Microwave-assisted synthesis and biological activity of new Schiff bases derived from dimers of 4-amino-3-[3-(1-benzyl)indole]-5-thiomethyl-1,2,4- triazole

Article abstract of DOI:10.1007/s11164-012-0723-6

An expeditious method with microwave irradiation has been developed for synthesis of novel Schiff bases from dimers of 4-amino-3-[3-(1-benzyl)indole]-5- thiomethyl-1,2,4-triazole. Its distinct advantages are short reaction times and good conversion. The s

Full text of DOI:10.1007/s11164-012-0723-6

Res Chem Intermed (2013) 39:1897–1905
DOI 10.1007/s11164-012-0723-6
Microwave-assisted synthesis and biological activity
of new Schiff bases derived from dimers of 4-amino-3-
[3-(1-benzyl)indole]-5-thiomethyl-1,2,4-triazole
•
Yongle Peng Zhigang Zhao Xingli Liu Guohua Li
•
•
Received: 28 April 2012 / Accepted: 7 July 2012 / Published online: 31 July 2012
Ó Springer Science+Business Media B.V. 2012
Abstract An expeditious method with microwave irradiation has been developed
for synthesis of novel Schiff bases from dimers of 4-amino-3-[3-(1-benzyl)indole]-
5-thiomethyl-1,2,4-triazole. Its distinct advantages are short reaction times and good
conversion. The structures of these new Schiff bases were established by 1H NMR,
IR, and mass spectroscopy, and elemental analysis. The antibacterial activity of ten
novel Schiff bases against three bacterial strains was studied by the disk diffusion
method. Preliminary results indicated that some of the compounds had strong
antibacterial activity.
Keywords Microwave irradiation Á Synthesis Á Indole Á Schiff base Á
1,2,4-Triazole
Introduction
During the last few years derivatives of indole have attracted much attention
because of their special biological activity in medicine and agriculture. Andreani
et al. [1–6] reported that indole derivatives have substantial biological activity, for
example cytotoxic, antibacterial, antiviral, anticancer, and antiproliferative, and as
plant growth regulators. Furthermore, the triazole structure is occurs widely in
natural medicines and synthetic drugs. Currently available anti-microbial [7] or anti-
tumor [8] drugs, for example terconazole, itraconazole, fluconazole, fosfluconazole,
vibunazole, letrozole, anastrozole, and vorozole all contain the triazole ring.
Moreover, Schiff base compounds [9–13] and heterocyclic sulfide compounds [14]
were also reported to have cytotoxic, anticonvulsant, antiproliferative, anticancer,
Y. Peng Á Z. Zhao (&) Á X. Liu Á G. Li
College of Chemistry and Environmental Protection Engineering, Southwest University
for Nationalities, Chengdu 610041, China
e-mail: zzg63129@yahoo.com.cn
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Y. Peng et al.
antifungal, and antibacterial activity. In view of these research results and because
of the principle of active superposition, we synthesized a series of triazole Schiff
bases containing indole and heterocyclic sulfide structures. We can expected this
kind of new triazole Schiff base to have good biological activity. We also hoped
they could be used for other applications in the chemical industry.
Microwave synthesis, because of its unique advantages, has been widely applied
in organic synthesis in recent years [15–17]. We are interested in the pharmaceutical
synthesis using microwave methods [18–21]. As a continuation of this work, herein
we report the synthesis, under microwave irradiation, of novel triazole Schiff bases
containing indole and heterocyclic sulfide structures. The synthetic route is shown in
Scheme 1.
Results and discussion
Spectroscopic studies
The structures of 6 and 7a–j were confirmed on the basis of spectral data and
elemental analysis. The IR spectrum of 6 contained an absorption band at
3,326–3,123 cm-1, because of the NH2 group; this was absent from the IR spectra
of 7a–j. Strong bands at 1,588–1,526 cm-1 were assigned to absorption of C=N.
