Synthesis of tri-, hexa-, and nonasaccharide subunits of the atypical O-antigen polysaccharide of the lipopolysaccharide from Danish Helicobacter pylori strains

Article abstract of DOI:10.1021/jo701531x

(Chemical Equation Presented) Synthesis of trisaccharide repeating unit, →3)-α-D-Rhap-(1→2)-α-D-Manp3CMe-(1→3)-α-L-Rha p-(1→, and its dimeric hexa- and trimeric nonasaccharide subunits of the atypical O-antigen polysaccharide of the lipopolysaccharide fro

Full text of DOI:10.1021/jo701531x

Synthesis of Tri-, Hexa-, and Nonasaccharide Subunits of the
Atypical O-Antigen Polysaccharide of the Lipopolysaccharide from
Danish Helicobacter pylori Strains
Dinanath Baburao Fulse,† Heung Bae Jeon,‡ and Kwan Soo Kim*,†
Center for BioactiVe Molecular Hybrids and Department of Chemistry, Yonsei UniVersity, Seoul, 120-749,
and Department of Chemistry, Kwangwoon UniVersity, Seoul, 139-701, Korea
kwan@yonsei.ac.kr
ReceiVed July 13, 2007
Synthesis of trisaccharide repeating unit, f3)-R-D-Rhap-(1f2)-R-D-Manp3CMe-(1f3)-R-L-Rha p-(1f,
and its dimeric hexa- and trimeric nonasaccharide subunits of the atypical O-antigen polysaccharide of
the lipopolysaccharide from Danish H. pylori strains D1, D3, and D6 has been accomplished. Successful
synthesis of the hexasaccharide and the nonasaccharide was possible by dimerization and trimerization
of the suitably protected trisaccharide repeating unit, in which three monosaccharide moieties were arranged
in a proper order by placing the sterically demanding 3-C-methyl-D-mannose moiety in between D- and
L-rhamnoses. Key steps include the coupling of three monosaccharide moieties and dimerization and
trimerization of the trisaccharide unit by glycosylations employing the 2′-carboxybenzyl glycoside method.
Also presented is a method for the synthesis of the novel branched sugar, 3-C-methyl-D-mannose moiety
by elaboration of its equatorial hydroxyl and axial methyl groups at C-3′ in the disaccharide stage.
Since the first isolation of Helicobacter pylori,1 extensive
studies have led to recognition of this bacterium as the major
cause of chronic gastritis and gastric and duodenal ulcers.2
Moreover, persistent infection with H. pylori is strongly
associated with the risk of development of gastric cancer.2,3 H.
pylori is estimated to infect over one-half of the world’s
population and thus has been classified as a category 1 (definite)
human carcinogen.4 Although the antibiotic therapy is currently
used to manage H. pylori infections, this strategy has several
drawbacks as antibiotic-resistant strains have emerged.5 Like
the cell envelope of other gram-negative bacteria, that of H.
pylori contains lipopolysaccharides (LPS), which is known to
contribute to the pathogenesis. It has also been reported that
LPS from some H. pylori strains can act as antagonists for Toll-
like receptor 4.6 The O-antigen polysaccharide is a part of the
LPS, which interacts with the bacterial microenvironment and
the infected host. Structural studies on the LPS of a number of
H. pylori strains have shown that the O-antigen polysaccharide
exhibits mimicry of Lewis blood group antigens by expression
of the corresponding determinants in the O-chain or located at
nonreducing end of the O-chain polysaccharide.7 Consequently,
† Yonsei University.
‡ Kwangwoon University.
(1) (a) Warren, J. R.; Mashall, B. J. Lancet 1983, 321, 1273-1275. (b)
Mashall, B. J.; Warren, J. R. Lancet 1984, 323, 1311-1315.
(2) (a) Dunn, B. E.; Cohen, H.; Blaser, M. J. Clin. Microbiol. ReV. 1997,
10, 720-741. (b) Blaser, M. J. Sci. Am. 1996, 274, 104-109. (c) Dubois,
A. Emerg. Infect. Dis. 1995, 1, 79-85.
(3) Uemura, N.; Okamoto, S.; Yamamoto, S.; Matsumura, N.; Yamagu-
chi, S.; Yamakido, M.; Taniyama, K.; Sasaki, N.; and Schlemper, R. J.
New Engl. J. Med. 2001, 345, 784-789.
(4) (a) Covacci, A.; Telford, J. L.; Giudice, G. D.; Parsonnet, J.;
Rappuole, R. Science 1999, 284, 1328-1333. (b) Logan, R. P. H. Lancet
1994, 344, 1078-1079.
(5) Graham, D. Y. Gastroenterology 1998, 115, 1272-1277.
(6) Lepper, P. M.; Triantafilou, M.; Schumann, C.; Schneider, E. M.;
Triantafilou, K. Cell Microbiol. 2005, 7, 519-528.
(7) (a) Monteiro, M. A.; Chan, K. H. N.; Rasko, D. A.; Taylor, D. E.;
Zheng, P. Y.; Appelmelk, B. J.; Wirth, H. P.; Yang, M. Q.; Blaser, M. J.;
Hynes, S. O.; Moran, A. P.; Perry, M. B. J. Biol. Chem. 1998, 273, 11533-
11543. (b) Aspinall, G. O.; Monteiro, M. A. Biochemistry 1996, 35, 2498-
2504. (c) Aspinall, G. O.; Monteiro, M. A.; Pang, H.; Walsh, E. J.; Moran,
A. P. Biochemistry 1996, 35, 2489-2497.
10.1021/jo701531x CCC: $37.00 © 2007 American Chemical Society
Published on Web 11/16/2007
J. Org. Chem. 2007, 72, 9963-9972
9963

Fulse et al.
SCHEME 1. Model Study for the Glycosylation with CB
C-3-Methyl-glycosides 3, 4, and 5 as Glycosyl Donors
FIGURE 1. The repeat unit of the O-antigen polysaccharide of LPS
from Danish H. pylori strains.
a number of studies have been performed to account for the
pathogenic relevance of Lewis antigen mimicry by H. pylori.8
And there have also been immunization studies with inactivated
H. pylori whole-cell vaccines having homologous and heter-
ologous LPS O-antigens expressing different Lewis antigens9
and with H. pylori outer membrane vesicles, which is enriched
with LPS.10 It has also been reported that H. pylori LPS in a
whole cell sonicate vaccine promotes a Th1 immune response
that may aid in protection or clearance of H. pylori infections.11
Recently, however, an atypical O-antigen polysaccharide of LPS
from Danish H. pylori strains D1, D3, and D6 was isolated and
the following structure of the trisaccharide repeating unit of the
O-polysaccharide was established: f3)-R-L-Rhap-(1f3)-R-D-
Rhap-(1f2)-R-D-Manp3CMe-(1f (A) (Figure 1).12 Unusual
feature of this O-polysaccharide is the occurrence of a novel
branched sugar, 3-C-methyl-D-mannose, which has not been
found in Nature before and the simultaneous occurrence of both
L-rhamnose and D-rhamnose. Owing to its structural uniqueness
and biological and medical potential, not only the trisaccharide
repeating unit A but also its dimeric hexasaccharide and trimeric
nonasaccharide subunits are attractive synthetic targets. A few
years ago, therefore, we reported the synthesis of trisaccharide
1 as a protected form of the repeating unit A by coupling of
three monosaccharide building blocks13 employing the 2′-
carboxybenzyl (CB) glycoside method.14 However, we have
found that the trisaccharide 1 was not the proper monomeric
unit for the synthesis of its oligomeric subunits. Herein we report
the synthesis of newly designed trisaccharide 2, in a suitably
protected form of repeating unit A′ and the synthesis of its
dimeric hexasaccharide and trimeric nonasaccharide as well.
In order to achieve our goal for the synthesis of oligosac-
charide subunits of the O-antigen polysaccharide of LPS from
Danish H. pylori strains, it was essential to establish the efficient
procedure for oligomerizations of the trisaccharide 1 by gly-
cosylation reactions. Before dimerization and trimerization of
1, we carried out a model study for the glycosylation with CB
trisaccharide 3 as the glycosyl donor, which was obtained from
1 by selective hydrogenolysis. The CB trisaccharide 3 found to
be unreactive as the glycosyl donor, and thus the coupling
reaction of 3 with cyclohexanol did not provide a desired
cyclohexyl glycoside (Scheme 1). We also found that CB
monosaccharide donors 4 and 5 both having an axial C-3 methyl
group were quite unreactive as glycosyl donors. Thus, the
glycosylation of L-rhamnoside 6 with CB monosaccharide 4 or
5 did not proceed under the general reaction condition of the
CB glycoside method14,15 but rather provided a mixture of
unknown products upon warming or for prolonged reaction time.
Unreactivities of 3, 4, and 5 as glycosyl donors in the coupling
reactions with cyclohexanol or 6 might be attributed to the steric
hindrance imposed by the C-3 axial methyl group to the C-1
reactive site. Therefore, we changed our synthetic strategy by
planning to synthesize new trisaccharide repeating unit A′, f3)-
R-D-Rhap-(1f2)-R-D-Manp3CMe-(1f3)-R-L-Rhap-(1f, in
which the sterically demanding R-D-Manp3CMe moiety was
placed in between two other monosaccharide moieties, D- and
L-rhamnose so that the axial 3-C-methyl group in the 3-C-
methyl-D-mannose would not interfere with dimerization and
(8) Raghavan, S.; Hjulsrtom, M.; Holgren, J.; Svennerholm, A.-M. Infect.
Immun. 2002, 70, 6383-6388.
