Synthesis and Biological Evaluation of O-Methylated Glycolipids Related to PGLs via Direct Stereoselective Glycosidation and Sequential Suzuki–Miyaura Coupling using Boracyclane

Article abstract of DOI:10.1002/chem.201703684

Synthesis of O-methylated glycolipids via direct stereoselective glycosidation whose sugar moieties are related to those in phenolic glycolipids (PGLs) is reported. Treatment of 2-O-methyl-rhamnosyl imidates with I₂ and nBu₄NOTf resulted in their activation under low temperature and provided the α-rhamnosides with excellent α-selectivity. nBu₄NOTf enhanced the electorophilicity of iodine. This methodology improved the efficiency of the synthesis of both PGL-1 and PGL-tb1 sugars. The process involved the formation of 2-O-naphthylmethyl-α-rhamnoside and 2-O-methyl-α-fucoside. Sequential Suzuki–Miyaura coupling using synthetic glycosides, boracyclane, and aryl bromides provided glycolipids related to PGL sugars, and was accomplished with a one-pot process. Finally, we elucidated the immunosuppressive activities of all these synthetic compounds and found that a phenyl 3-O-α-rhamnosyl-2-O-methyl-α-rhamnoside possessing a 6-(2-naphthyl)hexyl group exhibited the strongest inhibitory effect.

Full text of DOI:10.1002/chem.201703684

A Journal of
Accepted Article
Title: Synthesis and biological evaluation of O-methylated glycolipids
related to PGLs via direct stereoselective glycosidation and
sequential Suzuki-Miyaura coupling using boracyclane
Authors: Ko Sato, Zakaria Omahdi, Kensuke Shibata, Koh-hei Sonoda,
Sho Yamasaki, and Hiroshi Tanaka
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To be cited as: Chem. Eur. J. 10.1002/chem.201703684
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Chemistry - A European Journal
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FULL PAPER
Synthesis and biological evaluation of O-methylated glycolipids
related to PGLs via direct stereoselective glycosidation and
sequential Suzuki-Miyaura coupling using boracyclane
[
a]
[b,d,e]
[b,c,e]
[c]
[b,d,e]
Ko Sato, Zakaria Omahdi,
Kensuke Shibata,
Koh-hei Sonoda, Sho Yamasaki,
and
[
a]
Hiroshi Tanaka*
Abstract: Synthesis of O-methylated glycolipids related to the
anti-mycobacteria vaccines. In 2004, Barry and co-workers
found that the PGLs contained in M. tuberculosis inhibited an
innate immune response mediated by Toll-like receptor 2 (TLR2).
sugars in PGLs via direct stereoselective glycosidation is reported.
Treatment of 2-O-methyl-rhamnosyl imidates with I
resulted in their activation under low temperature and provided the
α-rhamnosides with excellent α-selectivity. n-Bu NOTf enhanced the
2 4
and n-Bu NOTf
[
4]
The Prandi and Astarie-Dequeker group recently revealed that
PGL-1 inhibited TNF-α secretion in complement receptor 3-
4
[
5]
electorophilicity of iodine. This methodology improved the efficiency
of the synthesis of both PGL-1 and PGL-tb1 sugars. The process
involved the formation of 2-O-naphthylmethyl-α-rhamnoside and 2-
O-methyl-α-fucoside. Sequential Suzuki-Miyaura coupling using
synthetic glycosides, boracyclane, and aryl bromides provided
glycolipids related to PGL sugars, and was accomplished with a one-
pot process. Finally, we elucidated the immunosuppresive activities
of all these synthetic compounds and found that a phenyl 3-O-α-
mediated (CR3) phagocytosis. The inhibitory effect reduces
inflammatory responses in infected human macrophages, which
[
6,7]
helps their survival in
a
host human body.
Biological
evaluation of chemically synthesized glycosides related to PGLs
has revealed that O-methylated sugars are the structural
determinant that attenuates the inhibitory effect. On the other
hand, the lipids are recognition elements that are essential for
[
9c]
receptor binding.
However, the mechanisms and precise
rhamnosyl-2-O-methyl-α-rhamnoside
possessing
a
6-(2-
structure-activity relationships remain unclear. Therefore, an
effective method for the synthesis of partially O-methylated
glycosides varied at the lipid portion in order to understand the
naphthyl)hexyl group exhibited the strongest inhibitory effect.
structure/activity
relationships
and
develop
effective
immunomodulating compounds.
