Synthesis and fluorescence studies of novel bis(azacrown ether) type chemosensors containing an acridinone unit

Article abstract of DOI:10.1016/j.tet.2010.02.076

Three new bis(azacrown ether)s containing an acridinone fluorescent signalling unit were prepared by reacting 9-chloro-4,5-bis(chloromethyl)acridine with monoazacrown ethers with different cavity sizes followed by a hydrolysis step. Their fluorescent char

Full text of DOI:10.1016/j.tet.2010.02.076

Tetrahedron 66 (2010) 2953–2960
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis and fluorescence studies of novel bis(azacrown ether) type
chemosensors containing an acridinone unit
a
b
c
d,
e
a,b,
*
´
´
´
´
´
´
´
´
Ildiko Moczar , Agnes Peragovics , Peter Baranyai , Klara Toth , Peter Huszthy
a Research Group for Alkaloid Chemistry of the Hungarian Academy of Sciences, PO Box 91, H-1521 Budapest, Hungary
b Department of Organic Chemistry and Technology, Budapest University of Technology and Economics, PO Box 91, H-1521 Budapest, Hungary
c Chemical Research Center, Hungarian Academy of Sciences, PO Box 17, H-1525 Budapest, Hungary
d Department of Inorganic and Analytical Chemistry, Budapest University of Technology and Economics, PO Box 91, H-1521 Budapest, Hungary
e Research Group of Technical Analytical Chemistry of the Hungarian Academy of Sciences, PO Box 91, H-1521 Budapest, Hungary
a r t i c l e i n f o
a b s t r a c t
Article history:
Three new bis(azacrown ether)s containing an acridinone fluorescent signalling unit were prepared by
reacting 9-chloro-4,5-bis(chloromethyl)acridine with monoazacrown ethers with different cavity sizes
followed by a hydrolysis step. Their fluorescent characteristics and the complexation properties of the
one containing two monoaza-18-crown-6 ether receptors towards selected metal ions were studied. The
operation of the latter ligand is based on the photoinduced electron transfer (PET) process, thus it shows
fluorescence enhancement in the presence of metal ions. Since the sensor molecule contains two re-
ceptor moieties, it is able to form two types of complex with 1:1 and 1:2 ligand to metal ion ratios, which
have different emission spectra. The reason for this spectral difference may be that the 1:1 complex is
a sandwich type one in which the acridinone unit can undergo structural changes.
Received 2 November 2009
Received in revised form
1 February 2010
Accepted 22 February 2010
Available online 25 February 2010
Keywords:
Azacrown ethers
Acridinones
Ó 2010 Elsevier Ltd. All rights reserved.
Fluorescent chemosensors
Metal ion recognition
Photoinduced electron transfer
Fluorescence spectroscopy
1. Introduction
several achiral and chiral mono(azacrown ether) type PET sensor
molecules containing an acridinone or an N-methylacridinone
Fluorescent chemosensors for metal ion analysis are of great
importance due to their potential applications in a wide range of
areas such as cell biology, biochemical analysis, medical diagnosis
and monitoring of contamination by heavy metals.1 Fluorescence
spectroscopy is an attractive tool owing to its sensitivity, selec-
tivity, versatility and relatively simple handling.2,3 Furthermore,
the concept of a photoinduced electron transfer (PET) system
for designing sensor molecules based on a fluorophore–spacer–
receptor structure is quite useful due to its capability of signalling
the recognition event very sensitively.4–8 PET type fluorescence
behaviour means that the free sensor molecule exhibits poor
fluorescence due to an efficient intramolecular quenching process
(PET) in the excited state, but shows large fluorescence enhance-
ment in the presence of cations without spectral shifts.4–8
Incorporating an acridinone moiety as a signalling unit into a
sensor molecule is very advantageous because of its strong fluo-
rescence9–11 and great photostability.12 Recently, we synthesized
fluorescent unit and studied their complexation properties to-
wards various cationic guests.13 Bis(azacrown ether) type ligands,
which have two receptor moieties within a molecule, can form
complexes of different structures, thus they exhibit particular
complexing abilities compared to the mono(azacrown ether) type
ones.14 Among the complex formation modes, the intramolecular
sandwich complex can be emphasized from our point of view, the
formation of which depends on the flexibility of the sensor mol-
ecule and the proximity of the crown ether rings.14 This complex
form can cause an enhanced selectivity towards large metal ions.14
Several reported sensor molecules match the bis(azacrown ether)
and the PET system concepts based on a fluorophore–short alky-
lene spacer–azacrown receptor structure using different signalling
units and their complexation properties were examined towards
metal ions and a,u
-alkanediammonium ions.15–21
Herein we report the synthesis of three new fluorescent bis(aza-
crown ether) type sensor molecules inwhich an acridinone signalling
unit was attached to two monoazacrown ethers through methylene
bridges. Their fluorescent characteristics and the complexation
properties of the one having two monoaza-18-crown-6 ether
* Corresponding author. Tel.: þ36 1 463 1071; fax: þ36 1 463 3297.
E-mail address: huszthy@mail.bme.hu (P. Huszthy).
