Concentration- and time-dependent eccentric changes in circular dichroism of saccharide-linked ethynylpyridine oligomer with copper(II) ions

Article abstract of DOI:10.1021/jo300735j

We studied the preparation and circular dichroism (CD) behavior of 2,6-pyridylene ethynylene octameric oligomer linked to a β-d-glucoside moiety with a C20-alkylene chain. The addition of Cu(OTf)₂ salt led to a remarkable enhancement of the first CD band of the oligomer, and an unexpected concentration and time dependency were observed. For example, when 1.0 × 10^-3 M of Cu(OTf)₂ was added to a 1,2-dichloroethane solution of the oligomer (5.0 × 10^-4 M, unit concentration), the CD band appeared in the positive at first and gradually inverted into the negative with time.

Full text of DOI:10.1021/jo300735j

Note
pubs.acs.org/joc
Concentration- and Time-Dependent Eccentric Changes in Circular
Dichroism of Saccharide-Linked Ethynylpyridine Oligomer with
Copper(II) Ions
Hajime Abe,* Yuki Ohishi, and Masahiko Inouye*
Graduate School of Pharmaceutical Sciences, University of Toyama, Toyama 930-0194, Japan
S
* Supporting Information
ABSTRACT: We studied the preparation and circular
dichroism (CD) behavior of 2,6-pyridylene ethynylene
octameric oligomer linked to a β-D-glucoside moiety with a
C20-alkylene chain. The addition of Cu(OTf)2 salt led to a
remarkable enhancement of the first CD band of the oligomer,
and an unexpected concentration and time dependency were
observed. For example, when 1.0 × 10−3 M of Cu(OTf)2 was
added to a 1,2-dichloroethane solution of the oligomer (5.0 ×
10−4 M, unit concentration), the CD band appeared in the
positive at first and gradually inverted into the negative with time.
host−guest interaction plays an important role in
A
supramolecular systems not only in the laboratory but
also in nature. Recently, various supramolecular polymers have
been prepared on the basis of such host−guest associations of
self-assembling motifs.1 Among such motifs, tandem hetero-
ditopic monomers, in which a host moiety H is covalently
linked with a guest moiety G as H−G, have been employed to
build ··H−G···H−G·· forms of “daisy chain” supramolecular
polymers by self-assembly. This type of supramolecular
polymer has been represented by that having hydrogen-
bonding motifs1a,c,d and pseudorotaxane motifs.1a,b,2,3 In some
cases, the switching of higher order structure is observed
between cyclic and linear daisy chains, as well as switching
among a monomeric self-complex, an oligomeric self-assembly,
and a polymeric self-assembly. Sometimes, such switching can
be controlled by concentration3a,c,f,g,i,m,n and additives.3c,p,q
These properties enable one to control the dynamics and
functions of the supramolecular polymers.
Figure 1. Tandem saccharide-linked ethynylpyridine oligomer 1 and
helix formation.
oligomer. Moreover, the CD spectra of the oligomer/
copper(II) complexes underwent unexpected and eccentric
changes depending on time as well as the concentrations of 2
and the copper salt.
The glucoside−C20-linked ethynylpyridine oligomer 2 was
synthesized as shown in Scheme 1. Condensation of 2,6-
dibromo-4-nitropyridine (3)6 and tetraethylene glycol mono-
methyl ether gave 4-pyridyl ether 4. Then, dibromide 4 was
subjected to two steps of the Sonogashira reaction with 2-
methyl-3-butyn-2-ol and tert-butyldimethylsilylacetylene
(TBSA) to give diyne 6, which liberated acetone to yield
monoprotected diethynylpyridine 7. Similar to the two steps of
the Sonogashira reaction, trimeric diiodide 84f was also
derivatized to monoprotected diethynyl trimer 11, which was
further subjected to the Sonogashira reaction and treatment
with excess diiodide 8 to afford a hexameric building block 12.
On the other hand, 20-bromoicosanyl glucoside tetra-O-acetate
(13) was obtained from glucose penta-O-acetate7 and 20-
bromoicosan-1-ol8 by Fischer synthesis. Williamson synthesis
of 13 with 6-iodopyridin-2-ol9 and the deprotection of the
acetyl groups gave iodopyridine−C20-linked glucoside 15.
Recently, our research group has been investigating synthetic
host molecules that recognize saccharide guests by hydrogen
bonding. Among them, the oligomeric and polymeric
“ethynylpyridine” hosts have been developed to incorporate a
saccharide guest within the helical higher order structures of the
hosts.4,5 We have previously reported a new class of
ethynylpyridine oligomers 1, covalently linked with a saccharide
moiety, which were found to efficiently form a helical structure
by intramolecular hydrogen bonding and showed strong
Cotton effects (Figure 1).5 Subsequently, we planned to
construct daisy-chain-type supramolecular polymers by using a
saccharide-linked ethynylpyridine oligomer 2, in which the host
and guest moieties are linked by a much longer alkylene chain
(C20) linker, as shown in Figure 2. During the course of this
study, the addition of copper(II) salt was found to enhance the
circular dichroism (CD) activity of the saccharide-linked
Received: April 13, 2012
Published: May 12, 2012
© 2012 American Chemical Society
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Note
Figure 2. Supramolecular polymer formed with glucoside−C20-linked ethynylpyridine 2.
Scheme 1. Preparation of the Glucoside−C20-Linked Ethynylpyridine Oligomer 2
a
a
4, 2-methyl-3-butyn-2-ol, PdCl2(PPh3)2, CuI, i-Pr2NH, THF; (b) tert-butyldimethylsilylacetylene, PdCl2(PPh3)2, CuI, i-Pr2NH, THF; (c) NaOH,
toluene; (d) 2-methyl-3-butyn-2-ol, Pd(PBu-t3)2, CuI, i-Pr2NH, THF; (e) tert-butyldimethylsilylacetylene, Pd(PBu-t3)2, CuI, i-Pr2NH, THF; (f) 8,
Pd(PBu-t3)2, CuI, i-Pr2NH, THF; (g) 6-iodo-2-pyridinol, K2CO3, acetone; (h) MeOH, Et3N, H2O; (i) 7, Pd(PBu-t3)2, CuI, K2CO3, i-Pr2NH, THF;
(j) TBAF, H2O, THF; (k) 12, Pd(PBu-t3)2, CuI, K2CO3, i-Pr2NH, THF.
