The synthesis of 1,2,3-triazole derivatives of deoxycholic acid for molecular tweezer metal ion recognition

Article abstract of DOI:10.3184/174751912X13352834523329

A series of molecular tweezer metal receptors based on [1,2,3-triazolo- acetyl]esters of methyl deoxycholate have been synthesised via the 3,12-azidoester using a click chemistry method. Their structures were characterized by 1H NMR, IR, MS spectra and el

Full text of DOI:10.3184/174751912X13352834523329

340 RESEARCH PAPER
JUNE, 340–342
JOURNAL OF CHEMICAL RESEARCH 2012
The synthesis of 1,2,3-triazole derivatives of deoxycholic acid for molecu-
lar tweezer metal ion recognition
Yuyu Cheng, Zhigang Zhao*, Min Liu and Yongle Peng
College of Chemistry and Environmental Protection Engineering, Southwest University for Nationalities, Chengdu 610041, P. R. China
A series of molecular tweezer metal receptors based on [1,2,3-triazolo-acetyl]esters of methyl deoxycholate have
been synthesised via the 3,12-azidoester using a click chemistry method. Their structures were characterized by
1H NMR, IR, MS spectra and elemental analysis. Their binding properties were examined by UV-Vis spectra titration.
The preliminary results indicate that this type of molecular tweezers have good recognition for metal ions.
Keywords: cation recognition, 1,2,3-triazole, click chemistry, deoxycholic acid
Cations have a variety of biochemical functions affecting
enzymes, coenzymes, and cofactors.1–5 The synthesis of new
sensors for the efficient detection of trace metal ions is among
the more important research topics in environmental chemistry
and biology. Heavy metal ions are significant environmental
pollutants that accumulate in plants, soil, and water.7 A defi-
ciency or an excess presence of these in biological fluids is
harmful to health.8–12 Accordingly, it is imperative to develop
analytical methods for the sensitive and selective detection of
trace amounts of cations.
Recently, the importance of the role of the 1,2,3-triazole
ring as a potential ligand in the formation of stable metal com-
plexes has been enhanced and some triazole-based receptors
and dendrimers for the recognition of cation have been
reported.13,14 The application of click chemistry developed by
Meldal and Sharpless involving a Cu(I)-catalysed 1,3-dipolar
cycloaddition reaction between an azide and a terminal alkyne
to yield the unique properties of the 1,4-disubstituted 1,2,3-
triazole ring is rapidly growing. This is an easy way to synthe-
sise 1,2,3-triazole ring under simple reaction conditions using
a simple product isolation, and in high yield.15–17 Moreover, the
bile acids have attracted considerable interest for the design of
receptors for molecular recognition due to their rigid frame-
work, facial amphiphilicity, and suitably oriented hydroxyl
groups.18,19 However, steroid-based molecular tweezers with a
1,2,3-triazole ring for metal recognition through click chemis-
try have not been reported. We provide a route for the synthesis
of a new series of molecular tweezers with this type of
structure. The synthetic route is shown in Scheme 1.
Results and discussion
In searching for the best reaction conditions for the synthesis
of molecular tweezer artificial receptors, we took the synthesis
of 5a as an example and carried out several experiments under
different conditions, varying the solvent, temperature, and
concentration of the catalyst to obtain the best results for this
reaction. The results are shown in the following tables.
As shown in Table 1, the effect of DMSO, a mixture of DMSO
and H2O (10:1, V/V), CH3OH and t-BuOH on the reaction
was investigated. The results showed that although different
Scheme 1 The synthetic route of molecular tweezers 5a–j. Reagents and conditions: (i) CH3OH, CH3COCl, ice bath; (ii) ClCH2COCl,
CHCl3, pyridine, triethylamine, 60 °C; (iii) NaN3, DMF, 60 °C; (iv) R-C H, t-BuOH, CuI, triethylamine, 50 °C.
