Preparation of novel molecular tweezers based on 3,6-O-(2- acylhydrazinocarbonyl) esters of hyodeoxycholic acid using microwave irradiation

Article abstract of DOI:10.3184/174751911X13088531486610

Ten novel molecular tweezers based on the 3,6-O-(2-acylhydrazinocarbonyl) esters of hyodeoxycholic 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 Cl^-, Br^-, I^-.

Full text of DOI:10.3184/174751911X13088531486610

364 RESEARCH PAPER
JUNE, 364–367
JOURNAL OF CHEMICAL RESEARCH 2011
Preparation of novel molecular tweezers based on
3,6-O-(2-acylhydrazinocarbonyl) esters of hyodeoxycholic acid
using microwave irradiation
Xiaorui Li, Liying Qiu, Qinggang Mei, Qingwei Bi and Zhigang Zhao*
College of Chemistry and Environmental Protection Engineering, Southwest University for Nationalities, Chengdu 610041, P. R. China
Ten novel molecular tweezers based on the 3,6-O-(2-acylhydrazinocarbonyl) esters of hyodeoxycholic 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 Cl−, Br−, I−.
Keywords: molecular tweezer, microwave irradiation, molecular recognition, hyodeoxycholic acid, cholic acids
Molecular recognition of biologically important substrates
by artificial receptors has been a subject of intense research
interest to give a better understanding of recognition phenom-
ena in nature as well as for potential applications in separation
processes, catalysis, sensing, and biochemical studies.1–3 The
study of synthetic artificial receptors can contribute to the
understanding of these processes.4–6 Among the various types
of artificial receptors, molecular tweezers have received
considerable attention.7–14 Molecular tweezer artificial
receptors not only offer the advantage of efficient construction
but also their surfaces can be tailored for specific applications.
The natural rigid concave structure and inherent asymmetry of
cholic acid make it an ideal building block for the construction
of molecular clefts.
The application of microwave techniques for organic
synthesis has attracted considerable interest in recent years.15–16
It provides a unique chemical process with special attributes
such as ease of manipulation, enhanced reaction rates, clean
reactionoutcomesandhighyields.Finally,step-by-stepreaction
is time-consuming (involving multiply reaction steps) and
expensivecomparedwithone-potreaction. Henceweattempted
a one-pot reaction. In view of these, herein we report an one
pot synthesis method for molecular tweezers derived from
hyodeoxycholic acid using microwave irradiation. These
receptors have the NH groups directed towards the centre of
the cavity resulting to good binding properties for anions. The
synthetic route is shown in Scheme 1.
heating. Compared to conventional thermal hearting, micro-
wave irradiation greatly decreased the reaction time from
420–600 min to 12–20 min. It was obvious that yields were
increased from 34–51% to 85–96%. From these data, we
conclude that microwave irradiation method is a rapid,
efficient methodology.
The variations in the UV-Vis absorption of these complexing
system and 1H NMR experiment have been used as two effec-
tive and simple methods to measure the association constants
of complexes in supramolecular systems.
Titration experiments for the anion recognition of receptors
7a, 7d, 7f were performed using UV-Vis spectroscopy in
CHCl3 at 25 °C. Using the linear fitting method, we obtained
the associate constants of complex (as shown in Table 5). The
preliminary results showed that these molecular tweezers
possessed the ability to form complexes with the guest anions
(as shown Fig. 1). The supramolecular complexes consisted of
1:1 host and guest molecules (as shown in Fig. 2).
As shown in Table 5, the preliminary results indicate that 7a,
7d, 7f show selective recognition properties for I−, Br−, Cl−.
The association constants are I− >Cl− >>Br−. There are two
reasons. First of all, the diameters of Cl−, Br−, I− are 3.34, 3.64,
4.21 Å respectively. The diameter of I− is the largest which can
match the cavity of host. The hydrogen bond distance is the
shortest and therefore the hydrogen bond formed between the
host and halide anion is the strongest. Moreover, the diameter
of Br− and Cl− has a little difference. However, the charge
density of Cl− is much bigger than that of Br−. Cl− can form
stabilised hydrogen bond with host. So the association
constant is Cl− >>Br−.
Results and discussion
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 identify the best conditions for 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 (12 min). As a result,
200 W was the identified as optimum power.
As shown in Table 2, we found that 12 min was the optimum
reaction time when the yield was the highest under the same
power (200 W). However, more byproducts were obtained
when the reaction time was increased.
