahedron Lett. 1999, 41, 169-173.
(25) Gaunt, M. J.; Yu, J.; Spencer, J. B. J. Org. Chem. 1998, 63, 4172-
4173.
(11) Guo, H.; O’Doherty, G. A. Angew. Chem. Int. Ed. 2007, 46, 5206-
5208.
(12) According to current recommendations for carbohydrate nomen-
clature, the reducing end of an oligosaccharide is the downstream end.
McNaught, A. D. Carbohydr. Res. 1997, 297, 1-92.
(13) Saksena, R.; Adamo, R.; Kovacˇ, P. Carbohydr. Res. 2005, 340,
1591-1600.
(14) Gotoh, M.; Kovacˇ, P. J. Carbohydr. Chem. 1994, 13, 1193-1213.
(15) Eis, M. J.; Ganem, B. Carbohydr. Res. 1988, 176, 316-323.
(16) Bundle, D. R.; Gerken, M.; Peters, T. Carbohydr. Res. 1988, 174,
239-251.
(17) Liu, M.; Yu, B.; Wu, X.; Hui, Y.; Fung, K.-P. Carbohydr. Res.
2000, 329, 745-754.
(26) David, S. In PreparatiVe Carbohydrate Chemistry; Hanessian, S.,
(18) In the process of our investigation â-selective glycosylation by the
Ed.; Dekker: New York, 1997, pp 69-86.
R-nitrilium ion method was reported.6
(27) David, S.; Hanessian, S. Tetrahedron 1985, 41, 643-663.
6514 J. Org. Chem., Vol. 72, No. 17, 2007

Antigenic Tetrasaccharide Side Chain
SCHEME 2. Synthesis of Monosaccharide 18
SCHEME 4. Trisaccharide Synthesis
SCHEME 3. Synthesis of Monosaccharide 19
SCHEME 5. Exploratory Couplings to the Anthrose Donor
the presence of the secondary 4-OH with a phenylseleno group,28
gave 12. Reduction with tributyltin hydride29,30 gave the
6-deoxygalactose derivative 13. Displacement of the 4-O-triflate,
introduced by the reaction of 13 with triflic anhydride, with
azide gave desired donor 14.
With 14 in hand, we proceeded to the synthesis of the
trirhamnan building blocks. Benzylation of known n-pentenyl
rhamnoside 15,31 readily available through Fischer glycosylation
of l-rhamnose and further acetonide protection,31 gave 16
(Scheme 2). Cleavage of the 2,3-O-isopropylidene group in
acidic media, followed by stannyl-activated regioselective
benzylation, gave 17,7 which was converted, using a known
procedure,32 to the desired dibromide acceptor 18. Building
block 1933 was synthesized using a known procedure33 and then
converted to the acceptor 20,33 following the protocol outlined
in Scheme 3. A higher yield of 20 was achieved by utilizing a
mixture of methanol and dichloromethane as a solvent than in
the pure dichloromethane used previously.
The assembly of the trirhamnan moiety 22 started with
preactivation of donor 19, followed by the addition of acceptor
20. Subsequent quenching of the reaction mixture with triethyl
phosphite34,35 provided disaccharide 21, predominantly as the
R-anomer. In a similar manner, but omitting the quenching step,
21R was allowed to react with 18, to give the crude trisaccharide,
which was further deprotected under oxidative conditions to give
the desired trisaccharide building block 22 (Scheme 4).
In order to find an optimal promoter/solvent combination for
the synthesis of the tetrasaccharide, the glycosylation of donor
14 was investigated using model acceptor 2336 and the activation
systems outlined in Scheme 5. In the case of preactivation of
14 with 1-benzenesulfinylpiperidine (BSP)/Tf2O37 in the pres-
ence of 2,4,6-tri-tert-butylpyrimidine (TTBP) and subsequent
addition of acceptor 23, a considerable improvement in the
â-selectivity was observed, as expected, when the solvent was
changed from dichloromethane to propionitrile.19,20 Use of
analogous promoters (Ph2SO,35 1 or 2 equiv) did not improve
the selectivity. However, activation of the donor 14 in the
presence of acceptor 23 by the NIS/TfOH system38-40 resulted
(28) Mizuno, M.; Cava, M. P.; Garito, A. F. J. Org. Chem. 1976, 41,
1485-1486.
(29) Clive, D. L. J.; Chittattu, G.; Wong, C. K. J. Chem. Soc., Chem.
Commun. 1978, 41-42.
(30) Clive, D. L. J.; Chittattu, G. J.; Farina, V.; Kiel, W. A.; Menchen,
S. M.; Russell, C. G.; Singh, A.; Wong, C. K.; Curtis, N. J. J. Am. Chem.
Soc. 1980, 102, 4438-4447.
(31) Heidelberg, T.; Martin, O. R. J. Org. Chem. 2004, 69, 2290-2301.
(32) Debenham, J. S.; Rodebaugh, R.; Fraser-Reid, B. J. Org. Chem.
1997, 62, 4591-4600.
(36) Pozsgay, V. Carbohydr. Res. 1979, 69, 284-286.
(37) Crich, D.; Smith, M. J. Am. Chem. Soc. 2001, 123, 9015-9020.
(38) Veeneman, G. H.; van Leeuwen, S. H.; Zuurmond, H.; van Boom,
J. H. J. Carbohydr. Chem. 1990, 9, 783-796.
(39) Konradsson, P.; Udodong, U. E.; Fraser-Reid, B. Tetrahedron Lett.
1990, 31, 4313-4316.
(40) Konradsson, P.; Mootoo, D. R.; McDevitt, R. E.; Fraser-Reid, B.
J. Chem. Soc., Chem. Commun. 1990, 270-272.
(33) Crich, D.; Vinogradova, O. J. Org. Chem. 2007, 72, 3581-3584.
(34) Code´e, J. D. C.; van den Bos, L. J.; Litjens, R. E. J. N.; Overkleeft,
H. S.; van Boeckel, C. A. A.; van Boom, J. H.; van der Marel, G. A.
Tetrahedron 2004, 60, 1057-1064.
(35) Code´e, J. D. C.; Litjens, R. E. J. N.; den Heeten, R.; Overkleeft, H.
S.; van Boom, J. H.; van der Marel, G. A. Org. Lett. 2003, 5, 1519-1522.
J. Org. Chem, Vol. 72, No. 17, 2007 6515

Crich and Vinogradova
SCHEME 6. Completion of the Synthesis
ride 2, whose spectroscopic data was identical to that previously
reported (Scheme 6).7
In conclusion, a synthesis of an antigenic tetrasaccharide from
Bacillus anthracis has been accomplished in a [3 + 1] manner.
A straightforward route to the anthrose building block from
D-galactose was developed in which no extensive protective
group manipulations or expensive starting materials were
necessary. The assembly of the trirhamnan building block via
an iterative glycosylation strategy, and the construction of the
1,2-trans-glycosidic linkage to the terminal anthrose moiety
through the R-nitrilium ion-mediated â-selective glycosylation
methodology, enables the use of a minimal protecting group
strategy and increases the efficiency of the overall synthesis.
Experimental Section
General. Unless otherwise noted, reactions were conducted under
1
an inert atmosphere of argon or nitrogen. All H and 13C spectra
were recorded in CDCl3, except for 2, where CD3OD was used as
a solvent.
S-Phenyl 4,6-O-Benzylidene-3-O-(2-naphthylmethyl)-â-D-
thiogalactopyranoside (9). A suspension of 822 (490 mg, 1.36
mmol) and dibutyltin oxide (610 mg, 2.45 mmol) in toluene (7
mL) was heated to reflux in a Dean-Stark apparatus for 4 h, after
which most of the solvent was distilled off. The reaction mixture
was cooled to room temperature, and the residual solvent was
evaporated under reduced pressure. CsF (414 mg, 2.72 mmol),
2-(bromomethyl)naphthalene (602 mg, 2.72 mmol), tetrabutylam-
monium iodide (1.00 g, 2.72 mmol), and DMF (6 mL) were then
added. The reaction mixture was heated to reflux overnight, diluted
with ethyl acetate, washed (sat. aq NaHCO3, brine), dried (Na2SO4),
and concentrated. Purification by column chromatography (SiO2,
1/9 to 1/3 ethyl acetate/hexanes) gave 9 (490 mg, 60%) as a white
in a significant enhancement of the steroselectivity, as well as
in the overall yield of the reaction.