≡
* Correspondent. E-mail: zzg63129@yahoo.com.cn

JOURNAL OF CHEMICAL RESEARCH 2012 341
solvents were employed under similar reaction conditions, the
results did not differ significantly. When t-BuOH was used, the
yield was a little higher and hence t-BuOH was the best
solvent for the reaction.
As shown in Table 2, different temperatures were employed
under the similar reaction conditions. Although the results
were different, 50 °C was the best temperature to obtain a good
yield.
As shown in Table 3, different concentrations of catalysts
were employed under similar reaction conditions. As a result,
CuI (10 mol%) and Et3N (40 mol%) was the optimum catalytic
system.
From these data that we obtained from in this experiment,
we concluded that this provided an easy and effective way
for the preparation of 1,2,3-triazole-based type molecular
cation receptors. There are obvious advantages in this method
including high yield, simple reaction conditions and an easy
separation of the products.
Fig. 1 UV-Vis spectra of molecular tweezers 5a (3.2×10−5 mol
L−1) in the presence of Hg2+ (a) 0 mol L−1 (b) 0.32×10−4 mol L−1
(c) 0.64×10−4 mol L−1 (d) 0.96×10−4 mol L−1 (e) 1.28×10−4 mol L−1
(f) 1.60×10−4 mol L−1 (g) 1.92×10−4 mol L−1 (h) 2.24×10−4 mol L−1
(i) 2.56×10−4 mol L−1 (j) 2.88×10−4 mol L−1 with λmax at 245.0 nm.
The molecular recognition properties of molecular tweezers
5a, 5b, 5g for metal ions were investigated by UV-Vis spectra
titration in CHCl3/MeOH (7:3, V/V) at 25 °C. The UV-Vis
plot of 5a for Hg2+ is shown in Fig.1. The titration data were
analysed by using the Hildebrand-Benesi equation. The plot of
1/∆A versus the 1/[G0] gave a straight line (Fig. 2). It showed
that these molecular tweezers possessed the ability to form
complexes with the guest cations which were examined and
that the complexes consisted of 1:1 host and guest molecules.
Using the linear fitting method, we obtained the association
constants for the complex. The results indicate that this kind
of molecular tweezers exhibit a selectivity for metal ions.
The association constants of the molecular tweezer 5a, for
example, are 3999, 62287, 13990 L mol−1 for Cu2+, Hg2+, Pb2+
metal ions respectively.
The main reason is that when the host 5a is at the minimum
energy, its conformation is a tweezer type, which has the abil-
ity to form complex with guest molecules. The main driving
force for recognition comes from coordination bond between
host and guest. The details of molecular recognition of 5a–j
are under further study.
Fig. 2 Typical plot of 1/∆A versus 1/[G]0 for the inclusion
complex of molecular tweezer 5a with Hg2+ in CHCl3/MeOH (7:3,
V/V) at 25 °C.
Table 1 The effect of solvent on yields
Experimental
Entry
Solvent
Yield/%
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
2
3
4
DMSO
23
39
60
84
1
DMSO and H2O
CH3OH
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 autoanalyser. Optical
rotations were measured on a Wzz-2B polarimeter. All the solvents
were purified before use. Intermediate 2 was prepared following a
reported procedure.20 It was obtained as a white solid, yield 90%, m.p.
79–80 °C (lit.20 74–76 °C). Intermediate 3 was prepared following a
reported procedure.21 It was obtained as a white solid, yield 88%, m.p.
122–124 °C (lit.21 120 °C).