Introduction
R
Phenolic glycolipids (PGLs) are a family of glycolipids found on
the cell surface of mycobacteria and are composed of the
combination of a partially O-methylated sugar and a diacylated
R
O
O
[
1]
[2]
O
O
HO
lipid — 3,6-di-O-methyl β-glucoside (PGL-1 1) and 2,3,4-tri-
HO
MeO
[
3]
O
OMe
O-methyl-α-fucoside (PGL-tb1 2) are isolated from M. leprae
and M. tuberculosis, respectively (Figure 1). Glycolipids are a
unique motif for mycobacteria and are targets for the epitopes of
MeO
HO
MeO
O
O
O
O
HO
O
O
OH MeO
OH
OMe
OMe
O
1
OMe
MeO
[
a]
b]
K. Sato and Prof Dr H. Tanaka
Department of Chemical Science and Engineering
Tokyo Institute of Technology
R =
O
2
C18H17
O
2-12-1-H101 Ookayama, Meguro Tokyo Japan152-8552
O
E-mail: thiroshi@apc.titech.ac.jp
O. Zakaria, Dr. K. Shibata and Prof Dr. Yamasaki
Division of Molecular Immunology, Medicinal Institute of
Bioregulation
C18H17
[
O
OMe
(
)14
Kyushu University
3-1-1 Maidashi, Higashiku, Fukuoka, Japan 812-8582
[
c]
d]
Prof Dr. K. Sonoda
Figure 1. Structures of PGL-1 (1) and PGL-tb1 (2)
Department of Ophthalmology, Graduate School of Medical
Sciences, Kyushu University, 3-1-1 Maidashi, Higashiku, Fukuoka,
Japan 812-8582
[
Current address: Department of Molecular Immunology, Research
Institute for Microbial Diseases, and Laboratory for Molecular
Immunology, Osaka University
Preparation of these PGL-1 and PGL-tb1-related compounds
[5,8-10]
has been reported by several research groups.
A total
synthesis of PGL-tb1 reported by Minnaard involved
Sonogashira coupling of a 4-iodophenyl glycoside and a terminal
3
-1 Yamadaoka, Suita 565-0871, Japan.Osaka University, Suita,
65-0871, Japan
5
[
8]
[d]
Current address: WPI Immunology Frontier Research Center
iFReC) Osaka University
alkyne for the synthesis of the 4-alkylphenyl glycoside.
(
Formation of 2-O-methyl-α-rhamnosides and fucosides is a key
step in preparation of the sugar part. O-methylation of the C2 ꢀ ꢀ ꢀ
3
-1 Yamadaoka, Suita 565-0871, Japan.Osaka University, Suita,
65-0871, Japan
5
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Chemistry - A European Journal
10.1002/chem.201703684
FULL PAPER
Br
B
HO
i)
ii) Br Ar
8
Br
SPh
6
PGL-1
Ar
4
5
O
Pd(0)
O
BzO
O
MeO
O
OAZMB
HO
O
HO
2
OR1
9
CCl3
NH
R O
2
OR1
R O
O
MeO
AcO
MeO
O
O
4
SPh NAPO
3
OAc
MeO
OMe
OH
B
11
10
4
Br
O
PGL-tb-1
O
HO
NH
HO
2
OR1
R O
8
7
d : R1 = OCH
O
CCl3
O
NAPO
TBSO
a : R2 = OCH
, R
= H
=
, R2 = H
3
2
3
A: Ar =
OMe
1
2
SPh
O
e : R1 = OCH , R
2
=
HO
O
b : R2 = OCH
, R
3
O
3
2
HO
MeO
NAPO
TBSO
HO
OH
OMe
Me
O
OBz
c : R2 = OCH
NH
CCl
13
3
, R
2
=
O
B : Ar =
HO
f : R1 = OCH
, R2
=
O
3
O
3
O
OH
OMe
MeO
O
OMe
HO
O
O
O
MeO
O
OMe
MeO
OH MeO
OMe
MeO
OH
14
OMe
Scheme 1. Strategy for the synthesis of the phenyl glycosides 3 based on the structure of PGL-1 (1) and PGL-tb1 (2).
hydroxy group renders neighboring group participation
unavailable. Anomeric effect, however, can promote α-selective
glycosylation without neighboring group participation, but the
stereoselectivity of the glycosidation derived from an anomeric
effect would be moderate and would frequently depend on the
O-methyl-glycosyl imidates and modification of the glycosides by
sequential Suzuki-Miyaura palladium-catalyzed cross-coupling
[
13]
using
a
boracyclane.
In addition, we also review the
immunosuppressive activity of glycolipids.
