Conformationally Selective Synthesis of Mononitrocalix[4]arene in Cone or Partial Cone

Article abstract of DOI:10.1002/hlca.201600391

Nitro-substituted calixarenes in a cone and a partial cone conformation were prepared selectively using distinct synthetic routes. The selective nitration of tris- or penta-substituted phenols of calix[4]arene or calix[6]arene provided mononitrocalix[n]arenes (n?=?4, 6). Subsequent addition of ethylene glycol (EG) moieties to mononitrocalix[4]arene provided tetraEGylcalix[4]arene in locked partial cone conformation. By an alternative route – initial addition of EG moieties to the non-derivatized calix[4]arene followed by the uncontrolled nitration – provided mononitro- and dinitro-tetraEGylcalix[4]arenes locked in the cone conformation. These nitrocalix[4]arenes with locked cone or partial cone conformation are useful building blocks for further assembly of supramolecular systems, especially in the area of material sciences.

Full text of DOI:10.1002/hlca.201600391

Received Date: 19-Dec-2016
Revised Date: 02-Mar-2017
Accepted Date: 07-Mar-2017
Article Type: Full Paper
Conformationally Selective Synthesis of
Mononitrocalix[4]arene in Cone or Partial Cone
a
a
a
a
a
Ana Rita N. S. Royappa, Maxime Ayer, Alessandro Fracassi, Marc-Oliver Ebert, Safwan Aroua
and Yoko Yamakoshi*,a
a
Laboratorium für Organische Chemie, ETH Zürich, Vladimir-Prelog-Weg 3, CH 8093 Zürich,
Switzerland, yamakoshi@org.chem.ethz.ch
Abstract Nitro-substituted calixarenes in a cone and a partial cone conformation were prepared selectively using
distinct synthetic routes. The selective nitration of tris- or penta- substituted phenols of calix[4]arene or calix[6]arene
provided mononitrocalix[n]arenes (n
= 4, 6). Subsequent addition of ethylene glycol (EG) moieties to
mononitrocalix[4]arene provided tetraEGylcalix[4]arene in locked partial cone conformation. By an alternative route –
initial addition of EG moieties to the non-derivatized calix[4]arene followed by the uncontrolled nitration – provided
mononitro- and dinitro-tetraEGylcalix[4]arenes locked in the cone conformation. These nitrocalix[4]arenes with locked
cone or partial cone conformation are useful building blocks for further assembly of supramolecular systems, especially in
the area of material sciences.
Keywords: calixarenes • conformation • NMR
Introduction
Calixarenes are macrocyclic compounds composed of phenolic units linked together by methylene
groups at the 2- and 6-positions. They have a defined structure with an upper rim, a lower rim, and a
central annulus. Their sizes can vary from four to eight, and sometimes 20 phenolic units and they
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can present different conformations that arise from the rotation of the methylene groups through
the annulus. Due to their unique physicochemical properties, calixarenes have found a wide variety
1
,2
3,4
5,6
of applications including ion-transport membranes, chemosensors, catalysts, and enzyme
7
mimetics. They also play an important role in research towards drug discovery. Calixarenes in a cone
conformation belong to a family of macrocyclic host compounds together with crown ethers,
8
-11
cyclodextrins, porphyrins, and cavitands. They present specific structures and properties such as
1) cavities with suitable sizes for ion and small molecule inclusion, (2) variable conformation, (3)
(
formation of complexes with larger molecules, (4) formation of ditopic ligands with binding sites at
the upper and lower rims, and (5) the capability of combining ligands for the formation of molecular
sensors, vectors, and switches. These features are desirable for constructing new molecular
platforms for the design and development of new materials and drugs.
In the field of supramolecular chemistry including host-guest complexation, calixarenes
play an important role. In the calixarene supramolecular systems, a guest and a calixarene host
can form a complex by non-covalent intermolecular interactions such as hydrogen bonding, ion
pairing, ion-π, CH–π dispersion, and π-π interactions. Compared to other host compounds, the
conformation of the calixarene annulus is not always locked; therefore, it is very important to
develop a convenient synthetic approach for their specific derivatization suitable for each
conformation. In addition, to construct functionalized calixarene derivatives covalently
connected to other functional moieties, mono- and di-substituted calixarenes are important
building blocks.
Scheme 1 Synthesis of mononitrocalix[n]arene 4a (n = 4) and 4b (n = 6) via tris- and penta-O-benzoylcalix[n]arenes 2a (n = 4) and 2b (n = 6). Reaction
conditions: i) BzCl (8.1 equiv), pyridine, 0 °C – rt, 1 h for 1b (83%); BzCl (7.4 equiv), pyridine, 0 °C – rt, 5 h for 2b (30%); ii) 65% HNO
3
(1.3 equiv),
CH Cl /AcOH, rt, 1 h, 3a (47%); 65% HNO (2.5 equiv) for 3b (20%); iii) NaOH, THF/EtOH/H O, reflux, 17 h, 4a (56%); 24 h, 4b (48%).
2
2
3
2
Preparation of mono-substituted calix[4]arene derivatives has already been intensively
studied.12-14 One useful approach includes a selective mono-nitration of the aromatic tri-O-
benzoylcalix[4]arene15-18 by taking advantage of the different reactivities of the aromatic carbon
1
9
at the para-position of the OH group with or without benzoyl groups. In the present study, this
strategy was used to prepare mononitrocalix[n]arenes 4a and 4b (n = 4, 6) starting from
calixarenes 1a and 1b through their tris- and pentabenzoyl derivatives 2a and 2b (Scheme 1).
Subsequent attachment of ethylene glycol (EG) moieties to the OH groups of 4a and 4b provided
respectively tetra-ethyoxyethyl (tetra-EGyl) derivative locked exclusively in the partial cone
conformation (5a in Fig. 3) and hexa-EGyl derivatives, which remained flexible. An alternative
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route with initial addition of EG groups to calix[4]arene 1a and subsequent non-controlled
nitration provided derivatives 5a’ and 9 (Fig. 4) locked into the cone conformation.
Results and Discussion
Benzoyl esterification of calix[n]arenes 1a and 1b (n = 4 and 6)
In order to carry out a selective nitration, it was necessary to have one activated aryl carbon in para
position to the phenol group. With that in mind, the initial step involved a selective tri-O-
1
5,19
benzoylation of calix[4]arene 1a (Scheme 1).
