Synthesis under microwave irradiation of [1,2,4]triazolo[3,4-b] [1,3,4]thiadiazoles and other diazoles bearing indole moieties and their antimicrobial evaluation

Article abstract of DOI:10.3390/molecules16108244

Microwave-assisted synthesis of some novel compounds, namely, 3-(2-methyl-1H-indol-3-yl)-6-aryl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazoles 5a,b was accomplished via bromination of 2-methyl-3-[4-(arylideneamino)-5-mercapto- 4H-[1,2,4]triazol-3-yl]-1H-indole

Full text of DOI:10.3390/molecules16108244

Molecules 2011, 16, 8244-8256; doi:10.3390/molecules16108244
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Synthesis under Microwave Irradiation of [1,2,4]Triazolo[3,4-b]
[1,3,4]thiadiazoles and Other Diazoles Bearing Indole Moieties
and Their Antimicrobial Evaluation
Sobhi M. Gomha * and Sayed M. Riyadh
Department of Chemistry, Faculty of Science, University of Cairo, Giza 12613, Egypt;
E-Mail: riyadh1993@hotmail.com (S.M.R.)
* Author to whom correspondence should be addressed; E-Mail: s.m.gomha@hotmail.com;
Tel.: +20-237-400-304; Fax: +20-225-685-799.
Received: 23 August 2011; in revised form: 21 September 2011 / Accepted: 22 September 2011 /
Published: 28 September 2011
Abstract: Microwave-assisted synthesis of some novel compounds, namely, 3-(2-methyl-
1H-indol-3-yl)-6-aryl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazoles 5a,b was accomplished via
bromination of 2-methyl-3-[4-(arylideneamino)-5-mercapto-4H-[1,2,4]triazol-3-yl]-1H-
indoles 3a,b. Also, new [1,3,4]thiadiazoles 12a,b, [1,2,4]triazoles 15a,b and [1,3,4]oxadiazoles
19a,b, with indole moieties, were prepared by cyclization of 1-[(2-methyl-1H-indole)-3-
carbonyl]thiosemicarbazides 8a,b under microwave irradiation using different reaction
conditions. Moreover, reaction of acid hydrazide 7 with ethyl 2-(N-phenylhydrazono)-3-
oxobutanoate (20) gave the respective phenylhydrazonopyrazole derivative 21 under the
reaction conditions employed. The structures of the synthesized compounds were assigned
1
based on elemental analyses and spectral data (IR, H-NMR, 13C-NMR, MS). The
antifungal and antibacterial activities of the new products were also evaluated.
Keywords: [1,2,4]triazolo[3,4-b][1,3,4]thiadiazoles; diazoles; Schiff’s bases; microwave
irradiation and antimicrobial activity
__________________________________________________________________________________
1. Introduction
Reports of the synthesis of [1,2,4]triazolo[3,4-b][1,3,4]thiadiazole derivatives have been recently
published [1-5]. A route for the construction of such ring systems involves reactions of 4-amino-5-

Molecules 2011, 16
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mercapto-4H-[1,2,4]triazoles with aromatic carboxylic acids in the presence of suitable dehydrating
agents [1-5]. Another route involves oxidative cyclization of hydrazones [6]. In view of these findings
and in continuation of our interest in the utility of 4-amino-5-mercapto-4H-[1,2,4]triazoles as
precursors for the synthesis of heterocycles [7,8], we wish to report herein a simple and convenient
route for the synthesis of [1,2,4]triazolo[3,4-b][1,3,4]thiadiazole derivatives. This route involves
bromination of hitherto unreported 4-(arylideneamino)-5-mercapto-4H-[1,2,4]triazoles with concurrent
elimination of hydrogen bromide. The interest in developing syntheses of [1,2,4]triazolo[3,4-b]
[1,3,4]thiadiazoles is due to the fact that these compounds are potent antioxidants and anticancer
agents [9] and have other pharmacological activities [10]. On the other hand, the chemistry of indole
derivatives has been the subject of much interest in recent years due to the use of this ring system as
the core structure in many heterocyclic compounds covering wide range of pharmacological
applications [11,12]. Merging of these two bioactive components, [1,2,4]triazolo[3,4-b][1,3,4]-
thiadiazole and indole, in one system affords a compact structure with promising potential
antimicrobial activities.
