Synthesis, anti-HIV activity, molecular modeling study and QSAR of new designed 2-(2-arylidenehydrazinyl)-4-arylthiazoles

Article abstract of DOI:10.1016/j.molstruc.2019.07.113

Taking into consideration the eminence of 1,3-thiazoles in medicinal chemistry and in a view of procuring more pronounced biological contour, the synthesis of 2-(2-arylidenehydrazinyl)-4-arylthiazoles 6–43 was made possible by the cyclization reaction of thiosemicarbazones and α-bromoacetophenones. The thiosemicarbazones 5a-m were in turn synthesized from substituted benzaldehydes or acetophenones and thiosemicarbazide. Optimization of the reaction conditions was carried out in order to attain the target molecules in good yields. All the new compounds were evaluated in vitro for their antiviral activity against the replication of HIV-1 and HIV-2 in MT4 cells using a MTT assay. Screening results indicated that compounds 32–34 are the only compounds in the series inhibiting HIV-1 and HIV-2 replication in cell cultures with IC₅₀ of >2.71, >2.19 and > 1.71 μM, respectively. The molecular docking of compounds 32 and 34 with some amino acids of human immunodeficiency virus reverse transcriptase (HIV RT) were also studied. The preliminary quantum structure-activity relationship (QSAR) among the newly synthesized congeners was obtained by two methods, Multiple Linear Regression (MRL) and Genetic Function Approximation (GFA).

Full text of DOI:10.1016/j.molstruc.2019.07.113

Journal of Molecular Structure 1198 (2019) 126866
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Synthesis, anti-HIV activity, molecular modeling study and QSAR of
new designed 2-(2-arylidenehydrazinyl)-4-arylthiazoles
, *, 1
Amna Rauf a, Muhammad K. Kashif a, Bahjat A. Saeed b, Najim A. Al-Masoudi c
,
,
**
Shahid Hameed a
a Department of Chemistry, Quaid-i-Azam University, Islamabad, 45320, Pakistan
b Department of Chemistry, College of Education for Pure Sciences, University of Basrah, Basrah, Iraq
c Department of Chemistry, College of Science, University of Basrah, Basrah, Iraq
a r t i c l e i n f o
a b s t r a c t
Article history:
Taking into consideration the eminence of 1,3-thiazoles in medicinal chemistry and in a view of pro-
Received 2 June 2019
Received in revised form
28 July 2019
Accepted 28 July 2019
Available online 31 July 2019
curing more pronounced biological contour, the synthesis of 2-(2-arylidenehydrazinyl)-4-arylthiazoles 6
e43 was made possible by the cyclization reaction of thiosemicarbazones and a-bromoacetophenones.
The thiosemicarbazones 5a-m were in turn synthesized from substituted benzaldehydes or acetophe-
nones and thiosemicarbazide. Optimization of the reaction conditions was carried out in order to attain
the target molecules in good yields. All the new compounds were evaluated in vitro for their antiviral
activity against the replication of HIV-1 and HIV-2 in MT4 cells using a MTT assay. Screening results
indicated that compounds 32e34 are the only compounds in the series inhibiting HIV-1 and HIV-2
Keywords:
Anti-HIV activity
Arylthiazoles
Cytotoxicity
Molecular docking study
QSAR
replication in cell cultures with IC50 of >2.71, >2.19 and > 1.71 mM, respectively. The molecular docking
of compounds 32 and 34 with some amino acids of human immunodeficiency virus reverse transcriptase
(HIV RT) were also studied. The preliminary quantum structure-activity relationship (QSAR) among the
newly synthesized congeners was obtained by two methods, Multiple Linear Regression (MRL) and
Genetic Function Approximation (GFA).
© 2019 Published by Elsevier B.V.
1. Introduction
[25], anti-inflammatory [26], analgesic [27], and anti-convulsant
[28]. Thiazole-containing drug molecules are currently being used
Thiazoles have exhibited a broad spectrum of pharmacological
activities as drugs for the treatment of a large number of diseases
including viral [1], tumor [2e5], tubercular [6], alzheimer's [7],
diabetes [8], leukemia [9], microbial [10], HIV, HCV, HAV and HSV
[11,12]. Some of the approved drugs having thiazole backbone are
dasatinib (anticancer) [13], ritonavir (anti-HIV-1) [14] (1, Fig. 1),
nizatidine (anti-ulcer) [15] and fentiazac (anti-inflammatory) [16].
