Synthesis, characterization and evaluation of antimicrobial activity of some novel 1,2,4-triazoles and 1,3,4-thiadiazoles bearing imidazole nuclues

Article abstract of DOI:10.3987/COM-12-12456

A series of N¹-[(4,5-di and 1,4,5-triphenylimidazol-2-yl) thioacetyl]- N⁴-alkyl/aryl-thiosemicarbazides 3-7 were synthesized from (4,5-di and 3,4,5- triphenylimidazol-2-yl)thioacetic acid hydrazide 1, 2. The treatment of compounds 3-7 with NaOH gave 5-[(4,5-di and 1,4,5-triphenylimidazol-2-yl)-3- thiomethyl]-4-alkyl/aryl-2H-1,2,4-triazoles-3- thione 8-12, while the acidic treatment of compounds 3-7 afforded 5-[(4,5-di- and 1,4,5-triphenylimidazol-2- yl)-3-thiomethyl]-2-alkyl/arylamino-1,3,4- thiadiazoles 13-17. Moreover, potassium hydrazinecarbothionates 18, 19 were obtained from the reaction of acyl hydrazides 1, 2 with carbon disulfides in basic media and converted into 4-amino- 1,2,4-triazole-3-thiones 20, 21 and 1,3,4-thiadiazole-2-thiols 22, 23 by the treatment with hydrazine hydrate and sulfuric acid, respectively. All newly synthesized compounds were screened for their antimicrobial activity.

Full text of DOI:10.3987/COM-12-12456

HETEROCYCLES, Vol. 85, No. 5, 2012
1141
HETEROCYCLES, Vol. 85, No. 5, 2012, pp. 1141 - 1154. © 2012 The Japan Institute of Heterocyclic Chemistry
Received, 26th February, 2012, Accepted, 30th March, 2012, Published online, 6th April, 2012
DOI: 10.3987/COM-12-12456
SYNTHESIS,
CHARACTERIZATION
AND
EVALUATION
OF
ANTIMICROBIAL ACTIVITY OF SOME NOVEL 1,2,4-TRIAZOLES
AND 1,3,4-THIADIAZOLES BEARING IMIDAZOLE NUCLUES
Mohamed Reda Aouad,a,b,* Nadjet Rezki,a,b Mohamed Kasmi,b Linda
Aouad,c and Merieme A. Rezkid
a Chemistry Department, Faculty of Science, Taibah University, P.O. Box 30002,
Madinah , Saudi Arabia
b
Chemistry Department, Faculty of Science, University of Science and
Technology, Mohamed Boudiaf-USTO-MB, Elm’nouar Oran, Algeria
c
Faculty of Medicine, Djillali Liabes University, P.O. Box 8, Sidi-Bel-Abbes,
Algeria
d
Faculty of Sciences, Biotechnology Departemnt, University dꞌOran Es-Senia
31000, Oran, Algeria
*Corresponding author: aouadmohamedreda@yahoo.fr
Abstract - A series of N1-[(4,5-di and 1,4,5-triphenylimidazol-2-yl)thioacetyl]-
N4-alkyl/aryl-thiosemicarbazides 3-7 were synthesized from (4,5-di and 3,4,5-
triphenylimidazol-2-yl)thioacetic acid hydrazide 1, 2. The treatment of
compounds 3-7 with NaOH gave 5-[(4,5-di and 1,4,5-triphenylimidazol-2-yl)-3-
thiomethyl]-4-alkyl/aryl-2H-1,2,4-triazoles-3-thione 8-12, while the acidic
treatment of compounds 3-7 afforded 5-[(4,5-di- and 1,4,5-triphenylimidazol-2-
yl)-3-thiomethyl]-2-alkyl/arylamino-1,3,4-thiadiazoles
13-17.
Moreover,
potassium hydrazinecarbothionates 18, 19 were obtained from the reaction of acyl
hydrazides 1, 2 with carbon disulfides in basic media and converted into 4-amino-
1,2,4-triazole-3-thiones 20, 21 and 1,3,4-thiadiazole-2-thiols 22, 23 by the
treatment with hydrazine hydrate and sulfuric acid, respectively. All newly
synthesized compounds were screened for their antimicrobial activity.
INTRODUCTION
1,2,4-Triazole and its derivatives belong to a class of exceptionally active compounds possessing a wide
spectrum of biological properties, including antibacterial,1 antimicrobial,2,3 antihypertensive,4 analgesic,5