2. Results and Discussion
2-Methyl-3-[4-amino-5-mercapto-4H-[1,2,4]triazol-3-yl]-1H-indole (1) [7] was condensed under
microwave irradiation with different aldehydes such as substituted benzaldehydes 2a-c, 2-
thiophenaldehyde (2d), and benzo[d]-[1,3]dioxole-4-carbaldehyde (2e) in dimethylformamide, in the
presence of catalytic amount of HCl, to give the corresponding 4-arylideneamino-[1,2,4]triazole
Schiff’s base derivatives 3a-e, respectively (Scheme 1). On the other hand, reaction of 1 with benzoin
in ethanol in the presence of KOH gave the corresponding benzylidene derivative 3a instead of the
expected [1,2,4]triazolo[3,4-b][1,3,4]thiadiazine derivative 6 (Scheme 1).
Scheme 1. Synthesis of [1,3,4]triazolo[3,4-b][1,3,4]thiadiazoles.

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The structures of the isolated products 3a-e were substantiated based on elemental analyses and
1
spectral data. The H-NMR spectra revealed, in each case, a singlet signal at δ 13.76-13.81 ppm
(exchangeable with D2O) assignable to a thiol proton [13-15] and another singlet signal at δ 9.91-10.0
ppm which was attributed to the azomethine proton [13-15]. Room temperature (25 °C) bromination of
4-arylideneamino[1,2,4]triazole derivatives 3a,b in acetic acid in the presence of anhydrous sodium
acetate afforded the respective [1,2,4]triazolo[3,4-b][1,3,4]thiadiazoles 5a,b via dehydrobromination
from the non-isolable intermediates 4a,b (cf. Scheme 1).
The synthetic utility of 1-[(2-methyl-1H-indole)-3-carbonyl]thiosemicarbazides 8a,b prepared
from acid hydrazide 7 [13,16] and potassium thiocyanate or phenyl isothiocyanate was investigated.
Thus, treatment of 8a,b with concentrated sulfuric acid at room temperature (25 °C) gave the
respective[1,3,4]thiadiazole derivatives 12a,b. The reaction proceeded via intramolecular nucleophilic
attack of thiol group into carbonyl group [17] to give intermediates 11a,b. Dehydration of these
intermediates 11a,b under the employed reaction conditions gave the isolated products 12a,b (Scheme 2).
Protonation of N-4 (NHR) in the thiosemicarbazide moiety under acidic condition (intermediates 9a,b)
reduces its nucleophilicity and increases the nucleophilicity of the thiol group [17].
Scheme 2. Reactions of thiosemicarbazides 8a,b under different pH conditions.
Changes of the pH of the reaction mixture led to the formation of different ring systems. Thus,
reactions of 8a,b with potassium hydroxide, as basic catalyst, led to the formation of [1,2,4]triazoles

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15a,b. The reaction started by abstraction of a hydrogen atom from the NH-R group to increase its
nucleophilicity [17] (intermediates 13a,b) followed by its attack on the carbonyl group with concurrent
dehydration of the non-isolable intermediates 14a,b (cf. Scheme 2) to give isolable products 15a,b.
The structures of the isolated products 12a,b, and 15a,b were established on the basis of elemental
analyses and spectral data (see Experimental). On the other hand, irradiation of 8a,b with mercuric
oxide furnished the corresponding [1,3,4]oxadiazoles 19a,b, via elimination of mercuric sulfide [17]
from the non-isolable intermediates 16a,b. Nucleophilic attack of hydroxyl group on the carbonyl
carbon gave intermediates 18a,b followed by loss of a water molecule to afford the isolated products
19a,b (Scheme 3).
Scheme 3. Reactions of thiosemicarbazides 8a,b with HgO.
Next, we studied the reactivity of hydrazone derivatives which are widely used as intermediates for
the synthesis of a large number of heterocyclic compounds [18]. Thus, treatment of (2-methyl-1H-
indol-3-yl)-3-acid hydrazide (7) with ethyl 2-(N-phenylhydrazono)-3-oxobutanoate (20) [19] in DMF
under microwave irradiation in the presence of a catalytic amount of HCl afforded the corresponding
3-[(3-methyl-4-phenylhydrazono-5-oxopyrazolin-1-yl)carbonyl]-2-methyl-1H-indole
(21)
via
elimination of ethanol and water molecules (Scheme 4).
Scheme 4. Synthesis of phenylhydrazonopyrazolinone derivative 21.