In addition, numerous 1,3-thiazole analogues exhibit remarkable
anti-HIV activity [17e19] (e.g: 2, IC50 HIV RT ¼ 0.016 nM, Fig.1) [20],
besides many other pharmacological activities such as anti-cancer
[21,22], urokinase inhibitors [23], anti-allergic [24], anti-oxidant
in the treatment of various central nervous system disorders [29].
Recently, Chimenti et al. [30] reported the synthesis and pharma-
cological activity of cyclopentylidene-[4-(40-chlorophenyl)thiazol-
2-yl]hydrazine (CPTH2, 3, Fig. 1) as a selective inhibitor of histone
acetyltransferase Gcn5P (HAT), both in vitro and in vivo
(IC50 ¼ 0.80
mM). Deregulated HAT and histone deacetylase (HDAC)
activity plays a role in the development of a range of cancers.
Consequently, inhibitors of these enzymes have potential as anti-
cancer agents.
Considering the pharmacological significance of thiazole de-
rivatives and in continuation of our attempts to develop new potent
HIV-1 NNRTIs [31e35] herein we report the synthesis of a new
series of 2-(2-arylidenehydrazinyl)-4-arylthiazoles and their effi-
cacy as anti-HIV agents together with the quantum structure-
activity relationship (QSAR) and molecular docking studies.
* Corresponding author.
** Corresponding author.
E-mail addresses: najim.al-masoudi@gmx.de (N.A. Al-Masoudi), shameed@qau.
edu.pk (S. Hameed).
URL: http://www.al-masoudi.de
Present address: Am Tannenhof 8, 78464 Konstanz, Germany.
1
https://doi.org/10.1016/j.molstruc.2019.07.113
0022-2860/© 2019 Published by Elsevier B.V.

2
A. Rauf et al. / Journal of Molecular Structure 1198 (2019) 126866
Fig. 1. Some thiazole derivatives as potentially active anti-HIV and anticancer agents.
2. Experimental section
(IIIB) and HIV-2 strain (ROD) in MT-4 cells was performed using an
MTT assay as described previously [36]. In brief, stock solutions (10-
times final concentration) of test compounds were added in 25-mL
volumes to two series of triplicate wells to allow simultaneous
evaluation of their effects on mock and HIV-infected cells at the
beginning of each experiment. Serial five-fold dilutions of test
compounds were made directly in flat-bottomed 96-well microtiter
trays using a Biomek 3000 robot (Beckman instruments). Untreated
control, HIV- and mock-infected cell samples were included for
Gallenkamp melting point apparatus MP-D (Northampton, UK)
was used for the determination of melting points. The melting
points were measured using open capillaries and are uncorrected.
The IR spectra were recorded on Thermo Scientific (Waltham, USA)
model Nicolet-6700 spectrophotometer and the strongest IR bands
are listed. 1H NMR and 13C NMR spectra were run on a Bruker
(Switzerland), Avance 300 MHz spectrophotometer. All the re-
actions were monitored using thin layer chromatography (TLC)
plates 60F254 purchased from Merck (Germany), using n-hexane:
ethyl acetate 3:2 as eluent.
each sample. HIV-1 (IIIB) [37] or HIV-2 (ROD) [38] stock (50 mL) at
100e300 CCID50 (50% cell culture infectious dose) or culture me-
dium was added to either of the infected or mock-infected wells of
the microtiter tray. Mock-infected cells were used to evaluate the
effect of test compound on uninfected cells in order to assess the
cytotoxicity of the test compounds. Exponentially growing MT-
4 cells [39] were centrifuged for 5 min at 1000 rpm (Minifuge T,
rotor 2250; Heraeus, Germany), and the supernatant was dis-
carded. The MT-4 cells were resuspended at 6 ꢁ 105 cells per mL,
2.1. General procedure for the synthesis of thiosemicarbazones (5a-
m)
The respective substituted aldehyde or acetophenone
(10.00 mol) was dissolved in MeOH (20 mL) followed by addition of
2e3 drops of HOAc as a catalyst. The reaction mixture was stirred
under reflux for 15 min. To this solution, equimolar thio-
semicarbazide was added and the mixture was heated under reflux
for 5e6 h, while the reaction progress was monitored using TLC.
