Microwave-assisted synthesis and antibacterial activity of novel chenodeoxycholic acid thiosemicarbazone derivatives

Article abstract of DOI:10.3184/174751911X13129090186347

A rapid and efficient method for the synthesis of novel chenodeoxycholic acid thiosemicarbazone derivatives under solvent-free conditions using microwave irradiation is reported. Ten novel compounds have been synthesised in good yields. Their structures were elucidated by ¹H NMR, IR, ESI-MS spectra and elemental analysis. Preliminary results showed that some of these compounds possess inhibitory effects against S. typhimurium and E. coli.

Full text of DOI:10.3184/174751911X13129090186347

456 RESEARCH PAPER
AUGUST, 456–459
JOURNAL OF CHEMICAL RESEARCH 2011
Microwave-assisted synthesis and antibacterial activity of novel
chenodeoxycholic acid thiosemicarbazone derivatives
Liying Qiu, Zhichuan Shi, Qinggang Mei and Zhigang Zhao*
College of Chemistry and Environmental Protection Engineering, Southwest University for Nationalities, Chengdu 610041, P. R. China
A rapid and efficient method for the synthesis of novel chenodeoxycholic acid thiosemicarbazone derivatives under
solvent-free conditions using microwave irradiation is reported. Ten novel compounds have been synthesised in
1
good yields. Their structures were elucidated by H NMR, IR, ESI-MS spectra and elemental analysis. Preliminary
results showed that some of these compounds possess inhibitory effects against S. typhimurium and E. coli.
Keywords: thiosemicarbazone, microwave irradiation, antibacterial activity, chenodeoxycholic acid, solvent-free conditions
Thiosemicarbazones and their metal complexes have received
considerable attention1–3 in view of their various biological
activities, variables bonding modes, and structural diversity.
The structural diversity of thiosemicarbazones varies by con-
densation with different carbonyl compounds and by alkylation
ofdifferentpartofthethiosemicarbazidemoiety.Thebiological
activity and the medicinal properties of thiosemicarbazones
depends upon the chemical nature of the moiety attached to
the C=S carbon atom.4,5 Compounds with thiosemicarbazone
structureareknowntopossesstranquilising, anti-viral, analgesic,
hypnotic, anti-tumour, anti-depressant, anti-bacterial, muscle
relaxing, anti-fungal and anti-inflammatory properties.6–9
Recent developments in “green chemistry” can minimise
the environmental harmfulness of classical reactions. One of
the most popular approaches is the application of microwave
techniques for organic synthesis. This technology can enhance
the selectivity and improve product yields.10–13 For this reason,
the application of microwave irradiation under solvent-free
conditions has gained popularity over the usual homogeneous
and heterogeneous reactions.
As is evident from the literature, research has been carried
out on steroidal thiosemicarbazone derivatives but no work
has been done on chenodeoxycholic acid thiosemicarbazones
and their screening against bacteria.14,15 Recently, our research
group has been working microwave solvent-free synthesis of
thiosemicarbazone derivatives.16,17 As a continuation of this
work, we report good yields in the synthesis of novel
chenodeoxycholic acid thiosemicarbazones under solvent-free
conditions using neutral aluminum oxide as a mineral support.
Some compounds were tested in vitro against bacteria such as
Staphylococcus pyogenes, Salmonella typhimurium and
Escherichia coli. The synthetic route is depicted in Scheme 1.
steroidal structure. The singlets at 3.67 ppm were assigned to
the protons of the COOCH3.
In searching for the best conditions, we also carried out a
series of experiments, varying the microwave irradiation
power, time and different supporters. We used the synthesis
of 4a for example and we found that the highest yield was
obtained when the time was 5.0 min at 450 W by using neutral
aluminum oxide as the solid support.
As shown in Table 1, we carried out the synthetic compari-
son of 4a–j between microwave irradiation in the solvent-
free conditions and conventional heating. It was easy to see
that microwave irradiation greatly decreased the reaction time
from 360–480 min to 4.0–6.0 min. However, the yields also
increased from 45–62% to 86–92%. Consequently, the use of
microwave technology in conjunction with the use of solvent-
free conditions allows expeditious and efficient procedures
in this organic synthesis.
