Synthesis of fluorine-containing core-2 tetrasaccharides

Article abstract of DOI:10.1055/s-2003-40342

Synthesis of core-2 branched tetrasaccharides 1-3, in which a fluorine atom was substituted at the 3 or 4-position of galactose residues is described. Glycosyl imidates 13, and 19 were prepared and used to provide novel glycosyl disaccharide donors 15 and

Full text of DOI:10.1055/s-2003-40342

LETTER
1291
Synthesis of Fluorine-Containing Core-2 Tetrasaccharides
Synthesis
iof Fluo
e
rine-Containing
C
X
ore-2
T
etrasaccha
i
rides a, James L. Alderfer, Conrad F. Piskorz, Robert D. Locke, Khushi L. Matta*
Molecular and Cellular Biophysics, Roswell Park Cancer Institute, Elm and Carlton Streets, Buffalo, NY 14263, USA
Fax +1(716)8453458; E-mail: khushi.matta@roswellpark.org
Received 31 March 2003
This manuscript presented in memory of Professor Ray Lemieux.
these glycotransferases. Moreover, these modified ana-
logs when per, or partially acetylated may have the ability
to prime core-2 oligosaccharide glycan synthesis and thus
inhibit biosynthesis of natural ligands for L and P selec-
Abstract: Synthesis of core-2 branched tetrasaccharides 1–3, in
which a fluorine atom was substituted at the 3 or 4-position of ga-
lactose residues is described. Glycosyl imidates 13, and 19 were
prepared and used to provide novel glycosyl disaccharide donors 15
and 21, respectively. Coupling of acceptor 7 with glycosyl bromide tins.5 Herein, we have described effective syntheses of
6 provides a disaccharide that was further converted into disaccha-
fluorinated core-2 branched oligosaccharides 1–3. Core-2
ride acceptor 8. The coupling of acceptor 14 with donor 13, and ac-
tetrasaccharides 1–3 and the related building blocks are
ceptor 20 with donor 19 provided disaccharides that were converted
shown in Scheme 1. There are two galactose residues in
to disaccharide donors 15 and 21, respectively. Regioselective gly-
each core-2 branched tetrasaccharide. Synthesis of these
cosylation of acceptors 8, and 16 with donors 9, 15, and 21 provided
tetrasaccharides was thereby divided into synthetic targets
1, of which the fluorine was located at the 3-position of
down-chain galactose residue and targets 2, 3 of which
fluorine was located at 3, or 4-position of up-chain galac-
tose residue. In order to synthesize tetrasaccharide 1, the
fluorinated bromide donor 6 was necessary. The fluorinat-
ed compound 4 was prepared according to a known meth-
od in good yield.6 Compound 4 was acetolysized with a
catalytic amount of concentrated sulfuric acid in acetic an-
hydride in an ice-bath for 2 h. The bromide donor 6 was
obtained via treatment of compound 5 with HBr–HOAc
(33%) at room temperature for 2 h (Scheme 2).7 The dis-
accharide acceptor 8 was then prepared in two steps in a
poor yield (28%) using a published methodology.8 The re-
gioselective glycosylation of acceptor 8 with disaccharide
donor 9 at low temperature provided tetrasaccharide 10 as
the only glycosylated product in a good yield (65%). The
stereochemistry and linkage of trisaccharide 10 was estab-
lished with a combination of two-dimensional NMR ex-
periments including 2D DQF-COSY, TOCSY, and
ROESY. Target 1 was obtained by systematic deprotec-
tion of compound 10 in three steps: 1) removal of Phth
group from C-2 of sugar residue; 2) complete acetylation;
3) removal of acetyl group in good yield (45%). Synthesis
of compound 2 is outlined in Scheme 3. Fluorine-contain-
ing disaccharide donor 15 was essential to produce com-
pound 2. Construction of the b(1→4) linkage of
disaccharide donor 15 was due to regioselective coupling
at the 4-hydroxyl of acceptor 14 with imidate donor 13.
An attempt to couple acceptor 14 with imidate donor 13,
at –45 °C to –40 °C, resulted in a mixture of the b(1→4)
and b(1→3) linked disaccharides, which made separation
by column chromatography difficult. However, when the
reaction temperature was lowered to –65 °C to –70 °C,
only the b(1→4) linked disaccharide was obtained as a
glycosylation product. This product was then treated with
dry pyridine and anhydrous acetic anhydride to provide
disaccharide donor 15 in two steps, and in good yield
(63%). Regioselective glycosylation of the 6-hydroxyl
group of disaccharide acceptor 16 with donor 15 at low
tetrasaccharides 10, 17, and 22 respectively, which were systemati-
cally deprotected to targets 1–3.