In good agreement to previous reports, tri-O-
benzoylcalix[4]arene 2a was obtained efficiently (73% yield), using pyridine as a base, from 1a as a
single product. This tris esterification was successful even in the presence of an excess amount of
1
benzoyl chloride (8.1 equiv) and no tetra-adduct was obtained. In a similar manner, calix[6]arene
1
b was subjected to the reaction with benzoyl chloride with the same amount (8.1 equiv) as in case
of 1a but provided a large amount of hexa-adduct in addition to the desired penta-adduct 2b. This
was due to the less hindered and more flexible structure of calix[6]arene with larger cavity.
Optimized reaction conditions with 7.4 equiv of benzoyl chloride in the presence of pyridine
afforded penta-O-benzoylcalix[6]arene 2b in 30% yield.
Figure 1.
1
8
H-NMR spectra of 2a at rt (a) and of 2b at rt (b), 50 °C (c), and 100 °C (d) in toluene-d (*: residue of a solvent).
1
The H-NMR spectrum of tri-O-benzoylcalix[4]arene 2a (Figure 1a) indicated that the
conformation of the cavity was locked into the partial cone based on the chemical shift patterns of
1
,2
1’,2’
20
the bridging methylenes (H , H ) in comparison to the reported values. Furthermore, DFT
1
calculations for the H-NMR chemical shift estimation of the bridging methylene protons suggested
that the recorded H-NMR chemical shift values were in a better agreement to the calculated values
1
for the partial cone rather than for the cone conformation (Table 1).
1
Tetra-benzoylester of calix[4]arene can be prepared in the presence of AlCl3 without providing any Friedel-Craft acylation product.
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Table 1. Observed and calculated H-NMR chemical shifts of the bridging protons of 2a.
1
1
H-NMR chemical shift [ppm]
2
’
1’
1
2
H (1)/(2)
H (1)/(2)
H (1)/(2)
H (1)/(2)
a
In CDCl3.
1
As shown in Fig. 1b, the H-NMR peaks of penta-O-benzoylcalix[6]arene 2b were very broad at
room temperature in toluene-d8, in contrast to the ones of tri-O-benzoylcalix[4]arene 2a (Figure
21
1
a). This indicated that 2b had a flexible conformation and the conformational exchange was in the
1
intermediate regime of NMR time scale. Upon increasing the temperature to 100 °C, the H-NMR
peaks of 2b in toluene-d became sharper due to the faster conformational interchange (Figure 1c,
8
d). Similar conformational flexibility was also observed in the nitro derivative of calix[6]arene 3b,
which was obtained by subsequent nitration as described below.
Selective mono-nitration of tri-O-benzoylcalix[4]arene 2a, penta-O-benzoylcalix[6]arene 2b, and triEGylcalix[4]arene 6
As expected, nitration of tri- and penta-O-benzoylcalix[n]arene 2a and 2b (n = 4, 6) using 65% HNO
3
and AcOH successfully provided mono-nitro derivative 3a and 3b in a selective manner and in
reasonable yields (47% and 20% respectively) (Scheme 1). Compounds 3a and 3b were subsequently
subjected to deprotection of the phenol groups by base to provide nitrocalixarenes 4a and 4b. The
conformations of 4a and 4b with free phenolic groups in the lower rim are not locked, as shown by
1
the H-NMR with broad peaks of the bridging methylene protons observed at around 3.5 - 4.2 ppm
(
Figures 3f and S17).
For an alternative but similar approach to the selective mononitration, calix[4]arene
derivative 6 having three phenol OH groups EGylated (instead of Bz) was synthesized (Scheme
). It was expected that this strategy would show the following advantages: (1)
2
triEGylcalix[4]arene 6 could produce mononitro derivative 7 selectively, and (2) there would
not be the need for the subsequent deprotection of the phenolic OH, so that the conformation of
the calix[4]arene would be kept as cone. Taking advantage of the previously reported study on
22
the metal-template alkoxylation of tetra-t-butylcalix[4]arene in cone conformation, a selective
tri-EGylation of 1a was achieved in the presence of barium hydroxide and barium oxide and in
DMF providing tris-EGyl derivative 6 in 80% yield (scheme 2). The conformation of 6 was
1
confirmed to be cone based on the H-NMR chemical shift of the bridging methylenes as
described below.
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Scheme 2 Tris EGylation of calix[4]arene and subsequent mononitration. Reaction conditions: i) C
2
H
5
OC
(1.2 equiv), DCM/AcOH (3:1), rt, 1.5 h, 52%. Last step of EGylation was not successful even using excess amount of
2 5 2 4
Br or C H OC H OTs.
2 4 2 2
H Br (20 equiv), Ba(OH) •8H O, BaO, DMF, rt -
80 °C, on, 80%; ii) 65% HNO
3
C
2
H
5
OC
2
H
4
1
The H-NMR of tris-EGylated derivative 6 showed two distinct types of bridging methylene
1
,2ax
1,2eq
protons (Figure 2c, the axial protons (H ) at 4.58 and 4.98 ppm and the equatorial protons (H
)
at 3.35 and 3.26 ppm), indicating clearly that 6 is in cone conformation. As described in the previous
section, the corresponding methylene protons of 2a were observed in closer chemical shift range
2
ax,2eq
1,1’
13
2
(H
andH in Figure 2a) corresponding to the partial cone conformation. In addition, C-NMR
chemical shifts of the bridging methylenes of 2a and 3a in partial cone conformation were 37.5, 32.5
ppm and 37.4, 32.6 ppm, respectively, while the ones of 6 and 7 were 30.9, 30.8 ppm and 30.8, 30.7
ppm, which corresponded to the cone conformation. Taken together, these results show that the tris
addition of EG to calix[4]arene afforded 6 in a cone conformation, while the tris addition of benzoyl
3
group provided 2a in a partial cone conformation. Selective nitration of 6 – at the most activated
aryl ring bearing a free phenol group – was successfully carried out in a mixture of HNO and
3
AcOH to provide mononitrocalix[4]arene 7 (Scheme 2, 52% yield).
