Synthesis, Characterization, and Antimicrobial Screening of Novel 1,2,4-Triazoles, 1,3,4-Thiadiazoles, and 1,3,4-Oxadiazoles Bearing the Indole Moiety

Full text of DOI:10.1080/00304948.2019.1599791

Organic Preparations and Procedures International
The New Journal for Organic Synthesis
ISSN: 0030-4948 (Print) 1945-5453 (Online) Journal homepage: https://www.tandfonline.com/loi/uopp20
Synthesis, Characterization, and Antimicrobial
Screening of Novel 1,2,4-Triazoles, 1,3,4-
Thiadiazoles, and 1,3,4-Oxadiazoles Bearing the
Indole Moiety
Adeeb A. Ali, Moataz A. Soliman, Mohamed R. Aouad, Mouslim Messali &
Nadjet Rezki
To cite this article: Adeeb A. Ali, Moataz A. Soliman, Mohamed R. Aouad, Mouslim Messali
& Nadjet Rezki (2019): Synthesis, Characterization, and Antimicrobial Screening of Novel
1,2,4-Triazoles, 1,3,4-Thiadiazoles, and 1,3,4-Oxadiazoles Bearing the Indole Moiety, Organic
Preparations and Procedures International, DOI: 10.1080/00304948.2019.1599791
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Organic Preparations and Procedures International, 0:1–17, 2019
# 2019 Taylor & Francis Group, LLC
ISSN: 0030-4948 print / 1945-5453 online
DOI: 10.1080/00304948.2019.1599791
Synthesis, Characterization, and Antimicrobial
Screening of Novel 1,2,4-Triazoles, 1,3,4-
Thiadiazoles, and 1,3,4-Oxadiazoles Bearing the
Indole Moiety
Adeeb A. Ali,1 Moataz A. Soliman,1 Mohamed R. Aouad,1,2
Mouslim Messali,1 and Nadjet Rezki1,2
1Department of Chemistry, Faculty of Sciences, Taibah University, Al-
Madinah Al-Munawarah 30002, Saudi Arabia
2Laboratoire de Chimie & Electrochimie des Complexes Metalliques
(LCECM) USTO-MB, Department of Chemistry, Faculty of Sciences,
University of Sciences and Technology Mohamed Boudiaf, B.p. 1505 El
M’nouar, Oran 31000, Algeria
Over the past few decades, many compounds bearing five membered heterocyclic moi-
eties, such as 1,2,4-triazoles, 1,3,4-oxadiazoles and 1,3,4-thiadiazoles, have been inten-
sively studied for their broad biomedical applications. A literature survey revealed that
the 1,3,4-thiadiazole ring has been associated with diverse pharmacological properties
including anticancer,1 antiviral,2 anti-depressant,3 anti-inflammatory,4–6 and anti-tuber-
culosis7,8 activities. 1,2,4-Triazoles are excellent candidates for medicinal and pharma-
cological applications. A large number of 1,2,4-triazole derivatives were reported in the
literature as anti-viral,2 anti-microbial,9,10 anti-inflammatory,6,11 anti-tuberculosis,12
anti-bacterial,13 and anti-cancer agents.14 Several pharmacological researches showed
that 1,3,4-oxadiazole derivatives have interesting biological properties.15–16 In fact, a
new series of 1,3,4-oxadiazoles carrying the indole moiety were reported for their
excellent in vitro antifungal activity.17 Indole derivatives were also reported with highly
potent biological properties such as anticancer18 anti-leishmanial19 and anti-depressant
activities.20 The clubbing of the indole moiety with different heterocyclic units has
been explored for biological applications.21–23
Driven by these observations, and continuing our interest in synthesizing biologic-
ally active molecules,16,24–26 we worked to combine two different biologically active
units. Direct alkylation of the commercially available indol-3-ylbutyric acid failed.
Refluxing the acid with ethanol in the presence of catalytic amounts of sulfuric acid
gave the corresponding ethyl (indol-3-yl)butyrate (1). Under thermal conditions using
different solvents and bases, the N-alkylation of ester 1 did not proceed even after
refluxing for several days.
Received April 7, 2018; in final form December 1, 2018.
Address correspondence to Adeeb A. Ali, Department of Chemistry, Faculty of Sciences, Taibah
University, Al-Madinah Al-Munawarah 30002, Saudi Arabia. E-mail: adeebali@dal.ca
1

2
Ali et al.
O
O
O
O
O
R
OH
EtOH
TBAB/DCM/NaOH
p-F-C6H4CH2Cl
N
H
N
N
H
H
2SO4
1
F
2 R = Ethyl
3 R = p-F-CH2Cl
2O
.H
NH2NH2
EtOH
O
HN NH2
N
F
4
Scheme 1. Synthesis of acid hydrazide 4.
In contrast, optimized N-alkylation was successfully achieved through tetra-butyl
ammonium bromide (TBAB). The desired compound was obtained by a phase transfer
catalyzed (PTC) reaction via the treatment of 1 with p-fluorobenzyl chloride in
dichloromethane (DCM) in the presence of TBAB and 50% aqueous NaOH. The reac-
tion produced p-fluorobenzyl [(N-p-fluorobenzyl)indol-3-yl]butyrate (3) as the major
product. Compound 2 was also formed as a minor product (79% overall yield).
The crude 1H NMR spectrum of the mixture of compounds 2 and 3 showed the dis-
appearance of the NH signal at 7.95 ppm related to the indolic NH moiety and the
appearance of two new sets of signals. The first one related to the N-p-fluorobenzyl
ethyl ester 2 where the ethyl group appeared at 0.99 ppm as a triplet and at 4.21 ppm as
a quartet. The NCH2-benzylic protons appeared as a singlet at 5.27 ppm. Moreover, the
13C spectrum confirmed the N-alkylation through the chemical shift of the benzylic
NCH2 carbon at 49.2 ppm for the N-p-fluorobenzyl ethyl ester 2. The 19F NMR spec-
trum also demonstrated the presence of the benzylic group where the chemical shift of
1
the fluoro group appeared at -114.9 ppm. The second set in the H NMR spectrum was
assigned for p-fluorobenzyl-(N-p-fluorobenzyl) ester 3 where the proton NMR showed
two signals at 5.14 and 5.26 ppm for the NCH2-p-fluorobenzyl and the OCH2-p-ben-
zylic protons respectively. Furthermore, the 13C NMR spectrum showed two signals at
49.2 ppm related to the N-benzylic carbon (NCH2Ph) and 65.5 ppm related to the O-
benzylic carbon (OCH2Ph) of compound 3. The 19F NMR spectrum showed an add-
itional signal at ꢀ113.5 ppm. In order to investigate the transesterification step, the
major product was successfully separated using flash chromatography and the NMR
spectra of the pure p-fluorobenzyl(N-p-fluorobenzyl indole) ester 3 confirmed the trans-
esterification of the ethyl ester. Condensation of ethyl/p-fluorobenzyl butyrate 2,3 with
hydrazine hydrate (100%) in refluxing ethanol gave the key product acid hydrazide 4 in
97% yield (Scheme 1).