1
The H NMR spectrum of 6 contained a singlet peak at 6.16 ppm because of the
NH2 group; this was absent from the spectra of compounds 7a–j. The singlet peak at
9.10–8.45 ppm was assigned to ArCHN. The protons of ArH appeared at
8.69–6.91 ppm. The singlet peak at approximately 5.45 ppm was assigned to
ArCH2N. The singlet peak at approximately 3.53 ppm was assigned to SCH2CH2S.
In the 13C NMR spectra of compounds 6 and 7a–j, the peak at approximately
50 ppm was assigned to PhCH2N, the carbon atom of SCH2CH2S appeared at
approximately 33 ppm. Other peaks were assigned to carbon atoms of the aromatic
nucleus and the indole ring. Their ESI mass spectra contained the correct molecular
ions with high intensity.
Antibacterial studies
The newly synthesized compounds were screened for their antibacterial activity
against Escherichia coli (ATCC-25922), Staphylococcus aureus (ATCC-25923),
and Pseudomonas aeruginosa (ATCC-27853) bacterial strains by the disk-diffusion
method [22, 23]. A standard inoculum, prepared from beef extract, peptone, sodium
chloride, blood serum, and agar, was applied to the surface of sterile agar plates.
A sterile glass spreader was used for even distribution of the inoculum. Disks
6.25 mm in diameter were prepared from ordinary filter paper and sterilized by dry
heat at 140 °C for an hour. The sterile disks, previously soaked in a fixed
concentration (500 lg/mL) of the test compounds, were placed on the nutrient agar
medium. The plates were inverted and incubated at 37 °C for 24 h. Solvent and
growth control experiments were also conducted. Sparfloxacin was used as standard
drug. The results from testing of bacterial inhibition are list in Table 1.
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Microwave-assisted synthesis and biological activity of new Schiff bases
1899
CONHNH2
Br
COOMe
NH2NH2·H2O
MWI
NH
DMF, K2CO3
MWI
N
N
+
COOMe
1
2
3
N
SH
N
CONHNHCSSK
N
CS2, KOH
NH2NH2·H2O
MWI
NH2
N
N
5
4
N
N
N
NH2
BrCH2CH2Br, KOH,
MWI
S
N
N
S
H2N
N
N
R
N
6
N
N
R
N
N
N
S
RCHO, AcOH
MWI
N
N
S
N
N
N
7
HO
F
7a: R =
7b: R =
7c: R =
7f: R =
7i: R =
Br
7e: R =
7h: R =
OH
7d: R =
OCH3
NO2
Br
7g: R =
7j: R =
Br
O
Scheme 1 Synthetic route for new Schiff bases derived from dimers of 4-amino-3-[3-(1-benzyl)indole]-
5-thiomethyl-1,2,4-triazole
As is obvious from Table 1, among the compounds screened, compounds 7b, 7d,
and 7f are the most biologically effective. Compound 7f had good antibacterial
activity against all three bacteria, compound 7b had satisfactory activity against
E. coli and P. aeruginosa, and compound 7d strongly inhibited growth of S. aureus.
123

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Y. Peng et al.
Table 1 Bacterial inhibition results for ten novel triazole Schiff bases
Compound
Bacteria
Escherichia coli
(ATCC-25922)
Staphylococcus aureus
(ATCC-25923)
Pseudomonas aeruginosa
(ATCC-27853)
7a
7b
7c
7d
7e
7f
R=C6H5
-
-
-
R=3-FC6H4
??
-
?
??
-
R=2-HOC6H4
R=4-CH3OC6H4
R=4-HOC6H4
R=3-BrC6H4
R=2-O2NC6H4
R=4-BrC6H4
R=2-BrC6H4
R=2-furyl
-
?
??
-
-
-
?
??
-
??
-
??
?
7g
7h
7i
?
?
-
?
?
-
7j
-
-
-
Sparfloxacin
??