1
The H-NMR spectra of 3a and 7 clearly confirmed successful mono-nitration of 2a and 6
by the appearance of a singlet at around 8 ppm corresponding to the protons in the ortho-
position to the nitro group (Hm1 in Fig. 2b, d). Simultaneously, the OH protons (H ) shifted to
lower field in both 3a (from 5.4 (in 2a) to 6.3 ppm) and 7 (from 5.0 (in 6) to 6.9 ppm) being
correlated to a decrease of pKa of phenolic OH due to the nitration in para-position (pKa of
phenol and nitrophenol are about 10 and 7 respectively). The conformation of nitro derivative 7
ox
1
was confirmed to be cone by H-NMR with two distinct types of bridging methylene protons
(
H1,2ax at 4.49 and 4.59 ppm and H1,2eq at 3.21 and 3.15 ppm) observed in a similar pattern to 6
but with a slight change of chemical shift (Figgure 2d). This result indicated that 7 was also in a
cone conformation with a small conformational change from 6 in the cavity, possibly due to the
bulky nitro group in 7. A similar situation was observed in the nitro derivative 3a, in
comparison to 2a (Figure 2a, b).
2
Also
referred (Figure 3e).
1
H NMR of a standard cone calix[4]arene 8, with distinct two types of bridging methylene protons (Hax at 4.50 ppm and Heq at 3.15 ppm), can be
3
13C-NMR chemical shift of bridging methylenes of 2a and 6 were respectively 37.5, 32.4 ppm (Figure S2) and 30.9, 30.8 ppm (Figure S30).
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Figure 2. Comparison of
1
3
H-NMR spectra of tri-substituted calix[4]arenes 2a (a), 3a (b), 6 (c) and 7 (d) in CDCl and their chemical structures. The
chemical shifts of CH
2
protons in equatorial (H1-2eq) and axial position (H1-2ax) were more apart in the presence of the EG groups (6 and 7), indicating
that compounds 6 and 7 have distinct cone conformations.
Unfortunately, as shown in Scheme 2, further EGylation of the remaining last OH in 7 was
not successful. The cone mononitro-tetraEGylcalix[4]arene 5a’ was not obtained in the presence
of NaH and 1-bromoethoxyethane in DMF even at elevated temperatures (0 to 80 °C) for longer
reaction time using a high excess (50 equiv) of the 1-bromoethoxyethane. Additional attempt
using 1-tosylethoxyethane with extended reaction time was not successful. Taken together, the
reported fact that calixarene 1a can be converted to tetraEGylcalix[4]arene 8 efficiently (see
4
also Fig. 3a in the following section), the reactivity difference in the phenolic groups of 6 and 7
may be explained that phenolic OH with para-substituted nitro group is less nucleophilic
although initial deprotonation step can occur easier due to it’s lower pKa. In addition, a slight
conformational change in the cavity due to the nitro group could impact the steric hindrance of the
phenol affecting the reaction kinetics, taken together the fact that tetraEGylation of calix[4]arene 1a
and nitrocalix[4]arene 4a were both successful as described in the following section.
EGylation of calix[4]arenes 1a and 4a
As described above, EGylation of the phenols in the lower rim can lock the conformation of
calix[4]arene cavity to restrict the interconversion. For this reason, EGylation of the flexible
mononitrocalix[4]arene 4a was carried out in the presence of NaH at 85 ºC to afford
4
Since tetraEGylcalix[4]arene 8 was obtained from 1a efficiently, it was speculated that additional EGylation of 7 to provide 5a’ was possible.
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tetraEGylcalix[4]arene 5a (Figure 3b). As a standard reaction, flexible calix[4]arene 1a was
subjected to the same EGylation condition. As previously reported, the reaction of 1a provided
+
tetra-EGylated compound 8 in only the cone conformation, owing to the Na coordinating in the
lower rim of the cavity (Figure 3a). 5
Figure 3. (a-c) Tetra EGylation of 1a (a) and 4a (b), and conformational determination of 5a by ROESY measurement (c). While unsubstituted 1a
provided 8 with locked cone conformation, mono-nitro derivative 4a provided 5a in locked partial cone conformation. Reagents and conditions: (a)
TsOC
g) in CDCl
the addition of EG groups as suggested from the sharper peaks of bridging protons (Ar-CH
of 8 and 5a indicated that they are in cone and partial cone conformations respectively, which was further confirmed by ROESY measurement in case of
a (c).
2
H
4
OC
2
H
5
, NaH, DMF, 85 °C, overnight, 55%, (b) BrOC
. The broadening of bridging methylene protons in 1a and 4a indicated that their cavities are in flexible conformation, which was locked by
-Ar) of 8 and 5a. The patterns of these protons (Hax and Heq
2
H
4
OC
2
H
5
, NaH, DMF, 85 °C, 4 days, 12%. (d-g) H NMR spectra of 1a (d), 8 (e), 4a (f), and 5a
1
(
3
2
)
5
ax
eq
1
As indicated by broad peaks for the bridging methylene protons (H and H ) in H-NMR,
mononitrocalix[4]arene 4a had a flexible conformation (Figure 3f) similar to 1a (Figure 3d). On
the other hand, the phenolic protons of both 1a and 4a were observed in > 10 ppm area
corresponding to the region for H-bonded OH groups. The OH signals of 4a were much broader
than the ones of 1a, which has less flexibility with stronger H-bonding. As previously reported,
after EGylation of 1a, the methylene bridging protons of 8 became sharper with two distinct
5
We also carried out hexa-EGylation of 1b and 4b, but obtained hexa adducts of calix[6]arenes remained flexible in CDCl3.
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ax
eq
doublets, which corresponded to the axial (H , 4.50 ppm) and equatorial (H , 3.15 ppm)
methylene protons confirming the successful lock to cone conformation of the cavity (Figure 3c).
This cone shape of 8 was also confirmed by 13C-NMR with the appearance of a single peak at
30.9 ppm corresponding to the bridging methylene carbons, which are in accordance to the
literature.22
Similarly, tetra-EGylated product 5a was obtained as a single conformer from flexible 4a.
