Microwave-assisted synthesis of new steroidal thiosemicarbazones derived from methyl 3-oxocholanate under solvent-free conditions

Article abstract of DOI:10.3184/030823410X12798092457988

A series of novel steroidal thiosemicarbazones derived from methyl 3-oxocholanate were synthesised in good yields via microwave irradiation under solvent-free conditions. The structures of the compounds were confirmed by spectroscopic data. Compared to the conventional method, microwave irradiation was a fast and simple method. These compounds were tested for antibacterial activity against S. aureus, S. pyogenes, and E. coli bacteria.

Full text of DOI:10.3184/030823410X12798092457988

JOURNAL OF CHEMICAL RESEARCH 2010
RESEARCH PAPER 455
AUGUST, 455–458
Microwave-assisted synthesis of new steroidal thiosemicarbazones
derived from methyl 3-oxocholanate under solvent-free conditions
Zhigang Zhao*, Xingli Liu, Lingling Liu and Guohua Li
College of Chemistry and Environmental Protection Engineering, Southwest University for Nationalities, Chengdu 610041, P. R. China
A series of novel steroidal thiosemicarbazones derived from methyl 3-oxocholanate were synthesised in good yields
via microwave irradiation under solvent-free conditions. The structures of the compounds were confirmed by
spectroscopic data. Compared to the conventional method, microwave irradiation was a fast and simple method.
These compounds were tested for antibacterial activity against S. aureus, S. pyogenes, and E. coli bacteria.
Keywords: steroidal thiosemicarbazones, microwave irradiation, solvent-free conditions
Thiosemicarbazones are important classes of compounds
which have attracted attention, owing to their remarkable
biological and pharmacological properties.1–3 The antibacterial
properties of thiosemicarbazones have been studied since
1946, when Domagk et al. reported their activity against M.
tuberculosis.4 The biological activity of thiosemicarbazones
were dependent on the substituents. Minor modifications in the
thiosemicarbazones can lead to significant change in biologi-
cal activity.5 Therefore, thiosemicarbazones are considered to
be important scaffolds and are embedded in many biologically
active compounds.6
structure. The singlet peaks between 3.67 and 3.69 ppm was
assigned to the protons in the COOCH3.
The effect of different oxidants
When we synthesised the intermediate 6 (Scheme 1), we
found that PCC was the best oxidant for this reaction. PCC is
a mild oxidant and this was a selective oxidation compared
to other stronger oxidants such as KMnO4, K2Cr2O7/H2SO4.
In addition, the oxidation reaction was carried out at room
temperature.
Microwave irradiation, a non-conventional energy source,
has emerged as a powerful technique for promoting a variety
of chemical reactions and has become a useful technology in
organic chemistry.7,8 The combination of solvent-free condi-
tions and microwave irradiation considerably reduces reaction
time, enhances conversions as well as selectivity and has
environmental advantages. These constitute an eco-friendly
green approach.9,10
The comparison of microwave irradiation and conventional
heating
In searching for the best conditions, we also carried out a
series of experiments, to study microwave irradiation power,
time and different supporters. We took the synthesis of 7a for
example and found that the highest yield would be obtained
when the time was 4 min at 460W using neutral aluminum
oxide as the solid support.
As shown in Table 1, we compared the synthesis of 7a–j
using microwave irradiation under the solvent-free conditions
and conventional heating. \this showed that that microwave
irradiation greatly decreased the reaction time from 180–300
min to 2–4 min. However, the yields were increased from
60–75% to 88–95%. The use of microwave technology in
conjunction with the use of solvent-free conditions allows
expeditious and efficient procedures for this synthesis.
In 2007, Salman et al.11 synthesised a series steroidal thios-
emicarbazones from the reaction of cholest-5-en-7-one with
thiosemicarbazides, and evaluated them for their antibacterial
activity against two Gram-positive and two Gram-negative
bacteria. The results showed that those compounds inhibit
growth of both types of the bacteria. Steroidal thiosemicarba-
zones have a considerable research potential.12–14
Recently, we reported the preparation of indole-based thios-
emicarbazones under solvent-free conditions using microwave
methods.15 As a continuation of this work, we have synthesised
a series of new steroidal thiosemicarbazones based on methyl
3-oxocholanate by the condensation of the steroidal ketones
with the thiosemicarbazides under these green conditions.
The synthetic route is shown in Scheme 1.
