Synthesis of a tetrasaccharide repeating unit of O-antigenic polysaccharide of Salmonella enteritidis by use of unique and odorless dodecyl thioglycosyl donors

Article abstract of DOI:10.1016/j.tetlet.2008.06.097

The first total synthesis of a unique tetrasaccharide repeating unit of lipopolysaccharide from Salmonella enteritidis has been accomplished by assembly of dodecyl thioglycosides. The crucial key steps were preparation of a rare branched dideoxy sugar, dtyvelose (3,6-dideoxy-d-arabino-d-hexose) and sequential regioselective glycosylation at 2,3-positions of a central d-mannose residue 5 with d-tyvelose 6 and d-galactose donors 7.

Full text of DOI:10.1016/j.tetlet.2008.06.097

Tetrahedron Letters 49 (2008) 5289–5292
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Synthesis of a tetrasaccharide repeating unit of O-antigenic polysaccharide of
Salmonella enteritidis by use of unique and odorless dodecyl thioglycosyl donors
Sang-Hyun Son a, Chiharu Tano a, Tetsuya Furuike b, Nobuo Sakairi a,
*
a Graduate School of Environmental Science, Hokkaido University, Kita-ku, Sapporo 060-0810, Japan
b Department of Chemical and Materials Engineering, Faculty of Chemistry, Materials and Bioengineering, and High Technology Research Center, Kansai University,
Suita, Osaka 564-8680, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
The first total synthesis of a unique tetrasaccharide repeating unit of lipopolysaccharide from Salmonella
enteritidis has been accomplished by assembly of dodecyl thioglycosides. The crucial key steps were prep-
Received 2 May 2008
Revised 18 June 2008
Accepted 20 June 2008
Available online 25 June 2008
aration of a rare branched dideoxy sugar,
D
-tyvelose (3,6-dideoxy-
D
-arabino-
D-hexose) and sequential
regioselective glycosylation at 2,3-positions of a central
D
-mannose residue 5 with
D
-tyvelose 6 and -gal-
D
actose donors 7.
Ó 2008 Elsevier Ltd. All rights reserved.
Salmonella enteritidis is known as a virulence food-borne en-
teric human pathogen,1 which colonize inert food contact sur-
faces to form biofilms.2 Like other Gram-negative bacteria, it
has lipopolysaccharide (LPS), which consists of anchoring lipid
A and O-antigenic polysaccharide, at the outer membrane. Isola-
tion and characterization of its lipopolysaccharide (LPS) have
been extensively studied to understand the molecular mecha-
nisms of Salmonella infection, adherence, and biofilm formation
on inert surfaces.3 Recently, it was reported that O-antigen poly-
saccharide of S. enteritidis has a repeating tetrasaccharide struc-
OH
O
HO
O
HO
O
HO
HO
O
OH
HO
O
O
O
HO
O
OH
O
ture, ?3)-
-Rhap-(1? (1).4 Its unusual feature is the occurrence of a rare
dideoxy sugar, -tyvelose (3,6-dideoxy- -arabino- -hexose),
which was deduced to play an important role in pathogenesis.5
Furthermore, central -mannose residue in the repeating tetrasac-
a-D-Galp-(1?2)-[a-D-Tyvp-(1?3)]-a-D-Manp-(1?4)-a-
n
L
1
D
D
D
Figure 1. The structure of O-antigenic polysaccharide isolated from Salmonella
enteritidis.
D
charide has three different monosaccharides at 1,2,3-positions.
Due to its structural uniqueness and biomedical potential, we
undertook to synthesize oligosaccharides related to 1. Herein,
we report the first total synthesis of a methyl glycoside 2 of
the repeating unit (see Fig. 1).
Key problems needing to be addressed in the synthesis of 2
were preparation of a tyvelose donor and introduction of three
monosaccharide moieties into the central mannose residue by effi-
cient glycosylation methods. Retrosynthetic analysis shown in
Scheme 1 suggested that sequential regioselective glycosylation
of a disaccharide acceptor 5 having two free hydroxyl groups with
synthesized from a mannosyl donor 4 and known methyl rhamno-
side acceptor6 3. In all glycosylation reactions required for the con-
struction of 2, we planned to use our recently developed dodecyl
thioglycosyl donor,7 of which advantage is that they are able to
prepare under almost odorless conditions.