Subsequently, one and six pyridine rings were introduced to 15
by stepwise Sonogashira reactions using 7 and 12 in order to
furnish the targeted oligomer 2.
The chiral higher order structures of 2 were studied by CD
measurements. A 1,2-dichloroethane (DCE) solution of 2 (5.0
× 10−4 M, unit concentration) showed a negative CD band
around 329 nm (Figure 3, orange line). This band was weak but
Expecting a similar effect, we treated the DCE solution of 2
with Cu(OTf)2 to stabilize its helical structure. When
Cu(OTf)2 (2.5 × 10−4 M, 0.5 equiv to unit concentration of
2) was added to the DCE solution of 2, a remarkable
enhancement of the first CD band was observed with red shift,
as shown in Figure 3 (deep blue line). This change in the CD
spectrum induced by Cu(OTf)2 addition resembled the one
observed in typical ethynylpyridine oligomers associated with
octyl glycosides in the presence of copper(II) salt.4a Therefore,
the stabilization of the chiral helical structure is also expected to
occur in the case of 2. On the other hand, an interesting time-
dependent change in CD was observed in this mixture. Just
after the addition of Cu(OTf)2, the [θ] value at 340 nm was
−2.4 × 104 deg cm2 dmol−1, and this negative CD band
intensified with time, as shown in Figure 3 (deep blue to light
blue lines). After 10 h, the CD band became steady, and the [θ]
value reached approximately twice of that at the start. This time
dependency could be due to the difference between the higher
order structures that are kinetically and thermodynamically
favored over the mixture of 2 and Cu(OTf)2. It would probably
take time for the mixture to achieve an equilibrium state.
To study the effect of copper salt in detail, CD measure-
ments were carried out for DCE solutions of 2 (5.0 × 10−4 M)
treated with various equivalents (0.5, 1.5, 2.0 equiv to unit
concentration of 2) of Cu(OTf)2. Contrary to the case of 0.5
equiv of Cu(OTf)2 (Figure 4A, blue line, see also Figure 3), the
addition of 2.0 equiv of Cu(OTf)2 induced the first positive CD
band at around 340 nm (Figure 4A, red line). The addition of
1.5 equiv of Cu(OTf)2 induced an intermediate CD spectrum
near zero (Figure 4A, purple line). It was suggested that helical
complexes of the opposite sense were kinetically formed
between 0.5 and 2.0 equiv of Cu(OTf)2. When enough time
had passed after the addition, all of the mixtures showed much
stronger negative CDs at around 340 nm. Thus, we observed
Figure 3. CD spectrum of 2 and the time-dependent CD change after
the addition of Cu(II) salt: (orange) before the addition of Cu(OTf)2;
(deep blue to light blue) after the addition of Cu(OTf)2, 0 to 10.5 h.
Conditions: 2 (6.3 × 10−5 M, unit concentration = 5.0 × 10−4 M),
Cu(OTf)2 (2.5 × 10−4 M), DCE, 25 °C. The path length is 1 mm.
typical, indicating the formation of chiral helical higher order
structure as our previous results.4,5 The intra- and intermo-
lecular host−guest association would be not so strong between
the ethynylpyridine and glucoside moieties of 2. Recently, our
group has found that the addition of copper(II) salt sometimes
improves the CD activity of ethynylpyridine oligomers.4a,b,10
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Note
Figure 4. (A) Concentration effect of Cu (OTf)2 on CD of 2/Cu(OTf)2 mixture. Conditions: 2 (6.3 × 10−5 M, unit concentration = 5.0 × 10−4 M),
Cu(OTf)2, DCE, 25 °C. (red) [Cu(OTf)2] = 1.0 × 10−3 M; (purple) [Cu(OTf)2] = 7.5 × 10−4 M; (blue) [Cu(OTf)2] = 2.5 × 10−4 M. Path length
=1 mm. CD spectra just after the addition of Cu(OTf)2. (B) Time-dependent change in the CD spectrum of 2 (6.3 × 10−5 M, unit concentration =
5.0 × 10−4 M)/Cu(OTf)2 (7.5 × 10−4 M) mixture (deep to light purple). (C) Time-dependent change in CD spectrum of 2 (6.3 × 10−5 M, unit
concentration = 5.0 × 10−4 M)/Cu(OTf)2 (1.0 × 10−3 M) mixture (deep to light red).
the enhancement of negative CD, the appearance of negative
CD, and the reversal of CD from positive to negative, as time
advanced from the addition of 0.5, 1.5, and 2.0 equiv of
Cu(OTf), respectively (Figures 3 and 4B,C). The thermody-
namically stable helical structures would be in the same sense in
all cases.
Next, the concentration dependency of 2 was studied. To
each DCE solution of 2 at 7.0 × 10−3 and 5.0 × 10−4 M (unit
concentration), we added 0.5 equiv of Cu(OTf)2 against the
unit concentration of 2. The first CD band was observed in the
positive at around 340 nm for the 7.0 × 10−3 M solution and in
the negative at around 340 nm for the 5.0 × 10−4 M solution
(Figure 5).
kinetically favored in higher concentrations. Intermolecular
complexation can be performed by two or more molecules of 2
with enough number of Cu(II) ions, potentially in a
supramolecular polymer form. As time advanced, all mixtures
fell into equilibrium states, in which the thermodynamically
stable helical structures are favored, and these structures could
be formed by intramolecular complexation, which is independ-
ent of concentrations. This hypothesis is summarized in
Scheme 2.
Scheme 2. Hypothetical Mechanism of Concentration- and
Time-Dependent CD Inversion
Figure 6 summarizes the types of time-dependent trans-
formation of the first CD band in the experiments as a function
of the concentrations of 2 and Cu(OTf)2. Blue, purple, and red
dots indicate negative-to-negative, zero-to-negative, and pos-
itive-to-negative transformations, respectively. The concentra-
tion dependency can be observed in the higher concentrations
of 2 and Cu(OTf)2, which exhibit the first positive CD band
kinetically, as mentioned above.