In vitro antibacterial activity
Compounds 7b, 7e, 7g, 7h were evaluated for their in vitro
antibacterial activity against S. aureus, S. pyogenes and E. coli
using agar dilution method. The preliminary results seemed
promising and these thiosemicarbazones had a good inhibitory
effect. Furtherresearch work is underway.
In conclusion, we have synthesised 10 novel streroidal
thiosemicarbazones derived from methyl 3-oxocholanate
under solvent-free conditions using microwave irradiation.
This method was a convenient and rapid procedure compared
to the conventional synthesis. In addition, these compounds
may have good antibacterial activity and this requires more
research. The importance of this work lies in the possibility
that these new compounds may be more helpful in designing
more potent antibacterial agents for therapeutic use.
Results and discussion
Spectroscopic studies
The structures of 7a–j were confirmed by IR, mass, 1H NMR
and elemental analysis. Their mass spectra showed the expected
molecular ion peaks with a high intensity. The IR spectra of
these compounds exhibited characteristic strong absorption at
3178–3456 cm−1 due to N–H stretching vibration; The strong
bands in the region 1731and 1747 cm−1 indicated the absorp-
tion of C=O; The strong absorption bands falling within the
range of 1511–1648 cm−1 and the range of 1229–1286 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. Infrared spectra were obtained
NMR spectra, the singlets between δ 9.11 and 9.78 ppm were
assigned to the protons of the ArNH. A singlet due to the other
NH proton was observed at 8.55–8.77 ppm. In addition, the
singlet peaks at 0.63–0.68 ppm, 1.00–1.09 ppm and the double
peaks at 0.92–0.93 ppm were the characteristic of the steroidal
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 analyzer. Microwave irradiation was
carried out with a MCL-3 microwave oven (very safe) at full power
(700 W), which was modified from domestic microwave oven and
* Correspondent. E-mail: zzg63129@yahoo.com.cn

456 JOURNAL OF CHEMICAL RESEARCH 2010
Scheme 1 The synthetic route of the steroidal thiosemicarbazones 7a–j.
tested to conform to the performance index before use. All the
solvents were purified before use.
disulfide dropwise (0.8 mL), and 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 and the stirring continued at 60 °C for 4 h to give a solid.
The crude product was then recrystallised from ethanol to obtain
each thiosemicarbazide in 62–80% yields. The melting points of
thiosemicarbazides 3a–j are shown in Table 2.
Preparation of substituted thiosemicarbazides 3a–j; general
procedure16
A solution of substituted amine (0.01 mol) in ethanol (10 mL) and
concentrated aqueous ammonia (2 mL) was treated with carbon

JOURNAL OF CHEMICAL RESEARCH 2010 457
Table 1 Synthetic comparison of thiosemicarbazones 7a–j
between solvent-free conditions under microwave irradiation
and conventional heating
placed in a porcelain mortar, then concentrated sulfuric acid (two
drops) was added to it. After grinding, the mixture was put in a round-
bottom flask (25 mL) and was kept under microwave oven. Then it
was irradiated for 2–4 min at 200–460 W. The reaction mixture was
cooled to room temperature and was dissolved in DMSO and filtered.
The filtrate was added water and the product was formed. The product
was recrystallised from DMSO and H2O in 88–95% yields. The
physical and spectra data of the compounds 7a–j are as follows.
7a: White crystal, yield 88%, m.p. 126–128 °C, [α]2D0 = +141.7
(c 0.1, CH2Cl2); IR (KBr)(cm−1): 3278, 3178, 2946, 2863, 1731, 1536,
1428, 1262, 1188; 1H NMR (400 MHz, CDCl3) δ: 9.30 (s, 1H, ArNH),
8.59 (s, 1H, NH), 7.67 (d, 2H, J = 8.0 Hz, ArH), 7.40 (t, 2H, J = 7.6
Hz, ArH), 7.24–7.20 (m, 1H, ArH), 3.67 (s, 3H, COOCH3), 1.00 (s,
3H, 19-CH3), 0.93 (d, 3H, J = 6.4 Hz, 21-CH3), 0.68 (s, 3H, 18-CH3);
ESI-MS m/z (%): 538 ([M+1]+,100). Ana1.Calcd for C32H47N3O2S:
C, 71.47; H, 8.81; N, 7.81. Found: C, 71.40; H, 8.79; N, 7.82%.
