Molecular recognition by a novel boronate-containing CTG derivative for hydroxyanthraquinones

Article abstract of DOI:10.1016/j.tet.2019.03.005

C₃-functionalized cyclotriguaiacylene (CTG) derivatives were employed in the development of highly selective recognition compounds due to their unique molecular structures. Here, a novel C₃-functionalized CTG containing boronate (PPB

Full text of DOI:10.1016/j.tet.2019.03.005

Accepted Manuscript
Molecular recognition by a novel boronate-containing CTG derivative for
hydroxyanthraquinones
Tsubasa Inoue, Takayo Moriuchi-Kawakami, Kentaro Kuda, Shota Matsubara, Keiichi
Fujimori, Toshiyuki Moriuchi
PII:
S0040-4020(19)30264-9
https://doi.org/10.1016/j.tet.2019.03.005
TET 30191
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 30 November 2018
Revised Date: 1 March 2019
Accepted Date: 5 March 2019
Please cite this article as: Inoue T, Moriuchi-Kawakami T, Kuda K, Matsubara S, Fujimori K, Moriuchi
T, Molecular recognition by a novel boronate-containing CTG derivative for hydroxyanthraquinones,
Tetrahedron (2019), doi: https://doi.org/10.1016/j.tet.2019.03.005.
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Molecular recognition by a novel boronate-
containing CTG derivative for
hydroxyanthraquinones
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Tsubasa Inoue, Takayo Moriuchi-Kawakami, Kentaro Kuda, Shota Matsubara, Keiichi Fujimori, and Toshiyuki
Moriuchi
Department of Applied Chemistry, Faculty of Engineering, Osaka Institute of Technology
Division of Molecular Materials Science, Graduate School of Science, Osaka City University

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Tetrahedron
journal homepage: www.elsevier.com
Molecular recognition by a novel boronate-containing CTG derivative for
hydroxyanthraquinones
Tsubasa INOUEa , Takayo MORIUCHI-KAWAKAMIa, , Kentaro Kudaa, Shota Matsubaraa , Keiichi
Fujimoria and Toshiyuki Moriuchib
aDepartment of Applied Chemistry, Faculty of Engineering, Osaka Institute of Technology, 5-16-1 Omiya, Asahi, Osaka 535-8585, Japan
bDivision of Molecular Materials Science, Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
C3-functionalized cyclotriguaiacylene (CTG) derivatives were employed in the development of
highly selective recognition compounds due to their unique molecular structures. Here, a novel
C3-functionalized CTG containing boronate (PPB-CTG) was synthesized and its molecular
recognition ability for hydroxyanthraquinones was investigated by fluorescence spectroscopy.
The addition of the synthesized PPB-CTG led to a large increase in the fluorescence intensity of
only alizarin and not 1-hydroxyanthraquinone, 2-hydroxyanthraquinone nor quinizarin. It was,
thus, suggested that the cyclotriveratrylene (CTV) structure plays an important role in the
recognition ability toward alizarin since the mono-phenyl boronate compound (m-TPBAP)
showed poor fluorescence properties toward alizarin. Moreover, it was found that the 1:1
mixture of PPB-CTG and alizarin was effective as a fluorescence-enhanced probe toward
fluoride ions.
Available online
Keywords:
CTG derivative
molecular recognition
fluorescence enhancement
alizarin
2009 Elsevier Ltd. All rights reserved
.
selectivity for fluoride ion
———
Corresponding author. Tel.: +81-6-6954-4279; fax: +81-6-6957-2135; e-mail: takayo.moriuchi@oit.ac.jp

2
Tetrahedron
1. Introduction
Fig. 1 CTG derivative PPB-CTG and phenyl boronic acid pinacol ester m-
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TPBAP.
Fig. 2 Hydroxyanthraquinones.
Fig. 3 Synthesis of PPB-CTG.
Fig. 4 Fluorescence spectra of PPB-CTG, alizarin and PPB-CTG:alizarin =
1:1 acetone solutions (5×10–6 M) (λex=483 nm).
Cyclotriveratrylene (CTV) is a bowl-shaped molecule in
which the cavity is suitable for the inclusion of ions and other
molecules.1 CTV’s capacity for the inclusion of fullerenes has
attracted much interest2,3 and various CTV compounds have thus
far been proposed.4 However, it is difficult to include small ions
and molecules through the shallow bowl-shape cavity of CTV.
Therefore, in order to include and recognize relatively small
molecules, the introduction of various substituents is necessary.
Cyclotriguaiacylene (CTG) is well-known as a precursor for
CTV compounds and has three OH groups which can easily be
replaced by substituents.4–6
O
OH
O
OH
O
O
O
OH
OH
OH
OH
O
O
O
alizarin
1-HQ
2-HQ
quinizarin
Boron compounds are widely used in research laboratories
and various industries since they are stable in water and air, easy
to handle, and have low toxicity.7 It has also become apparent
that phenyl boronic acid reacts with various sugars and catechols
to form boronate esters.8 Therefore, there has been much progress
in the development of sugar sensors with phenyl boronic acid
moieties.9 A CTV compound containing boronate was first
proposed in 200810 and it provided organogels and xerogel
through the inclusion of toluenes. Other boronate-containing
CTV compounds have also been reported by Yu et al.11
In this study, we have synthesized a novel C3-functinalized
CTG derivative containing boronate PPB-CTG (Fig. 1).
Moreover, the molecular recognition ability of PPB-CTG for
hydroxyanthraquinones (Fig. 2) was investigated by fluorescence
spectrometry.
Fig. 5 Absorption spectra obtained during the titration of alizarin (5×10–5
M) with PPB-CTG (from 2.5 to 100 equiv) in acetone.
2. Results and discussion
2.1. Synthesis
CTV compounds have C1 and C3 symmetry, and C3-
functionalized CTV compounds exhibit good discrimination for
ions and molecules due to its highly symmetrical molecular
structure which enables the favorable capture of a guest. The
synthesis of PPB-CTG was carried out using commercially
available vanillyl alcohol as the starting compound. The synthetic
scheme of PPB-CTG is illustrated in Fig. 3. C3-
cyclotriguaiacylene (CTG) was obtained by following a previously
published procedure.12 C3-tris(allyl)trimethoxycyclononene was
prepared by the trimerization of allyl vanillyl alcohol with 70%