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HETEROCYCLES, Vol. 85, No. 5, 2012
antiviral,6 antioxidant,7 anti-inflammatory,8 antitumor,9,10 anti-HIV,11 pesticidal,12 insecticidal,13
herbicidal14 and fungicidal activity.15 Moreover, it was reported that compounds having triazole moieties,
such as vorozole, letrozole and anastrazole appeared to be very effective aromatase inhibitors, which in
turn prevented breast cancer.16-18
Furthermore, 1,3,4-thiadiazole nucleus takes part in the structure of several biologically active
compounds,
including
antibacterial,19-22
antifungal,21,22
antitubercular,23-25
analgesic,26
antiinflammatory,21,22,26 antidepressant,27 leishmanicidal28 activities.
Heterocycles containing an imidazole moiety constitute a class of compounds possessing a wide spectrum
of biological activities such as anti-bacterial,29 antiasthmatic30 and antiulcerative31 properties.
The binding of two or three heterocyclic rings having different sites or mode of action has commanded
the world-wide attention of many research groups because of their high potential to exhibit antimicrobial
activity.32-34
In view of these facts, the aim of the present study is to obtain 1,2,4-triazole and 1,3,4-thiadiazole
derivatives carrying imidazole moiety as antimicrobial agents.
RESULTS AND DISCUSSION
Chemistry
The synthesis of the 1,2,4-triazole and 1,3,4-thiadiazole derivatives is illustrated and outlined in Scheme 1.
Ph
Ph
N
N
R2NCS, EtOH
reflux
SCH2CONHNHCSNHR2
Ph
Ph
SCH2CONHNH2
N
N
R1
R1
1
2
3
R = H, R = Me
1
1
R = H
4 R1 = H, R2 = C6H4F(o-)
5 R1 = Ph, R2 = Me
2 R1 = Ph
1
2
6
R = Ph, R = C6H4F(o-)
7 R1 = Ph, R2 = Ph
10% NaOH
reflux
Ph
N
H
Ph
N
N
N
N
N
NHR2
Ph
SCH2
S
S
Ph
N
R1
SCH2
N
N
R1
R2
13 R1 = H, R2 = Me
8 R1 = H, R2 = Me
1
2
14
R = H, R = C6H4F(o-)
1
2
9
R = H, R = C6H4F(o-)
15 R1 = Ph, R2 = Me
10 R1 = Ph, R2 = Me
16 R1 = Ph, R2 = C6H4F(o-)
11 R1 = Ph, R2 = C6H4F(o-)
1
2
17
R = Ph, R = Ph
1
2
12
R = Ph, R = Ph
Scheme 1. Synthetic pathway for the preparation of compounds 8-17

HETEROCYCLES, Vol. 85, No. 5, 2012
1143
The key intermediates 1 and 2 were prepared from ethyl(4,5-di- and 1,4,5-triphenylimidazol-2-yl)-
thioacetate following the literature method.35 Treatment of the acid hydrazides 1 and 2 with various
alkyl/aryl isothiocyanates in ethanol gave corresponding N1-[(4,5-di- and 1,4,5-triphenyl)thioacetyl]-N4-
alkyl/aryl-thiosemicarbazides 3-7 in good yield.
The structure of the compounds investigated 3-7 was confirmed by their IR spectra which displayed
absorption peaks in the range of 3240-3365 cm-1 for NH, 1696-1703 cm-1 for C=O and 1296-1319 cm-1
1
corresponding to C=S stretching vibrations. Their H NMR spectra showed a multiplet at δH 7.13-7.91
ppm for aromatic protons. The CONH and CSNH protons were observed as singlets at 8.05-8.56 and
10.08-10.36 ppm, respectively confirming the formation of acid thiosemicarbazides (controlled with D2O).
The carbon signals of these groups were recorded between 163 and 184.16 ppm.
Thiosemicarbazides undergo different cyclization reactions to give five member heterocycles. The
product of cyclization depends on the reagent used. This cyclization leads to the formation of 1,3,4-
oxadiazole ring through the oxidative cyclization of thiosemicarbazides using iodine and potassium
36-37
iodide in ethanolic sodium hydroxide.
On the other hand, the 1,2,4-triazole and 1,3,4-thiadiazole
derivatives were obtained by the treatment of thiosemicarbazides with sodium hydroxide and sulfuric acid,
respectively.32,36-38
Therefore, the thiosemicarbazides 3-7 on heating with 10% aqueous NaOH underwent smooth cyclization
through dehydration to afford 5-[(4,5-di- and 1,4,5-triphenylimidazol-2-yl)-3-thiomethyl]-4-alkyl/aryl-
2H-1,2,4-triazoles-3-thione 8-12.
These compounds displayed 1H and 13C NMR spectra and elemental analyses consistent with the assigned
structures. The IR spectra of the triazoles 8-12 exhibited N-H bands in the region 3307-3341 cm-1. The
absorption bands at 1610-1630 cm-1 are due to the presence of C=N stretching of the triazole ring system.
Absence of the C=O absorptions in 8-12 provided definitive proof for the formation of new products.
The exhibited chemical shifts obtained from 1H NMR spectra were all supported the proposed structures
of 8-12. The 1H NMR of 10-12 chosen as prototypes showed single NH triazole resonances in the 14.40-
14.47 ppm regions (controlled with D2O). The SCH2 protons resonated at 4.62-4.79 ppm. Additional
signals belonging to phenyl ring were observed in the aromatic region in the 1H and 13C NMR spectra of
13
these compounds. Moreover, C=S group resonated at 181.80-183.64 ppm in the C NMR spectra of
compounds 8-12 confirming the presence of these compounds in their thione forms.
5-[(4,5-Di- and 1,4,5-triphenylimidazol-2-yl)-3-thiomethyl]-2-alkyl/arylamino-1,3,4-thiadiazoles 13-17
were obtained by cyclization of 3-7 by treating with cold concentrated sulfuric acid.
The IR spectra of the synthesized thiadiazoles 13-17 showed absorption peaks in the region 1613-1645
cm-1 due to C=N stretching vibrations. In the 1H NMR spectra of 13-17, the singlets of CONH and CSNH
of thiosemicarbazides had disappeared, and the NH proton at 2-position of 1,3,4-thiadiazoles ring

