Synthetic construction of a Lex determinant via gabriel amine synthesis and the glycopolymer involving highly clustered Lex residues

Article abstract of DOI:10.1016/j.tetlet.2009.03.099

Synthetic construction of a Le^x determinant was accomplished via slightly modified Gabriel amine synthesis from three building blocks. Further transformations followed by polymerization of the Le^x derivative gave a glycopolymer havin

Full text of DOI:10.1016/j.tetlet.2009.03.099

Tetrahedron Letters 50 (2009) 2593–2596
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Tetrahedron Letters
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Synthetic construction of a Lex determinant via gabriel amine synthesis
and the glycopolymer involving highly clustered Lex residues
*
Koji Matsuoka , Tatsuya Kohzu, Takashi Hakumura, Tetsuo Koyama, Ken Hatano, Daiyo Terunuma
Area for Molecular Function, Division of Material Science, Graduate School of Science and Engineering, Saitama University, Sakura, Saitama 338-8570, Japan
a r t i c l e i n f o
a b s t r a c t
Synthetic construction of a Lex determinant was accomplished via slightly modified Gabriel amine syn-
thesis from three building blocks. Further transformations followed by polymerization of the Lex deriva-
tive gave a glycopolymer having trisaccharidic units as pendant-type epitopes.
Ó 2009 Elsevier Ltd. All rights reserved.
Article history:
Received 24 February 2009
Accepted 13 March 2009
Available online 19 March 2009
Keywords:
Lewis x
Glycosides
Gabriel synthesis
Glycopolymers
Glycoclusters
Lewis x determinant [Lex; Galb1 ? 4(Fuc
a
1 ? 3)GlcNAc] is
derived from 1,6-anhydro-b-Man via Gabriel amine synthesis8 in
order to shorten the typical synthetic route. Scheme 1 shows the
preparation of each building block. A known b-acetogalactose 5
was allowed to react with lauryl mercaptan in the presence of
BF3–OEt2 to furnish b-lauryl glycoside 29 as building block A in
94.8% yield. Since building block B 3 had to be a fully benzylated
derivative in order to avoid neighboring participation by ester
function in O-glycoside formation, protective groups of the fucosyl
derivative were converted from acetate into benzylate. Thus, a
known as an extremely valuable core structure of glycoconjugates
such as glycoproteins and glycolipids.1 Synthetic assembly of the
trisaccharide has been a very attractive challenge for synthetic
chemists,2 and the cluster-type trisaccharide is also very attractive
from the point of view of biochemical as well as biomedical appli-
cations.3 In our previous study,4 synthesis of the Lex trisaccharidic
moiety and its polymer from a 1,6-anhydro-b-lactose as a key
starting material was accomplished. In spite of the successful syn-
thesis of a glycopolymer having trisaccharide moieties as pendant-
type epitopes, density of the sugar moiety was low. Since the gly-
comonomer had an alkenyl moiety as polymerizable aglycon, poly-
merizable activity was moderate. Consequently a practical and
versatile synthetic route for construction of a Lex derivative as a
glycomonomer having highly polymerizable potential is needed.
In this Letter, we describe efficient preparation of trisaccharidic
glycomonomer 1 via Gabriel amine synthesis5 from three building
known anomeric mixture 6 having an a:b ratio of 14:1 was treated
with 4 M equiv of lauryl mercaptan by means of mediation of
1.5 M equiv of BF3–OEt2 to afford thioglycoside 79 in 86.9% yield
after chromatographic purification, which showed an anomeric
mixture having
a
:b ratio of 20:1 according to the results of 1H
NMR. The acetate 7 underwent transesterification to provide corre-
sponding alcohol 8, which was further manipulated by Williamson
ether synthesis to give benzyl ether 3 as building block B in 81.1%
yield (two steps). For the preparation of building block C, Gabriel
amine synthesis was preformed on a known alcohol 9.6 Thus 9
was converted into triflate 10 as an unstable intermediate, which
was immediately treated with potassium phthalimide to provide
phthaloyl derivative 11 as crystals in 84.7% yield (two steps),
blocks and the chemical conversion into
glycopolymer.