We performed additional experiments to understand how 2
and Cu(OTf)2 aggregate, but unfortunately, little positive data
could be obtained. In dynamic light-scattering (DLS) analyses,
the observed scattering light was too weak to determine the size
of the aggregate, suggesting that it was not that big. ESI-MS
measurements indicated the existence of up to trimeric
aggregate involving copper ions (Figure S4 in the Supporting
Information), though time dependency could not be
established. NMR experiments were carried out under various
conditions; however, no definite results were obtained because
of the strong broadening (Figure S5 in Supporting
Figure 5. Concentration effect of 2 on CD of 2/Cu(OTf)2 mixture.
Conditions: 2, Cu(OTf)2, DCE, 25 °C. (red) [2] = 8.8 × 10−4 M (unit
concentration = 7.0 × 10−3 M), [Cu(OTf)2] = 3.5 × 10−3 M, path
length = 0.1 mm; (blue) [2] = 6.3 × 10−5 M (unit concentration = 5.0
× 10−4 M); [Cu(OTf)2] = 2.5 × 10−4 M, path length =1 mm. CD
spectra just after Cu(OTf)2 addition.
When enough time had passed after the addition of
Cu(OTf)2, both mixtures showed much stronger negative CD
activities at around 340 nm, as well as in the cases of the above-
mentioned [Cu(OTf)2]-varied experiments (Figure 4). Thus,
the reversal of CD from positive to negative was observed in
the case of 7.0 × 10−3 M of 2 with 3.5 × 10−3 M of Cu(OTf)2.
These findings suggested that switching of the helical sense of
the kinetically formed complex occurred in a concentration-
dependent manner probably from inter- to intramolecular
complexation.3a,c,f,g,i,m,n The positive CD at around 340 nm
could be caused by intermolecular complexation, which is
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Note
(ESI-TOF) calcd for C12H17Br2NNaO4 (M + Na+) 421.9402, found
421.9386.
Triethylene Glycol-Derived 2-Bromo-6-(3-hydroxy-3-meth-
yl-1-butynyl)pyridine 5. To a mixture of 4 (15.0 g, 37.6 mmol),
PdCl2(PPh3)2 (1.05 g, 1.50 mmol), and 2-methyl-3-butyn-2-ol (3.16 g,
37.6 mmol) in i-Pr2NH (150 mL) and THF (150 mL) was added CuI
(0.14 g, 0.75 mmol) at 0 °C. The mixture was stirred for 3 h at room
temperature, and the resulting mixture was diluted with ether (200
mL) and filtered. The filtrate was concentrated by a rotary evaporator,
and the resulting residue was purified by silica gel column
chromatography (eluent: AcOEt/hexane = 2:1) to yield 5 (8.9 g,
1
68%) as a yellow oil: H NMR (CDCl3, 300 MHz) δ 6.98 (d, J = 2.1
Hz, 1H), 6.93 (d, J = 2.1 Hz, 1H), 4.17 (t, J = 4.5 Hz, 2H), 3.86 (t, J =
4.2 Hz, 2H), 3.71−3.64 (m, 6H), 3.57−3.54 (m, 2H), 3.38 (s, 3H),
2.61 (s, 1H), 1.61 (s, 6H); 13C NMR (CDCl3, 75 MHz) δ 165.6,
143.5, 142.0, 113.7, 113.4, 94.7, 80.2, 71.7, 70.8, 70.49, 70.45, 69.0,
68.0, 65.2, 58.9, 31.0; IR (neat) νmax 3407, 2980, 2879, 2233, 1582,
1540 cm−1; HRMS (ESI-TOF) calcd for C17H24BrNNaO5 (M + Na+)
424.0736, found 424.0747.
Figure 6. Graphical summary of the time dependencies of the CD
changes plotted as a function of the unit concentration of 2 and the
molar ratio of Cu(OTf)2 to the unit of 2: (red) positive-to-negative,
(purple) zero-to-negative, (blue) negative-to-negative CD changes.
Conditions: DCE, 25 °C. For typical CD changes, see Figures 3 and
4B,C.
Triethylene Glycol-Derived 2-(tert-Butyldimethylsilylethyn-
yl)-6-(3-hydroxy-3-methyl-1-butynyl)pyridine 6. To a mixture of
5 (8.84 g, 25.4 mmol), PdCl2(PPh3)2 (0.89 g, 1.3 mmol), and tert-
butyldimethylsilylacetylene (10.7 g, 76.3 mmol) in i-Pr2NH (50 mL)
and THF (50 mL) was added CuI (97 mg, 0.51 mmol) at 0 °C. The
mixture was stirred for 11 h at room temperature, the resulting mixture
was diluted with ether (100 mL) and filtered. The filtrate was
concentrated by a rotary evaporator, and the resulting residue was
purified by silica gel column chromatography (eluent: AcOEt/hexane
Information), probably caused by the coordination with
copper(II) ion at the nitrogen atoms as our previous report.4a
In summary, saccharide-linked ethynylpyridine oligomer 2,
which consists of β-D-glucopyranoside and octameric ethynyl-
pyridine moieties linked with a C20−alkylene linker, was
prepared. The CD of oligomer 2 was enhanced by the addition
of Cu(OTf)2, and the shape of the CD spectrum changed
depending on time and concentration. During the measure-
ments, which depended on the concentrations of 2 and
Cu(OTf)2, we observed an unexpected positive-to-negative
inversion of the CD band at around 340 nm with time in
mixtures with high concentrations of 2 and Cu(OTf)2. In
contrast, negative-to-negative CD enhancement was observed
in the case of low concentrations. We assumed that the positive
CD was due to the complex that was kinetically produced and
turned into a thermodynamically stable product with time.
1
= 3:2) to yield 6 (8.7 g, 75%) as a yellow oil: H NMR (CDCl3, 300
MHz) δ 6.94 (d, J = 2.1 Hz, 1H), 6.91 (d, J = 2.4 Hz, 1H), 4.17 (t, J =
4.2 Hz, 2H), 3.85 (t, J = 4.5 Hz, 2H), 3.72−3.63 (m, 6H), 3.56−3.53
(m, 2H), 3.38 (s, 3H), 2.58 (s, 1H), 1.61 (s, 6H), 0.99 (s, 9H), 0.18 (s,
6H); 13C NMR (CDCl3, 75 MHz) δ 164.6, 144.13, 144.10, 113.8,
113.1, 103.8, 93.6, 93.3, 81.1, 71.8, 70.9, 70.6, 70.5, 69.1, 67.7, 65.2,
59.0, 31.1, 26.2, 16.7, −4.7; IR (neat) νmax 3410, 2929, 2226, 2162,
1580, 1553 cm−1; HRMS (ESI-TOF) calcd for C25H39NNaO5Si (M +
Na+) 484.2495, found 484.2471.