3
perchloric acid in methanol. Next, C -CTG was obtained by the
reaction of C3-tris(allyl)trimethoxycyclononene with Pd/C and
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3
60% perchloric acid in ethanol-dioxane (1:2) solution.
Subsequently,
the
reaction
of
C3-CTG
with
m-
(bromomethyl)phenyl boronic acid pinacol ester in acetone gave
PPB-CTG in 79% isolated yield. The obtained PPB-CTG
1
(C63H75B3O12) was then characterized in detail by H NMR, 13C
NMR, FTIR and HRMS. These detailed data for PPB-CTG are
described in the Experimental Section.
2.2. Response for alizarin
Alizarin is a component derived from the root of a madder.13–
It is known to form a metal complex accompanied by color
15
changes and fluorescence quenching.16–21 Alizarin and its metal
complexes are an environmentally benign dye17 and are thus
among the most useful hydroxyanthraquinones. In this study, we
have focused on the discrimination of alizarin. Since catechol is a
part of alizarin and has been reported to react with phenyl
boronates,22–28 the possibility of detecting alizarin using PPB-
CTG which has a phenyl boronate site was considered.
Fig. 8 Fluorescence intensities of 1-HQ, 2-HQ and quinizarin in the absence
or presence of 1 equiv PPB-CTG (5×10–6 M acetone solutions) (λex = 404
nm): 1-HQ and 2-HQ at λem = 568 nm and quinizarin at λem = 535 nm.
The recognition ability of PPB-CTG for alizarin was
examined by measuring their fluorescence emission intensities.
Fig. 4 shows the fluorescence spectra (excitation wavelength:
λex=483 nm) of PPB-CTG, alizarin and PPB-CTG:alizarin = 1:1
mixture acetone solutions. It was shown that PPB-CTG was not
a fluorescent compound. Alizarin itself showed very week
fluorescence intensity. Surprisingly, the PPB-CTG:alizarin = 1:1
mixture indicated strong fluorescence emission at 566 nm. These
results demonstrated that PPB-CTG does, in fact, possess a
strong and selective recognition ability for alizarin.
2.3. Recognition mechanism
In order to investigate the mechanism behind the recognition
properties of PPB-CTG, an evaluation of the molecular
recognition abilities for alizarin of m-tolyl phenyl boronic acid
pinacol ester (m-TPBAP) (Fig. 1), which is a constituent unit of
PPB-CTG, was carried out by measurement of the fluorescence
emission intensities. Fig. 7 shows the fluorescence spectra of m-
TPBAP, alizarin and m-TPBAP:alizarin = 1:1 solutions. m-
TPBAP exhibited no fluorescence. However, the m-
The recognition property for alizarin was studied in further
detail. Fig. 5 shows the absorption spectra of alizarin (5.0×10–5
M) by the addition of PPB-CTG (2.5–100 equiv). The peak at
468 nm exhibited an increase while the peak at 403 nm exhibited
a decrease. Upon the gradual addition of PPB-CTG (2.5–100
equiv), isosbestic points were confirmed at 372 and 420 nm.
These results suggest the formation of an adduct between PPB-
CTG and alizarin. Moreover, Fig. 6 shows a change in the
measured fluorescence emission intensities in the distilled
solutions (2.5×10–6 M). Even when PPB-CTG was added in an
amount equal to or more than 75 equiv, a gradual increase in
fluorescence was confirmed at 567 nm.
TPBAP:alizarin
= 1:1 solution showed an increase in
fluorescence. It was thus assumed that PPB-CTG captures
alizarin with the phenyl boronate site in a similar manner as m-
TPBAP. The m-TPBAP:alizarin=3:1 solution displayed further
increase in the fluorescence. In this way, the excessive addition
of m-TPBAP against alizarin caused an increase in the
fluorescence. Nevertheless, the fluorescence of the PPB-
CTG:alizarin = 1:1 solution was 3.1 times larger than the m-
TPBAP:alizarin = 3:1 solution. It was thus demonstrated that
PPB-CTG has better recognition ability than even 3 equiv of m-
TPBAP.
Fig. 6 Fluorescence spectra obtained during the titration of alizarin (2.5×10–6
M) with PPB-CTG (from 0 to 100 equiv) in acetone (λex=420 nm). Inset:
titration curve of the fluorescence intensity at 567 nm as a function of [PPB-
CTG]/[alizarin].
The discrimination ability of PPB-CTG was investigated in
further detail by examining the recognition of PPB-CTG for 1-
hydroxyanthraquinone (1-HQ), 2-hydroxyanthraquinone (2-HQ)
and quinizarin as hydroxyanthraquinones. Fig. 8 shows the
fluorescence spectra for the solutions of 1-HQ, 2-HQ and
quinizarin in the absence or presence of 1 equiv of PPB-CTG. It
clearly indicates that no change was observed in the fluorescence
spectra before or after mixing. It was, in fact, found that PPB-
CTG discriminates the adjacent diol moiety.
PPB-CTG has a structural advantage for recognition and it is
assumed that this structure enables alizarin to be encapsulated in
a PPB-CTG molecule, facilitating the substitution reaction
between PPB-CTG and alizarin. When the Job’s plots were
determined by keeping the sum of the initial concentrations of
PPB-CTG and alizarin constant at 10 µM and changing the
molar ratio of alizarin (XA = [alizarin]/[alizarin]+[PPB-CTG])
from 0 to 1,29 the plots for the fluorescence intensity at 567 nm
versus the molar ratio of alizarin XA showed that the intensity
value is highest at a molar fraction of ca. 0.33, indicating that a
2:1 stoichiometry is most probable for the adducting mode
between PPB-CTG and alizarin (see ESI, Fig. S2). The probable
Fig. 7 Fluorescence spectra of alizarin, PPB-CTG:alizarin = 1:1, m-
TPBAP:alizarin = 1:1 and 3:1 acetone solutions (5×10–6 M) (λex=483 nm).