The in vitro antibacterial activities of compounds 4a–d were
examined using cultures of S. pyogenes, S. typhimurium and
E. coli. Amoxicillin (30 µg) was used as the standard drug.
The MIC was evaluated by the macro-dilution test using
standard inoculums of 10−5 CFU mL−1. Serial dilutions of the
test compounds, previously dissolved in DMSO were prepared
to final concentrations of 512, 256, 128, 64, 32, 16, 8, 4, 2 and
1 µg mL−1. To each tube was added 100 µL of a 24 h old inocu-
lum. The MIC which inhibits the visible growth after 18 h,
was determined visually after incubation for 18 h, at 37°C. The
results are presented in Table 2. These compounds have good
inhibitory activity against S. typhimuriun and E. coli. More
antibacterial experiments are under study.
In summary, we have developed a highly efficient and
eco-friendly method for the preparation of chenodeoxycholic
acid thiosemicarbazones. The reaction was conducted in the
presence of neutral aluminum oxide, without using solvent,
and assisted by microwave irradiation. The present method
has many advantages compared to the conventional method,
including shorter reaction times, good product yields and
fulfills green chemistry protocols. The importance of such
work lies in the possibility that these new compounds might
be more helpful in designing more potent antibacterial agents
for biological and therapeutic use.
Results and discussion
The structures of the compounds 4a–j were confirmed by IR,
1
mass, H NMR and elementary analysis. Their mass spectra
showed the expected molecular ions in high intensity. The IR
spectra of these compounds exhibited a characteristic strong
absorption at 3174–3307 cm−1 due to N–H stretching vibration;
The strong bands in the region 1699–1740 cm−1 indicated the
absorption of C=O. Strong absorption bands falling within the
range of 1521–1609−cm−1 and the range of 1229–1293 cm−1
Experimental
1
were assigned to the C=N and C=S respectively. In the H
Melting points were determined on a micro-melting point apparatus
and the thermometer was uncorrected. IR spectra were obtained
NMR spectra, the singlets between δ 8.54 and 9.42 ppm were
assigned to the protons of the NH. A doublet signal due to the
other NH proton was observed at 8.54–9.76 ppm. In addition,
the singlet peaks at 1.26–1.29 ppm, 0.68–0.69 ppm and the
double peaks at 0.92–0.94 ppm were the characteristic of
1
on 1700 PerkinElmer FTIR using KBr disks. H NMR spectra were
recorded on a Varian INOVA 400 MHz spectrometer using CDCl3 as
solvent and TMS as internal standard. Mass spectra were determined
on FinniganLCQDECA instrument. Elemental analysis was performed
on a Carlo-Erba-1106 auto-analyser. All reactions were performed
in a commercial microwave reactor (XH-100A, 100–1000W, Beijing
XiangHu Science and Technology Development Co. Ltd, Beijing, P.R.
China). All the solvents were purified before use. Compound 2 were
prepared by known procedure.18
* Correspondent. E-mail: zzg63129@yahoo.com.cn

JOURNAL OF CHEMICAL RESEARCH 2011 457
Scheme 1 The synthetic route of the thiosemicarzones 4a–j.