Triethylene Glycol-Derived 2-(tert-Butyldimethylsilylethyn-
yl)-6-ethynylpyridine 7. To a suspension of pulverized NaOH (92
mg, 2.3 mmol) in toluene (43 mL) was added 6 (0.985 g, 2.13 mmol)
at room temperature. The mixture was refluxed for 30 min and
successively filtered and evaporated. The evaporated residue was
purified by silica gel column chromatography (eluent: AcOEt/hexane
= 1:1) to yield 7 (0.829 g, 96%) as a yellow oil: 1H NMR (CDCl3, 300
MHz) δ 6.97 (s, 2H), 4.18 (t, J = 4.5 Hz, 2H), 3.86 (t, J = 4.8 Hz, 2H),
3.72−3.63 (m, 6H), 3.55−3.53 (m, 2H), 3.38 (s, 3H), 3.09 (s, 1H),
0.99 (s, 9H), 0.18 (s, 6H); 13C NMR (CDCl3, 75 MHz) δ 164.7,
144.4, 143.4, 114.0, 113.8, 103.7, 93.5, 93.3, 82.3, 77.1, 71.9, 71.0, 70.7,
70.6, 69.2, 67.8, 59.1, 26.2, 16.8, −4.7; IR (neat) νmax 3235, 2951,
2928, 2885, 2858, 2165, 2109, 1580, 1554 cm−1; HRMS (ESI-TOF)
calcd for C22H33NNaO4Si (M + Na+) 426.2077, found 426.2090.
Triethylene Glycol-Derived 2-Bromo-6-(3-hydroxy-3-meth-
yl-1-butynyl)pyridine Trimer 9. To a mixture of glycol-derived
diiodo trimer 8 (1.05 g, 1.03 mmol), Pd(PPh3)4 (0.48 g, 0.0041
mmol), and 2-methyl-3-butyn-2-ol (0.26 g, 3.1 mmol) in i-Pr2NH (12
mL) and THF (12 mL) was added CuI (7.8 mg, 0.0041 mmol) at
room temperature. The mixture stirred for 6 h at room temperature.
The resulting mixture was diluted with ether (20 mL) and filtered. The
filtrate was concentrated by a rotary evaporator, and the resulting
residue was purified by silica gel column chromatography (eluent:
EXPERIMENTAL SECTION
■
General Methods. NMR spectra were recorded using tetrame-
thylsilane (TMS) as an internal reference. Melting points were not
corrected. THF was freshly distilled from sodium benzophenone ketyl
before use. 1,2-Dicholoroethane of anhydrous grade was used for the
spectroscopic analyses. 2,6-Dibromo-4-nitropyridine6 (3), triethylene
glycol-derived diiodo trimer4f 8, penta-O-acetyl-β-D-glucopyranose,7
20-bromoicosan-1-ol,8 and 6-iodo-2-pyridinol9 were prepared accord-
ing to the procedures in the literature.
Triethylene Glycol-Derived 2,6-Dibromopyridine 4. This
compound was prepared in a similar way to the case of diiodo
analogue.4f To a suspension of NaH (5.1 g, 0.13 mmol; commercial
60% dispersion was washed thoroughly with hexane prior to use) in
THF (330 mL) was slowly added triethylene glycol monomethyl ether
(17.4 g, 0.106 mol) at 0 °C, and subsequently 2,6-dibromo-4-
nitropyridine (3, 30 g, 0.11 mmol) was added to the mixture in one
portion at the same temperature. The reaction mixture was stirred for
1 h at 0 °C and additionally for 4 h at room temperature. The resulting
mixture was quenched with a saturated aqueous NH4Cl solution and
extracted with CH2Cl2 (300 mL × 3). The combined organic layer was
dried over MgSO4 and concentrated by a rotary evaporator. The
resulting syrup was subjected to silica gel column chromatography
(eluent; hexane/AcOEt = 1:1) to yield 4 (39 g, 92%) as a yellow oil:
1H NMR (CDCl3, 300 MHz) δ 7.02 (s, 2H), 4.20 (t, J = 4.2 Hz, 2H),
3.86 (t, J = 4.5 Hz, 2H), 3.71−3.63 (m, 6H), 3.56−3.53 (m, 2H), 3.37
(s, 3H); 13C NMR (CDCl3, 75 MHz) δ 166.4, 140.5, 113.5, 71.5, 70.6,
70.24, 70.21, 68.7, 68.2; IR (neat) νmax 2877, 1574, 1536 cm−1; HRMS
1
AcOEt/MeOH = 50:1) to yield 9 (0.29 g, 29%) as a brown oil: H
NMR (CDCl3, 300 MHz) δ 7.30 (d, J = 2.4 Hz, 2H), 7.16 (s, 2H),
7.14 (d, J = 2.1 Hz, 2H), 7.11 (d, J = 2.7 Hz, 2H), 4.22−4.16 (m, 6H),
3.91−3.85 (m, 6H), 3.76−3.64 (m, 18H), 3.58−3.54 (m, 6H), 3.38 (s,
9H), 2.68 (s, 1H), 1.63 (s, 6H); 13C NMR (CDCl3, 75 MHz) δ 164.9,
164.8, 164.5, 144.2, 143.7, 143.5, 143.4, 121.4, 117.5, 114.52, 114.46,
113.9, 113.8, 93.9, 88.0, 87.3, 87.0, 86.5, 80.9, 71.8, 70.9, 70.5, 69.1,
69.0, 68.0, 67.8, 65.2, 59.0, 31.1; IR (neat) νmax 3410, 2878, 2227,
1581, 1551, 1532 cm−1
C45H58IN3NaO13 (M + Na+) 998.2912, found 998.2894.