URL: http://www.och.bme.hu/org
receptors towards selected metal ions (Liþ, Naþ, Kþ, Agþ, Mg2þ, Ca2þ
Zn2þ, Cu2þ, Pb2þ, Cd2þ) were studied in detail.
,
0040-4020/$ – see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.02.076

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2954
2. Results and discussion
9-chloro-4-chloromethylacridine [a mixture of dioxane/water
(19:1) at rt],13 the reaction did not take place. Furthermore, acridine
derivative 7 withstood the conditions of purification by column
chromatography, so it was suitable for the alkylation reactions.
Bis(hydroxymethyl)acridinone 10 was prepared in two different
ways (Scheme 2). On the one hand the synthesis was started from
oxoacridine dicarboxylic acid 8,22 which was treated with thionyl
chloride in dry methanol to obtain its dimethyl ester 9. The latter (9)
was reduced by sodium tetrahydridoborate and lithium bromide in
drydiethylene gylcoldimethyl etherwith amodificationofa reported
procedure23 to give bis(hydroxymethyl) derivative 10. On the
other hand, bis(bromomethyl)acridine 1124,25 was reacted with the
sodium salt of benzyl alcohol in dry THF to yield bis(benzyloxy-
methyl)acridine 12, which was oxidized to acridinone derivative 13
under an oxygen atmosphere in dry DMSO in the presence of a strong
base sodium hydride as reported26 for similar acridine derivatives. To
obtain bis(hydroxymethyl) derivative 10, the benzyl protecting
groups were removed by boiling bis(benzyloxymethyl)acridinone 13
in a mixture of dioxane/10% aqueous hydrochloric acid (1:1).
2.1. Synthesis
Bis(azacrown ether) chemosensors 1–3 containing an acridi-
none fluorescent signalling unit were synthesized by alkylation of
monoazacrown ethers 4–6 with bis(chloromethyl)-substituted
acridine derivative 7 followed by a hydrolysis step (Scheme 1).
The alkylation reactions were performed in dry THF in the presence
of triethylamine as a base and the obtained crude products were
hydrolized in a mixture of dioxane/5% aqueous hydrochloric acid
(9:1) to give the desired bis(azacrown ether)s (1–3) containing the
acridinone unit. The overall yields for these two steps are rather
low (10% for 1 and 2, 9% for 3), probably, because the electrophilic
carbon atom having a chlorine atom at position 9 of the trichloro
derivative 7 can also react with the monoazacrown ethers 4–6, and
also, because during the hydrolysis the benzylic carbon atom of the
protonated benzyl amine type intermediates can be attacked by the
nucleophilic water molecules, too.
Scheme 1. Preparation of bis(azacrown ether) type fluorescent chemosensors 1–3.
Acridine derivative 7 was prepared by treating bis(hydroxy-
methyl)acridinone 10 with thionyl chloride in dry chloroform in the
presence of a catalytic amount of DMF (Scheme 2). Acridine de-
rivative 7 was expected to be easily convertable to the appropriate
acridinone derivative [4,5-bis(chloromethyl)acridin-9(10H)-one]
according to our previous observations.13 However, applying the
same experimental conditions as used for the hydrolysis of the crude
Comparing the efficiency of the two synthetic routes for
bis(hydroxymethyl) derivative 10, it should be mentioned that the
two precursors (8 and 11) were prepared from commercially
available starting materials, 2-chloro-1,3-dimethylbenzene and
acridine in three steps and one step, respectively. Although the
overall yield of bis(hydroxymethyl) derivative 10 following the
pathway started from 2-chloro-1,3-dimethylbenzene was twice as
Scheme 2. Preparation of acridine derivative 7 and acridinone derivative 10.

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2955
much (10%) as that of 10 applying the route started from acridine
(5%), the former pathway consisted of six steps and the latter route
only four steps. The synthesis of acridinone dicarboxylic acid 8 was
started from 2-chloro-1,3-dimethylbenzene, which was oxidized
with potassium permanganate in water to obtain dicarboxylic acid
14.27 The latter (14) was reacted with anthranilic acid in the pres-
ence of potassium carbonate, copper powder and copper(I) oxide in
dry 2-ethoxyethanol using a modification of the reported pro-
cedure of an analogous compound26 to give tricarboxylic acid 15,22
which was then heated in polyphosphoric acid to yield oxoacridine
dicarboxylic acid 822 (Scheme 3). Bis(bromomethyl)acridine 11 was
prepared by treating acridine with bromomethyl methyl ether in
sulfuric acid as reported.24,25
values are larger (2.6–5.7 times) in dichloromethane than in
acetonitrile and methanol, but less significantly than in the case of
chemosensors 16–1813 (Table 1).
Table 1
Fluorescence quantum yields of 1–3 and 16–18 in different solvents
Compound
Ff (CH2Cl2)
Ff (MeCN)
Ff (MeOH)
1
2
3
16
17
18
0.12
0.10
0.10
0.60a
0.59a
0.55a
0.021
0.019
0.043
d
0.046
0.022
0.027
0.15a
d
0.070a
0.038a
d
These values were taken from literature.13
a
Scheme 3. Modified preparation of oxoacridine dicarboxylic acid 8.