Novel 1,2,4-Triazoles, 1,3,4-Thiadiazoles, and 1,3,4-Oxadiazoles
3
O
N
NH
HN NH2
O
S
CS2 , KOH
N
N
F
F
18
4
N
N
NH
S
R
10% NaOH
N
RNCS
EtOH
F
9-12
O
N
N
R
S
HN
NH
H2SO4 , 0oC
N
H
NH
R
S
N
N
F
F
5-8
13-16
N
O
N
R
KI , I2
N
H
N
F
17
5 , 9 , 13 , 17: R = C6H5
6 , 10 , 14:
7 , 11 , 15:
8 , 12 , 16:
R = C2H5
R = CH3
R = C6H11
Scheme 2. Synthesis of heterocyclic compounds.

4
Ali et al.
Table 1
Yields for Compounds 3-18
Compound
Structure
Formula
Yield (%)
O
3
C26H23F2NO2
79
O
N
F
F
F
O
4
5
C19H20FN3O
97
98
HN
NH2
N
O
HN
C26H25FN4OS
NH
NH
C6H5
S
N
F
F
O
6
7
8
C22H25FN4OS
C21H23FN4OS
C26H31FN4OS
87
87
HN
NH
NH
C2H5
S
N
N
O
HN
NH
NH
CH3
S
F
F
O
77
HN
NH
NH
C6H11
S
N
(Continued)

Novel 1,2,4-Triazoles, 1,3,4-Thiadiazoles, and 1,3,4-Oxadiazoles
5
Table 1
(Continued)
N
9
C26H23FN4S
84
87
NH
S
N
C6H5
N
N
F
N
N
10
C22H23FN4S
NH
S
C2H5
F
F
N
N
11
12
C21H21FN4S
90
86
NH
S
H3C
N
N
C26H29FN4S
NH
S
N
C6H11
N
F
F
N
N
13
14
C26H23FN4S
87
87
S
NH
C6H5
N
N
C22H23FN4S
N
S
NH
C2H5
N
F
(Continued)

6
Ali et al.
Table 1
(Continued)
N
15
C21H21FN4S
C26H29FN4S
C26H23FN4O
89
86
65
N
S
NH
H3C
N
N
F
F
N
16
17
N
S
NH
C6H11
N
N
O
NH
C6H5
N
F
F
N
18
C20H18FN3OS
65
NH
S
O
N
Thermal condensation of acid hydrazide 4 with alkyl/aryl isothiocyanates in ethanol
for 6 hrs furnished the corresponding thiosemicarbazides 5-8 in 77–97% yields. The
synthesis of 1,2,4-triazoles 9-12 was achieved via the cyclodehydration reaction of their
precursors 5-8 in 84–90% yields. The reaction required heating under reflux for 8 hrs in
10% NaOH solutions. The novel series of amino-1,3,4-thiadiazoles 13-16 were prepared
via acid catalyzed dehydrocyclization of thiosemicarbazides 5-8 in the presence of
H2SO4 at 0ꢁC in 86–89% yields. Treatment of 4-N-phenyl thiosemicarbazide 5 with 5%
(I2/KI) in the presence of NaOH produced the corresponding 2-N-phenylamine-1,3,4-
oxadiazole 17. In a one pot reaction, 3H-1,3,4-oxadiazole-2-thione 18 was prepared in
65% yield from the treatment of acid hydrazide 4 with carbon disulfide in basic aque-
ous NaOH solution (Scheme 2).
The 1H NMR spectrum of compound 4 displayed no signals belonging to the
alkoxy groups. Alternatively, new signals assignable to the hydrazide moiety
(CONHNH2) appeared at 4.17 ppm and 8.96 ppm integrating for two protons (NH2) and
one proton (NH), respectively. The 13C NMR spectrum confirmed the disappearance of

Novel 1,2,4-Triazoles, 1,3,4-Thiadiazoles, and 1,3,4-Oxadiazoles
7
Table 2
Antimicrobial Activity (Inhibition Zone; Diameter in mm)
Gram-
positive
Gram-
negative
organismsa
organismsb
Fungic
Gc
Compounds
Bs
Sp
Ec
Pa
Ca
Sr
Af
4
5
6
7
8
9
10
11
12
13
14
15
14.6
NA
19.1
23.4
16
13.9
18.3
17.4
15.3
22.4
19.7
NA
24.5
32.4
–
13.2
NA
16.7
21.6
15.4
13.6
16
11.7
NA
15.2
18.9
13.5
13.6
13
16.8
11.3
24.7
19.6
NA
22.6
–
NA
NA
NA
14
NA
11.3
NA
12.9
NA
14.6
20.3
NA
15.7
–
NA
NA
NA
NA
NA
12.6
NA
17.9
NA
NA
18.5
13.7
18.9
–
12.6
NA
15.8
24.2
13.1
11.1
16.5
15.4
15.4
14.8
20.9
14.6
20.2
–
10.1
NA
14.5
17.9
14.6
NA
11.7
NA
11.4
17.8
16.5
13.2
19.8
–
11.2
NA
16.7
19.3
15.4
12.3
10.6
18.3
13.6
18.9
21.7
17.4
20.8
–
16.2
1.2
20.5
20.6
NA
22.1
23.8
–
16
Ampicillin
Gentamicin
Amphotericin B
19.9
–
17.3
–
–
–
–
–
–
–
25.4
28.7
17.9
23.7
aGram-positive bacteria: Bacillus subtilis (Bs), Streptococcus pneumonia (Sp).
bGram-negative bacteria: Escherichia coli (Ec), Pseudomonas aeuroginosa (Pa).
cYeasts: Candida albicans (Ca), Geotrichum candidum (Gc), Syncephalastrum racemosum (Sr),
Aspergillus fumigatus (Af).
the signals related to the ethoxy and/or the p-fluorobenzyloxy alkyl groups.
Additionally, the carbonyl chemical shift was decreased from 173.8 ppm (for the ester
moiety) to 171.6 (for the amide moiety). Moreover, the 19F NMR spectrum of the
hydrazide 4 showed only one peak at ꢀ115.5 ppm related to the N-p-fluorobenzy-
lated residue.
1
The H NMR spectra of the thiosemicarbazides 5-8 showed the disappearance of
the two protons at 4.17 ppm related to the NH2 group. An additional doublet of NH-sig-
nals derived from the thiosemicarbazides was observed at 7.55–9.22 ppm. The 13C
NMR spectra confirmed the formation of compounds 5-8 via the appearance of new N-
alkyl/aryl carbon signals bonded to the thiosemicarbazide residue.
1
From the H NMR spectra of the 1,2,4-triazole derivatives 9-12, the disappearance
of signals related to the NH groups of the corresponding thiosemicarbazides 5-8 was
clear evidence for the formation of the 1,2,4-triazole moiety. Moreover, a new signal
related to the NH group at 13.53–13.54 ppm appeared in compounds 9-12 confirming
their presence in the thione form. The 13C NMR spectrum of compounds 9-12 clearly
showed the disappearance of the C ¼ O group and the appearance of the C ¼ N and
C ¼ S signals assignable to the 1,2,4-triazole ring.
1
The H NMR analysis revealed the disappearance of the signals related to the two
NH groups at 9.07–9.64 ppm of the corresponding thiosemicarbazides. Moreover, the
1H NMR spectra of compounds 13-16 showed the NH protons of the 2-amino groups

