Synthesis and characterization of a novel chiral chromogenic calix[4](azoxa)crown-7

Article abstract of DOI:10.1016/j.tetasy.2004.09.028

Two new chromogenic compounds, 5 and 6, and a novel chiral chromogenic calix[4](azoxa)crown-7 8 have been synthesized using a calix[4]arene platform. The starting reagents chiral diamine e and calix[4]arene diacid chloride derivative 7 were prepared conve

Full text of DOI:10.1016/j.tetasy.2004.09.028

Tetrahedron:
Asymmetry
Tetrahedron: Asymmetry 15 (2004) 3595–3600
Synthesis and characterization of a novel chiral chromogenic
calix[4](azoxa)crown-7
Abdulkadir Sirit, Aysegul Karakucuk, Shahabuddin Memon,
Erdal Kocabas and Mustafa Yilmaz*
Department of Chemistry, Selc¸uk University, 42031 Konya, Turkey
Received 1 September 2004; accepted 27 September 2004
Abstract—Two new chromogenic compounds, 5 and 6, and a novel chiral chromogenic calix[4](azoxa)crown-7 8 have been synthe-
sized using a calix[4]arene platform. The starting reagents chiral diamine e and calix[4]arene diacid chloride derivative 7 were
prepared conveniently according to recent approaches. The 1H and 13C NMR, data showed that these compounds exist in a
cone conformation. Compounds 5 and 8 have shown broad absorption bands in UV–vis spectra suggesting their utility in different
fields, for example, as sensors for ions as well as for chiral molecules.
Ó 2004 Elsevier Ltd. All rights reserved.
1. Introduction
having an ability for visual discrimination between the
enantiomers of chiral guest species, have attracted con-
siderable attention from a wide range of chemists espe-
cially in the fields of organic, biological, and medicinal
chemistry. The design of such molecules constitutes as
a timely and challenging research topic, and has lead
to the synthesis of several chromogenic host molecules.14
Among them, calixarenes with well-defined cavities,
have been regarded as basic skeletons for the synthesis
of host molecules similar to cyclodextrins.15–20 The chi-
ral calixarenes are of pivotal importance if enantioselec-
tive recognition or discrimination is to be exploited.21
Chirality in calixarenes can be generated by either
attaching chiral substituents at one of the rims (lower
or upper) or synthesizing ÔinherentlyÕ chiral derivatives,
in which the nonplanarity of the molecule is exploited.
The inherent chirality suffers severe limitations, due to
the difficulties met in the resolution of racemates. There-
fore, the former approach appears to be preferable when
chiral derivatizing agents with high enantiometric excess
are available.22
Chiral recognition is one of the most important and
fascinating areas in host–guest chemistry or supramo-
lecular chemistry.1–3 The chiral nature of drug mole-
cules is essentially required after the synthesis because
the physiological effect of the enantiomers may signifi-
cantly differ;4 in this context, a tragic lesson is thalido-
mide,5 where one enantiomer acts as a sedative,
whereas the other leads to serious fetal abnormalities.
Therefore, determination of the enantiometric purity
has become one of the most important stages in the
pharmaceutical industry. Several methods have already
been developed for enantiometric purity determination
by using the specific rotation,6 circular dichroism,7 cap-
illary electrophoresis,8 and separation techniques,
including liquid and gas chromatography.9 Other tech-
niques such as polarimetry, absorbance spectrometry,10
infrared transmission spectrometry,11 X-ray anomalous
scattering,12 and NMR spectrometry13 have also been
used.
An alternative approach using the preparation and
properties of chiral macrocyclic sensor molecules,
Herein we report the synthesis of a novel calix[4]arene
derivative bearing a chiral (azoxa)crown-7 moiety at
the lower rim and chromogenic nitro groups at the
upper rim. This approach could provide an efficient
methodology for developing improved optical sensors
for biological and/or chemically important cations and
amines.