1
solid. Mp 175-176 °C. [R]21D +32.4 (c 0.38, CHCl3). H NMR
To complete the synthesis, the anthrose unit 14 was coupled
to trisaccharide 22 using the optimal NIS/TfOH/propionitrile
conditions to afford 25 as an approximately 3:1 â:R-mixture of
anomers in 92% overall yield. Thus, the increased efficiency
of the direct introduction of the anthrose moiety in this manner
is achieved at the expense of some loss of selectivity. Debro-
mination32 of 25â gave 26 from which oxidative cleavage of
the 2-naphthylmethyl group afforded tetrasaccharide 27, suitable
for further modifications in the terminal anthrose moiety, such
as were found to be essential for the constitution of the highly
specific antigenic determinant.41 The moderate yield of 27 is
attributable to the previously reported problem of the competing
debenzylation reactions in the course of the DDQ-promoted
cleavage of 2-naphthylmethyl/p-methoxyphenyl ethers.33 To
overcome this difficulty the mixture of debenzylated byproducts
from the 2-naphthylmethyl deprotection reaction was benzylated
under standard conditions to give 28, suitable for further
transformations to the target molecule through the same routes
as 27. Final removal of the benzyl protecting groups and
transformation of azide moiety to the amine was achieved by
application of sodium in liquid ammonia to the mixture of 27
and 28. Subsequent coupling to the 3-hydroxy-3-methylbutyric
acid under peptide-coupling conditions42 led to the tetrasaccha-
(400 MHz) δ: 7.73-7.85 (m, 4H), 7.66-7.72 (m, 2H), 7.44-7.52
(m, 3H), 7.34-7.44 (m, 5H), 7.22-7.32 (m, 3H), 5.42 (s, 1H),
4.90 (s, 2H), 4.51 (d, J ) 9.5 Hz, 1H), 4.34 (dd, J ) 12.3, 1.6 Hz,
1H), 4.15 (dd, J ) 3.4, 0.7 Hz, 1H), 3.92-4.02 (m, 2H), 3.56 (dd,
J ) 9.3, 3.3 Hz, 1H), 3.41-3.43 (m, 1H), 2.52 (d, J ) 1.9 Hz,
1H); 13C NMR (101 MHz) δ: 137.8, 135.5, 133.8, 133.2, 133.1,
130.6, 129.1 128.9, 128.3, 128.2, 127.9, 127.7, 126.8, 126.6, 126.2,
126.1, 125.8, 101.2, 87.1, 80.2, 73.4, 71.9, 70.1, 69.4, 67.3;
ESIHRMS Calcd for C30H28NaO5S [M + Na]+: 523.1555. Found
523.1562.
S-Phenyl 4,6-O-Benzylidene-2-O-methyl-3-O-(2-naphthyl-
methyl)-â-D-thiogalactopyranoside (10). A solution of 9 (9.34 g,
18.7 mmol) in DMF (300 mL) was cooled to -15 °C, NaH (60%
in mineral oil, 1.12 g, 28.0 mmol) was added slowly, and the
reaction mixture was allowed to stir for 30 min at this temperature.
Methyl iodide (1.98 mL, 31.7 mmol) was then added slowly, and
the reaction mixture was allowed to warm up to room temperature
and stirred overnight. The reaction mixture was quenched with
MeOH, diluted with CHCl3, washed (water, brine), dried (Na2SO4),
and concentrated. Purification by column chromatography (SiO2,
1/4 ethyl acetate/hexanes) gave 10 (7.7 g, 80%) as a white solid.
1
Mp 174-176 °C. [R]21 +28.4 (c 0.40, CHCl3). H NMR (400
D
MHz) δ: 7.76-7.87 (m, 4H), 7.68-7.73 (m, 2H), 7.45-7.55 (m,
5H), 7.36-7.43 (m, 3H), 7.19-7.27 (m, 3H), 5.46 (s, 1H), 4.93
(d, J ) 12.7 Hz, 1H), 4.86 (d, J ) 12.6 Hz, 1H), 4.49 (d, J ) 9.4
Hz, 1H), 4.33 (dd, J ) 12.3, 1.5 Hz, 1H), 4.12 (dd, J ) 3.4, 0.7
Hz, 1H), 3.94 (dd, J ) 12.4, 1.6 Hz, 1H), 3.64 (t, J ) 9.2 Hz, 1H),
3.59 (s, 3H), 3.57 (dd, J ) 9.2, 3.4 Hz, 1H), 3.35-3.37 (m, 1H);
13C NMR (101 MHz) δ: 137.9, 135.7, 133.2, 133.0, 132.9, 132.6,
(41) Wang, D.; Carroll, G. T.; Turro, N. J.; Koberstein, J. T.; Kovacˇ, P.;
Saksena, R.; Adamo, R.; Herzenberg, L. A.; Herzenberg, L. A.; Steinman,
L. Proteomics 2007, 7, 180-184.
(42) Carpino, L. A.; El-Faham, A.; Albericio, F. J. Org. Chem. 1995,
60, 3561-3564.
6516 J. Org. Chem., Vol. 72, No. 17, 2007

Antigenic Tetrasaccharide Side Chain
129.1, 128.8, 128.2, 127.9, 127.7, 127.5, 126.7, 126.6, 126.2, 126.0,
125.8, 101.4, 86.4, 81.1, 76.9, 74.0, 72.1, 69.8, 69.4, 61.1;
ESIHRMS Calcd for C31H30NaO5S [M + Na]+: 537.1712. Found
537.1696.
(m, 4H), 7.46-7.59 (m, 5H), 7.26-7.35 (m, 3H), 5.07 (d, J )
10.8 Hz, 1H), 5.02 (d, J ) 10.8 Hz, 1H), 4.53 (d, J ) 9.9 Hz, 1H),
3.67 (s, 3H), 3.51 (t, J ) 9.1 Hz, 1H), 3.20-3.28 (m, 2H), 3.18 (t,
J ) 9.6 Hz, 1H), 1.38 (d, J ) 6.1 Hz, 3H); 13C NMR (126 MHz)
δ: 135.2, 133.42, 133.35, 133.1, 132.1, 129.0, 128.3, 128.1, 127.8,
127.7, 127.2, 126.3, 126.2, 126.1, 87.4, 84.7, 83.0, 75.7, 74.8, 67.6,
61.2, 18.8; ESIHRMS Calcd for C24H25NaN3O3S [M + Na]+:
458.1514. Found 458.1505.
S-Phenyl 2-O-Methyl-3-O-(2-naphthylmethyl)-â-D-thiogalac-
topyranoside (11). A mixture of 10 (510 mg, 1.0 mmol), p-
toluenesulfonic acid monohydrate (19 mg, 0.1 mmol) and MeOH
(10 mL) was heated to reflux for 45 min, cooled to room
temperature, diluted with ethyl acetate, washed (sat. aq NaHCO3,
brine), dried (Na2SO4), and concentrated. Purification by column
chromatography (SiO2, 2/3 to 1/1 ethyl acetate/hexanes) gave 11
(401 mg, 95%) as a white solid. Mp 144-145 °C. [R]21D -11.7 (c
0.62, CHCl3). 1H NMR (400 MHz) δ: 7.78-7.87 (m, 4H), 7.46-
7.57 (m, 5H), 7.22-7.32 (m, 3H), 4.88 (s, 2H), 4.54 (d, J ) 9.2
Hz, 1H), 4.02-4.05 (m, 1H), 3.90-3.98 (m, 1H), 3.73-3.81 (m,
1H), 3.65 (s, 3H), 3.42-3.55 (m, 3H), 2.74 (br s, 1H), 2.28-2.34
(m, 1H); 13C NMR (101 MHz) δ: 135.1, 133.6, 133.2, 133.1, 131.7,
129.0, 128.5, 127.9, 127.8, 127.5, 126.8, 126.4, 126.2, 125.7, 87.4,
82.1, 78.8, 78.0, 72.4, 67.6, 62.7, 61.4; ESIHRMS Calcd for C24H26-
NaO5S [M + Na]+: 449.1399. Found 449.1391.
n-Pentenyl 4-O-Benzyl-2,3-O-isopropylidene-r-L-rhamnopy-
ranoside (16). To a solution of 1531 (1.46 g, 5.36 mmol) in DMF
(8 mL) was slowly added NaH (60% in mineral oil, 321 mg, 8.04
mmol) at 0 °C, followed by benzyl bromide (961 µL, 8.04 mmol),
and the reaction mixture was allowed to stir for 3 h at room
temperature. The reaction mixture was diluted with ethyl acetate,
washed (sat. aq NH4Cl, brine), dried (Na2SO4), and concentrated.