Key words: tetrasaccharides, galactose residues, core-2 O-linked
glycoproteins
The natural mucin ligands, and various tumor-associated
core-2 O-linked glycoproteins are known to contain the
Galb1→4GlcNAcb1→6Galb1→3GalNHAca-1 structure
(Scheme 1).1 These core-2 branched oligosaccharides are
important in many functional biological processes.2 How-
ever, there is little known about the detailed physiologic
roles of these sialylated and sulfated oligosaccharides as-
sociated with cancers and inflammations. Tremendous ef-
forts have been devoted to understanding the structure and
function of O-glycans in binding with L, P, and E selec-
tins, which were demonstrated by developing a variety of
synthetic methodologies including glycosylation forma-
tion, and protection-deprotection strategies by various re-
search groups.3 We have become interested in fluorinated
core-2 branched oligosaccharide analogues due to: (a) the
small size of fluorine is comparable to that of a hydroxyl
group;4 (b) the fluorine atom in a C-F bond is believed to
be capable of forming hydrogen bonds with hydrogen
bond donors but not hydrogen bond acceptors; (c) substi-
tution of 3-or 4-hydroxyl group from galactose residue
can
further
terminate
chain
elongation
of
Galb1→4GlcNAcb1→6Galb1→3GalNHAca-1 struc-
ture, which is believed to be a possible glycosylation site
for a(2,3)-sialyltransferase, 3-O-sulfotransferase and
a(1,4)-GlcNAc transferase. Blocking the C-3, or C-4 po-
sition of the pertinent galactose residue will provide an
opportunity to investigate and understand the biosynthetic
mechanism of core-2 branched oligosaccharides, and may
provide useful information in the search of inhibitors for
Synlett 2003, No. 9, Print: 11 07 2003.
Art Id.1437-2096,E;2003,0,09,1291,1294,ftx,en;S04503ST.pdf.
© Georg Thieme Verlag Stuttgart · New York

1292
J. Xia et al.
LETTER
HO
HO
HO
HO
GlcNAcβ(1→6)GalNAc Linkage
HO
HO
F
O HO
O
O HO
O
O HO
O
HO
F
O
O
O
OH
OH
OH
HO
HO
O
O
HO
O
NHAc
HO
NHAc
HO
NHAc
HO
O
O
O
OBn
NHAc
OBn
NHAc
OBn
NHAc
O
O
O
O
O
O
HO
HO
HO
HO
HO
HO
OH
OH
OH
F
OH
OH
2
3
1
O
Ph
AcO
AcO
AcO
AcO
AcO
AcO
O
O
O
O
O
O
F
OAc
OMe
O
SPh
OBn
HO
OAc
OAc
AcO
OAc
AcO
F
NPhth
AcO
NHAc
4
11
9
7
HO
HO
PivO
HO
NAPO
HO
O
O
OAc
O
SPh
OBn
NHAc
O
O
SPh
HO
14
NPhth
HO
AcO
NPhth
OAc
OAc
20
16
Scheme 1 Fluorine containing core 2 oligosaccharides 1–3 and related building blocks
temperature provided compound 17 in a high yield (76%). shown in Scheme 4. Fluorinated imidate donor 199 was
The structure of tetrasaccharide 17 was confirmed by a prepared in low yield (32%). Regioselective glycosylation
variety of 2D NMR experiments. Target compound 2 was of the 4-hydroxyl group of acceptor 20 with imidate donor
obtained by a similar procedure used for the deprotection 19 was achieved by a glycosylation procedure established
of compound 10 to compound 1 in three steps in a reason- in our laboratory. This method provided the b(1→4) link-
able yield (39%). Synthesis of target oligosaccharide 3 is age for disaccharide 21. Coupling of disaccharide accep-
HO
O
Ph
HO
O
OAc
OAc
OAc
O
OMe
OAc
OAc
OAc
Br
O
OAc
O
O
O
(a)
(c)-(d)
OBn
(b)
AcO
O
OBn
O
F
+
NHAc
AcO
OAc
AcO
HO
F
F
F
NHAc
OAc
AcO
6
5
7
4
8
AcO
AcO
AcO
HO
HO
HO
O
O
O
O
+
O
O
O
O
D
C
AcO
(f)-(g)
OAc
HO
OH
NPhth
HO
HO
AcO
AcO
AcO
O
NHAc
HO
AcO
O
O
O
O
(e)
SPh
A
OAc
OH
OBn
OBn
O
O
O
O
AcO
NHAc
NPhth
AcO
OAc
NHAc
B
AcO
OAc
HO
OH
F
F
1
10
9
Scheme 2 a) Ac2O–H2SO4, 0–5 °C, 2 h, 58%, b) HBr–HOAc, r.t., 65%, c) Hg(CN)2/CH3NO2–benzene, 65 °C, 12 h, d) 60% HOAc, 65 °C to
70 °C, 1.5 h, 28% in two steps, e) NIS–TfOH/CH2Cl2, –45 °C to –40 °C, 65%, f) i) NH2-NH2·H2O–CH3OH (1:5), 90 °C, 6 h, ii) Ac2O–pyridine
(1:1), DMAP, r.t., 12 h, g) 1 M CH3ONa–CH3OH/CH3OH–H2O, r.t., 12 h, 45% in three steps.
