Design, Synthesis, SAR and Molecular Modeling Studies of Novel Imidazo[2,1-b][1,3,4]Thiadiazole Derivatives as Highly Potent Antimicrobial Agents

Article abstract of DOI:10.1002/minf.201700083

In this study, a novel series of phenyl substituted imidazo[2,1-b][1,3,4]thiadiazole derivatives were synthesized, characterized and explored for antibacterial activity against Gram-negative Escherichia coli, Gram-positive Staphylococcus aureus and Bacillus subtilis and antifungal activity against Candida albicans. Most of the synthesized compounds exhibited remarkable antimicrobial activities, some of which being ten times more potent than positive controls. The most promising compound showed excellent activity with MIC value of 0.03 μg/ml against both S. aureus and B. subtilis (MIC values of positive compound Chloramphenicol are 0.4 μg/ml and 0.85 μg/ml, respectively). Furthermore, structure-activity relationship was also investigated with the help of computational tools. Some physicochemical and ADME properties of the compounds were calculated too. The combination of electronic structure calculations performed at PM6 level and molecular docking simulations using Glide extra-precision mode showed that the hydrophobic nature of keto aryl ring with no electron withdrawing substituents at para position enhances activity while electron-donating substituents at the second aryl ring is detrimental to activity.

Full text of DOI:10.1002/minf.201700083

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DOI: 10.1002/minf.201700083
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Design, Synthesis, SAR and Molecular Modeling Studies of
Novel Imidazo[2,1-b][1,3,4]Thiadiazole Derivatives as
Highly Potent Antimicrobial Agents
Hakan Tahtaci,*[a] Hatice Karacık,[a] Abdulilah Ece,*[b] Mustafa Er,[c] and Mine Gu¨l S¸eker[d]
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Abstract: In this study, a novel series of phenyl substituted 0.85 mg/ml, respectively).
imidazo[2,1-b][1,3,4]thiadiazole derivatives were synthe- Furthermore, structure-activity relationship was also inves-
sized, characterized and explored for antibacterial activity tigated with the help of computational tools. Some
against Gram-negative Escherichia coli, Gram-positive Staph- physicochemical and ADME properties of the compounds
ylococcus aureus and Bacillus subtilis and antifungal activity were calculated too. The combination of electronic structure
against Candida albicans.
calculations performed at PM6 level and molecular docking
Most of the synthesized compounds exhibited remarkable simulations using Glide extra-precision mode showed that
antimicrobial activities, some of which being ten times the hydrophobic nature of keto aryl ring with no electron
more potent than positive controls. The most promising withdrawing substituents at para position enhances activity
compound showed excellent activity with MIC value of while electron-donating substituents at the second aryl ring
0.03 mg/ml against both S. aureus and B. subtilis (MIC values is detrimental to activity.
of positive compound Chloramphenicol are 0.4 mg/ml and
Keywords: Imidazo[2,1-b][1,3,4]thiadiazole · Molecular Docking · Antimicrobial Activity · SAR · Electronic Structure Calculations.
28 1 Introduction
Besides being used as an anthelmintic drug, the fact
that these compounds are bio-isostere of Tetramisole and
its enantiomers Levamisole and Dexamisole[30,31] that are
used as regulating and strengthening elements for immune
system, has caused the anti-cancer activity studies to focus
on imidazo[2,1-b][1,3,4]thiadiazole derivatives.[32–38] It was
reported that, apart from their biological activities, imidazo
[2,1-b][1,3,4]thiadiazole and their heterocyclic derivatives
are also preferred in different industrial fields such as dye
production.[39] Therefore, imidazo[2,1-b][1,3,4]thiadiazole
and their derivatives have become important heterocyclic
29
30 There have been significant increases in the synthesis of
31 compounds having antimicrobial activities in recent years.[1]
32 However, the use of such compounds has been very limited
33 due to drug resistance, high toxicity, various side effects
34 and the deficiencies in biological activities. Medicinal
35 chemists, therefore, put great efforts to synthesize new
36 compounds having antimicrobial activities with minimum
37 side effects, which can be used as a precursor or lead
38 compound in the drug discovery.
39
Heterocyclic compounds are one of the most preferred
40 compounds in antimicrobial studies and many involve the
41 imidazole, 1,3,4-thiadiazole and their derivatives. Hence,
42 synthesis and characterization of such bioactive compounds
43 containing imidazole and 1,3,4-thiadiazole are being studied
44 intensely.[2–6] Furthermore, the synthesis of compounds
45 including these bioactive groups with various biological
46 activities is currently being studied.[7–9] These heterocyclic
47 systems where the imidazole and 1,3,4-thiadiazole rings are
48 fused with a bridgehead nitrogen atom are known as
49 imidazo[2,1-b][1,3,4]thiadiazoles.[10–12]
[a] H. Tahtaci, H. Karacık
Department of Polymer Engineering, Faculty of Technology, Kar-
abuk University, 78050 Karabuk, Turkey. Tel: +903704338374, Fax:
+903704338334
E-mail: hakantahtaci@karabuk.edu.tr
[b] A. Ece
Department of Pharmaceutical Chemistry, Faculty of Pharmacy,
Biruni University, 34010, Istanbul, Turkey. Tel: +902124151414,
Fax: +902124164646
E-mail: aece@biruni.edu.tr
[c] M. Er
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Owing to the fact that imidazo[2,1-b][1,3,4]thiadiazoles
Department of Chemical Engineering, Faculty of Engineering, Kar-
abuk University, 78050, Karabuk, Turkey.
[d] M. G. S¸eker
51 and their derivatives exhibit many biological activities such
52 as antimicrobial,[13,14] antifungal,[15] antibacterial,[16–18] anti-
53 inflammatory,[19–21] antituberculosis,[22–25] analgesic,[26] diu-
54 retic[27] activities, the synthesis of these compounds and
55 their derivatives increases gradually.[28,29]
Department of Molecular Biology and Genetics, Faculty of Science,
Gebze Technical University, 41400, Gebze, Turkey.
Supporting information for this article is available on the WWW
under https://doi.org/10.1002/minf.201700083
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compounds commonly studied in the pharmaceutical
chemistry and industry.
method employed to synthesize these compounds is given
in Scheme 1. Computational tools such as electronic
structure calculations and molecular docking studies were
also used to explain SAR of those compounds and
investigate their activities based on the binding interactions
with the receptor and their calculated molecular properties.
It is known that the most frequently used method in
synthesizing the imidazo[2,1-b][1,3,4]thiadiazole derivatives
is based on the reactions of 2-amino-1,3,4-thiadiazole
derivatives with 2-bromo acetophenone derivatives.[40,41]
The process of novel drug design also includes
computational applications. Molecular docking studies of
drug candidates are one of the important steps to enlighten
2 Material and Methods
10 ligand (candidate molecule)-receptor (target) interactions. A
11 relationship between a ligand’s activity and its interaction
12 with the target can provide useful information in future SAR
13 studies.[42]
2.1 Computational
2.1.1 Ligand Preparation
14
In the light of these aforementioned literature, the main
15 purpose of this study is to synthesize imidazo[2,1-b][1,3,4]
16 thiadiazole derivatives, to characterize those structures
17 using different spectroscopic methods, and to investigate
The 3D models of the compounds 5–28 and Chlorampheni-
col were prepared using the LigPrep[43] tool of the
[44]
¨
Schrodinger software with OPLS3 force field Ionization
18 the antimicrobial activities of all compounds. The synthetic
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Scheme 1. Synthetic route for the synthesis of substituted imidazo[2,1-b][1,3,4]thiadiazole derivatives (5–28).
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states at pH 7.0Æ2.0 as well as tautomers were generated
refined with the ShelXL[54] refinement package using Least
Squares minimization.
retaining up to 32 possible stereoisomers per ligand.
2.1.2 Protein Preparation
2.3 Chemistry
1
A high-resolution three-dimensional crystal structure of
enoyl-ACP reductase (FabI) in complexed with nicotinamide
cofactor (NAD+) and Triclosan (PDB id: 1C14) was down-
The H NMR and 13C NMR spectra of the compounds were
measured in DMSO-d6 using an Agilent NMR V NMRS
spectrometer at 400 MHz and 100 MHz, respectively. Chem-
ical shift values are given in ppm (d) relative to tetrame-
thylsilane (TMS) as internal standard. The IR spectra were
recorded in a Bruker Optics Alpha FT-IR in ATR. The mass
spectra were measured with a Thermo TSQ Quantum
Access Max LC-MS/MS spectrometer. Elemental analyses
were performed on a LECO 932 CHNS (Leco-932, St. Joseph,
MI, USA) instrument and the results were within Æ0.4% of
the theoretical values. Melting points were recorded on a
Thermo Scientific IA9000 series apparatus and were un-
corrected. X-Ray analysis was performed on a Bruker D8
QUEST instrument. All the chemicals, reagents and solvents
were purchased from Sigma-Aldrich (St. Louis, MO) and
used without further purification, unless mentioned other-
wise.
¨
10 loaded from the protein data bank. Schrodinger’s multi-step
11 Protein Preparation Wizard was used for the preparation of
12 the receptor site that was used as the target for molecular
13 docking. Charges and bond orders were assigned, hydro-
14 gens were added to the heavy atoms and chain B of the
15 protein and all waters were deleted.
16
Then, the hydrogen bonds were assigned and optimized
17 at neutral pH. Energy minimization was carried out using
18 default constraint of 0.3 A RMSD and OPLS3 force field.
19
20
21 2.1.3 Molecular Docking
22
23 The prepared Fab-NAD+ binary complex model was used
24 as the receptor model for docking simulations, which were
˚
25 performed using the Glide XP (extra precision) module of
[45–47]
¨
26 Schrodinger Suite.
Receptor grid has to be calculated
2.3.1 General Procedure for the Synthesis of
2-((5-Amino-1,3,4-thiadiazol-2-yl)thio)-1-(4-(un)
substitutedphenyl)ethanone (3 a–c)
27 to represent the binding pocket such that the ligand poses
28 bind within the active site during docking. Receptor Grid
29 was generated keeping the default parameters. A cubic box
30 of specific dimensions centered on the centroid of the
31 native ligand was generated for receptor.
32
Compounds 3a–c were synthesized according to a method
given in the literature.[55]
In a round-bottomed flask, 5-amino-1,3,4-thiadiazole-2-
thiol (1) (0.08 mol) and KOH (0.08 mol) were dissolved in
absolute ethanol. The solution was stirred for about 30
minutes at room temperature. 2-Bromoacetophenone de-
rivatives (0.08 mol) (2a–c) was dissolved in absolute ethanol
(25 mL) and added dropwise to this solution at room
temperature with the assistance of a dropping funnel. The
mixture was refluxed and stirred for 4–6 h. The progress of
reaction was monitored by TLC at appropriate time
intervals. After completion of the reaction, the mixture was
filtered and the solid matter was obtained. It was washed
with deionized water, ethanol and diethyl ether, respec-
tively. The solid was recrystallized from the appropriate
solvent. The physical properties and spectral data derived
from the obtained products are listed below.
