Synthesis of novel arylhydrazide molecular tweezer artificial receptors based on deoxycholic acid using microwave irradiation

Article abstract of DOI:10.3184/174751911X13026263307911

Eleven novel molecular tweezer anion receptors based on deoxycholic acid have been synthesised using microwave irradiation. Their structures were established by ¹H NMR, IR, MS spectra and elemental analysis. Their binding properties were examined by UV-Vis spectra titration. The preliminary results indicate that these molecular tweezers show good recognition properties for H₂PO₄^-, CH₃COO^- and NO₃^-.

Full text of DOI:10.3184/174751911X13026263307911

234 RESEARCH PAPER
APRIL, 234–237
JOURNAL OF CHEMICAL RESEARCH 2011
Synthesis of novel arylhydrazide molecular tweezer artificial receptors
based on deoxycholic acid using microwave irradiation
Xiaorui Li, Zhigang Zhao*, Yuyu Cheng and Hui Li
College of Chemistry and Environmental Protection Engineering, Southwest University for Nationalities, Chengdu 610041, P. R. China
Eleven novel molecular tweezer anion receptors based on deoxycholic acid have been synthesised using microwave
irradiation. Their structures were established by 1H NMR, IR, MS spectra and elemental analysis. Their binding prop-
erties were examined by UV-Vis spectra titration. The preliminary results indicate that these molecular tweezers
show good recognition properties for H2PO4−, CH3COO− and NO3−.
Keywords: molecular tweezers, microwave irradiation, molecular recognition, deoxycholic acid
Anions play an important role in biology, pharmacy, catalysis
and environmental science.1 The study of artificial receptors
for the detection of biologically relevant anions is an important
challenge in modern bioorganic chemistry.2–9 The basic strate-
gies which have been exploited for the construction of anion-
binding receptors involve electrostatic interactions, hydrogen
bonding, hydrophobicity, coordination to a metal ion, or a
combination of these. Among these noncovalent interactions,
we have been interested in developing hydrogen bond-based
neutral anion receptors. Owing to the relatively strong hydro-
gen bonding ability of the hydrazide and arylhydrazide groups,
a number of molecules possessing hydrazides or arylhydra-
zides groups have been designed as neutral receptors for vari-
ous anions.10–12 For strong and selective binding, these groups
should be preorganized to complement the target anion
and minimize intramolecular hydrogen bonding. One way
to achieve this goal is to make receptors with hydrazide or
arylhydrazide groups connected to rigid spacers. The steroid
nucleus is one of the largest rigid and chiral ubiquitous natural
products. Based on these preorganized structural characteris-
tics, the steroid cholic acid is an ideal building block for the
construction of molecular tweezer artificial receptors. We have
reported that alkoxycarbonyl thiosemicarbazide molecular
tweezer receptors which contain three NH bonds have good
recognition properties for anions.13 On the basis of this, we
have synthesised 11 novel arylhydrazide molecular tweezer
artificial receptors 7a–k, which contain four NH bonds. These
receptors based on arylhydrazide arms, have the NH groups
directed towards the centre of the cavity resulting in a high
selectivity in combining with the substrates. The recognition
properties of the receptors have been examined by UV-Vis
spectra titration. The preliminary results indicate that this kind
of molecular tweezers show good recognition properties for
H2PO4−, CH3COO−, NO3−. The synthetic route is shown in
Scheme 1.
As shown in Table 3, the effect of CH2Cl2, CHCl3 and THF
as a solvent on the reaction was investigated. The results
showed that when CH2Cl2 was used, the yield was a little higher
and considering CH2Cl2 is less toxic than CHCl3, THF, hence
CH2Cl2 was the best solvent for the reaction.
As shown in Table 4, we compared the synthesis of molecular
tweezers 7a–k by microwave irradiation and conventional
heating. Compared to conventional thermal heating, micro-
wave irradiation greatly decreased the reaction time from
480–600 min to 15–25 min. It was obvious that yields were
increased from 35–50% to 87–94%. From these data, we con-
clude that microwave irradiation method is a rapid, efficient
methodology.