4
Tetrahedron
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mechanism for the adducting between the PPB-CTG and
alizarin is proposed as shown in Fig. 9. However, since the
isolation of the adduct between PPB-CTG and alizarin was
unsuccessful, the reaction system between PPB-CTG and
alizarin remained in equilibrium. On the other hand, no
substitution reaction with 1-HQ, 2-HQ or quinizarin occurred due
to the absence of adjacent diol moieties.
O
OH
OH
O
OMe
O
MeO
MeO
O
OMe
OMe
O
O
O
OMe
O
O
O
B
O
B
O
O
B
O
B
O
O
B
O
O
O
B
O
HO
Fig. 10 a) Fluorescence intensities in the absence or presence of 3 equiv.
various anions and b) changes in the fluorescence intensity at λem=566 nm
toward fluoride ions in the presence of other co-existing ions (PPB-
CTG:alizarin = 1:1 mixtures (acetone/methanol (9:1, v/v) solutions (5×10–6
M), λex=483 nm). The gray bars represent the intensity changes in the
presence of 3 equiv. of other anions. The red bars represent the intensity
changes by adding 3 equiv. of fluoride ions in the presence of 3 equiv. of
other anions.
O
O
OH
PPB-CTG
HO
OH
O
OMe
OMe
MeO
O
O
O
O
B
O
B
O
O
O
B
O
O
O
O
B
O
O
B
O
B
O
O
OMe
OMe
O
MeO
O
PPB-CTG+alizarin
Fig. 9 Proposed mechanism for the adducting between PPB-CTG and
alizarin.
2.4. Anion selectivity
Anion selectivity of the PPB-CTG:alizarin = 1:1 mixture was
investigated further.30–33 The examined anions were F–, Cl–, Br–,
I–, SCN–, OH– and AcO–. Fig. 10a shows the fluorescence spectra
of the PPB-CTG:alizarin = 1:1 mixture by adding 3 equiv of
various anions (potassium salts). Among the examined anions,
the fluorescence emission intensity significantly increased only
when the F– ion was added. The fluorescence intensity of the
PPB-CTG:alizarin = 1:1 mixture in the presence of the F– ions at
566 nm was ca. 2 times larger than that of the mixture in the
absence of anions. The separate addition of the F– ions to the
solutions of the PPB-CTG or alizarin alone showed no change in
their fluorescence intensities. The influence of the other co-
existing anions on the fluorescence emission of the PPB-
CTG:alizarin = 1:1 mixture was also researched. Competitive
experiments were carried out by adding 3 equiv. of the F– ions to
the solutions of the PPB-CTG:alizarin = 1:1 mixture in the
presence of 3 equiv. of each co-existing anions. Fig. 10b displays
the changes in the fluorescence intensities monitored at 566 nm.
As shown in Fig. 10b, even under treatment with the other co-
existing ions, the influence of the co-existing ions was slightly
observed and the fluorescence enhancement of the PPB-
CTG:alizarin = 1:1 mixture by the addition of F– ions could be
confirmed. This fluorescence enhancement by the addition of F–
ions is assumed to be the result of the acceleration of the
substitution reaction between PPB-CTG and alizarin led by the
coordination of the F– ions to the boronate moieties. Thus, the
probable mechanism for anion recognition can be proposed as
shown in Fig. 11.
Fig. 11 Proposed mechanism for anion recognition.
1
It was clearly demonstrated by the H NMR spectra that the F–
ions promote the substitution reaction between PPB-CTG and
alizarin (see ESI, Fig. S5). When the Job’s plots in the presence
of 3 equiv. of the F– ions were determined by keeping the sum of
the initial concentrations of PPB-CTG and alizarin constant at
10 µM and changing the molar ratio of alizarin (XA+F
=
[alizarin]/[alizarin]+[PPB-CTG]) from 0 to 1,29 the plots for the
fluorescence intensity at 567 nm versus the molar ratio of alizarin
XA+F showed that the intensity value is highest at a molar fraction
of ca. 0.5, indicating that a 1:1 stoichiometry is most probable for
the binding mode between PPB-CTG and alizarin (see ESI, Fig.
S4). Moreover, the UV-vis spectra confirmed that the F– ions
interacted with the 2-position OH group of alizarin since none of
the anions changed the UV-vis spectra of the PPB-CTG:1-HQ =
1:1 mixture (see ESI, Figs. S6 and S7). Moreover, only negligible
influence to the PPB-CTG:alizarin = 1:1 mixture by adding the
Cl–, Br– , I– and SCN– ions was observed in the UV-vis spectra.
These ions, therefore, induced no changes in the fluorescence
intensities. On the other hand, the UV-vis spectra indicated that
the OH– and AcO– ions strongly interacted with the 2-position
OH group of alizarin. Since the OH– and AcO– ions provided
generated only negligible changes in the fluorescence intensities,
it was assumed that their interaction with the 2-position OH
group was not involved in the acceleration of the substitution

5
reaction between PPB-CTG and alizarin. It was, thus, suggested
that the F– ions moderately interacted with not only the 2-position
OH group but the boronate moiety, resulting in the acceleration
of the substitution reaction between PPB-CTG and alizarin.31
spectra were run in KBr discs on a Shimazu FTIR-8600
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spectrometer. High-resolution mass (HRMS) spectra (positive
mode of FAB mass) were recorded on a JEOL JMS-700 mass
spectrometer. The UV-vis spectra were recorded on a Shimazu
UV-2450 spectrophotometer. The fluorescence emission spectra
were recorded on a Shimazu RF-5300PC(S) luminescence
spectrometer.
2.5. Binding properties
4.3. Syntheses of C3-functionalized CTG derivatives
In order to investigate the binding stoichiometry of PPB-CTG
with alizarin in the absence or presence of the F– ions, Job’s plots
for the absorbance were determined by keeping the sum of the
initial concentrations of PPB-CTG and alizarin constant at 100
A C3-functionalized CTG derivative containing boronate
(PPB-CTG) was prepared by the synthetic schemes shown in Fig.
3. A C3-cyclotriguaiacylene (CTG) was obtained by following a
previously published procedure.12 Next, the reaction of C3-
cyclotriguaiacylene with m-(bromomethyl)phenyl boronic acid
pinacol ester in acetone gave the desired C3-functionalized CTG
derivative containing a boronate moiety (PPB-CTG).
µM and changing the molar ratio of alizarin (X
=
[alizarin]/[alizarin]+[PPB-CTG]) from 0 to 1.29 In the absence of
the F– ions, the plots for the absorbance at 483 nm versus the
molar ratio of alizarin XA indicated that a 2:1 stoichiometry is
most probable for the binding mode between PPB-CTG and
alizarin (see ESI, Figs. S1 and S2). Based on Job’s plot
determination of the 2:1 binding stoichiometry, the calculated
stability constant (K) for the complex formation of PPB-CTG to
alizarin was 5.53×102 M–2.34 On the other hand, in the presence
of the F– ions, the plots for the absorbance at 525 nm versus the
molar ratio of alizarin XA+F indicated that a 1:1 stoichiometry is
most probable for the binding mode between PPB-CTG and
alizarin (see ESI, Figs. S3 and S4). Based on Job’s plot
determination of the 1:1 binding stoichiometry, the calculated K
in the presence of 3 equiv. of the F– ions was 2.76×105 M-1.34
These results are in accordance with our assumptions of the
binding behavior between PPB-CTG and alizarin (Fig. 9 and
Fig. 11).
The trimerization of allyl vanillyl alcohol (21.0 g, 109 mmol)
was carried out in methanol (200 mL) by the dropwise addition
of 70% perchloric acid (41 mL) at -3 ℃for 3.5 h. The mixture
was stirred overnight at room temperature, affording a C3-
tris(allyl)trimethoxycyclononene (8.15 g) in a 43% yield.
To an ethanol-dioxane (1:2) solution (130 mL) of C3-
tris(allyl)trimethoxycyclononene (2.12 g, 4.01 mmol), 60%
perchloric acid (0.4 mL) was added dropwise in the presence of
Palladium-activated carbon (Pd 5%) (1.34 g), and the mixture
was heated with stirring at 70 ℃ for 2 days. The filtrate was
washed with water, giving a crude product. Further purification
was carried out by washing thoroughly with diethyl ether,
resulting in C3-cyclotriguaiacylene (1.07 g) in a 65% yield.
Cyclotriguaiacylene (0.61 g, 1.5 mmol) and m-
(bromomethyl)phenyl boronic acid pinacol ester (1.43 g, 4.8
mmol) were refluxed for 2 days in 50 mL of acetone with
potassium carbonate (2.08 g, 15 mmol). After filtration, the
solvent was removed by concentration in vacuo. For purification,
the residue was washed with hexane and diethyl ether to produce
pinacoyl-3-methyl phenyl boronate CTG (1.25 g) in a 79% yield;
3. Conclusion
A novel C3-functionalized cyclotriguaiacylene containing
boronate, pinacolyl-3-methyl phenyl boronate CTG (PPB-CTG),
exhibited favorable and selective recognition ability for alizarin.
It was also found that an adjacent diol moiety is necessary for
such discrimination by PPB-CTG, and the diol moiety was
recognized by its phenyl boronate site. The recognition ability of
PPB-CTG was 3.1 times greater than that of m-TPBAP.
Moreover, even in the presence of the other co-existing examined
anions, the PPB-CTG:alizarin=1:1 mixture showed high ion
selectivity for fluoride ions among the various examined anions
(F−, Cl−, Br−, I−, SCN−, OH− and AcO−). The PPB-CTG:alizarin
= 1:1 mixture is thus considered an effective candidate for a
fluoride ion sensor.
1
white solid; mp, 108.5-109.0 ℃. H NMR (CDCl3): δ1.35 (36H,
s, CCH3), 3.42 (3H, d, J 13.8 Hz, Heq of CH2), 3.67 (9H, s, OMe),
4.66 (3H, d, J 13.8 Hz, Hax of CH2), 5.12 (6H, s, OCH2), 6.61
(3H, s, C6H2), 6.80 (3H, s, C6H2), 7.35 (3H, dd, J 7.8, 7.2 Hz,
C6H4), 7.54 (3H, d, J 7.8 Hz, C6H4), 7.73 (3H, d, J 7.2 Hz, C6H4),
3
7.84 (3H, s, C6H4). 13C NMR (CDCl3): δ 24.86 (d, J(13C11B) 9.2
Hz), 24.90, 36.41, 56.13, 71.54, 83.85, 113.30, 115.83, 128.15,
129.04, 129.91, 131.43, 132.36, 132.92, 134.20, 136.89, 147.01,
148.27. IR (KBr): 2978, 2832, 1512, 1358 cm-1. HRMS (FAB+):
m/z calcd. for C63H75B3O12, 1056.5538; found, [M+H]
1056.5553.
4. Experimental
4.4. UV-vis and fluorescence spectrometry
4.1. Reagents and chemicals
The UV-visible absorption spectra and fluorescence emission
spectra were recorded at room temperature. A 1 cm ×1 cm quartz
cuvette was used for spectroscopic analysis. The stock solutions
(1 mM) of PPB-CTG and hydroxyanthraquinones (alizarin, 1-
hydroxyanthraquinone, 2-hydroxyanthraquinone and quinizarin)
in acetone were prepared for UV-visible and fluorescence
spectroscopic analysis. A stock solution of PPB-CTG was
diluted to a final concentration of 50µM (for UV-visible
spectroscopic analysis) and 5 µM (for fluorescence spectroscopic
analysis) by mixing a stock solution of hydroxyanthraquinones.
In the same way, a stock solution (1 mM) of m-TPBAP in
acetone was prepared for fluorescence spectroscopic analysis and
diluted to a final concentration of 5 and 15 µM by mixing a stock
Commercially available organic reagents were used. Before
use, the organic solvents, i.e., acetone, methyl alcohol, ethyl
alcohol, and dioxane, were dehydrated by molecular sieve 4 ꢀ.
All reactions were carried out under dry nitrogen.
4.2. Apparatus
1
The H and 13C NMR spectra were recorded at 300 and 100
MHz, respectively. The NMR spectra of the samples were
examined in CDCl3 solutions at 25.0 ℃ on a Varian 300 MHz
NMR spectrometer (XL-300) for 1H NMR and a JEOL 400 MHz
NMR spectrometer (JNM-ECZ400S/L1) for 13C NMR. Chemical
shifts are given in δ (ppm) relative to the deuterated solvents (13C
NMR) or to TMS (1H NMR) as an internal standard. The IR
solution
of
alizarin.
An
acetone
solution
of
hydroxyanthraquinone was added to the solution of PPB-CTG