Filtration of the crude reaction mixture through a pad of silica gel
(with ethyl acetate as an eluent) and purification by radial
chromatography (SiO2, hexanes to 1/19 ethyl acetate/hexanes) gave
16 (1.74 g, 90%) as a white solid. Mp 38-39 °C. [R]19D -46.4 (c
0.71, CHCl3). 1H NMR (500 MHz) δ: 7.26-7.40 (m, 5H), 5.77-
5.86 (m, 1H), 5.04 (ddd, J ) 17.1, 3.1, 1.5 Hz, 1H), 4.99 (dq, J )
10.2, 1.5 Hz, 1H), 4.96 (s, 1H), 4.92 (d, J ) 11.6 Hz, 1H), 4.64 (d,
J ) 11.6 Hz, 1H), 4.27-4.31 (m, 1H), 4.15 (d, J ) 5.7 Hz, 1H),
3.66-3.74 (m, 2H), 3.43 (dt, J ) 9.6, 6.4 Hz, 1H), 3.23 (dd, J )
9.8, 7.1 Hz, 1H), 2.09-2.17 (m, 2H), 1.64-1.74 (m, 2H), 1.53 (s,
3H), 1.39 (s, 3H), 1.29 (d, J ) 6.2 Hz, 3H); 13C NMR (126 MHz)
δ: 138.4, 138.0, 128.3, 128.0, 127.6, 115.0, 109.1, 97.0, 81.2, 78.7,
76.2, 73.0, 66.8, 64.5, 30.3, 28.6, 28.1, 26.4, 17.9; ESIHRMS Calcd
for C21H30NaO5 [M + Na]+: 385.1991. Found 385.1980.
S-Phenyl 2-O-Methyl-3-O-(2-naphthylmethyl)-6-deoxy-6-
phenylseleno-â-D-thiogalactopyranoside (12). A mixture of 11
(1.06 g, 2.49 mmol), diphenyl diselenide (3.89 g, 12.47 mmol),
tributylphosphine (4.3 mL, 17.43 mmol), and toluene (20 mL) was
heated to reflux for 24 h. Concentration of the reaction mixture,
followed by purification by column chromatography (SiO2, hexanes
to 2/3 ethyl acetate/ hexanes), gave 12 (1.09 g, 77%) as a white
1
solid. Mp 128-132 °C. [R]21D +16.4 (c 1.01, CHCl3). H NMR
(500 MHz) δ: 7.78-7.88 (m, 4H), 7.58-7.63 (m, 2H), 7.43-7.54
(m, 5H), 7.18-7.34 (m, 6H), 4.87 (s, 2H), 4.48 (d, J ) 9.5 Hz,
1H), 4.12 (t, J ) 2.5 Hz, 1H), 3.65 (s, 3H), 3.41-3.52 (m, 3H),
3.30 (dd, J ) 12.8, 6.7 Hz, 1H), 3.18 (dd, J ) 12.7, 7.2 Hz, 1H),
2.36 (d, J ) 1.8 Hz, 1H); 13C NMR (126 MHz) δ: 135.1, 133.7,
133.2, 133.1, 132.6, 132.1, 129.7, 129.2, 128.9, 128.5, 127.9, 127.8,
127.5, 127.1, 126.8, 126.3, 126.2, 125.8, 87.7, 82.4, 78.7, 77.6,
72.5, 67.5, 61.3, 27.5; ESIHRMS Calcd for C30H30NaO4SSe [M +
Na]+: 589.0928. Found 589.0900.
n-Pentenyl 2,4-Di-O-benzyl-r-L-rhamnopyranoside (17). A
mixture of 16 (1.25 g, 3.45 mmol) and acetic acid (80% in water,
10 mL) was heated for 4 h at 90 °C. Solvents were then evaporated,
and residual syrup was dried by addition of toluene, followed by
evaporation (two times). Bu2SnO (1.03 g, 4.14 mmol) was then
added to this syrup, followed by benzene (25 mL), and the mixture
was heated to reflux in a Dean-Stark apparatus for 3 h, after which
most of the solvent was distilled off. The reaction mixture was
cooled to room temperature, and the residual solvent was evaporated
under reduced pressure. CsF (1.05 g, 6.90 mmol), benzyl bromide
(536 µL, 4.49 mmol), and DMF (20 mL) were then added. The
reaction mixture was allowed to stir overnight, diluted with ethyl
acetate, washed (water, brine), dried (Na2SO4), and concentrated.
Filtration of the crude reaction mixture through a pad of silica gel
(with ethyl acetate as an eluent) and purification by radial
chromatography (SiO2, hexanes to 3/17 ethyl acetate/hexanes) gave
17 (1.06 g, 74%). Spectral data matched that reported in literature.7
4,5-Dibromopentyl 2,4-Di-O-benzyl-r-L-rhamnopyranoside
(18). A solution of 17 (300 mg, 0.73 mmol) in THF/acetonitrile (3
mL/ 6 mL) was added to a mixture of CuBr2 (812 mg, 3.64 mmol)
and LiBr (632 mg, 7.28 mmol) in THF/ acetonitrile (6 mL/ 12 mL).
The reaction mixture was stirred overnight in the dark at room
temperature, then diluted with ethyl acetate, washed (water, two
times), dried (Na2SO4), and concentrated. Filtration of the crude
reaction mixture through a pad of silica gel (with ethyl acetate as
an eluent) and purification by radial chromatography (SiO2, hexanes
to 1/4 ethyl acetate/hexanes) gave 18 as a mixture of two
diastereomers in the dibromopentyl chain (370 mg, 89%). 1H NMR
(500 MHz) δ: 7.28-7.41 (m, 10H), 4.91 (d, J ) 10.8 Hz, 1H),
4.81 (d, J ) 1.5 Hz, 1H), 4.72 (s, 2H), 4.66 (d, J ) 10.8 Hz, 1H),
4.15-4.22 (m, 1H), 4.01-4.04 (m, 1H), 3.84-3.89 (m, 2H), 3.69-
3.77 (m, 2H), 3.63 (t, J ) 10.1 Hz, 1H), 3.48 (t, J ) 9.4 Hz, 1H),
3.42-3.47 (m, 1H), 2.60 (s, 1H), 2.20-2.30 (m, 1H), 1.79-1.93
(m, 2H), 1.67-1.76 (m, 1H), 1.34 (d, J ) 6.4 Hz, 3H); 13C NMR
(126 MHz) δ: 138.4, 137.9, 128.6, 128.5, 128.1, 128.0, 127.9,
127.8, 99.1, 99.0, 80.0, 75.5, 72.1, 68.6, 67.5, 66.54, 66.51, 52.6,
52.5, 36.2, 33.01, 32.95, 26.9, 18.0; ESIHRMS Calcd for C25H32-
NaBr2O5 [M + Na]+: 593.0514. Found 593.0519.