1
13
6
Detailed H, C NMR and ROESY analyses confirmed that compound 5a was in a partial cone
conformation (Figures 3c, S23-28). Considering the fact that calix[4]arene 1a provided 8 in a
cone conformation, we speculated that 4a did not have preferred cone shape due to its rather
bulky NO
2
group, which simultaneously weakened the H-bonds of the phenolic protons. This
1
was also indicated by the broadening of H NMR peak corresponding to the OH groups in 4a that
appeared in H-bonding OH region at ≥ 10 ppm (Figure 3f).
Mononitrocalix[4]arene 5a’ in cone conformation
For the preparation of mononitro-tetraEGylcalix[4]arene in cone conformation,
tetraEGylcalix[4]arene 8 with a pre-locked cone conformation was subjected to the non-
controlled nitration to provide mononitro- and dinitro-tetraEGylcalix[4]arenes 5a’ and 9 both
in cone conformation (Fig. 4a). The conformations of the obtained products 5a’ and 9 were
1
confirmed to be cone by H-NMR by the two distinct types of bridging methylenes (Fig. 4c, d).
d
u
The chemical shift of bridging methylenes (H , H ) of 8, 5a’ and 9 showed only slight difference,
indicating that their conformations of the cavity parts were all similar showing little effect of the
nitro groups in the upper rim.
Figure 4. (a) Non-controlled nitration of calix[4]arene 8 with pre-locked cone conformation to form mononitro-and dinitro-tetraEGylcalix[4]arenes 5a’
and 9 and (b-d) their
1
H-NMR of 8, 5a’, and 9 in CDCl
substitution in the upper rim on the conformation of cavity as indicated chemical shifts of bridging methylene protons
Hax and Heq) of 8, 5a’, and 9 in a similar range.
3 3
. Reagents and condition: i) HNO (65%, 23 equiv), DCM/AcOH, rt, 3 h, 28% (5a’) and 38% (9).
There is little effect by the NO
2
(
6
13C-NMR chemical shifts of bridging methylenes of 5a were 34.4 and 30.4 ppm (Figure S24).
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Effect of EG groups in lower rim on the conformation of calix[4]arene cavity
As described above, EGylation of OH groups can lock the conformation of calix[4]arenes.
However, the hexaEGylation at the lower rim of calix[6]arenes 1b and 4b possessing larger
cavities was not successful locking in their conformation, as confirmed by the broad peaks of
1
their bridging methylene protons in H-NMR (data are not shown). To see the effect of EGylation
1
on the cavity conformation of calix[4]arenes, we compared H-NMR signals of bridging
methylene protons of EGylated calix[4]arenes with different numbers of EG groups in the lower
rim (Figure 5). As indicated in Figure 5b, the conformation of calix[4]arene 10 with just one EG
13
group was locked to cone conformation, which was additionally confirmed by C-NMR peaks of
ox
bridging methylenes (31.9 and 31.2 ppm). Consequently, the three phenolic protons (H ) of 10
were observed in H-bonded OH region (> 9 ppm), while one phenol OH in cone-tri-EG-
1
calix[4]arene 6 was observed at around 5 ppm in non-H-bonding region. The H-NMR chemical
ex
shifts of the bridging methylene protons, especially equatorial protons (H ) of mono-, tris-, and
tetraEGylcalix[4]arenes 10, 6, and 8, shifted to upper field upon increasing the numbers of EGs,
presumably by reflecting the different shapes of their cone cavities (Figures 5 and S51).
Figure 5 (a-d) 1H-NMR spectra of EGylated calix[4]arene derivatives 1a (a), 10 (b), 6 (c), and 8 (d) in CDCl
. The change in the chemical shift of the
3
2
methylene bridging protons (Ar-CH -Ar) by the addition of EG groups indicated that addition of EG in the lower rim affects the conformation of the
cone cavity.
Conclusions
Mono-nitro calix[4]arene derivatives in both locked partial cone and locked cone conformations
were successfully prepared by two different synthetic approaches. While EGylation of
calix[4]arene provided tetra-EGylated product in a cone conformation, the same reaction of
mononitro calix[4]arene provided the one in partial cone conformation. Even single EGylation
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was efficient to lock the conformation of calix[4]arenes but not in the case of calix[6]arenes.
Tetra EGylated calix[4]arene was subjected to the non-controlled nitration to provide mono-
and di-nitro calix[4]arene derivatives in cone conformation.
Experimental Section
General
NMR spectra were recorded on a Varian Mercury-vx 300 spectrometer (Varian, UK), a Brucker
Magnet System 400 Mhz/54 mm spectrometer (Brucker BioSpin, Fällanden, CH) and, a Brucker
Avance III 600 spectrometer (Brucker BioSpin AG, Fällanden, CH). IR spectra were recorded on
a JASCO FT/IR-4100 (JASCO, Tokyo, JPN). Mass Spectrometry was performed on a Brucker
Maxis (Brucker Daltonics GmbH, Bremen, D). HPLC analysis were carried out using a JASCO PU-
2
(
080 intelligent HPLC pump, solvent mixing module MX-2080-31, PDA detector MD-2018 Plus
JASCO, Tokyo, JPN). Melting points were measured on a Büchi Melting Point B-545 (Büchi
Labortechnik AG, Flawil, CH). All solvents were purchased from Sigma-Aldrich Chemie GmbH
Steinheim, D). Sodium hydroxide, hydrochloric acid and pyridine (distilled in calcium hydride)
(
were purchased from Fluka Chemie GmbH (Buchs, CH). Acetic acid and nitric acid were
purchased from Merck KGaA (Darmstadt, D). Calixarenes and Benzoyl chloride were purchased
from Acros Organics (Geel, BE) and, 2-bromoethyl ethyl ether from ABCR GmbH (Karlsruhe, D).