*
Corresponding author. E-mail: myilmaz@selcuk.edu.tr
0957-4166/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2004.09.028

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A. Sirit et al. / Tetrahedron: Asymmetry 15 (2004) 3595–3600
2. Results and discussion
Aluminum chloride catalyzed removal of the p-tert-
butyl groups of 1 proceeded in excellent yield to give
calix[4]arene 2, which thereby disubstituted on the lower
rim with benzyl bromide and K2CO3 followed by selec-
tive nitration of the upper rim to yield 4.26 Compound 4
was treated then with methyl bromoacetate in the pres-
ence of NaH in THF for the introduction of ester groups
onto the lower rim at the 1,3-positions. After purifica-
tion by column chromatography, compound 5 was ob-
tained in 71% yield (Scheme 2). Employing the general
protocol 5 was hydrolyzed with 15% aqueous NaOH
in ethanol to produce diacid derivative 6 in 85% yield.
The synthetic usefulness of the acid chloride is well
known and it has been demonstrated that it can be
bridged across the lower rim. Thus, the other reagent
diacid chloride derivative 7 was prepared by the reaction
of compound 6 with thionyl chloride, which is employed
directly in the subsequent reaction without further puri-
fication. The desired product chiral chromogenic
calix[4](azoxa)crown-7 8, as illustrated in Scheme 3
was synthesized under high dilution conditions from 7
and chiral diamine e in THF in the presence of pyridine
to bind the hydrogen chloride formed in situ to inhibit
the side reactions. This is a straightforward method
and gives us a moderate yield (46%).
2.1. Synthesis of intermediates b, d, and e
Calix[4]azacrowns containing a calix[4]arene element
and an azacrown unit in their framework, have received
much attention because of their special structures and
good complexing properties toward metal cations.23
Chiral calix(aza)crowns comprising of a calixarene and
a chiral polyamine derived from an amino acid, could
have chiral recognition abilities and could also serve as
good anion receptors24 by cooperation effects. However,
adopting recent approaches made by different research
groups,21,25 we have developed a convergent synthetic
pathway toward a novel chiral chromogenic macrocycle.
A multisteproute, as shown in Schemes 1–3, was chosen
for the synthesis of this new type of chiral calix[4](azoxa)-
crown-7 8.
Thus, following the standard procedures,25 one of the
starting materials, chiral diamine e, can be prepared in
a three-stepsynthesis ( Scheme 1) starting from enantio-
merically pure D-phenylglycine a, which has been firstly
converted by reduction with NaBH4–H2SO4 into the
corresponding D-phenylglycinol b. Since the tosylate
groupbehaves as a good leaving groupin S
reactions,
N
therefore in the second stepdiethyleneglycol c was there-
fore treated with p-toluenesulfonylchloride to afford
diethyleneglycol-p-ditosylate d. Finally, the condensa-
tion of b and d gives chiral diamine e in a quantitative
yield.
All new compounds were characterized by a combina-
tion of IR, 1H NMR, 13C NMR, FAB MS, and
elemental analysis. The conformational characteristics
of calixarenes were conveniently estimated by the split-
ting pattern of the ArCH2Ar methylene protons in the
13
1H and C NMR spectroscopy.15 1H and 13C NMR
2.2. Synthesis of 5–8
data showed that these compounds 5, 6, and 8 have a
cone conformation, the bridged methylene protons
appeared in two sets of doublets covering a range of
d 3.40 and 4.28ppm in the 1H NMR (J 12.8–
13.6Hz), and two signals covering a range of d 31.3
and 31.8ppm in the 13C NMR. Compound 8 is asym-
metric due to the formation of a chiral sub-ring onto
the lower rim of calix[4]arene. The splitting pattern
for other protons (see Section 4) as well may reflect
Chromogenic calix[4]arene 4 was obtained (Scheme 2)
using previously described procedures.26 p-tert-Butylca-
lix[4]arene 1, easily accessible via base-induced conden-
sation of p-tert-butylphenol and formaldehyde,
provides a basic skeleton for the preparation of calix-
arene-based precursors caring a wide variety of groups
on the upper and lower rims.15–20
Ph
Ph
O
i
H2N
OH
H2N
OH
b
a
ii
OTs
TsO
O
OH
HO
O
c
d
O
O
O
Ph
iii
+
OTs
TsO
O
H2N
OH
H2N
Ph
NH2
Ph
b
e
d
Scheme 1. Synthesis of b, d, and e. Reagents and conditions: (i) NaBH4, H2SO4, THF, rt, 12h; (ii) p-TsCl, NaOH, THF, 0°C, 2h; (iii) NaH, THF, rt,
72h.