33
34 2.1.4 Calculation of Physicochemical and ADME Properties
35
36 Highest molecular orbital (HOMO) energy values were
37 calculated using Wavefunction’s Spartan ‘16 parallel suite
38 (Spartan 16, Wavefunction Inc., Irvine CA). In calculations of
39 such descriptors, semi empirical PM6 method[48] was
40 reported to be of similar quality as DFT-based models,
41 which is much more expensive.[49] Thus, this level was
42 selected and the docked pose of each compound at neutral
43 form was used as equilibrium geometry. QikProp module of
44 Schrodinger was used to calculate molecular weight,
45 percent human oral absorption, polar surface area (PSA)
46 and logarithm of octanol-water partition coefficient (QPlog-
47 Po/w).[50]
2-((5-Amino-1,3,4-thiadiazol-2-yl)thio)-1-phenyletha-
none (3a)
48
49
Light gray solid, yield: 16.29 g (81%); mp: 176–1778C
(from DMF-EtOH, 1:4); 1H NMR (400 MHz, DMSO-d6) d
(ppm): 4.79 (s, 2H, ÀCH2), Phenyl-H [7.53 (t, J=16.0 Hz, 2H),
7.66 (t, J=16.0 Hz, 1H), 7.99 (d, J=8.0 Hz, 2H)], 7.28 (s, 2H,
NH2); 13C NMR (100 MHz, DMSO-d6, d ppm): 42.02 (ÀCH2),
Phenyl-C [128.94 (CH), 129.26 (CH), 134.19 (C), 135.61 (C)],
Thiadiazole-C [149.68 (C),170.27 (C)], 193.86 (C=O); IR (ATR,
cmÀ1): 3259, 3108 (ÀNH2), 3067 (ArÀCH), 2940 (Aliph. CH),
50 2.2 Crystallographic Analysis
51
52 X-ray diffraction data of compound 10 was collected with a
53 Bruker AXS APEX CCD[51] diffractometer using MoKa beam.
54 The crystal was kept at 293(2) K during data collection.
55 Using Olex2,[52] the structure was solved with the ShelXT[53]
56 structure solution program using Direct Methods and
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1693 (C=O), 1589 (C=N); MS: m/z 252.85 (M+1, 100); Anal.
Calcd. for C10H9N3OS2: C 47.79, H 3.61, N 16.72, found: C
47.71, H 3.59, N 16.77.
2-((5-Amino-1,3,4-thiadiazol-2-yl)thio)-1-(4-chlorophen-
yl)ethanone (3b)
129.80 (CH), 134.06 (C)], Imidazole-Phenyl-C [125.04 (CH),
129.04 (CH), 129.38 (CH), 133.72 (C)], Imidazole-C [110.99
(CH), 145.17 (C)], Thiadiazole-C [135.41 (C), 160.23 (C)],
193.05 (C=O); IR (ATR, cmÀ1): 3131 (ArÀCH), 2951 (Aliph. CH),
1686 (C=O), 1595 (C=N); MS: m/z 351.76 (M+, 100); Anal.
Calcd. for C18H13N3OS2: C 61.52, H 3.73, N 11.96, found: C
61.45, H 3.77, N 11.89.
White solid, yield: 18.75 g (82%); mp: 184–1868C (from
1
DMF-EtOH, 1:4); H NMR (400 MHz, DMSO-d6) d (ppm): 4.78
(s, 2H, ÀCH2), Phenyl-H [7.61 (d, J=8.0 Hz, 2H), 8.00 (d, J=
2-((6-(4-Bromophenyl)imidazo[2,1-b][1,3,4]thiadiazol-2-
yl)thio)-1-phenylethanone (6)
8.0 Hz, 2H)], 7.32 (s, 2H, NH2); 13C NMR (100 MHz, DMSO-d6,
10 d ppm): 41.92 (ÀCH2), Phenyl-C [129.38 (CH),130.88 (CH),
11 134.32 (C), 139.10 (C)], Thiadiazole-C [149.51 (C),170.32 (C)],
12 192.99 (C=O); IR (ATR, cmÀ1): 3263, 3116 (ÀNH2), 3059
13 (ArÀCH), 2936 (Aliph. CH), 1674 (C=O), 1588 (C=N); MS: m/z
14 287.81 (M+2, 100); Anal. Calcd. for C10H8ClN3OS2: C 42.03, H
15 2.82, N 14.70, found: C 42.00, H 2.77, N 14.68.
Light gray crystals, yield 0.95 g (55%); mp: 185–1868C
(from Acetone); H NMR (400 MHz, DMSO-d6, d ppm): 5.17
1
(s, 2H, ÀCH2), Phenyl-H [7.57 (d, J=4.0 Hz, 2H), 7.69 (t, J=
8.0 Hz, 1H), 8.05 (d, J=8.0 Hz, 2H], Imidazole-Phenyl-H [7.57
(d, J=8.0 Hz, 2H), 7.77 (d, J=8.0 Hz, 2H)], Imidazole-H [8.65
(s,1H)]; 13C NMR (100 MHz, DMSO-d6, d ppm): 42.46 (ÀCH2),
Phenyl-C [127.00 (CH), 128.98 (CH), 134.50 (C), 144.09 (C)],
Imidazole-Phenyl-C [120.61 (C), 129.38 (CH), 132.04 (C),
133.47 (CH)], Imidazole-C [111.43 (CH), 145.29 (C)], Thiadia-
zole-C [135.43 (C), 160.56 (C)], 193.05 (C=O); IR (ATR, cmÀ1):
3126 (ArÀCH), 2945 (Aliph. CH), 1679 (C=O), 1582 (C=N); MS:
m/z 430.56 (M+, 100); Anal. Calcd. for C18H12BrN3OS2: C
50.24, H 2.81, N 9.76, found: C 50.21, H 2.87, N, 9.69.
2-((6-(4-Chlorophenyl)imidazo[2,1-b][1,3,4]thiadiazol-2-
yl)thio)-1-phenylethanone (7)
16
17 yl)ethanone (3c)
18 Light gray solid, yield: 18.09 g (84%); mp: 162–1638C
2-((5-Amino-1,3,4-thiadiazol-2-yl)thio)-1-(4-fluorophen-
1
19 (from EtOH); H NMR (400 MHz, DMSO-d6) d (ppm): 4.76 (s,
20 2H, ÀCH2), Phenyl-H [7.36 (d, J=16.0 Hz, 2H), 8.08 (d, J=
21 16.0 Hz, 2H)], 7.27 (s, 2H, NH2); 13C NMR (100 MHz, DMSO-d6,
22 d ppm): 41.92 (ÀCH2), Phenyl-C [116.41 (CH),132.08 (CH),
23 164.48 (C), 166.99 (C)], Thiadiazole-C [149.53 (C),170.30 (C)],
24 192.54 (C=O); IR (ATR, cmÀ1): 3251, 3074 (ÀNH2), 3031
25 (ArÀCH), 2946 (Aliph. CH), 1671 (C=O), 1598 (C=N); MS: m/z
26 270.22 (M+1, 100); Anal. Calcd. for C10H8FN3OS2: C 44.60, H
27 2.99, N 15.60, found: C 44.58, H 3.01, N 15.55.
White solid, yield 0.96 g (62%); mp: 180–1818C (from
1
Acetone); H NMR (400 MHz, DMSO-d6, d ppm): 5.17 (s, 2H,
ÀCH2), Phenyl-H [7.57 (t, J=12.0 Hz, 2H), 7.70 (t, J=12.0 Hz,
1H), 8.05 (d, J=8.0 Hz, 2H], Imidazole-Phenyl-H [7.43 (d, J=
8.0 Hz, 2H), 7.83 (d, J=8.0 Hz, 2H)], Imidazole-H [8.64
(s,1H)]; 13C NMR (100 MHz, DMSO-d6, d ppm): 42.46 (ÀCH2),
Phenyl-C [126.68 (CH), 128.90 (CH), 133.11 (C), 144.06 (C)],
Imidazole-Phenyl-C [128.98 (CH), 129.32 (CH), 132.08 (C),
134.50 (C)], Imidazole-C [111.40 (CH), 145.27 (C)], Thiadia-
zole-C [135.42 (C), 160.53 (C)], 193.04 (C=O); IR (ATR, cmÀ1):
3121 (ArÀCH), 2971 (Aliph. CH), 1679 (C=O), 1596 (C=N); MS:
m/z 385.74 (M+, 100); Anal. Calcd. for C18H12ClN3OS2: C 56.02,
H 3.13, N 10.89, found: C 55.96, H 3.17, N 10.81.
28
29
30 2.3.2 General Procedure for the Synthesis of Imidazo[2,1-b]
31 [1,3,4]thiadiazole Derivatives (5-28)
32
33 In a two-necked flask, 2-amino-1,3,4-thiadiazole derivatives
34 (3a–c) (4 mmol) were dissolved in absolute ethanol (30 mL).
35 2-Bromoacetophenone derivatives (4a–h) (4 mmol) were
36 dissolved in absolute ethanol (20 mL) and then added
37 dropwise to this solution at room temperature with the
38 assistance of a dropping funnel. Then, the mixture was
39 refluxed and stirred for 20–24 h. The progress of reaction
40 was monitored by TLC at appropriate time intervals. The
41 excess of solvent was removed under reduced pressure and
42 neutralized by aqueous sodium carbonate (Na2CO3) solu-
43 tion. The solution was filtered and washed with deionized
44 water. The solid matter was recrystallized from acetone. The
45 synthesized compounds were dried with P2O5 in a vacuum
46 oven. The physical properties and spectral data derived
47 from the obtained products are listed below.
2-((6-(4-Fluorophenyl)imidazo[2,1-b][1,3,4]thiadiazol-2-
yl)thio)-1-phenylethanone (8)
White solid, yield 0.99 g (67%); mp: 164–1658C (from
1
Acetone); H NMR (400 MHz, DMSO-d6, d ppm): 5.16 (s, 2H,
ÀCH2), Phenyl-H [7.57 (bs,2H), 7.70 (bs, 1H), 8.04 (bs, 2H],
Imidazole-Phenyl-H [7.21 (t, J=12.0 Hz, 2H), 7.84 (bs, 2H)],
Imidazole-H [8.58 (s,1H)]; 13C NMR (100 MHz, DMSO-d6, d
ppm): 42.46 (ÀCH2), Phenyl-C [128.89 (CH), 129.38 (CH),
134.49 (CH), 144.36 (C)], Imidazole-Phenyl-C [116.09 (CH),
126.92 (C), 130.74 (CH), 163.16 (C)], Imidazole-C [110.83 (CH),
145.10 (C)], Thiadiazole-C [135.42 (C), 160.21 (C)], 193.05 (C=
O); IR (ATR, cmÀ1): 3067 (ArÀCH), 2941 (Aliph. CH), 1676 (C=
O), 1597 (C=N); MS: m/z 369.57 (M+, 100); Anal. Calcd. for
C18H12FN3OS2: C 58.52, H 3.27, N 11.37, found: C 58.48, H
3.21, N 11.35.