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The structure of the latter product was confirmed by the appearance of the hydrazone NH band at
3358 cm−1 in its IR spectrum [20]. The 1H- NMR spectrum also revealed two singlet signals at δ 11.20
and 13.11 ppm (D2O exchangeable) assignable to the NH of the pyrrole ring and hydrazone group
[20], respectively. An alternative synthesis of 21 was carried out as outlined in Scheme 4. Thus,
reaction of acid hydrazide 7 with ethyl 3-oxobutanoate under microwave irradiation for 6 min. gave
pyrazolinone derivative 22. Coupling of 22 with diazotized aniline in pyridine afforded the
corresponding hydrazone derivative 21, typical in all respects (mp., mixed mp., and IR) to that
obtained from acid hydrazide 7 and 20 (cf. Scheme 4).
3. Antimicrobial Activity
The in vitro antimicrobial activities of the synthesized products 3a-e, 5a,b, 8b, 12a,b, 15a,b, 19a,b,
and 21 were screened against the Gram-positive bacteria Staphylococcus aureus (S. aureus), Bacillus
subtilis (B. subtilis), Gram-negative bacteria Escherichia coli (E. coli) and the fungus Candida
albicans (C. albicans) under the same conditions using trimethoprim as reference. The bacteria and
fungus were subjected to susceptibility testing on Muller-Hinton agar medium by the disc agar
diffusion method [21,22]. The results are summarized in Table 1.
Table 1. Antimicrobial activity of the tested compounds.
Inhibition zone diameter (mm/mg sample)
Sample number Gram-positive Bacteria Gram-negative Bacteria
Fungus
S. aureus
B. subtilis
E. coli
16
-
16
-
C. albicans
3a
3b
3c
3d
15
12
14
-
14
11
13
16
17
-
15
-
3e
5a
5b
8b
12a
12b
15a
15b
12
17
16
12
13
-
16
15
15
15
12
-
-
14
18
18
17
-
15
14
18
-
-
10
-
-
12
13
-
12
-
-
19a
19b
21
-
12
-
15
19
11
9
17
21
10
11
16
21
15
13
19
Trimethoprim
(-) No inhibition zone.
The following conclusions may be drawn from the results:
a) Compounds 3a, 5a, 5b, and 19b exhibited high inhibitory effect against S. aureus, while
compounds 3b, 3c, 3e, 8b, 12a, 15a, and 21 have moderate inhibitory effect against same

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bacterium. On the other hand, compounds 3d, 12b, 15b, and 19a have no inhibitory effect
against S. aureus.
b) Compounds 3a, 3d, 3e, 5a, 5b, 8b, and 21 revealed high inhibitory activity against B.
subtilis, while compounds 3b, 3c, 12a, 15b, and 19a have moderate inhibitory activity
against this species and compounds 12b, 15a, and 19b have no activity against B. subtilis.
c) Compounds 3a, 3c, 3e, 5a, 5b, and 21 were effective against E. coli and C. albicans. Other
compounds, 12b, 15a, 19a, and 19b have moderate inhibitory activity against E. coli and C.
albicans. Compounds 3b, 3d, 8b, 12a, and 15b are inactive against E. coli and C. albicans.
5. Experimental
Melting points were measured on an Electrothermal IA 9000 series digital melting point apparatus.
The IR spectra were recorded in potassium bromide discs on a Pye Unicam SP 3300 and Shimadzu FT
IR 8101 PC infrared spectrophotometers. The NMR spectra were recorded on a Varian Mercury
VX-300 NMR spectrometer operating at 300 MHz (1H-NMR) or 75 MHz (13C-NMR) and run in
deuterated dimethylsulphoxide (DMSO-d6). Chemical shifts were related to that of the solvent. Mass
spectra were recorded on a Shimadzu GCMS-QP1000 EX mass spectrometer at 70 eV. Elemental
analyses (using a German made Elementar vario LIII CHNS analyzer) and the biological evaluation of
the products were carried out at the Microanalytical Centre of Cairo University, Giza, Egypt. All
reactions were followed by TLC (silica gel, aluminum Sheets 60 F254, Merck). Irradiation was done in
a domestic microwave oven (R-658WM, 2500 MHz, 400 W). The reactions were carried out in a
closed Teflon vessel which was placed at the center of the oven for irradiation. 2-Methyl-3-[4-amino-
5-mercapto-4H-[1,2,4]triazol-3-yl]-1H-indole (1) [7], 2-methyl-1H-indole-3-carbohydrazide (7) [16],
1-[(2-methyl-1H-indole)-3-carbonyl]thiosemicarbazide (8a) [16] and ethyl 2-(N-phenylhydrazono)-3-
oxobutanoate (20) [19] were prepared as previously reported in the respective literature.