(9) (a) Lozniewski, A.; Haristoy, X.; Rasko, D. A.; Hatier, R.; Plenat,
F.; Taylor, D. E.; Angioi-Duprez, K. Infect. Immun. 2003, 71, 2902-2906.
(b) Appelmelk, B. J.; Simmons-Smit, I.; Negrini, R.; Moran, A. P.; Aspinall,
G. O.; Forte, J. G.; De Vries, T.; Quan, H.; Verboom, T.; Maaskant, J. J.;
Ghiara, P.; Kuipers, E. J.; Bloemena, E.; Tadema, T. M.; Townsend, R. R.;
Tyagarajan, K.; Crothers, J. M.; Monteiro, M. A.; Savio, A.; Graaff, J. D.
Infect. Immun. 1996, 64, 2031-2040.
(10) (a) Keenan, J. I.; Rijpkema, S. G.; Durrani, Z.; Roake, J. A. FEMS
Immun. Med. Microbiol. 2003, 36, 199-205. (b) Keenan, J.; Oliaro, J.;
Domigan, N.; Potter, H.; Aitken, G.; Allardyce, R.; Roake, J. Infect. Immun.
2000, 68, 3337-3343.
(14) Kim, K. S.; Kim, J. H.; Lee, Y. Joo; Lee, Y. Jun; Park, J. J. Am.
Chem. Soc. 2001, 123, 8477-8481.
(11) Taylor, J. M.; Ziman, M. E,; Huff, J. L.; Moroski, N. M.; Vajdy,
M.; Solnick, J. V. Vaccine 2006, 24, 4987-4994.
(15) (a) Kim, K. S.; Park, J.; Lee, Y. J.; Seo. Y. S. Angew. Chem., Int.
Ed. 2003, 42, 459-462. (b) Kim, K. S.; Kang, S. S.; Seo. Y. S.; Kim, H.
J.; Lee, Y. J.; Jeong, K.-S. Synlett 2003, 1311-1314. (c) Lee, B. R.; Jeon,
J. M.; Jung, J. H.; Jeon, H. B.; Kim, K. S. Can. J. Chem. 2006, 84, 506-
515. (d) Lee, Y. J.; Lee, B. Y.; Jeon, H. B.; Kim, K. S. Org. Lett. 2006, 8,
3971-3974.
(12) Kocharova, N. A.; Knirel, Y. A.; Widmalm, G.; Jansson, P.-E.;
Moran, A. P. Biochemistry 2000, 39, 4755-4760.
(13) Kwon, Y. T.; Lee, Y. J.; Lee, K.; Kim, K. S. Org. Lett. 2004, 6,
3901-3904.
9964 J. Org. Chem., Vol. 72, No. 26, 2007

Synthesis of Saccharide Subunits of a Lipopolysaccharide
SCHEME 2. Retrosynthesis of Trisaccharides 2 and 11, Hexasaccharide 7, and Nonasaccharide 8
trimerization of the trisaccharide unit. The trisaccharide repeating
unit A′ would eventually give same oligosaccharides as the
trisaccharide repeat unit A after oligomerization, and thus we
designed new target trisaccharide 2 as a suitably protected form
of the repeating unit A′.
12 and disaccharide acceptor 13. At this juncture it was assumed
that the disaccharide 13 could not be obtained directly by
coupling of completely elaborated monosaccharide building
blocks, namely, a 3-C-methyl mannoside donor and an L-
rhamnoside acceptor, based on the consideration of the model
study shown in Scheme 1. So we envisaged that the axial methyl
and equatorial hydroxyl groups at C-3′ in 13 would be elaborated
in the disaccharide stage from the C-3′ methylene group of
disaccharide 15. Synthesis of 15 would be possible by the
glycosylation of acceptor 18 with donor 17, of which the C-3
methylene group is less sterically demanding than the C-3 axial
methyl group and thus would not interfere with the glycosyla-
tion. Trisaccharide 11 having cyclohexyl L-rhamnoside moiety
at reducing end would be also synthesized in a manner similar
to the synthesis of the BCB trisaccharide 2.
Synthesis of the C-3-methylene-D-mannose building block
17 started with the known 2′-(allyloxycarbonyl)benzyl (ACB)
mannoside 2015c (Scheme 3). Introduction of the ACB group
in the place of the previously used BCB group was necessary
because the alkene functionality at C-3 in 29 was also reduced
during conversion of the BCB group into the CB group under
the hydrogenolysis condition. The hydroxy group at C-3 of the
diol 20 was selectively protected with the p-methoxybenzyl
Retrosynthesis of the trisaccharide 2 and its dimeric hexas-
accharide 7 and trimeric nonasaccharide 8 leads to three
monosaccharide building blocks 12, 17, and 18 or 19 (Scheme
2). The CB glycoside method would be here used extensively
for the coupling of all three monosaccharide components of
trisaccharides 2 and 11 as well as for the assembly of
trisaccharide units of hexasaccharide 7 and nonasaccharide 8.
The protective groups were carefully chosen for the synthesis
of the first target trisaccharides 2 and 11 since they should be
selectively removed in the next stage for the synthesis of
hexasaccharide 7 and nonasaccharide 8 by dimerization and
trimerization of 2 and 11. Thus, the latent 2′-(benzyloxycarbo-
nyl)benzyl (BCB) group13-15 at C-1 in the reducing end of the
trisaccharide 2 would be readily converted into the active 2′-
carboxybenzyl (CB) group to give trisaccharide donor 9. The
p-methoxybenzyl (PMB) group at C-3 in the nonreducing end
of 11 would also be selectively cleaved to provide trisaccharide
acceptor 10. Retrosynthesis of 2 leads to CB D-rhamnoside donor
J. Org. Chem, Vol. 72, No. 26, 2007 9965

Fulse et al.
SCHEME 3. Synthesis of CB 3-C-Methylene-mannoside 17
SCHEME 4. Synthesis of l-Rhamnosides 18 and 19
SCHEME 5. Synthesis of CB d-Rhamnoside 12
(PMB) group by using the dibutyltin oxide method16 to give
C-3 PMB ether 21 in 93% yield in two steps with complete
regioselectivity. Treatment of 21 with TBSCl afforded fully
protected sugar 22, and the deprotection of PMB group in 22
with DDQ provided C-3 hydroxyl sugar 23 in high yield.
Oxidation of 23 with Dess-Martin periodinane17 gave ketosugar
24 in 95% yield, while that with PDC afforded 24 in 70% yield.
Wittig reaction of 24 with triphenylphosphonium methylide,
formed in situ, smoothly gave olefin 25 in 78% yield. The TBS
group in 25 was removed by Bu4NF, and the subsequent
protection of resulting C-2 hydroxy sugar 26 with levulinic acid
in the presence of diisopropylcarbodiimide (DIC) afforded C-2
Lev-protected sugar 27. We decided in this stage to change the
4,6-O-benzylidene protective group of 27 to the benzyl group
because the benzylidene group of the CB glycoside, derived
from the ACB glycoside 27, was cleaved even at low temper-
ature during the glycosylation, in which a slight excess of Tf2O
over DTBMP has been used in order to suppress the generation
of an orthoester. The unusual instability of the benzylidene group
might be attributable to the effect of the nearby C-3 methylene
group since the usual 4,6-O-benzylidene group having no C-3
methylene group is stable under the acidic CB glycosylation
condition. When excess of DTBMP was employed to prevent
the cleavage of the benzylidene group during the glycosylation,
indeed, the orthoester was generated exclusively. Therefore, the
4,6-O-benzylidene sugar 27 was transformed to 4,6-di-O-benzyl
sugar 29. However, cleavage of the benzylidene group of 27
under acidic condition and the subsequent benzylation of the
resulting diol under basic condition did not provide a desired
product but rather afforded an undesired 6-O-levulinyl sugar
by migration of the levulinyl group from O-2 to O-6 under the
basic condition. Migration of the TBS group from O-2 to O-6
also occurred in the same reaction with compound 25. To
prevent the migration of the levulinyl group during benzylation,
C-6 benzyl ether 28 was prepared directly from 27 by the
reductive cleavage of the benzylidene acetal of 27 with BF3‚
OEt2 and Et3SiH18 in 85% yield, and the subsequent benzylation
of the C-4 hydroxyl group of 28 gave desired dibenzyl ether
29. Then, the latent ACB glycoside 29 was readily converted
into active CB glycoside 17 in 92% yield by deallylation with
a catalytic amount of Pd(Ph3P)4 in the presence of morpholine.19
(16) For a review on stannylene acetals of carbohydrates, see: Grindley,
T. B. AdV. Carbohydr. Chem. Biochem. 1998, 53, 17-142.
(17) Dess, D. B.; Martin, J. C. J. Org. Chem. 1983, 48, 4155-4156.
(18) Debenham, S. D.; Toone, E. J. Tetrahedron: Asymmetry 2000, 11,
385-387.
(19) Kunz, H.; Waldmann, H. Angew. Chem., Int. Ed. 1984, 23, 71-72.
9966 J. Org. Chem., Vol. 72, No. 26, 2007

Synthesis of Saccharide Subunits of a Lipopolysaccharide
SCHEME 6. Synthesis of Trisaccharides 2 and 11
TABLE 1. Chemoselective Reduction of Epoxide 43 to 13 under
Various Conditions
This result indicates that ACB glycosides are the useful
precursor for CB glycosides especially in the presence of the
alkene functionality, which could not survive during conversion
of BCB glycosides into CB glycosides by hydrogenolysis.