48
49 yl)thio)ethanone (5)
50 White solid, yield 0.93 g (66%); mp: 158–1608C (from
1-Phenyl-2-((6-phenylimidazo[2,1-b][1,3,4]thiadiazol-2-
1
51 Acetone); H NMR (400 MHz, DMSO-d6, d ppm): 5.17 (s, 2H,
52 ÀCH2), Phenyl-H [7.57 (t, J=16.0 Hz, 2H), 7.70 (t, J=16.0 Hz,
53 1H), 8.05 (d, J=8.0 Hz, 2H], Imidazole-Phenyl-H [7.25 (t, J=
54 16.0 Hz, 1H), 7.38 (t, J=16.0 Hz, 2H), 7.81 (d, J=8.0 Hz, 2H)],
55 Imidazole-H [8.61 (s,1H)]; 13C NMR (100 MHz, DMSO-d6, d
56 ppm): 42.46 (ÀCH2), Phenyl-C [127.78 (CH), 128.74 (CH),
2-((6-(4-Methoxyphenyl)imidazo[2,1-b][1,3,4]thiadiazol-
2-yl)thio)-1-phenylethanone (9)
Light white crystals, yield 1.13 g (74%); mp: 138–1398C
1
(from Acetone); H NMR (400 MHz, DMSO-d6, d ppm): 3.76
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(s, 3H, ÀOCH3), 5.17 (s, 2H, ÀCH2), Phenyl-H [7.57 (t, J=
16.0 Hz, 2H), 7.70 (t, J=16.0 Hz, 1H), 8.04 (d, J=8.0 Hz, 2H],
Imidazole-Phenyl-H [6.96 (d, J=8.0 Hz, 2H), 7.73 (d, J=
8.0 Hz, 2H)], Imidazole-H [8.51 (s,1H)]; 13C NMR (100 MHz,
DMSO-d6, d ppm): 42.50 (ÀCH2), 55.63 (ÀOCH3), Phenyl-C
[125.56 (CH), 128.96 (CH), 134.46 (C), 141.47 (C)], Imidazole-
Phenyl-C [114.54 (CH), 128.00 (C), 129.36 (CH), 159.41 (C)],
Imidazole-C [109.91 (CH), 144.34 (C)], Thiadiazole-C [135.53
(C), 161.09 (C)], 193.33 (C=O); IR (ATR, cmÀ1): 3067 (ArÀCH),
(C)], Thiadiazole-C [134.11 (C), 166.53 (C)], 191.75 (C=O); IR
(ATR, cmÀ1): 3105 (ArÀCH), 2972 (Aliph. CH), 1673 (C=O),
1597 (C=N), 1522, 1338 (ÀNO2); MS: m/z 396.56 (M+, 100);
Anal. Calcd. for C18H12N4O3S2: C 54.53, H 3.05, N 14.13, found:
C 54.50, H 3.00, N 14.05.
1-(4-Chlorophenyl)-2-((6-phenylimidazo[2,1-b][1,3,4]
thiadiazol-2-yl)thio)ethanone (13)
White solid, yield 1.13 g (73%); mp: 154–1568C (from
1
Acetone); H NMR (400 MHz, DMSO-d6, d ppm): 5.15 (s, 2H,
10 2997 (Aliph. CH), 1667 (C=O), 1595 (C=N); MS: m/z 381.55
11 (M+, 100); Anal. Calcd. for C19H15N3O2S2: C 59.82, H 3.96, N
12 11.02, found: C 59.85, H 3.91, N 10.98.
ÀCH2), 4Cl-Phenyl-H [7.65 (d, J=8.0 Hz, 2H), 8.06 (d, J=
8.0 Hz, 2H)], Imidazole-Phenyl-H [7.25 (t, J=12.0 Hz, 1H),
7.37 (t, J=12.0 Hz, 2H), 7.81 (d, J=8.0 Hz, 2H)], Imidazole-H
[8.59 (s,1H)]; 13C NMR (100 MHz, DMSO-d6, d ppm): 42.36
(ÀCH2), 4Cl-Phenyl-C [129.10 (CH), 129.51 (CH), 139.42 (C),
145.06 (C)], Imidazole-Phenyl-C [125.04 (CH), 127.76 (CH),
129.41 (CH), 130.90 (C)], Imidazole-C [110.99 (CH), 145.27
(C)], Thiadiazole-C [134.14 (C), 160.01 (C)], 192.25 (C=O); IR
(ATR, cmÀ1): 3039 (ArÀCH), 2932 (Aliph. CH), 1674 (C=O),
1599 (C=N); MS: m/z 385.78 (M+, 100); Anal. Calcd. for C18H12
ClN3OS2: C 56.02, H 3.13, N 10.89, found: C 55.96, H 3.04, N
10.93.
13
4-(2-((2-Oxo-2-phenylethyl)thio)imidazo[2,1-b][1,3,4]
14 thiadiazol-6-yl)benzonitrile (10)
Light white crystals, yield 1.01 g (67%); mp: 210–2118C
15
1
16 (from Acetone); H NMR (400 MHz, DMSO-d6, d ppm): 5.19
17 (s, 2H, ÀCH2), Phenyl-H [7.58 (t, J=12.0 Hz, 2H), 7.70 (t, J=
18 12.0 Hz, 1H), 8.05 (d, J=8.0 Hz, 2H], Imidazole-Phenyl-H
19 [7.83 (d, J=12.0 Hz, 2H), 7.99 (d, J=12.0 Hz, 2H)], Imidazole-
20 H [8.82 (s,1H)]; 13C NMR (100 MHz, DMSO-d6, d ppm): 42.42
21 (ÀCH2), Phenyl-C [128.98 (CH), 129.40 (CH), 134.51 (CH),
22 143.36 (C)], Imidazole-Phenyl-C [109.73 (C), 125.48 (CH),
23 133.21 (CH), 138.72 (C)], Imidazole-C [111.07 (CH), 145.88
24 (C)], 119.48 (CꢀN), Thiadiazole-C [135.42 (C), 161.48 (C)],
25 192.98 (C=O); IR (ATR, cmÀ1): 3067 (ArÀCH), 2957 (Aliph. CH),
26 2219 (CꢀN), 1677 (C=O), 1595 (C=N); MS: m/z 376.57 (M+,
27 100); Anal. Calcd. for C19H12N4OS2: C 60.62, H 3.21, N 14.88,
28 found: C 60.55, H 3.16, N 14.81.
2-((6-(4-Bromophenyl)imidazo[2,1-b][1,3,4]thiadiazol-2-
yl)thio)-1-(4-chlorophenyl)ethanone (14)
White solid, yield 1.19 g (64%); mp: 215–2178C (from
1
DMF-EtOH, 1:4); H NMR (400 MHz, DMSO-d6, d ppm): 5.15
(s, 2H, ÀCH2), 4Cl-Phenyl-H [7.65 (d, J=8.0 Hz, 2H), 8.06 (d,
J=8.0 Hz, 2H)], Imidazole-Phenyl-H [7.57 (d, J=8.0 Hz, 2H),
7.77 (d, J=8.0 Hz, 2H)], Imidazole-H [8.65 (s,1H)]; 13C NMR
(100 MHz, DMSO-d6, d ppm): 42.34 (ÀCH2), 4Cl-Phenyl-C
[129.51 (CH),130.91 (CH), 139.42 (C), 144.40 (C)], Imidazole-
Phenyl-C [120.62 (C), 127.00 (CH), 132.05 (C), 133.58 (CH)],
Imidazole-C [111.44 (CH), 145.31 (C)], Thiadiazole-C [134.16
(C), 160.11 (C)], 192.24 (C=O); R (ATR, cmÀ1): 3124 (ArÀCH),
2976 (Aliph. CH), 1678 (C=O), 1590 (C=N); MS: m/z 465.20
(M+1, 100); Anal. Calcd. for C18H11BrClN3OS2: C 46.51, H
2.39, N 9.04, found: C 46.56, H 2.30, N 9.01.
29
2-((6-([1,1’-Biphenyl]-4-yl)imidazo[2,1-b][1,3,4]thiadia-
30 zol-2-yl)thio)-1-phenylethanone (11)
Gray solid, yield 1.16 g (68%); mp: 185–1878C (from
31
1
32 DMF-EtOH, 1:3); H NMR (400 MHz, DMSO-d6, d ppm): 5.17
33 (s, 2H, ÀCH2), Phenyl-H [7.58 (t, J=12.0 Hz, 2H), 7.71 (t, J=
34 12.0 Hz, 1H), 8.05 (d, J=8.0 Hz, 2H], Imidazole-Phenyl-H
35 [7.34 (t, J=16.0 Hz, 1H), 7.45 (t, J=16.0 Hz, 2H), 7.69 (d, J=
36 8.0 Hz, 4H), 7.91 (d, J=8.0 Hz, 2H)], Imidazole-H [8.66
37 (s,1H)]; 13C NMR (100 MHz, DMSO-d6, d ppm): 42.49 (ÀCH2),
38 Phenyl-C [127.86 (CH), 128.99 (CH), 133.34 (CH), 144.93 (C)],
39 Imidazole-Phenyl-C [125.59 (CH), 126.89 (CH), 127.35 (CH),
40 129.39 (CH), 134.50 (CH), 139.33 (C), 140.16 (CH)], Imidazole-
41 C [111.17 (CH), 145.19 (C)], Thiadiazole-C [135.44 (C), 160.21
42 (C)], 193.06 (C=O); IR (ATR, cmÀ1): 3033 (ArÀCH), 2933 (Aliph.
43 CH), 1675 (C=O), 1597 (C=N); MS: m/z 427.81 (M+, 100);
44 Anal. Calcd. for C24H17N3OS2: C 67.42, H 4.01, N 9.83, found:
45 C 67.36, H 3.97, N 9.89.
1-(4-Chlorophenyl)-2-((6-(4-chlorophenyl)imidazo[2,1-b]
[1,3,4]thiadiazol-2-yl)thio)ethanone (15)
White solid, yield 1.14 g (68%); mp: 216–2188C (from
1
DMF-EtOH, 1:4); H NMR (400 MHz, DMSO-d6, d ppm): 5.15
(s, 2H, ÀCH2), 4Cl-Phenyl-H [7.65 (d, J=8.0 Hz, 2H), 8.06 (d,
J=8.0 Hz, 2H)], Imidazole-Phenyl-H [7.44 (d, J=8.0 Hz, 2H),
7.83 (d, J=8.0 Hz, 2H)], Imidazole-H [8.64 (s,1H)]; 13C NMR
(100 MHz, DMSO-d6, d ppm): 42.34 (ÀCH2), 4Cl-Phenyl-C
[129.51 (CH),130.91 (CH), 139.42 (C), 144.08 (C)], Imidazole-
Phenyl-C [126.70 (CH), 129.14 (CH), 132.09 (C), 133.10 (C)],
Imidazole-C [111.41 (CH), 145.29 (C)], Thiadiazole-C [134.16
(C), 160.39 (C)], 192.25 (C=O); IR (ATR, cmÀ1): 3120 (ArÀCH),
2947 (Aliph. CH), 1678 (C=O), 1591 (C=N); MS: m/z 420.69
(M+, 100); Anal. Calcd. for C18H11Cl2N3OS2: C 51.43, H 2.64, N
10.00, found: C 51.38, H 2.69, N 10.09.