5.1. Reaction of 2-methyl-3-[4-amino-5-mercapto-4H-[1,2,4]triazol-3-yl]-1H-indole (1) with
aldehydes
A mixture of 1 (0.245 g, 1 mmol), and the appropriate aldehyde (1 mmol) in DMF (5 mL)
containing a few drops of concentrated HCl was irradiated by MW at 400 Watt in a closed Teflon
vessel until all the starting material was consumed (2–3 min., as monitored by TLC). Excess of solvent
was removed under reduced pressure and the reaction mixture was added to crushed ice. The product
separated was filtered, washed with water, dried and recrystallized from the proper solvent to give
compounds 3a-e.
2-Methyl-3-[4-(phenylmethyleneamino)-5-mercapto-4H-[1,2,4]triazol-3-yl]-1H-indole (3a): Yield
84%; pale yellow microcrystals (from ethanol); mp = 352 °C. IR: v 1627 (CH=N), 3398 (NH) cm−1.
1H-NMR: δ 2.51 (s, 3H, CH3), 6.98-7.92 (m, 9H, ArH), 9.98 (s, 1H, CH=N), 11.16 (s, 1H, D2O
13
exchangeable, NH), 13.81 (s,1H, D2O exchangeable, SH); C-NMR: δ 14.75 (CH3), 111.15, 117.75,
120.29, 120.85, 121.86, 123.75, 124.33, 125.75, 127.16, 127.31, 129.73, 132.61, 148.13, 156.47,
160.11 (Ar-C); MS m/z (%): 334 (M+ +1, 10), 333 (M+, 10), 229 (100), 155 (32), 103 (35), 77 (23).

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Anal. Calcd for C18H15N5S (333.10): C, 64.84; H, 4.53; N, 21.01; S, 9.62. Found C, 64.54; H, 4.35; N,
20.84; S, 9.48%.
2-Methyl-3-[4-(4-methylphenylmethyleneamino)-5-mercapto-4H-[1,2,4]triazol-3-yl]-1H-indole (3b):
Yield 85%; pale yellow microcrystals (from ethanol); mp = 338 °C. IR: v 1627 (CH=N), 3398 (NH)
cm−1. 1H-NMR: δ 2.37 (s, 3H, CH3), 2.51 (s, 3H, CH3), 6.85–7.83 (m, 8H, ArH). 9.96 (s, 1H, CH=N),
11.19 (s, 1H, D2O exchangeable, NH), 13.78 (s,1H, D2O exchangeable, SH). MS m/z (%): 348 (M+ +1,
12), 347 (M+, 36), 229 (100), 197 (32), 155 (31), 117 (79), 102 (8), 77 (16). Anal. Calcd for C19H17N5S
(347.12): C, 65.68; H, 4.93; N, 20.16; S, 9.23%. Found C, 65.56; H, 4.85; N, 19.69; S, 9.11%.
2-Methyl-3-[4-(4-chlorophenylmethyleneamino)-5-mercapto-4H-[1,2,4]triazol-3-yl]-1H-indole (3c):
Yield 82%; pale yellow microcrystals (from ethanol/dioxane); mp = 358 °C. IR: v 1628 (CH=N), 3401
(NH) cm−1. 1H-NMR: δ 2.51 (s, 3H, CH3), 6.87-7.93 (m, 8H, ArH), 9.99 (s, 1H, CH=N), 11.51 (s, 1H,
D2O exchangeable, NH), 13.76 (s, 1H, D2O exchangeable, SH). MS m/z (%): 368 (M+ +1, 11), 367
(M+, 36), 229 (100), 155 (38), 117 (59), 77 (41). Anal. Calcd for C18H14ClN5S (367.07): C, 58.77; H,
3.84; N, 19.04; S, 8.72%. Found C, 58.65; H, 3.82; N, 18.78; S, 8.88%.
2-Methyl-3-[4-(thiophen-2-ylmethyleneamino)-5-mercapto-4H-[1,2,4]triazol-3-yl]-1H-indole
(3d):
Yield 84%; pale yellow microcrystals (from ethanol); mp = 325 °C. IR: v 1624 (CH=N), 3409 (NH)
cm−1. 1H-NMR: δ 2.51 (s, 3H, CH3), 6.47-7.60 (m, 7H, ArH), 10.00 (s, 1H, CH=N), 10.72 (s, 1H, D2O
13
exchangeable, NH), 13.80 (s, 1H, D2O exchangeable, SH); C-NMR: δ 14.38 (CH3), 112.05, 118.45,
120.29, 121.05, 122.36, 123.75, 124.73, 125.75, 128.16, 129.31, 132.73, 137.61, 150.13, 156.77,
160.16 (Ar-C); MS m/z (%): 339 (M+, 38), 229 (100), 197 (12), 156 (12), 128 (10), 109 (8), 77 (7).