t-BuOH
Table 2 The effect of reaction temperatures on yields of
compounds 5a
Entry
Temperature/ °C
Yield/%
Synthesis of 3β, 12β-bis-(azidoacetyl)deoxycholate (4):22 Sodium
azide (9.24 mmol) was added to a solution of 3 (1.54 mmol) in 20 mL
of DMF, and the solution was stirred at 60 °C for 12 h. The solution
was diluted with water (40 mL) and extracted with ethyl acetate
(30 mL) twice. The organic layer was washed with water and then
with brine and dried over Na2SO4 and evaporated under a vacuum. The
residue was purified by column chromatography on silica gel H with
petroleum ether/ethyl acetate (5:1, V/V) as eluant and the product
was obtained as a white solid, yield 95%, m.p. 91–93 °C; [α]2D0–104.5
(c 0.2, CH2Cl2); IR (KBr) (cm−1): 2948, 2868, 2103, 1735, 1444, 1359,
1
2
3
4
0
25
50
70
–
40
84
80
Table 3 The effect of concentration of catalysts on yields
Entry
Concentration/mol%
Yield/%
1
CuI
Et3N
1283, 1198, 1115, 968; H NMR (400 MHz, CDCl3) δ: 5.26 (s, 1H,
12β-H), 4.78–4.85 (m, 1H, 3β-H), 3.90 (s, 2H, CH2N3), 3.84 (s, 2H,
CH2N3), 3.66 (s, 3H, COOCH3), 0.93 (s, 3H, 19-CH3), 0.82 (d, J =
6.4 Hz, 3H, 21-CH3), 0.76 (s, 3H, 18-CH3); ESI-MS m/z (%): 595.42
([M+Na]+, 100). Anal. Calcd for C29H45N6O6: C, 60.82; H, 7.74; N,
14.67. Found: C, 60.65; H, 7.75; N, 14.64%.
1
2
3
4
10
10
10
10
0
20
40
60
0
63
84
78

342 JOURNAL OF CHEMICAL RESEARCH 2012
Synthesis of acyclic compound 5a–j
-OCOCH2), 5.16 (s, 1H, 12β-H), 4.78–4.83 (m, 1H, 3β-H), 3.67 (s,
3H, COOCH3), 2.62–2.72 (m, 4H,Ar-CH2), 1.18–1.29 (m, 6H,ArCH2-
CH3), 0.87 (s, 3H, 19-CH3), 0.80 (d, J = 5.6 Hz, 3H, 21-CH3), 0.69 (s,
3H, 18-CH3); ESI-MS m/z (%): 833.60 ([M+H]+, 100). Anal. Calcd
for C49H64N6O6: C, 70.65; H, 7.74; N, 10.09. Found: C, 70.55; H, 7.76;
N, 10.10%.
Phenyl acetylene or substituted phenylacetylene (1.14 mmol) were
added to a solution of 3β, 12β-bis-(azidoacetyl)deoxycholate 4
(0.52 mmol) in t-BuOH (15 mL), CuI (10 mol%) and triethylamine
(40 mol%) were added to this solution. The solution was stirred at
50 °C for 8–24 h. The solution was evaporated under vacuum. The
residue was purified by column chromatography on silica gel H with
petroleum ether/ethyl acetate/ethanol (4:1:1–15:1:1, V/V/V) as the
eluant. The whole progress was monitored by TLC. The physical and
spectra data of the compounds 5a–j are as follows.
5h: White solid, yield 90%, m.p. 82–84 °C; [α]2D0–52.3 (c 0.2,
CH2Cl2); IR (KBr) (cm−1): 2950, 2871, 1743, 1614, 1563, 1499, 1461,
1416, 1382, 1356, 1267, 1223, 1159, 1095, 977; 1H NMR (400 MHz,
CDCl3) δ: 8.04 (s, 1H, triazole-H), 7.89 (s, 1H, triazole-H), 7.78–7.81
(m, 2H, ArH), 7.71–7.75 (m, 2H, ArH), 7.13 (t, J = 8.4 Hz, 2H, ArH),
7.04 (t, J = 8.4 Hz, 2H, ArH), 5.30 (s, 2H, -OCOCH2), 5.11–5.22
(m, 2H, -OCOCH2), 5.16 (s, 1H, 12β-H), 4.78–4.84 (m, 1H, 3β-H),
3.68 (s, 3H, COOCH3), 0.88 (s, 3H, 19-CH3), 0.81 (d, J = 5.6 Hz, 3H,
21-CH3), 0.69 (s, 3H, 18-CH3); ESI-MS m/z (%): 813.52 ([M+H]+,
100). Anal. Calcd for C45H54F2N6O6: C, 66.48; H, 6.70; N, 10.34.