Synthesis of BCB L-rhamnoside 18, which would become
the reducing terminal of the trisaccharide 2, started from known
BCB L-rhamnoside 3013 as shown in Scheme 4. Treatment of
diol 30 with (Bu3Sn)2O in refluxing benzene and the subsequent
reaction of resulting stannylene acetal with benzoyl chloride
afforded C-2 benzoate 32 in 75% yield. Benzylation of 32
followed by the deprotection of PMB group in resultant fully
protected sugar 34 with trifluoroacetic acid provided C-3
hydroxyl sugar 18 in high yield. Cyclohexyl L-rhamnoside 19,
which would become the permanent reducing end of the tri-,
hexa-, and nonasaccharide, was also readily obtained from 3120
in a manner similar to the synthesis of 18 from 30.
D-Rhamnose moiety 12 was prepared starting from known
BCB mannoside 3613 (Scheme 5). Benzoylation of 36 followed
by the reductive cleavage of the benzylidene group in resulting
benzoate 37 with borane in the presence of Bu2BOTf21 afforded
C-4 benzyl ether 38 having a free hydroxyl group at C-6 in
high yield. Iodination of the primary alcohol 38 with Ph3P and
I2 provided iodide 39 without difficulty. Free radical-mediated
reduction of the iodide 39 with Bu3SnH in the presence of AIBN
resulted in the formation of 6-deoxy sugar 40 in high yield.
Hydrogenolysis of the latent BCB D-rhamnoside 40 in the
presence of ammonium acetate afforded active CB D-rhamnoside
12 in excellent yield.
yield
(%)
entry
reagents
NaI, AIBN, Bu3SnH21 DME
solvent reaction temp (oC)
1
2
3
4
5
rt to 90
reflux
0 to rt
rt
31
58
No rxn.
No rxn.
82
LiI, AIBN, Bu3SnH
LiClO4, BH3‚Et3N22
ZnCl2, BH3‚Et3N
DME
Et2O
CH2Cl2
CH2Cl2
BF3‚Et2O, BH3‚Et3N
rt
group in 15 was removed by hydrazine, and the epoxidation of
resulting allylic alcohol 41 with mCPBA at 40 °C afforded
desired spiroepoxide 43 in high yield with complete stereose-
lectivity. The exclusive â-face delivery of oxygen by mCPBA
to the C-3′ double bond of the disaccharide 41 could be
attributed to a steric effect and to the hydrogen bond between
mCPBA and the C-2′ OH of 41. Reductive ring opening of the
spiroepoxy sugar 43 with Bu3SnH in the presence of NaI and
AIBN,22 which we used previously for the same purpose in the
synthesis of the trisaccharide 1,13 gave desired 3′-C-methyl-
mannosyl disaccharide 13 in only 31% yield (entry 1 in Table
1) while the same reaction with Bu3SnH/LiI/AIBN gave 13 in
58% yield (entry 2). A satisfactory result was obtained by
reduction of the spiroepoxy disaccharide 43 with BH3‚Et3N in
the presence of a Lewis acid. Thus, chemoselective reduction
of the epoxide 43 with BH3‚Et3N/BF3‚Et2O in CH2Cl2 afforded
desired disaccharide 13 in 82% yield (entry 5) whereas the same
reaction did not proceed with BH3‚Et3N/LiClO4 in Et2O and
23
The stage was set for the assembly of properly protected
monosaccharide building blocks 12, 17, 18, and 19 to make
trisaccharides 2 and 11 (Scheme 6). Coupling of the CB C-3-
methylene-mannoside 17 with the BCB L-rhamnoside 18 or with
the cyclohexyl L-rhamnoside 19 was achieved by the addition
of Tf2O to the mixture of 17 and 18 or 19 in the presence of
2,6-di-tert-butyl-4-methylpyridine (DTBMP) and 4 Å MS in
CH2Cl2 at -78 °C followed by warming up the reaction mixture
to room temperature. The desired R-disaccharides 15 and 16
were obtained in 85% and 90% yield, respectively. The levulinyl
with BH3‚Et3N/ZnCl2 in CH2Cl2 (entries 3 and 4). The
stereochemistry at C-3′ of 13 was confirmed by its NOESY
spectrum, which showed correlations between the methyl group
at C-3′ with H-2′ and with H-5′ but not with H-4′. Glycosylation
of the BCB disaccharide acceptor 13 with CB D-rhamnoside
donor 12 using Tf2O in the presence of DTBMP afforded desired
R-trisaccharide 2 as a single isomer in 75% yield. The
stereochemistry at the newly generated anomeric center of 2
was unequivocally determined on the basis of their 1H and 13
NMR spectral data, especially one-bond C1-H1 coupling
C
(20) Compound 31 was readily prepared from cyclohexyl 2,3,4 tri-O-
acetyl-R-L-rhamnopyranoside (C-1), see Supporting Information.
(21) Jiang, L.; Chan, T.-H. Tetrahedron Lett. 1998, 39, 355-358.
(22) Bonini, C.; Fablo, R. D. Tetrahedron Lett. 1988, 29, 819-822.
(23) Heydari, A.; Mehrdad, M.; Maleki, A, Ahmadi, N. Synthesis 2004,
1563-1565.
J. Org. Chem, Vol. 72, No. 26, 2007 9967

Fulse et al.
SCHEME 7. Synthesis of Nonasaccharide 8, Deprotected Trisaccharide 45, and Deprotected Hexasaccharide 47
1
1
constants: JC1′-H1′) 171 Hz in Man, JC1-H1 ) 171 Hz in
respectively. Saponification of the benzoyl ester functionality
of 10 with sodium methoxide in methanol and subsequent
hydrogenolysis over Pd/C catalyst to remove all benzyl protect-
ing groups afforded fully deprotected trisaccharide 45 as a
cyclohexyl glycoside in 82% yield. NMR spectral data, espe-
cially one-bond C1-H1 coupling constants of 45, 171, 171,
and 172 Hz, clearly indicated that the deprotection procedure
did not affect the stereochemistry at all three anomeric centers.
Saponification of the protected hexasaccharide 7 and subsequent
hydrogenolysis, as described for 10, also provided fully depro-
tected hexasaccharide 47 as a cyclohexyl glycoside in high yield
without difficulty. One-bond C1-H1 coupling constants of 47
indicated that all six glycosyl bonds had R-configurations.25 The
nonasaccharide, meanwhile, was synthesized by coupling of the
CB trisaccharide donor 9 and cyclohexyl hexasaccharide ac-
ceptor 46, which was obtained by deprotection of the PMB
group of the hexasaccharide 7 with trifluoroacetic acid. Thus,
the coupling was carried out by addition of the donor 9 to the
solution of the acceptor 46 in the presence of Tf2O and DTBMP
in CH2Cl2 to afford desired R-nonasaccharide 8 in 45% yield.
1
L-Rha, and JC1′′-H1′′ ) 173 Hz in D-Rha.24 Hydrogenolysis of
the BCB trisaccharide 2 in the presence of ammonium acetate
afforded CB trisaccharide 9 in 92% yield. Trisaccharide 11 as
a cyclohexyl glycoside was also obtained from cyclohexyl
disaccharide 16 in a manner similar to the synthesis of 2 from
15.
Deprotection of the PMB group in the fully protected
trisaccharide 11 with trifluoroacetic acid gave C-3′′ hydroxyl
sugar 10 as the trisaccharide acceptor for the hexasaccharide
synthesis (Scheme 7). Dimerization of the trisaccharide to the
hexasaccharide was carried out by glycosylation of the cyclo-
hexyl trisaccharide acceptor 10 with the CB trisaccharide donor
9. Thus, slow addition of 9 to the solution of 10 in the presence
of Tf2O and DTBMP in CH2Cl2 at -20 °C followed by warming
up the reaction mixture to room temperature afforded desired
R-hexasaccharide 7 as a single isomer in 72% yield. The
protected trisaccharide 10 and hexasaccharide 7 were converted
into fully deprotected trisaccharide 45 and hexasaccharide 47,
(24) For C-H coupling constants in pyranoses, see: Bock, K.; Pedersen,
C. J. Chem. Soc., Perkin Trans. 2 1974, 293-297.
(25) See one-bond C1-H1 coupling constants in experimental section.
9968 J. Org. Chem., Vol. 72, No. 26, 2007

Synthesis of Saccharide Subunits of a Lipopolysaccharide
by silica gel flash column chromatography (CH2Cl2/EtOAc, 10:1,
v/v) to give compound 41 (233 mg, 0.25 mmol, 86%) as a colorless
viscous oil. Rf ) 0.38 (CH2Cl2/EtOAc, 10:1); [R]D +43.8 (c 0.50,
CHCl3); IR (CHCl3 film) 3400, 2939, 2850, 1716, 1454, 1407, 1362,
1267, 1257, 1093, 1082, 1047, 741, 698 cm-1. 1H NMR (400 MHz,
CDCl3) δ 1.37 (d, J ) 6.4 Hz, 3H), 2.67 (brs, 1H, OH), 3.42-3.58
(m, 3H), 3.83-3.87 (m, 1H), 3.98-4.00 (m, 1H), 4.10 (s, 1H),
4.30-4.39 (m, 4H), 4.46 (d, J ) 10.0 Hz, 1H), 4.54 (d, J ) 12.0
Hz, 1H), 4.62 (d, J ) 11.2 Hz, 1H), 4.80 (d, J ) 10.4 Hz, 1H),
4.94-4.96 (m, 2H), 5.06-5.10 (m, 2H), 5.17 (s, 1H), 5.27 (s, 1H),
5.33 (s, 2H), 5.64 (t, J ) 3.2 Hz, 1H), 7.19-7.64 (m, 26H), 8.00
(dd, J ) 7.6, 1.2 Hz, 1H), 8.10 (d, J ) 7.2 Hz, 2H); 13C NMR
(100 MHz, CDCl3): δ 18.2, 66.9, 67.5, 68.4, 68.7, 69.3, 72.4, 73.3,
73.6, 74.1, 74.4, 75.9, 79.5, 97.7, 98.4, 112.4, 127.4, 127.6, 127.8,
128.0, 128.1, 128.4, 128.7, 128.8, 128.9, 129.9, 130.1, 130.8, 132.7,
133.6, 136.0, 137.9, 138.2, 138.4, 139.7, 143.0, 166.3, 166.7. HRMS
(FAB): [M + Na]+ calcd for C56H56O12Na: 943.3669; found:
943.3663.