; HRMS (ESI−TOF) calcd for
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Note
Triethylene Glycol-Derived 2-(tert-Butyldimethylsilylethnyl)-
6-(3-hydroxy-3-methyl-1-butynyl)pyridine Trimer 10. To a
mixture of 9 (3.02 g, 3.09 mmol), Pd(PBu-t3)2 (79 mg, 0.16 mmol),
and tert-butyldimethylsilylacetylene (1.30 g, 9.28 mmol) in i-Pr2NH
(47 mL) and THF (47 mL) was added CuI (29 mg, 0.16 mmol) at
room temperature, and the mixture was stirred for 10 h at room
temperature. The resulting mixture was filtered, the filtrate was
concentrated by a rotary evaporator, and the resulting residue was
purified by silica gel column chromatography (eluent: AcOEt/MeOH
3.41 (t, J = 6.6 Hz, 2H), 2.09 (s, 3H), 2.04 (s, 3H), 2.03 (s, 3H), 2.01
(s, 3H), 1.90−1.81 (m, 2H), 1.44−1.40 (m, 2H), 1.36−1.18 (m,
32H); 13C NMR (CDCl3, 75 MHz) δ 170.5, 170.2, 169.2, 169.1,
100.8, 72.9, 71.7, 71.4, 70.3, 68.5, 62.0, 34.2, 32.9, 29.8, 29.7, 29.6,
29.5, 28.9, 28.3, 25.9, 20.9, 20.8; IR (KBr) νmax 2921, 2851, 1763,
1741, 1473 cm−1; HRMS (ESI-TOF) calcd for C34H59BrNaO10 (M +
Na+) 729.3189, found 729.3216.
2-Iodo-6-(20-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyloxy)-
icosanyl)pyridine 14. To a suspension of K2CO3 (1.96 g, 14.2
mmol) in acetone (20 mL) were added 13 (1.67 g, 2.36 mmol) and 6-
iodo-2-pyridinol (0.63 g, 2.8 mmol) subsequently at room temper-
ature. The reaction mixture was refluxed for 7 h, and the resulting
mixture was filtered. The filtrate was concentrated by a rotary
evaporator, and the resulting residue was purified by silica gel column
chromatography (eluent: AcOEt/hexane = 2:1) to yield 14 (1.72 g,
22%) as a colorless solid: mp 72−73 °C; 1H NMR (CDCl3, 300 MHz)
δ 7.29−7.26 (m, 1H), 7.19−7.14 (m, 1H), 6.68−6.65 (m, 1H), 5.24−
5.17 (m, 2H), 5.12−5.06 (m, 1H), 5.01−4.96 (m, 1H), 5.48 (d, J = 7.8
Hz, 1H), 4.30−4.22 (m, 3H), 4.16−4.11 (m, 1H), 3.91−3.83 (m, 1H),
3.66−3.50 (m, 1H), 3.50−3.43 (m, 1H), 2.09 (s, 3H), 2.04 (s, 3H),
2.03 (s, 3H), 2.01 (s, 3H), 1.78−1.69 (m, 2H), 1.59−1.20 (m, 34H);
13C NMR (CDCl3, 75 MHz) δ 170.5, 170.2, 169.2, 169.1, 163.2, 139.4,
1
= 200:1) to yield 10 (2.4 g, 79%) as a brown oil: H NMR (CDCl3,
300 MHz) δ 7.18 (s, 2H), 7.14 (d, J = 2.1 Hz, 2H), 7.01 (d, J = 2.4 Hz,
2H), 6.98 (d, J = 2.4 Hz, 2H), 4.24−4.18 (m, 6H), 3.91−3.86 (m,
6H), 3.75−3.62(m, 18H), 3.58−3.54 (m, 6H), 3.38 (s, 9H), 1.63 (s,
6H), 1.00 (s, 9H), 0.20 (s, 6H); 13C NMR (CDCl3, 75 MHz) δ 164.9,
164.8, 164.7, 144.3, 144.2, 143.7, 143.6, 143.4, 143.3, 114.6, 114.5,
114.4, 114.3, 113.9, 113.8, 113.7, 103.6, 94.0, 93.6, 87.5, 87.3, 87.1,
87.0, 80.9, 71.8, 70.9, 70.53, 70.50, 69.1, 68.0, 67.9, 67.8, 65.2, 59.0,
31.1, 26.1, 16.7, −4.7; IR (neat) νmax 3394, 3009, 2929, 2885, 2228,
1583, 1551 cm−1; HRMS (ESI-TOF) calcd for C53H73N3NaO13Si (M
+ Na+) 1010.4810, found 1010.4796.
Triethylene Glycol-Derived 2-(tert-Butyldimethylsilylethyn-
yl)-6-ethynylpyridine Trimer 11. To a suspension of pulverized
NaOH (92 mg, 2.3 mmol) in toluene (80 mL) was added 10 (2.67 g,
2.70 mmol) at room temperature. The mixture was refluxed for 30
min, and the resulting mixture was filtered. The filtrate was
concentrated by a rotary evaporator, and the resulting residue was
purified by silica gel column chromatography (eluent: AcOEt/MeOH
127.1, 113.6, 109.8, 100.8, 72.9, 71.7, 71.3, 70.3, 68.5, 66.9, 62.0, 29.8,
29.7, 29.6, 29.5, 29.4, 28.9, 26.1, 25.9, 20.9, 20.74, 20.71; IR (KBr) νmax
2918, 2850, 1755, 1581, 1551 cm−1; HRMS (ESI-TOF) calcd for
C39H62INNaO11 (M + Na+) 870.3265, found 870.3303.
2-(20-(β-D-Glucopyranosyloxy)icosanyl)-6-iodopyridine (15).
To a mixed solution of MeOH (30 mL), Et3N (6 mL), and water (6
mL) was added 14 (1.67 g, 2.01 mmol) at room temperature. The
reaction mixture was refluxed for 2 h. The resulting mixture was
concentrated by a rotary evaporator, and the resulting residue was
purified by silica gel column chromatography (eluent: CH2Cl2/MeOH
= 10:1) to yield 15 (1.27 g, 93%) as a colorless solid: mp 96−98 °C;
1H NMR (CDCl3/CD3OD = 1:1, 300 MHz) δ 7.32−7.30 (m, 1H),
7.25−7.20 (m, 1H), 6.72−6.69 (m, 1H), 4.28 (d, J = 7.5 Hz, 1H),
4.26−4.22 (m, 2H), 3.94−3.85 (m, 2H), 3.77−3.71 (m, 1H), 3.59−
3.51 (m, 1H), 3.42−3.21 (m, 4H), 1.80−1.71 (m, 2H), 1.68−1.59 (m,
2H), 1.48−1.20 (m, 32H); 13C NMR (CDCl3/CD3OD = 1:1, 75
MHz) δ 162.8, 139.2, 126.8, 112.9, 109.0, 102.4, 76.1, 75.6, 73.1, 69.8,
69.7, 66.4, 61.2, 29.22, 29.17, 29.11, 29.08, 28.9, 25.52, 25.49; IR
(KBr) νmax 3357, 2920, 2850, 1583, 1549 cm−1; HRMS (ESI-TOF)
calcd for C31H54INNaO7 (M + Na+) 702.2843, found 702.2828.