a highly clustered
Prior to construction of synthetic route for a Lex determinant,
1,6-anhydro-b-mannnose6 was selected as a key building block
for GlcNAc residue as shown in Figure 1. Our synthetic plan, there-
28
fore, was convergent synthesis of the Lex structure from
D
-galact-
½aꢀD +34.7 (c 1.00, CHCl3), mp 176.5–177.2 °C, 1H NMR (CDCl3) d
ose (Gal),
L-fucose (Fuc), and
D-mannose (Man) as key starting
5.47 (s, 1 H, H-1), 4.73 (d, 1 H, J3,4 = 7.6 Hz, H-4), 4.30 (dd, 1 H,
J2,3 = 9.6 Hz, H-3), 4.15 (d, 1 H, H-2), and 2.16 (s, 3 H, Ac). The SN2
reaction at C-2 by the anion from the phthalimide as the nucleophile
involved Walden’s inversion and gave a corresponding glucosaminyl
materials. Building blocks A 2 and B 3 were derived from Gal and
Fuc, respectively, by means of Lewis acid-mediated glycosidation
with 1-dodecanethiol (lauryl mercaptan).7 Building block C 4 was
* Corresponding author. Tel./fax: +81 48 858 3099.
E-mail address: koji@fms.saitama-u.ac.jp (K. Matsuoka).
All new compounds with the specific rotation data gave satisfactory results of
elemental analyses.
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.03.099

2594
K. Matsuoka et al. / Tetrahedron Letters 50 (2009) 2593–2596
HO OH
O
OH
O
H
N
O
O
HO
O
NHAc
OH
O
O
OH
Me
OH
OH
1
O
OBn
O
AcO OAc
O
SLau
OBn
O
Me
O
HO
N
O
SLau
AcO
OBn
OBn
OAc
2
3
4
Building block A
Building block B
Building block C
HO OH
O
OH
OH
OH
O
OH
Me
OH
OH
HO
O
HO
HO
OH
OH
OH
D-Galactose
L-Fucose
D-Mannose
Figure 1. Synthetic plan for construction of Lex derivative.
Building block A
AcO OAc
O
AcO OAc
O
i)
OAc
SLau
AcO
AcO
OAc
OAc
5
2
Building block B
OAc
OAc
SLau
OBn
SLau
OH
SLau
OAc
O
OH
O
O
Me
Me
Me
O
iii)
Me
ii)
i)
OBn
OAc
OAc
OH
OBn
OAc
OAc
6
7
8
3
Building block C
O
O
OBn
OBn
O
O
O
O
OBn
O
OBn
O
vi)
v)
iv)
OTf
O
O
OH
AcO
HO
N
O
N
O
AcO
AcO
4
9
10
11
Scheme 1. Reagents and conditions: (i) BF3ꢂOEt2, CH3(CH2)11SH, ClCH2CH2Cl, 0 °C ? rt, 3.5–4 h, 94.8% for 2, 86.9% for 7, (ii) NaOMe, MeOH, rt, 4 h, quant., (iii) NaH, BnBr, DMF,
0 °C ? rt, 5 h, 81.1%, (iv) Tf2O, CH2Cl2–pyridine, 0 °C, 1 h, (v) potassium phthalimide, DMF, 45 °C, 10 h, 84.7% (two steps), (vi) K2CO3, DMF–MeOH, 0 °C, 3 h, then, toluene,
reflux, 75.8%.