1144
HETEROCYCLES, Vol. 85, No. 5, 2012
appeared as singlet at 10.21-10.35 ppm (controlled with D2O).
On the other hand, in ethanol solution of potassium hydroxide, carbohydrazides 1, 2 interacted with
carbon disulfide to potassium hydrazine carbodithionates 18 and 19, which were used as precursors for
the synthesis of 4-amino-1,2,4-triazole-3-thiones 20, 21 and 1,3,4-thiadiazole-2-thiols 22, 23 (scheme 2).
Ph
N
KOH, EtOH
1, 2
Ph
SCH2CONHNHCSS K
N
CS2
R1
18 R1 = H
19 R1 = Ph
NH2NH2.H2O, reflux
H2SO4, 0 oC
H
Ph
Ph
N
N
N
N
N
N
S
Ph
SH
Ph
SCH2
SCH2
N
N
N
S
R1
R1
NH2
20 R1 = H
21 R1 = Ph
22 R1 = H
23 R1 = Ph
Scheme 2. Synthetic pathway for the preparation of compounds 18-23
The refluxing of 18, 19 and hydrazine hydrate led to the preparation of 4-amino-5-[(4,5-di and 1,4,5-
triphenylimidazol-2-yl)-3-thiomethyl]-2H-1,2,4-triazole-3-thiones 20, 21 in good yields. NMR spectral
characteristic of the amino-1,2,4-triazoles 20, 21, revealed in their 1H NMR spectra the two characteristic
singlets of the NH2 and NH (triazole) in the regions 7.90-8.03 ppm and 14.15-14.20 ppm, respectively
(controlled with D2O). In the NMR spectra of compounds 20 and 21, the exocyclic C=S signals were
observed at 182.30 and 183.76 ppm, respectively.
In sulfuric acid medium, the precursors 18, 19 formed 5-[(4,5-di and 1,4,5-triphenylimidazol-2-yl)-3-
13
thiomethyl]-1,3,4-thiadiazole-2-thiols 22, 23. In the C NMR spectra of compounds 22, 23, the absence
of the signals >180 ppm attributed to the thiocarbonyl carbons (C=S), confirmed the formation of the
thiadiazoles in their thiol forms.
In addition, the chemical shifts of SH thiadiazole protons were detected as singlet at 13.92-13.98 ppm
(controlled with D2O), which confirmed the thiol form. The remaining protons and carbons were
observed at the expected regions (see experimental part).

HETEROCYCLES, Vol. 85, No. 5, 2012
1145
Antimicrobial activity
The antibacterial and antifungal activity, assay (Table 1) indicated that the acid hydrazides 1 and 2 show
slight activity only against E. coli and P. aeruginosa. 1-[(4,5-Diphenylimidazol-2-yl)thioacyl]-4-
methylthiosemicarbazide (3) displayed moderate to good activities against all tested microorganisms
except C. albicans and C. tropicalis, whereas its 2-fluorophenyl analogue 4 displayed good activity
against all bacterial and yeast strains. On the other hand, 1-[(1,4,5-triphenylimidazol-2-yl)thioacyl]-4-
methylthiosemicarbazide (5) showed moderate antimicrobial activities towards E. coli and P. aeruginosa,
while 1-[(1,4,5-triphenylimidazol-2-yl)thioacyl]-4-(2-fluorophenyl)thiosemicarbazide (6) showed good
activity against all bacterial and yeast strains. 1-[(1,4,5-Triphenylimidazol-2-yl)thioacyl]-4-
phenylthiosemicarbazide (7) indicated excellent activity against E. coli, P. aeruginosa, C. albicans and C.
tropicalis. The antimicrobial activity of 4-alkyl/aryl-5-[(4,5-di- and 1,4,5-triphenylimidazole-2-yl)-
thiomethyl]-2H-1,2,4-triazole-3-thiones 8-12 divulged that compound 9 showed good antimicrobial
activity against tested bacterial and good antifungal activity against C. albicans.
Compounds 10 and 11 possessing three phenyl groups on imidazole ring exhibited excellent antibacterial
activity against S. aureus and B. subtilis and good activity against E. coli and P. aeruginosa. The
compound 12 having phenyl group on N-4 triazole ring showed excellent antifungal activity than
antibacterial action. On other hand, the antimicrobial activity of the thiadiazoles 13-16 revealed that all
the tested compounds possessed moderate to good inhibition, compounds 13 and 14 showed
comparatively moderate activity against E. coli and P. aeruginosa and good inhibition towards C.
albicans and C. tropicalis. Similarly, compounds 15 and 16 also showed significant activity against all
tested microbial strains. In contradiction, compound 17 possessing phenyl substitution on thiadiazole ring
displayed no activity.
The conversion of hydrazide structure in compound 1 to 1,2,4-triazole ring of 4-amino-5-[(4,5-
diphenylimidazol-2-yl)thiomethyl]-2H-1,2,4-triazole-3-thione (20) caused excellent antimicrobial
activities against all bacterial strains and C. albicans. 5-[(4,5-Diphenylimidazol-2-yl)thiomethyl]-1,3,4-
thiadiazole-2-thiol (21), which is the thiadiazole derivative of compound 1, demonstrated slight activity
only towards E. coli. The conversion of compound 2 to compound 22 caused important antimicrobial
activity. On the contrary to the activity of compound 22, compound 23, which was obtained from the
reaction of compound 2 with H2SO4, indicated no activities towards all microbial strains.
Based on the activity data of all the synthesized compounds, it is concluded that imidazole bearing 1,2,4-
triazole moiety exhibits better antibacterial activity than 1,3,4-thiadiazole moiety. Moreover, the presence
of amino group at N-4 of triazole ring seems to have marginal effect on biological activity. In fact, upon
N-amination the antibacterial activity marginally increases.