Found: C, 66.39; H, 6.71; N, 10.32%.
5a: White solid, yield 84%, m.p. 94–96 °C [α]2D0–120.5 (c 0.15,
CH2Cl2); IR (KBr) (cm−1): 2949, 2869, 1742, 1612, 1467, 1443, 1382,
1357, 1270, 1221, 1078, 1046, 976; H NMR (400 MHz, CDCl3)
1
δ: 8.08 (s, 1H, triazole-H), 7.90 (s, 1H, triazole-H), 7.84 (d, J = 8.2 Hz,
2H, ArH), 7.77 (d, J = 7.6 Hz, 2H, ArH), 7.28–7.46 (m, 6H, ArH),
5.31 (s, 2H, -OCOCH2), 5.06–5.18 (m, 2H, -OCOCH2), 5.16 (s, 1H,
12β-H), 4.79–4.84 (m, 1H, 3β-H), 3.68 (s, 3H, COOCH3), 0.87 (s, 3H,
19–CH3), 0.80 (d, J = 5.6 Hz, 3H, 21-CH3), 0.69 (s, 3H, 18-CH3);
ESI-MS m/z (%): 777.57 ([M+H]+, 100). Anal. Calcd for C45H56N6O6:
C, 69.56; H, 7.26; N, 10.82. Found: C, 69.45; H, 7.25; N, 10.79%.
5b: Fine solid, yield 90%, m.p. 114–116 °C; [α]2D0–136.4 (c 0.2,
CH2Cl2); IR (KBr) (cm−1): 3449, 3369, 2949, 2870, 17380, 1621,
5i: White solid, yield 94%, m.p. 92–94 °C; [α]2D0–125 (c 0.2,
CH2Cl2); IR (KBr) (cm−1): 2955, 2869, 1743, 1499, 1459, 1381, 1357,
1265, 1217, 1077, 1045, 977; 1H NMR (400 MHz, CDCl3) δ: 8.06 (s,
1H, triazole-H), 7.86 (s, 1H, triazole-H), 7.74 (d, J = 8 Hz, 2H, ArH),
7.68 (d, J = 8.4 Hz, 2H, ArH), 7.24 (d, J = 8 Hz, 2H, ArH), 7.17 (d,
J = 7.6 Hz, 2H, ArH), 5.30 (s, 2H, -OCOCH2), 5.06–5.19 (m, 2H,
-OCOCH2), 5.16 (s, 1H, 12β-H), 4.77–4.83 (m, 1H, 3β-H), 3.68 (s,
3H, COOCH3), 2.57–2.64 (m, 4H, Ar-CH2), 1.64–1.72 (m, 4H,
Ar-CH2-CH2), 0.93–0.97 (m, 6H, Ar-C2H4-CH3), 0.87 (s, 3H, 19-CH3),
0.80 (d, J = 5.6 Hz, 3H, 21-CH3), 0.69 (s, 3H, 18-CH3); ESI-MS m/z
(%): 861.68 ([M+H]+, 100). Anal. Calcd for C51H68N6O6: C, 71.13; H,
7.96; N, 9.76. Found: C, 71.05; H, 7.98; N, 9.74%.
1
1593, 1451, 1358, 1270, 1222, 1079, 1048, 1001, 785; H NMR
(400 MHz, CDCl3) δ: 8.00 (s, 1H, triazole-H), 7.81 (s, 1H, triazole-H),
7.11–7.23 (m, 6H, ArH), 6.69 (d, J = 6.4 Hz, 1H, ArH), 6.63 (d,
J = 6.8 Hz, 1H, ArH), 5.30 (s, 2H, -OCOCH2), 5.02–5.15 (m, 2H,
-OCOCH2), 5.14 (s, 1H, 12β-H), 4.77–4.82 (m, 1H, 3β-H), 3.68 (s,
3H, COOCH3), 3.09–3.11 (bs, 4H, Ar-NH2), 0.86 (s, 3H, 19-CH3),
0.80 (d, J = 5.2 Hz, 3H, 21-CH3), 0.68 (s, 3H, 18-CH3); ESI-MS m/z
(%): 1635.94 ([2M+H]+, 100). Anal. Calcd for C45H58N8O6: C, 66.97;
H, 7.24; N, 13.89. Found: C, 66.86; H, 7.22; N, 13.91%.