Anal. Calcd for C16H13N5S2 (339.06): C, 56.61; H, 3.86; N, 20.63; S, 18.89%. Found C, 56.51; H,
3.80; N, 20.44; S, 18.76%.
2-Methyl-3-[4-(benzo[d][1,3]dioxol-4-ylmethyleneamino)-5-mercapto-4H-[1,2,4]triazol-3-yl]-1H-
indole (3e): Yield 84%; yellow microcrystals (from DMF); mp = 330 °C. IR: v 1628 (CH=N), 3402
1
(NH) cm−1; H-NMR: δ 2.50 (s, 3H, CH3), 5.96 (s, 2H, CH2), 6.14-7.76 (m, 7H, ArH), 9.61 (s, 1H,
CH=N), 11.17 (s, 1H, D2O exchangeable, NH), 13.76 (s,1H, D2O exchangeable, SH). MS m/z (%): 378
(M+ +1, 10), 377 (M+, 43), 229 (100), 197 (9), 155 (12), 146 (82), 77 (10). Anal. Calcd for
C19H15N5O2S (377.09): C, 60.46; H, 4.01; N, 18.56; S, 8.50%. Found C, 60.51; H, 3.86; N, 18.40; S,
8.62%.
5.2. Reaction of 2-methyl-3-(4-amino-5-mercapto-4H-[1,2,4]triazol-3-yl)-1H-indole (1) with 2-
hydroxy-1,2-diphenylethanone (benzoin)
To a solution of 1 (0.245g, 1 mmol) in DMF (5 mL) containing a solution of potassium hydroxide
(0.084 g, 1.5 mmol) in water (1 mL), benzoin (0.212 g, 1 mmol) was added in a closed Teflon vessel.
The reaction mixture was irradiated by MW at 400 Watt for 3 min. then poured into crushed ice. The
reaction product was acidified with dilute hydrochloric acid. The solid product was collected by
filtration, washed with water and finally recrystallized from ethanol to give a product identical in

Molecules 2011, 16
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all respects (mp, mixed mp and IR spectra) with product 3a which was obtained from reaction of 1
with benzaldehyde.
5.3. Synthesis of 3-(2-methyl-1H-indol-3-yl)-6-aryl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazoles 5a,b
Bromine (0.44 g, 5.5 mmol) in acetic acid (5 mL) was added dropwise to a stirred mixture of the
appropriate Schiff’s bases 3a,b (5 mmol) and sodium acetate (1.2 g, 15 mmol) in acetic acid (30 mL).
The reaction mixture was stirred for 12 h at room temperature. The mixture was then poured onto
ice-cold water (250 mL). The solid that precipitated was filtered off, washed with 5% sodium
bicarbonate solution and then with water, dried and crystallized from ethanol to give the respective
[1,2,4]triazolo[3,4-b][1,3,4]thiadiazoles 5a,b.
3-(2-Methyl-1H-indol-3-yl)-6-phenyl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole (5a): Yield 74%; yellow
crystals; mp = 228 °C. IR: v 3407 (NH) cm−1. 1H-NMR: δ 2.54 (s, 3H, CH3), 6.87–7.89 (m, 9H, ArH),
11.21 (s, 1H, D2O exchangeable, NH); 13C-NMR: δ 14.33 (CH3), 112.15, 118.75, 120.26, 121.05,
122.36, 123.75, 124.33, 125.75, 127.16, 127.31, 129.73, 130.61, 153.13, 156.57, 159.84 (Ar-C); MS
m/z (%): 332 (M+ +1, 9), 331 (M+, 42), 243 (53), 158 (100), 102 (26), 77 (34). Anal. Calcd for
C18H13N5S (331.09): C, 65.24; H, 3.95; N, 21.13; S, 9.68%. Found C, 65.14; H, 3.91; N, 21.11; S,
9.54%.