The stereochemistry at the newly generated glycosyl bond in 8
was unambiguously determined on the basis of the one-bond
C1-H1 coupling constant.25
We have described synthesis of trisaccharides 2 and 11, the
suitably protected form of the trisaccharide repeating unit of
an atypical O-antigen polysaccharide of the LPS from Danish
H. pylori strains D1, D3, and D6. Synthesis of protected
hexasaccharide 7 and nonasaccharide 8 was also accomplished
by dimerization and trimerization of the trisaccharide, in which
the sterically demanding 3-C-methyl-D-mannose moiety was
placed in between two other sugars, D- and L-rhamnoses. The
axial methyl and equatorial hydroxyl groups at C-3 of 3-C-
methyl-D-mannose were elaborated in disaccharide stage, in
compounds 13 and 14, by epoxidation of the C-3′ double bond
of disaccharides 41 and 42 and followed by reduction of
resultant epoxides 43 and 44, respectively. In addition, we have
described the synthesis of fully deprotected trisaccharide 45 and
hexasaccharide 47 as cyclohexyl glycosides. The 2′-carboxy-
benzyl (CB) glycoside method proved to be effective in the
coupling of three monosaccharide components for the trisac-
charide and the coupling of the trisaccharide repeating unit for
hexasaccharide 7 and nonasaccharide 8.
2′-(Benzyloxycarbonyl)benzyl (3,3′-Anhydro-4,6-di-O-benzyl-
3-C-hydroxymethyl-r-D-manno-hexopyranosyl )-(1f3)-2-O-ben-
zoyl-4-O-benzyl-r-L-rhamnopyranoside (43). A solution of com-
pound 41 (260 mg, 0.28 mmol), mCPBA (150 mg, 0.87 mmol),
and NaHCO3 (104 mg, 1.24 mmol) in CH2Cl2 (25 mL) was stirred
at 0 °C for 30 min and warmed up to 40 °C. After being stirred for
further 4 h at 40 °C, the reaction mixture was quenched with
saturated aqueous NaHCO3, and extracted with CH2Cl2. The
combined organic phase was washed with brine, dried over MgSO4,
and concentrated in vacuo. The residue was purified by silica gel
flash column chromatography (CH2Cl2/EtOAc, 10:1, v/v) to afford
compound 43 (230 mg, 0.25 mmol, 87%) as a white foam. Rf )
0.38 (CH2Cl2/EtOAc, 50:1); [R]D +38.8 (c 0.50, CHCl3); IR (CHCl3
film) 3507, 3030, 2926, 2850, 1716, 1601, 1496, 1453, 1267, 1095,
Experimental Section
2′-(Benzyloxycarbonyl)benzyl (4,6-Di-O-benzyl-2-O-levulinyl-
3-deoxy-3-methylene-r-D-arabino-hexopyranosyl)-(1f3)-2-O-
benzoyl-4-O-benzyl-r-L-rhamnopyranoside (15). A solution of
CB glycoside 17 (417 mg, 0.71 mmol), BCB glycoside 18 (495
mg, 0.85 mmol, 1.2 equiv), and 2,6-di-tert-butyl-4-methylpyridine
(262 mg, 1.27 mmol) in CH2Cl2 (20 mL) in the presence of 4 Å
molecular sieves was stirred for 20 min at room temperature and
then cooled down to -78 °C. After addition of Tf2O (240 µL, 0.85
mmol) to the above solution, the reaction mixture was stirred at
-78 °C for 30 min, allowed to warm up over 30 min to room
temperature, stirred for further 1.5 h, filtered through Celite, and
quenched with saturated aqueous NaHCO3. Organic phase was
washed with brine, dried over MgSO4, and concentrated in vacuo.
The residue was purified by silica gel flash column chromatography
(hexane/EtOAc, 7:2, v/v) to give compound 15 (614 mg, 0.60 mmol,
85%) as a white foam. Rf ) 0.13 (hexane/EtOAc, 7:2); [R]D +61.2
(c 0.50, CHCl3); IR (CHCl3 film) 3022, 2939, 2850, 1716, 1454,
1407, 1362, 1257, 1082, 1047, 741, 698 cm-1. 1H NMR (400 MHz,
CDCl3) δ 1.39 (d, J ) 6.0 Hz, 3H), 2.13 (s, 3H), 2.60-2.65 (m,
2H), 2.72-2.76 (m, 2H), 3.48 (t, J ) 9.6 Hz, 1H), 3.55 (dd, J )
6.4, 1.6 Hz, 1H), 3.66 (dd, J ) 11.0, 3.2 Hz, 1H), 3.83-3.87 (m,
1H), 4.02 (d, J ) 8.8 Hz, 1H), 4.32 (s, 1H), 4.35 (s, 1H), 4.39-
4.47 (m, 3H), 4.61-4.67 (m, 2H), 4.77 (d, J ) 10.4 Hz, 1H), 4.96
(s, 1H), 4.98 and 5.09 (ABq, J ) 12.4 Hz, 2H), 5.17 (s, 1H), 5.20
(s, 1H), 5.24 (s, 1H), 5.32 (s, 1H), 5.44 (s, 1H), 5.64 (t, J ) 1.4
Hz, 1H), 7.05-7.09 (m, 2H), 7.15-7.50 (m, 22H), 7.57-7.63 (m,
1
1059, 914, 742, 713, 697 cm-1. H NMR (400 MHz CDCl3) δ
1.38 (d, J ) 6.0 Hz, 3H), 2.50 (d, J ) 5.6 Hz, 1H), 3.20 (d, J )
5.2 Hz, 1H), 3.44-3.60 (m, 3H), 3.85-3.93 (m, 1H), 4.08-4.12
(m, 1H), 4.24-4.33 (m, 3H), 4.43 (dd, J ) 9.6, 3.2 Hz, 1H), 4.52-
4.66 (m, 4H), 4.96 (s, 1H), 5.00 and 5.08 (ABq, J ) 13.6 Hz, 2H),
5.30 (s, 1H), 5.32 (s, 2H), 5.67 (brs, 1H), 7.02-7.62 (m, 26H),
8.00 (d, J ) 7.6 Hz, 1H), 8.06 (d, J ) 7.2 Hz, 2H); 13C NMR (100
MHz, CDCl3) δ 18.2, 29.9, 49.4, 61.3, 66.9, 67.6, 68.3, 68.4, 68.8,
69.7, 71.8, 73.4, 73.5, 74.0, 75.2, 76.0, 77.4, 79.9, 96.9, 97.7, 127.5,
127.66, 127.69, 127.90, 127.95, 127.99, 128.0, 128.1, 128.3, 128.4,
128.41, 128.45, 128.49, 128.7, 128.8, 129.8, 130.0, 130.9, 132.8,
133.6, 136.0, 137.4, 138.2, 138.4, 139.7, 165.9, 166.8. Anal. calcd
for C56H56O13: C, 71.78; H, 6.02. Found: C, 71.51; H, 6.11.