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HETEROCYCLES, Vol. 85, No. 5, 2012
Interestingly, it was found that thiadiazole derivatives 13-16 are more active against fungal pathogens as
compared to bacterial pathogens.
The antimicrobial activity of all the synthesized compounds could be attributed to the presence of triazole
ring. This ring is incorporated into a wide variety of drugs used in medical therapy.
Table 1. Screening for antimicrobial activity of the synthesized compounds (MIC mcg/mL)
Comp. No.
E. coli
9
P. aur.
10
11
18
21
20
22
34
9
B. sub
-
S. au.
-
C. trop.
C. alb
-
1
2
-
-
11
20
22
17
20
32
8
-
-
-
3
15
20
-
22
22
-
-
-
4
20
-
22
-
5
6
22
-
20
-
21
21
-
21
22
-
7
8
7
8
9
24
21
22
20
21
20
24
22
-
23
19
21
18
20
21
22
23
-
21
34
35
16
8
22
31
34
22
11
11
18
19
-
12
-
20
-
10
11
12
13
14
15
16
17
20
21
22
23
DMF
Amp
Flu
-
-
25
20
20
19
20
-
25
20
19
20
20
-
10
20
20
-
31
9
30
-
32
-
35
-
9
21
-
-
33
-
30
-
30
-
35
-
18
-
19
-
-
-
-
-
-
-
10
18
15
35
25
25
Ec: Escherichia coli, Pa: Pseudomonas aeruginosa, Bs: Bacillus. Subtilis, Sa: Staphylococcus aureus, Ct: Candida
tropicalis, Ca: Candida albicans. Amp: Ampicillin, Flu: Fluconazole, (-): no activity, solvent is DMF.

HETEROCYCLES, Vol. 85, No. 5, 2012
1147
CONCLUSION
The research study reports the successful synthesis and antimicrobial activity of new 4-alkyl/aryl-2H-
1,2,4-triazole-3-thiones, 4-amino-2H-1,2,4-triazole-3-thiones, 2-aminoalkyl/aryl-1,3,4-thiadiazoles and
1,3,4-thiadiazoles-3-thiols, carrying biologically active imidazole ring. Their antimicrobial activity study
revealed that some of the compounds tested showed moderate to excellent antibacterial and antifungal
activities against pathogenic strains.
EXPERIMENTAL
Chemistry
Melting points were determined on a Melt-temp apparatus and are uncorrected. 1H and 13C NMR spectra
were recorded on a Jeol 500 MHz spectrometer. The IR spectra were measured as potassium bromide
pellets using a Perkin-Elmer 1430 series FTIR spectrometer. The microanalyses for C, H and N were
performed on Perkin-Elmer elemental analyzer.
General method for the synthesis of compounds 3-7. A mixture of corresponding compound 1 or 2 (10
mmol) and the appropriate isothiocyanate derivatives (10 mmol) was refluxed in EtOH for 6 h. The
solution was cooled and a white solid appeared. The obtained precipitate was filtered and recrystallized
from ethanol to afford the desired product.
1-[(4,5-Diphenylimidazol-2-yl)thioacetyl]-4-methylthiosemicarbazide (3). Yield 88%, mp 158 °C; IR:
1
3355, 3270 (NH), 1700 (C=O), 1315 cm-1 (C=S); H NMR (500 MHz, DMSO-d6) δH 2.85 (3H, s, CH3),
4.70 (2H, s, SCH2), 7.18-7.63 (10H, m, arH), 8.05 (1H, s, NH), 8.55 (1H, s, NH), 10.10 (1H, s, NH),
13
12.54 (1H, s, NH imidazole); C NMR (125 MHz, DMSO-d6) δc 34.40 (CH3), 40.97 (CH2), (127.10,
127.94, 128.81, 129.21, 129.98, 131.66, 135.75, 137.89) arC, 163.00 (C=O), 181.70 (C=S). Anal. Calcd
(%) for C19H19N5OS2: C, 57.41; H, 4.82; N, 17.62. Found: C, 57.30; H, 4.98; N, 17.52.
1-[(4,5-Diphenylimidazol-2-yl)thioacetyl]-4-(2-fluorophenyl)thiosemicarbazide (4). Yield 80%, mp
1
200-201 °C; IR: 3343, 3265 (NH), 1701 (C=O), 1296 cm-1 (C=S); H NMR (500 MHz, DMSO-d6)
δH 4.61 (2H, s, SCH2), 7.23-7.76 (14H, m, arH), 8.10 (1H, s, NH), 8.56 (1H, s, NH), 10.08 (1H, s, NH),
12.43 (1H, s, NH imidazole); 13C NMR (500 MHz, DMSO-d6) δC 41.75 (SCH2), (125.33, 127.56, 128.07,
128.78, 129.15, 129.87, 130.45, 132.65, 131.80, 135.89, 138.24, 141.34) arC, 167.89 (C=O), 182.49
(C=S). Anal. Calcd (%) for C24H20FN5OS2: C, 60.36; H, 4.22; N, 14.66. Found: C, 60.12; H, 4.45; N,
14.46.
1-[(1,4,5-Triphenylimidazol-2-yl)thioacetyl]-4-methylthiosemicarbazide (5). Yield 84%, mp 167 °C;
IR: 3345 and 3258 (NH), 1698 (C=O), 1319 cm-1 (C=S). 1H NMR (500 MHz, DMSO-d6) δH 2.92 (3H, s,
CH3), 4.74 (2H, s, SCH2), 7.15-7.78 (15H, m, arH), 8.20 (1H, s, NH), 8.36 (1H, s, NH), 10.24 (1H, s,