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 and THF it
was chosen as the best solvent for the reaction.
Generally speaking, the chemical shift of protons which
take part in hydrogen bond will move to low field, however,
when π-π stacking was formed, the protons chemical shift
move to high field. In order to further proof the main driving
1
force is the multiple hydrogen bonds. H NMR experiments
were carried out. The preliminary results showed that the
chemical shift of NH proton moved to low field (as shown in
Fig. 3). This explains that the host and guest have formed
strong hydrogen bond. The specific data which the changes in
chemical shift are shown Table 6.
Experimental
Melting points were determined on a micro-melting point apparatus
and were uncorrected. IR spectra were obtained on 1700 Perkin-Elmer
1
FTIR using KBr disks. H NMR spectra were recorded on a Varian
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 rotation was measured on a Wzz-2B polarimeter. All the
solvents were purified before use.
As shown inTable 4, we compared the synthesis of molecular
tweezers 7a–j by microwave irradiation and conventional
* Correspondent. E-mail: zzg63129@yahoo.com.cn

JOURNAL OF CHEMICAL RESEARCH 2011 365
Scheme 1 The synthetic route of molecular tweezers 7a–j.
Table 1 The effect of microwave powers on yields
Table 4 Synthetic comparison of molecular tweezers 7a–j
between microwave irradiation and conventional heating
Power/W
Yield/%
50
65
100
78
150
80
200
95
250
83
a
b
Comp. Conventional method
t/min Yield/%
Microwave method tC /tMW
t/min Yield/%
Table 2 The effect of microwave irradiation time on yields
7a
7b
7c
7d
7e
7f
420
580
500
480
540
600
500
600
500
490
48
40
34
43
46
48
50
49
41
51
12.0
19.0
13.0
15.0
13.0
20.0
18.0
20.0
16.0
13.0
95
90
85
87
92
90
91
93
90
96
35
31
38
32
42
30
28
30
31
38
Time/min
Yield/%
6
8
10
78
12
95
14
86
16
77
65
70
Table 3 The effect of solvent on yields
7g
7h
7i
Entry
Solvent
Yield (%)
Volume of solvent (mL)
1
2
3
CH2Cl2
CHCl3
THF
95
83
72
10
10
15
7j
TC , time of conventional heating method; TMW b, time of micro-
wave irradiation method.
a
Microwave method for preparation of 7a–j
Preparation of 3a–j; general procedure
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 12 min at 200 W
to give compound 6. The arylhydrazide (1.5 mmol) and dry pyridine
0.2 mL were added directly to the mixture, and this was then irradi-
ated continually for 12–20 min at 200 W. The solvent was removed
The aromatic acid was converted to the hydrazides 3a–j following a
reported procedure.17
Preparation of compound 5; general procedure
Hyodeoxycholic acid was converted to methyl 3α,6α-dihydroxy-5β-
cholan-24-oate 5 following a reported procedure.18

366 JOURNAL OF CHEMICAL RESEARCH 2011
Table 5 Association constants (Ka) and free energy changes
(−∆Gθ) for the inclusion complexes of iodine anion with
molecular tweezers 4a, 4d, 4f in CHCl3 at 25 °C
Host
Guest
Ka(L·mol−1)
−∆Gθ(kJ·mol−1)
4a
I−
2210.44
449.43
19.08
15.13
17.50
17.93
11.73
14.79
18.40
13.71
17.79
Br−
Cl−
I−
1169.52
1390.31
113.81
4d
4f
Br−
Cl−
I−
391.74
1679.29
252.79
Br−
Cl−
1312.42
Fig. 2 Typical plot of 1/ΔA versus 1/[G]0 for the inclusion
complex of molecular tweezer 7a with I− in CHCl3 at 25 °C.
eluant. The whole progress was monitored by TLC. The physical and
spectra data of the compounds 7a–j are as follows.