The variations in the UV-Vis absorption of these complexing
system has been used as an effective and simple method to
measure the association constants of complexes in supramo-
lecular systems.
Titration experiments for the anion recognition of receptors
7a, 7e, 7i, 7j were performed using UV-Vis spectroscopy in
CHCl3 at 25 °C. Using the linear fitting method, we obtained
the association constants for complex formation. The prelimi-
nary results showed that these molecular tweezers possessed
the ability to form complexes with the guest anions which
were examined as shown in Fig. 1. The supramolecular com-
plexes consisted of 1:1 host and guest molecules. The associa-
tion constants of molecular tweezer 7i, for example, are
465348, 124961, 32359 L mol−1 for H2PO4−, CH3COO−, NO3−
anions respectively. The main driving force are the multiple
hydrogen bonds in molecular recognition. The UV-Vis plot of
7i for H2PO4− is shown in Fig. 2.
The main reason is that when the host 7i is at the minimum
energy, its conformation is similar to the X-ray crystal struc-
ture of desoxycholic acid p-bromoanilide, which has the
ability to form complex with guest molecules.14 The crystal
structure of desoxycholic acid p-bromoanilide is shown in
Fig. 3.
Results and discussion
Experimental
In searching for the best reaction conditions of the synthesis of
molecular tweezer artificial receptors, we used the synthesis of
7a as an example and carried out several experiments under
different conditions, such as microwave irradiation power,
time and solvent to obtain the best results of this reaction. The
results are shown in the following tables.
As shown in Table 1, we irradiated the reaction using differ-
ent powers under the same reaction time (15 min). As a result,
150 W was the optimum power.
As shown in Table 2, we found that 15 min was the optimum
reaction time when the yield was the highest using the same
power (150 W). However, more byproducts were obtained
when the reaction time was increased.
Melting points were determined on a micro-melting point apparatus
and were uncorrected. IR spectra were obtained on 1700 Perkin-Elmer
FTIR using KBr disks. H NMR spectra were recorded on a Varian
1
INOVA 400 MHz spectrometer using TMS as internal standard. Mass
spectra were determined on FinniganLCQDECA instrument. Elemental
analysis was performed on a Carlo-Erba-1106 autoanalyzer. All reac-
tions were performed in a commercial microwave reactor(XH-100A,
100–1000 W, Beijing Xianghu Science and Technology Development
Co. Ltd, Beijing, P.R. China). All the solvents were purified before
use. Optical rotations were measured on a Wzz-2B polarimeter.
All the solvents were purified before use.
Preparation of 3a–k; general procedure
The aromatic acid (5 mmol), thionyl chloride (0.2 mL) and ethanol
(15 mL) were placed in a dried round-bottomed flask and the mixture
was irradiated by microwaves (75 W) for 4 min. On completion of the
reaction, the mixture was cooled to room temperature. The excess
* Correspondent. E-mail: zzg63129@yahoo.com.cn

JOURNAL OF CHEMICAL RESEARCH 2011 235
Scheme 1 The synthetic route of molecular tweezers 7a–k.
Table 1 The effect of microwave power on yield
Table 4 Synthetic comparison of molecular tweezers 7a–7k
between microwave irradiation and conventional heating
Power/W
Yield/%
50
60
100
85
150
92
200
89
250
78
a
b
tC /tMW
Compd Conventional method
Microwave method
t/min
Yield/%
t/min
Yield/%
7a
7b
7c
7d
7e
7f
7g
7h
7i
480
600
480
540
480
600
480
600
540
480
540
50
36
50
48
45
35
48
48
37
48
45
15.0
25.0
15.0
18.0
15.0
25.0
16.0
20.0
19.0
15.0
20.0
92
90
89
91
92
89
88
87
94
93
90
32
24
32
30
32
24
30
30
28
32
27
Table 2 The effect of microwave irradiation time on yield
Time/min
Yield/%
7
67
9
73
11
78
13
83
15
92
17
87
Table 3 The effect of solvent on yield
Entry
Solvent
Yield/%
Volume of solvent/mL
7j
7k
1
2
3
CH2Cl2
CHCl3
THF
92
86
75
10
10
15
a
TC , time of conventional heating method; TMWb, time of micro-
wave irradiation method.

