Phenyliodine bis(trifluoroacetate) (PIFA) as an excellent promoter of 2-deoxy-2-phthalimido-1-thioglycosides in the presence of triflic acid in glycosylation reactions

Article abstract of DOI:10.1002/ejoc.201500186

A combination of phenyliodine bis(trifluoroacetate) (PIFA) and trifluoromethanesulfonic acid was found to be an effective activator for the glycosylation reaction, of which the glycosyl donor was p-(octyloxy)phenyl 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido

Full text of DOI:10.1002/ejoc.201500186

SHORT COMMUNICATION
DOI: 10.1002/ejoc.201500186
Phenyliodine Bis(trifluoroacetate) (PIFA) as an Excellent Promoter of 2-
Deoxy-2-phthalimido-1-thioglycosides in the Presence of Triflic Acid in
Glycosylation Reactions
[a]
[a]
[a]
[a]
Tetsuya Kajimoto, Koji Morimoto, Ryosuke Ogawa, Toshifumi Dohi, and
Yasuyuki Kita*[
a]
Keywords: Iodine / Phenyliodine bis(trifluoroacetate) / Glycosylation / Thioglycosides
A combination of phenyliodine bis(trifluoroacetate) (PIFA)
and trifluoromethanesulfonic acid was found to be an effec-
tive activator for the glycosylation reaction, of which the
glycosyl donor was p-(octyloxy)phenyl 3,4,6-tri-O-acetyl-2-
kauranol, were employed as acceptor substrates. Interest-
ingly, the glycosylation reaction of sterically hindered terpe-
noid alcohols, such as (–)- and (+)-borneols and (+)-fenchyl
alcohol, with p-(octyloxy)phenyl 3,4,6-tri-O-acetyl-2-deoxy-
deoxy-2-phthalimido-1-thio-
oxy)phenyl 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-1-thio-
-galactopyranoside. The reaction proceeded with good
D
-glucopyranoside or p-(octyl-
2-phthalimido-1-thio-D-glucopyranoside afforded the de-
sired β-glycoside in quantitative yield. Moreover, the present
reaction was useful to synthesize disaccharides of which the
D
yields when naturally occurring and derived alkanols, such
as cholestanol, (–)-menthol, 1- and 2-adamantanols and nor-
non-reducing end was composed of a
galactosamine unit.
D-glucosamine or D-
Introduction
glycosylation of thioglycosides have relied on a toxic heavy
metal oxidant for product formation. A key contribution to
The developing of glycosciences revealed that complex ol- the glycosylation with thioglycosides was made in 1990 by
[
6]
igosaccharides on cell surfaces play important roles in bio- van Boom and co-workers, who first reported the use of
logical events concerning cell-to-cell adhesions, and medi- a combination of a stoichiometric amount of N-iodosuccin-
cines having glycosidic bonds or glycosyl structures have imide (NIS) with a catalytic amount of triflic acid as a pro-
become widely used to treat diabetes, infection by influenza moter to activate the disarmed thioglycosides. The use of
viruses, and heart diseases.[ Thus, the synthesis of biolo- strong acid salts in conjunction with N-bromosuccinimide
gically active oligosaccharides still attracts organic chem- to activate the thioglycosides has been investigated by
1]
ists.[ Among them, the chemistry of thioglycosides has Kusumoto and co-workers. Recently, the alternative com-
been well developed in the past three decades due to their binations of NIS and a Lewis acid were also exploited as
stability and ease of preparation. The conventional the promoter of the thioglycoside activation.[
2]
[3]
[7]
8–13]
glycosylation of thioglycosides was performed by using a
Recently, the environmentally benign hypervalent iodine
mercury salt, such as HgSO , HgCl , Hg(OBz) , or oxidation has witnessed profound progress in the field of
4
2
2
[
4]
[14]
Hg(NO ) . The use of Cu(OTf) (Mukaiyama) or CuBr / organic chemistry.
The low toxicity, ready availability
3
2
2
2
Bu NBr/AgOTf (Ogawa and Ito) as an activator was fur- and easy handling of hypervalent iodine compounds are ex-
4
[
5]
ther explored. However, these reported systems for the pected to be useful features for the activation of the sulfur
Scheme 1. Hypervalent iodine induced metal-free glycosylation.
[
a] College of Pharmaceutical Sciences, Ritsumeikan University,
atom. We have been engaged in the development of the
oxidation of the sulfur atom utilizing hypervalent iodine
1
-1-1 Nojihigashi, Kusatsu, Shiga 525-8577, Japan
E-mail: kita@ph.ritsumei.ac.jp
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201500186.
[
15,16]
reagents to form an active iodonium intermediate.
In-
spired by these studies, other chemists have also reported
2138
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2015, 2138–2142

