Synthesis of a water-soluble macrocyclic anthracenophane and its size-selective molecular recognition

Article abstract of DOI:10.1007/s10847-016-0611-6

A tetraazacyclophane having two anthracene moieties (3) was synthesized by a reaction of nosyl-protected diaminodiphenylmethane with 9,10-bis(bromomethyl)anthracene, followed by removal of the protecting groups. Water-soluble anthraceophane (1) was prepar

Full text of DOI:10.1007/s10847-016-0611-6

J Incl Phenom Macrocycl Chem (2016) 85:121–126
DOI 10.1007/s10847-016-0611-6
ORIGINAL ARTICLE
Synthesis of a water-soluble macrocyclic anthracenophane and its
size-selective molecular recognition
Kazuhiro Nakamura1 Shuhei Kusano1 Osamu Hayashida1
•
•
Received: 16 March 2016 / Accepted: 7 April 2016 / Published online: 11 April 2016
Ó Springer Science+Business Media Dordrecht 2016
Abstract A tetraazacyclophane having two anthracene
moieties (3) was synthesized by a reaction of nosyl-protected
diaminodiphenylmethane with 9,10-bis(bromomethyl)an-
thracene, followed by removal of the protecting groups.
Water-soluble anthraceophane (1) was prepared by con-
densation of 3 with Fmoc-b-alanine, followed by removal
of the Fmoc groups. Host 1 showed size-selective guest
discrimination in aqueous media. Bis-ANS (4,40-dianilino-
1,10-binaphthyl-5,50-disulfonate) having a suitable molecu-
lar size was incorporated in the internal cavity of 1 with
binding constant (K) of 2.6 9 105 M-1, although slightly
smaller guests such as 1,8-ANS (8-anilinonaphthalene-1-
sulfonate) were not, as confirmed by fluorescence titration
experiments.
Especially, there is a lot of flexibility in the design of
cyclophanes by changing in shape and size of the macro-
cyclic skeleton. In addition, azacyclophanes [8] are
chemically modified by introducing various functional
groups [9] into the nitrogen atom. For instance, a
tetraaza[6.1.6.1]paracyclophane [10] containing diphenyl-
methane units, prepared by Koga et al., is frequently used
as a macrocyclic skeleton because durene, a guest mole-
cule, was accommodated in its cavity. Moreover, water-
soluble azacyclophanes based on the tetraaza[6.1.6.1]-
paracyclophane can provide a hydrophobic cavity for
inclusion of naphthalene derivatives as a guest molecule in
aqueous media [11]. For example, cationic water-soluble
cyclophane 2 [12] was found to form 1:1 host–guest
complexes with naphthalene derivatives such as 1,8-ANS
(8-anilinonaphthalene-1-sulfonate) [13] with binding con-
stant (K) in the order of 104 M-1 (Figs. 1, 2) [12]. On the
other hand, there is very little affinity for 2 to bind larger
guest molecules such as Bis-ANS (4,40-dianilino-1,10-bi-
naphthyl-5,50-disulfonic acid) (Fig. 2) [14]. Several
approaches have been applied so as to enhance the guest-
binding ability [15]. A possible approach for that is mul-
tiplying in the macrocycle; i.e., cyclophane oligomers
having several macrocyclic binding sites shows multivalent
effects in the guest-binding [16]. Alternative approach is
rational molecular design of macrocyclic hosts having a
suitable internal cavity for the binding of Bis-ANS
derivatives. On these grounds, we interested in the devel-
opment of macrocyclic compounds as a host for Bis-ANS
as a guest molecule. Bis-ANS has about two-times larger
molecular size than that of 1,8-ANS. Here, we designed
water-soluble anthracenophane (1) as a water-soluble
macrocyclic host having a nano-sized internal cavity
(Fig. 1). The host molecule was expected to provide an
internal cavity for the binding Bis-ANS and two anthracene
Keywords Anthracenophane Á Host–guest chemistry Á
Enhanced guest-binding
Introduction
Current topics of host–guest chemistry are development of
synthetic hosts that form host–guest complexes with tar-
geted organic compounds [1–3]. Recently, macrocyclic
hosts such as calixarenes [4], pillararenes [5], cyclophanes
[6], and the others [7] have been designed and developed.
Electronic supplementary material The online version of this
article (doi:10.1007/s10847-016-0611-6) contains supplementary
material, which is available to authorized users.