236 JOURNAL OF CHEMICAL RESEARCH 2011
Fig. 1 Typical plot of 1/∆A versus 1/[G]0 for the inclusion
complex of molecular tweezer 7i with H2PO4− in CHCl3 at 25 °C.
Fig. 3 A view of the contents of a unit cell in the crystal of
desoxycholic acid p-bromoanilide(we thank John P. Schaefer
and Larry L. Reed for the X-ray crystal structure of desoxycholic
acid p-bromoanilide support).
Table 5 The melting points of hydrazides 3a–k
Entry Compound
Yield/%
M.p./°C
Lit. m.p./°C
1
2
3a
3b
3c
3d
3e
3f
3g
3h
3i
85
80
80
82
78
83
78
75
83
85
88
112–114
160–163
249–251
135–137
117–118
160–163
116–118
121–123
78–80
112.512
162–16612
251–25312
137–13912
118–12012
160–162.512
11512
3
4
5
6
7
8
122–12415
78–8012
9
10
11
3j
3k
63–65
62–6412
98–100
101–10312
Fig. 2 UV-vis spectra of molecular tweezers 7i (1.2×10−4mol L−1)
in the presence of H2PO4− (a) 0 molL−1; (b) 0.002×10−3molL−1; (c)
0.002×10−3mol L−1; (d) 0.002×10−3molL−1; (e) 0.002×10−3molL−1; (f)
0.002×10−3molL−1; (g) 0.004×10−3mol L−1 with λmax at 242.0 nm.
on silica gel H with dichloromethane/ethyl acetate as eluant. The
whole progress was monitored by TLC. The physical and spectra data
of the compounds 7a–k are as follows.
7a: White crystals, yield 92%, m.p. 130–132 °C; [α]2D0 +83.6
(c 0.11, CH2Cl2); IR (KBr, cm−1): 3287, 2950, 2869, 1736, 1673, 1525,
1486, 1245, 1024, 693; 1H NMR (CDCl3, 400 MHz, δ ppm): 8.80 (s,
2H, CONH), 7.92 (d, J = 7.6 Hz, 2H, ArH), 7.84 (d, J = 7.2 Hz, 2H,
ArH), 7.52 (t, J = 7.0 Hz, 3H, ArH and NHCOO), 7.43–7.37 (m, 5H,
ArH), 5.02 (s, 1H, 12β-H), 4.63 (s, 1H, 3β-H), 3.66 (s, 3H, COOCH3),
0.95 (s, 3H, 19-CH3), 0.85 (d, J = 6.8 Hz, 3H, 21-CH3), 0.68 (s, 3H,
18-CH3); ESI-MS m/z (%): 1483.91 ([2M+Na]+, 100). Anal. Calcd
for C41H54N4O8: C, 67.38; H, 7.45; N, 7.67. Found: C, 67.25; H, 7.47;
N, 7.66%.
thionyl chloride was removed. Then the reaction mixture was added to
85% hydrazine hydrate (2 mL) and subjected to microwave irradiation
(75 W) for 3 min. The mixture was evaporated to give the crude
product. The crude product was recrystallised from ethanol to give a
pure sample. The melting points of the hydrazides 3a–k are shown in
Table 5.
Preparation of compound 5; general procedure
Deoxycholic acid 4 was converted to methyl 3α,12α-dihydroxy-7-
deoxy-5β -cholan-24-oate 5 following the literature procedure.16
7b: White crystals, yield 90%, m.p. 138–139 °C; [α]2D0 +150.8
(c 0.12, CH2Cl2); IR (KBr, cm−1): 3299, 2949, 2870, 1736, 1671, 1604,
1501, 1238, 1160, 1039, 852, 762, 605; 1H NMR (CDCl3, 400 MHz,
δ ppm): 8.86 (s, 2H, CONH), 7.95 (s, 2H, ArH), 7.85 (s, 2H, ArH),
7.52 (s, 2H, NHCOO), 7.26–7.06 (m, 4H, ArH), 5.02 (s, 1H, 12β-H),
4.62 (s, 1H, 3β-H), 3.67 (s, 3H, COOCH3), 0.96 (s, 3H, 19-CH3), 0.86
(d, J = 6.8 Hz, 3H, 21-CH3), 0.69 (s, 3H, 18-CH3); ESI-MS m/z (%):
767.71 ([M+H]+, 100). Anal. Calcd for C41H52F2N4O8: C, 64.21; H,
6.83; N, 7.31. Found: C, 64.09; H, 6.85; N, 7.32%.