[
11]
structures of glycosyl donors and acceptors.
We speculated
that a post-glycosidation modification approach involving α-
selective glycosidation promoted by a 2-O-acyl protecting group
followed by O-methylation after selective removal of the acyl
protecting group could be a highly reliable method for the
synthesis of 2-O-methyl-α-rhamnosides. Obviously, the required
modification step after construction of the sugar chain would
increase the number of synthetic steps, and these would not be
adaptable to the synthesis of 2-O-methyl-α-fucosides
possessing an equatorial-orientated C2 oxygen functional group.
On the other hand, we had previously reported an efficient
synthesis of 2-deoxy-α-glycosides via the glycosidation of 2-
Results and Discussion
Scheme 1 shows our strategy for the synthesis of the phenyl
glycosides 3a-fA and 3a-cB, which are related to PGL-1 and
PGL-tb1 trisaccharides. The phenyl glycosides 3a-fA and 3a-cB
possessing an alkyl chain and terminally functionalized with
either a naphthyl group or a fluorescent dye were designed as
targets in this project. The naphthyl group mimics the lipid
portion of PGLs. The fluorescent-labelled glycosides 3a-cB were
used as chemical probes for the identification and detection of
target proteins. The 4-alkylphenyl glycosides 3a-fA and 3a-cB
were prepared from the corresponding 4-bromophenyl
glycosides 4a-f via sequential Suzuki-Miyaura palladium-
catalyzed cross-coupling using boracyclane 5 and the aryl
4
deoxyglycosyl imidates with IBr and n-Bu NBr under basic
[
12]
conditions.
involve a S
We further speculated that this method could
N
2-like substitution of in situ-generated and unstable
[
13]
β-glycosyl halides with glycosyl acceptors that could provide the
-deoxy-α-glycosides, which would make it adaptable to the
bromides 6A and 6B. Suzuki-Miyaura coupling of glycosides
a-f with boracyclane 5 provided the acyclic borinic acid 7. The
acyclic borinic acid shows low reactivity toward
2
4
direct synthesis of 2-O-methyl-α-glycosides. Herein, we report
the preparation of PGL-1 and PGL-tb1 containing 4-
bromophenyl glycosides by direct α-selective glycosidation of 2-
7
transmetallation to palladium species compared with the cyclic
trialkylborane 5 and undergoes Suzuki-Miyaura cross coupling
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Chemistry - A European Journal
10.1002/chem.201703684
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SPh
at a higher reaction temperature to provide an asymmetrically
[
14]
O
9
functionalized alkyl chain.
Functional group compatibility of
BzO
MeO
Br
Suzuki-Miyaura cross coupling allows the direct use of
protecting group-free carbohydrates 4a-f as building blocks. This
would allow 4-bromopheny glycoside 4c containing PGL-1
glycosides to be prepared from 4-bromophenol (8), 2-O-methyl-
thiorhamnoside 9, 2-O-acyl-rhamnosyl imidate 10, and 3,6-di-O-
methyl-thioglucoside 11. The 2-O-methyl-α-rhamnosyl bond
could be prepared using our previously reported conditions for
the synthesis of 2-deoxyl-α-glycosides. The 4-bromophenyl
glycoside 4f containing the PGL-tb1 glycosides could be
prepared from 4-bromophenol (8), 2-O-methyl-rhamnosyl
imidate 12, rhamnoside 13, and 2,3,4-tri-O-methyl-fucosyl
imidate 14.
OAZMB
Br
NIS, TfOH
O
O
BzO
MeO
HO
MS4A, CH2Cl2
o
-
78 C
OR
8
PPh , H O/THF
60 C, 78 % in 2 steps
15 : R = AZMB
16 : R = H
3
2
o
CCl3
NH
Br
O
O
NAPO
O
Entry 1
in Table 1
MeO
O
OMe
BzO
MeO
Synthesis of the trisaccharide 4c from p-bromophenol (8)
was examined (Scheme 2). Treatment of thioglycoside 9 and p-
O
10
O
RO
MeO OMe
o
bromophenol with NIS and a catalytic amount of TfOH at -78 C,
[
15]
followed by removal of the 2-(azidomethyl)benzoate (AZMB)
with PPh , provided α-rhamnoside 16 in 78% yield with a
DDQ, H O/CH Cl
2
17 : R = NAP
18 : R = H
2
2
3
r.t., 97%
Br
complete α-selectivity. We next examined α-selective
glycosidation of the 2,3-di-O-methylglycosyl imidate 10 (Table 1).