7a: White crystal, yield 95%, m.p. 144–145 °C; [α]2D0 + 85.4 (c 0.11,
CH2Cl2); IR (KBr, cm−1): 3303, 2947, 2872, 1740, 1665, 1528, 1491,
1
1246, 1043, 711; H NMR (CDCl3, 400 MHz, δ ppm): 9.57 (s, 1H,
CONH), 9.23 (s, 1H, CONH), 7.78 (s, 1H, NHCOO), 7.71 (brs, 4H,
ArH), 7.38 (brs, 2H, ArH), 7.27 (brs, 4H, ArH), 7.04 (s, 1H, NHCOO),
4.93 (s, 1H, 6β-H), 4.53 (s, 1H, 3β-H), 3.67 (s, 3H, COOCH3), 0.96
(s, 3H, 19-CH3), 0.93 (d, J = 6.8 Hz, 3H, 21-CH3), 0.64 (s, 3H,
18-CH3); ESI-MS m/z (%): 1461.75 [(2M+H)+, 100]. Anal. Calcd
Fig.1 UV-Vis spectra of molecular tweezers 7a (3×10−4 molL−1)
in the presence of I− (a) 0 mol L−1 (b) 1.2×10−5 mol L−1 (c) 2.4×
10−5 mol L−1 (d) 3.6×10−5 mol L−1 (e) 4.8×10−5 mol L−1 (f) 6.0×
10−5 mol L−1 (g) 7.2×10−5 mol L−1 (h) 8.4×10−5 molL−1 (i) 9.6×10−5 mol
L−1 with λmax at 241.0 nm.
Table 6 1H NMR spectral data of NH for 7a and the complex of
7a with BuN+I− in CDCl3
Proton
δ(host)
δ(complex) ∆δH = δ(complex) -δ(host)
CONH
9.569
9.229
7.777
7.003
9.701
9.309
7.790
7.023
0.132
0.080
0.013
0.020
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 petroleum ether/ethyl acetate as
CONH
NHCOO
NHCOO
Fig. 3 1H NMR spectra of host 7a (A) and complex 7a with BuN+I− (B) in CDCl3.

JOURNAL OF CHEMICAL RESEARCH 2011 367
1
for C41H54N4O8: C, 67.38; H, 7.45; N, 7.67. Found: C, 67.49; H, 7.43;
N, 7.68%.
1470, 1234, 757; H NMR (CDCl3, 400 MHz, δ ppm): 9.86 (s, 1H,
CONH), 9.78 (s, 1H, CONH), 8.23–8.19 (m, 2H, NHCOO), 7.49–7.43
(m, 2H, ArH), 7.19 (s, 1H, ArH), 7.11–7.05 (m, 3H, ArH), 7.00 (dd,
J1 = 3.8 Hz, J2 = 8.0 Hz, 2H, ArH), 5.16–5.11 (m, 1H, 6β-H), 4.72 (s,
1H, 3β-H), 4.28–4.21 (m, 4H, OCH2), 3.67 (s, 3H, COOCH3), 1.60–
1.57 (m, 6H, CH3), 0.97 (s, 3H, 19-CH3), 0.92 (d, J = 6.0 Hz, 3H,
21-CH3), 0.64 (s, 3H, 18-CH3). IR (KBr) ν: 3382, 2951, 2868, 1744,
1669, 1599, 1470, 1234, 757; ESI-MS m/z (%): 1637.97 [(2M+H)+,
100]. Anal. Calcd for C45H62N4O10: C, 65.99; H, 7.63; N, 6.84. Found
C 65.91; H, 7.65; N, 6.86%.
7b: White crystal, yield 90%, m.p. 151–152 °C; [α]2D0 + 145.8
(c 0.10, CH2Cl2); IR (KBr, cm−1): 3295, 2947, 2872, 1731, 1673, 1607,
1
1503, 1238, 1039, 761; H NMR (CDCl3, 400 MHz, δ ppm): 9.64
(s, 1H, CONH), 9.24 (s, 1H, CONH), 7.78 (s, 1H, NHCOO), 7.71
(brs, 4H, ArH), 6.93 (brs, 4H, ArH), 6.75 (s, 1H, NHCOO), 4.91
(s, 1H, 6β-H), 4.56 (s, 1H, 3β-H), 3.67 (s, 3H, COOCH3), 0.96 (s, 3H,
19-CH3), 0.94 (d, J = 6.4 Hz, 3H, 21-CH3), 0.66 (s, 3H, 18-CH3); ESI-
MS m/z (%): 1555.56 [(2M+Na)+, 100]. Anal. Calcd for C41H52F2N4O8:
C, 64.21; H, 6.83; N, 7.31. Found: C, 64.29; H, 6.81; N, 7.30%.