2.2. Fluorescence characterization
2.3. Complexation studies on chemosensor 3
The fluorescence spectra of ligands 1–3 in dichloromethane
(Fig. 1) are very similar to those of their mono(azacrown ether)
analogues 16–18 (Fig. 2) both in dichloromethane and methanol.13
However, in acetonitrile and methanol new bands appeared in the
emission spectra of ligands 1–3 in the wavelength region above
450 nm (Fig. 1). The fluorescence quantum yields of chemosensors
1–3 were determined in these solvents and it can be stated that the
Since chemosensor 3 has a modular (fluorophore–methylene
spacer–azacrown receptor) structure, a PET type fluorescence
response was expected upon complexation with cationic guests
similar to our previous experiences in the case of its mono(azacrown
ether) analogue 18.13 We started our complexation studies in
methanol as in the case of ligand 18.13 In general, ligand 3 showed
fluorescence enhancement upon addition of various metal ions as
expected, but in most cases the positions of the emission spectra of
metal ion complexes were different from those of ligand 18 (Fig. 3).
Six of the ten metal ions studied (Kþ, Agþ, Mg2þ, Ca2þ, Zn2þ, Cd2þ
)
caused similar type emission spectral changes, namely a fluores-
cence increase upon complexation mainly in the wavelength region
above 450 nm (Fig. 4). However, in the case of Cu2þ, Pb2þ and Naþ,
after addition of an excess of the metal ion in question, a second
spectrum form appeared on the titration series of spectra (Fig. 5), the
position of which was similar to the emission spectra of ligand 18
Figure 1. Fluorescence emission spectra of 3 (20
lex¼370 nm.
mM) in MeOH, MeCN and CH2Cl2,
Figure 3. Fluorescence emission spectra of free ligand 18 (20
with Cu2þ (200 equiv) in MeOH, lex¼370 nm.
mM) and its complex
Figure 2. Reported mono(azacrown ether) analogues 16–18.

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2956
Figure 6. UV–vis titration series of spectra of 3 (20 m
M) on increasing addition of Agþ
(0–100 equiv) in MeOH. Inset: titration curve (0–200 equiv) at 447 nm, solid line:
fitted curve.
Figure 4. Fluorescence emission series of spectra of 3 (20 mM) on increasing addition
of Ca2þ (0–400 equiv) in MeOH, lex¼370 nm. Inset: titration curve (0–400 equiv) at
458 nm, solid line: fitted curve.
All of the fluorescence spectral changes were evaluated
using global nonlinear regression analysis by means of the
SPECFIT/32Ô program and the stability constants of metal
ion–ligand complexes were determined (Table 2). In the latter
cases (Cu2þ, Pb2þ and Naþ), the best fits were obtained when we
assumed two complex forms with 1:1 and 1:2 ligand to metal ion
ratios, whereas in the other cases the spectra could be fitted
satisfactorily using only one species with 1:1 stoichiometry. It is
noteworthy to mention that the log b1 value of complex 3–Agþ
determined from the UV–vis titration series of spectra (4.08) was
in good agreement with that obtained from the emission changes
(3.85, Table 2).
Table 2
Stability constants for metal ion complexes of 3 in MeOH and MeCNa
MeOH
MeCN
log b1
log b2
log b1
log b2
Liþ
db
db
7.02
d
3.86
4.97
5.06
4.71
6.78
7.78
5.31
dc
5.79
8.28
7.35
7.99
13.12
11.70
7.75
dc
Naþ
Kþ
4.77
4.14
2.88
2.66
3.13
2.94
4.36
3.85
5.21
Mg2þ
Ca2þ
Zn2þ
Cd2þ
Cu2þ
Agþ
Pb2þ
d
d
d
d
5.77
d
4.15
7.12
6.53
13.46
7.79
a
The values b1 and b2 denote the overall equilibrium constants of the 1:1 and 1:2
stoichiometric complexes, respectively.
b
No complexation could be observed.
Complexation took place, but the emission spectral changes could not be fitted
c
satisfactorily.
The presence of both 1:1 and 1:2 complex forms during the ti-
tration experiments with metal ions was more pronounced in
acetonitrile than in methanol. In acetonitrile, the two spectrum
forms mentioned above appeared on the emission series of spectra
in all cases (Fig. 7). Thus, we had to consider both 1:1 and 1:2
stoichiometric complexes to obtain the best fit of the fluorescence
spectra in order to determine the complex stability constants (Table
2). The absorption spectrum in acetonitrile was also unchanged
upon complexation. The difference between the complexation be-
haviour of ligand 3 in the presence of metal ions in the two sol-
vents, methanol and acetonitrile, is demonstrated in the case of
Ca2þ (Figs. 4 and 7).
Figure 5. Fluorescence emission series of spectra of 3 (20 mM) on increasing addition
of Cu2þ (A: 0–60 equiv, B: 60–400 equiv) in MeOH, lex¼370 nm. Insets: titration curves
(A: 0–60 equiv at 458 nm, B: 0–400 equiv at 421 and 458 nm), solid lines: fitted curves.
and its metal ion complexes (Fig. 3). The absorption spectrum
remained essentially unchanged upon titration of ligand 3 with
metal ions in almost all cases, which is typical for PET type sensor
molecules, the only exception was the effect of Agþ (Fig. 6).