??
??
??, strong activity; ?, moderate activity; -, weak or poor activity
So, we have reason to believe these three compounds or their derivatives can be
developed as antibacterial drugs.
Comparison of microwave irradiation and conventional heating
As shown in Table 2, microwave irradiation had two large advantages over
conventional heating—reaction times were reduced from 1,440–1,800 min to
4–8 min, i.e. reaction was 225–360 times faster, and yields increased from 72–78 %
to 85–94 %. We can therefore conclude that the microwave-enhanced procedure
enables rapid and efficient synthesis of triazole Schiff base compounds containing
indole and heterocyclic sulfide structures.
Experimental
Melting points were measured on a micro-melting point apparatus and are
uncorrected. Infrared spectra were obtained with a 1700 Perkin–Elmer FTIR using
KBr disks. NMR spectra were recorded on a Varian Inova 400-MHz spectrometer
with TMS as internal standard, DMSO-d6 or pyridine-d5 as solvent, operating at
400 MHz for 1H and 100 MHz for 13C. Mass spectra were determined on Finnigan
LCQDECA instrument. Elemental analysis was performed with a Carlo Erba 1106
autoanalyzer. All microwave-assisted reactions were performed in a commercial
microwave reactor (XH-100A, 100–1,000 W; Beijing Xianghu Science and
Technology Development, Beijing, PR China). All solvents were purified before
use. Intermediates 2, 3, 4, and 5 were prepared in accordance with reported
procedures [24, 25].
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Microwave-assisted synthesis and biological activity of new Schiff bases
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Table 2 Comparison of microwave irradiation and conventional heating for synthesis of triazole Schiff
base compounds 7a–j
a
Compound
Traditional method
Microwave method
tc/tm
Time (min)
Yield (%)
Time (min)
Yield (%)
7a
7b
7c
7d
7e
7f
7g
7h
7i
R=C6H5
1,440
1,560
1,680
1,440
1,500
1,620
1,800
1,500
1,680
1,800
75
75
76
70
78
76
72
78
76
74
4
5
6
5
5
5
8
6
7
5
86
85
87
86
91
86
90
87
94
88
360
312
280
288
300
324
225
250
240
360
R=3-FC6H4
R=2-HOC6H4
R=4-CH3OC6H4
R=4-HOC6H4
R=3-BrC6H4
R=2-O2NC6H4
R=4-BrC6H4
R=2-BrC6H4
R=2-furyl
7j
a
tc, time required by conventional method; tm, time required by microwave method
Procedure for preparation of intermediate 6
Compound 5 (1.7 mmol), KOH (1.6 mmol), 1,2-dibromoethane (0.8 mmol), and
methanol (5 mL) were placed in a vessel which was then sealed and shaken to
homogenize the mixture. The mixture was irradiated at 350 W for 10 min. After
cooling to room temperature, filtration, and recrystallization, we obtained the pure
compound 6 as a white solid, yield 91 %, m.p. 247–249 °C; IR (KBr) (cm-1): 3326,
1
3123, 1622, 1581, 1448, 1386, 1338, 1187, 1021, 930, 740; H NMR (400 MHz,
DMSO-d6, ppm) d: 8.50 (s, 2H, ArH), 8.31(d, J = 7.6 Hz, 2H, ArH), 7.55(d,
J = 8.0 Hz, 2H, ArH), 7.33–7.15 (m, 14H, ArH and indole-CH); 6.16(s, 4H, NH2),
5.46 (s, 4H, PhCH2N), 3.34 (s, 4H, SCH2CH2S); 13C NMR (100 MHz, DMSO-d6,
ppm) d: 152.08, 151.10, 138.14, 136.06, 129.71, 129.06, 127.98, 127.53, 126.45,
122.90, 122.24, 121.03, 111.00, 102.08, 49.91, 31.91; ESI–MS m/z (%): 669
[(M ? 1)?, 100]. Anal. Calcd. for C36H32N10S2: C, 64.65; H, 4.82, N, 20.94. Found:
C, 64.70; H, 4.75; N, 20.87 %.