6
Tetrahedron
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that corresponded to 1 equiv of the hydroxyanthraquinones.
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High concentration of potassium salt solutions (1 mM) were
prepared with methanol. That is, a stock solution (1 mM,
acetone) of PPB-CTG was diluted to a final concentration of 5
µM (acetone:methanol = 9:1 solution) by mixing a stock solution
(1 mM, methanol) of inorganic potassium salts (KF, KCl, KBr,
KI, KSCN, KOH or AcOK). A methanol solution of inorganic
potassium salts was added to the solution of PPB-CTG that
corresponded to 3 equiv. of the inorganic anions. The excitation
wavelengths were 483 and 404 nm by fluorescence spectroscopic
analysis and the emission spectra from ca. 500 to 770 nm were
collected every 1 nm. The widths of the excitation and emission
slits were 5 nm. The obtained spectra are shown in Figs. 4–8, and
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19. Churchill MR, Keil KM, Bright FV, Pandey S, Baker GA, Keister
JB Inorg. Chem. 2000; 39:5807−5816.
A stock solution of PPB-CTG in acetone (1.0 mM) was
prepared for UV-vis spectrophotometric titration and diluted to a
final concentration of 50 µM by mixing a 1.0 mM stock solution
of alizarin in acetone. In the case of the addition of the F– ions, a
stock solution (1.0 mM, methanol) of KF was also added to a
stock solution of PPB-CTG that corresponded to 3 equiv. of the
F– ions. The acetone solution of alizarin was added to each
solution of PPB-CTG corresponding to 0−90 equiv. of alizarin.
The concentration dependence of the absorbance, A, at a fixed
wavelength was applied to determine the molar absorbance
coefficient ε of the PPB-CTG complex with alizarin. The
stability constants K for the complex formations were calculated
from the Job’s plot data. Stock solutions of PPB-CTG and of
alizarin in acetone (1.0 mM) were prepared for Job’s plot data.
Job’s plots for the absorbance were determined by keeping the
sum of the initial concentrations of PPB-CTG and alizarin
constant at 0.1 mM and changing the molar ratio of alizarin (X =
[alizarin]/[alizarin]+[PPB-CTG]) from 0 to 1. In the case of the
adding of the F– ions, KF was added to the stock solution of
PPB-CTG that corresponded to 3 equiv. of the F– ions. The
measured solutions were then prepared in acetone:methanol = 9:1
solutions. Job’s plots indicated that a 2:1 (in the absence of the F–
ions) and 1:1 (in the presence of the F– ions) complexes are
formed.
20. Lopez NR, Callejon MM, Guiraum PA Anal. Chim. Acta 1987;
192:119−124.
21. Feigl F, Caldas A Anal. Chim. Acta 1953; 8:339−343.
22. Wu X, Chen XX, Jiang YB Analyst 2017; 142:1403−1414.
23. Brooks WLA, Sumerlin BS Chem. Rev. 2016; 116:1375−1397.
24. Ellis GA, Palte MJ, Raines RT J. Am. Chem. Soc. 2012;
134:3631−3634.
25. Cakal C, Ferrance JP, Landers JP, Caglar P Anal. Chim. Acta
2011; 690:94−100.
26. Springsteen G, Wang B Tetrahedron 2002; 58:5291−5300.
27. Yan J, Springsteen G, Wang B Tetrahedron 2004;
60:11205−11209.
28. Gamoh K, Takatsuto S Anal. Chim. Acta 1989; 222:201−204.
29. Job, P Ann. Chim.Appl. 1928; 9:113−203.
30. Martínez-Aguirre MA, Otero DM, Álvarez-Hernández ML,
Torres-Blancas T, Dorazco-González A, Yatsimirsky AK
Heterocycl. Commun. 2017; 23:171−180.
31. Su ZM, Lin CX, Zhou YT, Xie LL, Yuan YF J. Organomet.
Chem. 2015; 788:17−26.
32. Maeda H, Bando Y, Shimomura K, Yamada I, Naito M,
Nobusawa K, Tsumatori H, Kawai T J. Am. Chem. Soc. 2011;
133:9266−9269.
33. Maeda H, Haketa Y, Nakanishi T J. Am. Chem. Soc. 2007;
129:13661−13674.
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Tetrahedron 2014; 70: 9805−9813.
References and notes
1. Collet A Tetrahedron 1987; 43:5725−5759.
2. Steed JW J.Am.Chem.Soc. 1994; 116:10346−10347.