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2957
spectrum was unchanged upon complexation (with the only ex-
ception of Agþ), these structural changes could take place only in
the excited singlet state. A confirmation of the deprotonation of the
acridinone NH in the assumed sandwich complex may be provided
by the fact that the emission spectrum of the latter was very similar
to that of the deprotonated form of ligand 3 in the presence of
a large excess of Me4NOH (Fig. 8). Either the tautomerism or the
deprotonation of the acridinone unit could promote the partici-
pation of the nitrogen atom of the latter in the complexation pro-
cess with a metal ion or vice versa.
Figure 8. Fluorescence emission series of spectra of 3 (20
of Me4NOH (0–3000 equiv) in MeOH, lex¼370 nm.
mM) on increasing addition
In general, it can be stated about the complexation ability of
ligand 3 that it formed stronger complexes in acetonitrile than in
methanol (Table 2) and the presence of the 1:2 stoichiometric
complex during the titration experiments was much more pro-
nounced in the former solvent as discussed earlier (Figs. 4 and 7,
Table 2). Comparing the effects of various metal ions in methanol,
in the presence of 4 equiv of them, the largest fluorescence en-
hancements were caused by Cu2þ, Pb2þ and Agþ (Fig. 9), but in
Figure 7. Fluorescence emission series of spectra of 3 (20 mM) on increasing addition
of Ca2þ (A: 0–0.4 equiv, B: 0.4–100 equiv) in MeCN, lex¼370 nm. Inset: titration curves
(0–100 equiv) at 413 and 465 nm, solid lines: fitted curves.
The fluorescence behaviour of chemosensor 3 upon complexa-
tion with metal ions significantly differs from its mono(azacrown
ether) analogue 18.13 While ligand 18 showed only emission in-
crease upon complexation without spectral shifts,13 in the case of
ligand 3, spectral shifts were also observed in the presence of cat-
ions besides the fluorescence enhancement, which is untypical in
the case of PET sensor molecules. Based on our observations
mentioned above, we can explain this behaviour as follows. The
spectrum shown in the presence of a larger excess of metal ion (e.g.,
at 100 equiv of Ca2þ in acetonitrile, Fig. 7B) belongs to the 1:2
stoichiometric complex in which the two crown ethers bind two
metal ions independently from each other. This can be confirmed
by that the position and shape of the spectrum were similar to
those of the spectrum of ligand 18 in its complexed form (Fig. 3).
The other spectrum, which arose at the beginning of a titration
process (e.g., at 0–60 equiv of Cu2þ in methanol, Fig. 5A) can be
attributed to the presence of the 1:1 stoichiometric complex. We
assume that it is a sandwich type complex in which the two crown
ethers bind one metal ion. The presence of a simple 1:1 complex in
which one crown ether ring binds one cation and the other crown
cavity remains unbound can be excluded, since the position and
shape of the spectrum were different from those of the 1:2 com-
plex. The difference in the spectra of 1:1 and 1:2 complexes of li-
gand 3 can be explained by that the acridinone unit undergoes
structural changes in the sandwich complex. The latter changes can
be attributed to the acridinone–9-hydroxyacridine tautomerism28
or the deprotonation of the acridinone NH.29 Since the absorption
larger excesses the other metal ions (Naþ, Kþ, Mg2þ, Ca2þ, Zn2þ
,
Cd2þ) also induced significant changes. In the case of ligand 18, only
Cu2þ, Pb2þ and Kþ caused considerable fluorescence enhancement
Figure 9. Fluorescence enhancement of 3 (20 mM) in the presence of 4 equiv of various
metal ions (Cu2þ, Pb2þ, Agþ and the others in order of increasing fluorescence in-
tensity: Liþ, Naþ, Mg2þ, Ca2þ, Kþ, Cd2þ, Zn2þ) in MeOH, lex¼370 nm.

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2958
in 400-fold excess.13 This means that ligand 3 formed stronger
complexes with the metal ions studied as compared to its mono-
(azacrown ether) analogue 18, probably due to the presence of two
receptor moieties in the same molecule, but no sufficient selectivity
between the metal ions examined could be observed. Furthermore,
the spectral shifts and simultaneous presence of the two complex
forms upon complexation made it difficult to compare these fluo-
rescence changes with each other, thereby it cannot be susceptible
for sensing a metal ion in a wider concentration range.
grade THF stored under argon was used as purchased. All other
solvents were dried and purified according to well-established
methods.30 Evaporations were carried out under reduced pres-
sure. Ratios of solvents are given in volumes (v/v).
UV–vis spectra were taken on an UNICAM UV4-100 spectro-
photometer controlled by VISION 3.4 software (ATI UNICAM,
Cambridge, UK). Fluorescence spectra were recorded on a Perkin–
Elmer LS 50B luminescent spectrometer supplied with an FL Win-
Lab 3.0Ô software (Perkin–Elmer Corp., USA). Both the emission
and excitation spectra were corrected by the spectrometer soft-
ware. Quartz cuvettes with path length of 1 cm were used. Fluo-
rescence quantum yields were determined relative to quinine
sulfate (Ff¼0.546 in 0.5 M H2SO4).2 Spectrophotometric titrations
were carried out according to the literature.31,32 Perchlorate salts of
the metal cations were used in general with the exception of AgNO3
and KSCN. All of metal ion salts were of analytical grade. The sta-
bility constants were determined by global nonlinear regression
analysis using SPECFIT/32Ô program.