8
Ali et al.
Table 3
MIC Test Results for Selected Compounds
Gram-
Gram-
positive
negative
organismsa
organismsb
Fungic
Compounds
Bs
Sp
Ec
Pa
Ca
Gc
24
62.5
1.95
3.9
–
Sr
Af
7
13
14
16
0.49
0.98
3.9
0.12
0.007
–
0.98
1.95
1.95
0.98
0.24
–
7.81
0.24
3.9
0.49
–
125
125
3.9
62.5
–
NA
NA
7.81
7.81
–
15.63
15.63
31.25
3.9
7.81
7.81
0.98
1.95
–
Ampicillin
Gentamicin
Amphotericin B
–
3.9
–
15.6
–
–
–
–
–
–
–
0.12
0.015
3.9
0.24
aGram-positive bacteria: Bacillus subtilis (Bs), Streptococcus pneumonia (Sp).
bGram-negative bacteria: Escherichia coli (Ec), Pseudomonas aeuroginosa (Pa).
cYeasts: Candida albicans (Ca), Geotrichum candidum (Gc), Syncephalastrum racemosum (Sr),
Aspergillus fumigatus (Af).
of the 1,3,4-thiadiazole rings between 7.54–7.57 ppm for the methyl, ethyl and cyclo-
hexyl derivatives and at 10.50 ppm for the phenyl derivative. The 13C NMR experiment
indicated the disappearance of the signals related to the C ¼ O and C ¼ S groups and
new signals indicated the formation of the new aromatic C ¼ N at 157.7–169.1 ppm.
1
The H NMR analysis of compound 17 showed the disappearance of the signals
related to the three NH groups at 9.56 and 9.86 ppm of the corresponding phenyl thiose-
micarbazide 5. Only one NH appeared at 10.33 ppm related to the 2-NH-phenyl of the
amino group. All other protons appeared at their expected chemical shifts. The 13C
NMR spectrum of 17 indicated the appearance of the 1,3,4-oxadiazole’s aromatic
C ¼ N at 159.6 and 159.8 ppm. The dept-135 revealed all the aliphatic and aromatic CH
carbons at their expected chemical shifts.
1
In the H NMR spectrum of compound 18, a new –NH signal derived from 5-{3-
[(N-p-fluorobenzylindol-3-yl]}propyl-1,3,4-oxadiazole-2-thione was observed at
12.03 ppm as the major product. Moreover, a small amount of the second isomer (5-
[(N-p-fluorobenzyl indol-3-yl] propyl-1,3,4-oxadiazole-2-thiol) was observed and con-
firmed through the appearance of the SH signal at 14.31 ppm. On the other hand, the
NH2 and the NH signals of the acid hydrazide 4 at 4.17 and 8.96 ppm had vanished.
Additionally, the 13C NMR spectrum showed a signal at 175.2 ppm related to the C ¼ S
which confirmed the formation of the major thione isomer. Table 1 summarizes the
yields for compounds 3-18.
In preliminary studies, compounds 4-16 were examined in vitro for their antibacter-
ial activity against the following pathogenic bacterial strains: Gram negative bacteria
(Escherichia coli, P. aeruginosa) and Gram positive bacteria (Bacillus subtilis, S. pneu-
monia); results were obtained using Mueller-Hinton agar medium by the agar diffusion
method.27,28 Results summarized in Table 2 showed that compounds 7, 13, 14 and 16
exhibited potential anti-bacterial activity against Escherichia coli compared to
Gentamicin. Moreover, compound 14 also showed good anti-P. aeruginosa activity
compared to Gentamicin. In addition, compounds 7 and 16 showed good anti-bacterial
activity against the Gram positive S. pneumonia compared to Ampicillin. Compounds