25,26,27-tribenzoyloxy-28-hydroxycalix[4]arene (2a). To a solution of calix[4]arene 1a
(0.935 g, 2.20 mmol) in anhydrous pyridine (11 mL), benzoyl chloride (2.07 mL, 2.5050 g, 17.81
mmol) was added at 0 ºC (ice bath). The reaction mixture was stirred at 0 °C for 1 h and then
allowed to warm slowly to room temperature over another 1 h. Then water (70 mL) was added
to produce the insoluble material, which was filtered off and washed with methanol. The white
precipitate was then recrystallized from MeOH-CHCl (1:2) to yield small colorless crystals 2a
3
-
1
-1
1
(
1.34 g, Y = 82%); mp 274-275 °C; IR 3541 cm (OH), 1727 cm (C=O); H-NMR (300 MHz,
1
3
CDCl
3
, RT) δ (ppm) 3.4-3.9 (m, 8H), 5.4 (s, OH), 6.5-8.1 (m, 36H); C-NMR (100 MHz, CDCl
3
, RT)
δ (ppm) 32.4, 37.5, 119.8, 125.2, 126.0, 127.8, 127.9, 128.1, 129.2, 129.5, 130.3, 130.7, 130.8,
1
31.3, 132.6, 132.9, 133.2, 133.5, 138.8, 146.7, 148.3, 152.8, 163.9, 164.5; HR-ESI-MS(+) [M+H]+
+•
calcd. for C49
37
H O
7
737.2534 m/z, found 737.2531 m/z.
3
7,38,39,40,41-pentabenzoyloxy-42-hydroxy-calix[6]arene (2b). To a stirred solution of
calix[6]arene (2.5 g, 3.93 mmol) in dry pyridine (30 mL) was added benzoyl chloride (3.4 mL,
9.04 mmol) at 0 °C under nitrogen atmosphere. After 1 h, the reaction mixture was allowed to
2
warm up to room temperature and it was stirred for another 4 hours. The reaction was
quenched with an aqueous HCl solution (2 M, 150 mL) and the precipitate was filtered. The
precipitated was further washed with an aqueous NaOH solution (2 M), water and methanol in
1
order to afford pentabenzoylcalix[6]arene 2b as colorless crystals (1.37 g, 30%); H-NMR (300
MHz, toluene, 100 °C) δ (ppm) 3.8 (s, 4H), 3.9 (s, 4H), 3.95 (s, 4H), 5.4 (s, 1H), 6.6-7.3 (m, 34H),
+
+
7
.7-8.0 (m, 9H); HRMALDI-TOF(+) (3-HPA) [M+Na] calcd for C57
H
56NaO11 1179.37 m/z, found
+
+
1179.373 m/z, [M+K] calcd for C57
H56KO11 1195.35 m/z, found 1196.349 m/z..
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5
-nitro-25,26,27-tribenzoyloxy-28-hydroxycalix[4]arene (3a). HNO
added to a stirred solution of 2a (100 mg, 0.136 mmol) in a mixture of CH
0.67 mL) at room temperature. The reaction mixture stirred for 1 h and was then quenched
with water (10 mL). The organic layer was washed twice with water (10 mL) and dried over
MgSO . The solvent was removed under reduced pressure and purified by a silica gel flash
column chromatography to give 3a as a yellow solid (50 mg, 47%); mp 270-272 °C (dec.); IR
3
(65%, 17.46 μL) was
2
Cl (2 mL) and AcOH
2
(
4
-1
[cm ] 3497m (O-H), 2924m, 1729s (C=O), 1601w, 1519m, 1451m, 1337m (NO ), 1265s, 1169m,
2
1
1
8
1
1
C
061m, 1024m, 755m 708s; H NMR (300 MHz, CDCl
3
, RT) δ

: 3.5-3.9 (m, 8H), 6.35 (s, OH) 6.5-
13
.0 (m, 26H), 7.9 (s, 2H); C-NMR (150 MHz, CDCl
28.0, 128.3, 128.4, 128.8, 129.3, 130.6, 130.9, 131.0, 131.2, 131.3, 133.3, 133.5, 133.8, 134.1,
40.4, 146.9, 148.3, 158.6, 163.8, 164.2; HRMS (MALDI TOF (–)) (matris: 3-HPA) m/z calcd for
3
, RT) δ 32.6, 37.4, 125.0, 125.3, 126.3, 127.9,
c
34NO
−: 780.2234, found: 780.2239 [M−H]−.
49
H
9
5
-nitro-37,38,39,40,41-pentabenzoyloxy-42-hydroxy-calix[6]arene (3b). HNO
μL) was added to a solution of 2b (67.7 mg, 0.0585 mmol) in CH Cl (0.9 mL) and AcOH (0.3 mL)
and stirred at room temperature for 1 h. Then, the reaction mixture was quenched with water,
and the organic layer was washed twice with water and dried over MgSO . The solvent was
removed under reduce pressure and the residue was purified by a silica gel flash column
3
(65%, 10
2
2
4
chromatography (Hexane/CHCl
n-hexane-toluene (2:1)) to give 3b as a pale yellow solid (13.6 mg, 20%); H-NMR (300 MHz,
3
/EtOAc 8:4:2) followed by a semi-prep HPLC (10% of EtOAc in
1
toluene, 100 °C) δ (ppm) 3.7 (s, 4H), 3.8 (s, 4H), 3.9 (s, 4H), 6.3 (s, 1H), 6.6-7.3 (m, 31), 7.7-8.0
+
55NNaO13+
(
1
m, 11), 7.9 (s, 2H). HRMALDI-TOF(+) (matrix: 3-HPA) [M+Na] calcd for C77
H
+
+
224.3571 m/z, found 1224.357 m/z, [M+K] cacld for C77
H
55NKO13 1240.3310 m/z, found
1240.334 m/z.
5-nitro-25,26,27,28-hydroxycalix[4]arene (4a). NaOH (3.0 g, 75 mmol) was added to a
solution of 3a (797 mg, 1.02 mmol) in a mixture of THF (50 mL), EtOH (30 mL), and water (20
mL). The reaction mixture was heated at 85 °C overnight. After the solvents were removed
under reduced pressure, the residue was acidified with 2M HCl (60 mL), and the precipitate was
collected by filtration and dried overnight at 60 °C. The crude mixture was purified by a silica
gel flash column chromatography (dry loading, Haxena/CHCl 19:1 to 7:1) to give 4a as a pale
3
-1
yellow solid (267 mg, 56%); mp 244-246 °C (dec.); IR (KBr) [cm ] 3414s (O-H), 2929m, 1617m,
1
1
521w, 1466s, 1450s, 1406w, 1340m (NO
NMR (400 MHz, CDCl ) δ : 3.61 (brd, 4H, J 46.1 Hz, CH
.6 Hz, HAr), 6.81 (dd app t, 2H, J 7.6 Hz, HAr), 7.06 (d, 2H, J 7.6 Hz, HAr), 7.12 (dq, 4H, J 1.7 and
.6 Hz, HAr), 8.00 (s, 2H, HAr), 10.15 (brs, 4H, OH); 13C-NMR (100 MHz, CDCl
) δ : 31.5 (CH ),
1.6 (CH ), 122.5 (CHAr), 122.7 (CHAr), 124.7 (CHAr), 126.5 (CAr), 127.8 (CAr), 128.5 (CAr),
29.0 (CHAr), 129.0 (CHAr), 129.3 (CAr), 129.6 (CHAr), 141.9 (CAr), 148.4 (CAr), 148.5 (CAr);
, found: 470.1598 [M+H]+.