According to the synthetic plan mentioned above, we initiated
to prepare three dodecyl thioglycoside donors 4, 6, and 7 as de-
picted in Scheme 2. Saponification of the acetylated thiomannopyr-
anoside7 8 and subsequent O-benzylidenation and O-benzoylation
afforded the fully protected derivative 4 in 71% yield. For the con-
D
-tyvelose 6 and D-galactose donors 7 provides the target tetrasac-
charide 2. The sterically less hindered equatorial hydroxyl group at
struction of a-mannosidic linkage, benzoyl group with neighboring
C-30 would be the first glycosylation site. Furthermore, 5 was to be
group participation was anticipated to be the best choice to protect
the C2 hydroxyl group, and it can be readily converted to free
hydroxylic sites on the key intermediate 5 for the installation of
the branched tyvelose moiety and galactose moiety. Moreover, 4
* Corresponding author. Tel./fax: +81 11 706 2257.
E-mail address: nsaka@ees.hokudai.ac.jp (N. Sakairi).
0040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.06.097

5290
S.-H. Son et al. / Tetrahedron Letters 49 (2008) 5289–5292
OH
O
AcO
HO
HO
OBz
O
OAc
O
O
Ph
AcO
AcO
O
i
BzO
HO
HO
O
SC12H25
SC12H25
O
HO
8
4
OH
HO
O
O
HO
O
HO
OBz
O
OBz
O
O
OH
OMe
BnO
BzO
2
BnO
BzO
ii
iii
SC12H25
SC12H25
BnO
BnO
OBn
O
9
10
SC12H25
2nd glycosylation
BnO
7
OBz
O
OBz
O
BnO
RO
vi
SC12H25
iv
BnO
OH
O
Ph
O
O
SC12H25
O
HO
O
11 : R = H
12 : R = C(S)Im
O
SC12H25
6
v
O
5
OMe
Scheme 2. Preparation of D-mannose and D-tyvelose donors. Reagents and condi-
BnO
O
OBz
tions: (i) (a) NaOMe/MeOH, rt, 3 h; (b) PhCH(OMe)2, cat. CSA, DMF, 50 °C, 4 h; (c)
BzCl, DMAP, pyridine, 50 °C, 3 h, 71% over three steps; (ii) BH3ꢀMe2NH, BF3ꢀEt2O,
CH2Cl2, 0 °C, 1 h, 82% (Ref. 8); (iii) (a) TsCl, DMAP, pyridine, 0 °C to 50 °C, overnight;
(b) NaBH4, DMF, 70 °C, 3 h 81% over two steps (Ref. 9); (iv) (a) NaOMe/MeOH–
CH2Cl2, rt, 3 h; (b) PhC(EtO)3, cat. CSA, CH2Cl2, rt, 3 h; (c) 80% AcOH in H2O, 80 °C,
2 h, 79% over three steps (Refs. 10b and c); (v) C(S)Im2, imidazole, (CH2Cl)2, 80 °C,
18 h, 98%; (vi) Bu3SnH, AIBN, toluene, reflux, 30 min, 82% (Ref. 10).
1st glycosylation
6
OBz
O
OMe
O
Ph
O
O
HO
BzO
selective glycosylation in order to shorten the synthetic route to 2.
For selective glycosylation at the equatorial hydroxyl group at 30-
position, we used excess amount of the diol acceptor 5. Thus, a
mixture of 5 (0.25 mmol) and the tyvelose donor 6 (0.125 mmol)
was activated with NIS–TfOH at ꢁ40 °C. As a result, the desired tri-
SC12H25
O
O
4
3
saccharide12 14 was obtained with completed
a
-stereoselectivity
-(1?3)
D-mannose units in 14 was unam-
Scheme 1. Retrosynthetic analysis.