Novel 1,2,4-Triazoles, 1,3,4-Thiadiazoles, and 1,3,4-Oxadiazoles
9
4-16 were also studied for their antifungal activity compared to Amphotericin B against
the following fungi: Candida albicans (RCMB 05036), Geotricum candidum (RCMB
05097), Syncephalastrum racemosum (RCMB 05922) and Aspergillus fumigates
(RCMB 02568); again, we used the Mueller-Hinton agar medium. Results are summar-
ized in Table 2. The study showed that compounds 4, 13 and 16 exhibited remarkable
anti-fungi against Syncephalastrum racemosum fungus compared to Amphotericin B.
Moreover, compound 14 has an activity close to its reference against A. fumigatus.
Evaluated compounds that showed promising antimicrobial and anti-fungal results
were further tested for their minimum inhibitory concentration (MIC). Results are sum-
marized in Table 3. The compounds 13 and 16 exhibited excellent results, where their
MIC was found to be lower than the corresponding reference. On the other hand, com-
pound 14 showed a close MIC value to that of Gentamicin against E. coli, and it gave a
lower MIC value against P. aeruginosa. Compound 16 showed a good MIC against the
Syncephalastrum racemosum fungus compared to Amphotericin B. Given these encour-
aging results, further studies, including evaluation of toxicity, will be justified.
Summing up, a novel group of heterocycles, including 1,2,4-triazoles, 1,3,4-thiadia-
zoles and 1,3,4-oxadiazoles incorporating the indole moiety were synthesized and char-
acterized. The activities of the synthesized compounds exhibited moderate to high
antibacterial and antifungal activities compared to reference drugs.
Experimental Section
All chemicals and solvents were reagent-grade and were used without further purifica-
tion unless otherwise stated. Indol-3-butyric acid was purchased from Sigma-Aldrich,
hydrazine hydrate (100%) was purchased from Fluka. Melting points were determined
1
on an electrothermal apparatus and were uncorrected. H, 13C and 19F NMR spectra
were recorded on a Brucker 400 and 600 MHz spectrometer. Mass spectra were meas-
ured using a Shimadzu GC/MS-QP5050A spectrometer. Elemental analyses were per-
formed using an Elementar Analyses System GmbH-Vario EL III Element
Analyzer (Germany).
p-Fluorobenzyl {4-[(N-p-fluorobenzyl)indol-3-yl]} butyrate (3)
To a solution of ethyl (indol-3-yl) butyrate 1 (4.0 mmol, 0.92 g) in DCM (25 mL),
NaOH (50%, 80 mL) and tetrabutylammonium bromide (0.77 mmol, 0.25 g) were added
p-fluorobenzyl chloride (4.4 mmol, 0.63 g). The mixture was heated overnight at 40ꢁC.
After consumption of the starting material shown using TLC (silica gel, ethyl acetate-
hexane 1:4), the reaction mixture was extracted with DCM, dried over Na2SO4 and the
product was obtained as oil; yield 79% (mixture of ethyl ester, p-fluorobenzyl ester)
1
which was confirmed by H NMR. The mixture of esters was used for the next step
without further purification. The p-fluorobenzyl [(N-p-fluoro benzyl)indol-3-yl] butyrate
3 was successfully separated using flash chromatography and characterized using
1
600 MHz NMR as illustrated in the following: H NMR (600 MHz, CDCl3, d ppm):
6.88–7.61 (m, 9H, ArH), 5.24 (s, 2H, OCH2Ar), 5.08 (s, 2H, NCH2Ar), 2.82 (t, 2H,
CH2CH2CO, J ¼ 12.0 Hz), 2.44 (t, 2H, ArCH2CH2, J ¼ 12.0 Hz), 2.08 (pent, 2H,
CH2CH2CH2, J ¼ 6.0 Hz); 13C NMR (150 MHz, CDCl3, d ppm) 173.47 (C ¼ O),
163.5, 163.0, 161.8, 161.4, 136.6, 133.5, 133.5, 132.0, 132.0, 130.3, 130.3, 128.5,
128.4, 128.2, 125.6, 121.9, 119.2, 119.1, 115.7, 115.6, 115.6, 115.4, 115.0, 109.6 (Ar-

10
Ali et al.
C, C¼N), 65.4 (ArCH2O), 49.2 (ArCH2N), 33.9 (COCH2CH2), 25.5 (CH2CH2Ar),
24.5 (CH2CH2CH2); 19F NMR (377 MHz, CDCl3, d ppm) ꢀ115.4.
Anal. Calcd for C26H23F2NO2: C, 74.45; H, 5.53; N, 3.34. Found: C, 74.27; H,
5.46; N, 3.51.
{4-[(N-p-Fluorobenzylindol-3-yl]}butyric acid hydrazide (4)
A mixture of compound 3 (10 mmol, 3.11 g) and hydrazine hydrate (100%) (10 mmol,
0.50 g) in ethanol (25 mL) was refluxed overnight. After the consumption of the starting
material using TLC (silica gel, ethyl acetate-hexane 1:1), the reaction mixture was
cooled to room temperature, the precipitate was filtered, and the product was recrystal-
1
lized from ethanol. Yield 97%, m.p. 142–144ꢁC. H NMR (400 MHz, DMSO-d6, d
ppm): 8.96 (s, 1H, NH), 6.98–7.53 (m, 9H, ArH), 5.34 (s, 2H, NCH2Ar), 4.17 (s, 2H,
NH2), 2.66 (t, 2H, CH2CH2CO, J ¼ 8.0 Hz), 2.10 (t, 2H, ArCH2CH2, J ¼ 8.0 Hz),
1.87 (pent, 2H, CH2CH2CH2, J ¼ 8.0 Hz); 13C NMR (100 MHz, DMSO-d6, d ppm)
171.6 (C ¼ O), 162.5, 160.1, 136.0, 134.7, 134.6, 129.0, 129.0, 127.8, 126.0, 121.2,
118.7, 118.5, 115.3, 115.1, 114.2, 109.9 (Ar-C, C¼N), 48.1 (ArCH2N), 33.3
(COCH2CH2), 26.0 (CH2CH2Ar), 24.2 (CH2CH2CH2), 19F NMR (377 MHz, DMSO-
d6, d ppm) ꢀ115.5; mass: m/z 326.3 (M þ 1)þ.
Anal. Calcd for C19H20FN3O: C, 70.13; H, 6.20; N, 12.91. Found: C, 70.30; H,
6.28; N, 12.77.
General Method for the Synthesis of Acid Thiosemicarbazides 5-8
A mixture of compound 4 (10 mmol, 3.1 g) and the appropriate isothiocyanate deriva-
tive (10 mmol) was refluxed in ethanol for 6 h. The reaction mixture was cooled and a
white solid was precipitated. The obtained precipitate was filtered and recrystallized
from ethanol to afford the desired product.
1-{4-[(N-p-Fluoro benzyl)indol-3-yl]}butyl-4-phenyl thiosemicarbazide (5)
1
Yield 98%, m.p. 159–161ꢁC. H NMR (400 MHz, DMSO-d6, d ppm): 9.22–9.98 (3H,
NH), 6.98–7.56 (m, 14H, ArH), 5.35 (s, 2H, NCH2Ar), 2.73 (t, 2H, CH2CH2CO,
J ¼ 8.0 Hz), 2.26 (t, 2H, ArCH2CH2, J ¼ 8.0 Hz), 1.92 (pent, 2H, CH2CH2CH2,
J ¼ 8.0 Hz); 13C NMR (100 MHz, DMSO-d6, d ppm) 162.5, 160.1, 139.1, 135.9, 134.7,
134.6, 129.1, 129.0, 128.0, 127.8, 126.1, 121.2, 118.8, 118.5, 115.4, 115.2, 114.2, 110.0
(Ar-C, C¼N, C¼S), 48.1 (ArCH2N), 33.2 (COCH2CH2), 25.4 (CH2CH2Ar), 24.1
(CH2CH2CH2), 19F NMR (377 MHz, DMSO-d6, d ppm) ꢀ115.4; mass: m/z
461.30 (M þ 1)þ.
Anal. Calcd for C26H25FN4OS: C, 67.80; H, 5.47; N, 12.16. Found: C, 67.62; H,
5.58; N, 12.28.
1-{4-[(N-p-Fluorobenzyl)indol-3-yl]}butyl-4-ethylthiosemicarbazide (6)
1
Yield 87%, m.p. 155–157ꢁC. H NMR (400 MHz, DMSO-d6, d ppm): 9.10–9.64 (4s,
2H, NH), 7.90 (t, 1H, CH2NHCS, J ¼ 4 Hz), 6.98–7.56 (m, 9H, ArH), 5.35 (s, 2H,