configuration. Transesterification10 of acetate 11 gave alcohol 4
accompanied by a phthalimide ring-opened byproduct, which was
refluxed in toluene in order to facilitate recyclization of the byprod-
in Scheme 2. Condensation of galactosyl donor 2 and glucosaminyl
acceptor 4 was carried out in the presence of appropriate amounts
of NIS and TMSOTf11 in CH2Cl2 at ꢁ20 °C to give lactosaminyl
disaccharide 12 involving newly formed b-glycosidic linkage in
83.8% yield, in which the benzyl moiety at C-3 was immediately
deprotected by means of hydrogenolysis to furnish alcohol 13 as
25
uct to afford building block C in 75.8% yield, ½aꢀD +59.6 (c 1.01,
CHCl3), mp 196.5–197.3 °C, 1H NMR (CDCl3)
d 5.52 (d, 1 H,
J4,OH = 11.8 Hz, OH-4), 5.33 (s, 1 H, H-1), 4.46 (s, 1 H, H-2), 3.77 (s,
1 H, H-4), 3.76 (s, 1 H, H-3).
Since three building blocks were successfully constructed, our
attention was turned to condensation of the building blocks. A
schematic image of the assembly of these building blocks is shown
crystals in 85.8% yield, ½a D26
ꢁ16.3 (c 1.00, CHCl3), mp 302.4–
ꢀ
303.9 °C, 1H NMR (CDCl3) d 5.63 (s, 1 H, H-1), 4.62 (d, 1 H,
J1 ,2 = 8.0 Hz, H-10), 3.78 (d, 1 H, J3,OH = 2.8 Hz, OH-3), 13C NMR
(CDCl3) d 102.18 (C-1), 101.93 (C-10).
-Stereoselective glycosida-
0
0
a

K. Matsuoka et al. / Tetrahedron Letters 50 (2009) 2593–2596
2595
O
O
O
O
O
O
OBn
OH
AcO OAc
O
O
O
iii)
3
AcO OAc
O
AcO OAc
O
O
ii)
i)
N
O
AcO
2
4
O
O
N
N
O
O
O
OAc
AcO
AcO
O
Me
O
OAc
OAc
OBn
OBn
12
13
BnO
14
AcO OAc
O
OAc
O
AcO OAc
O
OAc
O
AcO OAc
O
OAc
O
O
OR
O
O
OR
AcO
AcO
O
O
AcO
OAc
ix)
v)
O
O
iv)
N
NHAc
OAc
OAc
O
N
OAc
O
O
O
O
Me
Me
O
OAc
OAc
Me
OBn
OAc
OAc
OBn
OAc
OAc
OBn
16 : R = OAc
17 : R = H
18 : R = C(=NH)CCl3
19 : R =
N3
15
20 : R =
vi)
vii)
viii)
N3
HO OH
O
OH
O
O
OR
NHAc
HO
O
x)
OH
O
OH
Me
OH
OH
N3
21 : R =
22 : R =
1 : R =
xi)
NH2
H
N
xii)
O
Scheme 2. Reagents and conditions: (i) NIS–TMSOTf, CH2Cl2, MS 4 Å, ꢁ20 °C, 1.5 h, 83.8%, (ii) Pd/C, H2, EtOAc, rt, 5 h, 85.8%, (iii) NIS–TMSOTf, CH2Cl2, MS 4 Å, ꢁ15 °C, 1.5 h,
93.3%, (iv) CF3COOH, Ac2O, 0 °C, 1 h, 93.2%, (v) Pd/C, H2, EtOAc, 45 °C, 4 h, then Ac2O, Pyr, DMAP, 45 °C, 6 h, 99.4% (two steps), (vi) N2H4–AcOH, DMF, rt, 1 h, 96.9%, (vii) CCl3CN,
DBU, CH2Cl2, 0 °C, 2 h, 97.8%, (viii) TMSOTf, 5-azidopentanol, CH2Cl2, ꢁ40 °C, 1 h, 70.7%, (ix) n-BuNH2, MeOH, reflux, 2 days, then Ac2O, pyridine, DMAP, rt, 20 h, 83.1% (two
steps), (x) NaOMe, MeOH, rt, overnight, quant., (xi) Pd/C, H2, MeOH, 0 °C ? rt, 4 h, 83.7%, (xii) acryloyl chloride, Et3N, MeOH, 0 °C ? rt, 43.0%.