3. Conclusion
The synthesis and characterization of three new bis(azacrown
ether)s containing an acridinone fluorescent signalling unit and
their unreported precursors have been performed. The key in-
termediate of the fluorescent unit [bis(hydroxymethyl) derivative
10] was prepared in two different ways. Comparing the efficiency of
them, the overall yield of bis(hydroxymethyl) derivative 10 fol-
lowing the pathway started from 2-chloro-1,3-dimethylbenzene
was twice as much (10%) as that of 10 applying the route started
from acridine (5%), although the former pathway consisted of six
steps and the latter route only four steps. The complexation prop-
erties of the chemosensor containing two monoaza-18-crown-6
ether receptors (3) towards selected metal ions (Liþ, Naþ, Kþ, Agþ,
Mg2þ, Ca2þ, Zn2þ, Cu2þ, Pb2þ, Cd2þ) were studied in detail. Based on
its structure, it was expected to show PET type fluorescence re-
sponse upon complexation with metal ions, namely a fluorescence
increase without spectral shifts. However, besides the fluorescence
enhancement in the presence of cationic guests, spectral shifts
were also observed due to the formation of two types of complex
with 1:1 and 1:2 ligand to metal ion ratios, which have different
emission spectra. The reason for this spectral difference can be that
the 1:1 complex is proposed to be a sandwich type one in which the
acridinone unit undergoes structural changes. These structural
changes could be either the deprotonation or tautomerism of the
acridinone unit. The spectra of the complexes of ligand 3 with 1:2
stoichiometry were similar to those of the complexes of mono-
(azacrown ether) analogue 18. Because of the ability of ligand 3 to
form two types of complex having different emission spectra and
stability constants, it is complicated to compare the fluorescence
intensity changes upon complexation with metal ions and to define
selectivity, thereby it would be difficult to use it as a selective
sensor molecule. However, these observations allowed us to get
a deeper insight into the complexation process, which can con-
tribute to the future design of more selective sensor molecules
suitable for practical applications.
4.2. General procedure for the synthesis of crown ethers 1–3
A solution of monoazacrown ether 4 (543 mg, 3.1 mmol) or 5
(680 mg, 3.1 mmol) or 6 (816 mg, 3.1 mmol), acridine derivative 7
(404 mg,1.3 mmol) and triethylamine (1.1 mL, 7.8 mmol) in dry THF
(6 mL) was stirred under Ar at reflux for 2 days. The volatile com-
pounds were evaporated and the residue was stirred in a mixture of
freshly distilled dioxane/5% aqueous HCl solution (9:1, 20 mL) at
60 ꢀC for a day. The volatile materials were removed and the resi-
due was dissolved in a mixture of CH2Cl2 (24 mL) and water
(24 mL). The pH of the aqueous phase was adjusted to 9 by addition
of 5% aqueous Me4NOH solution and the phases were mixed well
and separated. The aqueous phase was extracted with CH2Cl2
(3ꢁ12 mL). The combined organic phase was dried over MgSO4,
filtered and the solvent was removed. The crude products were
purified by column chromatography on silica gel using 3:1:0.04
acetone/hexane/triethylamine as an eluent to give bis(azacrown
ether)s 1–3 as described below for each compound.
4.2.1. 4,5-Bis(1,4,7-trioxa-10-azacyclododecan-10-ylmethyl)acridin-
9(10H)-one (1). Yield: 74 mg (10%). Yellow oil; Rf¼0.72 (silica gel
TLC, 1:0.5:20 MeOH/triethylamine/acetone); IR (neat) nmax 3481,
3080, 2854, 1621, 1614, 1594, 1523, 1435, 1358, 1256, 1093,
758 cmꢂ1 1H NMR (500 MHz, CDCl3)
; d 2.17 (br s, 0.5 mol of com-
plexed H2O, 1H), 2.92 (t, J¼5 Hz, 8H), 3.51–3.64 (m, 24H), 4.08 (s,
4H), 7.19 (t, J¼8 Hz, 2H), 7.69 (d, J¼8 Hz, 2H), 8.41 (d, J¼8 Hz, 2H),
11.00 (s, 1H); 13C NMR (125.8 MHz, CDCl3)
d 54.87, 59.15, 69.93,
70.68, 71.36, 121.07, 121.68, 125.56, 126.48, 133.94, 139.86, 178.82;
MS: 570 (Mþ1)þ. Anal. Calcd for C31H43N3O7$0.5H2O: C, 64.34; H,
7.66; N, 7.26. Found: C, 64.29; H, 7.47; N, 7.03.