S-Phenyl 2-O-Methyl-3-O-(2-naphthylmethyl)-â-D-thiofucopy-
ranoside (13). A solution of 12 (820 mg, 1.45 mmol), AIBN (98
mg, 0.58 mmol), and Bu3SnH (576 µL, 2.17 mmol) in benzene
(145 mL) was heated to reflux for 3 h. The solvent was evaporated,
and the residual syrup was dissolved in acetonitrile, washed twice
with hexanes, and concentrated. Filtration of the crude reaction
mixture through a pad of silica gel (with ethyl acetate as an eluent)
and purification by radial chromatography (SiO2, 1/19 to 1/4 ethyl
acetate/hexanes) gave 13 (504 mg, 85%) as a white solid. Mp 108-
1
111 °C. [R]20D -11.2 (c 0.33, CHCl3). H NMR (501 MHz) δ:
7.79-7.87 (m, 4H), 7.55-7.59 (m, 2H), 7.46-7.53 (m, 3H), 7.22-
7.33 (m, 3H), 4.89 (s, 2H), 4.50 (d, J ) 9.7 Hz, 1H), 3.80 (d, J )
2.8 Hz, 1H), 3.65 (s, 3H), 3.51-3.55 (m, 2H), 3.43 (t, J ) 9.4 Hz,
1H), 2.33 (br s, 1H), 1.35 (d, J ) 6.6 Hz, 3H); 13C NMR (126
MHz) δ: 135.3, 133.9, 133.2, 133.1, 132.0, 128.9, 128.5, 128.0,
127.8, 127.4, 126.8, 126.3, 126.2, 125.8, 87.4, 82.6, 78.7, 74.2,
72.3, 69.7, 61.4, 16.8; ESIHRMS Calcd for C24H26NaO4S [M +
Na]+: 433.1450. Found 433.1445.
S-Phenyl 4-Azido-4-deoxy-2-O-methyl-3-O-(2-naphthylmethyl)-
â-D-thioquinovopyranoside (14). To a solution of 13 (313 mg,
0.76 mmol) and pyridine (185 µL, 2.29 mmol) in CH2Cl2 (7 mL)
was added Tf2O (256 µL, 1.52 mmol) at 0 °C. The reaction mixture
was stirred for 1.5 h at room temperature, diluted with CH2Cl2,
washed (sat. aq NaHCO3, brine), dried (Na2SO4), and concentrated.
The residue was dissolved in DMF (3 mL), and NaN3 (64 mg, 0.98
mmol) was added. The reaction mixture was allowed to stir for
2.5 h, diluted with ethyl acetate, washed (brine), dried (Na2SO4),
and concentrated. Filtration of the crude reaction mixture through
a pad of silica gel (with ethyl acetate as an eluent) and purification
by radial chromatography (SiO2, hexanes to 1/ 19 ethyl acetate/
hexanes) gave 14 (288 mg, 87%) as a white solid. Mp 85-86 °C.
[R]23D +32.3 (c 0.25, CHCl3). 1H NMR (501 MHz) d: 7.81-7.90
S-Phenyl 2,4-Di-O-benzyl-r-L-thiorhamnopyranoside (20). To
a solution of 1933 (1.83 g, 3.17 mmol) in MeOH/CH2Cl2 (10 mL/
J. Org. Chem, Vol. 72, No. 17, 2007 6517

Crich and Vinogradova
30 mL) was added DDQ (2.16 g, 9.51 mmol) at 0 °C. After 30
min, the reaction mixture was warmed to room temperature and
stirred for a further 5 h before it was diluted with CH2Cl2 and
quenched with sat. aq Na2CO3. The organic phase was separated,
washed (sat. aq Na2CO3), dried (Na2SO4), and concentrated.
Filtration of the crude reaction mixture through a pad of silica gel
(with ethyl acetate as an eluent) and purification by radial
chromatography (SiO2, hexanes to 1/9 ethyl acetate/hexanes) gave
20 (1.03 g, 74%), whose spectral data matched that reported in
literature.33
dropwise. After being stirred for 30 min at -60 °C, the reaction
mixture was warmed to room temperature, filtered, diluted with
CH2Cl2, washed (sat. aq Na2CO3), dried (Na2SO4), and concentrated.
The crude reaction mixture was filtered through a pad of silica gel
(with ethyl acetate as an eluent) and purified by radial chromatog-
raphy (SiO2, hexanes to 1/9 ethyl acetate/hexanes). Fractions
containing product were combined and concentrated to give a clear
oil. To a solution of this oil in CH2Cl2/MeOH (18 mL/6 mL) was
added DDQ (400 mg, 1.76 mmol) at 0 °C. After 30 min, the reaction
mixture was warmed to room temperature and further stirred for 9
h before it was diluted with CH2Cl2 and quenched with sat. aq Na2-
CO3. The organic phase was separated, washed (sat. aq Na2CO3),
dried (Na2SO4), and concentrated. Filtration of the crude reaction
mixture through a pad of silica gel (with ethyl acetate as an eluent)
and purification by radial chromatography (SiO2, hexanes to 3/17
ethyl acetate/hexanes) gave 22 as a mixture of two diastereomers
S-Phenyl 2,4-Di-O-benzyl-3-O-(2-naphthylmethyl)-r-L-rham-
nopyranosyl-(1f3)-2,4-di-O-benzyl-r-L-thiorhamnopyrano-
side (21r) and S-Phenyl 2,4-Di-O-benzyl-3-O-(2-naphthyl-
methyl)-â-L-rhamnopyranosyl-(1f3)-2,4-di-O-benzyl-r-L-thio-
rhamnopyranoside (21â). To a solution of 19 (304 mg, 0.53
mmol), TTBP (262 mg, 1.05 mmol), Ph2SO (107 mg, 0.53 mmol),
and activated 3 Å powdered molecular sieves in CH2Cl2 (10 mL)
was added Tf2O (98 µL, 0.58 mmol) at -60 °C. The reaction
mixture was stirred for 1 h at this temperature, and a solution of
20 (391 mg, 0.90 mmol) in CH2Cl2 (4 mL) was added dropwise.
The reaction mixture was stirred for an additional 30 min at -60
°C and then quenched by the addition of P(OEt)3 (184 µL, 1.05
mmol). The reaction mixture was warmed to room temperature,
filtered, diluted with CH2Cl2, washed (sat. aq Na2CO3), dried (Na2-
SO4), and concentrated. Filtration of the crude reaction mixture
through a pad of silica gel (with ethyl acetate as an eluent) and
purification by radial chromatography (SiO2, hexanes to 1/9 ethyl
acetate/hexanes), followed by the HPLC (SiO2, hexanes to 1/9 ethyl
acetate/ hexanes), gave 21R (235 mg, 49%), 21â (34 mg, 7%), and
20 (70 mg, 18%) was recovered. 21R. [R]24D -61.2 (c 0.20, CHCl3).
1H NMR (501 MHz) δ: 7.66-7.83 (m, 4H), 7.41-7.49 (m, 5H),
7.35-7.40 (m, 6H), 7.18-7.35 (m, 17H), 5.52 (s, 1H), 5.18 (s,
1H), 5.04 (d, J ) 11.2 Hz, 1H), 4.78 (d, J ) 12.1 Hz, 1H), 4.67-
4.74 (m, 3H), 4.60 (d, J ) 11.9 Hz, 1H), 4.45-4.55 (m, 4H), 4.12-
4.20 (m, 1H), 4.07 (dd, J ) 9.5, 2.9 Hz, 1H), 4.01-4.04 (m, 1H),
3.99 (dd, J ) 9.5, 3.0 Hz, 1H), 3.81-3.88 (m, 1H), 3.73-3.76 (m,
1H), 3.70 (t, J ) 9.4 Hz, 1H), 3.58 (t, J ) 9.4 Hz, 1H), 1.35 (d, J
) 6.2 Hz, 3H), 1.30 (d, J ) 6.2 Hz, 3H); 13C NMR (126 MHz) δ:
139.0, 138.4, 137.8, 136.0, 134.6, 133.3, 133.0, 131.5, 129.1, 128.6,
128.5, 128.4, 128.3, 128.1, 128.0, 127.9, 127.84, 127.81, 127.71,
127.66, 127.6, 127.5, 127.4, 127.0, 126.5, 126.1, 125.9, 99.9 (1JCH
) 168.7 Hz), 85.5 (1JCH ) 164.9 Hz), 80.8, 80.5, 79.9, 79.6, 76.0,
75.2, 74.7, 72.6, 72.5, 72.2, 69.5, 68.9, 18.2, 17.9; ESIHRMS Calcd
for C57H58NaO8S [M + Na]+: 925.3750. Found 925.3741. 21â.