Novel 1,2,4-Triazoles, 1,3,4-Thiadiazoles, and 1,3,4-Oxadiazoles
11
NCH2Ar), 3.43 (q, 2H, NCH2CH3, J ¼ 8.0 Hz), 2.71 (t, 2H, CH2CH2CO, J ¼ 8.0 Hz),
2.21 (t, 2H, ArCH2CH2, J ¼ 8.0 Hz), 1.89 (pent, 2H, CH2CH2CH2, J ¼ 8.0 Hz), 1.04 (t,
3H, CH2CH3, J ¼ 8.0 Hz); 13C NMR (100 MHz, DMSO-d6, d ppm) 172.0 (C5O),
162.5, 160.1, 135.9, 134.7, 134.6, 129.1, 129.0, 127.8, 126.1, 121.2, 118.8, 118.5,
115.4, 115.2, 114.2, 110.0 (Ar-C, C¼N), 48.1 (ArCH2N), 38.3 (CH3CH2N), 33.1
(COCH2CH2), 25.4 (CH2CH2Ar), 24.1 (CH2CH2CH2), 14.5 (CH2CH3), 19F NMR
(377 MHz, DMSO-d6, d ppm) ꢀ115.4; mass: m/z 413.45 (M þ 1)þ.
Anal. Calcd for C22H25FN4O: C, 64.05; H, 6.11; N, 13.58. Found: C, 63.87; H,
6.35; N, 13.44.
1-{4-[(N-p-Fluorobenzyl)indol-3-yl]}butyl-4-methylthiosemicarbazide (7)
1
Yield 87%, m.p. 156–158ꢁC. H NMR (400 MHz, DMSO-d6, d ppm): 9.64 (brs, 1H,
CONH), 9.17 (brs, 1H, CSNHNH), 7.87 (brs, 1H, CSNHCH3), 7.00–7.56 (m, 9H,
ArH), 5.35 (s, 2H, NCH2Ar), 2.85 (d, 3H, NHCH3, J ¼ 4.0 Hz), 2.71 (t, 2H,
CH2CH2CO, J ¼ 8.0 Hz), 2.21 (t, 2H, ArCH2CH2, J ¼ 8.0 Hz), 1.89 (pent, 2H,
CH2CH2CH2, J ¼ 8.0 Hz); 13C NMR (100 MHz, DMSO-d6, d ppm) 182.2 (C ¼ S),
172.1 (C ¼ O), 162.6, 160.2, 136.0, 134.7, 129. 1, 129.0, 127.8, 126.1, 121.3, 118.8,
118.6, 115.4, 115. 2, 114.3, 110.0 (Ar-C, C¼N), 48.1 (ArCH2N), 33.2 (CH3NH), 30.9
(CH2CH2CO), 25.4 (ArCH2CH2), 24.2 (CH2CH2CH2), 19F NMR (377 MHz, DMSO-
d6, d ppm) ꢀ115.4; mass: m/z 398.50 (M)þ.
Anal. Calcd for C21H23FN4OS: C, 63.29; H, 5.82; N, 14.06. Found: C, 63.46; H,
6.06; N, 13.82.
1-{4-[(N-p-Fluoro benzyl)indol-3-yl]}butyl-4-cyclohexylthiosemicarbazide (8)
1
Yield 77%, m.p. 147–149ꢁC. H NMR (400 MHz, DMSO-d6, d ppm): 8.96–9.61 (4s,
2H, NH), 7.55 (d,1H, CSNHC6H11., J ¼ 8.0 Hz), 6.99-7.41 (m, 9H, ArH), 5.34 (s, 2H,
NCH2Ar), 4.05 (d, 1H, NCH, J ¼ 8.0 Hz), 2.72 (t, 2H, CH2CH2CO, J ¼ 8.0 Hz), 2.23
(t, 2H, ArCH2CH2, J ¼ 8.0 Hz), 1.89 (pent, 2H, CH2CH2CH2, J ¼ 8.0 Hz), 1.05–1.26
(m, 10H, 5xCH2); 13C NMR (100 MHz, DMSO-d6, d ppm) 176.6 (C ¼ S), 171.9
(C ¼ O), 162.5, 160.1, 135.5, 134.6, 134.6, 129.0, 129.0, 127.8, 121.2, 118.8, 118.5,
115.3, 115.1, 114.2, 109.9 (Ar-C, C¼N), 52.7 (CHNH (C6H11)), 48.1 (ArCH2N), 33.1
(CH2CH2CO), 31.9 (ArCH2CH2), 25.5, 25.1, 24.8, 24.1 (6xCH2), 19F NMR (377 MHz,
DMSO-d6, d ppm) ꢀ115.4; mass: m/z 644.20 (M)þ.
Anal. Calcd for C26H31FN4OS: C, 66.92; H, 6.70; N, 12.01. Found: C, 66.68; H,
6.51; N, 11.87.
General Method for the Synthesis of Compounds 9-12
A solution of the respective thiosemicarbazides 5-8 (10 mmol) in a mixture of NaOH
(2N) (100 mL) was refluxed for 8 h. After the consumption of the starting material as
indicated by TLC (silica gel, ethyl acetate-hexane 2:1), the hot reaction mixture was fil-
tered and the solution was cooled to room temperature and then acidified with conc.
HCl. The formed precipitate was filtered, washed with water and recrystallized from
ethanol to afford the desired 1,2,4-triazoles 9-12.