2
), 1282m, 1259m, 1211m, 1098m, 1025m, 756m; H
3

2
), 4.28 (bs, 4H, CH ), 6.74 (dd app t, 1H, J
2
7
7
3
1
3
c
2
2
HRMS (ESI+) m/z 470.1598 calcd for C28
H
24NO +
6
5-nitro-37,38,39,40,41,42-hydroxycalix[6]arene (4b). To a stirred solution of 3b (56 mg,
0.046 mmol) in a mixture of THF (2.5 mL), EtOH (1.5 mL), and water (1 mL), NaOH (0.24 g) was
added at room temperature. The reaction mixture was allowed to stir overnight at 85 °C. The
solvents were removed under reduced pressure and the residue was acidified with an aq. sol.
HCl (2 M). The precipitate was filtered and the residue was purified by flash column
chromatography (DCM/hexane: 1:1 to 4:1) to afford 4b as a yellowish solid (15 mg, 48%); δ
600 MHz, CDCl ): 3.90 (brs, 12H, CH ), 6.73-7.21 (m, 15H, HAr), 7.96 (brs, 2H, HAr), 10.20 (brs,

(
3
2
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2
1
1
1
C
H, OH), 10.28 (brs, 2H, OH), 11.33 (brs, 1H, OH). δ
21.9 (CHAr), 122.2 (CHAr), 122.5 (CHAr), 125.3 (CHAr), 125.8 (CAr), 127.2 (CAr), 127.4 (CAr),
27.7 (CAr), 128.4 (CAr), 129.6 (CHAr), 129.8 (CHAr), 129.8 (CHAr), 130.2 (CHAr), 141.8 (CAr),
49.3 (CAr), 149.4 (CAr), 149.6 (CAr), 155.9 (CAr); HRMALDI-TOF(−) (3-HPA) [M−H] calcd for
C
(150 MHz, CDCl
3
): 32.1 (CH
2
), 32.2 (CH ),
2
−
−
42
H34NO
8
680.2284 m/z, found 680.2281 m/z.
5-nitro-25,26,27,28-tetra(ethoxyethoxy)calix[4]arene (partial cone 5a). To a solution of 4a
(90 mg, 0.191 mmol) in a mixture of THF (4.6 mL) and DMF (15.0 mL), NaH (92 mg, 3.83 mmol)
and 2-bromoethyl ethyl ether (0.646 mL, 5.73 mmol) were added and the reaction mixture was
refluxed (85 °C) for 4 days. THF was removed under reduced pressure and the excess of NaH
was destroyed by addition of water. The mixture was neutralized with 2M HCl and the product
was extracted with dichloromethane. The organic layer was washed twice with water and dried
over MgSO and the solvent was removed under reduced pressure to give a brown oily residue,
4
which was purified by a silica gel flash column chromatography which was followed by semi-
1
prep HPLC to give 5a as a white solid (17.26 mg, 12%); H-NMR (300 MHz, CDCl
3
) δ (ppm) 1.1
(t, J = 7.0 Hz, 1H), 1.2-1.4 (m, 9H), 3.0 (d, J = 13.4 Hz, 1H), 3.2-3.4 (m, 4H), 3.5-4.0 (m, 22H), 4.0-
4
.1 (m, 2H), 4.15 (d, J = 13.3 Hz, 1H), 6.3 (dd, J = 7.7, 1.1 Hz, 1H), 6.45 (t, J = 7.6 Hz, 1H), 6.9 (t, J =
1
3
7
CDCl
1
.4 Hz, 1H), 7.0 (dd, J = 7.4, 1.6 Hz, 1H), 7.05 (d, J = 7.4 Hz, 1H), 8.4 (s, 2H); C-NMR (150 MHz,
, rt) δ (ppm) 15.20, 15.5, 30.4, 34.4, 65.7, 66.7, 66.8, 69.1, 69.6, 69.8, 71.7, 72.6, 73.9, 122A,
22.3, 126.1, 128.9 (2 carbons), 131.3, 133.7, 135.5, 136.5, 134.6, 142.6, 154.9, 157.3, 162.7;
3
+
+
HRMALDI-TOF(+) (3-HPA) [M+Na] calcd for C44
H
55NaO10 780.3724 m/z, found 780.3713 m/z,
+
+
[M+K] calcd for C44H55KO10 796.3463 m/z, found 796.3457 m/z.