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HETEROCYCLES, Vol. 85, No. 5, 2012
13
NH); C NMR (125 MHz, DMSO-d6) δC 35.61 (CH3), 40.46 (CH2), (126.87, 127.33, 127.27, 128.09,
128.74, 129.45, 129.81, 131.80, 136.09, 138.24) arC, 166.35 (C=O), 183.05 (C=S). Anal. Calcd (%) for
C25H23N5OS2: C, 63.40; H, 4.89; N, 14.79. Found: C, 63.28; H, 4.80; N, 14.52.
1-[(1,4,5-Triphenylimidazol-2-yl)thioacetyl]-4-(2-fluorophenyl)thiosemicarbazide (6). Yield 80%,
mp 216-217 °C; IR: 3346 and 3279 (NH), 1703 (C=O), 1310 cm-1 (C=S); 1H NMR (500 MHz, DMSO-d6)
δH 4.61 (2H, s, SCH2), 7.13-7.91 (19H, m, arH), 8.15 (1H, s, NH), 8.27 (1H, s, NH), 10.19 (1H, s, NH);
13C NMR (125 MHz, DMSO-d6) δC 41.94 (SCH2), (124.77, 126.45, 127.80, 127.98, 128.22, 128.51,
128.86, 129.05, 129.74, 132.11, 136.41, 138.40, 141.60) arC, 163.78 (C=O), 182.32 (C=S). Anal. Calcd
(%) for C30H24FN5OS2: C, 65.08; H, 4.37; N, 12.65. Found: C, 64.89; H, 4.13; N, 12.51.
1-[(1,4,5-Triphenylimidazol-2-yl)thioacetyl]-4-phenylthiosemicarbazide (7). Yield 78%, mp 145 °C.
IR: 3365 and 3240 (NH), 1696 (C=O), 1300 cm-1 (C=S); 1H NMR (500 MHz, DMSO-d6) δH 4.80 (2H, s,
SCH2), 7.20-7.75 (20H, m, arH), 8.10 (1H, s, NH), 8.25 (1H, s, NH), 10.34 (1H, s, NH),13C NMR (125
MHz, DMSO-d6) δC 40.07 (SCH2), (127.88, 127.97, 128.14, 128.46, 129.80, 129.89, 130.24, 130.68,
131.80, 132,90, 136.65, 138.24) arC, 163.70 (C=O), 184.16 (C=S). Anal. Calcd (%) for C30H25N5OS2: C,
67.26; H, 4.70; N, 13.07. Found: C, 67.09; H, 4.55; N, 13.19.
General procedure for the synthesis of compounds 8-12. A solution of the corresponding
thiosemicarbazide 3-7 (10 mmol) in 2 N NaOH was refluxed for 8 h. The resulting solution was cooled to
room temperature and acidified with 37% HCl. The precipitate formed was filtered, washed with water
and recrystallized from EtOH to afford the desired compounds.
4-Methyl-5-[(4,5-diphenylimidazol-2-yl)thiomethyl]-2H-1,2,4-triazole-3-thione (8). Yield 82%, mp
185-186 °C; IR: 3330 (NH), 1630 (C=N), 1306 cm-1 (C=S); 1H NMR (500 MHz, DMSO-d6) δH 3.42 (3H,
s, CH3), 4.72 (2H, s, SCH2), 7.20-7.60 (10H, m, arH), 12.54 (1H, s, NH imidazole), 14.28 (1H, s, NH
triazole); 13C NMR (125 MHz, DMSO-d6) δC 33.88 (CH3), 38.43 (CH2), (126.68, 127.80, 128.20, 129.56,
129.75, 130.98, 134.78, 137.20) arC, 155.36 (triazole C=N), 182.45 (C=S). Anal. Calcd (%) for
C19H17N5S2: C, 60.13; H, 4.52; N, 18.45. Found: C, 60.29; H, 4.42; N, 18.61.
4-(2-Fluorophenyl)-5-[(4,5-diphenylimidazol-2-yl)thiomethyl]-2H-1,2,4-triazole-3-thione (9). Yield
77%, mp 230-231 °C; IR: 3341 (NH), 1624 (C=N), 1300 cm-1 (C=S); 1H NMR (500 MHz, DMSO-d6) δH
4.71 (2H, s, SCH2), 7.18-7.73 (14H, m, arH), 12.45 (1H, s, NH imidazole), 14.37 (1H, s, NH triazole);
13C NMR (125 MHz, DMSO-d6) δC 40.76 (SCH2), (125.33, 127.42, 127.80, 128.16, 128.51, 129.40,
130.70, 131.93, 134.38, 139.06, 141.56) arC, 154.52 (triazole C=N), 183.61 (C=S). Anal. Calcd (%) for
C24H18FN5S2: C, 62.72; H, 3.95; N, 15.24. Found: C, 62.95; H, 4.10; N, 15.07.
4-Methyl-5-[(1,4,5-triphenylimidazol-2-yl)thiomethyl]-2H-1,2,4-triazole-3-thione (10). Yield 80%,