in excellent yield. The presence of the newly introduced
a
linkage between -tyvelose and
D
biguously ascertained by 1H COSY NMR spectroscopy after conver-
sion of the acetylated derivative12 15. Careful examination of the
spectrum showed H-2 protons for the mannose residue at lower
magnetic field (d 5.21) as a double doublet which was assigned
by a cross-peak between H-1 and H-2 protons. The regioselectivity
is explainable by the facts that the equatorial 30-hydroxyl group is
less hindered than the axial 20-hydroxyl group and that presence
was also considered to be a precursor of the tyvelose donor 6. Thus,
the benzylidene acetal in 4 was regioselectively opened with
BH3ꢀMe2NH–BF3ꢀEt2O in dichloromethane furnished the primary
alcohol8 9 in 82% yield. Next deoxygenation seemed to be a crucial
step in our synthesis, because 9 has a reducible thioacetal function
at the anomeric center. For deoxygenation of the primary alcohol,9
9 was subjected to O-tosylation followed by reduction with NaBH4
of bulky L-rhamnose residue at the anomeric position of the man-
in DMF to provide the dodecyl thio
D
-rhamnoside 10 in a yield of
nose residue reduced the reactivity of neighboring 20-hydroxyl
group. Furthermore, comparison of decoupling and non-decou-
pling HSQC spectra revealed signals of anomeric carbons at d
81%. The second deoxygenation10 at C3 was performed after trans-
formation into a monobenzoate 11 in three steps including de-O-
benzoylation, formation of an orthoester, and its acid-catalyzed
ring opening. The resulting kinetically preferred axial benzolate
11 obtained in an overall yield of 79% was converted into thiocarb-
onylimidazole intermediate 12, which was subjected to radical
reduction with Bu3SnH10b,c in toluene to give the tyvelose donor
6 in 82% (see Scheme 3).
99.0 (JC1 ;H1 ¼ 175:9 Hz, C-10), 97.8 (JC1,H1 = 170.0 Hz, C-1), and
0
0
¼ 172:9 Hz, C-100), suggesting 15 had all
a-glycosidic
00;H100
97.7 (JC1
linkages. The next coupling between the donor 7 and the trisac-
charide 14 was performed using a powerful promoter of thioglyco-
sides so far reported, because of the prediction of the extremely
poor reactivity of 14. Thus, the donor 7 was pre-activated with
the 1–benzenesulfinyl piperidine and triflic anhydride (BSP–
Tf2O)13 combination in the presence of 2,6-di-tert-butyl-4-methyl-
pyridine (DTBP) in dichloromethane at ꢁ78 °C, and then treated
with the acceptor 14. Interestingly, desired tetrasaccharide12 16
Assembly of these thioglycosyl donors toward 2 was performed
by use of thiophyllic reagents as the promoters. The first coupling
of 3 and 4 proceeded at ꢁ20 °C to 0 °C in the presence of molecular
sieves and a promoter, N-iodosuccinimide and catalytic triflic acid
(NIS–TfOH),11 giving the disaccharide12 13 in 90% yield. Subse-
quently, two benzolyl groups at 20,30-positions of 13 were removed
by Zemplén method to give the disaccharide acceptor12 5 in 96%
yield. Using this diol acceptor, we examined sequential and regio-
was isolated in 72% yield with complete
a-stereoselectivity. No
trace of the b-anomer was detected by both chromatographic
and NMR spectroscopic analyses of the crude reaction mixture.
Similar results had been obtained previously with fully benzylated

S.-H. Son et al. / Tetrahedron Letters 49 (2008) 5289–5292
5291
Supplementary data
OR
O
O
Ph
O
O
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2008.06.097.
O
RO
i
O
3 + 4
O
OMe
O
References and notes
13 : R = Bz
5 : R = H
ii
1. (a) Dhir, V. K.; Dodd, C. E. Appl. Environ. Microbiol. 1995, 61, 1731–1738; (b)
Jones, K.; Bradshaw, S. B. J. Appl. Bacteriol. 1996, 80, 458–464.
2. Austin, J. W.; Sanders, G.; Kay, W. W.; Collinson, S. K. FEMS Microbiol. Lett. 1998,
162, 295–301.