25,26,27-tris(ethoxyethoxy)calix[4]arene (6). To a stirred solution of calix[4]arene 1a (1.93
g, 4.10 mmol) in dry DMF (100 mL) was added barium hydroxide octahydrate (3.88 g, 12.30
mmol) and barium oxide (3.29 g, 19.3 mmol, 90%) at room temperature under nitrogen
atmosphere. After 2 h, the temperature was increased to 80 °C and the reaction mixture was
allowed to stir overnight. The solvent was evaporated and the oil residue was dissolved in DCM
(
100 mL). The organic layer was washed with water (4x100 mL) and the combined organic
fractions were dried over MgSO and concentrated under reduced pressure. The oil residue was
purified by flash column chromatography (hexane/ethyl acetate 9:1) to afford tri-
EGylatedcalix[4]arene 6 as a colorless solid (2.11 g, 80%);  (400 MHz, CDCl ): 1.27 (t, 3H, J 7.0
Hz, CH ), 1.28 (t, 6H, J 7.0 Hz, CH ), 3.26 (d, 2H, J 13.3 Hz, CH ), 3.35 (d, 2H, J 13.7 Hz, CH ), 3.64
q, 4H, J 7.0 Hz, OCH CH ), 3.65 (q, 2H, J 7.0 Hz, OCH CH ), 3.83-3.86 (m, 4H, OCH O), 4.00-
O), 4.13-4.17 (m, 2H, OCH CH O), 4.21-4.25 (m, 4H, OCH O), 4.47 (d,
), 4.58 (d, 2H, J 13.3 Hz, CH
4

3
3
3
2
2
(
4
2
2
3
2
3
2
CH
2
.10 (m, 4H, OCH
H, J 13.7 Hz, CH
2
CH
2
2
2
2
CH
2
2
2
), 4.98 (s, 1H, OH), 6.44-6.50 (m, 6H, HAr), 6.81 (dd
apt t, 1H, J 7.5 Hz, HAr), 7.00 (dd apt t, 1H, J 7.5 Hz, HAr), 7.14 (d, 2H, J 7.5 Hz, HAr), 7.20 (d, 1H, J
.5 Hz, HAr);  (100 MHz, CDCl ): 15.3 (CH ), 15.6 (CH ), 30.1 (CH ), 31.0 (CH ), 66.4
), 66.7 (OCH CH ), 69.2 (OCH CH O), 69.4 (OCH CH O), 71.9 (OCH CH O), 74.6
O), 119.2 (CHAr), 123.1 (CHAr), 123.3 (CHAr), 127.9 (CHAr), 128.1 (CHAr), 128.5
7
C
3
3
3
2
2
(
(
(
(
OCH
OCH
2
2
CH
CH
3
2
3
2
2
2
2
2
2
2
CHAr), 129.2 (CHAr), 130.7 (CAr), 132.8 (CAr), 133.6 (CAr), 137.0 (CAr), 153.4 (CAr), 154.1
CAr), 156.7 (CAr); HRMS (ESI): m/z calculated for C40 [M+NH
]+ 658.3738, found
58.3732.
H
52NO
7
4
6
5
-nitro-26,27,28-tris(ethoxyethoxy)calix[4]arene
tripEylatedgcalix[4]arene 6 (185 mg, 0.29 mmol) in a mixture of DCM/AcOH 3:1 (10 mL) was
added dropwise fuming HNO (15 μL, 0.34 mmol) at 0 °C under nitrogen atmosphere. The
(7).
To
a
solution
of
3
reaction mixture was allowed to warm up to room temperature. After 1.5 h water (3x10 mL)
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was added to the reaction mixture and it was extracted with CH
layer was then washed with aq solution K CO (5%) until pH 7. The combined organic layers
were dried over MgSO and concentrated under reduced pressure. The residue was purified by
flash column chromatography (hexane/ethyl acetate 0.5:9.5 to 9:1) to give the product as a
yellowish solid (103 mg, 52%).  (400 MHz, CDCl ): 1.58 (t, 3H, J 7.0 Hz, CH ), 1.59 (t, 6H, J 7.0
Hz, CH ), 3.58 (d, 2H, J 13.1 Hz, CH ), 3.75 (d, 2H, J 13.9 Hz, CH ), 3.94 (q, 2H, J 7.0 Hz, OCH CH ),
.96 (q, 4H, J 7.0 Hz, OCH CH ), 4.11-4.12 (m, 4H, OCH CH O), 4.34-4.45 (m, 4H, OCH CH O),
.34-4.45 (m, 2H, OCH CH O), 4.50-4.54 (m, 2H, OCH CH O), 4.83 (d, 2H, J 13.8 Hz, CH ), 4.84 (d,
H, J 13.1 Hz, CH ), 6.81-6.89 (m, 6H, HAr), 7.23 (s, 1H, OH), 7.29 (dd apt t, 1H, J 7.5 Hz, HAr),
.48 (d, 2H, J 7.5 Hz, HAr), 8.40 (s, 2H, HAr).  (100 MHz, CDCl ): 15.2 (CH ), 15.5 (CH ), 30.7
), 30.8 (CH ), 66.4 (OCH CH ), 66.7 (OCH CH ), 69.1 (OCH CH O), 69.3 (OCH CH O), 71.9
OCH CH O), 74.9 (OCH CH O), 123.3 (CHAr), 123.7 (CHAr), 124.5 (CHAr), 127.8 (CHAr), 128.9
CHAr), 129.1(CHAr), 129.7 (CAr), 131.2 (CAr), 134.0 (CAr), 136.5 (CAr), 139.6, (CAr), 153.9
CAr), 156.3 (CAr), 159.7 (CAr). HRMS (ESI): m/z calculated for C40 [M+NH
]+ 703.3589,
2 2
Cl
(2x10 mL). The organic
2
3
4

3
3
3
2
2
2
3
3
4
2
7
2
3
2
2
2
2
2
2
2
2
2
2
C
3
3
3
(
(
(
(
CH
2
2
2
3
2
3
2
2
2
2
2
2
2
2
H
51
N
2
O
9
4
found 703.3581.
25,26,27,28-tetra(ethoxyethoxy)calix[4]arene (8). Calix[4]arene 1a (2.54 g, 5.41 mmol) was
dissolved in dry DMF (76 mL) and cooled down to 0 °C. Sodium hydride (2.16 g of a 60%
dispersion in oil, 54.1 mmol) was added portionwise and the reaction mixture was stirred for 30
min under nitrogen atmosphere. 2-ethoxyethyl 4-methylbenzenesulfonate (6.44 g, 0.10 mmol)
was then added portionwise and the reaction mixture was allowed to warm up to room
temperature during 1.5 h. After that time the reaction warmed up to 80 °C and stirred overnight.