Phenyliodine Bis(trifluoroacetate) in Glycosylation Reactions
the hypervalent iodine induced oxidation of sulfides.[17,18] yliodine bis(trifluoroacetate) (PIFA) (Entry 2), PhI(OH)
In contrast, apart from the initial studies of oxidation of OTs (HTIB) (Entry 3), and three other kinds of iodine rea-
III
the sulfur atom, the I -promoted glycosylation reaction of gents (Entries 4–6) in the presence of TfOH (2 equiv.) in
[19]
thioglycosides has rarely been studied.
This oxidation dichloromethane at –78 °C. As a result, the reaction with
ability led us to find an efficient glycosylation reaction of PIFA and TfOH (Entry 2) afforded the best yield (40%)
thioglycosides. We would now like to report the efficient among the reactions from Entries 1 to 6. It is worth noting
hypervalent iodine induced glycosylation reaction (Scheme 1). that the isolated yield (40%) of product 3a in Entry 2 was
two times higher than that of the previously reported reac-
tion, in which the same substrates 1, 2 were treated with
Results and Discussion
[
19a,19b]
PhI=O in the presence of Tf O in acetonitrile.
Thus,
2
We initially examined the glycosylation with methyl several acids were then utilized as the additive instead of
[
20]
2,3,4,6-tetra-O-acetyl-1-thio-β-d-glucopyranoside (1a)
TfOH under the same reaction conditions. By choosing tri-
with methyl 2,3,4-tri-O-benzyl-α-d-glucopyranoside (2) methylsilyl triflate as the additive, the product 3a was ob-
using the combination of hypervalent iodine reagent and an tained in the same yield as that shown in Entry 2; however,
acid. First, the reaction mixture was treated with 1 equiv. the use of tris(pentafluorophenyl)borane, the trifluoro-
of phenyliodine diacetate (PIDA) (Table 1, Entry 1), phen- borane–diethyl ether complex, bis(cyclohexyl)(trifluoro-
Table 1. Glycosylation reactions of 1a, 1b and 2 with various hypervalent iodine reagents.[a,b]
Entry
Donor
Hypervalent iodine reagent (1 equiv.)
Product
Yield [%]
1
2
3
4
5
6
7
1a
1a
1a
1a
1a
1a
1b
PIDA
PIFA
PhI(OH)OTs
3a
3a
3a
3a
3a
3a
3b
20
40
trace
23
30
30
p-MeC
p-F CC
6
H
H
4
I(OCOCF
3 2
)
3
6
4
I(OCOCF
3
)
2
C
6
F
5
I(OCOCF
PIFA
3
)
2
77
[
a] Reactions were carried out by adding the IIII reagent (0.2 mmol) to a stirred solution of the starting glycosyl donor 1 (0.2 mmol) and
glycosyl acceptor 2 (0.3 mmol) in CH Cl (4 mL) in the presence of TfOH (0.4 mmol) at –78 °C. [b] Yield of isolated product.
2
2
Figure 1. Structures of thioglycosides 5 and 6 and hydrophobic alcohols 7–13 chosen as the glycosyl acceptor.
Eur. J. Org. Chem. 2015, 2138–2142
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2139