Synlett 2003, No. 9, 1291–1294 ISSN 1234-567-89 © Thieme Stuttgart · New York

LETTER
Synthesis of Fluorine-Containing Core-2 Tetrasaccharides
1293
OAc
OAc
OAc
OPiv
AcO
F
PivO
O
O
OAc
OAc
O
OH
O
O
CCl3
SPh
O
(a)
(b)
(c)-(d)
O
O
+
SPh
NH
OAc
OAc
F
HO
F
F
NPhth
OAc
AcO
OAc
OAc
NPhth
OH
AcO
OAc
11
12
13
14
15
AcO
F
PivO
HO
F
HO
O
+
O
O
O
HO
HO
O
O
D
C
O
O
O
AcO
(f)-(g)
OAc
HO
OH
HO
(e)
AcO
NHAc
HO
NPhth
HO
OAc
OBn
NHAc
O
O
O
O
A
OAc
OH
OBn
NHAc
OBn
NHAc
AcO
O
O
OAc
O
O
OAc
B
AcO
HO
OAc
OH
16
OAc
OH
2
17
Scheme 3 a) NH2NH2·HOAc/DMF, 50 °C, 2 h, b) CCl3CN/DBU, CH2Cl2, 0 °C to 25 °C, 2 h, 80% in two steps, c) TMSOTf/CH2Cl2, 4 Å MS,
–65 °C to –70 °C, 2 h, 41%, d) Ac2O–pyridine (1:1), DMAP, r.t., 12 h, 63%, e) NIS–TfOH/CH2Cl2, 4 Å MS, –65 °C to –60 °C, 2 h, 76%,
f) Ac2O–pyridine (1:1), DMAP, r.t.,12 h, 45%, g) (i) NH2-NH2·H2O–CH3OH (1:5), 90 °C, 6 h, (ii) Ac2O–pyridine (1:1), DMAP, r.t, 12 h, (iii)
1 M CH3ONa–CH3OH/CH3OH–H2O, r.t., 12 h, 39% in three steps.
tor 16 with disaccharide donor 21 afforded the desired vergent method. Biochemical investigation of fluorinated
b(1→6) linkage of tetrasaccharide 22 in a reasonable carbohydrates-enzyme interactions and fluorinated carbo-
yield (52%). Target oligosaccharide 3 was obtained by hydrate-selectin interactions are underway.
complete deprotection of compound 22 in four steps in a
reasonable yield.
Acknowledgment
In summary, fluorine core-2 oligosaccharide analogues
This work was supported by Grant Nos. CA 35329, CA63218 and,
1–310 having the fluorine atom located at different posi-
in part by P30CA16056, all awarded by National Cancer Institute.
