Communications
doi.org/10.1002/cplu.202000603
ChemPlusChem
1
2
3
4
5
6
7
8
9
A Pyridine-Acetylene-Aniline Oligomer: Saccharide
Recognition and Influence of this Recognition Array on the
Activity as Acylation Catalyst
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
In order to create new functions of foldamer-type hosts, various
kinds of recognition arrays are expected to be developed. Here,
a pyridine-acetylene-aniline unit is presented as a new class of a
saccharide recognition array. The conformational stabilities of
this array were analyzed by DFT calculation, and suggested that
a pyridine-acetylene-aniline oligomer tends to form a helical
structure. An oligomer of this array was synthesized, and its
1
association for octyl β-D-glucopyranoside was confirmed by H
NMR measurements. UV/Vis, circular dichroism, and
fluorescence titration experiments revealed its high affinity for
octyl glycosides in apolar solvents (Ka =104 to 105 MÀ 1). This
oligomer was relatively stable under basic conditions, and
therefore this array was expected to be applied to the
Figure 1. a) A pyridine-acetylene-phenol oligomer 1. b) A pyridine-acetylene-
aniline oligomer 2.
derivatization of saccharides. A 4-(dialkylamino)pyridine at-
tached pyridine-acetylene-aniline oligomer proved to catalyze
the acylation of the octyl glucoside.
gen-bonding acceptor and donor, respectively, in a push-pull
fashion for the saccharide hydroxy groups.[4] For example,
chain-type oligomers, such as 1, strongly associated with
saccharides to form helical complexes in apolar solvents.[3f]
During the course of this study, we imagined that a pyridine-
acetylene-aniline unit could also show effective hydrogen-
bonding ability (Figure 1b).[5] Since amino groups of the aniline
rings can work as a hydrogen-bonding donor, this unit was
expected to form a push-pull hydrogen-bonding with saccha-
ride hydroxy groups. To apply this unit for saccharide recog-
Saccharide recognition is a challenging topic in the field of
host-guest chemistry due to the three-dimensional complexity
of saccharide structures.[1] Various types of artificial hosts have
been studied for saccharide recognition. Among these studies,
much interest has been focused on helical-foldamer type
hosts.[2] The design using helical foldamers is rational for
efficiently forming a hydrogen-bonding network with multiple
hydroxy groups of saccharides. In addition, their affinity and
selectivity can be regulated by modifying the recognition array
in the foldamers. In order to create new functions of foldamer-
type hosts, various kinds of recognition arrays are expected to
be developed.
nition, we newly synthesized
a pyridine-acetylene-aniline
oligomer 2. DFT calculations proposed that a model oligomer of
2 winds around methyl β-D-glucopyranoside by forming a
hydrogen-bonding network (Figure 2). From another perspec-
tive, this recognition array seemed not to be influenced by
basic conditions, usually used in acylation of saccharides,
because pyridine and aniline rings have no acidic proton unlike
a phenol ring. Therefore, this unit was expected to be applied
to catalysts for derivatization of saccharides. Catalysts bearing
saccharide-recognition arrays are expected to catalyze regiose-
lective derivatization of saccharides like natural enzymes.[6–8] For
example, Kawabata and coworkers reported successful exam-
ples of regioselective acylation for monosaccharides with a 4-
(dimethylamino)pyridine (DMAP)-based catalyst bearing hydro-
gen-bonding sites with saccharides.[8c,e] Herein, we report
saccharide recognition abilities of a pyridine-acetylene-aniline
oligomer 2 and catalytic abilities of a DMAP-attached oligomer
3 (Figure 3).
Recently, we have developed oligomers consisting of
pyridine-acetylene-phenol units as hosts for saccharides (Fig-
ure 1a).[3] The pyridine and phenol rings can work as a hydro-
[a] Dr. Y. Ohishi, Prof. Dr. M. Inouye
Graduate School of Pharmaceutical Sciences
University of Toyama
2630 Sugitani, Toyama 930-0194 (Japan)
E-mail: ohishi@pha.u-toyama.ac.jp
[b] Prof. Dr. T. Takata
Graduate School of Advanced Science and Engineering
Hiroshima University
Higashi-Hiroshima, Hiroshima 739-8527 (Japan)
Supporting information for this article is available on the WWW under
Generally, helix-forming ability of m-aryleneethynylene
foldamers is affected by the difference between cisoid- and
ChemPlusChem 2020, 85, 1–6
1
© 2020 Wiley-VCH GmbH
��
These are not the final page numbers!