3. (a) Carpentier, B.; Cerf, O. J. Appl. Bacteriol. 1993, 75, 499–511; (b) Austin, J. W.;
Bergeron, G. J. Dairy Res. 1995, 62, 509–519.
OR
O
O
O
Ph
O
iii
O
4. Snyder, D. S.; Gibson, D.; Heiss, C.; Kay, W.; Azadi, P. Carbohydr. Res. 2006, 341,
2388–2397.
O
O
BnO
5. (a) Appleton, J. A.; Schain, L. R.; McGregor, D. D. Immunology 1988, 65, 487–492;
(b) Denkers, E. Y.; Hayes, C. E.; Wassom, D. L. Exp. Parasitol. 1991, 72, 403–410;
(c) Nitz, M.; Bundle, D. R. J. Org. Chem. 2000, 65, 3064–3073; (d) Hirooka, M.;
Yoshimura, A.; Saito, I.; Ikawa, F.; Uemoto, Y.; Koto, S.; Takabatake, A.;
Taniguchi, A.; Shinoda, Y.; Morinaga, A. Bull. Chem. Soc. Jpn. 2003, 76, 1409–
1421. and references cited therein.
O
OBz
iv
OMe
14 : R = H
15 : R = Ac
6. Davis, B.; Brandstetter, T. W.; Smith, C.; Hackett, L.; Winchester, B. G.; Fleet, G.
W. J. Tetrahedron Lett. 1995, 36, 7505–7510.
OBn
O
BnO
BnO
Ph
7. (a) Matsui, H.; Furukawa, J.; Awano, T.; Nishi, N.; Sakairi, N. Chem. Lett. 2000,
326–327; (b) Matsuoka, K.; Onaga, T.; Mori, T.; Sakamoto, J.-I.; Koyama, T.;
Sakairi, N.; Hatano, K.; Terunuma, D. Tetrahedron Lett. 2004, 45, 9383–9386; (c)
Son, S.-H.; Tano, C.; Furukawa, J.-i.; Furuike, T.; Sakairi, N. Org. Biomol. Chem.
2008, 6, 1441–1449.
BnO
O
O
O
v
O
O
8. Oikawa, M.; Liu, W.-C.; Nakai, Y.; Koshida, S.; Fukase, K.; Kusumoto, S. Synlett
1996, 1179–1180.
O
O
9. Van den Bos, L. J.; Boltje, T. J.; Provoost, T.; Mazurek, J.; Overkleeft, H. S.; van der
Marel, G. A. Tetrahedron Lett. 2007, 48, 2697–2700.
10. (a) Rasmussen, J. R. J. Org. Chem. 1980, 45, 2725–2727; (b) Bart, R.; Pavol, K.
Synthesis 2004, 2505–2508; (c) Turek, D.; Sundgren, A.; Lahmann, M.;
Oscarson, S. Org. Biomol. Chem. 2006, 4, 1236–1241.
O
O
BnO
O
OBz
OMe
16
11. Veeneman, G. H.; van Leeuwen, S. H.; van Boom, J. H. Tetrahedron Lett. 1990, 31,
1331–1334.
12. Representative 1H NMR, and other physical data of compounds 13, 5, 14, 15, 16,
and 2.
vi
2
Compound 13: ½a D20:0
ꢂ
ꢁ94.3 (c 1.00, CHCl3); 1H NMR (300 MHz, CDCl3): d 5.81
(dd, 1H, J3 ;4 ¼ 3:4 Hz, H-30), 5.65 (dd, 1H, J2 ;3 ¼ 3:5 Hz, H-20), 5.12 (s, 1H,
H-10), 4.88 (s, 1H, H-1), 1.37 (d, 3H, J = 6.1 Hz, H-6); HRMS (FAB) calcd for
0
0
0
0
Scheme 3. Construction of tetrasaccharide 2 by assembly of dodecyl thioglyco-
sides. Reagents and conditions: (i) NIS, TfOH, CH2Cl2, MS4 Å, ꢁ20 °C to 0 °C, 30 min,
90%; (ii) NaOMe/MeOH–CH2Cl2, rt, 3 h, 96%; (iii) 6, NIS, TfOH, CH2Cl2, MS4 Å,
ꢁ40 °C, 30 min, 92%; (iv) Ac2O, pyridine; (v) 7, BSP, Tf2O, DTBM, CH2Cl2, MS4 Å,
ꢁ78 °C, 72%; (vi) (a) 80% AcOH in H2O, 50 °C, 24 h; (b) NaOMe/MeOH, rt, 6 h; (c) Pd/
C, MeOH–H2O–AcOH, H2, rt, 24 h, 76% over three steps.