46
2-((6-(4-Nitrophenyl)imidazo[2,1-b][1,3,4]thiadiazol-2-
47 yl)thio)-1-phenylethanone (12)
Yellow solid, yield 1.22 g (77%); mp: 231–2338C (from
48
1
49 DMF-EtOH, 1:1); H NMR (400 MHz, DMSO-d6, d ppm): 5.07
50 (s, 2H, ÀCH2), Phenyl-H [7.52 (t, J=16.0 Hz, 2H), 7.65 (t, J=
51 16.0 Hz, 1H), 7.99 (d, J=8.0 Hz, 2H], Imidazole-Phenyl-H
52 [8.23 (d, J=8.0 Hz, 2H), 8.40 (d, J=8.0 Hz, 2H)], Imidazole-H
53 [8.88 (s,1H)]; 13C NMR (100 MHz, DMSO-d6, d ppm): 42.25
54 (ÀCH2), 4Cl-Phenyl-C [129.31 (CH),130.38 (CH), 139.40 (C),
55 143.50 (C)], Imidazole-Phenyl-C [113.25 (C), 124.58 (CH),
56 133.70 (CH), 135.63 (C)], Imidazole-C [109.12 (CH), 145.77
1-(4-Chlorophenyl)-2-((6-(4-fluorophenyl)imidazo[2,1-b]
[1,3,4]thiadiazol-2-yl)thio)ethanone (16)
Light gray solid, yield 1.06 g (66%); mp: 188–1908C
1
(from Acetone); H NMR (400 MHz, DMSO-d6, d ppm): 5.14
(s, 2H, ÀCH2), 4Cl-Phenyl-H [7.65 (d, J=8.0 Hz, 2H), 8.05 (d,
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J=8.0 Hz, 2H)], Imidazole-Phenyl-H [7.21 (t, J=12.0 Hz, 2H),
7.85 (t, J=12.0 Hz, 2H)], Imidazole-H [8.57 (s,1H)]; 13C NMR
(100 MHz, DMSO-d6, d ppm): 42.34 (ÀCH2), 4Cl-Phenyl-C
[129.50 (CH),130.89 (CH), 139.43 (C), 144.38 (C)], Imidazole-
Phenyl-C [116.09 (CH), 127.01 (CH), 130.89 (C), 160.74 (C)],
Imidazole-C [110.84 (CH), 145.11 (C)], Thiadiazole-C [134.13
(C), 160.05 (C)], 192.24 (C=O); IR (ATR, cmÀ1): 3116 (ArÀCH),
2946 (Aliph. CH), 1673 (C=O), 1591 (C=N); MS: m/z 403.66
(M+, 100); Anal. Calcd. for C18H11ClFN3OS2: C 53.53, H 2.75, N
1673 (C=O), 1588 (C=N); MS: m/z 461.63 (M+, 100); Anal.
Calcd. for C24H16ClN3OS2: C 62.40, H 3.49, N 9.10, found: C
62.32, H 3.53, N 9.06.
1-(4-Chlorophenyl)-2-((6-(4-nitrophenyl)imidazo[2,1-b]
[1,3,4]thiadiazol-2-yl)thio)ethanone (20)
Yellow solid, yield 1.26 g (73%); mp: 238–2408C (from
DMF-EtOH, 1:1); H NMR (400 MHz, DMSO-d6, d ppm): 5.17
1
(s, 2H, ÀCH2), 4Cl-Phenyl-H [7.66 (d, J=8.0 Hz, 2H), 8.07 (d,
J=8.0 Hz, 2H)], Imidazole-Phenyl-H [8.07 (d, J=8.0 Hz, 2H)),
8.25 (d, J=8.0 Hz, 2H)], Imidazole-H [8.88 (s,1H)]; 13C NMR
(100 MHz, DMSO-d6, d ppm): 42.30 (ÀCH2), 4Cl-Phenyl-C
[129.51 (CH),130.91 (CH), 139.44 (C), 143.38 (C)], Imidazole-
Phenyl-C [113.07 (C), 125.42 (CH), 133.27 (CH), 138.72 (C)],
Imidazole-C [109.72 (CH), 145.89 (C)], Thiadiazole-C [134.12
(C), 161.33 (C)], 192.17 (C=O); IR (ATR, cmÀ1): 3048 (ArÀCH),
2923 (Aliph. CH), 1673 (C=O), 1587 (C=N), 1506, 1343 (-NO2);
MS: m/z 430.76 (M+, 100); Anal. Calcd. for C18H11ClN4O3S2: C
50.17, H 2.57, N 13.00, found: C 50.12, H 2.59, N 13.08.
1-(4-Fluorophenyl)-2-((6-phenylimidazo[2,1-b][1,3,4]
thiadiazol-2-yl)thio)ethanone (21)
Light yellowish crystals, yield 0.96 g (65%); mp: 183–
1848C (from Acetone); 1H NMR (400 MHz, DMSO-d6, d ppm):
5.15 (s, 2H, ÀCH2), 4F-Phenyl-H [7.41 (t, J=12.0 Hz, 2H), 8.14
(t, J=12.0 Hz, 2H)], Imidazole-Phenyl-H [7.25 (t, J=12.0 Hz,
1H), 7.37 (t, J=12.0 Hz, 2H), 7.82 (d, J=8.0 Hz, 2H)],
Imidazole-H [8.59 (s,1H)]; 13C NMR (100 MHz, DMSO-d6, d
ppm): 42.34 (ÀCH2), 4F-Phenyl-C [116.37 (CH),132.22 (CH),
164.66 (CH), 167.17 (C)], Imidazole-Phenyl-C [125.04 (CH),
127.75 (CH), 129.10 (CH), 132.14 (C)], Imidazole-C [110.99
(CH), 145.27 (C)], Thiadiazole-C [145.06 (C), 160.05 (C)],
191.75 (C=O); IR (ATR, cmÀ1): 3072 (ArÀCH), 2951 (Aliph. CH),
1686 (C=O), 1593 (C=N); MS: m/z 369.82 (M+, 100); Anal.
Calcd. for C18H12FN3OS2: C 58.52, H 3.27, N 11.37, found: C
58.49, H 3.36, N 11.30.
10 10.40, found: C 53.48, H 2.67, N 10.31.
1-(4-Chlorophenyl)-2-((6-(4-methoxyphenyl)imidazo[2,1-
12 b][1,3,4]thiadiazol-2-yl)thio)ethanone (17)
Gray solid, yield 1.25 g (75%); mp: 184–1858C (from
11
13
1
14 Acetone); H NMR (400 MHz, DMSO-d6, d ppm): 3.75 (s, 3H,
15 ÀOCH3), 5.13 (s, 2H, ÀCH2), 4Cl-Phenyl-H [7.65 (d, J=8.0 Hz,
16 2H), 8.06 (d, J=8.0 Hz, 2H)], Imidazole-Phenyl-H [6.95 (d, J=
17 12.0 Hz, 2H), 7.74 (d, J=12.0 Hz, 2H)], Imidazole-H [8.47
18 (s,1H)]; 13C NMR (100 MHz, DMSO-d6, d ppm): 42.37 (ÀCH2),
19 55.58 (ÀOCH3), 4Cl-Phenyl-C [129.51 (CH),130.90 (CH),
20 139.40 (C), 144.79 (C)], Imidazole-Phenyl-C [114.54 (CH),
21 126.39 (C), 126.80 (CH), 159.14 (C)], Imidazole-C [109.87
22 (CH), 145.37 (C)], Thiadiazole-C [134.16 (C), 160.02 (C)],
23 192.31 (C=O); IR (ATR, cmÀ1): 3067 (ArÀCH), 2931 (Aliph. CH),
24 1673 (C=O), 1587 (C=N); MS: m/z 415.74 (M+, 100); Anal.
25 Calcd. for C19H14ClN3O2S2: C 54.87, H 3.39, N 10.10, found: C
26 54.81, H 3.30, N 10.02.
27
4-(2-((2-(4-Chlorophenyl)-2-oxoethyl)thio)imidazo[2,1-b]
28 [1,3,4]thiadiazol-6-yl)benzonitrile (18)
White solid, yield 1.18 g (72%); mp: 235–2368C (from
29
1
30 DMF-EtOH, 1:4); H NMR (400 MHz, DMSO-d6, d ppm): 5.16
31 (s, 2H, ÀCH2), 4Cl-Phenyl-H [7.65 (d, J=8.0 Hz, 2H), 8.06 (d,
32 J=8.0 Hz, 2H)], Imidazole-Phenyl-H [7.84 (d, J=8.0 Hz, 2H),
33 7.99 (d, J=8.0 Hz, 2H)], Imidazole-H [8.81 (s,1H)]; 13C NMR
34 (100 MHz, DMSO-d6, d ppm): 42.30 (ÀCH2), 119.48 (CꢀN),
35 4Cl-Phenyl-C [129.52 (CH),130.90 (CH), 139.43 (C), 143.37
36 (C)], Imidazole-Phenyl-C [113.06 (C), 125.48 (CH), 133.21
37 (CH), 138.70 (C)], Imidazole-C [109.74 (CH), 145.90 (C)],
38 Thiadiazole-C [134.14 (C), 161.34 (C)], 192.18 (C=O); IR (ATR,
39 cmÀ1): 3122 (ArÀCH), 2944 (Aliph. CH), 2220 (CꢀN), 1677 (C=
40 O), 1589 (C=N); MS: m/z 411.76 (M+1, 100); Anal. Calcd. for
41 C19H11ClN4OS2: C 55.54, H 2.70, N 13.64, found: C 55.50, H
42 2.62, N 13.54.
2-((6-(4-Bromophenyl)imidazo[2,1-b][1,3,4]thiadiazol-2-
yl)thio)-1-(4-fluorophenyl)ethanone (22)
Gray solid, yield 1.27 g (71%); mp: 198–1998C (from
Acetone); H NMR (400 MHz, DMSO-d6, d ppm): 5.15 (s, 2H,
1
ÀCH2), 4F-Phenyl-H [7.41 (t, J=12.0 Hz, 2H), 8.14 (t, J=
12.0 Hz, 2H)], Imidazole-Phenyl-H [7.57 (d, J=8.0 Hz, 2H),
7.77 (d, J=8.0 Hz, 2H)], Imidazole-H [8.65 (s,1H)]; 13C NMR
(100 MHz, DMSO-d6, d ppm): 42.31 (ÀCH2), 4F-Phenyl-C
[116.37 (CH),132.16 (CH), 162.25 (CH), 164.37 (C)], Imidazole-
Phenyl-C [120.61 (C), 127.01 (CH), 132.05 (C), 133.46 (CH)],
Imidazole-C [111.43 (CH), 145.31 (C)], Thiadiazole-C [144.10
(C), 160.49 (C)], 191.74 (C=O); IR (ATR, cmÀ1): 3128 (ArÀCH),
2954 (Aliph. CH), 1679 (C=O), 1596 (C=N); MS: m/z 449.65
(M+1, 100); Anal. Calcd. for C18H11BrFN3OS2: C 48.22, H 2.47,
N 9.37, found: C 48.15, H 2.51, N 9.32.