7c: White crystal, yield 85%, m.p. 145–146 °C; [α]2D0 +153.6 (c 0.12,
CH2Cl2); IR (KBr, cm−1): 3312, 2942, 2860, 1731, 1661, 1607, 1499,
7j: White crystal, yield 96%, m.p. 142–143 °C; [α]2D0 +32.3 (c 0.12,
CH2Cl2); IR (KBr, cm−1): 3299, 2947, 2872, 1740, 1677, 1532, 1478,
1
1259, 1039, 752; H NMR (CDCl3, 400 MHz, δ ppm): 9.46 (s, 1H,
1
1254, 1026, 852; H NMR (CDCl3, 400 MHz, δ ppm): 9.48 (s, 1H,
CONH), 9.06 (s, 1H, CONH), 7.67 (s, 1H, NHCOO), 7.66–7.60 (m,
4H, ArH), 7.27–7.20 (m, 4H, ArH), 7.16 (s, 1H, NHCOO), 4.94 (s,
1H, 6β-H), 4.55 (s, 1H, 3β-H), 3.67 (s, 3H, COOCH3), 2.34 (s, 3H,
CH3), 2.30 (s, 3H, CH3), 0.93 (s, 3H, 19-CH3), 0.87 (d, J = 6.4 Hz, 3H,
21-CH3), 0.64 (s, 3H, 18-CH3); ESI-MS m/z (%): 759.81 [(M+H)+,
100]. Anal. Calcd for C43H58N4O8: C, 68.05; H, 7.70; N, 7.38. Found
C 68.15; H, 7.72; N, 7.37%.
CONH), 9.02 (s, 1H, CONH), 7.77 (brs, 5H, NHCOO and ArH), 6.73
(brs, 5H, NHCOO and ArH), 4.92 (s, 1H, 6β-H), 4.56 (s, 1H, 3β-H),
3.78 (s, 6H, OCH3), 3.67 (s, 3H, COOCH3), 0.92 (s, 3H, 19-CH3), 0.89
(d, J = 6.8 Hz, 3H, 21-CH3), 0.63 (s, 3H, 18-CH3); ESI-MS m/z (%):
1603.57 [(2M+Na)+, 100]. Anal. Calcd for C43H58N4O10: C, 65.30;
H, 7.39; N, 7.08. Found C, 65.23; H, 7.40; N, 7.07%.
7d: White crystal, yield 87%, m.p. 148–149 °C; [α]2D0 + 93.2 (c 0.11,
CH2Cl2); IR (KBr, cm−1): 3299, 2942, 2872, 1740, 1669, 1599, 1482,
Conventional heating method for preparation of 7a–j
1
1246, 1100, 1043, 844; H NMR (CDCl3, 400 MHz, δ ppm): 9.65
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 solution was refluxed for 4 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 7–10 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 petroleum ether/ethyl
acetate as eluant, in 34–51% yields.
(s, 1H, CONH), 9.08 (s, 1H, CONH), 7.90 (s, 1H, NHCOO), 7.68
(brs, 4H, ArH), 7.27 (brs, 4H, ArH), 6.57 (s, 1H, NHCOO), 4.93 (s,
1H, 6β-H), 4.58 (s, 1H, 3β-H), 3.66 (s, 3H, COOCH3), 0.95 (s, 3H,
19-CH3), 0.93 (d, J = 6.4 Hz, 3H, 21-CH3), 0.66 (s, 3H, 18-CH3); ESI-
MS m/z (%): 1599.54 [(2M+H)+,100]. Anal. Calcd for C41H52Cl2N4O8:
C, 61.57; H, 6.55; N, 7.01. Found C, 61.62; H, 6.57; N, 7.02%.
7e: White crystal, yield 92%, m.p. 158–159 °C; [α]2D0 +126.6 (c 0.13,
CH2Cl2); IR (KBr, cm−1): 3287, 2942, 2868, 1744, 1669, 1466, 1246,
1039, 786; 1H NMR (CDCl3, 400 MHz, δ ppm): 8.33 (brs, 3H, CONH
and ArH), 8.20 (s, 1H, CONH), 7.87–7.81 (m, 4H, ArH), 7.62 (brs,
2H, ArH), 7.57 (brs, 4H, ArH), 7.29–7.26 (m, 4H, CONH and ArH),
5.08 (s, 1H, 6β-H), 4.67 (s, 1H, 3β-H), 3.67 (s, 3H, COOCH3), 0.91 (s,
3H, 19-CH3), 0.88 (d, J = 6.8 Hz, 3H, 21-CH3), 0.63 (s, 3H, 18-CH3);
ESI-MS m/z (%): 1684.60 [(2M+Na)+,100]. Anal. Calcd for
C49H58N4O8: C, 70.82; H, 7.03; N, 6.74. Found C, 70.89; H, 7.01;
N, 6.75%.