C
37H41O12 [M+H]+: 677.2593; found, 677.2592.
Compound 5: ½a D20:0
ꢂ
ꢁ43.9 (c 1.00, CHCl3); 1H NMR (300 MHz, CDCl3): d 4.90 (s,
1H, H-10), 4.85 (s, 1H, H-1), 1.27 (d, 1H, J = 6.3 Hz, H-6); HRMS (FAB) calcd for
C
23H33O10 [M+H]+: 469.2068; found, 469.2075.
Compound 14: ½a D21:8
ꢂ
+38.6 (c 1.00, CHCl3); 1H NMR (600 MHz, CDCl3): d 8.01–
7.18 (m, 15H, CHarom), 5.59 (s, 1H, PhCH), 5.31 (s, 1H, H-200), 5.28 (s, 1H, H-100),
4.95 (s, 1H, H-10), 4.84 (s, 1H, H-1), 4.62 (d, 1H, J = 11.0 Hz, PhCH2), 4.47 (d, 1H,
J = 11.6 Hz, PhCH2), 4.31–4.28 (m, 1H, H-60a), 4.25–4.18 (m, 1H, H-60b), 4.16–
4.02 (m, 5H, H-2, 3, 20, 30, 40), 3.89–3.85 (m, 1H, H-500), 3.84–3.78 (m, 1H, H-50),
3.69–3.62 (m, 1H, H-5), 3.49–3.44 (m, 1H, H-400), 3.58–3.42 (m, 1H, H-4), 3.36
(s, 3H, OMe), 2.53 (s, 1H, OH), 2.40–2.34 (m, 1H, H-300), 2.04–1.96 (m, 1H, H-300),
1.52 (s, 3H, CH3), 1.35 (d, 3H, J = 6.6 Hz, H-600), 1.33 (s, 3H, CH3), 1.27 (d, 3H,
J = 6.6 Hz, H-6); HRMS (FAB) calcd for C43H53O14 [M+H]+: 793.3430; found,
793.3437.
thiogalactosyl donors using sulfonium triflate per-activation
procedure.14
Finally, global deprotection of 16 was successfully carried out
by a three-step procedure that involved the hydrolysis of the acetal
protecting groups by treatment with aqueous AcOH, transesterifi-
cation of the O-benzoyl groups with sodium methoxide in metha-
nol, and catalytic hydrogenolysis over Pd/C to remove the O-benzyl
groups. The unprotected tetrasaccharide12 2 thus obtained was
characterized spectroscopic analyses. Representative 1H and 13C
NMR chemical shift data of the synthetic tetrasaccharide 2 is in
excellent agreement with the reported data4 of the natural poly-
saccharide 1.
In conclusion, total synthesis of a tetrasaccharide repeating unit
of O-antigenic polysaccharide of S. enteritidis was achieved by
assembly of dodecyl thioglycosyl donors. Our finding such as reg-
ioselective and sequential glycosylation 2,3-positions of core man-
nose residue would make it possible to provide easily various
oligosaccharides analogous of 2, which are useful substrates for
biological examinations toward its infection control.