tions on the galactose residue were synthesized by a con-
OAc
OAc
OAc
AcO
AcO
NAPO
O
NAPO
CCl3
OAc
OAc
O
OH
(a)
O
(c)-(d)
O
O
O
(b)
O
SPh
O
SPh
+
NH
OAc
AcO
AcO
OAc
HO
AcO
NPhth
AcO
F
F
NPhth
F
F
OAc
HO
20
5
18
19
21
+
HO
HO
HO
O
HO
O
AcO
AcO
NAPO
O
O
HO
O
O
D
C
O
O
O
O
OAc
F
OH
HO
NHAc
HO
OBn
(e)
(f)-(h)
O
F
OAc
NPhth
HO
NHAc
AcO
O
A
OH
AcO
O
OAc
OBn
O
O
OAc
OAc
NHAc
OBn
NHAc
B
O
O
16
HO
OH
OH
AcO
OAc
OAc
3
22
Scheme 4 a) NH2NH2·HOAc/DMF, 50 °C, 2 h, b) CCl3CN/DBU, CH2Cl2, 0°C to 25 °C, 32% in two steps, c) TMSOTf, CH2Cl2, 4 Å MS,
–65 °C, 2 h, 43%, d) Ac2O–pyridine (1:1), DMAP, r.t., 12 h, 76%,e) NIS–TfOH/CH2Cl2, 4 Å MS, –65 °C to –60 °C, 2 h, 52%, f) Ac2O–pyridine
(1:1), DMAP, r.t.,12 h, 45%, g) (i) NH2-NH2·H2O–CH3OH (1:5), 90 °C, 6 h, (ii) Ac2O–pyridine (1:1), DMAP, r.t., 12 h, (h) 1 M CH3ONa–
CH3OH/CH3OH–H2O, r.t., 12 h, 45% in three steps.
Synlett 2003, No. 9, 1291–1294 ISSN 1234-567-89 © Thieme Stuttgart · New York

1294
J. Xia et al.
LETTER
8.6 Hz, HC-1), 4.48 (d, 1 H, J1,2 = 7.6 Hz, HD-1), 4.35 (dd, 1
H, HA-2), 4.23 (d, 1 H, J = 2.8 Hz, HA-4), 4.20 (dd, 1 H, HB-
4), 4.15 (dd, 1 H, HA-5), 4.07 (dd, 1 H, HA-6b), 4.04 (dd, 1
H, HA-3), 4.01 (dd, 1 H), 3.94 (d, 1 H, J = 2.7 Hz, HD-4),
3.90–3.50 (m, 15 H, HB-2, HD-2), 2.31 (s, 3 H, Ac), 2.21 (s,
3 H, Ac); 13C NMR (D2O, 100.6 MHz): d = 175.76 (C=O),
175.52 (C=O), 138.24, 130.07, 129.96, 129.71, 105.12 (d,
References
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3JC-F = 11.3 Hz), 104.21, 102.76, 97.62, 94.10 (d, 1JC-F
=
183.4 Hz), 79.90, 78.48, 76.65, 76.06, 75.02, 74.96, 73.84,
73.80, 72.27, 70.91, 70.86, 70.77, 70.59 (d, 2JC-F = 18.6 Hz),
69.97 (d, 2JC-F = 20.4 Hz), 62.31, 61.94, 61.89, 61.40, 56.39,
49.83, 23.58 (NAc), 23.25 (NAc). ESIMS (negative mode)
Calcd for C35H53O20N2F (m/z)[M = 840]. Found: 839.5
[M]–, 875.5 [M + Cl]–. Compound 2: 1 H NMR (D2O, DQF-
COSY, TOCSY and ROESY, 400 MHz): d = 7.50–7.00 (m,
5 H, ArH), 5.00 (d, 1 H, J1,2 = 3.2 Hz, HA-1), 4.87 (dd, 1 H,
J = 2.8 Hz, 2JH-F = 52.0 Hz, HD-4), 4.73 (d, 1 H, Jgem = 12.3
Hz, PhCHAO, ABq), 4.59 (d, 1 H, J1,2 = 7.6 Hz, HD-1), 4.58
(d, 1 H, J1,2 = 8.0 Hz, HC-1), 4.53 (d, 1 H, Jgem = 12.4 Hz,
PhCHBO, ABq), 4.46 (d, 1 H, J1,2 = 7.8 Hz, HB-1), 4.34 (dd,
1 H, HA-2), 4.25 (d, 1 H, J = 2.8 Hz, HA-4), 4.16 (dd, 1 H,
HA-5), 4.10 (dd, 1 H, HA-6b), 4.08 (dd, 1 H, HA-3), 4.02 (dd,
1 H), 3.92–3.80 (m, 6 H, HC-4), 3.81 (dd, 1 H, HD-3), 3.80–
3.50 (m, 10 H, HD-2, HA-6a, HC-3, HD-2, HC-2), 2.31 (s, 3 H,
Ac), 2.29 (s, 3 H, Ac); 13C NMR (D2O, 100.6 MHz): d =
175.80 (C=O), 175.65 (C=O), 129.60, 129.40, 129.30,
105.90, 104.10, 102.85, 97.85, 79.80 (d, 1JC-F = 178.5 Hz),
76.10 (d, 2JC-F = 50.6 Hz), 73.90, 72.15 (d, 2JC-F = 50.9 Hz),
71.50, 71.23, 70.25, 70.00, 62.25, 61.23, 56.20, 49.95, 23.50
(NAc), 23.20 (NAc). 19F NMR (CDCl3, 376.4 MHz): d =
–172.95 ppm. ESIMS (negative mode) Calcd for
(f) Lergenmuler, M.; Ito, Y.; Ogawa, T. Tetrahedron 1998,
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Chandrasekaran, E. V.; Matta, K. L. Chem. Commun. 1997,
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Matta, K. L. Chem.–Eur. J. 2000, 6, 3442. (k) Xia, J.;
Alderfer, J. L.; Piskorz, C. F.; Matta, K. L. Chem.–Eur. J.