The mixture was cooled to ambient temperature, the precipitated
product filtered, washed with water followed by MeOH and dried.
Recrystallization from MeOH or EtOH afforded the desired
thiosemicarbazone.
and volumes of 50 mL were transferred to the microtiter tray wells.
Five days after infection, the viability of the mock- and HIV-infected
cells was examined spectrophotometrically.
4. Results and discussion
4.1. Chemistry
The synthesis of 2-(2-arylidenehydrazinyl)-4-arylthiazoles was
achieved in two steps by reacting aldehydes/acetophenones with
thiosemicarbazide using acetic acid as a catalyst according to a
reported procedure [40] to afford thiosemicarbazones 5a-m
2.2. General procedure for the synthesis of 2-(2-
arylidenehydrazinyl)-4-arylthiazoles (6e43)
Phenacyl bromide analogue (1.00 mmol) was dissolved in a
mixture of MeOH-EtOH (20 mL) and the solution was stirred with
heating at 50e60 ꢀC for 20 min. Equimolar amount of thio-
semicarbazone 5a-m (1.00 mmol) was added, the reaction mixture
heated under reflux for 5e6 h and monitored using TLC. After the
completion of reaction, the precipitated product was filtered or
alternatively the solvent was evaporated to get the crude product.
The product was recrystallized from MeOH or EtOH to give the
desired product.
(Scheme 1) followed by their treatment with
a-bromoacetophe-
nones to result in the synthesis of target molecules, 2-(2-
arylidenehydrazinyl)-4-arylthiazoles 6e43 (Scheme 2).
The structures of compounds 5a-m were ingrained using IR, 1H
and 13C NMR spectroscopy. The IR spectra depicted absorption
bands in the range of 1507-1450 cmꢂ1 assigned to newly formed
C]N bond. The N-H stretching absorptions were detected in the
region of 3500-3100 cmꢂ1, whereas the absorption bands from
1380 to 1340 cmꢂ1 were assigned to C]S functionality. In the 1H
NMR spectra of 5a-m, the singlet in the region d 7.95e8.42 ppm was
3. Biological activity assays
assigned to the azomethine proton (-HC]N) and affirmed the
formation of thiosemicarbazones. The broad singlet in the region
3.1. In vitro anti-HIV assay
d
10.10e11.71 ppm corresponded to N-H proton, while the two
broad singlets in the region 7.77e8.43 ppm were ascribed to NH2
protons. Majority of the target compounds were witnessed to be
d
Evaluation of the antiviral activity of 6e43 against HIV-1 strain

A. Rauf et al. / Journal of Molecular Structure 1198 (2019) 126866
3
Scheme 1. Synthesis of thiosemicarbazones (5a-m).
Scheme 2. Synthesis of 2-(2-arylidenehydrazinyl)-4-arylthiazoles (6e43).
amorphous and were attained in moderate to very good yields
(65e90%).
Next, treatment of the thiosemicarbazones 5a-m with phena-
cylbromides in MeOH and catalytic amount of HOAc gave 2-(2-
arylidenehydrazinyl)-4-arylthiazole analogues 6e43 in 64e95%
yield (Scheme 2).
The structures of thiazoles 6e43 were confirmed from their IR,
1H, and 13C NMR spectra, which showed rather similar patterns of
the proton and carbon signals of thiazole scaffold. The IR spectra
were characterized by the presence of only one absorption band for
NH stretching vibrations in the range 3250e3500 cmꢂ1. The ab-
sorption band in the range of 1498e1604 cmꢂ1 was attributed to
C]N functionality of the thiazole backbone and imine residue,
while the absorptions in the range 1591e1638 cmꢂ1 was assigned
to C]C streching vibrations. In 1H NMR spectra, a singlet in the
range
meanwhile NH proton appeared in the range of
as a broad singlet. The azomethine (-HC]N) proton in compounds
6e43 appeared as a singlet in the region of 7.39e8.19 ppm. The
aromatic and pyridine protons as well as the other substituents
have also been fully assigned (cf. Experimental section). In the 13C
NMR spectra, the low field resonances in the regions
d
6.92e8.15 ppm was assigned to H-5 of the thiazole ring,
d
10.10e13.00 ppm
d
d
166.5e173.8 ppm were assigned to C-2 of the thiazole moiety. C-4
and C-5 of the thiazole backbone resonated in the regions
141.9e150.1 and 101.8e110.8 ppm, respectively, while azome-
thine carbon (HC]N) in compounds 6e13 and 14e43 resonated in
the region 135.1e143.4 ppm. The carbon atom of the azomethine
group (MeC ¼ N) in thiazoles 14e27 appeared in the region
170.0e173.8 ppm together with C-2 of the thiazole ring. Com-
pounds 16e19 showed resonances in the regions 132.2e135.7 and
d
d
d
d

4
A. Rauf et al. / Journal of Molecular Structure 1198 (2019) 126866
139.1e141.1 ppm assigned to C-2000 and C-4000 of the imidazole
Table 1
In vitro anti-HIV-1a and HIV-2b activity of 2-(2-arylidenehydrazinyl)-4-arylthiazoles
6e43.