Exposure of the glycosyl imidate 10 under the previously
reported conditions for α-selective glycosidation of 2,6-dideoxy
O
MeO
AcO
MeO
O
O
2
SPh
R O
MeO
OAc
11
MeO
R O
MeO
O
1
O
O
sugar using IBr and n-Bu
4
NBr resulted in a poor coupling yield of
O
NIS, TfOH, MS4A
OR1 MeO
o
OMe
CH Cl , -78
C
1
7 after 40 h (entry 1). Substitution with an electron-withdrawing
2
2
oxygen at the C2 position could reduce the reactivity of glycosyl
19 : R1 = Ac, R = Bz
2
KOMe, MeOH
imidate 10 at a greater rate than that of 2,6-dideoxylglycosyl
o
4c : R1 = R = H
2
5
0 C, 76% in 2 steps
imidates. On the other hand, treatment of glycosyl imidate 10
o
and acceptor 16 with I
2
and n-Bu
4
NOTf at -50 C in toluene
Scheme 2. Synthesis of the trisaccharide 4c from 4-bromophenol (8)
provided disaccharide 17 in 92% yield with α/β = 96:4 (entry 2).
The use of CH Cl , EtCN and Et O as solvents reduced the α-
selectivity of 17 (entries 3-5). The use of neither I alone nor I
combined with n-Bu NI at the same temperature could not
2
2
2
2
2
Table 1. α-Selective glycosidation of the 2,3-O-dimethylrhamnosyl imidate 10
4
activate glycosyl imidate 10 (entries 6 and 7). These results
]
[c]
[d]
Entry Activator
Solvent
Temp
Yield
(%)
α/β
o
suggested that the triflate anion might play an important role in
[ C]
2 3 2
the activation of I . Use of TMSOTf or BF •OEt as an activator
[
a]
1
IBr, n-Bu
4
NBr,
CH
2
Cl
2
r.t.
43
α only
for the glycosyl donor 10 resulted in a reduction in the α-
selectivity of 17. These results clearly indicated that these
activation conditions would be effective for the α-selective
glycosidation of 2-O-methyl-rhamnoside. Oxidative removal of
the NAP ester with DDQ provided alcohol 18 in 97% yield.
Glycosylation of alcohol 18 with thioglycoside 11 and NIS and a
then DIEA
2
3
4
5
6
7
8
9
I
I
I
I
I
I
2
2
2
2
2
2
, n-Bu
, n-Bu
, n-Bu
, n-Bu
4
4
4
4
NOTf
NOTf
NOTf
NOTf
toluene
CH Cl
EtCN
Et2O
toluene
toluene
toluene
toluene
-50
-50
-50
-50
-50
-50
-78
-78
92
93
50
73
-
96:4
2
2
78:22
58:42
50:50
, n-Bu
4
NI
-
88
87
[
b]
catalytic amount of TfOH, followed by solvolysis of the esters,
TMSOTf
85:15
85:15
1
[b]
provided trisaccharide 4c in 76% yield in 2 steps. The
J
CH
-
BF
3
•OEt
2
coupling constants (161, 169 and 171 Hz) of the anomeric
positions of 4c indicated that the trisaccharide 4c involved two
α-glycosides and a β-glycoside.
[a] Reaction time is 40 h. [b] AW300 was used instead of MS4A. [c] isolated
1
yields. [d] The ratio was determined based on H NMR spectra
Synthesis of the trisaccharide 4f from p-bromophenol (8)
was examined (Scheme 3). Treatment of glycosyl imidate 12
TfOH provided α-rhamnoside 22 in 75% yield. Removal of the
TBS ether of α-glycoside 22 with HF•pyridine provided the
alcohol 23 in 98% yield. Treatment of disaccharide 23 and 2,3,4-
2 4
and p-bromophenol (8) with I and n-Bu NOTf at -50 °C in
toluene provided disaccharide 20, followed by cleavage of the
tert-butyldimethylsilyl (TBS) ether with tetrabutylammonium
fluoride (TBAF) to provide α−rhamnoside 21 in 91% yield with
complete α-selectivity. Glycosylation of the α-rhamnoside 21 at
the C3 hydroxyl group with thiorhamnoside 13 possessing an
ester-protecting group at the C2 hydroxyl group with NIS and
tri-O-methyl-fucosyl imidate 14 with I
in toluene provided an anomeric mixture of trisaccharide 24 in
3% yield with an α/β ratio of 54:46. We envisaged that the
2 4
and n-Bu NOTf at -50 °C
9
insufficient α-selectivity might be caused by the low reactivity of
the C3 hydroxyl group due to the electronwithdrawing acyl-
protecting group at the O2 hydroxyl group. We next planned a
stereoselective preparation and glycosylation of a 2-O-alkyl
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Chemistry - A European Journal
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FULL PAPER
protected disaccharide. Treatment of α-rhamnoside 23 and the
We next examined one-pot sequential Suzuki-Miyaura
coupling using the 4-bromophenyl glycosides 4a-g, the cyclic
boron compound 5, and 1-bromonapthalene (6A) (Table 2).