3-(2-Methyl-1H-indol-3-yl)-6-(4-methylphenyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole (5b). Yield
78%; yellow crystals; mp = 212 °C. IR: v 3409 (NH) cm−1. 1H-NMR: δ 2.32 (s, 3H, Ar-CH3), 2.58 (s,
3H, CH3), 6.86–7.88 (m, 8H, Ar-H), 11.20 (s, 1H, D2O exchangeable, NH); 13C-NMR: δ 14.35 (CH3),
35.65 (Ar-CH3), 111.77, 117.75, 120.16, 120.95, 121.36, 122.75, 123.93, 124.85, 127.16, 128.71,
129.73, 130.61, 152.16, 155.53, 159.14 (Ar-C); MS m/z (%): 346 (M+ +1, 7), 345 (M+, 33), 243 (43),
158 (100), 77 (29). Anal. Calcd for C19H15N5S (345.10): C, 66.07; H, 4.38; N, 20.27; S, 9.28%. Found
C, 65.97; H, 4.18; N, 20.20; S, 9.33%.
5.4. Synthesis of 1-[(2-methyl-1H-indole)-3-carbonyl]phenylthiosemicarbazide (8b)
A mixture of acid hydrazide 7 (1.89, 10 mmol) and phenyl isothiocyanate (1.35 g, 10 mmol) in
DMF (5 mL) was irradiated by MW at 400 Watt for 5 min. in a closed Teflon vessel (monitored by
TLC). After cooling, chloroform (10 mL) was added and the reaction mixture was stirred for 5 min.,
then filtered and the crude product was crystallized from ethanol to yield phenylthiosemicarbazide
derivative 8b. Yield 87%; pale yellow microcrystals; mp = 165 °C. IR: v 3407, 3292, 3157, 3124
1
(4NH), 1646 (CO) cm−1. H-NMR: δ 2.51(s, 3H, CH3), 6.24-7.76 (m, 9H, ArH ), 9.34 (s, 1H, D2O
exchangeable, NH), 9.83 (s, 1H, D2O exchangeable, NH), 10.90 (s, 1H, D2O exchangeable, NH), 11.12
(s, 1H, D2O exchangeable, NH). MS m/z (%): 324 (M+, 18), 229 (100), 197 (23), 155 (42), 77 (32).
Anal. Calcd for C17H16N4OS (324.10): C, 62.94; H, 4.97; N, 17.27; S, 9.88%. Found C, 62.77; H, 4.94;
N, 17.18; S, 9.72%.

Molecules 2011, 16
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5.5. Reaction of 1-[(2-methyl-1H-indole)-3-carbonyl]thiosemicarbazide derivatives 8a,b with conc.
H2SO4
A solution of 8a or 8b (1 mmol) in conc. sulfuric acid (5 mL) was stirred at room temperature for 4
h. The reaction mixture was poured into cold water. The solid was collected by filtration, washed with
water, dried and crystallized from DMF to give product 12a or 12b.
3-(5-Amino-[1,3,4]thiadiazol-2-yl)-2-methyl-1H-indole (12a): Yield 82%; white microcrystals; mp =
1
162 °C. IR: v 3401 (NH), 3281, 3177 (NH2) cm−1. H-NMR: δ 2.53 (s, 3H, CH3), 4.34 (s, 2H, D2O
exchangeable, NH2), 7.06–7.63 (m, 4H, ArH), 11.12 (s, 1H, D2O exchangeable, NH); 13C-NMR: δ
15.13 (CH3), 112.55, 119.75, 120.26, 122.36, 123.75, 124.33, 125.75, 129.73, 150.13, 152.57 (Ar-C);
MS m/z (%): 231 (M+ +1, 2), 230 (M+, 23), 189 (31), 158 (100), 130 (36), 103 (23), 77 (32). Anal.
Calcd for C11H10N4S (230.06): C, 57.37; H, 4.38; N, 24.33; S, 13.92%. Found C, 57.23; H, 4.34; N,
24.18; S, 13.86%.
3-(5-Phenylamino-[1,3,4]thiadiazol-2-yl)-2-methyl-1H-indole (12b): Yield 82%; white microcrystals;
1
mp = 140 °C. IR: v 3401, 3177 (2NH) cm−1. H-NMR: δ 2.51 (s, 3H, CH3), 6.34–7.74 (m, 9H, ArH),
10.36 (s, 1H, D2O exchangeable, NH), 11.12 (s, 1H, D2O exchangeable, NH). MS m/z (%): 307
(M+ +1, 43), 306 (M+, 100), 229 (14), 197 (32), 155 (43), 77 (54). Anal. Calcd for C17H14N4S (306.09):
C, 66.64; H, 4.61; N, 18.29; S, 10.47%. Found C, 66.54; H, 4.55; N, 18.10; S, 10.39%.