moiety, respectively, while C-5000 of the same group appeared in the
region of
methylenedioxy (residue (OCH2O) in compounds 23e26 appeared
in the region 105.5e105.9 ppm. The other substituents and aro-
d
120.9e121.6 ppm. The carbon atom of 3,4-
Compd.
Virus strain
av. IC50
(
m
M)c
av. CC50
(
m
M)d
SIe
d
6
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
>48.70
>48.70
48.70
48.70
101.62
101.62
103.84
103.84
125.00
125.00
125.00
125.00
10.55
10.55
73.58
73.58
125.00
125.00
10.23
10.23
66.15
66.15
87.33
87.33
92.25
92.25
73.95
73.95
38.90
38.90
13.05
13.05
17.10
17.10
14.07
14.07
41.93
41.93
21.83
21.83
68.28
68.28
97.20
97.20
16.39
16.39
11.30
11.30
27.90
27.90
10.04
10.04
2.97
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
matic carbons were also fully analysed (cf. Experimental section).
7
>101.62
>101.62
>103.84
>103.84
>125.00
>125.00
>125.00
>125.00
>10.55
>10.55
>73.58
>73.58
>125.00
>125.00
>10.23
>10.23
>66.15
>66.15
>87.33
>87.33
>92.25
>92.25
>73.95
>73.95
>38.90
>38.90
>13.05
>13.05
>17.10
>17.10
>14.07
>14.07
>41.93
>41.93
>21.83
>21.83
>68.28
>68.28
>97.20
>97.20
>16.39
>16.39
>11.30
>11.30
>27.90
>27.90
>10.04
>10.04
>2.97
4.2. In vitro anti-HIV activity
8
Compounds 6e43 were evaluated for their inhibitory activity
against HIV-1 (strain IIIB) and HIV-2 (strain ROD) and monitored by
the inhibition of the virus-induced cytopathic effect in the human
T-lymphocyte (MT-4) cells, using 3-(4,5-dimethylthiazol-2-yl)-2,5-
diphenyltetrazolium bromide (MTT) assay [36]. The results are
summarized in Table 1, in which the data for nevirapin, (BOE/
BIRG587) [41] and azidothymidine (AZT) (DDN/AZT) [42] are
included for comparison purpose. Compounds-induced cytotox-
icity was also measured in MT-4 cells, parallel with the antiviral
activity. Of the title compounds tested, compounds 32
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
(IC50 > 2.71 mM), 33 (IC50 > 2.91 mM), and 34 (IC50 > 1.71 mM), were
found to be the active compounds which inhibited HIV-1 ad HIV-2
replication in cell culture, however, no selectivity was observed
(SI < 1).
With respect to structure-activity relationship studies, D'Cruz
et al. [43,44], and Sudbeck et al. [45] have reported that the
molecule containing an intramolecular hydrogen bonding would
lock the molecule into a more rigid conformation and impart a
more compact molecular shape. The presence of this hydrogen
bond is consistent with modeling studies undertaken to predict
how the inhibitor could bind to the non-nucleoside inhibitors'
(NNI) binding site of HIV RT, as shown in the anti-HIV drug trovi-
drine [46], PHI236 [44], and our target molecule 34 (Fig. 2). Such
compact conformation would allow these molecules to more easily
fit into the pocket of the reverse transcriptase binding site.
Accordingly, the combined three portions (2-pyridyl moiety,
hydrazono group as a spacer, and thiazole scaffold) of compounds
32e34 are considered as the optimal substituents that would give
rise to the optimal activity. After proceeding with docking studies,
it was observed that compounds 34 is well tolerated in the hy-
drophobic region of HIV RT and showed higher activity than those
of 32 and 33 analogues. In conclusion, compound 34 was found to
be a potent agent against HIV and identified as a new candidate to
act as a NNRTI; it might be considered a promising agent for further
structural modifications and pharmacological evaluation.