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Molecular recognition by a novel boronate-
containing CTG derivative for
hydroxyanthraquinones
Leave this area blank for abstract info.
Tsubasa Inoue, Takayo Moriuchi-Kawakami, Kentaro Kuda, Shota Matsubara, Keiichi Fujimori, and Toshiyuki
Moriuchi
Department of Applied Chemistry, Faculty of Engineering, Osaka Institute of Technology
Division of Molecular Materials Science, Graduate School of Science, Osaka City University

1
ACCEPTED MANUSCRIPT
Tetrahedron
journal homepage: www.elsevier.com
Molecular recognition by a novel boronate-containing CTG derivative for
hydroxyanthraquinones
Tsubasa INOUEa , Takayo MORIUCHI-KAWAKAMIa, ∗ , Kentaro Kudaa, Shota Matsubaraa , Keiichi
Fujimoria and Toshiyuki Moriuchib
aDepartment of Applied Chemistry, Faculty of Engineering, Osaka Institute of Technology, 5-16-1 Omiya, Asahi, Osaka 535-8585, Japan
bDivision of Molecular Materials Science, Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
C3-functionalized cyclotriguaiacylene (CTG) derivatives were employed in the development of
highly selective recognition compounds due to their unique molecular structures. Here, a novel
C3-functionalized CTG containing boronate (PPB-CTG) was synthesized and its molecular
recognition ability for hydroxyanthraquinones was investigated by fluorescence spectroscopy.
The addition of the synthesized PPB-CTG led to a large increase in the fluorescence intensity of
only alizarin and not 1-hydroxyanthraquinone, 2-hydroxyanthraquinone nor quinizarin. It was,
thus, suggested that the cyclotriveratrylene (CTV) structure plays an important role in the
recognition ability toward alizarin since the mono-phenyl boronate compound (m-TPBAP)
showed poor fluorescence properties toward alizarin. Moreover, it was found that the 1:1 mixture
of PPB-CTG and alizarin was effective as a fluorescence-enhanced probe toward fluoride ions.
Available online
Keywords:
CTG derivative
molecular recognition
fluorescence enhancement
alizarin
2009 Elsevier Ltd. All rights reserved.
selectivity for fluoride ion
1. Introduction
the molecular recognition ability of PPB-CTG for
hydroxyanthraquinones (Fig. 2) was investigated by fluorescence
Cyclotriveratrylene (CTV) is a bowl-shaped molecule in which
the cavity is suitable for the inclusion of ions and other molecules.1
CTV’s capacity for the inclusion of fullerenes has attracted much
interest2,3 and various CTV compounds have thus far been
proposed.4 However, it is difficult to include small ions and
molecules through the shallow bowl-shape cavity of CTV.
Therefore, in order to include and recognize relatively small
molecules, the introduction of various substituents is necessary.
Cyclotriguaiacylene (CTG) is well-known as a precursor for CTV
compounds and has three OH groups which can easily be replaced
by substituents.4–6
spectrometry.
O
MeO
O
OMe
H
3C
O
O
OMe
O
O
O
B
B
O
B
O
O
B
m-TPBAP
O
PPB-CTG
Boron compounds are widely used in research laboratories and
various industries since they are stable in water and air, easy to
handle, and have low toxicity.7 It has also become apparent that
phenyl boronic acid reacts with various sugars and catechols to
form boronate esters.8 Therefore, there has been much progress in
the development of sugar sensors with phenyl boronic acid
moieties.9 A CTV compound containing boronate was first
proposed in 200810 and it provided organogels and xerogel through
the inclusion of toluenes. Other boronate-containing CTV
compounds have also been reported by Yu et al.11
Fig. 1 CTG derivative PPB-CTG and phenyl boronic acid pinacol ester m-
TPBAP.
O
OH
O
OH
O
O
OH
OH
OH
O
O
O
O
OH
alizarin
1-HQ
2-HQ
quinizarin
Fig. 2 Hydroxyanthraquinones.
In this study, we have synthesized a novel C3-functinalized
CTG derivative containing boronate PPB-CTG (Fig. 1). Moreover,
———
∗ Corresponding author. Tel.: +81-6-6954-4279; fax: +81-6-6957-2135; e-mail: takayo.moriuchi@oit.ac.jp