2-((6-(4-Chlorophenyl)imidazo[2,1-b][1,3,4]thiadiazol-2-
yl)thio)-1-(4-fluorophenyl)ethanone (23)
Gray solid, yield 0.95 g (59%); mp: 197–1998C (from
Acetone); H NMR (400 MHz, DMSO-d6, d ppm): 5.15 (s, 2H,
ÀCH2), 4F-Phenyl-H [7.41 (t, J=12.0 Hz, 2H), 8.14 (t, J=
12.0 Hz, 2H)], Imidazole-Phenyl-H [7.43 (d, J=8.0 Hz, 2H),
7.83 (d, J=8.0 Hz, 2H)], Imidazole-H [8.64 (s,1H)]; 13C NMR
43
2-((6-([1,1’-Biphenyl]-4-yl)imidazo[2,1-b][1,3,4]thiadia-
44 zol-2-yl)thio)-1-(4-chlorophenyl)ethanone (19)
Gray solid, yield 1.31 g (71%); mp: 215–2178C (from
45
1
46 from DMF-EtOH, 1:3); H NMR (400 MHz, DMSO-d6, d ppm):
47 5.16 (s, 2H, ÀCH2), 4Cl-Phenyl-H [7.65 (d, J=8.0 Hz, 2H), 8.07
48 (d, J=8.0 Hz, 2H)], Imidazole-Phenyl-H [7.34 (t, J=12.0 Hz,
49 1H), 7.45 (t, J=12.0 Hz, 2H), 7.69 (d, J=8.0 Hz, 4H), 7.91 (d,
50 J=8.0 Hz, 2H)], Imidazole-H [8.66 (s,1H)]; 13C NMR (100 MHz,
51 DMSO-d6, d ppm): 42.37 (ÀCH2), 4Cl-Phenyl-C [129.52 (CH),
52 130.92 (CH), 139.42 (C), 144.94 (C)], Imidazole-Phenyl-C
53 [125.58 (CH), 126.90 (CH), 127.36 (CH), 127.87 (CH), 129.40
54 (CH), 133.31 (C), 139.35 (C), 140.15 (C)], Imidazole-C [111.18
55 (CH), 145.22 (C)], Thiadiazole-C [134.16 (C), 160.06 (C)],
56 192.28 (C=O); IR (ATR, cmÀ1): 3040 (ArÀCH), 2932 (Aliph. CH),
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(100 MHz, DMSO-d6, d ppm): 42.32 (ÀCH2), 4F-Phenyl-C
[116.36 (CH),132.23 (CH), 164.66 (CH), 167.18 (C)], Imidazole-
Phenyl-C [126.69 (CH), 129.14 (CH), 132.06 (C), 133.10 (C)],
Imidazole-C [111.40 (CH), 145.28 (C)], Thiadiazole-C [144.07
(C), 160.45 (C)], 191.74 (C=O); IR (ATR, cmÀ1): 3124 (ArÀCH),
2945 (Aliph. CH), 1680 (C=O), 1596 (C=N); MS: m/z 403.73
(M+, 100); Anal. Calcd. for C18H11ClFN3OS2: C 53.53, H 2.75, N
10.40, found: C 53.60, H 2.69, N 10.31.
2-((6-([1,1’-Biphenyl]-4-yl)imidazo[2,1-b][1,3,4]thiadia-
zol-2-yl)thio)-1-(4-fluorophenyl)ethanone (27)
Gray solid, yield 1.28 g (72%); mp: 185–1868C (from
1
Acetone); H NMR (400 MHz, DMSO-d6, d ppm): 5.16 (s, 2H,
ÀCH2), 4F-Phenyl-H [7.41 (t, J=12.0 Hz, 2H), 8.15 (t, J=
12.0 Hz, 2H)], Imidazole-Phenyl-H [7.35 (t, J=12.0 Hz, 1H),
7.45 (t, J=12.0 Hz, 2H), 7.69 (d, J=8.0 Hz, 4H), 7.91 (d, J=
8.0 Hz, 2H)], Imidazole-H [8.66 (s,1H)]; 13C NMR (100 MHz,
DMSO-d6, d ppm): 42.36 (ÀCH2), 4F-Phenyl-C [116.36 (CH),
132.17 (CH), 164.66 (CH), 167.15 (C)], Imidazole-Phenyl-C
[125.58 (CH), 126.90 (CH), 127.36 (CH), 127.87 (CH), 129.40
(CH), 133.33 (C), 139.34 (C), 140.15 (C)], Imidazole-C [111.17
(CH), 145.21 (C)], Thiadiazole-C [144.94 (C), 160.14 (C)],
191.78 (C=O); IR (ATR, cmÀ1): 3137 (ArÀCH), 2932 (Aliph. CH),
1674 (C=O), 1596 (C=N); MS: m/z 445.73 (M+, 100); Anal.
Calcd. for C24H16FN3OS2: C 64.70, H 3.62, N 9.43, found: C
64.59, H 3.58, N 9.50.
1-(4-Fluorophenyl)-2-((6-(4-fluorophenyl)imidazo[2,1-b]
10 [1,3,4]thiadiazol-2-yl)thio)ethanone (24)
11
White solid, yield 1.07 g (69%); mp: 183–1848C (from
1
12 Acetone); H NMR (400 MHz, DMSO-d6, d ppm): 5.17 (s, 2H,
13 ÀCH2), 4F-Phenyl-H [7.41 (t, J=12.0 Hz, 2H), 8.14 (t, J=
14 12.0 Hz, 2H)], Imidazole-Phenyl-H [7.22 (t, J=12.0 Hz, 2H),
15 7.85 (t, J=12.0 Hz, 2H)], Imidazole-H [8.58 (s,1H)]; 13C NMR
16 (100 MHz, DMSO-d6, d ppm): 42.33 (ÀCH2), 4F-Phenyl-C
17 [116.36 (CH),132.15 (CH), 164.66 (CH), 167.17 (C)], Imidazole-
18 Phenyl-C [116.10 (CH), 127.00 (CH), 130.74 (C), 163.17 (C)],
19 Imidazole-C [110.84 (CH), 145.11 (C)], Thiadiazole-C [144.38
20 (C), 160.75 (C)], 191.76 (C=O); IR (ATR, cmÀ1): 3120 (ArÀCH),
21 2941 (Aliph. CH), 1677 (C=O), 1596 (C=N); MS: m/z 387.70
22 (M+, 100); Anal. Calcd. for C18H11F2N3OS2: C 55.80, H 2.86, N
23 10.85, found: C 55.71, H 2.78, N 10.80.
24
1-(4-Fluorophenyl)-2-((6-(4-methoxyphenyl)imidazo[2,1-
25 b][1,3,4]thiadiazol-2-yl)thio)ethanone (25)
Yellowish solid, yield 1.10 g (69%); mp: 161–1628C (from
26
1
27 DMF-EtOH, 1:3); H NMR (400 MHz, DMSO-d6, d ppm): 3.75
28 (s, 3H, ÀOCH3), 5.13 (s, 2H, ÀCH2), 4F-Phenyl-H [7.41 (t, J=
29 12.0 Hz, 2H), 8.14 (t, J=12.0 Hz, 2H)], Imidazole-Phenyl-H
30 [6.94 (d, J=8.0 Hz, 2H), 7.74 (d, J=8.0 Hz, 2H)], Imidazole-H
31 [8.46 (s,1H)]; 13C NMR (100 MHz, DMSO-d6, d ppm): 42.36
32 (ÀCH2), 55.56 (ÀOCH3), 4F-Phenyl-C [116.35 (CH),132.15 (CH),
33 164.66 (CH), 167.16 (C)], Imidazole-Phenyl-C [114.53 (CH),
34 126.39 (C), 126.82 (CH), 159.14 (C)], Imidazole-C [109.86
35 (CH), 145.37 (C)], Thiadiazole-C [144.78 (C),159.40 (C)],
36 191.80 (C=O); IR (ATR, cmÀ1): 3148 (ArÀCH), 2944 (Aliph. CH),
37 1671 (C=O), 1593 (C=N); MS: m/z 399.74 (M+, 100); Anal.
38 Calcd. for C19H14FN3O2S2: C 57.13, H 3.53, N 10.52, found: C
39 57.06, H 3.60, N 10.48.
Figure 1. The crystal structure of compound 10.
1-(4-Fluorophenyl)-2-((6-(4-nitrophenyl)imidazo[2,1-b]
[1,3,4]thiadiazol-2-yl)thio)ethanone (28)
Yellow solid, yield 1.19 g (72%); mp: 229–2308C (from
1
DMF-EtOH, 1:1); H NMR (400 MHz, DMSO-d6, d ppm): 5.13
(s, 2H, ÀCH2), 4F-Phenyl-H [7.41 (t, J=12.0 Hz, 2H), 8.14 (t,
J=12.0 Hz, 2H)], Imidazole-Phenyl-H [8.07 (d, J=12.0 Hz,
2H), 8.24 (d, J=12.0 Hz, 2H))], Imidazole-H [8.87 (s,1H)]; 13C
NMR (100 MHz, DMSO-d6, d ppm): 42.36 (ÀCH2), 4F-Phenyl-C
[116.57 (CH),131.28 (CH), 163.89 (CH), 164.14 (C)], Imidazole-
Phenyl-C [125.73 (CH), 126.94 (CH), 139.11 (C), 141.27 (C)],
Imidazole-C [110.61 (CH), 145.37 (C)], Thiadiazole-C [144.48
(C), 161.47 (C)], 195.74 (C=O); IR (ATR, cmÀ1): 3115 (ArÀCH),
2986 (Aliph. CH), 1679 (C=O), 1596 (C=N), 1505, 1336
(ÀNO2); MS: m/z 432.85 (M+H2O, 100); Anal. Calcd. for C18
H11FN4O3S2: C 52.17, H 2.68, N 13.52, found: C 52.22, H 32.62,
N 13.48.
40
4-(2-((2-(4-Fluorophenyl)-2-oxoethyl)thio)imidazo[2,1-b]
41 [1,3,4]thiadiazol-6-yl)benzonitrile (26)
Light gray solid, yield 0.99 g (63%); mp: 211–2128C
42
1
43 (from Acetone); H NMR (400 MHz, DMSO-d6, d ppm): 5.17
44 (s, 2H, ÀCH2), 4F-Phenyl-H [7.41 (t, J=12.0 Hz, 2H), 8.14 (t,
45 J=12.0 Hz, 2H)], Imidazole-Phenyl-H [7.83 (d, J=8.0 Hz, 2H),
46 7.99 (d, J=8.0 Hz, 2H)], Imidazole-H [8.81 (s,1H)]; 13C NMR
47 (100 MHz, DMSO-d6, d ppm): 42.30 (ÀCH2), 119.48 (CꢀN), 4F-
48 Phenyl-C [116.37 (CH),132.15 (CH), 164.67 (CH), 167.13 (C)],
49 Imidazole-Phenyl-C [113.06 (C), 125.47 (CH), 133.20 (CH),
50 138.71 (C)], Imidazole-C [109.73 (CH), 145.88 (C)], Thiadia-
51 zole-C [143.37 (C), 161.38 (C)], 191.67 (C=O); IR (ATR, cmÀ1):
52 3129 (ArÀCH), 2944 (Aliph. CH), 2226 (CꢀN), 1674 (C=O),
53 1594 (C=N); MS: m/z 394.84 (M+, 100); Anal. Calcd. for C19H11
54 FN4OS2: C 57.85, H 2.81, N 14.20, found: C 57.79, H 2.75, N
55 14.23.
2.4 Determination of in vitro Antimicrobial Activity and
Minimal Inhibition Concentration (MIC)
2.4.1 The Screening of Antimicrobial Activity
Antimicrobial activities of all compounds were screened by
agar well method. The test was performed on Mueller
56
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34
35
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37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
Figure 2. Docked pose of compound 5 in the active site of the enoyl-ACP reductase mapped with electrostatic potential (left) and 2D ligand
interaction diagram (right).