A. Sirit et al. / Tetrahedron: Asymmetry 15 (2004) 3595–3600
3597
OH
HO
OH
OH
OH
i
+ HCHO
1
ii
HO
OH
OH
HO
OH
OH
O
O
iii
3
2
iv
OMe
O
OMe
O
HO
O
O
OH
O
O
O
O
v
NO2
NO2
O2N
O2N
5
4
Scheme 2. Synthesis of 1–5. Reagents and conditions: (i) NaOH, diphenyl ether, reflux, 3h; (ii) AlCl3, phenol, toluene, rt, 1h; (iii) benzylbromide,
K2CO3, NaI; acetone, rt, 6h; (iv) HNO3 (70%), glacial AcOH, 0°C, 2h; (v) methyl bromoacetate, NaH, THF, reflux, 24h.
the presence of a chiral moiety in the molecule because
it is similar to what was observed in other chiral
calix[4]arenes.21 Moreover, compound 8 gave satisfac-
tory elemental analysis and MS spectra which indicated
that it was Ô1 + 1Õ cyclization product.
ent absorption bands in the UV–vis spectra. Further
investigations on their ionic and chiral recognition prop-
erties are currently in progress.
4. Experimental
Figures 1 and 2 show UV–vis spectra of 5 and 8 in chlo-
roform. Examination of the spectra showed broad
absorption bands at 267 and 318nm suggesting that
compound 5 could be used in the recognition studies
of cations, while compound 8 could be used as sensor
for anions and chiral molecules.
Melting points were determined on a Electrothermal
9100 apparatus in a sealed capillary and are uncor-
1
rected. H and 13C NMR spectra were recorded using
a Varian 500MHz spectrometer in CDCl3 with TMS
as internal standard. IR spectra were obtained on a Per-
kin–Elmer 1605 FTIR spectrometer as KBr pellets.
Optical rotations were measured on A-Kruss Optronic
¨
3. Conclusions
polarimeter. UV–vis spectra were obtained on a Shim-
adzu 160 A UV–vis recording spectrophotometer.
FAB-MS spectra were taken on a Varian MAT 312
spectrometer. Elemental analysis data were performed
on a Leco CHNS-932 analyzer.
In conclusion, we have designed and synthesized two
new chromogenic compounds 5 and 6 and a novel chiral
chromogenic calix[4](azoxa)crown-7 8 for applications
in ionic as well as chiral recognition sensors. All com-
pounds have been characterized by IR, H NMR, 13C
All starting materials and reagents used were of stand-
ard analytical grade from Fluka, Merck, and Aldrich,
and used without further purification. Commercial
grade solvents, such as chloroform, methanol, acetone,
1
NMR, MS, and elemental analysis. The 1H and 13C
NMR, data showed that these compounds exist in a
cone conformation. Compounds 5 and 8 showed differ-

3598
A. Sirit et al. / Tetrahedron: Asymmetry 15 (2004) 3595–3600
OH
OH
OMe
OMe
O
O
O
O
O
O
O
O
O
O
O
O
i
NO2
O2N
NO2
O2N
6
5
ii
O
O
N
O
H
H
O
N
Ph
Ph
Cl
Cl
O
O
O
O
O
O
O
O
O
O
O
iii
NO2
O2N
NO2
O2N
7
8
Scheme 3. Synthesis of 6 and 8. Reagents and conditions: (i) aqueous NaOH (15%), EtOH, reflux, 24h; (ii) SOCl2, THF, reflux, 4h; (iii) chiral
diamine e, pyridine, THF, rt, 2days.