2
Tetrahedron
available vanillyl alcohol as the starting compound. The synthetic
ACCEPTED MANUSCRIPT
MeO
MeO
O
K2CO3
70% HClO4
OH
OH
scheme of PPB-CTG is illustrated in Fig. 3. C3-cyclotriguaiacylene
Br
+
HO
in Acetone
in Methanol
(CTG) was obtained by following a previously published procedure.12
C3-tris(allyl)trimethoxycyclononene was prepared by the
trimerization of allyl vanillyl alcohol with 70% perchloric acid in
methanol. Next, C3-CTG was obtained by the reaction of C3-
tris(allyl)trimethoxycyclononene with Pd/C and 60% perchloric
acid in ethanol-dioxane (1:2) solution. Subsequently, the reaction
of C3-CTG with m-(bromomethyl)phenyl boronic acid pinacol
ester in acetone gave PPB-CTG in 79% isolated yield. The
obtained PPB-CTG (C63H75B3O12) was then characterized in
60% HClO
4, Pd/C
O
MeO
OMe
O
OH
MeO
in Ethanol, Dioxane
O
OMe
OMe
OH
HO
OMe
Br
detail by H NMR, 13C NMR, FTIR and HRMS. These detailed
1
O
B
data for PPB-CTG are described in the Experimental Section.
O
O
MeO
OMe
O
O
K2CO3
OMe
2.2. Response for alizarin
O
B
in Acetone
O
Alizarin is a component derived from the root of a madder.13–15
It is known to form a metal complex accompanied by color
changes and fluorescence quenching.16–21 Alizarin and its metal
complexes are an environmentally benign dye17 and are thus
among the most useful hydroxyanthraquinones. In this study, we
have focused on the discrimination of alizarin. Since catechol is a
part of alizarin and has been reported to react with phenyl
boronates,22–28 the possibility of detecting alizarin using PPB-
CTG which has a phenyl boronate site was considered.
B
O
O
B
O
O
Fig. 3 Synthesis of PPB-CTG.
The recognition ability of PPB-CTG for alizarin was examined
by measuring their fluorescence emission intensities. Fig. 4 shows
the fluorescence spectra (excitation wavelength: λex=483 nm) of
PPB-CTG, alizarin and PPB-CTG:alizarin = 1:1 mixture acetone
solutions. It was shown that PPB-CTG was not a fluorescent
compound. Alizarin itself showed very week fluorescence
intensity. Surprisingly, the PPB-CTG:alizarin = 1:1 mixture
indicated strong fluorescence emission at 566 nm. These results
demonstrated that PPB-CTG does, in fact, possess a strong and
selective recognition ability for alizarin.
Fig. 4 Fluorescence spectra of PPB-CTG, alizarin and PPB-CTG:alizarin =
1:1 acetone solutions (5×10–6 M) (λex=483 nm).
The recognition property for alizarin was studied in further
detail. Fig. 5 shows the absorption spectra of alizarin (5.0×10–5 M)
by the addition of PPB-CTG (2.5–100 equiv). The peak at 468 nm
exhibited an increase while the peak at 403 nm exhibited a
decrease. Upon the gradual addition of PPB-CTG (2.5–100 equiv),
isosbestic points were confirmed at 372 and 420 nm. These results
suggest the formation of an adduct between PPB-CTG and
alizarin. Moreover, Fig. 6 shows a change in the measured
fluorescence emission intensities in the distilled solutions (2.5×10–
6 M). Even when PPB-CTG was added in an amount equal to or
more than 75 equiv, a gradual increase in fluorescence was
confirmed at 567 nm.
Fig. 5 Absorption spectra obtained during the titration of alizarin (5×10–5
M) with PPB-CTG (from 2.5 to 100 equiv) in acetone.
2. Results and discussion
2.1. Synthesis
CTV compounds have C1 and C3 symmetry, and C3-
functionalized CTV compounds exhibit good discrimination for
ions and molecules due to its highly symmetrical molecular
structure which enables the favorable capture of a guest. The
synthesis of PPB-CTG was carried out using commercially
Fig. 6 Fluorescence spectra obtained during the titration of alizarin (2.5×10–6
M) with PPB-CTG (from 0 to 100 equiv) in acetone (λex=420 nm). Inset:
titration curve of the fluorescence intensity at 567 nm as a function of [PPB-
CTG]/[alizarin].

3
fluorescence spectra for the solutions of 1-HQ, 2-HQ and
ACCEPTED MANUSCRIPT
quinizarin in the absence or presence of 1 equiv of PPB-CTG. It
clearly indicates that no change was observed in the fluorescence
spectra before or after mixing. It was, in fact, found that PPB-
CTG discriminates the adjacent diol moiety.
PPB-CTG has a structural advantage for recognition and it is
assumed that this structure enables alizarin to be encapsulated in a
PPB-CTG molecule, facilitating the substitution reaction between
PPB-CTG and alizarin. When the Job’s plots were determined by
keeping the sum of the initial concentrations of PPB-CTG and
alizarin constant at 10 µM and changing the molar ratio of PPB-
CTG alizarin (XCTGA = [PPB-CTG]/[PPB-CTG]+[alizarin]
[alizarin]/[alizarin]+[PPB-CTG]) from 0 to 1,29 the plots for the
fluorescence intensity at 567 nm versus the molar ratio of PPB-
CTG alizarin XCTGA showed that the intensity value is highest at a
molar fraction of ca. 0.67 0.33, indicating that a 2:1 stoichiometry
is most probable for the adducting mode between PPB-CTG and
alizarin (see ESI, Figs. S1 and S2). The probable mechanism for
the adducting between the PPB-CTG and alizarin is proposed as
shown in Fig. 9. However, since the isolation of the adduct
between PPB-CTG and alizarin was unsuccessful, the reaction
system between PPB-CTG and alizarin remained in equilibrium.
On the other hand, no substitution reaction with 1-HQ, 2-HQ or
quinizarin occurred due to the absence of adjacent diol moieties.
Fig. 7 Fluorescence spectra of alizarin, PPB-CTG:alizarin = 1:1, m-
TPBAP:alizarin = 1:1 and 3:1 acetone solutions (5×10–6 M) (λex=483 nm).
O
OH
OH
MeO
O
OMe
MeO
O
O
OMe
OMe
O
O
O
OMe
O
O
O
O
B
B
O
O
B
O
B
O
O
B
O
O
O
B
O
HO
O
O
OH
PPB-CTG
HO
OH
MeO
O
OMe
OMe
O
O
O
O
B
O
B
O
O
O
B
O
B
O
O
O
O
B
O
O
B
Fig. 8 Fluorescence intensities of 1-HQ, 2-HQ and quinizarin in the absence or
presence of 1 equiv PPB-CTG (5×10–6 M acetone solutions) (λex = 404 nm):
1-HQ and 2-HQ at λem = 568 nm and quinizarin at λem = 535 nm.
O
O
OMe
OMe
O
MeO
O
PPB-CTG+alizarin
2.3. Recognition mechanism
Fig. 9 Proposed mechanism for the adducting between PPB-CTG and
alizarin.
In order to investigate the mechanism behind the recognition
properties of PPB-CTG, an evaluation of the molecular
recognition abilities for alizarin of m-tolyl phenyl boronic acid
pinacol ester (m-TPBAP) (Fig. 1), which is a constituent unit of
PPB-CTG, was carried out by measurement of the fluorescence
emission intensities. Fig. 7 shows the fluorescence spectra of m-
TPBAP, alizarin and m-TPBAP:alizarin = 1:1 solutions. m-
TPBAP exhibited no fluorescence. However, the m-
TPBAP:alizarin = 1:1 solution showed an increase in fluorescence.
It was thus assumed that PPB-CTG captures alizarin with the
phenyl boronate site in a similar manner as m-TPBAP. The m-
TPBAP:alizarin=3:1 solution displayed further increase in the
fluorescence. In this way, the excessive addition of m-TPBAP
against alizarin caused an increase in the fluorescence.
Nevertheless, the fluorescence of the PPB-CTG:alizarin = 1:1
solution was 3.1 times larger than the m-TPBAP:alizarin = 3:1
solution. It was thus demonstrated that PPB-CTG has better
recognition ability than even 3 equiv of m-TPBAP.
2.4. Anion selectivity
Anion selectivity of the PPB-CTG:alizarin = 1:1 mixture was
investigated further.30–33 The examined anions were F–, Cl–, Br–, I–,
SCN–, OH– and AcO–. Fig. 10a shows the fluorescence spectra of
the PPB-CTG:alizarin = 1:1 mixture by adding 3 equiv of various
anions (potassium salts). Among the examined anions, the
fluorescence emission intensity significantly increased only when
the F– ion was added. The fluorescence intensity of the PPB-
CTG:alizarin = 1:1 mixture in the presence of the F– ions at 566
nm was ca. 2 times larger than that of the mixture in the absence
of anions. The separate addition of the F– ions to the solutions of
the PPB-CTG or alizarin alone showed no change in their
fluorescence intensities. The influence of the other co-existing
anions on the fluorescence emission of the PPB-CTG:alizarin =
1:1 mixture was also researched. Competitive experiments were
carried out by adding 3 equiv. of the F– ions to the solutions of the
PPB-CTG:alizarin = 1:1 mixture in the presence of 3 equiv. of
each co-existing anions. Fig. 10b displays the changes in the
fluorescence intensities monitored at 566 nm. As shown in Fig.
10b, even under treatment with the other co-existing ions, the
The discrimination ability of PPB-CTG was investigated in
further detail by examining the recognition of PPB-CTG for 1-
hydroxyanthraquinone (1-HQ), 2-hydroxyanthraquinone (2-HQ)
and quinizarin as hydroxyanthraquinones. Fig. 8 shows the