& Osamu Hayashida
hayashida@fukuoka-u.ac.jp
1
Department of Chemistry, Faculty of Science, Fukuoka
University, Nanakuma 8-19-1, Fukuoka 814-0180, Japan
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chloride to give 4 in a 75 % yield. N,N0,N00,N000-nosyl-pro-
tected tetraaza-anthracenophane 5 was obtained by a reac-
tion of 4 with 9,10-bis(bromomethyl)anthracene [18] in the
presence of K2CO3 in dry DMF in a 26 % yield. Then,
tetraazaanthracenophane 3 was synthesized by removal of
the protecting groups with benzenethiol. On the other hand,
the use of tosyl chloride in place of nosyl chloride afforded
the corresponding tosyl-protected tetraazaanthracenophane
in a manner similar to that applied synthesis of 5. However,
we have not been successful in obtaining 4 by acidic
hydrolysis of the tosyl-protected tetraazaanthracenophane,
due to an unfavorable decomposition side reaction. Inter-
estingly, it is possible to introduce various functional groups
into tetraazaanthracenophane 3 by condensation of the cor-
responding carboxylic acid derivatives. Actually, anthra-
cenophane having four side-chains 6 was obtained by
condensation of 3 with Fmoc-b-alanine in the presence of
1-ethyl-3(3-dimethyl-aminopropyl)carbodiimide
(EDC).
After removal of the Fmoc groups, anthracenophane having
four side-chains with a terminal amino group 1 was syn-
thesized. We fully characterized all the new compounds
unambiguously by elemental analysis as well as by MALDI-
1
TOF MS and H and 13C NMR spectroscopy (see ESM).
Fig. 1 Cationic azacyclophanes 1 and 2
Binding behavior of macrocyclic anthracenophane
with Bis-ANS
According to the computer-aided molecular CPK modeling
studies [19], macrocyclic anthracenophane 1 provides a
nano-sized hydrophobic cavity, which is constructed with
two 9,10-disubstituted anthracene derivatives and two
diaminodiphenylmethane moieties (see ESM). In addition,
four terminal ammonium moieties place at the exterior of
the macrocyclic skeleton, which contribute to water-solu-
bility. In actuality, anthracenophane 1 shows good solu-
bility in water (0.04 g/ml).
Fig. 2 Hydrophobic guests, 1,8-ANS and Bis-ANS
The guest-binding behavior of 1 was investigated by
using hydrophobic guests such as 1,8-ANS and Bis-ANS,
with regard to the size-selective molecular recognition
(Fig. 2). These guests are fluorescent probes for evaluation
of microenvironmental properties of the cyclophane cavity,
because their emission of both intensity and wavelength is
sensitive to change in microenvironmental polarity of the
surrounding medium [13]. As regards a characteristic
aspect of anthracenophane, 1 shows fluorescence emission
maxima at 403, 427, and 452 nm in aqueous HEPES (2-[4-
(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid) buffer
(0.01 M, pH 7.4, 0.15 M with NaCl). Interestingly, upon
addition of BisANS to the HEPES buffer containing 1, the
fluorescence intensity originating from 1 at 403, 427, and
452 nm was decreased accompanying an increase of the
fluorescence intensity of entrapped Bis-ANS molecules at
around 520 nm, as shown in Fig. 3a, indicating a formation
fluorophore moieties for sensing the guest molecules. In
this context, we report synthesis of 1 and its guest-binding
behavior with emphasis on the size-selective molecular
recognition.