β-D-Glucoside-Linked TBS-Protected Dimer 16. To a mixture
of 7 (0.465 g, 1.15 mmol), 15 (0.623 g, 0.917 mmol), Pd(PBu-t3)2 (23
mg, 0.0046 mmol), i-Pr2NH (16 mL), and THF (16 mL) was added
CuI (8.9 mg, 0.0046 mmol) at room temperature. The mixture was
stirred for 5 h at room temperature, and then to the mixture was added
3-aminopropyl-functionalized silica gel (11.1 mg). After 1 h, the
mixture was filtered to remove the insoluble materials. The filtrate was
concentrated by a rotary evaporator and the resulting residue was
purified by a silica gel column chromatography (eluent: AcOEt/
1
= 200:1) to yield 11 (1.66 g, 66%) as a yellow oil: H NMR (CDCl3,
300 MHz) δ 7.16−7.11 (m, 4H), 7.04 (d, J = 2.4 Hz, 2H), 7.01 (d, J =
2.4 Hz, 2H), 4.21−4.18 (m, 6H), 3.91−3.86 (m, 6H), 3.75−3.64 (m,
18H), 3.58−3.54 (m, 6H), 3.39−3.38 (m, 9H), 3.12 (s, 1H), 1.00 (s,
9H), 0.20 (s, 6H); 13C NMR (CDCl3, 75 MHz) δ 164.9, 164.8, 144.5,
143.8, 143.6, 143.5, 121.4, 117.5, 114.6, 114.0, 113.8, 93.9, 88.0, 87.4,
87.0, 86.5, 80.9, 71.9, 71.0, 70.6, 69.2, 68.0, 67.9, 67.8, 59.1, 26.2, 16.8,
−4.6; IR (neat) νmax 3236, 2927, 2885, 2859, 2163, 2111, 1582, 1551
cm−1; HRMS (ESI−TOF) calcd for C50H67N3NaO12Si (M + Na+)
952.4392, found 952.4432.
Triethylene Glycol-Derived 2-Bromo-6-(3-hydroxy-3-meth-
yl-1-butynyl) Hexamer 12. To a mixture of 8 (5.05 g, 4.95 mmol),
11 (0.767 g, 8.25 mmol), and Pd(PBu-t3)2 (21.1 mg, 0.00413 mmol)
in i-Pr2NH (30 mL) and THF (30 mL) was added CuI (7.9 mg,
0.0041 mmol) at room temperature. The mixture stirred for 11 h at
room temperature, and the resulting mixture was filtered. The filtrate
was concentrated by a rotary evaporator, and the resulting residue was
purified by silica gel column chromatography (eluent: AcOEt/MeOH
1
= 25:1) to yield 12 (1.20 g, 82%) as a brown oil: H NMR (CDCl3,
300 MHz) δ 7.30 (d, J = 2.4 Hz, 2H) 7.28 (s, 1H), 7.18−7.17 (m,
7H), 7.15 (d, J = 2.4 Hz, 2H), 7.13 (d, J = 2.7 Hz, 2H), 7.01 (d, J = 2.4
Hz, 2H), 4.21−4.15 (m, 14H), 3.91−3.85 (m, 14H), 3.76−3.64 (m,
36H), 3.58−3.54 (m, 14H), 3.39 (s, 18H), 1.00 (s, 9H), 0.20 (s, 6H);
13C NMR (CDCl3, 75 MHz) δ 164.9, 164.7, 164.5, 144.4, 143.7, 143.6,
1
121.5, 117.5, 114.6, 113.8, 103.7, 93.6, 88.1, 87.3, 87.2, 87.0, 86.5, 71.9,
70.9, 70.6, 69.1, 68.0, 67.8, 59.0, 26.2, 16.7, −4.7; IR (neat) νmax 3009,
2928, 2883, 2226, 2163, 1582, 1550 cm−1; HRMS (ESI-TOF) calcd
for C90H117IN6NaO24Si (M + Na+) 1844.6862, found 1844.6882.
20-Bromoicosanyl 2,3,4,6-Tetra-O-acetyl-β-D-glucopyrano-
side (13). To a solution of penta-O-acetyl-β-D-glucopyranose (7.11
g, 18.2 mmol) and 20-bromoicosan-1-ol (5.5 g, 15 mmol) in CH2Cl2
(65 mL) was added BF3·Et2O (11.5 mL, 91.1 mmol) dropwise during
90 min at 0 °C. The reaction mixture was stirred for 32 h at 0 °C, and
the resulting mixture was poured into a mixture of ice and aqueous
NaHCO3 with being stirred. The organic layer was separated and
washed successively with additional water, saturated aqueous
NaHCO3, and brine. The organic layer was dried over Na2SO4 and
concentrated by a rotary evaporator. The resulting residue was purified
by silica gel column chromatography (eluent: AcOEt/hexane = 1:4) to
MeOH = 20:1) to yield 15 (0.66 g, 99%) as a brown oil: H NMR
(CDCl3, 300 MHz) δ 7.55−7.50 (m, 1H), 7.19−7.17 (m, 1H), 7.01
(d, J = 2.4 Hz, 1H), 6.99 (d, J = 2.4 Hz, 1H), 6.73−6.70 (m, 1H),
4.32−4.28 (m, 3H), 4.21−4.18 (m, 2H), 3.88−3.80 (m, 5H), 3.74−
3.50 (m, 11H), 3.44−3.28 (m, 5H), 1.80−1.70 (m, 2H), 1.68−1.54
(m, 2H), 1.48−1.20 (m, 32H), 1.00 (s, 9H), 0.19 (s, 6H); 13C NMR
(CDCl3, 75 MHz) δ 164.7, 163.6, 144.4, 144.0, 139.1, 138.3, 122.2,
114.1, 113.6, 111.9, 103.8, 102.7, 93.5, 88.1, 86.7, 76.3, 75.4, 73.3, 72.0,
70.9, 70.63, 70.58, 69.4, 69.2, 67.8, 66.4, 61.5, 59.0, 29.84, 29.80, 29.76,
29.7, 29.6, 29.1, 26.2, 25.9, 16.8, −4.7; IR (neat) νmax 3396, 3013,
2926, 2855, 1579, 1553 cm−1; HRMS (ESI−TOF) calcd for
C53H86N2NaO11Si (M + Na+) 977.5899, found 977.5922.