HETEROCYCLES, Vol. 85, No. 5, 2012
1149
mp 209-211 °C; IR: 3307 (NH), 1615 (C=N), 1297 cm-1 (C=S); 1H NMR (500 MHz, DMSO-d6) δH 3.50
13
(3H, s, CH3), 4.79 (2H, s, SCH2), 7.24-7.82 (15H, m, arH), 14.45 (1H, s, NH triazole); C NMR (125
MHz, DMSO-d6) δC 33.54 (CH3), 39.22 (CH2), (126.60, 127.09, 127.41, 127.69, 128.40, 129.16, 130.00,
131.56, 135.78, 137.68) arC, 154.78 (triazole C=N), 181.80 (C=S). Anal. Calcd (%) for C25H21N5S2: C,
65.91; H, 4.65; N, 15.37. Found: C, 66.08; H, 4.51; N, 15.28.
4-(2-Fluorophenyl)-5-[(1,4,5-triphenylimidazol-2-yl)thiomethyl]-2H-1,2,4-triazole-3-thione
(11).
Yield 79%, mp 243-244 °C; IR: 3339 (NH), 1627 (C=N), 1313 cm-1 (C=S); 1H NMR (500 MHz, DMSO-
d6) δH 4.62 (2H, s, SCH2), 7.10-7.77 (19H, m, arH), 14.40 (1H, s, NH triazole); 13C NMR (125 MHz,
DMSO-d6) δC 39.46 (SCH2), (123.87, 126.45, 127.24, 128.34, 128.56, 129.24, 129.45, 130.50, 131.79,
131.78, 136.05, 138.24, 140.68) arC, 152.95 (triazole C=N), 183.00 (C=S). Anal. Calcd (%) for
C30H22FN5S2: C, 67.27; H, 4.14; N, 13.07. Found: C, 67.43; H, 4.30; N, 12.90.
4-Phenyl-5-[(1,4,5-triphenylimidazol-2-yl)thiomethyl]-2H-1,2,4-triazole-3-thione (12). Yield 75%,
mp 167-168 °C. IR: 3320 (NH), 1610 (C=N), 1308 cm-1 (C=S); 1H NMR (500 MHz, DMSO-d6) δH 4.74
13
(2H, s, SCH2), 7.19-7.90 (20H, m, arH), 14.47 (1H, s, NH triazole); C NMR (125 MHz, DMSO-d6) δC
38.73 (SCH2), (127.29, 127.70, 128.34, 128.98, 129.50, 130.05, 130.38, 130.72, 131.44, 132,67, 136.16,
139.78) arC, 152.84 ( triazole C=N), 182.90 (C=S). Anal. Calcd (%) for C30H23N5S2: C, 69.60; H, 4.48; N,
13.53. Found: C, 69.74; H, 4.66; N, 13.59.
General method for the synthesis of compounds 13-17. A mixture of the corresponding
thiosemicarbazide 3-7 (10 mmol) in cold concentrated sulfuric acid (30 mL) was stirred for 30 min. Then,
the mixture was allowed reach to cool to room temperature. After stirring for an additional 3 h, the
resulting solution was poured into ice-cold water and made alkaline to pH 8 with ammonia. The
precipitated product was filtered and recrystallized from EtOH to afford the desired product.
5-[(4,5-Diphenylimidazol-2-yl)thiomethyl]-2-(N-methylamino)-1,3,4-thiadiazole (13). Yield 73%,
mp 249-250 °C; IR: 3230 (NH), 1645 and 1624 cm-1 (C=N); 1H NMR (500 MHz, DMSO-d6) δH 3.34 (3H,
s, CH3), 4.72 (2H, s, SCH2), 7.20-7.67 (10H, m, arH), 10.22 (1H, s, NH), 12.40 (1H, s, NH imidazole);
13C NMR (125 MHz, DMSO-d6) δC 32.65 (CH2), 35.12 (CH3), (125.90, 127.45, 127.77, 129.09, 129.57,
131.60, 134.89, 136.73) arC, 154.45 and 157.05 (thiadiazole C=N). Anal. Calcd (%) for C19H17N5S2: C,
60.13; H, 4.52; N, 18.45. Found: C, 60.30; H, 4.39; N, 18.36.
5-[(4,5-Diphenylimidazol-2-yl)thiomethyl]-2-[N-(2-fluorophenyl)]amino-1,3,4-thiadiazole
(14).
Yield 72%, mp 269-270 °C; IR: 3246 (NH), 1629 and 1613 cm-1 (C=N); 1H NMR (500 MHz, DMSO-d6)
13
δH 4.66 (2H, s, SCH2), 7.14-7.82 (14H, m, arH), 10.33 (1H, s, NH), 12.42 (1H, s, NH imidazole); C
NMR (125 MHz, DMSO-d6) δC 39.05 (SCH2), (123.88, 126.73, 127.23, 127.80, 128.34, 128.70, 129.57,