4.3. Molecular modeling analysis
>2.97
>2.71
>2.71
>2.19
>2.19
>1.71
>1.71
>17.30
>17.30
>11.60
>11.60
>23.39
>23.39
>7.73
2.97
2.71
2.71
2.19
2.19
1.71
1.71
17.30
17.30
11.60
11.60
23.39
23.39
7.73
The molecular docking was performed using the Molecular
Operating Environment 2016 (MOE 2016) software and the docking
results were also shown by MOE [47]. Molecular docking analysis of
the new analogues is based on the modeling study, which was
performed to understand the binding mode of these analogues
with HIV-RT binding pocket (NNIBP) (PDB ID: 3DLG) [48]. The
molecular binding simulation results of the most active compounds
in this study, 32 and 34, with HIV-1 RT are displayed in Fig. 3, panels
A and B.
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
According to the HIV-1 RT docking results, it was observed that
compound 32 was able to display one
p-cationic interaction be-
>7.73
7.73
tween the thiazolyl ring of the molecule and the Leu100 of the
active site. Moreover, it was found that compound 34 binds to RT
with only one H-bond between its thiazole NH and Lys101. As
shown in Fig. 3, the aromatic ring of compound 32 and 2-pyridine
ring of compound 34 fitted into an arene-rich subpocket sur-
rounded by the aromatic side chains of Tyr318 and His235 residues.
>62.40
>62.40
>125.00
>125.00
>125.00
>125.00
>53.10
62.40
62.40
125.00
125.00
125.00
125.00
53.10
ROD
IIIB
Overall, the combination of hydrophobic interaction and
p
ꢂ

A. Rauf et al. / Journal of Molecular Structure 1198 (2019) 126866
5
Table 1 (continued )
quantitative structure activity relationship analyses as the response
variables.
Compd.
Virus strain
av. IC50
(
m
M)c
av. CC50
(m
M)d
SIe
With the selected descriptors, we have built a linear model us-
ing the set data of 31 substituted thiazole analogues and the
following equation was obtained:
ROD
IIIB
ROD
IIIB
ROD
IIIB
ROD
IIIB
>53.10
>75.60
>75.60
0.05
53.10
75.60
75.60
>4.00
>4.00
>25
>25
>20
>20
<1
<1
<1
>80
<1
>13144
>14245
>39
>10
43
Nevirapin
Model 1:
4.00
pIC50
0.001357558 [Dipole z*Octupole xxx] - 0.008655028 [Quadrupole
xx*AlogP 0.000019295 [Octupole xxx*Octupole
yyy] þ 2.081215644.
¼
- 0.096429907 [HOMO*Hydrogen bond donor] -
AZT
3 TC
0.0019
0.0018
0.51
þ
ROD
2.02
S value ¼ 0.55697600, F value ¼ 29.85550000, Regression coef-
a
Anti-HIV-1 activity measured against strain IIIB.
anti-HIV-2 activity measured against strain ROD.
Compound concentration required to achieve 50% protection of MT-4 cells from
R2 ¼ 0.82121,
Cross
validation,
b
c
ficient,
R ¼ 0.906206,
R2(CV) ¼ 0.633876.
HIV-1 and 2-induced cytopathogenic effect.
Average CC50: compound concentration that reduces the viability of mock-
infected MT-4 cells by 50%.
Compounds 22 and 35 are outliers and, therefore, were
d
excluded.
e
SI: selectivity index (CC50/IC50). All data represents the mean values of at least
two separate experiments.
4.4.2. Genetic function approximation (GFA)
The Genetic Function Approximation (GFA) algorithm has a
number of important advantages over other standard regression
analysis techniques [51], since it forms multiple models instead of a
single model. It uses a genetic algorithm to perform a search over
the space of possible QSAR/QSPR models using the LOF score to
estimate the fitness of each model. Genetic Function Approxima-
tion has the advantage of producing more than one combination of
descriptors using lack of fit function to eliminate over fitting, while
Multi-linear regression Approach (MLR) provides the user with the
choice of multi equation. A set data of 31 substituted thiazole an-
alogues with selected descriptors has been chosen to study their
QSAR using GFA method to generate a linear model 2 with the
equation obtained for calculating predictive anti-HIV activity as
shown in Table 3 (Supplementary Material).
p
stacking appears to govern the binding of compounds 32 and 34
with HIV RT.