1
in the dibromopentyl chain (413 mg, 45%, two steps). H NMR
(501 MHz) δ: 7.14-7.40 (m, 30H), 5.23 (s, 1H), 5.13 (d, J ) 1.7
Hz, 1H), 4.90 (d, J ) 11.2 Hz, 1H), 4.89 (d, J ) 10.9 Hz, 1H),
4.80 (d, J ) 11.7 Hz, 1H), 4.70-4.75 (m, 2H), 4.57-4.69 (m,
4H), 4.48-4.55 (m, 2H), 4.36 (d, J ) 11.6 Hz, 1H), 4.20 (dd, J )
9.6, 3.0 Hz, 1H), 4.16-4.22 (m, 1H), 4.12 (d, J ) 11.7 Hz, 1H),
4.01-4.05 (m, 1H), 3.97 (td, J ) 9.0, 3.5 Hz, 1H), 3.79-3.89 (m,
4H), 3.60-3.77 (m, 6H), 3.42-3.47 (m, 1H), 3.42 (t, J ) 9.5 Hz,
1H), 3.31 (t, J ) 9.3 Hz, 1H), 2.29 (d, J ) 9.5 Hz, 1H), 2.20-2.30
(m, 1H), 1.79-1.92 (m, 2H), 1.67-1.77 (m, 1H), 1.33 (d, J ) 6.2
Hz, 3H), 1.30 (d, J ) 6.1 Hz, 3H), 1.25 (d, J ) 6.2 Hz, 3H); 13C
NMR (126 MHz) δ: 138.8, 138.6, 138.5, 138.3, 138.1, 137.8,
128.50, 128.47, 128.4, 128.1, 127.84, 127.78, 127.6, 126.9, 99.2
(1JCH ) 170.0 Hz), 99.1(1JCH ) 168.7 Hz), 99.0 (1JCH ) 170.0
Hz), 98.5 (1JCH ) 170.0 Hz), 82.2, 81.1, 80.6, 79.9, 79.2, 77.9,
76.8, 75.5, 74.9, 74.7, 74.6, 72.6, 72.5, 72.4, 71.7, 68.9, 68.2, 67.7,
66.4, 52.6, 52.5, 36.1, 33.03, 33.00, 26.9, 18.2, 18.1, 18.0;
ESIHRMS Calcd for C65H76Br2NaO13 [M + Na]+: 1245.3550.
Found 1245.3521.
Methyl 2,4-Di-O-benzyl-3-O-(2-naphthylmethyl)-r-L-rham-
nopyranosyl-(1f3)-2,4-di-O-benzyl-r-L-rhamnopyranoside (24r)
and Methyl 2,4-Di-O-benzyl-3-O-(2-naphthylmethyl)-â-L-rham-
nopyranosyl-(1f3)-2,4-di-O-benzyl-r-L-rhamnopyranoside (24â).
Method A. To a solution of 14 (17 mg, 0.039 mmol), TTBP
(19 mg, 0.078 mmol), BSP (8 mg, 0.039 mmol), and activated 3 Å
powdered molecular sieves in CH2Cl2 (1.5 mL) was added Tf2O
(7.2 µL, 0.043 mmol) at -60 °C. The reaction mixture was stirred
for 5 min at this temperature, and solution of 23 (17 mg, 0.048
mmol) in CH2Cl2 (0.6 mL) was added dropwise. The reaction
mixture was stirred for an additional 2 min at -60 °C, slowly
warmed to room temperature, filtered, washed (sat. aq Na2CO3),
dried (Na2SO4), and concentrated. Filtration of the crude reaction
mixture through a pad of silica gel (with ethyl acetate as an eluent)
and purification by means of radial chromatography (SiO2, hexanes
to 3/17 ethyl acetate/hexanes) gave 24R (19 mg, 72%) and 24â (3
1
[R]22D +7.4 (c 0.50, CHCl3). H NMR (501 MHz) δ: 7.69-7.86
(m, 4H), 7.37-7.51 (m, 9H), 7.26-7.37 (m, 13H), 7.18-7.25 (m,
6H), 5.54 (d, J ) 2.9 Hz, 1H), 5.05 (d, J ) 10.6 Hz, 1H), 5.01 (d,
J ) 10.8 Hz, 1H), 5.00 (d, J ) 12.5 Hz, 1H), 4.92 (d, J ) 12.5
Hz, 1H), 4.66-4.75 (m, 2H), 4.69 (d, J ) 12.1 Hz, 1H), 4.63 (d,
J ) 12.1 Hz, 1H), 4.55 (d, J ) 10.6 Hz, 1H), 4.48 (d, J ) 12.3
Hz, 1H), 4.29 (s, 1H), 4.18 (dd, J ) 7. 9, 3.1 Hz, 1H), 4.11-4.17
(m, 1H), 3.91 (t, J ) 3.0 Hz, 1H), 3.82 (d, J ) 2.9 Hz, 1H), 3.63-
3.70 (m, 2H), 3.40 (dd, J ) 9.5, 3.0 Hz, 1H), 3.22-3.29 (m, 1H),
1.39 (d, J ) 6.2 Hz, 3H), 1.37 (d, J ) 6.1 Hz, 3H); 13C NMR (126
MHz) δ: 138.9, 138.7, 138.6, 137.7, 135.9, 134.8, 133.3, 133.0,
131.6, 129.1, 128.5, 128.44, 128.37, 128.24, 128.18, 128.14, 128.10,
128.0, 127.9, 127.8, 127.6, 127.4, 127.3, 126.2, 125.9, 125.6, 99.0
(1JCH ) 154.9 Hz), 85.4 (1JCH ) 166.2 Hz), 82.2, 80.3, 80.2, 76.5,
76.3, 75.5, 74.7, 74.3, 74.1, 72.12, 72.09, 71.6, 69.0, 18.4, 18.2;
ESIHRMS Calcd for C57H58NaO8S [M + Na]+: 925.3750. Found
925.3744.
1
mg, 10%). 24R. [R]23D +252.3 (c 0.13, CHCl3). H NMR (500
MHz) δ: 7.79-7.87 (m, 4H), 7.54 (d, J ) 8.4 Hz, 1H), 7.41-
7.48 (m, 4H), 7.28-7.40 (m, 8H), 5.10 (d, J ) 3.3 Hz, 1H), 5.06
(d, J ) 10.8 Hz, 1H), 4.96 (d, J ) 11.0 Hz, 1H), 4.82-4.87 (m,
2H), 4.74 (d, J ) 12.1 Hz, 1H), 4.69 (s, 1H), 4.59 (d, J ) 10.6 Hz,
1H), 4.04 (dd, J ) 8.9, 2.7 Hz, 1H), 3.92 (t, J ) 9.5 Hz, 1H),
3.81-3.88 (m, 2H), 3.62-3.71 (m, 2H), 3.55 (s, 3H), 3.39 (dd, J
) 9.4, 2.9 Hz, 1H), 3.31 (s, 3H), 3.13 (t, J ) 9.8 Hz, 1H), 1.35 (d,
J ) 5.5 Hz, 3H), 1.15 (d, J ) 6.1 Hz, 3H); 13C NMR (126 MHz)
δ: 138.4, 138.0, 135.6, 133.3, 133.0, 128.4, 128.1, 128.0, 127.8,
4,5-Dibromopentyl 2,4-Di-O-benzyl-r-L-rhamnopyranosyl-
(1f3)-2,4-di-O-benzyl-r-L-rhamnopyranosyl-(1f2)-3,4-di-O-
benzyl-r-L-rhamnopyranoside (22). To a solution of 21R (677
mg, 0.75 mmol), TTBP (373 mg, 1.50 mmol), Ph2SO (151 mg,
0.75 mmol), and activated 3 Å powdered molecular sieves in CH2-
Cl2 (22 mL) was added Tf2O (139 µL, 0.82 mmol) at -60 °C. The
reaction mixture was stirred for 1 h at this temperature, and a
solution of 18 (644 mg, 1.13 mmol) in CH2Cl2 (7 mL) was added
127.73, 127.71, 127.67, 127.0, 126.2, 126.0, 125.9, 98.8 (1JCH
)
168.7 Hz), 93.5 (1JCH ) 167.4 Hz), 82.6, 79.8, 75.64, 75.56, 75.4,
74.3, 72.8, 68.3, 68.0, 66.4, 59.5, 54.7, 18.5, 18.1; FABHRMS
Calcd for C39H45N3NaO8 [M + Na]+:706.3104. Found 706.3097.