7b: White crystal, yield 95%, m.p. 120–123 °C. [α]2D0 = +33.3
(c 0.1, CH2Cl2); IR (KBr) (cm−1): 3270, 3191, 2929, 1739, 1602, 1544,
1233, 1163, 740; 1H NMR (400 MHz, CDCl3) δ: 9.78 (s, 1H, ArNH),
8.71 (s, 1H, NH), 8.55 (d, 1H, J = 5.2 Hz, ArH), 7.15 (t, 1H, J = 7.2
Hz, ArH), 7.02 (t, 1H, J = 7.2Hz, ArH), 6.93 (d, 1H, J = 8.0 Hz, ArH),
3.89 (s, 3H, OCH3), 3.67 (s, 3H, COOCH3), 1.00 (s, 3H, 19-CH3), 0.93
(d, 3H, J = 6.4 Hz, 21-CH3), 0.68 (s, 3H, 18-CH3); ESI-MS m/z (%):
568 ([M+1]+,100). Ana1.Calcd for C33H49N3O3S: C, 69.80; H, 8.70;
N, 7.40. Found: C, 69.73; H, 8.68; N, 7.43%.
a
Comp.
Conventional
method
Microwave
method
tC/tMW
t/min Yield/%
t/min Yield/%
7a
7b
7c
7d
7e
7f
300
180
240
240
240
240
300
240
300
300
60
75
65
65
70
70
70
65
70
60
4.0
2.0
3.0
3.0
4.0
4.0
4.0
3.0
3.0
4.0
88
95
88
88
90
90
90
89
90
88
75
90
80
80
60
60
75
80
100
75
7g
7h
7i
7j
tC, Conventional method time; tMW, microwave method time.
Table 2 The melting points of thiosemicarbazide 3a–j
Product
Formula
M.p./°C
Lit M.p./°C
3a
3b
3c
3d
3e
3f
C7H10N3OS
C8H11N3OS
137–139
155–157
157–158
147–149
178–180
165–168
137–138
135–136
126–127
135–137
136–13817
15918
7c: White crystal, yield 88%, m.p. 150–153 °C, [α]2D0 = +130.0
C8H N3OS
16119
(c 0.1, CH2Cl2); IR (KBr) (cm−1): 3286, 3211, 2941, 2863, 1743, 1593,
11
C8H N3OS
15220
1
11
1539, 1286, 1158, 780; H NMR (400 MHz, CDCl3) δ: 9.30 (s, 1H,
C7H N3ClS
17821
8
ArNH), 8.55 (s, 1H, NH), 7.49 (s, 1H, ArH), 7.28 (t, 1H, J = 7.6 Hz,
ArH), 7.15 (d, 1H, J = 7.6 Hz, ArH), 6.77 (d, 1H, J = 8.0 Hz, ArH),
3.83 (s, 3H, OCH3), 3.67 (s, 3H, COOCH3), 1.00 (s, 3H, 19-CH3), 0.93
(d, 3H, J = 6.4 Hz, 21-CH3), 0.68 (s, 3H, 18-CH3); ESI-MS m/z (%):
568 ([M+1]+,100). Ana1.Calcd for C33H49N3O3S: C, 69.80; H, 8.70;
N, 7.40. Found: C, 69.72; H, 8.72; N, 7.42%.
C7H8N3BrS
C7H8N3FS
C8H11N3S
C7H8N3ClS
C11H11N3S
163–16521
13822
3g
3h
3i
13723
12524
3j
138–13918
7d: White crystal, yield 88%, m.p. 175–177 °C, [α]2D0 = +193.0
(c 0.1, CH2Cl2); IR (KBr)(cm−1): 3434, 3286, 2917, 2842, 1731, 1631,
Synthesis of methyl 3α-hydroxy-5β-cholan-24-oate (5)25
1
1528, 1229, 1163, 823; H NMR (400 MHz, CDCl3) δ: 9.11 (s, 1H,
Lithocholic acid (1g, 2.7mmol), anhydrous methanol (20 mL) and
p-toluenesulfonic acid (0.1g, 0.52mmol) were added to a round bottom
flask and this was stirred at room temperature for 24 h. Then the
solvent was evaporated and the residue dissolved with ethyl acetate
(30 mL). The solution was washed with NaHCO3 (3 × 20 mL) and
saturated brine (3 × 20 mL). After driying over anhydrous sodium
sulfate, the solvent was removed under reduced pressure, and the
crude product was purified by chromatography on silica gel using
(CH2Cl2):(CH3COOC2H5) V/V 10:1 to give a white solid, yield 94%,
m.p. 126–127 °C, [α]2D0 = +34.7 (c 0.9, CH2Cl2); IR (KBr) (cm−1):
ArNH), 8.55 (s, 1H, NH), 7.49 (d, 2H, J = 8.4 Hz, ArH), 6.92 (d, 2H,
J = 8.4 Hz, ArH), 3.82 (s, 3H, OCH3), 3.67 (s, 3H, COOCH3), 1.00 (s,
3H, 19-CH3), 0.93 (d, 3H, J = 6.4 Hz, 21-CH3), 0.67 (s, 3H, 18-CH3);
ESI-MS m/z (%): 568 ([M+1]+,100). Ana1.Calcd for C33H49N3O3S:
C, 69.80; H, 8.70; N, 7.40. Found: C, 69.76; H, 8.68; N, 7.39%.