Microwave method for preparation of 7a–k
Triphosgene (0.37 mol) was added to a solution of compound 5
(0.5 mmol) in 10 mL dry CH2Cl2 and 0.2 mL dry pyridine at room
temperature. The reaction mixture was irradiated for 15 min at 150 W
to give compound 6. The arylhydrazide (1.5 mmol) and dry pyridine
0.2 mL were added directly to the mixture, Which was then irradiated
continually for 15–25 min at 150 W. The solvent was removed and the
residue was diluted with 20 mL ethyl acetate and washed with 10%
HCl (10 mL×3), brine (10 mL×3), and finally dried over anhydrous
Na2SO4. The crude product was purified by column chromatography
7c: White crystals, yield 89%, m.p. 145–146 °C; [α]2D0 +136.0
(c 0.15,CH2Cl2); IR (KBr, cm−1): 3285, 2951, 2869, 1736, 1665, 1592,

JOURNAL OF CHEMICAL RESEARCH 2011 237
1481, 1248, 1071, 1011, 845, 754, 617; 1H NMR (CDCl3, 400 MHz,
δ ppm): 8.92 (s, 2H, CONH), 7.78 (d, J = 7.2 Hz, 3H, ArH), 7.69 (d,
J = 6.8 Hz, 2H, ArH), 7.55 (d, J = 8.0 Hz, 5H, ArH and NHCOO),
5.02 (s, 1H, 12β-H), 4.62 (s, 1H, 3β-H), 3.67 (s, 3H, COOCH3), 0.94
(s, 3H, 19-CH3), 0.87 (d, J = 6.4 Hz, 3H, 21-CH3), 0.69 (s, 3H, 18-
CH3); ESI-MS m/z (%): 1799.33 ([2M+Na]+, 100). Anal. Calcd for
C41H52Br2N4O8: C, 55.41; H, 5.90; N, 6.30. Found: C, 55.56; H, 5.89;
N, 6.29%.
7j: White crystals, yield 93%, m.p. 93–94 °C; [α]2D0 +125.0 (c 0.12,
CH2Cl2); IR (KBr, cm−1): 3387, 2948, 2870, 1736, 1674, 1474, 1236,
1
1035, 757, 613; H NMR (CDCl3, 400 MHz, δ ppm): 9.90–9.82 (m,
2H, CONH), 8.23 (s, 1H, NHCOO), 8.2 (d, J = 7.6 Hz, 1H, NHCOO),
7.45 (s, 3H, ArH), 7.32 (s, 1H, ArH), 7.09–6.96 (m, 4H, ArH), 5.08 (s,
1H, 12β-H), 4.72 (s, 1H, 3β-H), 4.26–4.21 (m, 4H, OCH2), 3.66 (s,
3H, COOCH3), 1.64–1.56 (m, 6H, CH3), 0.99 (s, 3H, 19-CH3), 0.91
(d, J = 6.4 Hz, 3H, 21-CH3), 0.72 (s, 3H, 18-CH3); ESI-MS m/z (%):
819.70 ([M+H]+, 100). Anal. Calcd for C45H62N4O10: C, 65.99; H,
7.63; N, 6.84. Found: C, 66.08; H, 7.61; N, 6.86%.