24â. [R]23D +12.2 (c 0.18, CHCl3). 1H NMR (400 MHz) δ: 7.81-
7.89 (m, 4H), 7.56 (dd, J ) 8.3, 1.5 Hz, 1H), 7.44-7.51 (m, 2H),
7.39-7.43 (m, 4H), 7.27-7.37 (m, 6H), 5.1 (d, J ) 11.0 Hz, 1H),
4.96-5.02 (m, 2H), 4.84 (d, J ) 12.3 Hz, 1H), 4.74 (d, J ) 12.3
6518 J. Org. Chem., Vol. 72, No. 17, 2007

Antigenic Tetrasaccharide Side Chain
Hz, 1H), 4.55-4.65 (m, 3H), 4.03 (dd, J ) 8.9, 3.2 Hz, 1H), 3.82
(dd, J ) 3.1, 1.8 Hz, 1H), 3.69 (s, 3H), 3.59-3.68 (m, 2H), 3.45
(t, J ) 9.0 Hz, 1H), 3.29 (s, 3H), 3.11-3.22 (m, 3 H), 1.36 (d, J
) 5.9 Hz, 3H), 1.29 (d, J ) 5.4 Hz, 3H); 13C NMR (101 MHz) δ:
138.8, 138.5, 135.5, 133.3, 133.1, 128.4, 128.24, 128.18, 128.0,
127.9, 127.8, 127.7, 127.5, 127.1, 126.3, 126.1, 126.0, 103.7 (1JCH
) 160.9 Hz), 99.7 (1JCH ) 168.3 Hz), 84.9, 82.8, 80.8, 79.1, 78.4,
75.5, 74.8, 73.5, 70.3, 67.9, 67.7, 60.8, 54.5, 18.6, 18.0; FABHRMS
Calcd for C39H45N3NaO8 [M + Na]+: 706.3104. Found 706.3080.
Method B. To a solution of 14 (18 mg, 0.042 mmol), TTBP
(21 mg, 0.085 mmol), BSP (9 mg, 0.042 mmol), and activated 3 Å
powdered molecular sieves in propionitrile (1.5 mL) Tf2O (7.9 µL,
0.047 mmol) was added at -60 °C. The reaction mixture was stirred
for 5 min at this temperature, and solution of 23 (19 mg, 0.052
mmol) in propionitrile (0.6 mL) was added dropwise. The reaction
mixture was stirred for an additional 2 min at -60 °C, warmed to
room temperature, filtered, diluted with CH2Cl2, washed (sat. aq
Na2CO3), dried (Na2SO4), and concentrated. Filtration of the crude
reaction mixture through a pad of silica gel (with ethyl acetate as
an eluent) and purification by radial chromatography (SiO2, hexanes
to 3/17 ethyl acetate/ hexanes) gave 24R (10.3 mg, 36%) and 24â
(9.7 mg, 34%).
Method C. A solution of 14 (27 mg, 0.062 mmol), 23 (18 mg,
0.050 mmol), and activated 3 Å powdered molecular sieves in
propionitrile (1 mL) was stirred for 10 min at room temperature
and then cooled to -60 °C, and N-iodosuccinimide (14 mg, 0.062
mmol), followed by TfOH (1.1 µL, 0.012 mmol), was added. The
reaction mixture was stirred for 8 h at -60 to -65 °C, quenched
with Et3N (9 µL, 0.062 mmol), filtered, diluted with CH2Cl2, washed
(sat. aq Na2S2O3, sat. aq Na2CO3), dried (Na2SO4), and concentrated.
Filtration of the crude reaction mixture through a pad of silica gel
(with ethyl acetate as an eluent) and purification by radial
chromatography (SiO2, hexanes to 3/17 ethyl acetate/hexanes) gave
24R (8 mg, 23%) and 24â (25 mg, 70%).
4,5-Dibromopentyl 4-Azido-4-deoxy-2-O-methyl-3-O-(2-naph-
thylmethyl)-r-D-quinovopyranosyl-(1f3)-2,4-di-O-benzyl-r-L-
rhamnopyranosyl-(1f3)-2,4-di-O-benzyl-r-L-rhamnopyranosyl-
(1f2)-3,4-di-O-benzyl-r-L -rhamnopyranoside (25r) and 4,5-
Dibromopentyl4-Azido-4-deoxy-2-O-methyl-3-O-(2-naphthylmethyl)-
â-D-quinovopyranosyl-(1f3)-2,4-di-O-benzyl-R-L-rhamnopyranosyl-
(1f3)-2,4-di-O-benzyl-r-L-rhamnopyranosyl-(1f2)-3,4-di-O-
benzyl-r-L-rhamnopyranoside (25â). A solution of 22 (118 mg,
0.096 mmol), 14 (50 mg, 0.115 mmol), and activated 3 Å powdered
molecular sieves in propionitrile (2.4 mL) was stirred for 10 min
at room temperature and then cooled to -60 °C, and N-iodosuc-
cinimide (26 mg, 0.116 mmol), followed by TfOH (1.7 µL, 0.019
mmol), was added. The reaction mixture was stirred for 9 h at -60
to -65 °C, quenched with Et3N (16 µL, 0.115 mmol), filtered,
diluted with CH2Cl2, washed (sat. aq Na2S2O3, sat. aq Na2CO3),
dried (Na2SO4), and concentrated. Filtration of the crude reaction
mixture through a pad of silica gel (with ethyl acetate as an eluent)
and purification by radial chromatography (SiO2, hexanes to 3/17
ethyl acetate/hexanes) gave 25R as a mixture of two diastereomers
in the dibromopentyl chain (32 mg, 21%) and 25â as a mixture of
two diastereomers in the dibromopentyl chain (105 mg, 71%). 25R.