7e: White crystal, yield 90%, m.p. 176–179 °C, [α]2D0 = +176.7
(c 0.1, CH2Cl2); IR (KBr)(cm−1): 3444, 3278, 2925, 2855, 1731, 1648,
1
1511, 1270, 1175, 827; H NMR (400 MHz, CDCl3) δ: 9.27 (s, 1H,
ArNH), 8.60 (s, 1H, NH), 7.60 (d, 2H, J = 8.4 Hz, ArH), 7.50 (d, 2H,
J = 8.4 Hz, ArH), 3.67 (s, 3H, COOCH3), 1.09 (s, 3H, 19-CH3), 0.93
(d, 3H, J = 6.4 Hz, 21-CH3), 0.68 (s, 3H, 18-CH3); ESI-MS m/z (%):
572 ([M+1]+,100). Ana1.Calcd for C32H46ClN3O2S: C, 67.16; H, 8.10;
N, 7.34. Found: C, 67.10; H, 8.05; N, 7.30%.
1
3520, 2981, 2959, 1719, 1101; H NMR (400 MHz, CDCl3) δ: 3.63
(s, 3H, COOCH3), 3.63–3.59 (m, 1H, 3β-H), 0.94 (s, 3H, 19-CH3),
0.90 (d, J = 6.4 Hz, 3H, 21-CH3), 0.64 (s, 3H, 18-CH3); ESI-MS m/z
(%): 803 ([2M+Na]+, 100).
7f: White crystal, yield 90%, m.p. 185–187 °C, [α]2D0 = +111.7
(c 0.1, CH2Cl2); IR (KBr)(cm−1): 3444, 3278, 2925, 2855, 1731, 1648,
Synthesis of methyl 3α-oxo-5β-cholano-24-oate (6)26
1
1511, 1270, 1175, 827; H NMR (400 MHz, CDCl3) δ: 9.27 (s, 1H,
Pyridinium chlorochromate (PCC) (0.74g, 0.34 mmol) was added to
a solution of compound 5 (0.78g, 0.2 mmol) in dried CH2Cl2 (30 mL)
at room temperature. The reaction was completed in 12h. The solvent
was removed under reduced pressure, and the crude product was puri-
fied by chromatography on silica gel using ethyl acetate to give white
solid, yield 87%; m.p. 115–117 °C [α]2D0 = +190.0 (c 0.1, CH2Cl2); IR
ArNH), 8.58 (s, 1H, NH), 7.60 (d, 2H, J = 8.4 Hz, ArH), 7.50 (d, 2H,
J = 8.4 Hz, ArH), 3.69 (s, 3H, COOCH3), 1.00 (s, 3H, 19-CH3),
0.93 (d, 3H, J = 6.4 Hz, 21-CH3), 0.68 (s, 3H, 18-CH3); ESI-MS
m/z (%): 616 ([M+1]+,100). Ana1.Calcd for C32H46BrN3O2S: C, 62.32;
H, 7.52; N, 6.81. Found: C, 62.30; H, 7.49; N, 6.79%.
1
7g: White crystal, yield 90%, m.p. 130–131 °C. [α]2D0 = +170.0
(KBr) (cm−1): 2940, 2860, 1731, 1536, 1180; H NMR (400 MHz,
(c 0.1, CH2Cl2); IR (KBr)(cm−1): 3286, 3195, 2938, 2863, 1743, 1606,
CDCl3) δ: 3.67 (s, 3H, COOCH3), 1.02 (s, 3H, 19-CH3), 0.93 (d,
J = 6.4 Hz, 3H, 21-CH3), 0.68 (s, 3H, 18-CH3); ESI-MS m/z (%):
799 ([2M+Na]+, 100).