Glycoside 4g was an anomeric isomer of 2,3,4-tri-O-methy-α-
fucoside. Treatment of trisaccharide 4c and 2.0 equiv. of cyclic
2
-O-(2-naphthyl)methyl-rhamnosyl imidate 25 with I
2
and n-
o
Bu
4
NOTf at -50 C provided the α-rhamnoside 26 in 86% yield
with a complete α-selectivity. Subsequent solvolysis of benzoate
with MeOH under basic conditions provided disaccharide 27 in
o
9
5% yield. Treatment of disaccharide 27 and 2,3,4-tri-O-methyl
fucosyl imidate 14 under the same reaction conditions as that for
4 provided trisaccharide 28 in 91% yield with an improved α-
boron compound 5 at 60 C for 5.0 h, followed by reaction with
o
5.0 equiv. of 1-naphthylbromide (6A) at 80 C for 19 h provided
2
phenyl glycoside 4cA possessing a 6-(2-naphthyl)hexyl group in
75% yield (entry 3). Use of other phenyl glycosides, 4a, 4b and
4d-g, as the first substrate resulted in the corresponding 4-(6-(2-
naphthyl)hexyl)phenyl glycosides 3aA, 3bA and 3d-gA in good
yields (70 to 90%) (entries 1,2,4-6). The reaction temperature
required for the first cross-coupling reaction varied depending on
the substrate. We next examined the fluorescent labelling of
selectivity (α/β = 85:15). The oxidative removal of the NAP ether
of an anomeric mixture of 28 with DDQ provided an anomeric
mixture of trisaccharide 4f in 88% yield. Further purification of
the mixture of 4f by HPLC provided pure α-glycoside 4f. The
1
J
CH-coupling constants (166, 168 and 171 Hz) of the anomeric
positions of 4f indicated that all of the glycosyl bonds of 4f are α.
®
[16]
glycosides 3 using brominated TokyoGreen
reaction of phenyl glycoside 4c and the cyclic boron compound
under the above-described conditions, the brominated
unit 6B. After the
NH
5
O
CCl
3
®
TokyoGreen unit 6B was added to the reaction mixture. The
O
NAPO
TBSO
o
Br
reaction mixture was stirred at 80 C. However, the desired
1
2
OMe
fluorescent-labelled product was not observed. High solubility of
O
Br
I2, n-Bu4NOTf
®
the brominated TokyoGreen unit 6B in H
2
O under basic
O
NAPO
HO
MS4A, toluene
RO
conditions might reduce the concentration of the reagent 6B in
the organic solvent. In addition, a strong electron-donating
phenoxide would coordinate the palladium species and might
reduce its reactivity towards oxidative addition. To overcome
these problems, we used the methoxymethyl ether 6C as the
third building block. After the reaction of phenyl glycoside 4a-c
and the cyclic boron compound 5 under the above-described
conditions, the methoxymethyl ether 6C was added to the
o
-50 C,
OMe
8
TBAF, THF, r.t.
1% in 2 steps
2
2
0 : R = TBS
1 : R = H
9
NH
CCl
SPh
O
O
3
NIS, TfOH
I2, n-Bu4NOTf
O
NAPO
TBSO
MS4A, CH Cl
MS4A, toluene
2
2
NAPO
BzO
-40 oC, 75%
-50 oC, α only
OBz
8
6%
ONAP
2
5
1
3
Table 2. Sequential Suzuki-Miuayra coupling using the boracyclane 5
Br
Br
Br
O
O
O
then
O
5 mol%
PdCl2(dppf)
KOH
THF/H2O
Temp
ArBr 6 (5.0 equiv)
O
NAPO
NAPO
O
B
o
8
0 C
HO
O
O
OMe
OMe
2
OR1
R O
O
O
NAPO
NAPO
5
(2.0 equiv.)
RO
RO
OBz
ONAP
4
2
) 3 M HCl, THF
50 C for 3a-cB
HF•Py, THF, r.t.