Preparation of substituted thiosemicarbazides 1a–j;19 general
procedure
Synthesis of methyl 3,7-dioxocholan-24-oate (3)20
Pyridinium chlorochromate (PCC) (3.03 mmol) was added to a solu-
tion of compound 2 (0.25 g, 0.615 mmol) in dry CH2Cl2 (20 ml) at
room temperature. The reaction was completed in 12 h. The solvent
was removed under reduced pressure, and the crude product was
purified by chromatography on silica gel using ethyl acetate to give
white solid, yield 86%; m.p. 155–156°C (lit.21 m.p. 154–156°C);
[α]2D0 = –21.5 (c 0.12, CH2Cl2); IR (KBr) (cm−1): 2953, 2873, 1709,
Carbon disuldfide was added dropwise (0.8 mL) to a solution of
substituted amine (0.01 mol) in ethanol (10 mL) and concentrated
aqueous ammonia (2 mL) was added The mixture was stirred at 15–
20°C for 1–2 h to form a solid. Sodium chloroacetate (1.2 g) was
added to the stirred mixture and then 85% hydrazine hydrate (1.2 mL)
was added. Stirring continued at 60°C for 4 h to obtain a solid. The
crude product was then recrystallised from ethanol to obtain each
thiosemicarbazides 1a–j. The melting points of thiosemicarbazides
1a–j are shown in Table 3.
1
1403, 1375, 1214, 1174, 1010, 966; H NMR (400 MHz, CDCl3) δ:
3.67 (s, 3H, COOCH3), 1.31 (s, 3H, 19-CH3), 0.93 (d, 3H, J = 6.4 Hz,
21-CH3), 0.69 (s, 3H, 18-CH3); ESI-MS m/z (%): 827 ( [2M+23]+, 100).

458 JOURNAL OF CHEMICAL RESEARCH 2011
Table 1 Synthetic comparison of thiosemicarbzaones 4a–j
between solvent-free conditions under microwave irradiation
and conventional heating
4b: White solid, yield 94%, m.p. 164–165°C, [α]2D0 = –100.80
(c 0.10, CH2Cl2); IR (KBr) (cm−1): 3286, 3174, 2951, 2875, 1721,
1594, 1547, 1516, 1244, 1177, 1033, 833; 1H NMR (400 MHz, CDCl3)
δ: 9.07 (s, 1H, NH), 8.58 (d, 1H, J = 7.2 Hz, NH), 7.46 (d, 2H, J =
8.8 Hz, ArH), 6.91 (d, 2H, J = 7.6 Hz, ArH), 3.81 (s, 3H, Ar-OCH3),
3.67 (s, 3H, COOCH3), 1.27 (s, 3H, 19-CH3), 0.93 (d, 3H, J = 6.4 Hz,
21-CH3), 0.69 (s, 3H, 18-CH3); ESI-MS m/z (%): 604 ([M+23]+, 100).
Ana1. Calcd for C33H47N3O4S: C, 68.12; H, 8.14; N, 7.22. Found: C,
68.04; H, 8.12; N, 7.18%.
a
Compd
Conventional method Microwave method tC/tMW
t/min
Yield/%
t/min
Yield/%
4a
4b
4c
4d
4e
4f
400
360
420
480
360
420
420
480
360
300
57
53
62
51
52
47
55
49
45
55
5.0
4.0
5.5
5.5
4.0
4.5
5.0
6.0
5.5
4.0
87
94
86
88
90
90
89
87
89
92
80
90
76
87
90
93
84
80
65
75
4c: White solid, yield 86%, m.p. 115–116°C, [α]2D0 = −78.37 (c 0.10,
CH2Cl2); IR (KBr) (cm−1): 3293, 2950, 2871, 1738, 1710, 1609, 1521,
1
1258, 1186, 1053, 835; H NMR (400 MHz, CDCl3) δ: 9.15 (s, 1H,
NH), 8.75 (d, 1H, J = 7.2 Hz, NH), 7.56 (t, 2H, J = 8.0 Hz , ArH),
7.07 (t, 2H, J = 8.4 Hz, ArH), 3.67 (s, 3H, COOCH3), 1.27 (s, 3H,
19-CH3), 0.93 (d, 3H, J = 6.4 Hz, 21-CH3), 0.69 (s, 3H, 18-CH3); ESI-
MS m/z (%): 570 ([M+1]+, 100). Ana1. Calcd for C32H44FN3O3S:
C, 67.46; H, 7.78; N, 7.37. Found: C, 67.43; H, 7.75; N, 7.34%.