2001, 7, 356.
C35H53O20N2F (m/z) [M = 840]. Found: 839.6 [M]–.
(4) (a) O’Hagan, D.; Rzepa, H. S. Chem. Commun. 1997, 645.
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(10) Physical data: Compound 1: Rf = 0.5 (i-C3H9OH–HOAc–
H2O, 3:1:1); 1H NMR (D2O, DQF-COSY and ROESY, 400
MHz): d = 7.50–7.20 (m, 5 H, ArH), 4.99 (d, 1 H, J1,2 = 3.4
Hz, HA-1), 4.72 (d, 1 H, Jgem = 12.6 Hz, PhCHAO, ABq),
4.61 (dq, 1 H, HB-3), 4.58 (d, 1 H, J1,2 = 7.6 Hz, HB-1), 4.53
Compound 3: Rf = 0.5 (i-C3H9OH–HOAc–H2O, 3:1:1). 1
H
NMR (D2O, DQF-COSY and ROESY, 400 MHz): d = 7.50–
7.20 (m, 5 H, ArH), 4.99 (d, 1 H, J1,2 = 3.4 Hz, HA-1), 4.73
(d, 1 H, Jgem = 12.6 Hz, PhCHAO, ABq), 4.61 (dq, 1 H, J =
2.8 Hz, J = 9.6 Hz, 2JH-F = 68.0 Hz, HD-3), 4.58 (d, 1 H,
J
1,2 = 7.6 Hz, HD-1), 4.55 (d, 1 H, J1,2 = 8.6 Hz, HC-1), 4.52
(d, 1 H, Jgem = 12.5 Hz, PhCHBO), 4.46 (d, 1 H, J1,2 = 7.6 Hz,
HB-1), 4.33 (dd, 1 H, HA-2), 4.24 (d, 1 H, J = 2.8 Hz, HA-4),
4.03 (d, 1 H, J = 3.2 Hz, HD-4), 4.16 (m, 1 H, HA-5), 4.07 (dd,
1 H, HA-6b), 4.04 (dd, 1 H, HA-3), 4.00 (dd, 1 H, HC-3), 3.91
(d, 1 H, J = 2.8 Hz, HB-4), 3.91–3.72 (m, 9 H), 3.64 (m, 2 H,
HC-5, HB-3), 3.52 (dd, 1 H, HB-2), 2.31 (s, 3 H, Ac), 2.28 (s,
3 H, Ac); 13C NMR (D2O, 100.6 MHz): d = 175.77 (C=O),
175.54 (C=O), 138.22, 130.07, 129.95, 129.71, 105.89,
103.41 (d, 3JC-F = 12.7 Hz), 102.76, 97.58, 94.08 (d, 1JC-F
=
183.9 Hz), 79.81, 78.26, 76.15 (d, 2JC-F = 17.8Hz), 75.32 (d,
3JC-F = 6.8 Hz), 73.79, 73.75, 71.93, 71.05, 70.99, 70.86,
70.73, 70.13, 69.89, 68.15, 67.97, 62.29, 61.99, 61.97,
61.32, 56.43, 49.87, 23.57 (NAc), 23.26 (NAc). ESIMS
(negative mode) Calcd for C35H53O20N2F (m/z) [M = 840].
Found: 839.5 [M]-, 875.5 [M + Cl]–.
(d, 1 H, Jgem = 12.4 Hz, PhCHBO, ABq), 4.49 (d, 1 H, J1,2
=
Synlett 2003, No. 9, 1291–1294 ISSN 1234-567-89 © Thieme Stuttgart · New York