Results and discussion
Synthesis of macrocyclic anthracenophane
We designed N,N0,N00,N000-tetrakis(3-aminopropanoyl)-
1,18,32,49-tetraaza[2.2.1.2.2.1]paracyclo-(9,10)anthraceno-
phane (3) as a water-soluble macrocyclic host having a
nano-sized internal cavity. Anthracenophane 3 was synthe-
sized according to Scheme 1. First, 4,40-diaminodiphenyl-
methane was protected by nosyl groups [17] using nosyl
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J Incl Phenom Macrocycl Chem (2016) 85:121–126
123
Scheme 1 Preparation of cationic anthracenophane 1
of host–guest complexes. Such quenching of the anthra-
cene fluorophores of 1 seems to be caused by the energy
transfer between the anthracene moieties of 1 and the
incorporated Bis-ANS molecules in the host–guest com-
plexes. With increasing concentrations of Bis-ANS, the
fluorescence intensity originating from 1 decreased,
showing a saturation behavior for the complexation of 1
and Bis-ANS (Fig. 3c). In addition, Job’s continuous
variation plot revealed that 1 bound Bis-ANS in a 1:1
molar ratio of host to guest (Fig. 4). The 1:1 host:guest
binding constant (K) was evaluated by Benesi-Hildebrand
analysis [20] applied to the fluorescence titration data
under the condition of large excess amount of Bis-ANS
(K = 2.6 9 105 M-1). Unfortunately, NMR measurements
for the complexation of 1 and Bis-ANS were unsuccessful
due to a limited solubility of the host–guest complexes at
higher concentration for NMR experiments. As regards
size-sensitive molecular recognition by the host, the slight
fluorescence spectral changes of 1 were observed upon the
addition of small guests such as 8-anilinonaphthalene-1-
sulfonate (1,8-ANS), as shown in Fig. 3b. In addition,
neither 6-anilinonaphthalene-2-sulfonate (2,6-ANS) nor
6-p-toluidinonaphthalene-2-sulfonate (TNS) showed the
change of fluorescence spectrum of 1 (see ESM). There-
fore, the K values of 1 with 1,8-ANS, 2,6-ANS, and TNS
were not determined due to the low affinity. These results
indicate that the binding affinity of 1 toward Bis-ANS was
relatively selective among the adopted guests. In addition,
the opposite is true, because host 2 [12] having a slightly
small macrocycle (vide supra) bound small guests such as
1,8-ANS, 2,6-ANS, and TNS with K values of 3.6 9 103,
1.4 9 104, and 1.5 9 104 M-1, respectively [12], whereas
the K value of 2 toward Bis-ANS was not determined
accurately due to weak fluorescence spectral changes (see
ESM).
Conclusions
We successfully synthesized cationic anthracenophane
having a nano-sized internal cavity 1. Anthracenophane 1
shows characteristic fluorescence emission maxima at 403,
427, and 452 nm that are capable of sensing the guest-
binding in aqueous HEPES. It was found that anthraceno-
phane 1 strongly bounds Bis-ANS with K of 2.6 9 105
M-1, while the fluorescence spectral changes of 1 were
almost negligible upon the addition of 1,8-ANS, 2,6-ANS,
and TNS, reflecting size-selective guest discrimination. On
the other hand, multivalency effect in macrocycles is
promising in order to enhance the K value with the guest,
because we have previously clarified that effective local
concentration in the macrocycles of cyclophane oligomers
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(dimer, trimer, tetramer, and pentamer) caused favorable
decrease in dissociation rate constants by surface plasmon
resonance measurements [16]. Currently, the development
of multivalent anthracenophane hosts is in progress along
this concept.
Experimental section
Materials
HEPES (2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic
acid) buffer (0.01 M, pH 7.4, 0.15 M with NaCl) was pur-
chased from GE Healthcare. The following compounds were
obtained from commercial sources and used without further
purification: 8-anilinonaphthalene-1-sulfonate (1,8-ANS)
and 4,40-dianilino-1,10-binaphthyl-5,50-disulfonate (Bis-
ANS) (both from Sigma-Aldrich Japan, Tokyo, Japan). A
cationic water-soluble cyclophane (2) was prepared after a
method reported previously [12].
General methods
Elemental analyses were recorded on a Yanako CHN
1
Corder MT-5. H and 13C spectra were taken on Bruker
AVANCE III 400 N spectrometer. Fluorescence spectra
were recorded on a Perkin Elmer LS55 spectrometer.
Fluorescence spectra, IR spectra, and MALDI TOF MS
were recorded on Perkin Elmer LS55, Perkin-Elmer spec-
trum one, and Bruker autoflex speed spectrometers,
respectively.
Nosyl-protected 4,40-diaminodiphenylmethane 4
A
solution of 4,40-diaminodiphenylmethane (5.0 g,
25.2 mmol) and triethylamine (TEA, 7.6 ml) in dry
dichloromethane (DCM, 30 ml) was added dropwise to a
solution of 2-nitrobenzenesulfonylchloride (NsCl, 17.4 g,
63.0 mmol) in dry DCM (10 ml) at 0 °C, and then the
mixture was stirred for 24 h at the same temperature. The
solvent was distilled off on a rotatory evaporator to give a
pale yellow solid. The solid was washed with hexane, dried
in vacuo at room temperature to give a pale yellow solid
(10.7 g, 75 %): 1H NMR (400 MHz, CDCl3, 298 K) d 3.85
(s, 2H), 7.03 (d, J = 8.5 Hz, 4H), 7.10 (d, J = 8.5 Hz,
4H), 7.21(m, 4H), 7.72 (m, 4H), and 7.87 (m, 4H). 13C
NMR (100 MHz, DMSO-d6, 298 K) d 39.8, 121.4, 125.0,
129.8, 130.3, 131.9, 132.9, 134.9, 135.0, 138.1, and 148.3.