5.6. Reaction of 1-[(2-methyl-1H-indole)-3-carbonyl]thiosemicarbazide derivatives 8a,b with
potassium hydroxide
A suspension of 8a or 8b (1 mmol) in potassium hydroxide solution (5 mL, 7%) in a closed Teflon
vessel was irradiated by MW at 400 watt for 5 min. The reaction mixture was cooled then acidified
with 10% hydrochloric acid to pH 6. The solid that formed was filtered off, washed with water, dried
and finally crystallized from DMF to give product 15a or 15b.
3-(5-Mercapto-4H-[1,2,4]triazol-3-yl)-2-methyl-1H-indole (15a): Yield 76%; white crystals (from
1
DMF); mp = 236 °C. IR: v 3401, 3294, 3155 (3NH) cm−1. H-NMR: δ 2.52 (s, 3H, CH3), 6.11–7.75
(m, 4H, ArH), 9.39 (s, 1H, D2O exchangeable, NH), 9.88 (s, 1H, D2O exchangeable, NH), 11.09 (s,
1H, D2O exchangeable, NH); 13C-NMR: δ 14.83 (CH3), 111.95, 117.75, 120.36, 121.15, 122.16,
123.25, 124.23, 125.25, 155.13, 162.84 (Ar-C); MS m/z (%): 231 (M+ +1, 6), 230 (M+, 100), 158 (98),
130 (19), 155 (32), 77 (12). Anal. Calcd for C11H10N4S (230.06): C, 57.37; H, 4.38; N, 24.33; S,
13.92%. Found C, 57.26; H, 4.32; N, 24.21; S, 13.73%.
3-(5-Mercapto-4-phenyl-4H-[1,2,4]triazol-3-yl)-2-methyl-1H-indole (15b): Yield 82%; white crystals;
1
mp = 220 °C. IR: v 3401, 3177 (2NH) cm−1. H-NMR: δ 2.52 (s, 3H, CH3), 6.54–7.72 (m, 9H, ArH),
11.10 (s, 1H, D2O exchangeable, NH), 13.21 (s, H, D2O exchangeable, NH). MS m/z (%): 307 (M+ +1,
43), 306 (M+, 100), 229 (14), 197 (32), 155 (43), 77 (54). Anal. Calcd for C17H14N4S (306.09): C,
66.64; H, 4.61; N, 18.29; S, 10.47%. Found C, 66.52; H, 4.53; N, 18.12; S, 10.53%.

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5.7. Reaction of 1-[(2-methyl-1H-indole)-3-carbonyl]thiosemicarbazide derivatives 8a,b with mercuric
oxide
A solution of 8a or 8b (1 mmol) in dimethylformamide (10 mL), containing mercuric oxide (0.216 g,
1 mmol), was irradiated by MW at 400 Watt for 6 min. in a closed Teflon vessel. The reaction mixture
was left overnight at room temperature and poured into cold water. The precipitate formed was filtered
off, washed with water, dried and finally crystallized from ethanol/DMF to give product 19a or 19b.
3-(5-Amino-[1,3,4]oxadiazol-2-yl)-2-methyl-1H-indole (19a): Yield 84%; white crystals; mp = 188 °C.
1
IR: v 3401 (NH), 3284, 3179 (NH2) cm−1. H-NMR: δ 2.52 (s, 3H, CH3), 4.39 (s, 2H, D2O
exchangeable, NH2), 6.11–7.75 (m, 4H, ArH), 11.12 (s, 1H, D2O exchangeable, NH). MS m/z (%): 215
(M+ +1, 44), 214 (M+, 100), 229 (19), 197 (32), 155 (42), 77 (68). Anal. Calcd for C11H10N4O(214.09): C,
61.67; H, 4.71; N, 26.15%. Found C, 61.61; H, 4.42; N, 26.00%.
3-(5-Phenylamino-[1,3,4]oxadiazol-2-yl)-2-methyl-1H-indole (19b): Yield 87%; white crystals; mp =
248 °C. IR: v 3404, 3179 (2NH) cm−1. 1H-NMR: δ 2.52 (s, 3H, CH3), 6.33–7.78 (m, 9H, ArH), 10.63
(s, 1H, D2O exchangeable, NH), 11.12 (s, 1H, D2O exchangeable, NH); 13C-NMR: δ 15.23 (CH3),
114.15, 119.75, 121.45, 122.39, 123.85, 124.73, 125.78, 127.96, 128.31, 129.73, 130.61, 132.74,
153.13, 156.57 (Ar-C); MS m/z (%): 290 (M+, 3.4), 242 (100), 158 (28), 143 (27), 72 (74). Anal. Calcd
for C17H14N4O (290.12): C, 70.33; H, 4.86; N, 19.30%. Found C, 70.13; H, 4.80; N, 19.11%.