4. Experimental
4.1. General
4.2.2. 4,5-Bis(1,4,7,10-tetraoxa-13-azacyclopentadecan-13-ylmethyl)-
acridin-9(10H)-one (2). Yield: 86 mg (10%). Yellow oil; Rf¼0.61
(silica gel TLC, 1:0.5:20 MeOH/triethylamine/acetone); IR (neat)
nmax 3484, 3080, 2864, 1616, 1608, 1600, 1528, 1440, 1352, 1256,
Infrared spectra were recorded on a Zeiss Specord IR 75 spec-
trometer. NMR spectra were recorded either on a Bruker DRX-500
Avance spectrometer (at 500 MHz for 1H and 125.8 MHz for 13C
spectra) or on a Bruker 300 Avance spectrometer (at 300 MHz for
1H and 75.5 MHz for 13C spectra) and it is indicated in each in-
dividual case. Mass spectra were recorded on a ZQ2000 MS in-
strument (Waters Corp.) using ESI method. Elemental analyses
were performed in the Microanalytical Laboratory of the De-
partment of Organic Chemistry, Institute of Chemistry, L. Eo¨tvo¨s
University, Budapest, Hungary. Melting points were taken on
a Boetius micro-melting point apparatus and were uncorrected.
Starting materials were purchased from Aldrich Chemical Company
unless otherwise noted. Silica gel 60 F254 (Merck) plates were used
for TLC. Silica gel 60 (70–230 mesh, Merck) was used for column
chromatography. Romil Ltd (Cambridge, UK) SuperPurity Solvent
1128, 760 cmꢂ1 1H NMR (300 MHz, CDCl3)
; d 2.13 (br s, 0.5 mol of
complexed H2O, 1H), 2.87 (t, J¼6 Hz, 8H), 3.50–3.66 (m, 32H), 3.99
(s, 4H), 7.12 (t, J¼8 Hz, 2H), 7.60 (d, J¼8 Hz, 2H), 8.34 (d, J¼8 Hz, 2H),
11.27 (s, 1H); 13C NMR (75.5 MHz, CDCl3)
d 54.12, 58.54, 69.39,
70.36, 70.56, 71.14, 121.02, 121.72, 125.22, 126.44, 133.75, 139.99,
178.87; MS: 658 (Mþ1)þ. Anal. Calcd for C35H51N3O9$0.5H2O: C,
63.04; H, 7.86; N, 6.30. Found: C, 62.98; H, 7.60; N, 6.27.
4.2.3. 4,5-Bis(1,4,7,10,13-pentaoxa-16-azacyclooctadecan-16-yl-
methyl)acridin-9(10H)-one (3). Yield: 87 mg (9%). Yellow oil;
Rf¼0.43 (silica gel TLC, 1:0.5:20 MeOH/triethylamine/acetone); IR
(neat) nmax 3478, 3080, 2864, 1616, 1608, 1596, 1528, 1440, 1352,

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I. Mo´czar et al. / Tetrahedron 66 (2010) 2953–2960
2959
1256, 1116, 760 cmꢂ1; 1H NMR (500 MHz, CDCl3)
d
1.69 (br s, 1 mol
1H); 13C NMR (75.5 MHz, DMSO-d6)
d
61.79, 120.75, 120.84, 125.24,
of complexed H2O, 2H), 2.90 (t, J¼6 Hz, 8H), 3.47–3.66 (m, 40H),
128.39, 131.92, 139.29, 177.01. Anal. Calcd for C15H13NO3$H2O: C,
65.93; H, 5.53; N, 5.13. Found: C, 65.81; H, 5.62; N, 5.09.
4.02 (s, 4H), 7.13 (t, J¼8 Hz, 2H), 7.63 (d, J¼8 Hz, 2H), 8.34 (d, J¼8 Hz,
2H), 11.54 (s, 1H); 13C NMR (125.8 MHz, CDCl3)
d 53.43, 57.76, 69.30,
70.27, 70.72 (very high, probably two carbon 13 signals together),
70.93, 120.80, 121.50, 125.27, 126.10, 133.38, 139.86, 178.73; MS: 746
(Mþ1)þ. Anal. Calcd for C39H59N3O11$H2O: C, 61.32; H, 8.05; N, 5.50.
Found: C, 61.04; H, 7.93; N, 5.29.
4.5.2. Starting from bis(benzyloxymethyl)acridinone 13. A solution
of acridinone derivative 13 (1.0 g, 2.3 mmol) in a mixture of freshly
distilled dioxane/10% aqueous HCl solution (1:1, 100 mL) was stir-
red at reflux for 2 days. The volatile compounds were evaporated at
40 ꢀC and the residue was triturated with MeOH (10 mL). It was
kept at rt for overnight then in the freezer for a day. The precipitate
was filtered off and dried to give 10 (0.31 g, 53%) as a yellow solid.
The crude product was pure enough to use it in the next step
without purification. A small amount of 10 was recrystallized from
DMF to give an analytical sample as yellow crystals. Compound 10
obtained this way was identical in every aspect to that prepared by
the previous procedure.
4.3. 9-Chloro-4,5-bis(chloromethyl)acridine (7)
A
mixture of bis(hydroxymethyl)acridinone 10 (1.63 g,
6.4 mmol), thionyl chloride (14 mL, 0.19 mol), dry DMF (0.2 mL)
and dry CHCl3 (70 mL) was stirred at reflux until the TLC analysis
showed that the reaction was completed (approximately 6 h). The
volatile compounds were evaporated at 40 ꢀC and the residue was
dissolved in a mixture of CH2Cl2 (80 mL) and ice-cold 5% aqueous
NaOH solution (40 mL). The phases were mixed well and separated.