1
1548, 1266, 1163, 781; H NMR (400 MHz, CDCl3) δ: 9.36 (s, 1H,
ArNH), 8.58 (s, 1H, NH), 7.70 (d, 1H, J = 10.4 Hz, ArH), 7.39 (d, 1H,
J = 7.6 Hz, ArH), 7.34–7.28 (m, 1H, ArH), 6.92 (t, 1H, J = 6.8 Hz,
ArH), 3.67 (s, 3H, COOCH3), 1.00 (s, 3H, 19-CH3), 0.93 (d, 3H,
J = 6.4 Hz, 21-CH3), 0.68 (s, 3H, 18-CH3); ESI-MS m/z (%): 556
([M+1]+,100). Ana1.Calcd for C32H46FN3O2S: C, 69.15; H, 8.34;
N, 7.56. Found: C, 69.10; H, 8.30; N, 7.60%.
General procedure for the preparation of thiosemicarbazones 7a–j
Conventional method
Steroidal ketones (6) (0.1g, 0.258mmol) and substituted thiosemicar-
bazide (3) (0.258 mmol) were dissolved in ethanol (10 mL). After
completely dissolving, two drops of concentrated sulfuric acid
were added. The mixture was stirred for 3–5 h at room temperature.
A solid was separated, which was recrystallised from DMSO and H2O
in 60–75% yields.
7h: White crystal, yield 89%, m.p. 186–188 °C, [α]2D0 = +190.0
(c 0.1, CH2Cl2); IR (KBr)(cm−1): 3419, 3274, 2925, 2863, 1747, 1615,
1
1536, 1279, 1179, 739; H NMR (400 MHz, CDCl3) δ: 9.20 (s, 1H,
ArNH), 8.55 (s, 1H, NH), 7.51 (d, 2H, J = 8.0 Hz, ArH), 7.19 (d, 2H,
J = 8.0 Hz, ArH), 3.67 (s, 3H, COOCH3), 2.69 (s, 3H, Ar-CH3),
1.00 (s, 3H, 19-CH3), 0.93 (d, 3H, J = 6.4 Hz, 21-CH3), 0.68 (s, 3H,
18-CH3); ESI-MS m/z (%): 552 ([M+1]+,100). Ana1.Calcd for
C33H49N3O2S: C, 71.83; H, 8.95; N, 7.61. Found: C, 71.77; H, 8.90;
N, 7.59%.
Microwave irradiation method
Steroidal ketones (6) (0.1g, 0.258mmol), substituted thiosemicarba-
zide (0.258 mmol) (3) and neutral aluminium oxide (0.3 g) were

458 JOURNAL OF CHEMICAL RESEARCH 2010
7i: White crystal, yield 90%, m.p. 144–146 °C, [α]2D0 = +106.7
(c 0.1, CH2Cl2); IR (KBr)(cm−1): 3293, 3207, 2938, 2851, 1739, 1594,
1266, 1188, 698; 1H NMR (400 MHz, CDCl3) δ: 9.30 (s, 1H, ArNH),
8.59 (s, 1H, NH), 7.77 (s, 1H, ArH), 7.62 (d, 1H, J = 7.6 Hz, ArH),
7.32 (t, 1H, J = 8.0 Hz, ArH), 7.19 (d, 1H, J = 8.0 Hz, ArH), 3.67
(s, 3H, COOCH3), 1.00 (s, 3H, 19-CH3), 0.93 (d, 3H, J = 6.4 Hz,
21-CH3), 0.68 (s, 3H, 18-CH3); ESI-MS m/z (%): 572 ([M+1]+,100).
Ana1.Calcd for C32H46ClN3O2S: C, 67.16; H, 8.10; N, 7.34. Found:
C, 67.10; H, 8.09; N, 7.35%.
3
4
I.C. Mendes, F.B. Costa, G.M. de Lima, J.D. Ardisson and H. Beraldo,
Polyhedron., 2009, 28, 1179.
G. Domagk, R. Behnisch, F. and Mietzsch, H. Schimidt, Naturwissen-
chaften., 1946, 315.
H. Beraldo and D. Gambino, Mini Rev. Med. Chem., 2004, 4, 159.
H. Huang, Q. Chen, X. Ku, L.H. Meng and H. Liu, J. Med. Chem., 2010,
53, 3048.