IR 3299 cm-1 (N–H), 1531 cm-1 (N=O), 1349,
1163 cm-1 (SO2). Found: C, 50.94; H, 3.57; N, 9.26, Calcd
for C25H20N4O8S2ÁH2O: C, 51.19; H, 3.78; N, 9.55.
MALDI-TOF MS m/z 591 [M ? Na]?, where M shows
C25H20N4O8S2.
Fig. 3 Fluorescence spectra of 1 (0.05 lM) by adding incremental
amounts of Bis-ANS (a) and 1,8-ANS (b) in a HEPES buffer at
298 K. [Bis-ANS] = [1,8-ANS] = 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5,
4.0, 4.5, and 5.0 lM. The corresponding titration curves (c). Ex.
375 nm
Fig. 4 Job’s plot for host–guest complexation of 1 with Bis-ANS.
[1] ? [Bis-ANS] = 0.05 lM. Ex = 375 nm
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J Incl Phenom Macrocycl Chem (2016) 85:121–126
125
Nosyl-protected tetraazacyclophane 5
(Fmoc-b-Ala, 310 mg, 1.0 mmol) and 1-ethyl-3-(3-
dimethylaminopropyl)carbodiimide
(EDC)
(191 mg,
A solution of 4 (1.5 g, 2.6 mmol) and 9.10-bis(bro-
momethyl)anthracene (950 mg, 2.6 mmol) in dry DMF
(250 ml) was added dropwise over 4 h to a suspension of
potassium carbonate (1.8 g) in DMF (300 ml) at 90 °C,
resulting mixture was stirred for overnight at room tem-
perature. The solvent was evaporated to dryness under
reduced pressure. Distilled water (1000 ml) was added to
the residue. The resulting mixture was then stirred for 1 h
at room temperature, insoluble materials were collected by
filtration. The residue was chromatographed on a column
of silica gel (SiO2) with chloroform as eluent. The product
fraction was evaporated to dryness under reduced pressure
to give a pale yellow solid (510 mg, 26 %): 1H NMR
(400 MHz, CDCl3, 298 K) d 3.32 (s, 4 H), 5.84 (s, 8 H),
6.28 (d, J = 8.0 Hz, 8H), 6.58 (d, J = 8.0 Hz, 8H), 7.53
(m, 4H), 7.57 (dd, J = 10.1 Hz, 8H), 7.69 (m, 4H), 7.74
(m, 8H), and 8.32 (dd, J = 10.1 Hz, 8H). 13C NMR
(100 MHz, CDCl3, 298 K) d 42.4, 46.7, 123.9, 124.8,
125.9, 126.7, 130.6, 130.8, 131.4, 131.6, 132.2, 133.1,
133.7, 143.6, and 148.4. IR 3301 cm-1 (N–H), 1539 cm-1
(N=O), 1359, 1166 cm-1 (SO2). Found: C, 61.64; H, 4.05;
N, 6.81, Calcd for C82H60N8O16S4Á3H2O: C, 61.72; H,
4.17; N, 7.02.
1.0 mmol) in dry DCM (3 ml), and the mixture was stirred
for 24 h at room temperature. The solvent was distilled off
on a rotatory evaporator to give a pale yellow solid. The
residue was chromatographed on a column of silica gel
(SiO2) with chloroform as eluent. The product fraction was
evaporated to dryness under reduced pressure to give a pale
yellow solid (243 mg, 98 %): 1H NMR (400 MHz, CDCl3,
298 K) d 2.50 (t, J = 10.6 Hz, 8H), 3.36 (s, 4H), 3.56 (d,
J = 4.4 Hz, 8H), 4.27 (m, 4H), 4.39 (d, J = 7.1 Hz, 8H),
5.74 (s, 8H), 6.36 (d, J = 8.2 Hz, 8H), 6.57 (d, J = 8.2 Hz,
8H), 7.36 (t, J = 14.8 Hz, 8H), 7.44 (t, J = 14.8 Hz, 8H),
7.53 (dd, J = 10.1 Hz, 8H), 7.76 (d, J = 7.2 Hz, 8H), 7.80
(d, J = 7.2 Hz, 8H), and 8.08 (dd, J = 10.1 Hz, 8H). 13C
NMR (100 MHz, CDCl3, 298 K) d 35.6, 37.1, 42.2, 44.4,
47.3, 66.8, 120.0, 125.0, 125.0, 125.1, 125.4, 125.6, 127.1,
127.7, 129.3, 130.6, 136.1, 141.3, 143.7, 144.0, 156.4, and
171.8. IR 3300 cm-1 (N–H), 1634 cm-1 (C=O). Found: C,
76.91; H, 5.60; N, 5.28, Calcd for C130H108N8O12Á3H2O: C,
76.98; H, 5.67; N, 5.52. MALDI-TOF MS m/z 1996
[M ? Na]?, where M shows C130H108N8O12.