5j: Yellow solid, yield 94%, m.p. 115–117 °C, [α]2D0–36.4 (c 0.2,
CH2Cl2); IR (KBr) (cm−1): 2949, 2870, 1743, 1606, 1519, 1461, 1342,
1267, 1221, 1109, 1045, 976; 1H NMR (400 MHz, CDCl3) δ: 8.32 (s,
1H, triazole-H), 8.30 (s, 1H, triazole-H), 8.17–8.30 (m, 4H, ArH),
8.00 (d, J = 9.2 Hz, 2H, ArH), 7.95 (d, J = 9.2 Hz, 2H, ArH), 5.39 (s,
2H, -OCOCH2), 5.21–5.35 (m, 2H, -OCOCH2), 5.19 (s, 1H, 12β-H),
4.81–4.86 (m, 1H, 3β-H), 3.69 (s, 3H, COOCH3), 0.89 (s, 3H, 19-
CH3), 0.82 (d, J = 5.2 Hz, 3H, 21-CH3), 0.71 (s, 3H, 18-CH3); ESI-MS
m/z (%): 867.12 ([M+H]+, 100). Anal. Calcd for C45H54N8O10: C,
62.34; H, 6.28; N, 12.92. Found: C, 62.30; H, 6.27; N, 12.89%.
5c: White solid, yield 94%, m.p. 88–90 °C; [α]2D0–34.1 (c 0.2,
CH2Cl2); IR (KBr) (cm−1): 2950, 2870, 1743, 1619, 1564, 1501, 1460,
1357, 1250, 1223, 1108, 1078, 1031, 976; 1H NMR (400 MHz, CDCl3)
δ: 7.77 (s, 1H, triazole-H), 7.73 (s, 1H, triazole-H), 7.73–7.77 (m, 4H,
ArH), 6.97 (s, 2H, ArH), 6.89 (s, 2H, ArH), 5.30 (s, 2H, -OCOCH2),
5.11–5.15 (m, 2H, -OCOCH2), 5.15 (s, 1H, 12β-H), 4.81 (bs, 1H, 3β-
H), 3.86 (s, 3H, Ar-OCH3), 3.81 (s, 3H, Ar-OCH3), 3.67 (s, 3H,
COOCH3), 0.87 (s, 3H, 19-CH3), 0.80 (d, J = 5.2 Hz, 3H, 21-CH3),
0.69 (s, 3H, 18-CH3); ESI-MS m/z (%): 837.24 ([M+H]+,100). Anal.
Calcd for C47H60N6O8: C, 67.44; H, 7.23; N, 10.04. Found: C, 67.37;
H, 7.25; N, 10.05%.
This work was supported by the Fundamental Research Funds
for Central University, Southwest University for Nationalities
(No.11NZYTH05).
5d: White solid, yield 89%, m.p. 99–101 °C; [α]2D0–68.2 (c 0.2,
CH2Cl2); IR (KBr) (cm−1): 2950, 2869, 1743, 1467, 1381, 1356, 1266,
1
1223, 1096, 1070, 1045, 1009, 975; H NMR (400 MHz, CDCl3) δ:
8.08 (s, 1H, triazole-H), 7.93 (s, 1H, triazole-H), 7.69 (d, J = 8.4 Hz,
2H, ArH), 7.62 (d, J = 8.4 Hz, 2H, ArH), 7.56 (d, J = 8.4 Hz, 2H,
ArH), 7.46 (d, J = 8.4 Hz, 2H, ArH), 5.30 (s, 2H, -OCOCH2), 5.10–
5.21 (m, 2H, -OCOCH2), 5.16 (s, 1H, 12β-H), 4.78–4.84 (m, 1H, 3β-
H), 3.68 (s, 3H, COOCH3), 0.88 (s, 3H, 19-CH3), 0.80 (d, J = 7.2 Hz,
3H, 21-CH3), 0.69 (s, 3H, 18-CH3); ESI-MS m/z (%): 935.40 ([M+H]+,
100). Anal. Calcd for C45H54Br2N6O6: C, 57.82; H, 5.82; N, 8.99.