Figure 4. Electrostatic potential map surfaces of the compounds 5
(left), 13 (middle) and 21 (right).
was adjusted to 0.5 McFarland [about 108 cfu (colony
forming unit)/ml] in 0,85% (w/v) sterile phosphate buffer
saline (PBS) by using nephelometer (Crystal Specꢀ, Becton
Dickenson, USA). 100 ml of each 0.5 McFarland bacterial
suspension were streaked on MHA via sterile swab. Then,
20 mg of all compounds were dissolved in 1 ml Dimethyl
Sulfoxide (DMSO) separately. The wells on agar plate were
filled with 100 ml of these compounds in DMSO. A Petri dish
Figure 3. Binding interaction of compound 5 with the amino acid
residues of the enoyl-ACP reductase and NAD+.
was used for 4 compounds. Antimicrobial screening test
were performed duplicate for each sample. DMSO was used
as negative control, Chloramphenicol disk (30 mg) (HIMEDIA)
for bacteria and Nystatin (10000 u/ml) for fungi were used
as positive controls. Inoculated Petri dishes were incubated
53 Hinton Agar (MHA).[56] Agar surface were digged on wells.
54 Fresh cultures of E. coli ATCC 8739, S. aureus ATCC 29213, B.
55 subtilis ATCC 6633 and C. albicans ATCC 10231 were
56 prepared in Mueller Hinton Broth. Fresh bacterial culture
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at 378C for 24 h. After 24 h incubation, clear zones around
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ketones (2a–c). In 13C NMR spectra, the resonance values
related to C-2 and C-5 carbons were in consistent with
similar compounds found in the literature.[59–61]
the wells were measured and recorded as mm.
The most significant evidence of formation of the target
compounds (5-28) in the IR spectra is the disappearance of
-NH2 symmetric and asymmetric absorption bands, which
were observed in the 3263–3074 cmÀ1 range, in 2-amino-
1,3,4-thiadiazole derivatives (3a–c). Furthermore, -NH2 pro-
ton signals of the starting compounds observed in the d
2.4.2 Minimum Inhibitory Concentration (MIC)
According to antimicrobial activity screening test results,
compounds that have the most activity value against all
microorganisms were selected. The MIC values of selected
1
10 compounds were screened by 96 well plates in Mueller
11 Hinton Broth (MHB) using the twofold serial dilution
12 technique.[57,58] Dilutions of all compounds were prepared
13 from 256 mg/ml to 0.03 mg/ml with 14 serial dilutions in 96
14 well plates with MHB. All fresh bacteria culture in Mueller
15 Hinton broth was centrifuged at 4500 g for 10 min and
16 bacteria pellets were adjusted to 0.5 McFarland using sterile
17 PBS (pH 7.4). 100 ml from each bacterial suspension were
18 inoculated in plate wells, which included diluted com-
19 pounds. All plates were incubated on 378C for 24 h. Their
20 absorbance (OD600) was evaluated by micro plaque reader
21 (BMG LABTECH, FLUOstar Omega, USA). Chloramphenicol
22 was used as positive control. Fresh bacteria culture in MHB
23 was used as negative control. The results which have half of
24 negative control’s absorbance value were recorded as MIC
25 value (mg/ml). All assays for every dilution of MIC were
26 carried out duplicate.
7.27–7.32 ppm range (3a–c) were disappeared in the H
NMR spectra and instead, a singlet peak corresponding to
one proton of the C5-H was observed in the d 8.46–
8.88 ppm. This clearly proves the formation of compounds
5–28. These values are also similar to those given in
relevant studies in the literature.[13,35] The formation mecha-
nism[34] of target compounds is illustrated in Scheme 2.
Other 1H NMR and 13C NMR spectral data of the
compounds are given in detail in the experimental section.
The physical and structural properties of the target
compounds (5-28) are given in Table 1. In addition, mass
spectra of all synthesized compounds were also found as
Table 1. Physical and structural properties of target compounds (5–
28).
27
28
29 3 Results and Discussion
30
31 3.1 Chemistry
32
33 In this study, as the first step for the target compounds, 2-
34 amino-1,3,4-thiadiazole derivatives (3a–c) were synthesized
35 by reacting 5-amino-1,3,4-thiadiazole-2-thiol (1) with a-
36 bromoacetophenone derivatives (2a–c) via dehydrobromi-
37 nation mechanism, in the presence of ethanolic potassium
38 hydroxide in high yields (84-81%). These compounds were
39 obtained in analogy to the literature[55] but in higher yields.
40 The synthesized compounds 3a–c were then converted to
41 the target compounds 5–28 by reacting with a-bromoace-
42 tophenone derivatives (4a–h) in absolute alcohol with
43 moderate to good (55–77%) yields. The synthetic method
44 employed to synthesize these compounds is given in
45 Scheme 1.
Compound
R
R’
Yield (%)
m.p (8C)
5
6
7
8
ÀH
ÀH
ÀH
ÀH
ÀH
ÀH
ÀH
ÀH
ÀCl
ÀCl
ÀCl
ÀCl
ÀCl
ÀCl
ÀCl
ÀCl
ÀF
ÀH
66
55
62
67
74
67
68
77
73
64
68
66
75
72
71
73
65
71
59
69
69
63
72
72
158–160
185–186
180–181
164–165
138–139
210–211
185–187
231–233
154–156
215–217
216–218
188–190
184–185
235–236
215–217
238–240
183-184
198–199
197–199
183–184
161–162
211–212
185–186
229–230
ÀBr
ÀCl
ÀF
9
ÀOCH3
ÀCN
ÀPh
ÀNO2
ÀH
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
ÀBr
ÀCl
ÀF
46
The structures of the synthesized compounds were
ÀOCH3
ÀCN
ÀPh
ÀNO2
ÀH
47 elucidated based on physical constants, spectral data (FTIR,
48 1H NMR, 13C NMR, X-ray (compound 10) and MASS) and
49 elemental analysis. 1H NMR and 13C NMR spectra of all
50 synthesized compounds and X-ray data of compound 10
51 are provided in the Supplementary Material Section. The
52 crystal structure of compound 10 is shown in Figure 1.
ÀF
ÀBr
ÀF
ÀCl
ÀF
ÀF
53
In general, the characteristic singlet for ÀCH2 methylene
ÀF
ÀOCH3
ÀCN
ÀPh
ÀNO2
54 proton was observed in 1H NMR spectra of compounds 3a–
55 c around d 4.76-4.79 ppm, which confirmed the reaction
56 between 5-amino-1,3,4-thiadiazole-2-thiol (1) and a-bromo-
ÀF
ÀF
ÀF
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21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
Scheme 2. Mechanism for the synthesis of target compounds (5–28).
38 expected and the molecular ion peaks supported the
39 structures.
40
41
42 3.2 Computational Studies
43
44 Computational (in silico) methods are without doubt rapidly
45 advancing and proved to be essential tools that are widely
46 used for the design of novel enzyme inhibitors.
The results show that most of the active compounds
obey Lipinski’s rule of five, which is an indication of the
drug-likeness of a molecule, and PSA values are within the
range that Veber et al. suggested.[63] According to the
Table 2, electron-donating substituents are clearly one of
the factors that diminishes activity. As an example, the least
active compound 9 that has a powerful electron-donating
group (ÀOCH3) has highest HOMO value.
In the current study, molecular docking simulations were
also employed to gain insight into the major binding motifs
of the ligands. One of the main aim of the molecular
docking is to map the ligand/target interactions to assist
the rational drug design. The commonly used docking
software available at the market are able to accurately and
reliably predict the binding pose of the ligands in many
cases, however, the scoring functions have a lower success
rate in discriminating between active and inactive com-
pounds.[15,64,65] Docking scores of the compounds 5–28
together with that of the reference compound, Chloram-
47
As an initial step, we have calculated some molecular
48 descriptors commonly used in absorption, distribution,
49 metabolism and excretion (ADME) analysis (Table 2).
50
Accordingly, molecular weight (MW), percent human
51 oral absorption, predicted octanol/water partition coeffi-
52 cient (QPlogPo/w), polar surface area (PSA) and number of
53 violations of Lipinski’s rule of five[62] were estimated. Highest
54 molecular orbital (HOMO) energies were also calculated to
55 evaluate the effect of electronic structure on the activity.
56
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Table 2. Docking scores and selected molecular properties of compounds 5–28 and Chloramphenicol (reference drug).
Compound
Dscore
(kcal/mol)
MWa
(g/mol)
%Human
Oral
EHOMOc
(eV)
PSAd
A
QPlogPo/we
Rule
of
Five
2
˚
Absorptionb
5
28
10
27
21
8
6
12
9
15
11
24
7
26
25
22
À8.01
À7.74
À7.73
À7.51
À7.46
À7.43
À7.36
À7.34
À7.33
À7.28
À6.84
À6.78
À6.37
À6.20
À6.16
À6.08
À6.05
À6.04
À5.93
À5.90
À5.88
À5.84
À5.72
À5.57
À3.46
351.44
414.43
376.45
445.53
369.43
369.43
430.34
396.44
381.47
420.33
427.54
387.42
385.89
394.44
399.46
448.33
323.13
403.88
385.89
415.91
410.90
430.88
403.88
464.78
461.98
100.00
90.38
93.82
À8.98
À9.55
À9.38
À8.79
À9.04
À9.25
À9.16
À9.58
À8.64
À9.44
À8.77
À9.23
À9.05
À9.38
À8.70
À9.19
À10.76
À9.17
À9.04
À8.69
À9.44
À9.51
À9.04
À9.21
À8.69
55.94
102.04
82.59
55.89
57.31
56.84
58.09
102.60
65.78
59.68
56.04
58.84
57.84
83.76
66.55
58.19
121.13
58.29
57.85
66.48
84.16
102.29
53.26
58.10
52.51
4.52
3.86
3.69
6.26
4.60
4.78
4.94
3.88
4.46
5.46
6.15
4.87
4.87
3.67
4.57
5.10
1.14
5.02
4.78
4.83
3.92
4.10
5.33
5.36
6.63
+
+
+
À
+
+
+
+
+
À
À
+
+
+
+
À
+
À
+
+
+
+
À
À
À
100.00
100.00
100.00
100.00
89.79
100.00
100.00
100.00
100.00
100.00
92.82
100.00
100.00
65.67
100.00
100.00
100.00
93.30
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
Chloramphenicol
23
13
17
18
20
16
14
19
91.64
100.00
100.00
100.00
a Molecular weight (recommended value <500). b Percentage of human oral absorption (<25% is weak and >80% is strong). c Calculated at
Semi Empirical PM6 method with Spartan ‘16 parallel suite. d Polar surface area (recommended valueꢁ140 A ).[62] e Logarithm of the partition
2
˚
coefficient of the compound between n-octanol and water (recommended value <5)
33 phenicol are given in Table 2. Glide XP docking performed
34 well in ranking the active compound 5, which has the
35 highest inhibition zone and lowest MIC value. Another
36 active compound 28 ranked second at the top.