Conventional method for preparation of compounds 7a–j
Compound 6 (0.12 mmol), aldehyde (0.27 mmol), and glacial acetic acid (5 mL)
were placed in a round-bottomed flask and the reaction mixture was heated to reflux
for 24–30 h. When the reaction was complete (monitored by TLC) the flask was
cooled to room temperature and evaporated to remove the glacial acetic acid.
Ethanol (5 ml) was added into the residue. Solid formed immediately and was
collected by filtration and recrystallized from N,N-dimethylformamide to furnish the
pure compounds 7a–j.
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Y. Peng et al.
Microwave method for preparation of compounds 7a–j
Compound 6 (0.12 mmol), acetic acid (2 mL), and aldehyde (0.27 mmol) were
mixed thoroughly in a sealed vessel. The vessel was then placed in a microwave
oven and the mixture was irradiated at 300 W for 4–8 min. The reaction was
monitored by TLC until it was complete. The acetic acid was then removed by
reduced-pressure distillation. Ethanol (10 mL) was added to the residue. The solid
formed was isolated by filtration. After recrystallization, the pure product 7a–j was
obtained as a white, yellow, or green solid. The physical and spectra data of
compounds 7a–j are as follows.
7a: Yellow solid, yield 86 %, m.p. 230–232 °C; IR (KBr)(cm-1): 3055, 1578,
1439, 1387, 747, 693; 1H NMR (400 MHz, DMSO-d6, ppm) d: 8.88 (s, 2H,
ArCH=N), 8.27 (d, J = 7.6 Hz, 2H, ArH), 7.90–7.87 (m, 6H, ArH), 7.66–7.52 (m,
8H, ArH), 7.26–7.16 (m, 14H, ArH and indole-CH), 5.44 (s, 4H, PhCH2N), 3.53 (s,
4H, SCH2CH2S); 13C NMR (100 MHz, Pyridine-d5, ppm) d: 165.48, 144.49,
137.54, 137.02, 136.12, 135.09, 133.31, 132.54, 129.96, 129.70, 129.51, 129.24,
128.23, 127.78, 127.23, 123.06, 121.71, 110.80, 103.20, 50.26, 33.80; ESI–MS m/
z (%): 845 [(M ? 1)?, 100]. Anal. Calcd. for C50H40N10S2: C, 71.07; H, 4.77, N,
16.58. Found: C, 71.13; H, 4.70; N, 16.54 %.
7b: Pale yellow solid, yield 85 %, m.p. 232–234 °C; IR (KBr)(cm-1): 3063,
1
1615, 1583, 1449, 1379, 1270, 742; H NMR (400 MHz, DMSO-d6, ppm) d: 8.91
(s, 2H, ArCH=N), 8.25 (d, 2H, ArH), 7.90 (s, 2H, ArH), 7.74–7.50 (m, 10H, ArH),
7.26–7.15 (m, 14H, ArH and indole-CH), 5.44 (s, 4H, PhCH2N), 3.53 (s, 4H,
SCH2CH2S); 13C NMR (100 MHz, Pyridine-d5, ppm) d: 164.42, 163.97, 161.97,
144.44, 137.38, 136.88, 134.62, 131.50, 131.42, 129.89, 129.10, 128.13, 127.69,
127.14, 127.02, 125.88, 122.96, 121.60, 120.13, 119.91, 115.24, 115.01, 110.77,
102.85, 50.20, 33.81; ESI–MS m/z (%): 881 [(M ? 1)?, 100]. Anal. Calcd. for
C50H38F2N10S2: C, 68.16; H, 4.35; N, 15.90. Found: C, 68.21; H, 4.29; N, 15.87 %.