We thank the Special Financial Project of Central Chinese
University for the financial support (No. 11NZYQN05).
Received 16 May 2011; accepted 7 June 2011
Paper 1100697 doi: 10.3184/174751911X13088531486610
Published online: 11 July 2011
7f: White crystal, yield 90%, m.p. 149–150 °C; [α]2D0 +68.9 (c 0.11,
CH2Cl2); IR (KBr, cm−1): 3299, 2942, 2868, 1735, 1665, 1528, 1499,
1
1246, 1047, 753; H NMR (CDCl3, 400 MHz, δ ppm): 9.48 (s, 1H,
CONH), 9.00 (s, 1H, CONH), 7.86 (s, 1H, NHCOO), 7.69 (brs, 4H,
ArH), 7.05 (brs, 4H, ArH), 6.79 (s, 1H, NHCOO), 4.93 (s, 1H, 6β-H),
4.57 (s, 1H, 3β-H), 3.67 (s, 3H, COOCH3), 2.30 (brs, 6H, CH3),
0.98 (s, 3H, 19-CH3), 0.92 (d, J = 6.8 Hz, 3H, 21-CH3), 0.63 (s, 3H,
18-CH3); ESI-MS m/z (%): 1539.63 [(2M+Na)+,100]. Anal. Calcd
for C43H58N4O8: C, 68.05; H, 7.70; N, 7.38. Found C, 67.91; H, 7.72;
N, 7.39%.
References
1
2
3
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7g: White crystal, yield 91%, m.p. 142–143 °C; [α]2D0 + 123.6
(c 0.13, CH2Cl2); IR (KBr, cm−1): 3303, 2951, 2860, 1735, 1677, 1532,
1466, 1238, 1047, 748; 1H NMR (CDCl3, 400 MHz, δ ppm): 9.72 (s,
1H, CONH), 9.31 (s, 1H, CONH), 7.93 (s, 1H, NHCOO), 7.74–7.35
(m, 4H, ArH), 7.27 (brs, 2H, ArH), 7.23–7.14 (m, 2H, ArH), 6.89 (s,
1H, NHCOO), 4.92 (s, 1H, 6β-H), 4.60 (s, 1H, 3β-H), 3.66 (s, 3H,
COOCH3), 0.93 (s, 3H, 19-CH3), 0.88 (d, J = 6.8 Hz, 3H, 21-CH3),
0.66 (s, 3H, 18-CH3), ESI-MS m/z (%): 1621.53 [(2M+Na)+,100].
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61.66; H, 6.54; N, 7.02%.
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1279, 1047, 761; H NMR (CDCl3, 400 MHz, δ ppm): 10.03 (s, 2H,
CONH), 8.21–8.16 (m, 2H, NHCOO), 7.30 (brs, 2H, ArH), 7.15 (s,
1H, ArH), 7.01 (brs, 2H, ArH), 6.87 (s, 1H, ArH), 6.55 (brs, 2H, ArH),
5.13 (s, 1H, 6β-H), 4.68 (s, 1H, 3β-H), 3.73 (brs, 6H, OCH3), 3.68
(s, 3H, COOCH3), 0.94 (s, 3H, 19-CH3), 0.90 (d, J = 6.4 Hz, 3H,
21-CH3), 0.62 (s, 3H, 18-CH3); ESI-MS m/z (%): 791 [(M+H)+, 100].
Anal. Calcd for C43H58N4O8: C, 65.30; H, 7.39; N, 7.08. Found 65.40;
H, 7.37; N, 7.09%.
7i: White crystal, yield 90%, m.p. 114–115 °C; [α]2D0 + 128.9
(c 0.11, CH2Cl2); IR (KBr, cm−1): 3382, 2951, 2868, 1744, 1669, 1599,

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