T. Kajimoto, K. Morimoto, R. Ogawa, T. Dohi, Y. Kita
SHORT COMMUNICATION
methanesulfonyl)borane, and methanesulfonic acid pro- Table 2. Glycosylation of thioglycosides and several alkanols by the
activation of PIFA with TfOH.[
a,b]
duced no significant results. Thus, the combination of PIFA
and TfOH was hereafter employed as the activator of the
thioglycoside donor in the glycosylation reactions. Interest-
ingly, the glycosylation reaction with methyl 2-deoxy-2-
phthalimido-3,4,6-tri-O-acetyl-1-thio-d-glucopyranoside
(
1b) instead of compound 1a as the glycosyl donor afforded
the appropriate product 3b in a much higher yield (Entry 7).
-Thioglycosides bearing a phthalimido group at the C-2
1
position of a pyranose ring were then nominated as excel-
lent candidates for the glycosyl donor to study the effective-
ness of PIFA in the glycosylation reaction.
Moreover, the odorless p-(octyloxyl)benzenethiol
4)[
21,22]
was chosen as the source of the aglycon moiety
(
of the 1-thioglycosides to avoid tedious handling of
odoriferous organosulfur compounds like methanethiol or
benzenethiol, which were generated during the conventional
glycosylation reaction with methyl or phenyl 1-thioglycos-
ides. Based on these results, p-(octyloxy)phenyl 2-deoxy-2-
phthalimido-3,4,6-tri-O-acetyl-1-thio-β-d-glucopyranoside
(
5) was adopted as the first choice of the donor glycoside
[22,23]
and synthesized by the method in the literature.
In ad-
dition, p-(octyloxy)phenyl 2-deoxy-2-phthalimido-3,4,6-tri-
O-acetyl-1-thio-β-d-galactopyranoside (6) was also pre-
pared from 2-deoxy-2-phthalimido-d-galactose tetraacet-
ate[ and 4 with good yield (83%) in the same way as the
synthesis of 5; i.e., 6 was obtained by the reaction of 2-
deoxy-2-phthalimino-d-galactose tetraacetate with 4 in the
presence of BF ·Et O in CH Cl .
24]
3
2
2
2
Herein, (–)-menthol (7), cholestanol (8), ent-17-nor-kaur-
[
25]
anol (9),
2- and 1-adamantanols (10, 11), (–)- and (+)-
borneols (12a, b), and (+)-fenchyl alcohol (13) were chosen
as the acceptors (Figure 1).
In the beginning, thioglycoside 5 and alkanols bearing
the simple six-membered cyclohexane ring (7, 8) were
treated with PIFA in the presence of TfOH in dichloro-
methane at 0 °C (Table 2, Entries 1 and 2). The products 3c
and 3d were obtained in moderate to good yields. Next,
alkanols bearing a secondary alcohol on a rigid fused ring
(9, 10) were employed as the acceptor substrate in the same
reaction to afford the appropriate glycosylated products 3e
and 3f with almost the same yield (Entries 3 and 4). Sur-
prisingly, the tertiary alcohol (11) was glycosylated in 71%
under the same reaction condition in spite of the steric hin-
drance caused by the adamantane skeleton (Entry 5). More-
over, the substrates carrying a much more hindered alcohol,
such as the (–)- and (+)-borneols (12a, 12b) and (+)-fenchyl
alcohol (13), were glycosylated with 5 in quantitative yields
(Entries 6–8). As expected, 1-adamantanol (11) was glycos-
ylated with 6 to afford adamantanyl 2-deoxy-2-phthal-
imido-β-d-galactopyranoside 3k in a good yield (Entry 9).
Finally, the synthesis of disaccharides by the above
glycosylation was also performed with methyl 2,3,4-tri-O-
benzyl-α-d-glucopyanoside (2) and 5 as the acceptor and
[
a] Reactions were carried out by adding PIFA (0.2 mmol) to a
stirred solution of the starting glycosyl donor 5 or 6 (0.2 mmol)
and glycosyl acceptors 7–13 (0.3 mmol) in CH Cl (4 mL) in the
presence of TfOH (0.4 mmol) at 0 °C. [ Yield of isolated product.
2
2
b]
the donor substrates, respectively. Since the former was
armed” and the latter was “disarmed”,[ the combination an excellent yield (87%) (Table 3, Entry 1). Being encour-
24]
“
seemed to be one of the most undesired ones; however, the aged by the above result, the glycosylation reactions with 6
reaction occurred to provide the desired disaccharide 3b in as the donor and 2 as the acceptor substrate were chal-
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Eur. J. Org. Chem. 2015, 2138–2142

Phenyliodine Bis(trifluoroacetate) in Glycosylation Reactions
lenged to obtain the disaccharides 3l. As shown in Table 3, ogy (MEXT). T. K. acknowledges support from the Grant-in-Aid
for Scientific Research (C). K. M. also acknowledges support from
the appropriate disaccharides were provided in good yields.
the Grant-in-Aid for Young Scientists (B) from the JSPS.
Table 3. Disaccharide synthesis by thioglycosylation with PIFA/
[
a,b]
TfOH.
[
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Acknowledgments
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Research (A) from the Japan Society for the Promotion of Science
(
“
JSPS), a Grant-in-Aid for Scientific Research on Innovative Areas
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© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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