The reaction was quenched with water (100 mL) and the solvents were evaporated. The residue
was dissolved in DCM (100 mL) and washed with an aq. sat. solution of NH
organic layer was separated and washed 2x with water, dried over MgSO
under reduced pressure. The obtained oil was treated with cold methanol and the
tetrapegcalix[4]arene 8 was obtained by crystallization as a white solid (2.13 g, 55%); δ (400
MHz, CDCl ): 1.21 (t, 12 H, J 7.0 Hz, CH ), 3.15 (d, 4H, J 13.4 Hz, CH ), 3.55 (q, 8H, J 7.0 Hz,
OCH CH ), 3.85 (t, 8H, J 5.8 Hz, OCH CH O/H3), 4.12 (t, 8H, J 5.8 Hz, OCH CH O/H2), 4.50 (d, 4H,
J 13.4 Hz, CH ), 6.56-6.64 (m, 12 H, HAr); δ (100 MHz, CDCl ): 15.3 (CH ), 30.9 (CH ), 66.4
CH /C5), 69.7 (CH /C3), 73.1 (CH /C2), 122.2 (CHAr, C4’), 128.2 (CHAr, C3’), 135.0 (CAr/C2’),
56.3 (CAr/C1’).
4
Cl (100 mL). The
4
and concentrated

3
3
2
2
3
2
2
2
2
2
C
3
3
2
(
2
2
2
1
5
2
-nitro-25,26,27,28-tetra(ethoxyethoxy)calix[4]arene (cone 5b) and 5,x-dinitro-
5,26,27,28-tetra(ethoxyethoxy)calix[4]arene (9). To solution of tetra-EGylated
Cl /acetic acid 17:1 (50 mL) was added nitric
a
calix[4]arene 8 (1g, 1.40 mmol) in a mixture of CH
2
2
acid (5 mL, 70 mmol, 65% solution in water) at 0 °C under nitrogen atmosphere. The reaction
mixture was stirred for 2 h at 0 °C and 1 h at room temperature. It was observed that the color
of the reaction mixture changed as it warmed up, from pink to black. Water (100 mL) was added
to the reaction mixture and it was extracted with CH
then washed with an aq. solution K CO (5%) until pH 7. The combined organic layers were
dried over MgSO and concentrated under reduced pressure. The residue was purified by a
silica gel flash column chromatography (hexane/ethyl acetate 9:1 to 7:3) to afford
mononitrocalix[4]arene 5a’ as a white solid (292 mg, 27.5%) and 450 mg of
dinitrocalix[4]arene 9 which was further recrystallised in ethyl acetate/hexane; 5a’: δ (300
MHz, CDCl ): 1.17-1.25 (m, 12 H, CH ), 3.15 (d, 2H, J 13.3 Hz, CH ), 3.21 (d, 2H, J 13.3 Hz, CH ),
.49-3.59 (m, 8H, OCH CH ), 3.75-3.87 (m, 8H, OCH CH O), 4.02-4.23 (m, 8H, OCH CH O), 4.49
2
2
Cl (2x100 mL). The organic layer was
2
3
4

3
3
2
2
3
2
3
2
2
2
2
This article is protected by copyright. All rights reserved.

(
d, 2H, J 13.6 Hz, CH
2
), 4.59 (d, 2H, J 13.6 Hz, CH
(75 MHz, CDCl ): 15.3 (CH
), 66.4 (CH ), 69.7 (CH ), 69.7 (CH ), 69.7 (CH
), 122.0 (CHAr), 122.6 (CHAr), 123.3 (CHAr), 128.0 (CHAr), 128.3 (CHAr), 129.2 (CHAr),
2
), 6.33-6.40 (m, 3H, HAr), 6.73-6.86 (m, 6H,
), 15.3 (CH ), 30.9 (CH ), 31.0 (CH ), 62.3
), 73.0 (CH ), 73.4 (CH ), 74.0
HAr), 7.27 (s, 2H, HAr); δ
C
3
3
3
2
2
(
(
CH
CH
2
), 66.4 (CH
2
2
2
2
2
2
2
2
1
(
(
34.3 (CAr), 134.5 (CAr), 136.0 (CAr), 136.3 (CAr), 142.6 (CAr), 155.7 (CAr), 156.9 (CAr), 161.6
CAr); HRMS (ESI): m/z calculated for C44
]+ 775.4164, found 775.4156; 9: δ
400 MHz, CDCl ): 1.16 (t, 6 H, J 7.0 Hz, CH ), 1.21 (t, 6 H, J 7.0 Hz, CH ), 3.25 (d, 4H, J 13.7 Hz,
), 3.49 (q, 8H, J 7.0 Hz, OCH CH ), 3.54 (q, 8H, J 7.0 Hz, OCH CH ), 3.78 (t, 4H, J 5.2 Hz,
OCH CH O), 3.83 (t, 4H, J 5.1 Hz, OCH CH O), 4.07 (t, 4H, J 5.2 Hz, OCH CH O), 4.30 (t, 8H, J 5.1
Hz, OCH CH O), 4.58 (d, 4H, J 13.7 Hz, CH ), 6.53-6.59 (m, 6 H, HAr), 7.66 (s, 4H, HAr); δ (100
MHz, CDCl ): 15.3 (CH ), 15.3 (CH ), 30.9 (CH ), 66.3 (CH ), 66.4 (CH ), 69.5 (CH ), 69.8 (CH ),
), 73.6 (CH ), 123.1 (CHAr), 123.7 (CHAr), 128.6 (CHAr), 133.3 (CAr), 136.9 (CAr),
H
59
N
2
O
10 [M+NH
4

3
3
3
CH
2
2
3
2
3
2
2
2
2
2
2
2
2
2
C
3
3
3
2
2
2
2
2
7
1
8
3.6 (CH
2
2
42.5 (CAr), 155.6 (CAr), 162.6 (CAr); HRMS (ESI): m/z calculated for C44
20.4015, found 820.4009.
58
H N
3
O
12 [M+NH
]+
4
Supplementary Material
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/MS-number.
Acknowledgements
This study was supported in part by Swiss National Foundation (200021-140451, 200021-
1
1
56097), PRESTO program from Japan Science and Technology Agency, ETH Grants (ETH-25
1-1, ETH-21 15-2), and the SDG award from American Heart Association (0930140N). Authors
thank NMR service staff in the Laboratory of Organic Chemistry at ETH Zürich for the detailed
measurements.
Author Contribution Statement
A.R.S.N.R, S.A and Y.Y. designed the experiments and A.R.S.N.R and M.A conducted the
experiments of synthesis and characterization. A.R.S.N.R and YY carried out the data analysis
and wrote the manuscript.
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