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131.88, 134.50, 137.19, 140.80) arC, 153.57 and 157.30 (thiadiazole C=N). Anal. Calcd (%) for
C24H18FN5S2: C, 62.72; H, 3.95; N, 15.24. Found: C, 62.86; H, 3.76; N, 15.41.
5-[(1,4,5-Triphenylimidazol-2-yl)thiomethyl]-2-(N-methylamino)-1,3,4-thiadiazole (15). Yield 71%,
mp 260-261 °C; IR: 3245 (NH), 1639 and 1616 cm-1 (C=N); 1H NMR (500 MHz, DMSO-d6) δH 3.18 (3H,
13
s, CH3), 4.76 (2H, s, SCH2), 7.21-7.70 (15H, m, arH), 10.26 (1H, s, NH); C NMR (125 MHz, DMSO-
d6) δC 32.97 (CH2), 36.00 (CH3), (126.21, 126.78, 127.64, 127.80, 128.33, 128.96, 130.15, 130.67, 135.90,
137.46) arC, 153.94 and 159.14 (thiadiazole C=N). Anal. Calcd (%) for C25H21N5S2: C, 65.91; H, 4.65; N,
15.37. Found: C, 65.78; H, 4.81; N, 15.50.
5-[(1,4,5-Triphenylimidazol-2-yl)thiomethyl]-2-[N-(2-fluorophenyl)]amino-1,3,4-thiadiazole
(16).
Yield 74%, mp 279-280 °C; IR: 3278 (NH), 1638 and 1613 cm-1 (C=N); 1H NMR (500 MHz, DMSO-d6)
13
δH 4.63 (2H, s, SCH2), 7.13-7.80 (19H, m, arH), 10.21 (1H, s, NH); C NMR (125 MHz, DMSO-d6) δC
40.33 (SCH2), (123.87, 126.23, 127.67, 127.89, 128.75, 128.90, 129.34, 130.41, 131.51, 135.70, 137.66,
140.22) arC, 153.11 and 157.50 (thiadiazole C=N). Anal. Calcd (%) for C30H22FN5S2: C, 67.27; H, 4.14;
N, 13.07. Found: C, 67.01; H, 3.97; N, 13.32.
5-[(1,4,5-Triphenylimidazol-2-yl)thiomethyl]-2-(N-phenylamino)-1,3,4-thiadiazole (17). Yield 67%,
mp 223-224 °C; IR: 3217 (NH), 1640 and 1617 cm-1 (C=N); 1H NMR (500 MHz, DMSO-d6) δH 4.83 (2H,
s, SCH2), 7.10-7.78 (20H, m, arH), 10.35 (1H, s, NH); 13C NMR (125 MHz, DMSO-d6) δC 33.82 (SCH2),
(126.55, 127.86, 128.35, 129.14, 130.21, 130.42, 131.50, 131.67, 132,51, 135.83, 138.46) arC, 154.67
and 157.08 (thiadiazole C=N). Anal. Calcd (%) for C30H23N5S2: C, 69.60; H, 4.48; N, 13.53. Found: C,
69.47; H, 4.60; N, 13.40.
General method for the synthesis of compounds 18 and 19. Carbon disulfide (15 mmol) was added
dropwise to a solution of 1 or 2 (10 mmol) in absolute EtOH (30 mL) containing potassium hydroxide (15
mmol) at 0 ºC. The reaction was stirred at room temperature for 16 h, and then cooled and diluted with
Et2O. The precipitate was filtered, washed with Et2O and dried. The potassium dithiocarbazinates 18 and
19 were obtained in nearly quantitative yield and used without further purification as it were moisture
sensitive.
General method for the synthesis of compounds 20 and 21. Hydrazine hydrate (95%, 20 mmol) was
added to a suspension of the potassium salt 18 or 19 (10 mmol) in water (10 mL) and the mixture was
refluxed with stirring for 4 h. After cooling, it was diluted with water then acidified with aqueous
hydrochloric acid. The precipitate was filtered, washed with water and recrystallized from EtOH to give
yellow needles.
4-Amino-5-[(4,5-diphenylimidazol-2-yl)thiomethyl]-2H-1,2,4-triazole-3-thione (20). Yield 77%,