8%
22 : R = TBS
23 : R = H
NaOMe, MeOH
50 C, 95%
26 : R = Bz
27 : R = H
o
o
9
Br
Me
O
g : R1 = OCH3, R2
=
NH
CCl
OMe
I2, n-Bu4NOTf
MS4A, toluene
14, I2, n-Bu4NOTf
Ar
MS4A, toluene
O
O
3
o
o
4
-50 C,
-50 C,
O
9
3%, α/β = 54:46
91%, α/β = 85:15
O
O
HO
OMOM
O
OMe
O
O
OH
HO
OMe
MeO
6C
2
Br
OMe
R O
OR1
Br
3
MeO
1
4
O
O
Entry
4
6
Product
Yield [%]
O
O
RO
O
NAPO
1
2
4a
4b
4c
4d
4e
4f
6A
6A
6A
6A
6A
6A
6A
6C
6C
6C
3aA
3bA
3cA
3dA
3eA
3fA
69
73
75
83
92
78
80
50
75
86
O
OMe
OMe
O
O
RO
NAPO
3
4
O
O
OR
OBz
O
5
6
O
OMe
OMe
OMe
OMe
MeO
MeO
7
8
4g
4a
4b
4c
3gA
3aB
3bB
3cB
DDQ,
H2O/CH2Cl2
r.t., 88%
2
8 : R = NAP
2
4
9
4f : R = H
10
Scheme 3. Synthesis of the trisaccharide 4f from the phenol 8
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Chemistry - A European Journal
10.1002/chem.201703684
FULL PAPER
o
OMe
reaction mixture. After heating at 80 C for 17 h, the desired
coupling product was generated. The crude material was
exposed to acidic conditions for hydrolysis of the methoxymethyl
OMe
O
O
®
O
O
HO
ether to provide TokyoGreen labelled PGL-1 trisaccharide 3a-
HO
MeO
O
OMe
O
cB in 50, 75 and 86% yields in 2 steps based on 4a-c,
respectively.
MeO
HO
O
O
O
MeO
O
HO
HO
OH MeO
OH
Finally, we tested the immunomodulating functions of
synthetic glycosides 3a-gA and 4a-g on bone-marrow-derived
macrophage (BMM) stimulated with trehalose-6,6’-dimycolate
OMe
2
9
30
[
17]
(
TDM).
TDM is the most abundant glycolipid in the
Figure 3. Structure of the phenyl glycosides 30 and 31 reported by Lowary’s
mycobacterial cell wall and promotes an innate immunity
response mediated with Mincle, C-type lectin receptors on
group.
[
18]
macrophage.
In the first screening, BMMs stimulated with
TDM (25 mg) were incubated with 100 ng of the compounds 3a-
gA and 4a-g for 24 h. The phenyl bromides 4a-g did not inhibit
the secretion of TNF-α (shown in the supporting information). On
the other hand, some naphthyl derivatives showed inhibitory
activity in a dose-dependent manner (Figure 2). Moreover, a
proliferation assay confirmed that these results were not due to
the toxicity of the compounds. Among a series of PGL-1 related
glycosides, the trisaccharide 3cA exhibited the strongest activity.
There results are comparable to those of a previous report using
Conclusions
Herein, we report the synthesis of O-methylated glycolipids
related to PGL sugars by direct stereoselective glycosidation.
We prepared 4-bromophenyl glycoside 4a-c containing PGL-1
glycosides from 4-bromophenol (8), 2-O-acyl-thiorhamnoside 9,
2
-O-methyl-rhamnosyl imidate 10, and 3,6-di-O-methyl-
thioglucoside 11. Treatment of 2-O-methyl-rhamnosyl imidate
with I and n-Bu NOTf efficiently provided α-rhamnoside with
2
4
[
9c]
activated THP-1 cells with TLR2 ligands. On the other hand,
excellent α-selectivity, and enhanced the electorophilicity of
iodine. On the other hand, 4-bromophenyl glycoside 4d-f
containing PGL-tb1 glycosides were prepared from 4-
bromophenol (8), 2-O-methyl-rhamnosyl imidate 12, 2-O-(2-
naphthylmethyl)-rhamnosyl imidate 13b, and 2,3,4-tri-O-methyl-
fucosyl imidate 14. Use of the (2-naphthyl)methyl ether as an O-
we found 3-O-a-rhamnosyl-2-O-methyl-α-rhamnoside 3eA to be
the strongest ligand among
a series of PGL-tb1-realted
glycosides. Although the glycolipids containing the disaccharide
unit were found in mycobacteria, there exists only one report on
[
19]
the biological evaluation of related compounds.