2′-(Benzyloxycarbonyl)benzyl (4,6-Di-O-benzyl-3-C-methyl-
r-D-manno-hexopyranosyl)-(1f3)-2-O-benzoyl-4-O-benzyl-r-L-
rhamnopyranoside (13). A solution of compound 43 (377 mg,
0.40 mmol), BH3‚NEt3 (214 mg, 1.86 mmol), and BF3‚OEt2 (264
mg, 1.86 mmol) in Et2O (20 mL) was stirred at 0 °C for 20 min
and allowed to warm up over 40 min to room temperature. After
being stirred for further 1 h, the reaction mixture was quenched
with saturated aqueous NaHCO3 and extracted with Et2O. The
combined organic phase was washed with brine, dried over MgSO4,
and concentrated in vacuo. The residue was purified by silica gel
flash column chromatography (hexane/EtOAc, 2:1, v/v) to give
compound 13 (310 mg, 0.33 mmol, 82%) as a white foam. Rf )
0.35 (CH2Cl2/EtOAc, 6:1); [R]D +42.7 (c 0.70, CHCl3); IR (CHCl3
film) 3507, 3030, 2926, 2850, 1716, 1601, 1496, 1453, 1267, 1095,
2H), 8.00 (dd, J ) 7.6, 1.2 Hz, 1H), 8.10 (d, J ) 7.2 Hz, 2H); 13
C
NMR (100 MHz, CDCl3) δ 18.1, 28.3, 29.9, 38.0, 66.8, 67.4, 68.2,
68.4, 68.7, 72.8, 72.99, 73.02, 73.3, 73.5, 75.3, 75.9, 79.5, 94.5,
97.6, 114.4, 127.2, 127.5, 127.6, 127.8, 127.9, 128.0, 128.2, 128.3,
128.4, 128.6, 128.7, 129.0, 129.9, 130.0, 130.8, 132.7, 133.3, 136.0,
137.7, 138.3, 139.81, 139.83, 165.8, 166.6, 171.2, 206.4. Anal. calcd
for C61H62O14: C, 71.89; H, 6.13. Found: C 71.69; H, 6.46
2′-(Benzyloxycarbonyl)benzyl (4,6-Di-O-benzyl-3-deoxy-3-
methylene-r-D-arabino-hexopyranosyl)-(1f3)-2-O-benzoyl-4-O-
benzyl-r-L-rhamnopyranoside (41). A solution of compound 15
(300 mg, 0.29 mmol), NH2NH2 (1.0 M in THF, 1.0 mL), and acetic
acid (2.0 mL) in THF/MeOH (5:1, 6.0 mL) was stirred in THF/
MeOH (4:1, 25.0 mL). The reaction mixture was stirred at room
temperature for 2 h, quenched with saturated NaHCO3, and
extracted with ethyl acetate. The organic layer was separated, dried
over MgSO4, and concentrated in vacuo. The residue was purified
1
1059, 914, 742, 713, 697 cm-1. H NMR (400 MHz, CDCl3) δ
1.22 (s, 3H), 1.41 (d, J ) 6.4 Hz, 3H), 1.76 (brs, 1H), 2.77 (s,
1H), 3.30-3.39 (m, 3H), 3.48 (t, J ) 9.4 Hz, 1H), 3.70 (d, J ) 9.6
Hz, 1H), 3.80-3.83 (m, 1H), 3.89-3.93 (m, 1H), 4.25 and 4.51
(ABq, J ) 12.0 Hz, 2H), 4.31 (dd, J ) 9.2, 3.2 Hz, 1H), 4.43 and
4.76 (ABq, J ) 11.6 Hz, 2H), 4.66 (s, 2H), 4.96 (s, 1H), 5.00 and
5.09 (ABq, J ) 14.4 Hz, 2H), 5.15 (s, 1H), 5.34 (s, 2H), 5.62 (dd,
J ) 4.2, 1.6 Hz, 1H), 7.10-7.63 (m, 26H), 8.01 (d, J ) 8.8 Hz,
1H), 8.08 (d, J ) 8.4 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ
18.5, 19.8, 66.9, 67.6, 68.5, 68.8, 69.4, 70.7, 73.5, 73.8, 74.3, 74.6,
J. Org. Chem, Vol. 72, No. 26, 2007 9969

Fulse et al.
75.0, 75.3, 77.9, 80.0, 97.8, 98.0, 128.3, 128.36, 128.41, 128.44,
128.6, 128.7, 128.8, 129.9, 130.0, 130.9, 132.8, 133.6, 136.0, 137.7,
138.2, 139.1, 139.7, 166.2, 166.8. HRMS (FAB): [M + Na]+ calcd
for C56H58O13Na: 961.3775; found: 961.3771.
165.9, 170.2. HRMS (FAB): [M + Na]+ calcd for C77H80O19Na:
1331.5192; found, 1331.5187.
Cyclohexyl (2-O-Benzoyl-4-O-benzyl-3-O-p-methoxybenzyl-
r-D-rhamnopyranosyl)-(1f2) -(4,6-di-O-benzyl-3-C-methyl-r-
D-manno-hexopyranosyl)-(1f3)-2-O-benzoyl-4-O-benzyl-r-L-
rhamnopyranoside (11). A solution of compound 14 (160 mg,
0.20 mmol) and 2,6-di-tert-butyl-4-methylpyridine (90 mg, 0.44
mmol) in CH2Cl2 (20 mL) in the presence of 4 Å molecular sieves
was stirred for 20 min at room temperature and cooled down to
-20 °C. After addition of Tf2O (85 µL, 0.30 mmol), the resulting
solution was stirred at -20 °C for 10 min and compound 12 (195
mg, 0.32 mmol) was added to this solution by using syringe pump
over 30 min. The reaction mixture was allowed to warm up over
30 min to room temperature, stirred for further 1.5 h, filtered through
Celite, and quenched with saturated aqueous NaHCO3. Collected
organic phase was washed with brine, dried over MgSO4, and
concentrated in vacuo. The residue was purified by silica gel flash
column chromatography (hexane/CH2Cl2/EtOAc, 10:4:1, v/v) to
give compound 11 (220 mg, 0.17 mmol, 87%) as a white foam. Rf
) 0.25 (hexane/CH2Cl2/EtOAc, 10:4:1); [R]D +35.4 (c 0.85,
CHCl3); IR (CHCl3 film) 3031, 2929, 2855, 1725, 1613, 1585, 1514,
1452, 1361, 1268, 1114, 1065, 837, 749, 713, 698 cm-1. 1H NMR
(400 MHz, CDCl3) δ 1.22-1.28 (m, 8H), 1.35-1.43 (m, 6H), 1.52
(brs, 1H), 1.68-1.72 (m, 2H), 1.80-1.84 (m, 2H), 3.37-3.49 (m,
4H), 3.52-3.64 (m, 3H), 3.69 (s, 3H), 3.74-3.80 (m, 1H), 3.90-
4.00 (m, 2H), 4.05-4.08 (m, 1H), 4.23 (dd, J ) 9.6, 2.8 Hz, 1H),
4.31 (d, J ) 12.0 Hz, 1H), 4.43-4.51 (m, 2H), 4.58-4.69 (m,
5H), 4.84-4.96 (m, 3H), 5.20 (d, J ) 1.6 Hz, 1H), 5.29 (brs, 2H),
5.45 (t, J ) 2.4 Hz, 1H), 5.54 (t, J ) 2.4 Hz, 1H), 6.75 (d, J ) 8.4
Hz, 2H), 7.13-7.32 (m, 18H), 7.42-7.59 (m, 8H), 7.64-7.68 (m,
1H), 7.91 (d, J ) 7.6 Hz, 1H), 8.04-8.11 (m, 4H); 13C NMR (100
MHz, CDCl3): δ 18.2, 18.4, 19.4, 23.9, 24.1, 25.7, 31.5, 33.3, 55.2,
68.2, 68.9, 69.0, 69.7, 69.9, 70.0, 70.8, 71.6, 73.2, 73.7, 74.6, 75.0,
75.2, 75.3, 75.8, 78.4, 80.0, 80.1, 83.5, 95.9 (JC-H ) 170 Hz), 96.8
(JC-H ) 169 Hz), 100.0 (JC-H ) 172 Hz), 113.8, 122.2, 125.9,
127.3, 127.4, 127.5, 127.6, 127.8, 128.0, 128.1, 128.2, 128.3,
128.43, 128.46, 128.5, 129.1, 129.86, 129.89, 129.9, 130.02, 130.05,
130.09, 130.1, 133.25, 133.28, 134.1, 137.7, 138.7, 138.9, 139.2,
146.6, 159.3, 165.8. MALDI-TOF: [M + Na]+ calcd for C75H84O17-
Na: 1279.5606; found: 1279.5607.
2′-(Benzyloxycarbonyl)benzyl (2-O-Benzoyl-4-O-benzyl-3-O-
p-methoxybenzyl-r-D-rhamnopyranosyl)-(1f2) -(4,6-Di-O-ben-
zyl-3-C-methyl-r-D-manno-hexopyranosyl)-(1f3)-2-O-benzoyl-
4-O-benzyl-r-L-rhamnopyranoside (2). A solution of compound
13 (230 mg, 0.24 mmol) and 2,6-di-tert-butyl-4-methylpyridine (91
mg, 0.44 mmol) in CH2Cl2 (20 mL) in the presence of 4 Å
molecular sieves was stirred for 20 min at room temperature and
cooled to -20 °C. After addition of Tf2O (97 µL, 0.34 mmol), the
resulting solution was stirred at -20 °C for 10 min and then
compound 12 (195 mg, 0.32 mmol) was added to this solution by
using syringe pump over 30 min. The reaction mixture was allowed
to warm up over 30 min to room temperature and stirred for further
1.5 h, filtered through Celite, and quenched with saturated aqueous
NaHCO3. Collected organic phase was washed with brine, dried
over MgSO4, and concentrated in vacuo. The residue was purified
by silica gel flash column chromatography (hexane/CH2Cl2/EtOAc,
10:4:1, v/v) to give compound 2 (257 mg, 0.18 mmol, 75%) as a
white foam. Rf ) 0.20 (hexane/CH2Cl2/EtOAc, 10:4:1); [R]D +24.3
(c 0.65, CHCl3); IR (CHCl3 film) 3320, 3013, 2930, 1722, 1602,
1514, 1453, 1268, 1113, 1060, 917, 751, 712, 698 cm-1. 1H NMR
(400 MHz, CDCl3) δ 1.24 (s, 3H), 1.39(s, 3H), 1.41 (s, 3H), 3.34-
3.66 (m, 6H), 3.69 (s, 3H), 3.73-3.80 (m, 2H), 3.87-3.92 (m,
1H), 3.99 (dd, J ) 9.2, 3.2 Hz, 1H), 4.06-4.09 (m, 1H), 4.27-
4.31 (m, 1H), 4.44-4.50 (m, 2H), 4.56-4.69 (m, 5H), 4.83-5.02
(m, 4H), 5.13 (d, J ) 14.8 Hz, 1H), 5.21 (d, J ) 1.6 Hz, 1H), 5.33
(s, 3H), 5.53 (dd, J ) 2.8, 2.0 Hz, 1H), 5.62 (dd, J ) 2.8, 2.0 Hz,
1H), 6.75 (d, J ) 8.8 Hz, 2H), 7.12-7.65 (m, 38H), 8.00 (dd, J )
8.0, 1.2 Hz, 1H), 8.05-8.11 (m, 4H); 13C NMR (100 MHz, CDCl3)
δ 18.3, 18.5, 19.5, 55.3, 66.9, 67.5, 68.6, 69.0, 69.1, 69.3, 70.0,
70.9, 71.6, 73.2, 73.8, 74.6, 75.0, 75.2, 75.3, 78.4, 80.0, 80.2, 83.4,
96.9 (JC′-H′ ) 171 Hz), 97.8 (JC-H ) 171 Hz), 100.0 (JC′′-H′′
)
173 Hz), 113.9, 127.7, 127.9, 128.0, 128.1, 128.2, 128.3, 128.4,
128.47, 128.52, 128.6, 128.8, 129.9, 130.0, 130.2, 130.9, 132.8,
133.3, 136.1, 137.7, 138.8, 138.9, 139.3, 139.9, 159.3, 165.7, 165.9,
166.7. MALDI-TOF: [M + Na]+ calcd for C84H86O19Na: 1421.5661;
found: 1421.5663.