tion of Fuc for constructing trisaccharide 14 was performed using
fucosyl donor 3 and acceptor 13 by means of same activation sys-
tem as that for thioglycoside 2 to produce amorphous 14 having an
smoothly to afford an acetamide 20 in 83.1% yield, ½a D25
ꢁ54.6 (c
ꢀ
0.19, CHCl3), 1H NMR (CDCl3) d 5.50 (d, 1 H, JNH,2 = 8.4 Hz, NH),
5.43 (d, 1 H, J1 ,2 = 3.9 Hz, H-100), 4.65(d, 1 H, J1,2 = 7.5 Hz, H-1),
00 00
a
-fucosyl linkage in 93.3% yield, ½a D31
ꢀ
ꢁ24.3 (c 1.00, CHCl3), 1H NMR
4.48 (d, 1 H, J1 ,2 = 8.0 Hz, H-10), C NMR (CDCl3) d 100.40 (C-10),
99.99 (C-1), 95.27 (C-100). Quantitative de-O-acetylation by the
Zemplén manner10 for 20 was performed and gave azide alcohol
21, which was further transformed into the corresponding amine
22 followed by acryloylation to give water-soluble glycomonomer
1 as a white powder after lyophilization in 36.0% yield (two steps),
13
0
0
(CDCl3) d 5.60 (s, 1 H, H-1), 4.81 (d, 1 H, J1 ,2 = 3.1 Hz, H-100), 4.65
00 00
(d, 1 H, J1 ,2 = 8.0 Hz, H-10), 1.10 (d, 3 H, J5 ,6 = 6.4 Hz, H-600), 13C
NMR (CDCl3) d 102.31 (C-1), 98.44 (C-10), 97.92 (C-100). In order
to convert 14 into the corresponding glycosyl donor in one step,
1,6-anhydro ring opening of 14 by thiolysis12 in the presence of Le-
wis acid was initially tried, but thioglycoside was not obtained. Be-
cause of acid lability of glycosidic bond between the Fuc moiety
and the GlcN moiety, acetolysis in the presence of trifluoroacetic
acid as a milder acid source4 was applied for the fission of the
1,6-anhydro ring. Thus, 14 gave b-acetate 15 as a sole product in
0
0
00 00
½
a 2D5
ꢀ
ꢁ76.6 (c 0.96, CHCl3), 13C NMR (D2O) d 130.69 (CH@), 127.64
(CH2@), 102.47 (C-10), 101.54 (C-1), 99.27 (C-100).
In our ongoing synthetic study of artificial glycoconjugates,
synthetic assembly of carbohydrate moieties as pendant-type
epitopes using linear polymers has been achieved using bioactive
carbohydrates.16 In order to obtain highly clustered Lex determi-
nants, the potential of radical polymerization as a monomer was
examined by the previously reported method.17 Thus, the homo-
polymerization of 1 proceeded efficiently in aqueous media to
afford white powdery glycopolymer 23 in 83.5% yield after chro-
matographic purification by Sephadex G-50 followed by lyophili-
zation, Mn 51 kDa, Mw 72 kDa, Mw/Mn 1.4, 1H NMR d (D2O) 5.11
(br s, 1 H, H-100), 4.53 (br s, 1 H, H-1), 4.46 (br d, 1 H,
93.2% yield, ½a 2D3
ꢀ
+22.8 (c 1.00, CHCl3), 1H NMR (CDCl3) d 6.27(d,
1 H, J1,2 = 9.2 Hz, H-1), 4.80 (d, 1 H, J1 ,2 = 3.2 Hz, H-100), 4.59 (d,
00 00
13
1 H, J1 ,2 = 8.0 Hz, H-10), C NMR (CDCl3) d 99.72 (C-10), 97.61 (C-
0
0
100), 89.99 (C-1). Benzyl protection in 15 was changed by the usual