β-D-Glucoside-Linked Dimer 17. To a THF (28 mL) solution of
16 (0.585 g, 0.612 mmol) were added tetrabutylammonium fluoride
(TBAF, 1.0 M solution in THF, 0.92 mL, 0.92 mmol) and a few drops
of water. The reaction mixture was stirred for 30 min at room
temperature, and the resulting mixture was concentrated by a rotary
evaporator and the resulting residue was purified by silica gel column
chromatography (eluent: AcOEt/MeOH = 20:1) to yield 17 (0.49 g,
1
yield 13 (2.23 g, 22%) as a colorless solid: mp 84−86 °C; H NMR
(CDCl3, 300 MHz) δ 5.24−5.17 (m, 1H), 5.12−5.05 (m, 1H), 5.01−
4.95 (m, 1H), 4.49 (d, J = 7.8 Hz, 1H), 4.28−4.24 (m, 1H), 4.15−4.11
(m, 1H), 3.88−3.85 (m, 1H), 3.72−3.64 (m, 1H), 3.50−3.45 (m, 1H),
5213
dx.doi.org/10.1021/jo300735j | J. Org. Chem. 2012, 77, 5209−5214

The Journal of Organic Chemistry
Note
1
96%) as a brown oil: H NMR (CDCl3, 300 MHz) δ 7.57−7.51 (m,
Chem. Rev. 2009, 109, 5687−5754. (d) Brunsveld, L.; Folmer, B. J. B.;
Meijer, E. W.; Sijbesma, R. P. Chem. Rev. 2001, 101, 4071−4097.
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see: (a) Fang, L.; Olson, M. A.; Benítez, D.; Tkatchouk, E.; Goddard,
W. A., III; Stoddart, J. F. Chem. Soc. Rev. 2010, 39, 17−29. (b) Harada,
A.; Takashima, Y.; Yamaguchi, H. Chem. Soc. Rev. 2009, 38, 875−882.
(3) For recent examples for daisy-chain type supramolecules based
on pseudorotaxane structures, see: (a) Tomimasu, N.; Kanaya, A.;
Takashima, Y.; Yamaguchi, H.; Harada, A. J. Am. Chem. Soc. 2009, 131,
12339−12343. (b) Miyawaki, A.; Takashima, Y.; Yamaguchi, H.;
Harada, A. Tetrahedron 2008, 64, 8355−8361. (c) Deng, W.;
Yamaguchi, H.; Takashima, Y.; Harada, A. Chem.Asian J. 2008, 3,
687−695. (d) Deng, W.; Yamaguchi, H.; Takashima, Y.; Harada, A.
Angew. Chem., Int. Ed. 2007, 46, 5144−5147. (e) Miyawaki, A.;
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11419. (g) Harada, A.; Kawaguchi, Y.; Hoshino, T. J. Inclusion Phenom.
Macrocycl. Chem. 2001, 41, 115−121. (h) Hoshino, T.; Miyauchi, M.;
Kawaguchi, Y.; Yamaguchi, H.; Harada, A. J. Am. Chem. Soc. 2000, 122,
9876−9877. (i) Strutt, N. L.; Zhang, H.; Giesener, M. A.; Lei, J.;
Stoddart, J. F. Chem. Commun. 2012, 48, 1647−1649. (j) Rowan, S. J.;
Cantrill, S. J.; Stoddart, J. F.; White, A. J. P.; Williams, D. J. Org. Lett.
2000, 2, 759−762. (k) Ashton, P. R.; Parsons, I. W.; Raymo, F. M.;
Stoddart, J. F.; White, A. J. P.; Williams, D. J.; Wolf, R. Angew. Chem.,
Int. Ed. 1998, 37, 1913−1916. (l) Ashton, P. R.; Baxter, I.; Cantrill, S.
J.; Fyfe, M. C. T.; Glink, P. T.; Stoddart, J. F.; White, A. J. P.; Williams,
D. J. Angew. Chem., Int. Ed. 1998, 37, 1294−1297. (m) Zhang, Z.; Luo,
Y.; Chen, J.; Dong, S.; Yu, Y.; Ma, Z.; Huang, F. Angew. Chem., Int. Ed.
2011, 50, 1397−1401. (n) Wang, F.; Zhang, J.; Ding, X.; Dong, S.; Liu,
M.; Zheng, B.; Li, S.; Wu, L.; Yu, Y.; Gibson, H. W.; Huang, F. Angew.
Chem., Int. Ed. 2010, 49, 1090−1094. (o) Wang, F.; Han, C.; He, C.;
Zhou, Q.; Zhang, J.; Wang, C.; Li, N.; Huang, F. J. Am. Chem. Soc.
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Gattuso, G.; Notti, A.; Pappalardo, A.; Pappalardo, S.; Parisi, M. F.;
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47, 4504−4508. (r) Yamaguchi, N.; Nagvekar, D. S.; Gibson, H. W.
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1H), 7.20−7.17 (m, 1H), 7.13 (d, J = 1.8 Hz, 1H), 7.02 (d, J = 1.8 Hz,
1H), 6.74−6.71 (m, 1H), 4.32−4.28 (m, 3H), 4.22−4.19 (m, 2H),
3.88−3.80 (m, 5H), 3.74−3.50 (m, 11H), 3.44−3.28 (m, 5H), 3.15 (s,
1H), 1.81−1.71 (m, 2H), 1.68−1.54 (m, 2H), 1.48−1.20 (m, 32H);
13C NMR (CDCl3, 75 MHz) δ 164.9, 164.0, 163.7, 144.1, 143.5, 139.1,
138.3, 121.2, 114.1, 113.9, 112.0, 102.7, 88.3, 86.5, 82.2, 75.4, 73.5,
71.9, 71.0, 70.64 70.59, 69.7, 69.2, 67.9, 66.4, 59.1, 29.8, 29.6, 29.5,
29.1, 26.0; IR (neat) νmax 3393, 3305, 3019, 2926, 2854, 1582, 1555
cm−1; HRMS (ESI-TOF) calcd for C47H72N2NaO11 (M + Na+)
863.5034, found 863.4995.