12
Ali et al.
4-Phenyl-5-{3-[(N-p-fluorobenzyl)indol-3-yl]}propyl-1,2,4-triazole-3-thione (9)
1
Yield 84%, m.p. 67–69ꢁC. H NMR (400 MHz, DMSO-d6, d ppm): 6.96–7.48 (m, 14H,
ArH), 5.30 (s, 2H, NCH2), 2.64 (t, 2H, CH2CH2C ¼ N, J ¼ 8.0 Hz), 2.47 (t, 2H,
ArCH2CH2, J ¼ 8.0 Hz), 1.83 (pent, 2H, CH2CH2CH2, J ¼ 8.0 Hz); 13C NMR (100 MHz,
DMSO-d6, d ppm): 162.5, 160.1, 151.9, 135.9, 134.6, 134.2, 129.2, 129. 0, 128.9, 128.2,
127.6, 126.0, 121.2, 118.6, 118.5, 115.34, 115.1, 113.6, 109.9 (Ar-C, C¼N, C¼S), 48. 0
(ArCH2N), 25.9 (CH2CH2C ¼ N), 25.0 (ArCH2CH2), 23.7 (CH2CH2CH2), 19F NMR
(377 MHz, DMSO-d6, d ppm) ꢀ115.4; mass: m/z 443.10 (M þ 1)þ.
Anal. Calcd for C26H23FN4S: C, 70.56; H, 5.24; N, 12.66. Found: C, 70.43; H,
5.06; N, 12.51.
4-Ethyl-5-{3-[(N-p-fluoro benzyl)indol-3-yl]}propyl-1,2,4-triazole-3-thione (10)
1
Yield 87%, m.p. 158–160ꢁC. H NMR (400 MHz, DMSO-d6, d ppm): 13.54 (s, 1H,
NH), 6.98–7.55 (m, 9H, ArH), 5.34 (s, 2H, NCH2), 3.90 (q, 2H, CH3CH2NH,
J ¼ 8.0 Hz), 2.81 (t, 2H, CH2CH2C ¼ N J ¼ 8.0 Hz), 2.73 (t, 2H, ArCH2CH2,
J ¼ 8.0 Hz), 2.05 (pent, 2H,CH2CH2CH2, J ¼ 8.0 Hz) 1.13 (t, 3H, CH2CH3, J ¼ 8.0 Hz);
13C NMR (100 MHz, DMSO-d6, d ppm): 165.9, 162.5, 160.1, 151.9, 136.0, 134.6,
134.6, 129.0, 129.0, 127.7, 126.1, 121.3, 118.7, 118.6, 115.3, 115.1, 113.8, 110. 0 (Ar-
C, C¼N, C¼S), 48.1 (ArCH2N), 37.9 (CH3CH2N), 26.1 (CH2CH2C ¼ N), 24.1
(ArCH2CH2), 23.8 (CH2CH2CH2), 13.3 (CH2CH3), 19F NMR (377 MHz, DMSO-d6, d
ppm) ꢀ115.4; mass: m/z 395.40 (M þ 1)þ.
Anal. Calcd for C22H23FN4S: C, 66.98; H, 5.88; N, 14.20. Found: C, 66.76; H,
5.91; N, 14.41.
4-Methyl-5-{3-[(N-p-fluorobenzyl)indol-3-yl]}propyl-1,2,4-triazole-3-thione (11)
1
Yield 90%, m.p. 166–168ꢁC. H NMR (400 MHz, DMSO-d6, d ppm): 13.53 (brs, 1H,
NH), 7.00–7.57 (m, 9H, ArH), 5.34 (s, 2H, NCH2Ar), 3.38 (s, 3H, CH3N), 2.79 (t, 2H,
CH2CH2C ¼ N, J ¼ 8.0 Hz), 2.70 (t, 2H, ArCH2CH2, J ¼ 8.0 Hz), 2.02 (pent,
2H,CH2CH2CH2, J ¼ 8.0 Hz); 13C NMR (100 MHz, DMSO-d6, d ppm): 166.5, 162.5,
160.1, 152.5, 136.0, 134.6, 129.0, 128.95, 127.7, 126.2, 121.3, 118.7, 118.6, 115.3,
115.1, 113.8, 110.0 (Ar-C, C¼N, C¼S), 48.1 (ArCH2N), 29.6 (CH3N), 25.8
(CH2CH2C ¼ N), 24.4 (ArCH2CH2), 23.8 (CH2CH2CH2), 19F NMR (377 MHz,
DMSO-d6, d ppm) ꢀ115.4; mass: m/z 380.20 (M)þ.
Anal. Calcd for C21H21FN4S: C, 66.29; H, 5.56; N, 14.73. Found: C, 66.48; H,
5.85; N, 14.86.
4-Cyclohexyl-5-{3-[(N-p-fluoro benzyl)indol-3-yl]}propyl-1,2,4-triazole-3-thione (12)
1
Yield 86%, m.p. 128–130ꢁC. H NMR (400 MHz, DMSO-d6, d ppm): 6.98–7.56 (m,
9H, ArH), 5.35 (s, 2H, NCH2), 4.40 (brs, 1H,CHNH), 2.83 (t, 2H, CH2CH2C ¼ N,
J ¼ 8.0 Hz), 2.77 (t, 2H, ArCH2CH2, J ¼ 8.0 Hz), 2.02 (pent, 2H,CH2CH2CH2,
J ¼ 8.0 Hz), 0.95–1.23 (m,10H, 5xCH2); 13C NMR (100 MHz, DMSO-d6, d ppm):
165.9, 162.5, 160.1, 151.9, 136.0, 134.6, 134.6, 129.0, 129.0, 127.7, 126.3, 121.3,
118.7, 118.6, 115.3, 115.1, 113.7, 110.0 (Ar-C, C¼N, C¼S), 55.0 (CHN (C6H11)),