7d: White crystals, yield 91%, m.p. 137–138 °C; [α]2D0 +156.2
(c 0.13,CH2Cl2); IR (KBr, cm−1): 3307, 2948, 2869, 1735, 1664, 1608,
1503, 1250, 1175, 1027, 846, 764, 609; 1H NMR (CDCl3, 400 MHz,
δ ppm): 8.65 (s, 2H, CONH), 7.89–7.80 (m, 4H, ArH), 7.26 (s, 2H,
NHCOO), 6.91–6.85 (m, 4H, ArH), 5.02 (s, 1H, 12β-H), 4.63 (s, 1H,
3β-H), 3.83 (s, 3H, OCH3), 3.82 (s, 3H, OCH3), 3.67 (s, 3H, COOCH3),
0.95 (s, 3H, 19-CH3), 0.86 (d, J = 6.8 Hz, 3H, 21-CH3), 0.68 (s, 3H,
18-CH3); ESI-MS m/z (%): 1581.69 ([2M+H]+, 100). Anal. Calcd for
C43H58N4O10: C, 65.30; H, 7.39; N, 7.08. Found: C, 65.39; H, 7.37;
N, 7.09%.
7k: White crystals, yield 90%, m.p. 123–124 °C; [α]2D0 +34.5
(c 0.11, CH2Cl2); IR (KBr, cm−1): 3288, 2950, 2868, 1736, 1669, 1522,
1482, 1262, 1224, 1040, 744, 689; 1H NMR (CDCl3, 400 MHz,
δ ppm): 8.55 (s, 2H, CONH), 7.69 (s, 2H,ArH), 7.62 (s, 2H, NHCOO),
7.30 (d, J = 4.8 Hz, 6H, ArH), 5.03 (s, 1H, 12β-H), 4.65 (s, 1H, 3β-H),
3.66 (s, 3H, COOCH3), 2.34 (s, 3H, CH3), 2.32 (s, 3H, CH3), 0.94 (s,
3H, 19-CH3), 0.87 (d, J = 6.8 Hz, 3H, 21-CH3), 0.69 (s, 3H, 18-CH3);
ESI-MSm/z(%):1518.85([2M+H]+,100).Anal.CalcdforC43H58N4O8:
C, 68.05; H, 7.70; N, 7.38. Found: C, 67.92; H, 7.72; N, 7.39%.
7e: White crystals, yield 92%, m.p. 148–149 °C; [α]2D0 +95.6 (c 0.11,
CH2Cl2); IR (KBr, cm−1): 3395, 2951, 2871, 1720, 1665, 1485, 1250,
1
1092, 1040, 848, 758; H NMR (CDCl3, 400 MHz, δ ppm): 9.08 (s,
Conventional heating method for preparation of 7a–k
2H, CONH), 7.88 (d, J = 6.8 Hz, 2H, ArH), 7.77 (d, J = 6.8 Hz, 3H,
ArH), 7.39 (t, J = 7.8 Hz, 3H, ArH and NHCOO), 7.27 (s, 2H, ArH),
5.01 (s, 1H, 12β-H), 4.61 (s, 1H, 3β-H), 3.67 (s, 3H, COOCH3),
0.96 (s, 3H, 19-CH3), 0.86 (d, J = 6.8 Hz, 3H, 21-CH3), 0.68 (s, 3H,
18-CH3); ESI-MS m/z (%): 799.50 ([M+H]+, 100). Anal. Calcd for
C41H52Cl2N4O8: C, 61.57; H, 6.55; N, 7.01. Found: C, 61.49; H, 6.56;
N, 7.00%.
Triphosgene (0.37 mol) was added to a solution of compound 5 (0.5
mmol) in 10 mL dry CH2Cl2 and 0.2 mL dry pyridine at room tem-
perature. The solution was refluxed for 5 h, to give compound 6. The
arylhydrazide (1.5 mmol) and dry pyridine 0.2 mL were added directly
to the mixture which was refluxed for a further 6–10 h. The solvent
was removed and the residue was diluted with 20 mL ethyl acetate and
washed with 10% HCl (10 mL×3), brine (10 mL×3), and finally dried
over anhydrous Na2SO4. The crude product was purified by column
chromatography on silica gel H with dichloromethane/ethyl acetate as
eluant to give the products in 35–50% yields.