7c: Pale yellow solid, yield 87 %, m.p. 209–211 °C; IR (KBr)(cm-1): 3242,
1
3023, 1587, 1442, 1371, 1164, 737, 693; H NMR (400 MHz, DMSO-d6, ppm) d:
10.56 (s, 2H, ArOH), 9.00 (s, 2H, ArCH=N), 8.28 (d, J = 7.6 Hz, 2H, ArH), 7.96(s,
2H, ArH), 7.88(d, J = 7.6 Hz, 2H, ArH), 7.59 (d, J = 8.0 Hz, 2H, ArH), 7.46 (t,
J = 8.4 Hz, 2H, ArH), 7.24–7.16 (m, 14H, ArH and indole-CH), 7.00–6.92 (m, 4H,
ArH), 5.46 (s, 4H, PhCH2N), 3.56 (s, 4H, SCH2CH2S); 13C NMR (100 MHz,
Pyridine-d5, ppm) d: 162.13, 158.91, 143.22, 136.08, 135.47, 133.60, 128.48,
127.73, 127.70, 126.68, 126.22, 125.82, 125.82, 125.80, 121.98, 121.73, 120.14,
118.80, 117.86,116.06, 109.38, 101.83, 48.95, 32.36; ESI–MS m/z (%): 877
[(M ? 1)?, 100]. Anal. Calcd. for C50H40N10O2S2: C, 68.47; H, 4.60; N, 15.97.
Found: C, 68.53; H, 4.53; N, 15.95 %.
7d: White solid, yield 86 %, m.p. 210–212 °C; IR (KBr)(cm-1): 3038, 1588,
1427, 1249, 1161, 1023, 752; 1H NMR (400 MHz, DMSO-d6, ppm) d: 8.71 (s, 2H,
ArCH=N), 8.28 (d, J = 7.6 Hz, 2H, ArH), 7.85 (t, J = 8.8 Hz, 6H, ArH), 7.59 (d,
J = 8.0 Hz, 2H, ArH), 7.24–7.18 (m, 14H, ArH and indole-CH), 7.08 (d,
J = 8.4 Hz, 4H, ArH), 5.43 (s, 4H, PhCH2N), 3.85 (s, 6H, OCH3), 3.51 (s, 4H,
SCH2CH2S); 13C NMR (100 MHz, Pyridine-d5, ppm) d: 171.43, 164.38, 147.92,
136.09, 135.50, 130.07, 128.38, 127.73, 126.67, 126.19, 125.74, 123.57, 122.58,
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Microwave-assisted synthesis and biological activity of new Schiff bases
1903
121.85, 121.85, 121.55, 120.16, 113.77, 109.37, 101.85, 54.16, 48.87, 32.40;
ESI–MS m/z (%): 905 [(M ? 1)?, 100]. Anal. Calcd. for C52H44N10O2S2: C, 69.00;
H, 4.90; N, 15.48. Found: C, 69.09; H, 4.84; N, 15.45 %.
7e: White solid, yield 91 %, m.p. 269–271 °C; IR (KBr)(cm-1): 3233, 3023,
1587, 1442, 1371, 1265, 1164, 737; 1H NMR (400 MHz, DMSO-d6, ppm) d: 10.50
(s, 2H, PhOH), 8.70 (s, 2H, ArCH=N), 8.27 (d, J=7.6 Hz, 2H, ArH), 7.85–7.74 (m,
6H, ArH), 7.57 (d, J = 8.0 Hz, 2H, ArH), 7.26–7.16 (m, 14H, ArH and indole-CH),
6.91 (d, J = 8.4 Hz, 4H, ArH), 5.46 (s, 4H, PhCH2N), 3.32 (s, 4H, SCH2CH2S); 13
C
NMR (100 MHz, Pyridine-d5, ppm) d: 165.05, 162.55, 148.19, 143.18, 136.08,
135.47, 130.58, 128.35, 127.70, 126.64, 126.20, 125.77, 122.03, 121.86, 121.77,
120.12, 115.80, 109.34, 101.92, 48.88, 32.37; ESI–MS m/z (%): 877[(M ? 1)?,
100]. Anal. Calcd. for C50H40N10O2S2: C, 68.47; H, 4.60; N, 15.97. Found: C,
68.55; H, 4.58; N,15.94 %.