The aromatic ring next to the carbonyl of compound 5
is nested into hydrophobic pocket located at the bottom of
the deep cavity. It stacks parallel to the nicotinamide
cofactor (NAD+) and almost perpendicular to the TYR146
making p-p stacking interaction with NAD+ and a T shaped
p-p interaction with TYR146 (Figure 3). The carbonyl acts as
a hydrogen bond acceptor and it makes a hydrogen bond
with the Tyrosine 156 and NAD+.
37
Molecular modeling of the binding of the imidazo[2,1-b]
38 [1,3,4]thiadiazole derivatives on enoyl-acyl carrier protein
39 reductase, the molecular target site of several antibacterial
40 agents like triclosan or substituted imidazoles,[66–68] indicated
41 that these compounds fit within the binding pocket
42 occupied by triclosan. The binding pocket of the target
43 receptor can be divided into two main regions: the binding-
44 site entrance, which is lined with both hydrophobic and
45 hydrophilic groups, and a deep cavity, which is mainly
46 hydrophobic. The active compound 5, docked into the
47 active site mapped with electrostatic potential, and 2D
48 ligand interaction diagram are depicted in Figure 2. Red
49 color reveals lowest potential (electron-rich) while blue
50 color indicates highest potential (electron poor) regions.
51 Favorable interactions between compound 5 and the target
52 can be observed in the Figure 2. Negative potential of
53 carbonyl oxygen interacts with the high potential region of
54 the receptor (blue region), and hydrogens attached to the
55 rings are oriented towards the negative potential regions of
56 the receptor.
We believe that those overall favorable interactions
account for the high activity of compound 5.
3.3 In vitro Antimicrobial Activity and SAR
(Structure-activity Relationship) Studies
The in vitro antimicrobial activity of the synthesized com-
pounds (5-28) against Gram positive bacteria Staphylococ-
cus aureus and Bacillus subtilis, Gram-negative bacterium
Escherichia coli and a fungal species Candida albicans was
tested, and the inhibition zones are given in Table 3. The
compounds 5, 6, 7, 8, 15, 16, 17, 20, 27 and 28 showed
promising activities against all bacteria species (S. aureus, B.
subtilis, E. coli) when the inhibition zone diameters are
compared to that of the reference drug Chloramphenicol
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Table 3. Antimicrobial activity test results, inhibition zones of target
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(30 mg – C30). However, according to the comparison
between the inhibition zone diameters of the positive
control Nystatin and the synthesized compounds, no
remarkable antifungal activity was observed against C.
albicans, (Table 3).
compounds.
Inhibition zones diameter (mm)
S. aureus
ATCC
B. subtilis E. coli
C. albicans*
ATCC
Compound
ATCC
6633
ATCC
8739
Minimal inhibition concentration (MIC) values of the
compounds 5, 6, 7, 8, 15, 16, 17, 20, 27 and 28 were
determined and are given in Table 4. All compounds
showed noteworthy inhibition zone diameters against all
bacteria species.
29213
10231
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
40
38
34
40
24
30
30
40
30
38
40
40
36
30
28
38
24
36
36
30
20
26
38
40
–
36
34
34
32
22
26
24
34
26
26
34
30
34
28
22
32
24
30
30
30
20
27
30
32
–
35
35
32.5
33
31
27
24
29
26
31
30.8
36
31
27
24
30
23
30
36
24
30
30
30
30
–
8
7
7
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
The MIC values tabulated in Table 4 shows that almost
all of the selected compounds were found to be more
potent than the reference drug Chloramphenicol against S.
aureus and B. subtilis. Gram-negative bacterium Escherichia
coli seems to be more resistant to the synthesized
compounds. Gram-negative bacteria have an additional
outer membrane (lipopolysaccharide) which initially pro-
tects the bacteria. This behavior was observed in different
studies found in the literature.[69–72] Hence, the presence of
this outer membrane as a permeation barrier could be the
key reason for the diminished potency in Escherichia coli.
A direct correlation of the substituents’ effect on the
activities of the synthesized compounds could not be seen
at a first glimpse. At this point, we referred to the
computational calculations. A small change in a compound
might have a dramatic effect on the activity. Hence, in
discussing SAR, it would be more meaningful to compare
and focus on the compounds on which only one parameter
has been changed. All the synthesized compounds adopted
same orientations as compound 5 when docked into the
active site of the target: the aryl keto group is buried deeply
inside the hydrophobic pocket while the other aryl moiety
on which different R’ substituents were applied, interacts
with the binding site entrance. Hence, one would think that
increasing the hydrophobic character of the R should
increase the activity. If we compare the compounds 5, 13,
and 21 (R’: ÀH for all), although hydrophobicity increases
7
10
11
10
11
6
6
12
12
11
11
12
11
11
11
14
12
13
11
14
–
DMSO
(Negative
control)
Chloramphenicol 30
Nystatin
25
–
27
–
–
30
–
* C. albicans has high resistance to all compounds, according to
zone diameter of positive control nystatin.
Table 4. Minimum Inhibitory Concentration (MIC) of selected compounds.
Minimum Inhibitory Concentration in mg/ml (MIC)
Gr positive coccus
Gr positive rod
(spore forming bacteria)
B. subtilis
Gr negative rod
Compound
R
R’
S. aureus
E. coli
5
6
7
8
9
10
15
16
17
20
27
28
ÀH
ÀH
ÀH
ÀH
ÀH
ÀH
ÀCl
ÀCl
ÀCl
ÀCl
ÀF
ÀH
0.03
0.03
0.06
0.03
64
0.03
0.03
0.06
0.03
64
0.5
1
1
1
>256
32
1
1
4
2
1
2
0.4
ÀBr
ÀCl
ÀF
ÀOCH3
ÀCN
ÀCl
2
1
0.03
0.03
0.25
0.25
0.12
0.03
0.4
0.03
0.03
0.25
0.25
0.03
0.03
0.85
ÀF
ÀOCH3
ÀNO2
ÀPh
ÀNO2
ÀF
Chloramphenicol
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(Table 2) by replacing -H with ÀCl or ÀF, respectively, activity
decreases. As can be seen from Figure 3, there is a T shaped
p-p interaction of TYR146 with the positive quadrupole of
phenyl ring, proximal to the R. Inductive effect of the -F and
-Cl increases the electron density in this area that weakens
p-p interaction. This can clearly be seen in Figure 4 (Lower
left part of each molecule). Compound 5 has higher
potential (electron poor, more positive) where it interacts
with the negative quadrupole of TYR146, than compounds
hand, electron donating substituents at the second aryl ring
was observed to be detrimental to the activity. The results
obtained from the experimental and computational studies
in the present work provide insights in designing potential
antibacterial drug candidates.
Conflict of Interest
10 13 and 21.
None declared.
11
The effect of R’ on activity was also investigated. The
12 compounds with less hindered groups on R’ were found to
13 have potent activities against S. aureus and B. subtilis (5, 6, 7
14 and 8; R: ÀH for all). On the other hand, electron-donating
15 groups were observed to be detrimental to the activity. For
16 instance, keeping R as ÀH but applying a methoxy group on
17 R’ (compound 9) decreases activity by more than 1000-fold
18 (Table 4). As stated before, this compound has highest
19 HOMO energy value in consequence of this electron
20 donating feature (Table 2). This behavior can also be clearly
21 observed for the compounds 17 and 16 where R is ÀCl for
22 both. If the methoxy substituent on R’ of 17 is being
23 replaced with a strong e-withdrawing group -F as in 16, a
24 ten-fold increase in activity is observed (Table 4).
Acknowledgement
¨
The financial support under the contract (KBU-BAP-16/2-YL-
089) from Karabu¨k University is gratefully acknowledged.
References
[1] H. Tahtaci, M. Er, T. Karakurt, A. Onaran, J. Heterocycl. Chem.
2017, 54, 183–193.
[2] M. Petrusova, H. Smrticova, B. Pribulova, S. Vlckova, I.
Uhliarikova, T. Dosca, L. Somsak, L. Petrus, Tetrahedron 2016,
72, 2116–2121.
[3] B. Sun, K. Liu, J. Han, L. Zhao, X. Su, B. Lin, D. M. Zhao, M. S.
Cheng, Bioorg. Med. Chem. 2015, 23, 6763–6773.
[4] A. Lewis, M. McDonald, S. Scharbach, S. Hamaway, M. Plooster,
K. Peters, K. M. Fox, L. Cassimeris, J. M. Tanski, L. A. Tyler, J.
Inorg. Biochem. 2016, 157, 52–61.
25
Interestingly, the most active compound (5) against all
26 bacteria species has no substituents as R or R’. Leaving
27 hydrogen on both positions, removes a possible inductive
28 electron withdrawing effect on R that in turn weakens p-p
29 interaction with the amino acid residue of the target and
30 also avoids a possible steric clash of R’ with the target.
31
[5] P. Bharati, A. Bharti, P. Nath, S. Kumari, N. K. Singh, M. K. Bharty,
Inorg. Chim. Acta 2016, 443, 160–169.
[6] S. J. Singh, S. Rajaminickam, A. Gogoi, B. K. Patel, Tetrahedron
Lett. 2016, 57, 1044–1047.
32
33 4 Conclusion
34
35 In the current study, imidazo[2,1-b][1,3,4]thiadiazole deriva-
36 tives were synthesized using simple reaction methodologies
37 and evaluated for anti-bacterial activities against Gram-
38 negative (Escherichia coli), Gram-positive (Staphylococcus
39 aureus and Bacillus subtilis) bacteria and antifungal activities
40 against Candida albicans. Their structures were elucidated
41 by spectroscopic methods. Although none of the com-
42 pounds showed a remarkable antifungal activity, most of
43 the compounds were found to have potent anti-bacterial
44 activities, some were with MIC values as low as 0.03 mg/ml,
45 ten times more potent than positive control.
[7] A. Banu, R. S. Lamani, I. M. Khazi, N. S. Begum, Mol. Cryst. Liq.
Cryst. 2010, 533, 141–151.
[8] R. Romagnoli, P. G. Baraldi, F. Prencipe, J. Balzarini, S. Liekens, F.
Estevez, Eur. J. Med. Chem. 2015, 101, 205–217.
[9] A. Kamal, V. S. Reddy, K. Santosh, G. B. Kumar, A. B. Shaik, R.
Mahesh, S. S. Chourasiya, I. B. Sayeed, S. Kotamraju, Med. Chem.
Commun. 2014, 5, 1718–1723.
[10] A. Kaur, R. Kumar, U. Kalidhar, Res. J. Pharm. Biol. Chem. Sci.
2012, 3, 1084–1096.
[11] W. S. Alwan, R. Karpoormath, M. B. Palkar, H. M. Patel, R. A.
Rane, M. S. Shaikh, A. Kajee, K. P. Mlisana, Eur. J. Med. Chem.
2015, 95, 514–525.
[12] I. A. M. Khazi, A. K. Gadad, R. S. Lamani, B. A. Bhongade,
Tetrahedron 2011, 67, 3289–3316.
46
According to the electronic structure calculations, al-
47 most all active compounds obey the drug likeness proper-
48 ties. Molecular docking studies further supported inhibitory
49 activities of the compounds and helped understanding the
50 various interactions between the ligands and enzyme active
51 sites.
[13] R. S. Lamani, N. S. Shetty, R. R. Kamble, I. A. M. Khazi, Eur. J.
Med. Chem. 2009, 44, 2828–2833.
[14] S. G. Alegaon, K. R. Alagawadi, Eur. J. Chem. 2011, 2, 94–99.