4d: White solid, yield 88%, m.p. 131–132 ℃, [α]2D0 = −73.37
(c 0.10, CH2Cl2); IR (KBr) (cm−1): 3300, 3180, 2950, 2869, 1737,
1711, 1591, 1550, 1492, 1437, 1379, 1274, 1200, 1160, 1097, 1048,
4g
4h
4i
4j
tC, Conventional method time; tMW, microwave method time.
Table 2 MIC (µg mL−1) of thiosemicarbzaones and positive
Amoxicillin control
1
787; H NMR (400 MHz, CDCl3) δ: 9.19 (s, 1H, NH), 8.54 (d, 1H,
J = 8.4 Hz, NH), 7.45 (t, 2H, J = 5.6 Hz, ArH), 7.26 (t, 1H, J = 6.4 Hz,
ArH), 7.03 (d, 1H, J = 7.6 Hz, ArH), 3.67 (s, 3H, COOCH3), 2.37 (s,
3H, ArCH3), 1.27 (s, 3H, 19-CH3), 0.93 (d, 3H, J = 6.4 Hz, 21-CH3),
0.69 (s, 3H, 18-CH3); ESI-MS m/z (%): 1131 ([2M+1]+, 100). Ana1.
Calcd for C33H47N3O3S: C, 70.05; H, 8.37; N, 7.43. Found: C, 70.02;
H, 8.36; N, 7.40%.
Compd
S. pyogenes
S. typhimurium
E. coli
4a
256
128
128
256
32
128
64
32
64
32
64
64
32
64
32
4b
4c
4d
4e: White solid, yield 90%, m.p. 151–152°C, [α]2D0 = −123.78
(c 0.10, CH2Cl2); IR (KBr) (cm−1): 3282, 3220, 2951, 2870, 1737,
1708, 1591, 1546, 1481, 1439, 1269, 1176, 1045, 819; 1H NMR
(400 MHz, CDCl3) δ: 9.15 (s, 1H, NH), 8.59 (d, 1H, J = 7.2 Hz, NH),
7.48 (d, 2H, J = 8.0 Hz, ArH), 7.18 (t, 2H, J = 8.0 Hz, ArH), 3.67
(s, 3H, COOCH3), 2.35 (s, 3H, ArCH3), 1.27 (s, 3H, 19-CH3), 0.93
(d, 3H, J = 6.4 Hz, 21-CH3), 0.69 (s, 3H, 18-CH3); ESI-MS m/z (%):
1131 ([2M+1]+, 100). Ana1. Calcd for C33H47N3O3S: C, 70.05; H,
8.37; N, 7.43. Found: C, 69.99; H, 8.35; N, 7.40%.
Amoxicillin
Table 3 The melting points of substituted thiosemicarbazides
1a–j
Product
Formula
M.p./°C
Lit M.p./°C
136–13822
15223
4f: White solid, yield 90%, m.p. 179–180 ℃, [α]2D0 = −93.58 (c 0.10,
1a
1b
1c
1d
1e
1f
C7H9N3S
137–138
150–151
154–155
93–94
136–137
158–159
159–160
136–137
126–127
134–135
CH2Cl2); IR (KBr) (cm−1): 3256, 2947, 1740, 1702, 1598, 1542, 1463,
C8H11N3OS
C7H8FN3S
C8H11N3S
15324
1
1377, 1287, 1229, 1176, 1031, 750; H NMR (400 MHz, CDCl3) δ:
9225
9.76 (d, 1H, J = 9.6 Hz, NH), 8.69 (t, 1H, J = 8.4 Hz and J = 8.0 Hz,
ArH), 8.54 (s, 1H, NH), 7.13 (t, 1H, J = 8.0 Hz, ArH), 6.99 (t, 1H,
J = 8.0 Hz, ArH), 6.91 (d, 1H, J = 8.0 Hz, ArH), 3.88 (s, 3H,
COOCH3), 3.67 (s, 3H, COOCH3), 1.27 (s, 3H, 19-CH3), 0.93 (d, 3H,
J = 6.4 Hz, 21-CH3), 0.69 (s, 3H, 18-CH3); ESI-MS m/z (%): 604
([M+23]+, 100). Ana1. Calcd for C33H47N3O4S: C, 68.12; H, 8.14; N,
7.22. Found: C, 68.07; H, 8.13; N, 7.20%.
C8H N3S
13726
11
C8H N3OS
15927
11
1g
1h
1i
C8H N3OS
16128
11
C11H11N3S
C7H8ClN3S
C9H13N3S
138–13927
126–12729
13530
1j
4g: White solid, yield 89%, m.p. 151–152°C, [α]2D0 = −129.50
(c 0.10, CH2Cl2); IR (KBr)(cm-1): 3288, 2948, 2873, 1733, 1711,
1598, 1547, 1458, 1431, 1293, 1161, 1038, 779; 1H NMR (400 MHz,
CDCl3) δ: 9.26 (s, 1H, NH), 8.57 (d, 1H, J = 8.8 Hz, NH), 7.46 (d, 1H,
J = 7.6 Hz, ArH), 7.28–7.24 (m, 1H, ArH), 7.12 (d, 1H, J = 7.6 Hz,
ArH), 6.76 (d, 1H, J = 8.0 Hz, ArH), 3.82 (s, 3H, Ar-OCH3), 3.67
(s, 3H, COOCH3), 1.27 (s, 3H, 19-CH3), 0.93 (d, 3H, J = 6.4 Hz,
21-CH3), 0.69 (s, 3H, 18-CH3); ESI-MS m/z (%): 604 ([M+23]+, 100).
Ana1. Calcd for C33H47N3O4S: C, 68.12; H, 8.14; N, 7.22. Found: C,
68.10; H, 8.13; N, 7.20%.
Preparation of thiosemicarbazones 4a–j; general procedure
Conventional method: Steroidal ketones (3) (0.1 g, 0.26 mmol) and
substituted thiosemicarbazides (1a–j) (0.26 mmol) were dissolved
in 10 mL ethanol. After completely dissolving the substrates, two
drops of acetic acid were added. The mixture was stirred for 5–8 h at
80°C. After cooling the products were filtered and recrystallised from
ethanol in 45–62% yields.
Microwave irradiation method: Steroidal ketones (3) (0.1 g,
0.26 mmol), substituted thiosemicarbazides (1a–j) (0.26 mmol) and
neutral aluminium oxide (0.3 g) were put in a porcelain mortar,
and concentrated acetic acid (two drops) was added. After grinding,
the mixture was put in a round-bottom flask (25 mL) and placed in
a microwave oven. It was irradiated for 4.0–6.0 min at 400–600 W.
The reaction mixture was cooled to room temperature and dissolved
in DMSO and filtered. The filtrate was added to water and the product
was formed. The product was recrystallised from ethanol in 86–94%
yields. The physical and spectra data of the compounds 4a–j are as
follows.