1H NMR (500 MHz): 7.74-7.87 (m, 4H), 7.51 (dd, J ) 8.4, 1.7
Hz, 1H), 7.42-7.47 (m, 2H), 7.12-7.35 (m, 30H), 5.21 (s, 1H),
5.10 (d, J ) 1.5 Hz, 1H), 5.00-5.04 (m, 2H), 4.91 (d, J ) 11.0
Hz, 1H), 4.85 (d, J ) 10.8 Hz, 1H), 4.82 (d, J ) 10.8 Hz, 1H),
4.75 (d, J ) 11.7 Hz, 1H), 4.70 (d, J ) 1.5 Hz, 1H), 4.62-4.67
(m, 2H), 4.55-4.61 (m, 3H), 4.51-4.55 (m, 2H), 4.49 (s, 1H),
4.40 (d, J ) 11.6 Hz, 1H), 4.11-4.21 (m, 3H), 3.99-4.01 (m,
1H), 3.76-3.90 (m, 8H), 3.55-3.71 (m, 5H), 3.37-3.46 (m, 5H),
3.34 (dd, J ) 9.4, 3.5 Hz, 1H), 3.10 (t, J ) 9.8 Hz, 1H), 2.18-
2.27 (m, 1H), 1.77-1.89 (m, 2H), 1.63-1.74 (m, 1H), 1.282 (d, J
) 6.2 Hz, 3H), 1.278 (d, J ) 6.1 Hz, 3H), 1.24 (d, J ) 6.2 Hz,
3H), 1.06 (d, J ) 6.2 Hz, 3H); 13C NMR (126 MHz) δ: 138.6,
138.4, 138.3, 138.0, 135.6, 133.3, 133.0, 128.47, 128.42, 128.34,
128.26. 128.12, 128.09, 128.0, 127.8, 127.68, 127.65, 127.60,
127.56, 127.5, 127.0, 126.2, 126.0, 125.9, 99.5 (1JCH ) 169.9 Hz),
99.1 (1JCH ) 169.2 Hz), 99.0 (1JCH ) 169.2 Hz), 98.9 (1JCH
)
168.5 Hz), 93.1 (1JCH ) 165.3 Hz), 82.6, 80.8, 80.5, 79.9, 79.7,
77.6, 75.52, 75.49, 75.4, 75.2, 74.7, 74.5, 72.6, 72.4, 72.3, 68.8,
68.2, 68.1, 66.3, 59.1, 52.6, 52.5, 36.1, 33.01, 32.97, 26.8, 18.5,
18.10, 18.05; ESIHRMS Calcd for C83H95N3NaO16Br2 [M + Na]+:
1570.4977. Found 1570.4920. 25â. 1H NMR (501 MHz) δ: 7.82-
7.87 (m, 4H), 7.53 - 7.57 (m, 1H), 7.44-7.50 (m, 2H), 7.38-
7.42 (m, 2H), 7.16-7.37 (m, 28H), 5.12 (s, 1H), 5.09 (s, 1H), 5.06
(d, J ) 10.8 Hz, 1H), 4.95-5.00 (m, 2H), 4.87 (d, J ) 10.8 Hz,
1H), 4.66-4.72 (m, 2H), 4.54-4.66 (m, 7H), 4.44-4.50 (m, 3H),
4.10-4.21 (m, 3H), 3.99-4.01 (m, 1H), 3.88-3.91 (m, 1H), 3.81-
3.87 (m, 4H), 3.75-3.80 (m, 1H), 3.66-3.69 (m, 4H), 3.59-3.71
(m, 3H), 3.55 (t, J ) 9.1 Hz, 1H), 3.35-3.45 (m, 3H), 3.16 (t, J )
8.4 Hz, 1H), 3.08 (t, J ) 9.4 Hz, 1H), 3.00-3.08 (m, 1H), 2.17-
2.28 (m, 1H), 1.77-1.89 (m, 2H), 1.64-1.74 (m, 1H), 1.283 (d, J
) 6.1 Hz, 3H), 1.279 (d, J ) 6.1 Hz, 3H), 1.26 (d, J ) 6.2 Hz,
3H), 1.12 (d, J ) 5.5 Hz, 3H); 13C NMR (126 MHz) δ: 138.8,
138.5, 138.3, 138.2, 135.5, 133.4, 133.1, 128.5, 128.33, 128.28,
128.2, 128.13, 128.07, 128.0, 127.73, 127.69, 127.66, 127.60,
127.58, 127.42, 127.39, 127.1, 126.3, 126.1, 126.0, 103.6 (1JCH
)
161.2 Hz), 100.3 (1JCH ) 168.7 Hz), 99.0 (1JCH ) 170.0 Hz), 98.9
(1JCH ) 169.2 Hz), 84.9, 82.8, 81.0, 80.61, 80.55, 80.0, 79.4, 78.6,
78.1, 75.49, 75.46, 74.84, 74.76, 74.7, 73.4, 72.5, 72.2, 70.3, 68.7,
68.4, 68.1, 67.8, 66.3, 60.8, 52.6, 52.5, 36.1, 33.02, 32.99, 26.8,
18.5, 18.1, 18.0; ESIHRMS Calcd for C83H95N3NaO16Br2 [M +
Na]+: 1570.4977. Found 1570.4930.
n-Pentenyl 4-Azido-4-deoxy-2-O-methyl-3-O-(2-naphthyl-
methyl)-â-D-quinovopyranosyl-(1f3)-2,4-di-O-benzyl-r-L-rham-
nopyranosyl-(1f3)-2,4-di-O-benzyl-r-L-rhamnopyranosyl-(1f2)-
3,4-di-O-benzyl-r-L-rhamnopyranoside (26). A mixture of 25â
(98 mg, 0.063 mmol), NaI (190 mg, 1.268 mmol), and 2-butanone
(6 mL) was heated to reflux for 5 h. The reaction mixture was
cooled to room temperature, diluted with ethyl acetate, washed (sat.
aq Na2S2O3,), dried (Na2SO4), and concentrated. Filtration of the
crude reaction mixture through a pad of silica gel (with ethyl acetate
as an eluent) and purification by radial chromatography (SiO2,
hexanes to 1/9 ethyl acetate/hexanes) gave 26 (82 mg, 94%). [R]15
D
1
+10.0 (c 0.23, CHCl3). H NMR (501 MHz) δ: 7.83-7.91 (m,
4H), 7.56 (dd, J ) 8.5, 1.4 Hz, 1H), 7.45-7.51 (m, 2H), 7.15-
7.43 (m, 30H), 5.76-5.85 (m, 1H), 5.13 (br s, 1H), 5.11 (d, J )
1.5 Hz, 1H), 5.08 (d, J ) 11.0 Hz, 1H), 5.01-5.06 (m, 1H), 4.97-
5.01 (m, 3H), 4.88 (d, J ) 10.8 Hz, 1H), 4.59-4.73 (m, 8H), 4.57
(d, J ) 11.2 Hz, 1H), 4.44-4.51 (m, 3H), 4.11-4.17 (m, 2H),
4.02-4.04 (m, 1H), 3.90 (dd, J ) 2.6, 1.7 Hz, 1H), 3.82-3.87 (m,
3H), 3.77-3.82 (m, 1H), 3.62-3.71 (m, 6H), 3.56 (t, J ) 9.4 Hz,
1H), 3.35-3.45 (m, 3H), 3.17 (dd, J ) 8.9, 8.0 Hz, 1H), 3.09 (t,
J ) 9.5 Hz, 1H), 3.01-3.09 (m, 1H), 2.06-2.14 (m, 2H), 1.62-
1.69 (m, 2H), 1.30 (d, J ) 6.2 Hz, 3H), 1.29 (d, J ) 6.1 Hz, 3H),
1.27 (d, J ) 6.2 Hz, 3H), 1.12 (d, J ) 5.9 Hz, 3H); 13C NMR (126
MHz) δ: 138.7, 138.4, 138.33, 138.31, 138.2, 138.0, 135.5, 133.3,
133.1, 128.4, 128.3, 128.2, 128.14, 128.09, 128.05, 128.03, 127.98,
127.7, 127.64, 127.57, 127.53, 127.50, 127.4, 127.1, 126.2, 126.1,
125.9, 114.9, 103.5 (1JCH ) 161.2 Hz), 100.3 (1JCH ) 168.7 Hz),
98.9 (1JCH ) 168.7 Hz), 84.8, 82.7, 80.9, 80.58, 80.55, 80.1, 79.3,
78.5, 78.0, 75.5, 75.4, 74.7, 74.6, 73.3, 72.4, 72.1, 70.2, 68.6, 68.4,
67.9, 67.7, 66.7, 60.8, 30.3, 28.6, 18.4, 18.02, 17.98, 17.95;
ESIHRMS Calcd for C83H95N3NaO16 [M + Na]+: 1412.6610.
Found 1412.6560.
n-Pentenyl 4-Azido-4-deoxy-2-O-methyl-â-D-quinovopyrano-
syl-(1f3)-2,4-di-O-benzyl-r-L-rhamnopyranosyl-(1f3)-2,4-di-
O-benzyl-r-L-rhamnopyranosyl-(1f2)-3,4-di-O-benzyl-r-l-rham-
nopyranoside (27) and n-Pentenyl 4-Azido-3-O-benzyl-4-deoxy-
2-O-methyl-â-D-quinovopyranosyl-(1f3)-2,4-di-O-benzyl-r-L-
rhamnopyranosyl-(1f3)-2,4-di-O-benzyl-r-L-rhamnopyranosyl-
(1f2)-3,4-di-O-benzyl-r-L-rhamnopyranoside (28). To a solution
of 26 (122 mg, 0.088 mmol) in MeOH/CH2Cl2 (0.7 mL/ 2.1 mL)
was added DDQ (60 mg, 0.26 mmol) at 0 °C. After 30 min, the
reaction mixture was warmed to room temperature and further
J. Org. Chem, Vol. 72, No. 17, 2007 6519

Crich and Vinogradova
stirred for 5 h before it was diluted with CH2Cl2 and quenched
with sat. aq Na2CO3. The organic phase was separated, washed
(sat. aq Na2CO3), dried (Na2SO4), and concentrated. Filtration of
the crude reaction mixture through a pad of silica gel (with ethyl
acetate as an eluent) and purification by radial chromatography
(SiO2, hexanes to 1/9 ethyl acetate/hexanes) gave 27 (74 mg, 67%).