7f: White crystals, yield 89%, m.p. 133–134 °C; [α]2D0 +128.6
(c 0.14,CH2Cl2); IR (KBr, cm−1): 3299, 2947, 2868, 1735, 1677, 1511,
1470, 1244, 1218, 1040, 806, 782, 604; 1H NMR (CDCl3, 400 MHz,
δ ppm): 8.39 (s, 2H, CONH), 7.92–7.84 (m, 5H, ArH), 7.52 (s, 7H,
ArH and NHCOO), 7.40 (s, 3H, ArH), 6.48 (s, 1H, ArH), 5.07 (s, 1H,
12β-H), 4.79 (s, 1H, 3β-H), 3.67 (d, J = 2.0 Hz, 3H, COOCH3),
0.99 (s, 3H, 19-CH3), 0.93 (d, J = 6.8 Hz, 3H, 21-CH3), 0.75 (s, 3H,
18-CH3); ESI-MS m/z (%): 831.74 ([M+H]+, 100). Anal. Calcd for
C49H58N4O8: C, 70.82; H, 7.03; N, 6.74. Found: C, 70.71; H, 7.05;
N, 6.73%.
We thank the Natural Science Foundation of the State Ethnic
Affairs Commission of P.R.China (Project No.09XN08) for
the financial support, and we also thank John P. Schaefer and
Larry L. Reed for the X-ray crystal structure of desoxycholic
acid p-bromoanilide support.
7g: White crystals, yield 88%, m.p. 134–135 °C; [α]2D0 +70.0
(c 0.12,CH2Cl2); IR (KBr, cm−1): 3287, 2951, 2869, 1736, 1667, 1529,
1499, 1248, 1212, 1038, 1020, 837, 751; 1H NMR (CDCl3, 400 MHz,
δ ppm): 8.65 (s, 2H, CONH), 7.80–7.71 (m, 4H, ArH), 7.52 (s, 2H,
NHCOO), 7.26–7.16 (m, 4H, ArH), 5.02 (s, 1H, 12β-H), 4.63 (s, 1H,
3β-H), 3.67 (s, 3H, COOCH3), 2.37 (d, J = 3.6 Hz, 6H, CH3), 0.96 (s,
3H, 19-CH3), 0.86 (d, J = 6.8 Hz, 3H, 21-CH3), 0.68 (s, 3H, 18-CH3);
ESI-MS m/z (%): 1518.74 ([2M+Na]+, 100). Anal. Calcd for
C43H58N4O8: C, 68.05; H, 7.70; N, 7.38. Found: C, 67.93; H, 7.72;
N, 7.40%.
Received 20 January 2011; accepted 2 April 2011
Paper 1100537 doi: 10.3184/174751911X13026263307911
Published online: 3 May 2011
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1245, 1040, 747, 680; H NMR (CDCl3, 400 MHz, δ ppm): 8.92
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(c 0.13,CH2Cl2); IR (KBr, cm−1): 3385, 2949, 2869, 1736, 1673, 1602,
1
1482, 1279, 1238, 1018, 757, 616; H NMR (CDCl3, 400 MHz, δ
ppm): 9.60 (d, J = 3.6 Hz, 2H, CONH), 8.26–8.19 (m, 2H, NHCOO),
7.49 (t, J = 7.0 Hz, 4H, ArH), 7.10 (t, J = 7.4 Hz, 2H, ArH), 7.01 (t,
J = 8.4 Hz, 2H, ArH), 5.06 (s, 1H, 12β-H), 4.71 (s, 1H, 3β-H), 4.03 (s,
3H, OCH3), 3.99 (s, 3H, OCH3), 3.67(s, 3H, COOCH3), 0.99 (s, 3H,
19-CH3), 0.90 (d, J = 6.8 Hz, 3H, 21-CH3), 0.71 (s, 3H, 18-CH3); ESI-
MS m/z (%): 1581.60 ([2M+H]+, 100). Anal. Calcd for C43H58N4O8: C,
65.30; H, 7.39; N, 7.08. Found: C, 65.19; H, 7.41; N, 7.07%.

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