4h: White solid, yield 87%, m.p. 118–119°C, [α]2D0 = −83.37
(c 0.10, CH2Cl2); IR (KBr) (cm−1): 3307, 2946, 2871, 1735, 1708,
1596, 1505, 1470, 1380, 1268, 1199, 1166, 1093, 1019, 775; 1H NMR
(400 MHz, CDCl3) δ: 9.42 (s, 1H, NH), 8.75 (d, 1H, J = 9.2 Hz, NH),
7.93–7.85 (m, 3H, ArH), 7.82 (d, 1H, J = 8.0 Hz, ArH), 7.55–7.51 (m,
3H, ArH), 3.67 (s, 3H, COOCH3), 1.29 (s, 3H, 19-CH3), 0.94 (d, 3H,
J = 6.4 Hz, 21-CH3), 0.70 (s, 3H, 18-CH3); ESI-MS m/z (%): 1225
([2M+23]+, 100). Ana1. Calcd for C36H47N3O3S: C, 71.84; H, 7.87; N,
6.98. Found: C, 71.82; H, 7.85; N, 6.94%.
4i: White solid, yield 89%, m.p. 141–142°C, [α]2D0 = −79.50 (c 0.10,
CH2Cl2); IR (KBr) (cm−1): 3270, 2933, 2860, 1734, 1699, 1592, 1521,
4a: White solid, yield 87%, m.p. 99–100 ℃, [α]2D0 = –81.70 (c 0.10,
1
CH2Cl2); IR (KBr)(cm−1): 3259, 2948, 2870, 1739, 1701, 1598, 1536,
1486, 1378, 1269, 1172, 1055, 713; H NMR (400 MHz, CDCl3) δ:
1
9.11 (s, 1H, NH), 8.59 (d, 1H, J = 6.8 Hz, NH), 7.45 (t, 1H, J = 4.8 Hz
and J = 4.8 Hz, ArH), 7.26 (d, 1H, J = 6.8 Hz, ArH), 7.03 (d, 1H,
J = 7.2 Hz, ArH), 6.86 (d, 1H, J = 8.0 Hz, ArH), 3.82 (s, 3H,
Ar-OCH3), 3.67 (s, 3H, COOCH3), 1.27 (s, 3H, 19-CH3), 0.93 (d, 3H,
J = 6.0 Hz, 21-CH3), 0.69 (s, 3H, 18-CH3); ESI-MS m/z (%): 586
([M+1]+, 100). Ana1. Calcd for C32H44ClN3O3S: C, 65.56; H, 7.57; N,
7.17. Found: C, 65.44; H, 7.53; N, 7.15%.
1485, 1440, 1264, 1174, 1037, 754; H NMR (400 MHz, CDCl3) δ:
9.25 (s, 1H, NH), 8.62 (d, 1H, J = 8.0 Hz, NH), 7.64 (d, 2H, J =
8.0 Hz, ArH), 7.37 (t, 2H, J = 7.6 Hz , ArH), 7.22 (t, 1H, J = 7.2 Hz,
ArH), 3.66 (s, 3H, COOCH3), 1.26 (s, 3H, 19-CH3), 0.92 (d, 3H, J =
6.4 Hz, 21-CH3), 0.68 (s, 3H, 18-CH3); ESI-MS m/z (%): 1103
([2M+1]+, 100). Ana1. Calcd for C32H45N3O3S: C, 69.65; H, 8.22; N,
7.62. Found: C, 69.60; H, 8.18; N, 7.58%.

JOURNAL OF CHEMICAL RESEARCH 2011 459
4j: White solid, yield 92%, m.p. 175–176 ℃, [α]2D0 = −40.78 (c 0.10,
CH2Cl2); IR (KBr) (cm−1): 3281, 3196, 2952, 2870, 1739, 1711, 1593,
1549, 1491, 1442, 1272, 1230, 1172, 1044, 823; 1H NMR (400 MHz,
CDCl3) δ: 8.90 (d, 1H, J = 8.4 Hz, NH), 8.66 (s, 1H, NH), 7.43 (t, 1H,
J = 7.6 Hz, ArH), 7.06 (s, 1H, ArH), 7.04 (s, 1H, ArH), 3.67 (s, 3H,
COOCH3), 2.32 (s, 3H, ArCH3), 2.26 (s, 3H, ArCH3), 1.27 (s, 3H, 19-
CH3), 0.94 (d, 3H, J = 6.4 Hz, 21-CH3), 0.69 (s, 3H, 18-CH3); ESI-MS
m/z (%): 580 ([M+1]+, 100). Ana1. Calcd for C34H49N3O3S: C, 70.43;
H, 8.52; N, 7.25. Found: C, 70.37; H, 8.50; N, 7.23%.
6
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We thank the Special Financial Project of Central Chinese
University (No. 11NZYQN05) and the Science andTechnology
Bureau of Sichuan Province (No. 2011JY0035) for financial
support.
Received 26 June 2011; accepted 14 July 2011
Paper 1100763 doi: 10.3184/174751911X13129090186347
Published online: 29 August 2011
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