The organic phase was dried over MgSO4, filtered and the solvent
was removed. The residue was purified by column chromatography
on silica gel using 1:20 CHCl3/hexane as an eluent to give 7 (1.15 g,
58%) as yellow crystals. Mp: 151–153 ꢀC; Rf¼0.94 (silica gel TLC,
1:1:10 EtOH/AcOH/toluene); IR (KBr) nmax 3024, 2920, 1664, 1624,
1564, 1536, 1436, 1396, 1328, 1260, 1096, 1048, 824, 808, 760, 752,
4.6. 4,5-Bis(benzyloxymethyl)acridine (12)
A solution of benzyl alcohol (1.78 g, 16.5 mmol) in dry THF
(25 mL) was added dropwise under Ar at rt to a well stirred sus-
pension of NaH (0.66 g, 16.5 mmol, 60% dispersion in mineral oil) in
dry THF (5 mL). After addition of benzyl alcohol the mixture was
stirred at reflux for 1 h. The reaction mixture was cooled down to rt
and bis(bromomethyl)acridine 1124,25 (2.0 g, 5.5 mmol) was added
to it in one portion. Stirring was continued at rt for 3 days. The
volatile compounds were removed and the residue was dissolved in
a mixture of CH2Cl2 (100 mL) and water (100 mL). The phases were
mixed well and separated. The aqueous phase was extracted with
CH2Cl2 (3ꢁ50 mL). The combined organic phase was dried over
MgSO4, filtered and the solvent was removed. The crude product
was purified first by flash chromatography on silica gel using
1:1:200 i-PrOH/triethylamine/hexane as an eluent then by re-
crystallization from diisopropyl ether to give 12 (1.18 g, 51%) as pale
yellow crystals. Mp: 67–69 ꢀC; Rf¼0.62 (silica gel TLC, 1:30 EtOH/
toluene); IR (KBr) nmax 3088, 3027, 2869, 1619, 1604, 1600, 1537,
1497, 1455, 1394, 1354, 1304, 1131, 1118, 890, 754, 727, 694 cmꢂ1; 1H
736, 616, 592 cmꢂ1; 1H NMR (500 MHz, CDCl3)
d 1.57 (br s, 0.5 mol
of complexed H2O, 1H), 5.47 (s, 4H), 7.62–7.66 (m, 2H), 7.97 (d,
J¼8 Hz, 2H), 8.40 (d, J¼8 Hz, 2H); 13C NMR (125.8 MHz, CDCl3)
d
43.07, 124.44, 125.45, 127.06, 130.92, 136.46, 141.96, 145.92. Anal.
Calcd for C15H10Cl3N$0.5H2O: C, 56.37; H, 3.47; Cl, 33.28; N, 4.38.
Found: C, 56.43; H, 3.48; Cl, 33.07; N, 4.19.
4.4. Dimethyl 9-oxo-9,10-dihydroacridine-4,5-dicarboxylate (9)
To a suspension of oxoacridine dicarboxylic acid 822 (2.5 g,
8.8 mmol) in dry MeOH (600 mL) was added dropwise thionyl
chloride (25 mL, 0.34 mol) under Ar at 0 ꢀC. The reaction mixture
was stirred at this temperature for 1 h then it was allowed to warm
to rt, stirred at rt for 30 min and finally refluxed for a day. For
completion of the reaction, this procedure was repeated two more
times. The precipitate was filtered off and dried. The crude product
was recrystallized from DMF to give 9 (1.64 g, 60%) as yellow crystals.
Mp: 231–233 ꢀC; Rf¼0.48 (silica gel TLC, 1:5 AcOH/toluene); IR (KBr)
nmax 3160, 1708, 1648, 1612, 1520, 1464, 1436, 1400, 1296, 1280, 1192,
NMR (500 MHz, CDCl3)
10H), 7.57 (t, J¼8 Hz, 2H), 7.93 (d, J¼8 Hz, 2H), 7.98 (d, J¼8 Hz, 2H),
8.75 (s, 1H); 13C NMR (75.5 MHz, CDCl3)
68.90, 73.41, 125.86,
d 4.83 (s, 4H), 5.46 (s, 4H), 7.30–7.52 (m,
d
126.42, 127.53, 127.81, 127.96, 128.10, 128.64, 136.48, 137.00, 138.92,
146.15. Anal. Calcd for C29H25NO2: C, 83.03; H, 6.01; N, 3.34. Found:
C, 82.94; H, 5.98; N, 3.08.
1140, 752, 680, 496 cmꢂ1
;
1H NMR (300 MHz, DMSO-d6, T¼360 K)
d
4.03 (s, 6H), 7.41 (t, J¼8 Hz, 2H), 8.46 (d, J¼8 Hz, 2H), 8.54 (d,
J¼8 Hz, 2H), 13.42 (s, 1H). Anal. Calcd for C17H13NO5: C, 65.59; H,
4.7. 4,5-Bis(benzyloxymethyl)acridin-9(10H)-one (13)
4.21; N, 4.50. Found: C, 65.51; H, 3.98; N, 4.46.