Cationic cyclophane having anthracene moieties 1
To a solution of 6 (610 mg, 0.309 mmol) in dry DCM
(2 ml) was added piperidine (1 ml). The mixture was
stirred for overnight at room temperature. The solvent was
distilled off on a rotatory evaporator to give a pale yellow
solid. The residue was chromatographed on a column of
silica gel (SiO2) with chloroform as eluent. The product
fraction was evaporated to dryness under reduced pressure
to give a pale yellow solid (312 mg, 93 %): 1H NMR
(400 MHz, CD3OD, 298 K) d 2.50 (t, J = 12.9 Hz, 8H),
3.00 (t, J = 12.9 Hz, 8H), 3.34 (s, 4H), 5.73 (s, 8H), 6.50
(d, J = 8.5 Hz, 8H), 6.70 (d, J = 8.5 Hz, 8H), 7.58 (dd,
J = 10.1 Hz, 8H), 8.16 (dd, J = 10.1 Hz, 8H). 13C NMR
(100 MHz, CD3OD, 298 K) d 35.7, 39.8, 40.6, 48.2, 128.8,
129.3, 130.7, 130.9, 132.9, 134.3, 139.4, 148.1, and 148.1.
IR 3300 cm-1 (N–H), 1633 cm-1 (C=O). Found: C, 70.23;
H, 7.02; N, 9.39, Calcd for C70H68N8O4Á6H2O: C, 70.45;
H, 6.76; N, 9.39. MALDI-TOF MS m/z 1107 [M ? Na]?,
where M shows C70H68N8O4.
Tetraazacyclophane having anthracene moieties 3
Potassium carbonate (550 mg) was added to a solution of 5
(510 mg, 0.33 mmol) in DMF (4 ml). Benzenethiol
(0.29 ml, 2.65 mmol) was added and the mixture was
stirred for 6 h at room temperature. The mixture was
extracted with dichloromethane (DCM, 100 ml) and
washed with saturated aqueous sodium chloride (50 ml).
The organic solution was obtained and dried over MgSO4
and evaporated in vacuo to give a pale yellow solid. The
residue was chromatographed on a column of silica gel
(SiO2) with chloroform:EtOAc (9:1 v/v) as eluent. The
product fraction was evaporated to dryness under reduced
1
pressure to give a pale yellow solid (250 mg, 94 %): H
NMR (400 MHz, CDCl3, 298 K) d 3.22 (s, 4H), 5.34 (s,
8H), 6.16 (s, 16H), 7.28 (m, 4H), 7.54 (dd, J = 10.1 Hz,
8H), and 8.30 (dd, J = 10.1 Hz, 8H). 13C NMR (100 MHz,
CD3OD, 298 K) d 41.6, 42.9, 118.5, 124.3, 125.0, 126.9,
130.2, 131.5, 131.5, and 144.3. IR 3371 cm-1 (N–H).
Found: C, 85.31; H, 6.15; N, 6.76, Calcd for C58H48N4-
H2O: C, 85.05; H, 6.15; N, 6.84. MALDI-TOF MS m/z 801
[M ? H]?, M shows C58H48N4.
Fluorescence titration experiments
By adding incremental amounts of guests such as Bis-ANS,
1,8-ANS, 2,6-ANS, and TNS to a HEPES buffer (0.01 M,
pH 7.4, 0.15 M with NaCl) containing 1 (0.05 lM) at
298 K, the each fluorescence spectra were recorded with
employing excitation wavelength at 375 nm. Aqueous
stock solution of 1 (0. 1 mM) was prepared after addition
of small amount of HCl aq. (4 eq.).
Cyclophane having four Fmoc-b-Ala residues 6
A solution of 3 (100 mg, 0.12 mmol) in dry DCM (2 ml)
was added dropwise to a solution of Fmoc-b-alanine
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Acknowledgments The present work is supported in part by MEXT
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