4.4. Quantitative structure-activity relationship
QSAR plays a crucial role in drug development as it analyzes the
properties of the drug. It is a mathematical model that links the
structural features of the compounds (i.e. molecular descriptors) to
their quantity showing specific biological or chemical activity [49].
It gives description of how biological activity can vary as a function
of molecular descriptors derived from the chemical structure of a
set of molecules using regression models. Hence, a model con-
taining those calculated descriptors can be used to predict re-
sponses of the new compounds. The molecular descriptors for the
compounds are calculated and used to build QSAR Model. The QSAR
models were developed using different statistical methods like
stepwise multiple linear regression, genetic function approxima-
tion [50] and genetic partial least squares with descriptors of
different categories (quantum chemical, physicochemical, spatial
and substituent constants). In this study, the QSAR models were
built by means of Multiple Linear Regressions (MLR) and Genetic
Function Approximation (GFA) techniques embedded in Material
Studio, a modeling and simulation software using the experimen-
tally obtained biological activities as the dependent variables and
the computed molecular descriptors as independent variables.
Model 2.
pIC50 ¼ - 0.051946360 Quadrupole xy þ 0.006543703 Octutpole
yyy - 0.000066911 Heat of Formation þ0.004242579 Quadrupole
yz - 0.003485987 * (ramp(- 26.839130145 - Quadrupole xy))2
-
0.000066774
*
(ramp(83.535618337
e
Octupole
xyz))2 þ 5.125958689.
Friedman
L.O.F. ¼ 0.703197,
R2¼0.912995,
Adjusted
R2 ¼ 0.89291700, Cross validated R2 ¼ 0.86083700, Significant
regression: Yes, Significance-of-regression F value ¼ 45.472389.
Compounds 22, 33, 35, and 39e41 are outliers and were
excluded.
To determine which QSAR model better describes our data, we
evaluated several statistical parameters, such as the fraction of
variance (R2), the correlation coefficient (R) and the Friedman's
lack-offit (LOF). Among the QSAR models, we found the best cor-
relation between independent and dependent variables with
model 2. In the GFA analysis, the Friedman's lack-offit (LOF), F and
R2 scores evaluate the QSAR model. Thus, the lower the LOF, the less
likely it is that the GFA model will fit the data. The significant
regression is given by the F test, the higher the value, the better is
the model. In addition, the high value of the correlation coefficient,
4.4.1. Multiple-linear regressions (MLR)
The MLR model was employed to derive the quantitative
structure-activity relationship models for differently substituted 31
thiazole derivatives and as a training set has been developed for the
prediction of their pIC50 against HIV activity, using selected quan-
tum chemical descriptors (Table 2, Supplementary Material).
The activity data [IC50
(mM)] was converted to the logarithmic
scale pIC50 [-log IC50 (M)] and then used for the subsequent
Fig. 2. Rational design of trovirdine, PHI236 and thiazole 34. 2-Pyridine group is capable of forming an intramolecular H-bonded heterocyclic ring with NH of hydrazono group, and
enhance anti-HIV activity.

6
A. Rauf et al. / Journal of Molecular Structure 1198 (2019) 126866
Fig. 3. The binding mode of compounds 32 and 34 with HIV RT (PDB ID: 3DLG). Panels A and B represent the 2D and 3D binding modes of the ligands with essential active site
amino acids of HIV-RT, respectively.
R2 (0.912995), indicated that the model was satisfactory.
In conclusion, the proposed model has good stability,
Acknowledgements
2
robustness and predictability when verified by internal and
external validation. The binding scores for the tested compounds
were congruent with their anti-HIV activity. A good correlation
between the predicted and the experimentally observed inhibitory
activities (pIC50) (Table 3) of the most thiazole analogues suggested
that the identified binding conformations of these inhibitors are
reliable. The results of docking studies provided an insight into the
pharmacophoric structural requirements for HIV RT inhibitory ac-
tivity of this class of molecules.
We thank Prof. C. Pannecouque of Rega Institute for Medical
Research, Katholieke Universiteit, Leuven, Belgium, for the anti-HIV
screening.
Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.molstruc.2019.07.113.