2.50
2.50
267 NM
NM
318
0.500
0.500
(A / DIV)
(A / DIV)
0.00
0.00
250
450
500
200
(NM / DIV)
50
(NM / DIV)
50
Figure 2. The UV–vis spectrum of compound 8.
Figure 1. The UV–vis spectrum of compound 5.
ethyl acetate and hexane, were distilled and then stored
˚
over 4A molecular sieves. Toluene was dried with cal-
4.1. Synthesis of 5,17-dinitro-25,27-bis(benzyloxy)-
26,28-diacetonoyloxy calix[4]arene 5
cium hydride and stored over Na wire. THF was dried
with sodium/benzophenone. The drying agent employed
was anhydrous MgSO4. Thin layer chromatography
(TLC) was performed using aluminum sheet Merck 60
F254 silica gel plates. Column chromatography separa-
tions were performed on Merck Silica Gel 60 (230–
400mesh).
To a suspension of NaH (90.24g, 6mmol) in dry THF
was added compound 4 (1.4g, 2mmol) under a nitrogen
atmosphere, and stirred for half an hour at rt. Methyl
bromoacetate (0.73g, 4.8mmol) was added dropwise
into the mixture by syringe and refluxed for 24h. The
reaction was carried out by the addition of water
(2mL). The solvent was evaporated under reduced pres-
sure and the residue dried in vacuo. The crude product
was purified by column chromatography (EtOAc/hex-
ane) to give light yellow product 5 in 71% yield (1.2g).
Compounds b, d, e, and 1–4 were synthesized as de-
scribed in the literature.25,26 Compounds 5–8 were syn-
thesized as follows.

A. Sirit et al. / Tetrahedron: Asymmetry 15 (2004) 3595–3600
3599
Mp108–109 °C. IR (KBr, cmꢀ1): 1758 (CO); H NMR
(CDCl3): d 8.01 (s, 4H, ArH), 7.61–7.58 (m, 4H, ArH),
7.42–7.36 (m, 6H, ArH), 6.98 (d, 4H, ArH), 6.84 (t,
2H, ArH), 5.05 (s, 4H, CH2CO2Me), 4.75 (s, 4H,
ArCH2O), 4.27 (d, 4H, ArCH2Ar), 3.88 (s, 6H,
OCH3), 3.46 (d, 4H, ArCH2Ar); 13C NMR (CDCl3): d
169.4, 169.1 (CO), 151.9, 151.8, 149.8, 148.6, 147.7,
146.6, 145.6, 142.9, 141.3, 139.2, 133.7, 132.6, 131.9,
130.6, 129.7, 129.1, 128.9, 128.6, 127.7, 127.1, 126.5,
125.3 (Ar), 76.8, 75.1 (OCH2), 65.4, 64.6 (OCH2Ar),
31.7, 31.3 (ArCH2Ar), 23.9, 23.8 (OCH3); FAB-MS
m/z: (861.8) [M+Na]+ (calcd 861.8). Anal. Calcd for
C48H42N2O12 (838.85): C, 68.72; H, 5.04; N, 3.34.