Novel 1,2,4-Triazoles, 1,3,4-Thiadiazoles, and 1,3,4-Oxadiazoles
13
48.1 (ArCH2N), 29.2 (CH2CH2C ¼ N), 27.0 (ArCH2CH2), 25.4, 25.2, 24.4, 23.7 (6 x
CH2), 19F NMR (377 MHz, DMSO-d6, d ppm) ꢀ115.4; mass: m/z 449.35 (M þ 1)þ.
Anal. Calcd for C26H29FN4S: C, 69.61; H, 6.52; N, 12.49. Found: C, 69.97; H,
6.70; N, 12.27.
General Method for the Synthesis of Compounds 13-16
A mixture of the respective thiosemicarbazide 5-8 (10 mmol) in cold concentrated sul-
furic acid (20 mL) was stirred for 30 min at 0ꢁC. Then, the mixture was stirred over-
night at room temperature. The solution was poured into ice-cold water to form a
precipitate which was filtered and recrystallized from ethanol to afford the desired
1,3,4-thiadiazoles 13-16.
5-{3-[(N-p-Fluorobenzyl)indol-3-yl]}propyl-2-(N-phenylamino)-1,3,4-thiadiazole (13)
1
Yield 87%, m.p. 158–160ꢁC. H NMR (400 MHz, DMSO-d6, d ppm): 10.50 (brs,1H,
NH), 7.00–7.58 (m, 14H, ArH), 5.35 (s, 2H, NCH2Ar), 2.98 (t, 2H, CH2CH2C ¼ N,
J ¼ 8.0 Hz), 2.79 (t, 2H, ArCH2CH2, J ¼ 8.0 Hz), 2.06 (pent, 2H,CH2CH2CH2,
J ¼ 8.0 Hz); 13C NMR (100 MHz, DMSO-d6, d ppm): 163.9, 162.5, 160.1, 141.6, 140.7,
136.0, 134.6, 129.1, 129.0, 127.7, 126.6, 126.3, 121.2, 118.7, 118.6, 116.3, 115.3,
115.1, 113.7, 110.0 (Ar-C, C¼N, C¼S),), 48.1 (ArCH2N), 29.7 (CH2CH2C ¼ N), 29.0
(ArCH2CH2), 23.8 (CH2CH2CH2), 19F NMR (377 MHz, DMSO-d6, d ppm) ꢀ115.4;
mass: m/z 443.30 (M þ 1)þ.
Anal. Calcd for C26H23FN4S: C, 70.56; H, 5.24; N, 12.66. Found: C, 70.31; H,
5.05; N, 12.89.
5-{3-[(N-p-Fluorobenzyl)indol-3-yl]}propyl-2-(N-ethylamino)-1,3,4-thiadiazole (14)
1
Yield 87%, m.p. 138–140ꢁC. H NMR (400 MHz, DMSO-d6, d ppm): 6.98–7.57 (m,
10H, NH and ArH), 5.35 (s, 2H, NCH2Ar), 3.24 (pent, 2H, NHCH2CH3, J ¼ 8 Hz), 2.86
(t, 2H, CH2CH2C ¼ N, J ¼ 8 Hz), 2.75 (t, 2H, ArCH2CH2, J ¼ 8 Hz), 2.06 (pent,
2H,CH2CH2CH2, J ¼ 8 Hz) 1.15 (t, 3H, CH2CH3, J ¼ 8 Hz); 13C NMR (100 MHz,
DMSO-d6, d ppm): 168.1, 162.5, 160.1, 157.5, 135.9, 134.7, 134.6, 129.0, 129.0, 127.7,
126.2, 121.2, 118.7, 118.5, 115.3, 115.1, 113.8, 110.0 (Ar-C, C¼N), 48.1 (ArCH2N),
39.4 (NHCH2CH3), 29.8 (CH2CH2C ¼ N), 29.2 (ArCH2CH2), 23.8 (CH2CH2CH2), 14.3
(CH2CH3), 19F NMR (377 MHz, DMSO-d6, d ppm) ꢀ115.4; mass: m/z 394.40 (M)þ.
Anal. Calcd for C22H23FN4S: C, 66.98; H, 5.88; N, 14.20. Found: C, 67.18; H,
5.91; N, 13.96.
5-{3-[(N-p-Fluorobenzyl)indol-3-yl]}propyl-2-(N-methylamino)-1,3,4-thiadiazole (15)
1
Yield 89%, m.p. 135–137ꢁC. H NMR (400 MHz, DMSO-d6, d ppm): 6.98–7.54 (m,
10H, NH and ArH), 5.35 (s, 2H, NCH2Ar), 2.83–2.88 (m, 5H, NHCH3 and
CH2CH2C ¼ N), 2.75 (t, 2H, ArCH2CH2, J ¼ 8.0 Hz), 1.98 (pent, 2H,CH2CH2CH2,
J ¼ 8.0 Hz); 13C NMR (100 MHz, DMSO-d6, d ppm): 169.1, 162.5, 160.1, 157.7, 135.9,
134.7, 134.6, 129.0, 129.0, 127.7, 126.2, 121.2, 118.7, 118.5, 115.3, 115.1, 113.8, 110.0