hydrogenolysis followed by acetylation to afford known 1613
,
which was further transformed into hemiacetal 17 in the presence
of NH2NH2 in 96.9% yield, 1H NMR (CDCl3) d 5.29 (br dd, 1 H,
J1,2 = 8.8 Hz, J1,OH = 7.2 Hz, H-1). Treatment of hemiacetal 17 with
trichloroacetonitrile gave glycosyl imidate 18 in 97.8% yield, and
the imidate was activated in the presence of TMSOTf,14 coupled
with azidoalcohol15 to provide 19 having an azide function at the
J1 ,2 = 5.6 Hz, H-10). 1H NMR spectra of the glycomonomer 1
and the glycopolymer 23 are shown in Figure 2. Protons at-
tached to C@C in the monomer 1 (a) at around 5–6 ppm com-
pletely vanished after radical polymerizations (b) and
broadening of the peaks was observed. In addition, the weight-
average molecular weight (Mw) of the glycopolymer was esti-
mated according to the results of size exclusion chromatography
with 0.01 M aqueous NaCl solution as the eluent and the degree
0
0
x
-position in the aglycon in 70.7% yield, ½a D24
ꢁ65.1 (c 1.01, CHCl3),
ꢀ
1H NMR (CDCl3) d 5.02 (d, 1 H, J1,2 = 8.4 Hz, H-1), 4.94 (d, 1 H,
J1 ,2 = 4.0 Hz, H-100), 4.53 (d, 1 H, J1 ,2 = 8.4 Hz, H-10), 13C NMR
(CDCl3) d 100.60 (C-10), 98.05 (C-100), 95.05 (C-1). Deprotection of
phthaloyl protection in 19 followed by acetylation proceeded
00 00
0
0

2596
K. Matsuoka et al. / Tetrahedron Letters 50 (2009) 2593–2596
Figure 2. 1H NMR spectra of (a) glycomonomer 1 and (b) homopolymer 23 in D2O.
Toyokuni, T.; Dean, B.; Stroud, M.; Hakomori, S.-I. J. Biol. Chem. 1989, 264, 9476–
9484; (c) Phillips, M. L.; Nudelman, E.; Gaeta, F. C. A.; Perez, M.; Singhal, A. K.;
Hakomori, S.-I.; Paulson, J. C. Science 1990, 250, 1130–11332; (d) Hittelet, A.;
Camby, I.; Nagy, N.; Legendre, H.; Bronckart, Y.; Decaestecker, C.; Kaltner, H.;
Nifant’ev, N. E.; Bovin, N. V.; Pector, J.-C.; Salmon, I.; Gabuis, H.-J.; Kiss, R.;
Yeaton, P. Lab. Invest. 2003, 83, 777–787. and references cited therein.
2. For example, see: (a) Ball, E. G.; O’Neill, R. A.; Schultz, J. E.; Lowe, J. B.; Weston,
B. W.; Nagy, J. O.; Brown, E. G.; Hobbs, C. J.; Bednarski, M. D. J. Am. Chem. Soc.
1992, 114, 5449–5451; (b) Nicolaou, K. C.; Bockovich, N. J.; Carcanague, D. R. J.
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Am. Chem. Soc. 2001, 123, 10705–10714; (d) Nagai, Y.; Ito, N.; Sultana, I.; Sugai,
T. Tetrahedron 2008, 64, 9599–9606 and references cited therein.
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387, 164–166; (b) Thoma, G.; Patton, J. T.; Magnani, J. L.; Ernst, B.; Örlein, R.;
Duthaler, R. O. J. Am. Chem. Soc. 1999, 121, 5919–5929; (c) Buskas, T.; Li, Y.;
Boons, G.-J. Chem. Eur. J. 2005, 11, 5457–5467.