2′-Carboxybenzyl (2-O-Benzoyl-4-O-benzyl-3-O-p-methoxy-
benzyl-r-D-rhamnopyranosyl)-(1f2) -(4,6-di-O-benzyl-3-C-
methyl-r-D-manno-hexopyranosyl)-(1f3)-2-O-benzoyl-4-O-benzyl-
r-L-rhamnopyranoside (9). A solution of compound 2 (250 mg,
0.18 mmol) in MeOH (10 mL) was stirred under hydrogen
atmosphere using a balloon in the presence of Pd/C (10%, 20 mg)
and ammonium acetate (7.5 mg, 0.096 mmol) at room temperature
for 30 min. The reaction mixture was filtered through Celite, and
the filtrate was concentrated in vacuo. The residue was purified by
silica gel flash column chromatography (CH2Cl2/EtOAc, 10:1, v/v)
to give compound 9 (215 mg, 0.16 mmol, 92%) as a white foam.
Rf ) 0.22 (CH2Cl2/EtOAc, 5:1); [R]D +40.0 (c 0.30, CHCl3); IR
(CHCl3 film) 3020, 2928, 2890, 1767, 1722, 1602, 1514, 1453,
1361, 1268, 1060, 738, 712, 698 cm-1. 1H NMR (400 MHz, CDCl3)
δ 1.29 (s, 3H), 1.37 (d, J ) 6.4 Hz, 3H), 1.47 (d, J ) 6.4 Hz, 3H),
3.41-3.57 (m, 7H), 3.69 (s, 3H), 3.86-3.88 (m, 1H), 3.96-4.13
(m, 3H), 4.19 (d, J ) 12.8 Hz, 1H), 4.31 (dd, J ) 9.6, 3.2 Hz,
1H), 4.42-4.50 (m, 2H), 4.62-4.70 (m, 5H), 4.78-4.90 (m, 3H),
4.97 (d, J ) 1.2 Hz, 1H), 5.12 (d, J ) 12.0 Hz, 1H), 5.20 (s, 1H),
5.37 (s, 1H), 5.54 (t, J ) 2.6 Hz, 1H), 5.61 (t, J ) 2.4 Hz, 1H),
6.76 (d, J ) 11.6 Hz, 2H), 7.09-7.36 (m, 23H), 7.42-7.49 (m,
6H), 7.54-7.60 (m, 2H), 7.90 (d, J ) 7.6 Hz, 1H), 8.04-8.10 (m,
4H); 13C NMR (100 MHz, CDCl3) δ 18.1, 18.5, 19.6, 55.3, 68.4,
69.1, 69.2, 69.9, 70.2, 71.6, 72.7, 73.9, 74.1, 75.0, 75.3, 75.4, 77.2,
78.7, 79.8, 80.2, 83.2, 96.3, 98.0, 99.7, 113.9, 127.4, 127.5, 127.6,
127.7, 127.7, 127.8, 127.9, 128.2, 128.3, 128.4, 128.50, 128.53,
128.6, 129.1, 129.8, 129.96, 129.99, 130.0, 130.12, 130.15, 130.7,
132.4, 133.3, 133.4, 137.7, 138.4, 138.6, 139.0, 139.1, 159.3, 165.8,
Cyclohexyl (2-O-Benzoyl-4-O-benzyl-r-D-rhamnopyranosyl)-
(1f2)-(4,6-di-O-benzyl-3-C-methyl-r-D-manno-hexopyranosyl)-
(1f3)-2-O-benzoyl-4-O-benzyl-r-L-rhamnopyranoside (10). A
solution of compound 11 (150 mg, 0.12 mmol) and TFA (54 µL,
0.48 mmol) in CH2Cl2 (25 mL) was stirred at 0 °C for 15 min and
allowed to warm up over 15 min to room temperature. After being
stirred for further 30 min, the reaction mixture was quenched with
saturated aqueous NaHCO3 and extracted with CH2Cl2. The
combined organic phase was washed with brine, dried over MgSO4,
and concentrated in vacuo. The residue was purified by silica gel
flash column chromatography (hexane/EtOAc, 3:1, v/v) to give
compound 10 (129 mg, 0.11 mmol, 95%) as a colorless viscous
oil. Rf ) 0.30 (hexane/EtOAc, 3:1); [R]D +46.6 (c 0.45, CHCl3);
IR (CHCl3 film) 3473, 2932, 2850, 1723, 1452, 1359, 1269, 1113,
1
1066, 1058, 750, 713, 698 cm-1. H NMR (400 MHz, CDCl3) δ
1.21-1.29 (m, 8H), 1.40 (d, J ) 6.4 Hz, 3H), 1.46 (d, J ) 6.4 Hz,
3H), 1.51 (brs, 1H), 1.69-1.74 (m, 2H), 1.80-1.85 (m, 2H), 2.30
(s, 1H), 2.51 (s, 1H), 3.36-3.60 (m, 5H), 3.70-3.81 (m, 2H), 3.91-
3.98 (m, 1H), 4.07-4.15 (m, 1H), 4.23-4.32 (m, 3H), 4.47 (d, J
) 11.2 Hz, 2H), 4.58 (d, J ) 12.4 Hz, 1H), 4.65 (d, J ) 5.6 Hz,
2H), 4.73-4.86 (m, 3H), 4.97 (s, 1H), 5.23-5.28 (m, 2H), 5.46
(s, 1H), 5.48 (d, J ) 1.6 Hz, 1H), 7.12-7.35 (m, 20H), 7.41-7.49
(m, 4H), 7.51-7.61 (m, 2H), 8.05-8.08 (m, 4H); 13C NMR (100
MHz, CDCl3) δ 18.2, 18.4, 19.4, 23.9, 24.1, 25.7, 31.5, 33.4, 68.2,
68.6, 68.9, 70.0, 70.4, 70.8, 73.1, 73.2, 73.8, 74.6, 74.96, 74.98,
75.2, 75.8, 78.4, 80.1, 81.6, 83.7, 95.9, 96.9, 99.9, 127.30, 127.34,
127.6, 127.7, 127.8, 127.9, 128.0, 128.1, 128.2, 128.3, 128.4, 128.5,
128.6, 129.8, 129.90, 129.95, 129.99, 130.1, 133.3, 133.4, 137.7,
9970 J. Org. Chem., Vol. 72, No. 26, 2007

Synthesis of Saccharide Subunits of a Lipopolysaccharide
138.4, 138.8, 139.2, 165.8, 166.3. Anal. calcd for C67H76O16: C,
70.76; H, 6.74. Found: C 70.39; H, 6.71.
133.3, 137.6, 137.70, 137.77, 138.6, 138.74, 138.8, 139.1, 139.3,
159.2, 165.3, 165.84, 165.87,165.9. MALDI-TOF: [M + Na]+
calcd for C136H148O32Na: 2315.9851; found: 2315.9859.
Cyclohexyl (r-D-Rhamnopyranosyl)-(1f2)-(3-C-methyl-r-D-
manno-hexopyranosyl)-(1f 3)-r-L-rhamnopyranoside (45). A
solution of compound 10 (96 mg, 0.08 mmol) and NaOMe (4.6
mg, 0.08 mmol) in MeOH (10 mL) was stirred at 50 °C for 10 h.
After being cooled down to room temperature, the reaction mixture
was neutralized with DOEX CCR-3 (H+ mode) resin and filtered
through Celite, and the filtrate was concentrated in vacuo. The
residue, without further purification, was dried under vacuum and
dissolved in MeOH/AcOH/CH2Cl2 (5:2:3, 5 mL). The resulting
solution was stirred under hydrogen atmosphere using a balloon in
the presence of Pd/C (10%, 10.80 mg) at room temperature
overnight. The reaction mixture was filtered through Celite, and
the filtrate was concentrated in vacuo. The residue was purified by
column chromatography on Iatrobeads 6RS-8060 (CH2Cl2/MeOH/
H2O, 3:1.5:0.1, v/v) to afford compound 45 (39 mg, 0.07 mmol,
82%) as an amorphous solid. Rf ) 0.60 (CH2Cl2/MeOH/H2O, 30:
Cyclohexyl (2-O-Benzoyl-4-O-benzyl-3-hydroxy-r-D-rham-
nopyranosyl)-(1f2)-(4,6-di-O-benzyl-3-C-methyl-r-D-manno-
hexopyranosyl)-(1f3)-(2-O-benzoyl-4-O-benzyl-r-L-rhamnopy-
ranosyl)-(1f3)-(2-O-benzoyl-4-O-benzyl-r-D-rhamnopyranosyl)-
(1f2)-(4,6-di-O-benzyl-3-C-methyl-r-D-manno-hexopyranosyl)-
(1f3)-2-O-benzoyl-4-O-benzyl-r-L-rhamnopyranoside (46). A
solution of compound 7 (53 mg, 0.02 mmol) and TFA (13 µL 0.11
mmol) in CH2Cl2 (15 mL) was stirred at 0 °C for 30 min and
allowed to warm up over 30 min to room temperature. After being
stirred for further 4 h, the reaction mixture was quenched with
saturated aqueous NaHCO3 and extracted with CH2Cl2. The
combined organic phase was washed with brine, dried over MgSO4,
and concentrated in vacuo. The residue was purified by silica gel
flash column chromatography (hexane/EtOAc, 2:1, v/v) to give
compound 46 (45 mg, 0.02 mmol, 90%) as a colorless viscous oil.