[R]15D -11.6 (c 0.76, CHCl3). 1H NMR (501 MHz) δ: 7.13-7.39
(m, 30H), 5.74-5.85 (m, 1H), 5.11 (br s, 1H), 5.10 (d, J ) 1.7
Hz, 1H), 5.02 (dq, J ) 17.2, 1.5 Hz, 1H), 4.95-4.99 (m, 1H),
4.88 (t, J ) 10.5 Hz, 2H), 4.70 (d, J ) 11.4 Hz, 1H), 4.65-4.69
(m, 2H), 4.54-4.63 (m, 6H), 4.48 (d, J ) 11.9 Hz, 1H), 4.39-
4.44 (m, 2H), 4.12 (ddd, J ) 12.2, 9.4, 3.0 Hz, 1H), 4.00-4.02
(m, 1H), 3.87 (dd, J ) 2.8, 1.7 Hz, 1H), 3.81-3.86 (m, 3H), 3.76-
3.82 (m, 1H), 3.60-3.69 (m, 6H), 3.54 (t, J ) 9.0 Hz, 1H), 3.47
(td, J ) 9.1, 2.1 Hz, 1H), 3.41 (t, J ) 9.5 Hz, 1H), 3.34-3.39 (m,
1H), 3.01-3.09 (m, 1H), 3.01 (t, J ) 9.5 Hz, 1H), 2.97 (dd, J )
9.2, 7. 9 Hz, 1H), 2.66 (d, J ) 2.6 Hz, 1H), 2.06-2.13 (m, 2H),
1.60-1.69 (m, 2H), 1.27-1.29 (m, 6H), 1.26 (d, J ) 6.4 Hz, 3H),
1.11 (d, J ) 5.7 Hz, 3H); 13C NMR (126 MHz) δ: 138.7, 138.54,
138.47, 138.4, 138.2, 138.1, 128.5, 128.4, 128.3, 128.2, 128.1,
128.0, 127.74, 127.68, 127.62, 127.56, 127.41, 127.38, 115.0, 103.4
(1JCH ) 161.2 Hz), 100.2 (1JCH ) 166.2 Hz), 99.0 (1JCH ) 168.7
Hz), 84.0, 81.1, 80.62, 80.59, 80.1, 79.4, 78.2, 78.1, 75.5, 75.2,
74.8, 74.7, 73.4, 72.5, 72.1, 70.5, 68.6, 68.4, 67.9, 67.4, 66.8, 61.0,
30.3, 28.7, 18.3, 18.1, 18.02, 17.99; ESIHRMS Calcd for C72H87N3-
NaO16 [M + Na]+: 1272.5984. Found 1272.5943. Further elution
of with ethyl acetate gave a mixture of the debenzylated byproducts,
which was dissolved in DMF (2 mL). Benzyl bromide (60 µL, 0.50
mmol) was then added, followed by NaH (60% in mineral oil, 20
mg, 0.50 mmol), and the reaction mixture was stirred overnight,
diluted with ethyl acetate, washed (brine, water), dried (Na2SO4),
and concentrated. Purification by radial chromatography (SiO2,
hexanes to 3/17 ethyl acetate/hexanes) gave 28 (26 mg, 22%, two
steps). [R]14D +2.4 (c 1.08, CHCl3). 1H NMR (501 MHz): 7.12-
7.45 (m, 35H), 5.75-5.85 (m, 1H), 5.08-5.14 (m, 2H), 5.02 (dq,
J ) 17.2, 1.7 Hz, 1H), 4.96-4.99 (m, 2H), 4.90 (d, J ) 10.7 Hz,
1H), 4.87 (d, J ) 11.0 Hz, 1H), 4.81 (d, J ) 10.6 Hz, 1H), 4.65-
4.72 (m, 3H), 4.54-4.64 (m, 6H), 4.44-4.50 (m, 3H), 4.13 (td, J
) 9.5, 3.0 Hz, 2H), 4.01-4.02 (m, 1H), 3.89 (dd, J ) 2.8, 1.7 Hz,
1H), 3.76-3.86 (m, 4H), 3.61-3.70 (m, 6H), 3.55 (t, J ) 9.5 Hz,
1H), 3.42 (t, J ) 9.5 Hz, 1H), 3.31-3.39 (m, 2H), 3.13 (dd, J )
9.1, 8.0 Hz, 1H), 2.95-3.07 (m, 2H), 2.06-2.13 (m, 2H), 1.61-
1.69 (m, 2H), 1.284 (d, J ) 6.2 Hz, 3H), 1.279 (d, J ) 6.2 Hz,
3H), 1.26 (d, J ) 6.2 Hz, 3H), 1.11 (d, J ) 5.7 Hz, 3H); 13C NMR
(126 MHz) δ: 138.80, 138.78, 138.5, 138.40, 138.38, 138.2, 138.1,
138.0, 128.44, 128.40, 128.32, 128.26, 128.12, 128.08, 127.9,
127.71, 127.68, 127.60, 127.56, 127.5, 127.40, 127.37, 114.9, 103.6
(1JCH ) 161.2 Hz), 100.3 (1JCH ) 173.7 Hz), 99.1 (1JCH ) 167.4
Hz), 99.0 (1JCH ) 167.4 Hz), 84.8, 82.7, 81.0, 80.64, 80.63, 80.1,
79.4, 78.6, 78.1, 75.49, 75.45, 74.8, 74.6, 73.4, 72.5, 72.2, 70.3,
68.7, 68.4, 68.0, 67.7, 66.8, 60.8, 30.3, 28.7, 18.5, 18.1, 18.02,
17.99; ESIHRMS Calcd for C79H93N3NaO16 [M + Na]+: 1362.6454.
Found 1362.6404.
n-Pentenyl 4-Deoxy-4-(3-hydroxy-3-methylbutanamido)-2-O-
methyl-â-D-quinovopyranosyl-(1f3)-r-L-rhamnopyranosyl-(1f3)-
r-L-rhamnopyranosyl-(1f2)-r-L-rhamnopyranoside (2). Am-
monia was condensed at -78 °C in a reaction vessel, containing a
solution of 27 (26 mg, 0.021 mmol) and 28 (9 mg, 0.007 mmol) in
THF (6 mL), until a total volume of about 20 mL was reached.
Sodium (45 mg, 1.96 mmol) was then added in small pieces,
affording a solution of dark blue color. The reaction mixture was
stirred for 1 h at this temperature and then quenched by the addition
of the methanol. The reaction mixture was warmed to room
temperature in order to evaporate the ammonia, and then concen-
trated. Purification by column chromatography (eluting first with
CHCl3 to remove most of the byproducts and then with 1/4 MeOH/
CHCl3 and finally MeOH) gave a crude product, which was
dissolved in (i-Pr)2EtN and concentrated (two times). DMF (2 mL)
was then added, followed by 3-hydroxy-3-methylbutyric acid (5
mg, 0.042 mmol), HATU (16 mg, 0.042 mmol), and (i-Pr)2EtN
(28 µL, 0.16 mmol). The reaction mixture was stirred overnight
and then concentrated. Purification by column chromatography
(SiO2, CHCl3 to 9/31 MeOH/CHCl3), followed by purification by
preparative TLC (9/31 MeOH/CHCl3) and further column chro-
matography (SiO2, CHCl3 to 9/31 MeOH/ CHCl3), gave 2 (12 mg,
54%, 2 steps), whose spectral data matched that reported in the
literature.7 [R]20D -63.5 (c 0.2, MeOH); Lit.7 [R]D -7.9 (c 0.18,
CHCl3).43 IR (thin film): 3377, 2972, 2931, 2879, 1658, 1649, 1641,
1381, 1122, 1061 cm-1
.
Acknowledgment. We thank the NIH (GM 62160) for
support of this work.
Supporting Information Available: Full experimental details
for substrate preparation and copies of spectra of all compounds.
This material is available free of charge via the Internet at http://
pubs.acs.org.
JO070750S
(43) The literature specific rotation appears to be an error, as the
compound is not soluble in the recorded solvent.
6520 J. Org. Chem., Vol. 72, No. 17, 2007