HETEROCYCLES, Vol. 85, No. 5, 2012
1151
1
mp 190 °C; IR: 3210-3320 (NH, NH2), 1632 (C=N), 1308 cm-1 (C=S); H NMR (500 MHz, DMSO-d6)
δH 4.59 (2H, s, SCH2), 7.26-7.56 (10H, m, arH), 7.90 (2H, s, NH2), 12.31 (1H, s, NH imidazole), 14.15
(1H, s, NH triazole); 13C NMR (125 MHz, DMSO-d6) δC 36.16 (SCH2), (125.70, 126.38, 127.28, 128.44,
129.35, 130.92, 134.71, 136.08) arC, 153.08 (triazole C=N), 182.30 (C=S). Anal. Calcd (%) for
C18H16N6S2: C, 56.82; H, 4.24; N, 22.09. Found: C, 57.02; H, 4.31; N, 21.93.
4-Amino-5-[(1,4,5-triphenylimidazol-2-yl)thiomethyl]-2H-1,2,4-triazole-3-thione (21). Yield 76%,
1
mp 229 °C; IR: 3224-3330 (NH, NH2), 1620 (C=N), 1296 cm-1 (C=S); H NMR (500 MHz, DMSO-d6)
δH 4.66 (2H, s, SCH2), 7.12-7.60 (15H, m, arH), 8.03 (2H, s, NH2), 14.20 (1H, s, NH triazole); 13C NMR
(125 MHz, DMSO-d6) δC 37.20 (SCH2), (126.63, 126.86, 127.08, 127.67, 128.11, 128.84, 129.20, 130.48,
134.63, 136.52) arC, 152.14 ( triazole C=N), 183.76 (C=S). Anal. Calcd (%) for C24H20N6S2: C, 63.13; H,
4.42; N, 18.41. Found: C, 63.29; H, 4.60; N, 18.59.
General method for the synthesis of compounds 22 and 23. A mixture of the corresponding
dithiocarbazate 18 or 19 (10 mmol) in cold concentrated sulfuric acid (30 mL) was stirred for 30 min.
Then, the mixture was allowed reach to cool to room temperature. After stirring for an additional 5 h, the
resulting solution was poured into ice-cold water and made alkaline to pH 8 with ammonia. The
precipitated product was filtered and recrystallized from EtOH to afford the desired product.
5-[(4,5-Diphenylimidazol-2-yl)thiomethyl]-1,3,4-thiadiazole-2-thiol (22). Yield 68%, mp 260-261 °C;
IR: 2615 (SH), 1635, 1617 cm-1 (C=N); 1H NMR (500 MHz, DMSO-d6) δH 4.65 (2H, s, SCH2), 7.18-7.60
(10H, m, arH), 12.40 (1H, s, NH imidazole), 13.92 (1H, s, SH); 13C NMR (500 MHz, DMSO-d6) δC 34.50
(CH2), (126.24, 126.66, 127.50, 127.92, 128.71, 129.87, 134.56, 137.34) arC, 153.12 and 157.94
(thiadiazole C=N). Anal. Calcd (%) for C18H14N4S3: C, 56.52; H, 3.69; N, 14.65. Found: C, 56.38; H,
3.86; N, 14.52.
5-[(1,4,5-Triphenylimidazol-2-yl)thiomethyl]-1,3,4-thiadiazole-2-thiol (23). Yield 66%, mp 239-
1
240 °C; IR: 2600 (SH), 1640, 1621 cm-1 (C=N); H NMR (500 MHz, DMSO-d6) δH 4.72 (2H, s, SCH2),
13
7.20-7.73 (15H, m, arH), 13.98 (1H, s, SH); C NMR (125 MHz, DMSO-d6) δC 35.38 (CH2), (126.00,
126.51, 127.13, 127.63, 129.81, 130.69, 135.38, 137.93) arC, 154.26 and 159.40 (thiadiazole C=N). Anal.
Calcd (%) for C24H18N4S3: C, 62.85; H, 3.96; N, 12.22. Found: C, 63.03; H, 3.89; N, 12.37.
Antimicrobial activity
All bacterial and yeast strains were obtained from the microbiology Laboratory-Faculty of medicine,
University of Djillali Liabes (Sidi-Bel-Abbes-Algeria) and were as follows: Staphylococcus aureus,
Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, Candida tropicalis and Candida albicans.
All the newly synthesized 1,2,4-triazoles and 1,3,4-thiadiazoles were screened for their antimicrobial and

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HETEROCYCLES, Vol. 85, No. 5, 2012
antifungal activity. Thus, they were dissolved in dimethylformamide (DMF) to prepare chemical stock
solution of 10 mg/1 mL.
Agar-well diffusion method was the simple screening method used for this study.39-40 Thus, each
microorganism was suspended in Mueller Hinton (MH) broth and diluted approximately to 106 colony
forming unit (cfu)/mL. They were “flood-inoculated” onto the surface of MH agar and sabouraud
Dextrose Agar and then dried. For Candida tropicalis and Candida albicans, SDA were used. Five
millimeter diameter wells were cut from the agar using a sterile cork-borer, and 50 µL of the chemical
substances was delivered into the wells. The plates were incubated for 16-18 h at 37 ºC. Antimicrobial
activity was evaluated by measuring the zone of inhibition against the test organism. Ampicillin (10 µg)
and Fluconazole (100 µg) were standard drugs. Dimethylformamide was used as solvent controls. The
antimicrobial activity results are summarized in Table 1.
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