L. Perreux and A. Loupu, Tetrahedron, 2001, 57, 9199.
D.S. Ermolatev, V.N. Gimenez, E.V. Babaev and E.J. Van der Eycken, Eur.
J. Comb. Chem., 2006, 8, 659.
5
6
7
8
7j: White crystal, yield 88%, m.p. 163–165 °C, [α]2D0 = +150.0
(c 0.1, CH2Cl2); IR (KBr)(cm−1): 3435, 3290, 2929, 2863, 1731, 1631,
1548, 1233, 1167; 1H NMR (400 MHz, CDCl3) δ: 9.48 (s, 1H, ArNH),
8.77 (s, 1H, NH), 7.96 (d, 1H, J = 8.0 Hz, ArH), 7.91 (t, 2H, J = 7.2
Hz, ArH), 7.83 (d, 1H, J = 8.4 Hz, ArH), 7.55–7.51 (m, 3H, ArH),
3.67 (s, 3H, COOCH3), 1.02 (s, 3H, 19-CH3), 0.92 (d, 3H, J = 6.4 Hz,
21-CH3), 0.63 (s, 3H, 18-CH3); ESI-MS m/z (%): 588 ([M+1]+,100).
Ana1.Calcd for C36H49N3O2S: C, 73.55; H, 8.40; N, 7.15. Found:
C, 73.50; H, 8.42; N, 7.10%.
9
R.S. Varma, Green Chem., 1999, 1, 43.
10 V. Polshettiwar and R.S. Varma, Acc. Chem. Res., 2008, 41, 629.
11 S.A. Khan, P. Kumar, R. Joshi, P.F. Iqbal and K. Saleem, Eur. J. Med
Chem., 2008, 43, 2029.
12 M.H. Schoemaker, L.C. de la Rose, M. Buist-Homan, T.E. Vreken,
R. Havinga and K. Poelstra, Hepatology., 2004, 39, 1536.
13 P.B. Savage and C. Li, Expert Opin. Invest. Drugs., 2000, 9, 263.
14 T. Gilat, G.J. Somjem, Y. Mazur, A. Leikin-Frenkel, R. Rosenberg and
Z. Halpern, Gut., 2001, 48, 75.
15 L.L. Liu, J.Yang, Z.G. Zhao, P.Y. Shi and X.L. Liu, J. Chem. Res., 2010, 1,
57.
16 C.Y. Liu, G.W. Ying, J. Qian, Z. Li and A.H. Yu, Chem. Reag.(in Chinese),
2003, 25,160.
17 S.K. Chawla, Polyhedron., 2006, 25, 627.
18 M. Tisler, Croat. Chem. Acta., 1965, 28, 147.
19 K. Joseph, DE 832891 1952.
We thank the Natural Science Foundation of the State Ethnic
Affairs Commission of P.R.China (Project No.09XN08) for
the financial support.
20 R. Stanislav, Collect. Czech. Chem. Commun., 1986, 5, 1692.
21 U.K. Mazumber, M. Gupta, S.S. Karki, S. Bhattacharya, S. Rathinasamy,
S. Thangavel, Chem. Pharm. Bull., 2004, 52, 178.
22 D.L. Klayman, J.F. Bartosevich, T.S. Griffin, C.J. Mason and J.P. Scovill,
J. Med. Chem.,1979, 22, 855.
Received 13 June2010; accepted 9 July 2010
Paper 1000193 doi: 10.3184/030823410X12798092457988
Published online: 30 August 2010
23 R.W. Bost and W.F. Smith, J. Am. Chem. Soc.,1931, 53, 652.
24 A.J. Cowper, J. Indian. Chem. Soc., 1981, 58, 1087.
25 C.E. Zhou, Z.G. Zhao and X.L. Tang, Chin. J. Org. Chem.(in Chinese),
2007, 4, 513.
26 J.G. Cui, L.L. Huang, Y.M. Huang and J.C. Fan, Chin. J. Org. Chem.
(in Chinese), 2009, 6, 971.
References
1
M. Raposo, B. García-Acosta, T. Abalos, D. Calero, R. Martínez-Mánez,
J.V. Ros-Lis and J. Soto, J. Org. Chem., 2010, 75, 2922.
T.S. Lobana, S. Khanna, G. Hundal, R.J. Butcher and A. Catineiras,
Polyhedron., 2009, 28, 3899.
2