A
mixture of bis(benzyloxymethyl)acridine 12 (1.97 g,
4.5. 4,5-Bis(hydroxymethyl)acridin-9(10H)-one (10)
4.7 mmol), NaH (0.71 g, 28 mmol, dry, 95%) and dry DMSO (40 mL)
was stirred under O2 at rt for 4 days. The solvent was evaporated at
45 ꢀC and the residue was triturated with water (100 mL) then its
pH was adjusted to 7 by addition of AcOH. EtOAc (100 mL) was
added to the mixture and the phases were mixed well and sepa-
rated. The aqueous phase was extracted with EtOAc (3ꢁ50 mL). The
combined organic phase was dried over MgSO4, filtered and the
solvent was removed. The crude product was purified by column
chromatography on silica gel using 1:5 EtOAc/hexane as an eluent
to give 13 as a yellow solid (0.57 g, 28%). A small amount of 13 was
recrystallized from EtOH to give an analytical sample as yellow
crystals. Mp: 101–102 ꢀC; Rf¼0.43 (silica gel TLC, 1:2 EtOAc/hex-
ane); IR (KBr) nmax 3483, 3080, 2888, 2858, 1621, 1607, 1589, 1522,
4.5.1. Starting from oxoacridine dicarboxylic acid dimethyl ester 9. A
suspension of lithium bromide (9.55 g, 0.11 mol) and sodium tetra-
hydridoborate (4.54 g, 0.12 mol) in dry diglyme (18 mL) was stirred
under Ar at rt for 1 h. Dimethyl ester 9 (2.0 g, 6.4 mmol) was added
in one portion and the reaction mixture was stirred at rt for 3 days.
The mixture was poured into a stirred ice-cold 5% aqueous HCl so-
lution (160 mL) and the precipitate was filtered off. It was washed
with water (3ꢁ50 mL) and dried to give 10 (1.16 g, 71%) as a yellow
solid. The crude product was pure enough to use it in the next step
without purification. A small amount of 10 was recrystallized from
DMF to give an analytical sample as yellow crystals. Mp: 227–231 ꢀC;
Rf¼0.19 (silica gel TLC, 1:1:10 EtOH/AcOH/toluene); IR (KBr) nmax
3600–2400, 1628, 1608, 1600, 1576, 1532, 1448, 1416, 1360, 1272,
1437, 1357, 1256, 1097, 751 cmꢂ1; 1H NMR (300 MHz, CDCl3)
d 1.71
(br s, 1 mol of complexed H2O, 2H), 4.41 (s, 4H), 4.74 (s, 4H), 7.13–
1256, 1024, 1004, 752, 568 cmꢂ1
2.50 (br s,1 mol of complexed H2O, 2H), 4.91 (s, 4H), 5.86 (br s, 2H),
7.23 (t, J¼8 Hz, 2H), 7.66 (d, J¼8 Hz, 2H), 8.19 (d, J¼8 Hz, 2H),10.93 (s,
;
1H NMR (300 MHz, DMSO-d6)
7.34 (m, 12H), 7.44 (d, J¼8 Hz, 2H), 8.46 (d, J¼8 Hz, 2H), 10.54 (s,
d
1H); 13C NMR (75.5 MHz, CDCl3)
d 70.82, 72.05, 121.06, 122.12,
124.13, 127.77, 128.24, 128.44, 128.69, 133.78, 137.47, 140.16, 178.65.

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I. Mo´czar et al. / Tetrahedron 66 (2010) 2953–2960
2960
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4.8. 2-[(2-Carboxyphenyl)amino]isophthalic acid (15)
A mixture of 2-chloroisophthalic acid 14 (10.43 g, 52 mmol),
anthranilic acid (7.13 g, 52 mmol), finely powdered anhydrous
K2CO3 (14.37 g, 104 mmol), copper powder (110 mg), copper(I)
oxide (110 mg) and 2-ethoxyethanol (40 mL) was stirred vigorously
under Ar at reflux for a day. The solvent was removed at 50 ꢀC and
the residue was dissolved in 2% aqueous KOH solution (250 mL).
Charcoal (1.0 g) was added to the aqueous solution, boiled for
10 min, filtered then cooled to 0 ꢀC in an ice-water bath. The pH of
the aqueous solution was adjusted to 2 with concentrated aqueous
HCl solution. The precipitate was filtered off, washed with ice-cold
water (3ꢁ50 mL) and dried. The crude product was recrystallized
from water to give 15 (8.30 g, 53%) as yellow crystals. Mp: 253–
255 ꢀC [lit.22 mp: 258–259 ꢀC (aqueous MeOH)]; Rf¼0.44 (silica gel
TLC, 1:3 AcOH/toluene); IR (KBr) nmax 3600–2300, 1692, 1616, 1580,
1504, 1472, 1460, 1448, 1408, 1396, 1224, 1176, 1160, 1096, 828, 752,
676, 648 cmꢂ1; 1H NMR (500 MHz, DMSO-d6)
d 6.75–6.82 (m, 2H),
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