7f: Pale white solid, yield 86 %, m.p. 216–218 °C; IR (KBr)(cm-1): 3054, 2924,
1585, 1437, 1372, 1168, 740; 1H NMR (400 MHz, DMSO-d6, ppm) d: 8.89 (s, 2H,
ArCH=N), 8.24 (d, J = 8.0 Hz, 2H, ArH), 8.09 (s, 2H, ArH), 7.89–7.82 (m, 6H,
ArH), 7.60–7.46 (m, 4H, ArH), 7.29–7.15 (m, 14H, ArH), 5.43 (s, 4H, PhCH2N),
3.53 (s, 4H, SCH2CH2S); 13C NMR (100 MHz, Pyridine-d5, ppm) d: 161.88,
143.06, 136.06, 135.51, 133.20, 130.45, 129.89, 128.55, 127.77, 127.70, 126.76,
126.66, 126.30, 125.78, 125.67, 121.62, 120.24, 109.40, 101.51, 48.87, 32.45;
ESI–MS m/z (%): 1003 [(M ? 1)?, 100]. Anal. Calcd. for C50H38Br2N10S2: C,
59.88; H, 3.82; N,13.97. Found: C, 59.91; H,3.76; N, 13.95 %.
7g: Yellow solid, yield 90 %, m.p. 231–233 °C; IR (KBr)(cm-1): 3071, 2365,
1578, 1526, 1439, 1347, 738, 688; 1H NMR (400 MHz, DMSO-d6, ppm) d: 9.09 (s,
2H, ArCH=N), 8.69 (s, 2H, ArH), 8.43 (d, J = 8.4 Hz, 2H, ArH), 8.31–8.23 (m, 4H,
ArH), 7.93 (s, 2H, ArH), 7.80 (t, J = 8.0 Hz, 2H, ArH), 7.59 (d, J = 8.0 Hz, 2H,
ArH), 7.21–7.15 (m, 14H, ArH and indole-CH), 5.44 (s, 4H, PhCH2N), 3.56 (s, 4H,
SCH2CH2S); 13C NMR (100 MHz, Pyridine-d5, ppm) d: 161.34, 144.62, 138.10,
137.63, 135.07, 134.47, 133.70, 130.87, 130.23, 130.11, 129.28, 128.26, 128.06,
127.79, 127.29, 127.14, 126.89, 124.60, 123.02, 121.83, 116.85, 50.11, 32.33; ESI–
MS m/z (%): 935 [(M ? 1)?, 100]. Anal. Calcd. for C50H38N12O4S2: C, 64.23; H,
4.10; N, 17.98. Found: C, 64.29; H, 4.02; N, 17.96 %.
7h: Pale green solid, yield 87 %, m.p. 235–237 °C; IR (KBr)(cm-1): 3036, 1576,
1423, 1390, 1299, 1005, 750; 1H NMR (400 MHz, DMSO-d6, ppm) d: 8.87 (s, 2H,
ArCH=N), 8.25 (d, J = 8.0 Hz, 2H, ArH), 7.87 (s, 2H, ArH), 7.81–7.71 (m, 8H,
ArH), 7.58 (d, J = 8.4 Hz, 2H, ArH), 7.26–7.16 (m, 14H, ArH and indole-CH),
5.48 (s, 4H, PhCH2N), 3.52 (s, 4H, SCH2CH2S); 13C NMR (100 MHz, DMSO-d6,
ppm) d: 166.42, 148.52, 143.56, 137.10, 135.68, 132.27, 130.67, 128.46, 127.48,
127.26, 126.95, 125.53, 122.58, 121.41, 120.74, 115.80, 110.62, 100.95, 49.18,
29.46; ESI–MS m/z (%): 1003 [(M ? 1)?, 100]. Anal. Calcd. for C50H38Br2N10S2:
C, 59.88; H, 3.82; N 13.97. Found: C 59.92, H 3.73, N 13.94 %.