[15] M. Er, B. Ergꢁven, H. Tahtaci, A. Onaran, T. Karakurt, A. Ece, Med.
Chem. Res. 2017, 26, 615–630.
[16] Y. Luo, S. Zhang, Z. J. Liu, W. Chen, J. Fu, Q. F. Zeng, H. L. Zhu,
Eur. J. Med. Chem. 2013, 64, 54–61.
[17] B. Chandrakantha, A. M. Isloor, P. Shetty, H. K. Fun, G. Hedge,
Eur. J. Med. Chem. 2014, 71, 316–323.
52
While hydrophobicity was found to be an important
53 factor in the aryl keto part of the compounds, electron
54 withdrawing substituents on this region weakens a T
55 shaped p-p interaction with the amino acid residue of the
56 target that results in a decrease in the activity. On the other
[18] K. F. M. Atta, O. O. M. Farahat, A. Z. A. Ahmed, M. G. Marei,
Molecules 2011, 16, 5496–5506.
© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Mol. Inf. 2017, 36, 1700083
(13 of 15) 1700083

Full Paper
www.molinf.com
[19] A. A. Kadi, N. R. El-Brollosy, O. A. Al-Deeb, E. E. Habib, T. M.
Ibrahim, A. A. El-Emam, Eur. J. Med. Chem. 2007, 42, 235–242.
[20] A. K. Gadad, M. B. Palkar, K. Anand, M. N. Noolvi, T. S. Boreddy,
J. Wagwade, Bioorg. Med. Chem. 2008, 16, 276–283.
[21] V. B. Jadhav, M. V. Kulkarni, V. P. Rasal, S. S. Biradar, M. D. Vinay,
Eur. J. Med. Chem. 2008, 43, 1721–1729.
[22] J. Ramprasad, N. Nayak, U. Dalimba, P. Yogeeswari, D. Sriram,
Bioorg. Med. Chem. Lett. 2015, 25, 4169–4173.
[23] J. Ramprasad, N. Nayak, U. Dalimba, P. Yogeeswari, D. Sriram,
S. K. Peethambar, R. Achur, H. S. S. Kumar, Eur. J. Med. Chem.
2015, 95, 49–63.
J. K. Perry, P. Francis, P. S. Shenkin, J. Med. Chem. 2004, 47,
1739–1749.
1
2
3
4
5
6
7
8
9
[46] T. A. Halgren, R. B. Murphy, R. A. Friesner, H. S. Beard, L. L. Frye,
W. T. Pollard, J. L. Banks, J. Med. Chem. 2004, 47, 1750–1759.
[47] R. A. Friesner, R. B. Murphy, M. P. Repasky, L. L. Frye, J. R.
Greenwood, T. A. Halgren, P. C. Sanschagrin, D. T. Mainz, J. Med.
Chem. 2006, 49, 6177–6196.
[48] J. J. P. Stewart, J. Mol. Model. 2007, 13, 1173–1213.
[49] T. Puzyn, N. Suzuki, M. Haranczyk, J. Rak, J. Chem. Inf. Model.
2008, 48, 1174–1180.
[50] Schrçdinger Release 2017–1: QikProp. Schrçdinger, LLC, New
York, NY, 2017.
[51] Bruker. APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin,
USA, 2008.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
[24] S. G. Alegaon, K. R. Alagawadi, P. V. Sonkusare, S. M. Chaudhary,
D. H. Dadwe, A. S. Shah, Bioorg. Med. Chem. Lett. 2012, 22,
1917–1921.
[25] A. K. Gadad, M. N. Noolvi, R. V. Karpoormath, Med. Chem. 2004,
12, 5651–5659.
[26] A. I. Khazi, C. S. Mahajanshetti, A. K. Gadad, A. D. Tarnalli, C. M.
Sultanpur, Arzneimittelforschung 1996, 46, 949–952.
[27] A. Andreani, M. Rambaldi, G. Mascellani, P. Rugarli, Eur. J. Med.
Chem. 1987, 22, 19–22.
[28] M. Kumar, D. Jayappaa, J. P. Dasappaa, R. E. Puthallathb, P. A.
Castelinoa, Der Pharma Chemica 2016, 8, 178-190.
[29] M. A. Eldawy, S. A. S. El-Dine, K. M. El-Brambaly, Pharmazie,
1979, 34, 144.
[30] C. Bertuccia, D. Tedescoa, E. Fabinia, A. M. D. Pietra, F. Rossib,
M. Garagnani, E. D. Borrello, V. Andrisano, J. Chromatogr. A
2014, 1363, 150–154.
[31] N. Terzioglu, A. Gꢁrsoy, Eur. J. Med. Chem. 2003, 38, 781–786.
[32] A. K. Gadad, C. S. Mahajanshetti, S. Nimbalkar, A. Raichurkar,
Eur. J. Med. Chem. 2000, 35, 853–857.
[33] G. Tegginamath, R. R. Kamble, T. Taj, P. P. Kattimani, G. Y. Meti,
Med. Chem. Res. 2013, 22, 4367–4375.
[34] M. N. Noolvi, H. M. Patel, S. Kamboj, A. Kaur, V. Mann, Eur. J.
Med. Chem. 2012, 56, 56–69.
[35] S. S. Karki, K. Panjamurthy, S. Kumar, M. Nambiar, S. A.
Ramareddy, K. K. Chiruvella, C. Raghavan, Eur. J. Med. Chem.
2011, 46, 2109–2116.
[52] O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard, H.
Puschmann, J. Appl. Cryst. 2009, 42, 339–341.
[53] G. M. Sheldrick Acta Cryst. 2015, A71, 3–8.
[54] G. M. Sheldrick Acta Cryst. 2015, C71, 3–8.
[55] K. M. Agrawal, G. S. Talele, Med. Chem. Res. 2013, 22, 818–831.
[56] C. Valgas, S. M. De Souza, E. F. Smania, A. Smania, Braz. J.
Microbiol. 2007, 38, 369–80.
[57] I. Wiegand, K. Hilpert, R. E. W. Hancock, Nature Protocols 2008,
3, 163–175.
[58] CLSI/NCCLS Guidelines: Methods for Dilution Antimicrobial
Susceptibility Tests for Bacteria that Grow Aerobically; 7th Ed.
Approved Standard document M-7:A5, Villanova, PA, NCCLS,
2006.
[59] K. Sancak, Y. ꢂnver, M. Er, Turk. J. Chem. 2007, 31, 125–134.
˘
˘
[60] K. Serbest, H. Kayi, M. Er, K. Sancak, I. Degirmencioglu,
Heteroatom Chem. 2008, 19, 700–712.
[61] M. Er, Y. ꢂnver, K. Sancak, E. Dꢁgdꢁ, Arkivoc 2008, 15, 99–120.
[62] C. A. Lipinski, F. Lombardo, B. W. Dominy, P. J. Feeney, Adv. Drug
Delivery Rev. 1997 23, 3–25.
[63] D. F. Veber, S. R. Johnson, H. Y. Cheng, J. Med. Chem. 2002, 45,
2615–2623.
[64] A. Ece, F. Sevin, Med. Chem. Res. 2013, 22, 5832–5843.
[65] N. M. Mascarenhasa, N. Ghoshal, Eur. J. Med. Chem. 2008, 43,
2807–2818.
[66] D. A. Heerding, G. Chan, W. E. DeWolf, A. P. Fosberry, C. A.
Janson, D. D. Jaworski, E. McManus, W. H. Miller, T. D. Moore,
D. J. Payne, X. Qiu, S. F. Rittenhouse, C. Slater-Radosti, W. Smith,
D. T. Takata, K. S. Vaidya, C. C. K. Yuan, W. F. Huffman, Bioorg.
Med. Chem. Lett. 2001, 11, 2061–2065.
[67] D. J. Payne, P. V. Warren, D. J. Holmes, Y. Ji, J. T. Lonsdale, Drug
Discovery Today 2001, 6, 537–544.
[68] X. Qiu, C. A. Janson, R. I. Court, M. G. Smyth, D. J. Payne, S. S.
Abdel-Meguid, Protein Sci. 1999, 8, 2529–2532.
[69] J. Jin, Y. H. Hsieh, J. Cui, K. Damera, C. Dai, A. S. Chaudhary, M.
Vaara, ChemMedChem. 2016, 11, 2511-2521.
[70] N. H. A. Barudin, S. Sreekantan, M. T. Ong, C. W. Lai, Food
Control 2014, 46, 480-487.
[71] T. A. Dahl, W. R. Midden, P. E. Hartman, J. Bacteriol. 1989, 171,
2188-2194.
[36] D. Sunil, A. M. Isloor, P. Shetty, K. Satyamoorthy, A. S. B. Prasad,
Arabian J. Chem. 2010, 3, 211–217.
[37] M. N. Nolvi, H. M. Patel, N. Singh, A. K Gadad, S. S. Cameotra, A.
Badiger, Eur. J. Med. Chem. 2011, 46, 4411–4418.
[38] S. Kumar, M. Hedge, V. Gopalakrishnan, V. K. Renuka, S. A.
Ramareddy, E. De Clercq, D. Schols, A. K. G. Narasimhamurthy,
S. C. Raghavan, S. S. Karki, Eur. J. Med. Chem. 2014, 84, 687–697.
[39] S. Jalhan, A. Jındal, A. Gupta, Hemraj, Asian J. Pharm. Clin. Res.
2012, 5, 199–208.
[40] G. Kolavi, V. Hegde, I. A. Khazi, Tetrahedron Lett. 2006, 47, 2811–
2814.
[41] T. Z. Tzitzikas, C. G. Neochoristis, J. S. Stephanatou, C. A.
Tsoleridis, G. Buth, G. E. Kostakis, Tetrahedron 2013, 69, 5008–
5015.
[42] D. A. Gschwend, A. C. Good, I. D. Kuntz, J. Mol. Recognit. 1996,
9, 175–186.
[43] Schrçdinger Release 2017–1: LigPrep, Schrçdinger, LLC, New
York, NY, 2017.
[44] E. Harder, W. Damm, J. Maple, C. Wu, M. Reboul, J. Y. Xiang, L.
Wang, D. Lupyan, M. K. Dahlgren, J. L. Knight, J. W. Kaus, D. S.
Cerutti, G. Krilov, W. L. Jorgensen, R. Abel, R. A. Friesner, J.
Chem. Theory Comput. 2016, 12, 281–296.
[45] R. A. Friesner, J. L. Banks, R. B. Murphy, T. A. Halgren, J. J. Klicic,
D. T. Mainz, M. P. Repasky, E. H. Knoll, D. E. Shaw, M. Shelley,
[72] Y. Gao, M. J. van Belkum, M. E. Stiles, Appl. Environ. Microbiol.
1999, 65, 4329-4333.
Received: June 20, 2017
Accepted: August 19, 2017
Published online on && &&, 0000
© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Mol. Inf. 2017, 36, 1700083
(14 of 15) 1700083

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FULL PAPER
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H. Tahtaci*, H. Karacık, A. Ece*, M. Er,
M. G. S¸eker
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1 – 15
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Design, Synthesis, SAR and
Molecular Modeling Studies of
Novel Imidazo[2,1-b][1,3,4]Thiadia-
zole Derivatives as Highly Potent
Antimicrobial Agents
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