4
Tetrahedron
ACCEPTED MANUSCRIPT
influence of the co-existing ions was slightly observed and the
versus the molar ratio of PPB-CTG alizarin XCTGA+F showed that
fluorescence enhancement of the PPB-CTG:alizarin = 1:1 mixture
by the addition of F– ions could be confirmed. This fluorescence
enhancement by the addition of F– ions is assumed to be the result
of the acceleration of the substitution reaction between PPB-CTG
and alizarin led by the coordination of the F– ions to the boronate
moieties. Thus, the probable mechanism for anion recognition can
be proposed as shown in Fig. 11.
the intensity value is highest at a molar fraction of ca. 0.5,
indicating that a 1:1 stoichiometry is most probable for the binding
mode between PPB-CTG and alizarin (see ESI, Fig. S3 S4).
Moreover, the UV-vis spectra confirmed that the F– ions interacted
with the 2-position OH group of alizarin since none of the anions
changed the UV-vis spectra of the PPB-CTG:1-HQ = 1:1 mixture
(see ESI, Figs. S5 and S6 and S7). Moreover, only negligible
influence to the PPB-CTG:alizarin = 1:1 mixture by adding the
Cl–, Br– , I– and SCN– ions was observed in the UV-vis spectra.
These ions, therefore, induced no changes in the fluorescence
intensities. On the other hand, the UV-vis spectra indicated that
the OH– and AcO– ions strongly interacted with the 2-position OH
group of alizarin. Since the OH– and AcO– ions provided generated
only negligible changes in the fluorescence intensities, it was
assumed that their interaction with the 2-position OH group was
not involved in the acceleration of the substitution reaction
between PPB-CTG and alizarin. It was, thus, suggested that the
F– ions moderately interacted with not only the 2-position OH
group but the boronate moiety, resulting in the acceleration of the
substitution reaction between PPB-CTG and alizarin.31
2.5. Binding properties
In order to investigate the binding stoichiometry of PPB-CTG
with alizarin in the absence or presence of the F– ions, Job’s plots
for the absorbance were determined by keeping the sum of the
initial concentrations of PPB-CTG and alizarin constant at 100
Fig. 10 a) Fluorescence intensities in the absence or presence of 3 equiv.
various anions and b) changes in the fluorescence intensity at λem=566 nm
toward fluoride ions in the presence of other co-existing ions (PPB-
CTG:alizarin = 1:1 mixtures (acetone/methanol (9:1, v/v) solutions (5×10–6
M), λex=483 nm). The gray bars represent the intensity changes in the presence
of 3 equiv. of other anions. The red bars represent the intensity changes by
adding 3 equiv. of fluoride ions in the presence of 3 equiv. of other anions.
µM and changing the molar ratio of alizarin (X
=
[alizarin]/[alizarin]+[PPB-CTG]) from 0 to 1.29 In the absence of
the F– ions, the plots for the absorbance at 483 nm versus the molar
ratio of alizarin XA indicated that a 2:1 stoichiometry is most
probable for the binding mode between PPB-CTG and alizarin
(see ESI, Figs. S1 and S2). Based on Job’s plot determination of
the 2:1 binding stoichiometry, the calculated stability constant (K)
for the complex formation of PPB-CTG to alizarin was 5.53×102
M–2.34 On the other hand, in the presence of the F– ions, the plots
for the absorbance at 525 nm versus the molar ratio of alizarin XA+F
indicated that a 1:1 stoichiometry is most probable for the binding
mode between PPB-CTG and alizarin (see ESI, Figs. S3 and S4).
Based on Job’s plot determination of the 1:1 binding stoichiometry,
the calculated K in the presence of 3 equiv. of the F– ions was 2.76
×105 M-1.34 These results are in accordance with our assumptions
of the binding behavior between PPB-CTG and alizarin (Fig. 9
and Fig. 11).
3. Conclusion
A novel C3-functionalized cyclotriguaiacylene containing
boronate, pinacolyl-3-methyl phenyl boronate CTG (PPB-CTG),
exhibited favorable and selective recognition ability for alizarin. It
was also found that an adjacent diol moiety is necessary for such
discrimination by PPB-CTG, and the diol moiety was recognized
by its phenyl boronate site. The recognition ability of PPB-CTG
was 3.1 times greater than that of m-TPBAP. Moreover, even in
the presence of the other co-existing examined anions, the PPB-
CTG:alizarin=1:1 mixture showed high ion selectivity for fluoride
ions among the various examined anions (F−, Cl−, Br−, I−, SCN−,
OH− and AcO−). The PPB-CTG:alizarin = 1:1 mixture is thus
considered an effective candidate for a fluoride ion sensor.
Fig. 11 Proposed mechanism for anion recognition.
It was clearly demonstrated by the 1H NMR spectra that the F– ions
promote the substitution reaction between PPB-CTG and alizarin
(see ESI, Fig. S4 S5). When the Job’s plots in the presence of 3
equiv. of the F– ions were determined by keeping the sum of the
initial concentrations of PPB-CTG and alizarin constant at 10 µM
and changing the molar ratio of alizarin (XCTGA+F = [PPB-
CTG]/[PPB-CTG]+[alizarin] [alizarin]/[alizarin]+[PPB-CTG])
from 0 to 1,29 the plots for the fluorescence intensity at 567 nm