5.8. Synthesis of 3-[(3-methyl-4-phenylhydrazono-5-oxopyrazolin-1-yl)carbonyl]-2-methyl-1H-indole
(21)
Method A: To a solution of hydrazide 7 (1.89g, 10 mmol) in DMF (5 mL), ethyl 2-(N-
phenylhydrazono)-3-oxobutanoate (20) (10 mmol), a few drops of glacial acetic acid were added. The
reaction mixture was irradiated by MW at 400 Watt for 3 min, and then the reaction mixture was
evaporated to half its volume and kept at room temperature overnight. The solid product was collected
by filtration, then diluted with water, dried, and recrystallized from ethanol to give 21. Yield 84%;
yellow microcrystals (from ethanol); mp = 328 °C. IR: v 1706, 1664 (2C=O), 3407, 3346 (2NH) cm−1.
1H-NMR: δ 2.31 (s, 3H, CH3), 2.52 (s, 3H, CH3), 6.57-7.89 (m, 9H, ArH), 11.20 (s, 1H, D2O
exchangeable, NH), 13.11 (s, 1H, D2O exchangeable, Hydrazone-NH); 13C-NMR: δ 14.33 (CH3),
35.45 (CH3), 113.15, 119.75, 120.26, 121.05, 122.37, 123.79, 124.33, 125.78, 127.16, 128.01, 129.76,
130.61, 152.13, 154.27, 158.57, 159.84 (Ar-C); MS m/z (%): 360 (M+ +1, 7), 359 (M+, 33), 313 (18),
243 (43), 158 (100), 102 (16), 77 (29). Anal. Calcd for C20H17N5O2 (359.14): C, 66.84; H, 4.77; N,
19.49%. Found C, 66.74; H, 4.58; N, 19.26%.
Method B: Step 1: Synthesis of 3-[(3-methyl-5-oxopyrazolin-1-yl)carbonyl]-2-methyl-1H-indole
(22): A mixture of hydrazide 7 (1.89g, 10 mmol) and ethyl 3-oxobutanoate (10 mmol) in absolute
ethanol (20 mL) was irradiated by MW at 400 Watt for 6 min. in a closed Teflon vessel. The reaction
mixture was then cooled and the formed precipitate was filtered off, washed with ethanol, and finally
recrystallized from ethanol to afford 22. Yield 77%; yellow microcrystals; mp = 328 °C. IR: v 1708,
1
1664 (2C=O), 3409 (NH) cm−1. H-NMR: δ 2.31 (s, 3H, CH3), 2.52 (s, 3H, CH3), 3.24 (s, 2H, CH2),

Molecules 2011, 16
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6.87–7.93 (m, 4H, ArH), 11.21 (s, 1H, D2O exchangeable, NH). MS m/z (%): 255 (M+, 36), 189 (100),
155 (38), 117 (52), 77 (31). Anal. Calcd for C14H13N3O2 (255.10): C, 65.87; H, 5.13; N, 16.46%.
Found C, 65.80; H, 5.01; N, 16.31%.
Step 2: Coupling of 3-[(3-methyl-5-oxopyrazolin-1-yl)carbonyl]-2-methyl-1H-indole (22): To a
cold solution of compound 22 (2.55 g, 10 mmol) in pyridine (30 mL) was added phenyldiazonium salt
solution (10 mmol) [prepared by diazotizing aniline (10 mmol) dissolved in 6M hydrochloric acid
(6 mL) with a solution of sodium nitrite (0.7 g) in water (5 mL)]. The addition of diazonium salt was
carried out with rapid stirring over a period of 30 min. The reaction mixture was stirred for a further
30 min and left to stand in an ice bath for 12 h, The solid that separated was filtered off, washed with
water and finally recrystallized from ethanol to give product proved to be identical in all respects
(mp, mixed mp and IR spectra) with the phenylhydrazone 21 which obtained from method A.
5.9. Preliminary Antimicrobial Screening
Overnight culture was streaked on the surface of Muller-Hinton agar plate. Sterile filter paper disc
was saturated with 10 μL of 0.5 mg/mL w/v solution of the compound under investigation in DMF.
The plates and discs were then incubated at 37 °C (for bacteria) and at 28 °C (for fungi) for 24 h and
examined for inhibition zones to determine the activity of the tested compounds.
6. Conclusions
A number of heterocyclic azoles, incorporating indole moieties, were synthesized using microwave
irradiation and evaluated for their biological activities. The results of the antimicrobial activity of the
synthesized products were promising.
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