In 2014,
Lowary and co-workers reported that the cytokine inhibition
activity of synthetic disaccharide 30 on activated THP-1 cells
with TLR2 ligands was weaker than that of PGL-1 trisaccharide
2
-protecting group of rhamnoside 13b improved the total yield of
desired α-linked trisaccharide 4f. Sequential Suzuki-Miyaura
coupling using the synthetic glycosides 4a-g, boracyclane 5 and
arylbromide 6A and 6B smoothly proceeded to provide the
glycolipids 3a-gA in a one-pot process. Finally, we elucidated
the immunosuppresive activity of the synthetic compounds and
found that phenyl 3-O-α-rhamnosyl-2-O-methyl-α-rhamnoside
possessing a 6-(2-naphthyl)hexyl group exhibited the strongest
[
9c]
2
9
(Figure 3).
However, no reports have compared the
inhibitory activity of the PGL-tb1 series of glycosides.
inhibitory effect from among
a series of PGL-tb1-realted
glycosides. Attachment of tri-O-methyl-α-fucoside at the C3
hydroxyl group of the terminal rhamnoside reduced the inhibitory
activity. Elucidation of the role of non-O-methyl-rhamnoside and
a mode of action for phenyl glycoside that involves identification
of the target protein is now in progress.
Acknowledgements
This work was supported by
a Grant-in-Aid for Scientific
Research on Innovative Areas (Grant-in-aid No. 26102720).
Figure 2. Cytokine inhibition assay of the glycosides 3a-fA in dose dependent
manner. (* : p < 0.05)
Keywords: Innate immunity • Palladium coupling•
Glycosylation• Natural product synthesis• Immunosuppresive
activities
[
1]
a) M. B. Goren, P. J. Brennan in Tuberculosis (Eds.: G. P. Youmans),
W. B. Saunders, Philadelphia, 1979, pp. 69-193; b) D. D. Barnes, M. L.
E. Lundaha, Ed C. Lavelle, E. M. Scanlan, ACS Chem. Biol. 2017, 12,
1
969-1979.
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Chemistry - A European Journal
10.1002/chem.201703684
FULL PAPER
[
2]
a) S. W. Hunter, P. J. Brennan, J. Bacteriol. 1981, 728-735; b) S. W.
Hunter, T. Fujiwara, P. J. Brennan, J. Biol. Chem. 1982, 257, 15072-
Barreda, C. W. Cairo, T. L. Lowary, ChemBioChem 2013, 14, 2153-
2159.
1
5078.
M. Daffe, C. Lacave, M.-A. Laneelle, G. Laneelle, Eur. J. Biochem.
987, 167, 155-160.
[10] Synthesis of PGL-tb1 analogues, see: a) G. H. Veeneman, S. H. Van
Leeuwen, H. Zuurmond, J. H. J. Van Boom, Carbohydr. Chem. 1990, 9,
783-796; b) M. K. Gurjar, G. Viswanadham, J. Carbohydr. Chem. 1991,
10, 481-485; c) T. Fujiwara, Agric. Biol. Chem. 1991, 55, 2123; d) J.
Bourke, C. F.Brereton, S. V. Gordon, E. C. Lavelle, E. M. Scanlan, Org.
Biomol. Chem. 2014, 12, 1114-1123; e) H. R. H. Elsaidi and T. L.
Lowary, ChemBioChem 2014, 15, 1176-1182; f) H. R. H. Elsaidi, T. L.
Lowary, Chem. Sci. 2015, 6, 3161-3172.
[
[
[
[
3]
4]
5]
6]
1
M. B. Reed, P. Domenech, C. Manca, H. Su, A. K. Barczak, B. N.
Kreiswirth, G. Kaplan, C. E. Barry III, Nature 2004, 431, 84-87.
A. Arbues, W. Malaga, P. Constant, C. Guilhot, J. Prandi, C. Astarie-
Dequeker, ACS Chem. Biol. 2016, 11, 2865-2875.
Immunomodulatory effect of PGL-1, see: a) M. A. Neill, S. J. Klebanoff,
J. Exp. Med. 1988, 167, 30-42; b) C. L. Silva, L. H. Faccioli, N. T. Foss,
Int. J. Lepr. Other Mycovact. Dis. 1993, 61, 107-108; c) V. Ng, G.
Zanazzi, R. Timpl, J. F. Talts, J. L. Salzer, P. J. Brennan, A.