7i: Pale white solid, yield 94 %, m.p. 240–242 °C; IR (KBr)(cm-1): 3058, 2925,
1580, 1442, 1419, 1202, 1169, 1026, 745; 1H NMR (400 MHz, DMSO-d6, ppm) d:
9.10 (s, 2H, ArCH=N), 8.18(d, J = 8.4 Hz, 2H, ArH), 8.03–8.00 (m, 4H, ArH), 7.80
(t, J = 8.0 Hz, 2H, ArH), 7.61–7.47 (m, 6H, ArH), 7.28–7.15 (m, 14H, ArH and
indole-CH), 5.49 (s, 4H, PhCH2N), 3.60 (s, 4H, SCH2CH2S); 13C NMR (100 MHz,
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Pyridine-d5, ppm) d: 160.13, 143.28, 136.55, 136.17, 135.61, 133.56, 132.74,
132.58, 130.16, 128.80, 128.04, 127.09, 126.72, 126.03, 125.78, 125.63, 120.20,
109.44, 101.58, 48.84, 32.41; ESI–MS m/z (%): 1003 [(M ? 1)?, 100]. Anal. Calcd.
for C50H38Br2N10S2: C, 59.88; H, 3.82; N,13.97. found: C, 59.94; H, 3.78; N;
13.95 %.
7j: Yellow solid, yield 88 %, m.p. 214–216 °C; IR (KBr)(cm-1): 3031, 1583,
1442, 1386, 1291, 1156, 736, 702; 1H NMR (400 MHz, DMSO-d6, ppm) d: 8.76 (s,
2H, ArCH=N), 8.25 (d, J = 7.6 Hz, 2H, ArH), 8.11 (s, 2H, ArH,), 7.91 (s, 2H,
ArH), 7.57 (d, J = 8.0 Hz, 2H, 5-furyl-H), 7.34 (d, J = 3.6 Hz, 2H, 3-furyl-H),
7.29–7.16 (m, 14H, ArH), 6.80–6.79 (m, 2H, 4-furyl-H), 5.47 (s, 4H, PhCH2N), 3.52
(s, 4H, SCH2CH2S); 13C NMR (100 MHz, Pyridine-d5, ppm) d: 153.34, 148.40,
148.26, 144.64, 137.60, 136.95, 130.24, 129.52, 129.22, 128.15, 127.64, 127.29,
123.06, 121.69, 120.46, 113.45, 110.91, 103.06, 50.46, 33.95; ESI–MS m/z (%): 825
[(M ? 1)?, 100]. Anal. Calcd. for C46H36N10O2S2: C, 66.97; H, 4.40; N, 16.98.
Found: C, 67.90; H, 4.38; N,16.94 %.
Conclusions
We have developed a facile and efficient method for synthesis, under microwave
irradiation, of new Schiff bases derived from dimers of 4-amino-3-[3-(1-
benzyl)indole]-5-thiomethyl-1,2,4-triazole. The reactions proceeded much more
quickly and yields were higher than when conventional heating was used. Many of
the newly synthesized compounds had good antibacterial activity, especially those
containing methoxyphenyl and halogen substituents. We therefore believe there is
ample scope for further study and our work may have a beneficial outcome.
Acknowledgments This work was financially supported by the Science and Technology Bureau of
Sichuan Province (no. 2012JY0028) and the Postgraduate Degree Construction Project of Southwest
University for Nationalities of PR China (no. 2011XWD-S0703). We are thankful to the Southwest
University for Nationalities management for their support and facilities.
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