14
Ali et al.
(Ar-C, C¼N, C¼S), 48.1 (ArCH2N), 31.1 (NHCH3), 29.8 (CH2CH2C ¼ N), 29.2
(ArCH2CH2), 23.8 (CH2CH2CH2), 19F NMR (377 MHz, DMSO-d6, d ppm) ꢀ115.4;
mass: m/z 381.85 (M þ 1)þ.
Anal. Calcd for C21H21FN4S: C, 66.29; H, 5.56; N, 14.73. Found: C, 66.07; H,
5.44; N, 14.92.
5-{3-[(N-p-Fluorobenzyl)indol-3-yl]}propyl-2-(N-cyclohexylamino)-1,3,4-
thiadiazole (16)
1
Yield 86%, m.p. 128–130ꢁC. H-NMR (400 MHz, DMSO-d6, d ppm): 6.98–7.54 (m,
10H, NH and ArH), 5.35 (s, 2H, NCH2Ar), 3.44 (brs, 1H, NHCH), 2.85 (t, 2H,
CH2CH2C ¼ N, J ¼ 8.0 Hz), 2.76 (t, 2H, ArCH2CH2, J ¼ 8.0 Hz), 1.17–2.00 (m, 12H,
6x CH2); 13C-NMR (100 MHz, DMSO-d6, d ppm): 167.4, 157.2, 136.0, 134.7, 129.0,
129.0, 127.7, 126.2, 121.2, 118.7, 118.5, 115.3, 115.1, 113.8, 110.0 (Ar-C, C¼N,
C¼S), 53.5 (NHCH), 48.1 (ArCH2N), 32.1 (CH2CH2C ¼ N), 29.8 (ArCH2CH2), 29.2,
25.2, 24.3, 23.8 (6xCH2), 19F NMR (377 MHz, DMSO-d6, d ppm) ꢀ115.5; mass: m/z
449.40 (M þ 1)þ.
Anal. Calcd for C26H29FN4S: C, 69.61; H, 6.52; N, 12.49. Found: C, 69.42; H,
6.77; N, 12.23.
5-[(N-p-Fluorobenzyl)indol-3-yl] propyl-2-(N-phenylamino)-1,3,4-oxadiazole (17)
To a mixture of the respective thiosemicarbazide 5 (10 mmol, 4.60 gm) in ethanol
(20 mL) was added (5N) NaOH solution until the thiosemicarbazide completely dis-
solved. A 5% solution of I2/KI was added dropwise until the iodine color persisted. The
reaction mixture was heated under reflux overnight, the mixture was cooled to room
temperature, the precipitate was filtered, and the product was recrystallized
from ethanol.
1
Yield 65%, m.p. 135–137ꢁC. H NMR (400 MHz, DMSO-d6, d ppm):10.50 (s, 1H,
NH) 7.58–7.00 (m, 14H, ArH), 5.35 (s, 2H, NCH2Ar), 2.98 (t, 2H, CH2CH2C ¼ N,
J ¼ 8.0 Hz), 2.79 (t, 2H, ArCH2CH2, J ¼ 8.0 Hz), 2.06 (pent, 2H,CH2CH2CH2,
J ¼ 8.0 Hz); 13C NMR (100 MHz, DMSO-d6, d ppm): 163.9, 162.5, 160.1, 141.6, 140.7,
136.0, 134.60, 129.1, 129.0, 127.70, 126.6, 126.3, 121.2, 118.7, 118.6, 116.3, 115.3,
115.1, 113.7, 110.0 (Ar-C, C¼N), 48.1 (ArCH2N), 29.7 (CH2CH2C ¼ N), 29.0
(ArCH2CH2), 23.8 (CH2CH2CH2), 19F NMR (377 MHz, DMSO-d6, d ppm) ꢀ115.4;
mass: m/z 426.35 (M)þ.
Anal. Calcd for C26H23FN4O: C, 73.22; H, 5.44; N, 13.14. Found: C, 73.48; H,
5.17; N, 12.96.
{3-[(N-p-Fluorobenzyl indol-3-yl]}propyl-1,3,4-oxadiazole-2-thione (18)
Carbon disulfide (Safety Note: Carbon disulfide is a highly toxic, flammable, colorless,
volatile liquid. All workers must be thoroughly trained in its safe use before undertak-
ing experiments, including the proper protective gear (safety glasses, gloves, clothing),
adequate ventilation and procedures in the event of fire.) (15 mmol, 1.15 g) was added
dropwise to a solution of compound 4 (10 mmol, 3.11 g) in absolute ethanol (30 mL)
containing potassium hydroxide (15 mmol, 0.84 g). The reaction mixture was refluxed

Novel 1,2,4-Triazoles, 1,3,4-Thiadiazoles, and 1,3,4-Oxadiazoles
15
for 18 hrs. After the consumption of the starting material was confirmed using TLC (sil-
ica gel, ethyl acetate-hexane 2:1), the reaction mixture was extracted with ethyl acetate,
dried over Na2SO4, and the product was precipitated using hexane/DCM. Yield 65%,
1
m.p.136–138ꢁC. H NMR (600 MHz, DMSO-d6, d ppm): 12.03 (s, 1H, NH), 6.99–7.54
(m, 9H, ArH), 5.36 (s, 2H, NCH2Ar), 2.71 (t, 2H, CH2CH2C ¼ N, J ¼ 4.0 Hz), 2.28 (t,
2H, ArCH2CH2, J ¼ 4.0 Hz), 1.88 (pent, 2H,CH2CH2CH2, J ¼ 4.0 Hz); 13C NMR
(150 MHz, DMSO-d6, d ppm): 175.2 (C5S), 162.9, 161.3, 161.2, 159.5, 136.7, 135.4,
129.7, 129.7, 128.5, 126.8, 121.9, 119.4, 119.2, 116.0, 115.9, 114.8, 110.7 (Ar-C,
C¼N), 48.9 (ArCH2N), 34.0 (CH2CH2C ¼ N), 26.0 (ArCH2CH2), 24.3 (CH2CH2CH2),
19F NMR (566 MHz, DMSO-d6, d ppm) ꢀ115.4; mass: m/z 368.30 (M þ 1)þ.
Anal. Calcd for C20H18FN3OS: C, 65.38; H, 4.94; N, 11.44. Found: C, 65.11; H,
4.71; N, 11.62.
Antimicrobial Susceptibility Testing
The clinical isolates tested in this study were obtained from the culture collection main-
tained at the RCMB (Regional Center for Mycology and Biotechnology), Al Azhar
University, Cairo, Egypt. All compounds were tested in vitro for their antibacterial
activity against the following clinical bacterial strains: Gram negative bacteria,
Escherichia coli (RCMB 010052), Pseudomonas aeruginosa (RCMB 010043), and
Gram positive bacteria, Streptococcus pneumonia (RCMB 010010), Bacillus subtilis
(RCMB 010067), by the agar diffusion method27,28 using Muller-Hinton agar medium
€
for bacteria.
Antimicrobial susceptibility testing was performed by the agar disc-diffusion
method. Sterile filter paper discs (8 mm diameter) were moistened with the compound
(solution in dimethylsulfoxide of specific concentration). Forty lL of the solution con-
taining 200 lg of test compound or reference drug (amphotericin B, gentamicin or
ampicillin trihydrate) was loaded onto filter paper discs. Solvent was evaporated and
discs were transferred to the inoculated plates. That is, loaded discs were carefully
€
placed on Muller-Hinton for bacteria and Sabouraud’s agar for fungi that had previ-
ously been inoculated with the test microorganisms. The plates were incubated at 37ꢁC
for bacteria and 28ꢁC for fungi, diameters of the growth inhibition zones were measured
after 24 hours in the case of bacteria and after 48–96 hours in the case of fungi. The
antimicrobial activity was evaluated by measuring the zones of inhibition against the
tested organisms and compared with those of the standards. Antimicrobial activities
were expressed as the inhibition diameter zones in millimeters (mm) and are presented
in Tables 2 and 3. Each experiment was carried out in triplicate and the average zone
of inhibition was calculated.
Moreover, compounds 4–16 were also subjected to in vitro testing of antifungal
activity against the following four clinical fungal strains: Aspergillus fumigatus (RCMB
02568), Syncephalastrum racemosum (RCMB 05922), Geotricum candidum (RCMB
05097), and Candida albicans (RCMB 05036) the by agar diffusion method27,28 using
Sabouraud’s agar medium for fungi.
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