4. Nishimura, S.-I.; Matsuoka, K.; Furuike, T.; Nishi, N.; Tokura, S.; Nagami, K.;
Murayama, S.; Kurita, K. Macromolecules 1994, 27, 157–163.
5. Gibson, M. S.; Bradshaw, R. W. Angew. Chem., Int. Ed. Engl. 1968, 7, 919–930.
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HO OH
O
OH
O
H
N
i)
O
O
HO
O
1
OH
NHAc
O
O
Me
OH
107
OH
OH 23
Scheme 3. Reagents and conditions: (i) APS, TEMED, H2O, 50 °C, 3 h, 83.5%.
of polymerization of the glycopolymer 23 was estimated to be
107 on the basis of Mw (Scheme 3).
In summary, we have successfully described preparation of a Lex
derivative via Gabriel amine synthesis and its chemical modification
to provide a water-soluble glycomonomer. Homopolymerization
using the Lex glycomonomer was performed to give a water-soluble
glycopolymer having Mw 72 KDa in high yield, which displayed
highly clustered glycoepitopes. Biological activity of the glycopoly-
mer was preliminarily examined on the basis of fluorescence mea-
surement using a plant lectin of Lotus tetragonolobus, which binds
9. Son, S.-H.; Tano, C.; Furuike, T.; Sakairi, N. Carbohydr. Res. 2009, 344, 285.
10. Zemplén, G.; Pacsu, E. Ber. 1929, 62, 1613.
to an L
-fucose residue.18 Interestingly negative sugar clustering ef-
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Hatano, K.; Terunuma, D. Tetrahedron Lett. 2004, 45, 9383–9386.
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14. Schmidt, R. R. Angew. Chem., Int. Ed. Engl. 1986, 25, 212–235.
15. This alcohol was prepared from 5-bromopentanol and sodium azide by means
of usual SN2 reaction.
fect was observed since specific carbohydrate-protein interaction
was interfered by highly clustered sugar residues. Further polymer-
ization conditions including copolymerization conditions with acryl
amide are now under investigation, and the biological activities of
the glycopolymers will also be examined. The results of these exper-
iments will be reported in the near future.
16. (a) Miyagawa, A.; Kurosawa, H.; Watanabe, T.; Koyama, T.; Terunuma, D.;
Matsuoka, K. Carbohydr. Polym. 2004, 57, 441–450; (b) Matsuoka, K.; Goshu, Y.;
Takezawa, Y.; Mori, T.; Sakamoto, J.-I.; Yamada, A.; Onaga, T.; Koyama, T.;
Hatano, K.; Snyder, P. W.; Toone, E. J.; Terunuma, D. Carbohydr. Polym. 2007, 69,
326–335; (c) Matsuoka, K.; Takita, C.; Koyama, T.; Miyamoto, D.;
Yingsakmongkon, S.; Hidari, K. I. P. J.; Jampangern, W.; Suzuki, T.; Suzuki, Y.;
Hatano, K.; Terunuma, D. Bioorg. Med. Chem. Lett. 2007, 17, 3826–3830.
17. Nishimura, S.-I.; Matsuoka, K.; Kurita, K. Macromolecules 1990, 23, 4182–4184.
18. (a) Yariv, J.; Kalb, A. J.; Katchalski, E. Nature (London) 1967, 215, 890–891; (b)
Liener, I. E.; Sharon, N.; Goldstein, I. J. The Lectins; Academic Press: London,
1986; and the references cited therein.
Acknowledgment
We thank Professor Y. C. Lee of Department of Biology, the Johns
Hopkins University for valuable discussions and suggestions.
References and notes
1. For example, see: (a) Gooi, H. C.; Feizi, T.; Kapadia, A.; Knowles, B. B.; Solter, D.;
Evans, M. J. Nature (London) 1981, 292, 156–158; (b) Eggens, I.; Fenderson, B.;