Found: C, 68.84; H, 5.15; N, 3.42.
water. The yellow crude product was purified by column
chromatography (SiO2, hexane/CHCl3 2:1) and recrys-
tallized from THF/EtOH to give pure compound 8
1
22
in 46% yield (3.32g). Mp P190°C (decomp.). ½aŠ
¼
D
ꢀ47:5 (c 3.3, CHCl3); IR (KBr, cmꢀ1): 3061 (NH),
1682 (CO); 1H NMR (CDCl3): d 8.11 (s, 4H, ArH),
7.95–7.85 (m, 2H, CONH), 7.62–7.57 (m, 4H,
ArH), 7.42–7.39 (m, 6H, ArH), 7.38–7.20 (m, 10H,
ArH), 6.98 (d, 4H, ArH), 6.82 (t, 2H, ArH), 5.04 (s,
4H, CH2CONH), 4.72 (s, 4H, ArCH2O), 4.28 (d, 4H,
ArCH2Ar), 4.18 (m, 2H, NCH), 3.65–3.42 (m, 12H,
OCH2), 3.40 (d, 4H, ArCH2Ar); 13C NMR (CDCl3): d
169.1, 169.4 (CO), 151.9, 151.7 (CHNH), 149.8, 148.6,
148.3, 147.7, 147.1, 146.6, 145.4, 143.3, 142.3, 141.7,
138.9, 137.9, 135.5, 133.4, 132.6, 132.2, 131.9, 130.6,
129.8, 129.6, 129.2, 128.9, 128.6, 127.8, 127.7, 127.3,
126.5, 125.6, 125.1, 123.9, 122.2, 120.6 (Ar); 77.0, 76.8,
75.1, 74.8, 64.6, 64.4, 53.8, 53.3 (OCH2); 53.8, 53.4
(OCH2Ar), 31.8, 31.7 (ArCH2Ar); FAB-MS m/z:
(1142.2) [M+Na]+ (calcd 1142.2). Anal. Calcd for
C66H62N4O13 (1119.22): C, 70.83; H, 5.58; N, 5.01.
Found: C, 70.91; H, 5.64; N, 5.11.
4.2. Synthesis of 5,17-dinitro-25,27-bis(benzyloxy)-
26,28-dicarboxymethoxy calix[4]arene 6
A mixture of compound 5 (2g, 2.45mmol) and 15%
aqueous NaOH (10mL) in EtOH (150mL) was stirred
and heated under reflux for 24h after which most of
the ethanol was distilled off. The residue was taken in
CHCl3, acidified with 1M HCl until pH = 1 and washed
with water and then with brine. The organic phase was
dried over anhydrous magnesium sulfate and concen-
trated to give the crude product. Recrystallization of
the crude product from ethanol–acetone furnished 6.
Yield 1.93g (85%). Mp174–175 °C. IR (KBr, cmꢀ1):
Acknowledgements
We thank the Research Foundation of Selcuk Univer-
sity, Konya–Turkey (SUAF-EF-99/001) for financial
support of this work.
1
1736 (CO), 3364 (OH); H NMR (CDCl3): d 8.05 (s,
4H, ArH), 7.93 (br, 2H, CO2H), 7.60–7.56 (m, 4H,
ArH), 7.45–7.39 (m, 6H, ArH), 6.95 (d, 4H, ArH),
6.79 (t, 2H, ArH), 5.04 (s, 4H, CH2CO2H), 4.72 (s,
4H, ArCH2O), 4.26 (d, 4H, ArCH2Ar), 3.48 (d, 4H,
ArCH2Ar); 13C NMR (CDCl3): d 169.6, 169.2 (CO),
154.3, 152.0, 151.6, 149.9, 148.3, 147.8, 146.4, 145.1,
144.8, 139.9, 135.1, 133.3, 132.0, 131.8, 131.2, 130.6,
129.4, 128.7, 127.2, 126.3, 126.4, 124.7 (Ar), 75.7, 77.8
(OCH2), 68.3, 67.7 (OCH2Ar), 31.8, 31.6 (ArCH2Ar);
FAB-MS m/z: (833.8) [M+Na]+ (calcd 833.8). Anal.
Calcd for C46H38N2O12 (810.80): C, 68.14; H, 4.72; N,
3.46. Found: C, 68.22; H, 4.85; N, 3.53.
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