5
4. Experimental
The UV-visible absorption spectra and fluorescence emission
ACCEPTED MANUSCRIPT
spectra were recorded at room temperature. A 1 cm ×1 cm quartz
cuvette was used for spectroscopic analysis. The stock solutions (1
mM) of PPB-CTG and hydroxyanthraquinones (alizarin, 1-
hydroxyanthraquinone, 2-hydroxyanthraquinone and quinizarin)
in acetone were prepared for UV-visible and fluorescence
spectroscopic analysis. A stock solution of PPB-CTG was diluted
to a final concentration of 50µM (for UV-visible spectroscopic
analysis) and 5 µM (for fluorescence spectroscopic analysis) by
mixing a stock solution of hydroxyanthraquinones. In the same
way, a stock solution (1 mM) of m-TPBAP in acetone was
prepared for fluorescence spectroscopic analysis and diluted to a
final concentration of 5 and 15 µM by mixing a stock solution of
alizarin. An acetone solution of hydroxyanthraquinone was added
to the solution of PPB-CTG that corresponded to 1 equiv of the
hydroxyanthraquinones. High concentration of potassium salt
solutions (1 mM) were prepared with methanol. That is, a stock
solution (1 mM, acetone) of PPB-CTG was diluted to a final
concentration of 5 µM (acetone:methanol = 9:1 solution) by
mixing a stock solution (1 mM, methanol) of inorganic potassium
salts (KF, KCl, KBr, KI, KSCN, KOH or AcOK). A methanol
solution of inorganic potassium salts was added to the solution of
PPB-CTG that corresponded to 3 equiv. of the inorganic anions.
The excitation wavelengths were 483 and 404 nm by fluorescence
spectroscopic analysis and the emission spectra from ca. 500 to
770 nm were collected every 1 nm. The widths of the excitation
and emission slits were 5 nm. The obtained spectra are shown in
Figs. 4–98, and 10.
4.1. Reagents and chemicals
Commercially available organic reagents were used. Before use,
the organic solvents, i.e., acetone, methyl alcohol, ethyl alcohol,
and dioxane, were dehydrated by molecular sieve 4 Å . All
reactions were carried out under dry nitrogen.
4.2. Apparatus
1
The H and 13C NMR spectra were recorded at 300 and 100
MHz, respectively. The NMR spectra of the samples were
examined in CDCl3 solutions at 25.0 ℃ on a Varian 300 MHz
NMR spectrometer (XL-300) for 1H NMR and a JEOL 400 MHz
NMR spectrometer (JNM-ECZ400S/L1) for 13C NMR. Chemical
shifts are given in δ (ppm) relative to the deuterated solvents (13C
NMR) or to TMS (1H NMR) as an internal standard. The IR
spectra were run in KBr discs on a Shimazu FTIR-8600
spectrometer. High-resolution mass (HRMS) spectra (positive
mode of FAB mass) were recorded on a JEOL JMS-700 mass
spectrometer. The UV-vis spectra were recorded on a Shimazu
UV-2450 spectrophotometer. The fluorescence emission spectra
were recorded on a Shimazu RF-5300PC(S) luminescence
spectrometer.
4.3. Syntheses of C3-functionalized CTG derivatives
A C3-functionalized CTG derivative containing boronate (PPB-
CTG) was prepared by the synthetic schemes shown in Fig. 3. A
C3-cyclotriguaiacylene (CTG) was obtained by following a
previously published procedure.12 Next, the reaction of C3-
cyclotriguaiacylene with m-(bromomethyl)phenyl boronic acid
pinacol ester in acetone gave the desired C3-functionalized CTG
derivative containing a boronate moiety (PPB-CTG).
A stock solution of PPB-CTG in acetone (1.0 mM) was
prepared for UV-vis spectrophotometric titration and diluted to a
final concentration of 50 µM by mixing a 1.0 mM stock solution
of alizarin in acetone. In the case of the addition of the F– ions, a
stock solution (1.0 mM, methanol) of KF was also added to a stock
solution of PPB-CTG that corresponded to 3 equiv. of the F– ions.
The acetone solution of alizarin was added to each solution of
PPB-CTG corresponding to 0−90 equiv. of alizarin. The
concentration dependence of the absorbance, A, at a fixed
wavelength was applied to determine the molar absorbance
coefficient ε of the PPB-CTG complex with alizarin. The stability
constants K for the complex formations were calculated from the
Job’s plot data. Stock solutions of PPB-CTG and of alizarin in
acetone (1.0 mM) were prepared for Job’s plot data. Job’s plots for
the absorbance were determined by keeping the sum of the initial
concentrations of PPB-CTG and alizarin constant at 0.1 mM and
The trimerization of allyl vanillyl alcohol (21.0 g, 109 mmol)
was carried out in methanol (200 mL) by the dropwise addition of
70% perchloric acid (41 mL) at -3 ℃ for 3.5 h. The mixture was
stirred overnight at room temperature, affording
tris(allyl)trimethoxycyclononene (8.15 g) in a 43% yield.
a C3-
To an ethanol-dioxane (1:2) solution (130 mL) of C3-
tris(allyl)trimethoxycyclononene (2.12 g, 4.01 mmol), 60%
perchloric acid (0.4 mL) was added dropwise in the presence of
Pd/C Palladium-activated carbon (Pd 5%) (1.34 g), and the
mixture was heated with stirring at 70 ℃ for 2 days. The filtrate
was washed with water, giving a crude product. Further
purification was carried out by washing thoroughly with diethyl
ether, resulting in C3-cyclotriguaiacylene (1.07 g) in a 65% yield.
changing
the
molar
ratio
of
alizarin
(X
=
[alizarin]/[alizarin]+[PPB-CTG]) from 0 to 1. In the case of the
adding of the F– ions, KF was added to the stock solution of PPB-
CTG that corresponded to 3 equiv. of the F– ions. The measured
solutions were then prepared in acetone:methanol = 9:1 solutions.
Job’s plots indicated that a 2:1 (in the absence of the F– ions) and
1:1 (in the presence of the F– ions) complexes are formed.
Cyclotriguaiacylene (0.61 g, 1.5 mmol) and m-
(bromomethyl)phenyl boronic acid pinacol ester (1.43 g, 4.8
mmol) were refluxed for 2 days in 50 mL of acetone with
potassium carbonate (2.08 g, 15 mmol). After filtration, the solvent
was removed by concentration in vacuo. For purification, the
residue was washed with hexane and diethyl ether to produce
pinacoyl-3-methyl phenyl boronate CTG (1.25 g) in a 79% yield;
white solid; mp, 108.5-109.0 ℃. 1H NMR (CDCl3): δ1.35 (36H, s,
CCH3), 3.42 (3H, d, J 13.8 Hz, Heq of CH2), 3.67 (9H, s, OMe),
4.66 (3H, d, J 13.8 Hz, Hax of CH2), 5.12 (6H, s, OCH2), 6.61 (3H,
s, C6H2), 6.80 (3H, s, C6H2), 7.35 (3H, dd, J 7.8, 7.2 Hz, C6H4),
7.54 (3H, d, J 7.8 Hz, C6H4), 7.73 (3H, d, J 7.2 Hz, C6H4), 7.84
References and notes
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3
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24.90, 36.41, 56.13, 71.54, 83.85, 113.30, 115.83, 128.15, 129.04,
129.91, 131.43, 132.36, 132.92, 134.20, 136.89, 147.01, 148.27.
IR (KBr): 2978, 2832, 1512, 1358 cm-1. HRMS (FAB+): m/z calcd.
for C63H75B3O12, 1056.5538; found, [M+H] 1056.5553.
4.4. UV-vis and fluorescence spectrometry

6
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