Compound 15: 1H NMR (300 MHz, CDCl3): d 7.97–7.22 (m, 15H, CHarom), 5.63
(s, 1H, PhCH), 5.26 (br d, 1H, H-200), 5.21 (dd, 1H, J2 ;3 ¼ 3:5 Hz, H-20), 5.16 (s,
0
0
1H, H-100), 4.91 (d, 1H, J1 ;2 ¼ 1:2 Hz, H-10), 4.85 (s, 1H, H-1), 4.62 (d, 1H,
0
0
0
0
J = 11.6 Hz, PhCH2), 4.47 (d, 1H, J = 11.6 Hz, PhCH2), 4.34 (dd, 1H, J3 ;4 ¼ 9:5 Hz,
H-30), 4.27 (dd, 1H, J5 ;6 b ¼ 4:2 Hz, H-60b), 4.18–4.06 (m, 4H, H-2, 3, 40, 60a),
3.87–3.76 (m, 2H, H-50, 500), 3.70–3.61 (m, 1H, H-5), 3.55–3.33 (m, 2H, H-4, 400),
3.35 (s, 3H, OMe), 2.33–2.26 (m, 1H, H-300), 2.18 (s, 3H, acetyl), 2.08–1.92 (m,
1H, H-300), 1.51 (s, 3H, CH3), 1.33 (s, 3H, CH3), 1.32 (d, 3H, J = 6.3 Hz, H-600), 1.31
(d, 3H, J = 6.3 Hz, H-6); 13C NMR (150.9 MHz, CDCl3): d 170.3, 165.4, 138.2,
137.3, 133.2, 130.1, 129.8, 128.7, 128.4, 128.4, 128.1, 127.9, 127.7, 126.0, 109.2,
0
0
101.3, 99.0 (JC1 ;H1 ¼ 175:9 Hz, C-10), 97.8 (JC1,H1 = 170.0 Hz, C-1), 97.7
0
0
(JC1
¼ 172:9 Hz, C-100), 81.2, 78.7, 76.7, 76.0, 74.9, 72.1, 71.4, 71.0, 70.8,
00 ;H100
68.8, 68.7, 64.6, 63.8, 54.9, 29.3, 28.1, 26.4, 21.0, 18.2, 17.4.
Compound 16: ½a D21:0
ꢂ
+34.1 (c 1.00, CHCl3); 1H NMR (600 MHz, CDCl3): d 5.62
(d, 1H, J1
¼ 3:8 Hz, H-1000), 5.29 (s, 1H, H-100), 4.93 (s, 1H, H-10), 4.83 (s, 1H,
000 ;2000
H-1), 4.39 (dd, 1H, J3 ;4 ¼ 10:4 Hz, H-30), 4.17 (dd, 1H, J2 ;3 ¼ 5:0 Hz, H-20),
0
0
0
0
2.29–2.23 (m, 1H, H-300), 1.90–1.84 (m, 1H, H-300), 1.32 (d, 3H, J = 6.1 Hz, H-600),
1.18 (d, 3H, J = 6.1 Hz, H-6); HRMS (FAB) calcd for
C
77H87O19 [M+H]+:
1315.5836; found, 1315.5829.
Compound 2: 1H NMR (300 MHz, D2O, 333 K): (selected data) d 5.25 (d, 1H,
J1 ;2 ¼ 1:5 Hz, H-10), 5.21 (d, 1H, J1
¼ 3:7 Hz, H-1000), 4.90 (br d, 1H, H-1),4.70
0
0
000 ;2000
00 ;200
(d, 1H, J1
¼ 1:4 Hz, H-100), 4.18–3.52 (m, 29H), 3.40 (s, 3H, OMe), 2.08–2.01
(m, 1H, H-300), 1.90–1.78 (m, 1H, H-300), 1.34 (d, 3H, J5,6 = 6.4 Hz, H-6), 1.28 (d,
Acknowledgment
3H, J5 ;6 ¼ 6:2 Hz, H-60); 13C NMR (75 MHz, D2O): d 104.1, 104.0, 103.5, 102.5,
84.4, 81.8, 80.1, 76.3, 74.3, 73.2, 73.1, 72.1, 72.1, 71.5, 70.2, 70.2, 70.0, 69.1,
64.0, 63.3, 57.6, 19.9, 19.6; HRMS (ESI) calcd for C25H44O18 [MꢁH+]ꢁ: 631.2455;
found, 631.2452.
0
0
We would like to thank Ms. A. Meada (Center for Instrumental
Analysis, Hokkaido University) for elemental analyses.

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S.-H. Son et al. / Tetrahedron Letters 49 (2008) 5289–5292
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