β-D-Glucoside-Linked Octamer 2. To a mixture of 12 (1.14 g,
0.641 mmol), 17 (0.43 g, 0.51 mmol), and Pd(PBu-t3)2 (13 mg,
0.0026 mmol) in i-Pr2NH (60 mL) and THF (60 mL) was added CuI
(4.9 mg, 0.0026 mmol) at room temperature. The mixture was stirred
for 9 h at room temperature, and the resulting mixture was filtered off
to remove the insoluble materials. The filtrate was concentrated by a
rotary evaporator and the resulting residue was purified by silica gel
column chromatography (eluent: AcOEt/MeOH = 9:1) to yield 2
1
(0.79 g, 61%) as a brown oil: H NMR (CDCl3, 300 MHz) δ 7.58−
7.52 (m, 1H), 7.22−7.16 (m, 13H), 7.13 (d, J = 2.1 Hz, 1H), 7.01 (d, J
= 2.4 Hz, 1H), 6.75−6.72 (m, 1H), 4.34−4.30 (m, 3H), 4.26−4.18 (m,
14H), 3.94−3.86 (m, 17H), 3.76−3.55 (m, 59H), 3.49−3.31 (m,
23H), 1.82−1.73 (m, 2H), 1.50−1.19 (m, 34H); 13C NMR (CDCl3,
75 MHz) δ 165.0, 164.8, 163.6, 144.4, 144.1, 143.8, 143.7, 143.6,
139.0, 138.3, 121.2, 114.6, 114.2, 113.8, 112.0, 103.7, 102.8, 93.6, 88.4,
87.50, 87.45, 87.32, 87.27, 87.1, 86.5, 86.4, 75.5, 74.4, 73.8, 71.9, 70.9,
70.6, 69.1, 68.0, 67.8, 66.4, 59.1, 29.6, 29.4, 29.0, 26.2, 26.1, 26.0; IR
(neat) νmax 3422, 3012, 2927, 2857, 1584, 1551 cm−1; HRMS (ESI-
TOF) calcd for C137H188N8NaO35Si (M + Na+) 2556.2876, found
2556.2936
CD Experiments for Studying the Additive Effects of
Cu(OTf)2 and Time-Dependency. To prepare sample solution,
Cu(OTf)2 was added as DMSO solution (0.125 M) just before the
final dilution of a DCE solution of 2, and the resulting solution was
shaken for 1 min and then subjected to CD measurements. The
sample solution was kept in a cuvette with screw cap, and during the
intervals between the measurements, it was preserved in the dark at 25
°C.
(4) (a) Takashima, S.; Abe, H.; Inouye, M. Chem. Commun. 2012, 48,
3330−3332. (b) Takashima, S.; Abe, H.; Inouye, M. Chem. Commun.
2011, 47, 7455−7457. (c) Abe, H.; Takashima, S.; Yamamoto, T.;
Inouye, M. Chem. Commun. 2009, 2121−2123. (d) Abe, H.;
Machiguchi, H.; Matsumoto, S.; Inouye, M. J. Org. Chem. 2008, 73,
4650−4661. (e) Waki, M.; Abe, H.; Inouye, M. Angew. Chem., Int. Ed.
2007, 46, 3059−3061. (f) Waki, M.; Abe, H.; Inouye, M. Chem.Eur.
J. 2006, 12, 7639−7647. (g) Abe, H.; Masuda, N.; Waki, M.; Inouye,
M. J. Am. Chem. Soc. 2005, 127, 16189−16196. (h) Inouye, M.; Waki,
M.; Abe, H. J. Am. Chem. Soc. 2004, 126, 2022−2027.
ASSOCIATED CONTENT
■
S
* Supporting Information
UV−vis spectra of 2 and 2/Cu(OTf)2 mixtures, time-course
1
CD changes corresponding to Figure 5, H NMR and ESI-MS
spectra of 2/Cu(OTf)2 mixture, and H and 13C NMR spectra
1
for compounds 2, 4−7, and 9−17. This material is available
free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: abeh@pha.u-toyama.ac.jp, inouye@pha.u-toyama.ac.
■
(5) (a) Abe, H.; Murayama, D.; Kayamori, F.; Inouye, M.
Macromolecules 2008, 41, 6903−6909. (b) Abe, H.; Makida, H.;
Inouye, M. Tetrahedron 2012, 68, 4353−4361.
(6) Neumann, U.; Vogtle, F. Chem. Ber. 1989, 122, 589−591.
̈
jp.
(7) Lindhorst, T. K. Essentials of Carbohydrate Chemistry and
Biochemistry; Wiley-VCH: Weinheim, 2000.
Notes
The authors declare no competing financial interest.
(8) Jablonkai, I.; Oroszlan., P. Chem. Phys. Lipids 2005, 133, 103−
112.
(9) Curran, D. P.; Liu, H.; Josien, H.; Ko, S.-B. Tetrahedron 1996, 52,
11385−11404. 6-Iodo-2-pyridinol appears as its tautomer, 2(1H)-
pyridone, in this paper.
(10) See also for binding of saccharides with Cu(II) complexes:
(a) Striegler, S.; Dunaway, N. A.; Gichinga, M. G.; Barnett, J. D.;
Nelson, A. D. Inorg. Chem. 2010, 49, 2639−2648. (b) Striegler, S.;
Gichinga, M. G. Chem. Commun. 2008, 5930−5932. (c) Striegler, S.;
Dittel, M. Inorg. Chem. 2005, 44, 2728−2733. (d) Striegler, S.; Dittel,
M. J. Am. Chem. Soc. 2003, 125, 11518−11524. (e) Striegler, S.;
Tewes, E. Eur. J. Inorg. Chem. 2002, 487−495. (f) Striegler, S.
Tetrahedron 2001, 57, 2349−2354.
ACKNOWLEDGMENTS
■
We thank Prof. Kitano Hiromi (Graduate School of Science
and Engineering, University of Toyama) for DLS analyses and
helpful advices.
REFERENCES
■
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5214
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