Found: C, 57.78; H, 5.80; N, 8.97%.
Received 23 February 2012; accepted 20 March 2012
Paper 1201180 doi: 10.3184/174751912X13352834523329
Published online: 4 June 2012
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5e: White solid, yield 92%, m.p. 91–93 °C; [α]2D0–61.4 (c 0.2,
CH2Cl2); IR (KBr) (cm−1): 2950, 2869, 1743, 1500, 1459, 1381, 1356,
1268, 1218, 1077, 1045, 977; 1H NMR (400 MHz, CDCl3) δ: 8.03 (s,
1H, triazole-H), 7.84 (s, 1H, triazole-H), 7.71 (d, J = 8 Hz, 2H, ArH),
7.65 (d, J = 8 Hz, 2H, ArH), 7.24 (d, J = 8 Hz, 2H, ArH), 7.16 (d,
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C, 70.12; H, 7.51; N, 10.44. Found: C, 70.02; H, 7.53; N, 10.42%.
5f: White solid, yield 91%, m.p. 96–98 °C; [α]2D0–109.1 (c 0.2,
CH2Cl2); IR (KBr) (cm−1): 2960, 2870, 1743, 1458, 1412, 1382, 1356,
7
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1
1266, 1221, 1093, 1045, 1012, 926; H NMR (400 MHz, CDCl3) δ:
8.08 (s, 1H, triazole-H), 7.92 (s, 1H, triazole-H), 7.76 (d, J = 8.4 Hz,
2H, ArH), 7.69 (d, J = 8.4 Hz, 2H, ArH), 7.41 (d, J = 8 Hz, 2H, ArH),
7.31 (d, J = 8.4 Hz, 2H, ArH), 5.30 (s, 2H, -OCOCH2), 5.10–5.22 (m,
2H, -OCOCH2), 5.16 (s, 1H, 12β-H), 4.79–4.84 (m, 1H, 3β-H), 3.68
(s, 3H, COOCH3), 0.88 (s, 3H, 19-CH3), 0.81 (d, J = 4.8 Hz, 3H, 21-
CH3), 0.69 (s, 3H, 18-CH3); ESI-MS m/z (%): 845.46 ([M+H]+, 100).
Anal. Calcd for C45H54Cl2N6O6: C, 63.90; H, 6.43; N, 9.94. Found: C,
63.77; H, 6.45; N, 9.90%.
5g: White solid, yield 91%, m.p. 98–100 °C; [α]2D0–77.3 (c 0.2,
CH2Cl2); IR (KBr) (cm−1): 2956, 2870, 1743, 1500, 1459, 1381, 1356,
1267, 1218, 1076, 1046, 977; 1H NMR (400 MHz, CDCl3) δ: 8.06 (s,
1H, triazole-H), 7.86 (s, 1H, triazole-H), 7.74 (d, J = 8.4 Hz, 2H,
ArH), 7.69 (d, J = 8.4 Hz, 2H, ArH), 7.27 (d, J = 8 Hz, 2H, ArH), 7.19
(d, J = 8.4 Hz, 2H, ArH), 5.30 (s, 2H, -OCOCH2), 5.06–5.18 (m, 2H,
20 X.L. Liu, Z.G. Zhao and B.T. Zeng, Chin. J. Org. Chem., 2007, 27, 994(in
Chinese).
21 N.G. Aher, V.S. Pore and S.P. Patil, Tetrahedron, 2007, 63, 12927.
22 A. Kumar and P.S. Pandey, Org. Lett., 2008, 10, 165.

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