Rambukkana, Cell, 2000, 103, 511-524; d) G. Tabouret, C. Astarie-
Dequeker, C. Demangel, W. Malaga, P. Constant, A. Ray, N. Honore,
N. F. Bello, E. Perez, M. Daffe, C. Guilhot, PLoS Pathog. 2010, 6,
e1001159.
[11] a) R. R. Schmidt, J. Michel, Tetrahedron Lett. 1984, 25, 821; b) I.
Cumpstey, Org. Biomol. Chem. 2012, 10, 2503-2508.
[12] H. Tanaka, A. Yoshizawa, S. Chijiwa, J. Ueda, M. Takagi, K. Shinya, T.
Takahashi, Chem. Asian. J. 2009, 4, 1114-1125.
[13] R. Suzuki, S. Fuse, H. Tanaka, Eur. J. Org. Chem. 2016, 21, 3471-
3481.
[14] K. Matos, J. A. Soderquist, J. Org. Chem. 1988, 63, 461-470.
[15] T. Wada, A. Ohkubo, A. Mochizuki, M. Sekine, Tetrahedron Lett. 2001,
42, 1069-1072.
[
[
[
7]
8]
9]
Immunomodulatory effect of PGL-tb1, see: a) K. Pethe, D. L. Swenson,
S. Alonso, J. Anderson, C. Wang, D. G. Russell, Proc. Natl. Acad. Sci.
USA 2004, 101, 13642-13647; b) H. Gan, J. Lee, F. Ren, M. Chen, H.
Kornfeld, H. G. Remold, Nat. Immun. 2008, 9, 1189-1197.
[16] Y. Urano, M. Kamiya, K. Kanda, T. Ueno, K. Hirose, T. Nagano, J. Am.
Chem. Soc. 2005, 127, 4888-4894.
Total synthesis of PGL-tb1: S. Barroso, R. Castelli, M. P. Baggelaar, D.
Geerdink, B. T. Ter Horst, E. Casas-Arce, H. S. Overleeft, G. A. Van
der Marel, J. D. C. Codee, A. J. Minnaard, Angew. Chem. Int. Ed. 2012,
[17] H. Noll, H. Bloch, J. Asselineau, E. Lederer, Biochim. Biophys. Acta
1956, 20, 299-309.
[18] a) E. Ishikawa, T. Ishikawa, Y. S. Morita, K. Toyonaga, H. Yamada, O.
Takeuchi, T. Kinoshita, S. Akira, Y. Yoshikai, S. Yamasaki, J. Exp. Med.
2009, 206, 2879-2888; b) Y. Miyake, K. Toyonaga, D. Mori, S. Kakuta,
Y. Hoshino, A. Oyamada, H. Yamada, K. Ono, M. Suyama, Y. Iwakura,
Y. Yoshikai, S. Yamasaki, Immunity 2013, 38, 1050-1062.
5
1, 11774-11777.
Synthesis of PGL-1 analogues, see: a) T. Fujiwara, G. O. Aspicall, S. W.
Hunter, P. J. Brennan, Carbohydr. Res. 1987, 163, 41-52; b) A. Borbas,
A. Liptak, Carbohydr. Res. 1993, 241, 99-116; c) H. R. H. Elsaidi, D. R.
[
19] A. Vercellone, G. Puzo, J. Biol. Chem. 1989, 264, 7447-7454.
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Entry for the Table of Contents (Please choose one layout)
Layout 2:
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Br
Ko Sato, Omahdi Zakaria, Kensuke
O
Shibata, Koh-hei Sonoda, Sho
Yamasaki and Hiroshi Tanaka*
O
B
O
BzO
MeO
Br
OH
HO
MeO
O
I2, tBuNOTf
CCl3
MeO
O
O
NH
HO
MeO
O
O
O
MeO
AcO
MeO
OH MeO OMe
O
Pd(0)
Page No. – Page No.
O
NAPO
MeO OMe
SPh
OAc
Synthesis and biological evaluation
of O-methylated glycolipids related to
PGLs via direct stereoselective
Synthesis of O-methylated glycolipids related to the sugars in PGLs via direct
stereoselective glycosidation and sequential Suzuki-Miyaura coupling using
synthetic glycosides, boracyclane, and aryl bromides is reported. Among them,
The phenyl 3-O-α-rhamnosyl-2-O-methyl-α-rhamnoside possessing a 6-(2-
naphthyl)hexyl group exhibited the strongest immunosuppresive activity .
glycosidation and sequential Suzuki-
Miyaura coupling using boracyclane
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