Rf ) 0.17 (hexane/EtOAc, 2:1); [R]D +55.2 (c 0.40, CHCl3); IR
(CHCl3 film) 3498, 3031, 2930, 2855, 1727, 1613, 1585, 1514,
1452, 1361, 1269, 1114, 1069, 749, 712, 698 cm-1. 1H NMR (400
MHz, CDCl3) δ 1.16 (d, J ) 6.4 Hz, 3H), 1.21-1.28 (m, 11H),
1.39 (d, J ) 6.0 Hz, 3H), 1.50 (d, J ) 6.4 Hz, 3H), 1.65 (s, 4H),
1.71 (brs, 2H), 1.83 (brs, 2H), 2.12 (d, J ) 4.4 Hz, 1H), 2.29 (d,
J ) 4.4 Hz, 1H), 3.00 (d, J ) 10.0 Hz, 1H), 3.20 (dd, J ) 8.8, 2.4
Hz, 1H), 3.34-3.46 (m, 7H), 3.56-3.61 (m, 2H), 3.65-3.69 (m,
2H), 3.73-3.77 (m, 2H), 3.91-4.02 (m, 3H), 4.09-4.18 (m, 3H),
4.22-4.30 (m, 3H), 4.36-4.47 (m, 4H), 4.53-4.56 (m, 4H), 4.64-
4.70 (m, 3H), 4.75-4.83 (m, 3H), 4.89 (d, J ) 10.4 Hz, 2H), 5.15
(s, 1H), 5.19 (s, 1H), 5.22 (s, 1H), 5.26 (s, 1H), 5.30 (s, 1H), 5.39-
5.41 (m, 2H), 5.46 (t, J ) 2.4 Hz, 1H), 5.60 (brs, 1H), 7.04-7.09
(m, 6H), 7.11-7.21 (m,18H), 7.22-7.28 (m, 9H), 7.30-7.35 (m,
7H), 7.41-7.49 (m, 9H), 7.55-7.62 (m, 3H), 8.04-8.12 (m, 8H);
13C NMR (100 MHz, CDCl3) δ 17.7, 18.1, 18.4, 18.5, 19.52, 19.55,
23.9, 24.2, 25.7, 31.5, 33.4, 68.2, 68.4, 68.5, 68.9, 69.1, 70.0, 70.4,
70.5, 70.7, 72.3, 73.21, 73.21, 73.23, 73.4, 73.7, 74.0, 74.4, 74.8,
74.9, 75.0, 75.1, 75.2, 75.8, 76.5, 78.0, 78.3, 79.8, 79.9, 80.1, 81.7,
82.8, 83.5, 93.9, 95.9, 96.3, 96.8, 99.6, 100.0, 127.2, 127.3, 127.4,
127.61, 127.65, 127.69, 127.7, 127.8, 127.9, 128.0, 128.1, 128.2,
128.22, 128.25, 128.28, 128.3, 128.4, 128.50, 128.55, 128.61,
128.64, 128.7, 129.6, 129.8, 129.9, 130.02, 130.09, 130.1, 130.2,
133.2, 133.3, 133.4, 138.5, 138.7, 139.1, 139.2, 165.3, 165.8, 165.8,
166.3. MALDI-TOF: [M + Na]+ calcd for C128H140O31Na:
2195.9276; found: 2195.9263.
Cyclohexyl (r-D-Rhamnopyranosyl)-(1f2)-(3-C-methyl-r-D-
manno-hexopyranosyl)-(1f 3)-(r-L-rhamnopyranosyl)-(1f3)-
(r-D-rhamnopyranosyl)-(1f2)-(3-C-methyl-r-D-manno-hexopy-
ranosyl)-(1f3)-r-L-rhamnopyranoside (47). A solution of
compound 7 (80 mg, 0.04 mmol) and NaOMe (7.5 mg, 0.01 mmol)
in MeOH (10 mL) was stirred at 50 °C for 10 h. After being cooled
down to room temperature, the reaction mixture was neutralized
with DOEX CCR-3 (H+ mode) resin and filtered through Celite,
and the filtrate was concentrated in vacuo. The residue, without
further purification, was dried under vacuum and dissolved in
MeOH/AcOH/CH2Cl2 (5:2:3, 5 mL). The resulting solution was
stirred under hydrogen atmosphere using a balloon in the presence
of Pd/C (10%, 10 mg) at room temperature overnight. The reaction
mixture was filtered through Celite, and the filtrate was concentrated
in vacuo. The residue was purified by column chromatography on
Iatrobeads 6RS-8060 (CH2Cl2/MeOH/H2O, 25:15:1, v/v) to give
compound 47 (30 mg, 0.03 mmol, 83%) as a white solid. Rf )
0.62 (CH2Cl2/MeOH/H2O, 2.5:1.5:0.1); [R]D +34.0 (c 0.65, H2O).
1H NMR (400 MHz, D2O) δ 1.14-1.33 (m, 18H), 1.39 (d, J ) 3.2
Hz, 6H), 1.51 (brs, 1H), 1.70 (brs, 2H), 1.86-1.95 (brs, 2H), 3.42-
3.54 (m, 4H), 3.62-3.63 (brs, 1H), 3.69-3.84 (m, 18H), 3.89-
4.01 (m, 2H), 4.05 (brs, 1H), 4.09 (brs, 1H), 4.18 (brs, 1H), 4.30
(brs, 1H), 4.95 (s, 1H), 4.98 (s, 2H), 5.01 (s, 1H), 5.08 (s, 1H),
5.11 (s, 1H); 13C NMR (100 MHz, D2O) δ 16.72, 16.73, 16.8, 16.9,
18.1, 18.2, 23.8, 24.0, 25.1, 31.0, 32.9, 61.1, 61.2, 66.0, 66.3, 66.6,
1
15:1); [R]D +44.2 (c 0.95, H2O); H NMR (400 MHz, D2O) δ
1.25-1.31 (m, 10H), 1.67 (brs, 1H), 1.41 (s, 3H), 1.55 (brs, 1H),
1.91-1.97 (brs, 2H), 1.88-2.00 (brs, 2H), 3.48-3.51 (m, 2H), 3.66
(brs, 1H), 3.72-3.89 (m, 11H), 4.08 (d, J ) 1.6 Hz, 1H), 4.12 (d,
J ) 1.6 Hz, 1H), 4.97 (s, 1H), 5.01 (s, 1H), 5.11 (s, 1H); 13C NMR
(100 MHz, D2O) δ 16.7, 16.8, 18.1, 23.8, 24.0, 25.1, 31.0, 32.9,
61.2, 66.6, 68.9, 69.3, 69.4, 70.0, 70.1, 70.5, 71.5, 72.0, 73.2, 73.8,
76.3, 82.9, 95.4 (JC-H ) 171 Hz), 97.5 (JC-H ) 171 Hz), 102.9
(JC-H ) 172 Hz). MALDI-TOF: [M + Na]+ calcd for C25H44O14:
591.2628; found: 591.2623.
Cyclohexyl (2-O-Benzoyl-4-O-benzyl-3-O-p-methoxybenzyl-
r-D-rhamnopyranosyl)-(1f2)-(4,6-di-O-benzyl-3-C-methyl-r-D-
manno-hexopyranosyl)-(1f3)-(2-O-benzoyl-4-O-benzyl-r-L-rham-
nopyranosyl)-(1f3)-(2-O-benzoyl-4-O-benzyl-r-D-rhamnopy-
ranosyl)-(1f2)-(4,6-di-O-benzyl-3-C-methyl-r-D-manno-
hexopyranosy l)-(1f3)-2-O-benzoyl-4-O-benzyl-r-L-rhamnopyr-
anoside (7). A solution of compound 10 (40 mg, 0.04mmol) and
2,6-di-tert-butyl-4-methylpyridine (13 mg, 0.06mmol) in CH2Cl2
(20 mL) in the presence of 4 Å molecular sieves was stirred for 20
min at room temperature and cooled down to -20 °C. After addition
of Tf2O (13 µL, 0.05 mmol), the resulting solution was stirred at
-20 °C for 10 min, and compound 9 (55 mg, 0.04 mmol) was
added to this solution by using syringe pump over 30 min. The
reaction mixture was allowed to warm up over 30 min to room
temperature, stirred for further 1.5 h, filtered through Celite, and
quenched with saturated aqueous NaHCO3. Organic phase was
washed with brine, dried over MgSO4, and concentrated in vacuo.
The residue was purified by silica gel flash column chromatography
(hexane/CH2Cl2/EtOAc, 10:4:1, v/v) to give compound 7 (58 mg,
0.03 mmol, 72%) as a colorless viscous oil. Rf ) 0.43 (hexane/
CH2Cl2/EtOAc, 3:1:1); [R]D +37.5 (c 1.60, CHCl3); IR (CHCl3 film)
3655, 3031, 2930, 2855, 1725, 1613, 1585, 1514, 1452, 1361, 1268,
1113, 1069, 749, 713, 711, 698 cm-1. 1H NMR (400 MHz, CDCl3)
δ 1.14 (d, J ) 6.0 Hz, 3H), 1.22-1.44 (m, 18H), 1.50 (d, J ) 6.0
Hz, 3H), 1.72 (brs, 2H), 1.83 (brs, 2H), 3.01 (d, J ) 10.8 Hz, 1H),
3.20 (d, J ) 10.8 Hz, 1H), 3.33-3.53 (m, 7H), 3.56-3.65 (m,
5H), 3.68 (s, 3H), 3.76-3.85 (m, 2H), 3.91-4.05 (m, 6H), 4.08-
4.12 (m, 2H), 4.22-4.30 (m, 3H), 4.35-4.48 (m, 5H), 4.51-4.67
(m, 8H), 4.77-4.91 (m, 4H), 5.00 (s, 1H), 5.17 (s, 1H), 5.22 (s,
1H), 5.26 (s, 1H), 5.30 (s, 1H), 5.41 (brs, 1H), 5.46 (t, J ) 2.4 Hz,
1H), 5.49 (t, J ) 2.4 Hz, 1H), 5.65 (brs, 1H), 6.73 (d, J ) 8.8 Hz,
2H), 6.97-7.33 (m, 42H), 7.35-7.59 (m, 12H), 8.04-8.11 (m, 8H);
13C NMR (100 MHz, CDCl3) δ 17.7, 18.0, 18.4, 18.55, 19.53, 23.9,
24.2, 25.7, 29.8, 31.5, 33.3, 55.2, 67.9, 68.2, 68.5, 68.6, 68.7, 68.96,
69.0, 70.0, 70.5, 70.7, 71.6, 72.2, 73.21, 73.23, 73.5, 73.7, 73.9,
74.4, 74.8, 74.9, 75.1, 75.2, 75.3, 75.8, 76.5, 77.6, 78.1, 78.3, 79.7,
79.9, 80.1, 82.7, 83.6, 93.8, 95.9, 96.3, 96.81, 99.7, 100.0, 113.8,
127.54, 127.56, 127.64, 127.68, 127.8, 128.1, 128.21, 128.26,
128.27, 128.33,128.38, 128.45, 128.49, 128.54, 128.59, 128.6,
128.7, 129.6, 129.8, 129.9, 130.01, 130.08, 130.13, 130.18, 130.2,
133.1, 133.2,
J. Org. Chem, Vol. 72, No. 26, 2007 9971

Fulse et al.
68.9, 68.9, 69.2, 69.3, 69.42, 69.45, 69.7, 70.0, 70.1, 70.2, 70.3,
70.5, 71.64, 71.65, 72.0, 73.2, 73.7, 74.0, 74.2, 76.3, 82.8, 83.2,
95.3 (JC-H ) 170 Hz), 95.4 (JC-H ) 170 Hz), 96.1 (JC-H ) 172
Hz), 97.5 (JC-H ) 171 Hz), 102.7 (JC-H ) 172 Hz), 102.8 (JC-H
) 174 Hz). MALDI-TOF: [M + Na]+ calcd for C44H76O27Na:
1059.4471; found: 1059.4478.
2H), 2.14 (d, J ) 4.8 Hz, 2H), 2.25 (s, 1H), 2.99 (t, J ) 9.8 Hz,
2H), 3.15 (d, J ) 8.8 Hz, 1H), 3.22 (d, J ) 8.8 Hz, 1H), 3.34-
3.79 (m, 23H), 3.91-4.08 (m, 10H), 4.21-4.30 (m, 6H), 4.32-
4.41 (m, 5H), 4.44-4.50 (m, 3H), 4.53-4.65 (m, 7H), 4.71-4.82
(m, 3H), 4.86-4.90 (m, 3H), 4.96 (d, J ) 1.2 Hz, 1H), 5.14-5.17
(m, 4H), 5.22 (s, 1H), 5.26 (s, 2H), 5.30 (s, 1H), 5.40 (s, 1H), 5.42
(s, 1H), 5.46 (s, 1H), 5.48 (s, 1H), 5.54 (s, 1H), 5.59 (s, 1H), 6.73
(d, J ) 8.4 Hz, 2H), 7.01-7.14 (m, 43H), 7.16-7.33 (m, 20H),
7.40-7.47 (m, 19H), 8.06-8.11 (m, 12H); 13C NMR (100 MHz,
CDCl3) δ 17.6, 17.7, 18.1, 18.4, 18.50, 18.58, 19.5, 19.6, 24.0,
24.2, 25.7, 29.5, 29.8, 31.5, 32.0, 33.4, 55.2, 68.06, 68.08, 68.2,
68.5, 68.5, 68.6, 68.76, 68.76, 68.9, 69.0, 69.1, 70.03, 70.09, 70.4,
70.5, 70.8, 71.6, 72.3, 73.22, 73.26, 73.4, 73.5, 73.7, 73.9, 73.9,
74.5, 74.82, 74.89, 75.0, 75.1, 75.2, 75.3, 75.8, 76.5, 77.6, 78.0,
78.1, 78.4, 79.8, 80.0, 80.1, 82.7, 83.0, 83.6, 93.8 (JC-H ) 173
Cyclohexyl (2-O-Benzoyl-4-O-benzyl-3-O-p-methoxybenzyl-
r-D-rhamnopyranosyl)-(1f2)-(4,6-di-O-benzyl-3-C-methyl-r-
D-manno-hexopyranosyl)-(1f3)-(2-O-benzoyl-4-O-benzyl-r-L-
rhamnopyranosyl)-(1f3)-(2-O-benzoyl-4-O-benzyl-r-D-rhamnopy-
ranosyl)-(1f2)-(4,6-di-O-benzyl-3-C-methyl-r-D-manno-
hexopyranosyl)-(1f3)-(2-O-benzoyl-4-O-benzyl-r-L-rham-
nopyranosyl)-(1f3)-(2-O-benzoyl-4-O-benzyl-r-D-rhamnopyra-
nosyl)-(1f2)-(4,6-di-O-benzyl-3-C-methyl-r-D-manno-hexopy-
ranosyl)-(1f3)-2-O-benzoyl-4-O-benzyl-r-L-rhamnopyrano-
side (8). A solution of compound 46 (52 mg, 0.02 mmol) and 2,6-
di-tert-butyl-4-methylpyridine (7.30 mg, 0.03 mmol) in CH2Cl2 (20
mL) in the presence of 4 Å molecular sieves was stirred for 20
min at room temperature and cooled down to -20 °C. After addition
of Tf2O (7.30 µL, 0.03 mmol), the resulting solution was stirred at
-20 °C for 10 min and compound 9 (26 mg, 0.02 mmol) was added
to this solution by using syringe pump over 20 min. The reaction
mixture was allowed to warm up over 30 min to room temperature,
stirred for further 1.5 h, filtered through Celite, and quenched with
saturated aqueous NaHCO3. Collected organic phase was washed
with brine, dried over MgSO4, and concentrated in vacuo. The
residue was purified by silica gel flash column chromatography
(hexane/CH2Cl2/EtOAc, 2:1:1, v/v) to give compound 8 (30 mg,
0.01 mmol, 45%) as a white viscous oil. Rf ) 0.65 (hexane/CH2-
Cl2/EtOAc, 2:1:1); [R]D +30.1 (c 1.0, CHCl3); IR (CHCl3 film)
3600, 3062, 3030, 2930, 2856, 1727, 1602, 1585, 1513, 1496, 1452,
1360, 1316, 1269, 1176, 1114, 1017980, 918, 839, 751, 712, 698
Hz), 93.9 (JC-H ) 171 Hz), 95.9 (JC-H ) 169 Hz), 96.3 (JC-H
)
171 Hz), 96.3 (JC-H ) 171 Hz), 96.8 (JC-H ) 171 Hz), 99.7 (JC-H
) 175 Hz), 99.9 (JC-H ) 171 Hz), 100.1 (JC-H ) 175 Hz), 113.8,
128.4, 128.51, 128.54, 128.61, 128.67, 128.7, 129.71, 129.76, 129.8,
129.9, 130.0, 130.13, 130.16, 130.23, 130.27, 133.1, 133.2, 133.3,
137.6, 137.6, 137.7, 137.8, 138.5, 138.7, 138.7, 138.8, 139.1, 139.2,
139.3, 159.2, 165.3, 165.3, 165.83, 165.88, 165.9. MALDI-TOF:
[M + Na ]+ calcd for C197H212O47Na: 3352.4100; found: 3352.4094.
Acknowledgment. This work was supported by a grant from
the Korea Science and Engineering Foundation through Center
for Bioactive Molecular Hybrids (CBMH). D.B.F. thanks the
fellowship of the BK 21 program from the Ministry of Education
and Human Resources Development.
Supporting Information Available: General experimental
procedures, spectral/analytical data, and copies of 1H and 13C NMR
spectra for all new compounds. This material is available free of
charge via the Internet at http://pubs.acs.org.
1
cm-1. H NMR (400 MHz, CDCl3) δ 1.14 (d, J ) 6.4 Hz, 3H),
1.90-1.27 (m, 27H), 1.37 (d, J ) 12.4 Hz, 3H), 1.49 (d, J ) 6.0
Hz, 3H), 1.72 (brs, 2H), 1.84 (d, J ) 10.0 Hz,
JO701531X
9972 J. Org. Chem., Vol. 72, No. 26, 2007