References
5. Conclusion
[1] N.I. Zelisko, I.L. Demchuk, R.B. lesyk, New thiopyrano[2,3-d][1,3]thiazole de-
rivatives as potential antiviral agents, Ukran. Biochem. J. 88 (2016) 105e112,
https://doi.org/10.15407/ubj88.si01.105.
[2] R. Romagnoli, P.G. Baraldi, C.L. Cara, M.K. Salvador, R. Brotolozzi, G. Basso,
G. Viola, J. Balzarini, A. Brancale, X.-H. Fu, J. Li, S.-Z. Zhang, E. Hamel, One pot
synthesis and biological evaluation of 2-pyrolidinyl-4-amino-5-(3ʹ, 4ʹ, 5ʹ-tri-
methoxybenzoyl)thiazole: a unique highly active microtubule agent, Eur. J.
Med. Chem. 46 (2011) 6015e6024, https://doi.org/10.1016/j.ejmech. 2011.
10.013.
We have described herein the synthesis and evaluation of anti-
HIV-1 and HIV-2 activities of new 2-(2-arylidenehydrazinyl)-4-
arylthiazole derivatives 6e43. Compounds 32e34 showed signifi-
cant inhibition of HIV-1 and HIV-2 replication in cell cultures with
IC50 of >2.71, >2.19 and > 1.71 mM, respectively. The HIV-1 RT
[3] H.I. E1-Subbagh, A.M., A1-Obaid, 2,4-Disubstituted thiazoles II. A novel class of
antitumor agents, synthesis and biological evaluation, Eur. J. Med. Chem. 31
(1996) 1017e1021, https://doi.org/10.1016/S0223-5234(97)86181-8.
[4] G.S. Hassan, S.M. Al-Messery, F.A. Al-Omary, H.I. El-Subbagh, Substituted
thiazole VII. Synthesis and anti-tumor activity of certain 2-(substituted
amino)-4-phenyl-1,3-thiazole analogs, Bioorg. Med. Chem. Lett 22 (2012)
6318e6323, https://doi.org/10.1016/j.bmcl.2012.08.095.
docking results revealed that compound 34 binds to RT with a H-
bond between its thiazole NH and Lys101. This analogue could be a
promising candidate which may be a useful lead in HIV inhibition
studies. QSAR studies have given significant information of the
biological activity by using MLR and GFA methods, since their
models showed a good correlation between the predicted and the
experimentally observed inhibitory activities (pIC50).
[5] F. Ghanbari Pirbasti, N.O. Mahmoodi, Facile synthesis and biological assays of
novel 2,4-disubstituted hydrazinyl-thiazoles analogs, Mol. Divers. 20 (2016)

A. Rauf et al. / Journal of Molecular Structure 1198 (2019) 126866
7
497e506, https://doi.org/10.1007/s 11030-015-9654-7.
B.S. Dawane, Synthesis and in silico investigation of thiazoles bearing pyr-
azoles derivatives as anti-inflammatory agents, Comput. Biol. Chem. 61 (2016)
86e96, https://doi.org/10.1016/j.compbiolchem. 2016.01.007.
[6] E. Bellale, M. Naik, V.B. Varun, A. Ambady, A. Narayan, S. Ravishankar,
V. Ramachandran, P. Kaur, R. McLaughlin, J. Whiteaker, et al., Diarylthiazole:
an antimycobacterial scaffold potentially targeting PrrB-PrrA two-component
system, J. Med. Chem. 57 (2014) 6572e6582, https://doi.org/10.1021/
jm500833f.
[7] M.R. Shiradkar, K.C. Akula, V. Dasari, V. Baru, B. Chiningiri, S. Gandhi, R. Kaur,
A novel approach to cyclin dependent kinase 5/p25 inhibitors as a potential
treatment for Alzheimer's disease, Bioorg. Med. Chem. 15 (2007) 2601e2610,
https://doi.org/10.1016/j.bmc.2007.01.043.
[8] S.Y. Kang, K.S. Song, J. Lee, S.H. Lee, J. Lee, Synthesis of pyridazine and thiazole
analogues as SGLT2 inhibitors, Bioorg. Med. Chem. 18 (2010) 6069e6079,
https://doi.org/10.1016/j.bmc.2010.06.076.
[9] D.S. Prasanna, C.V. Kavitha, K. Vinaya, S.R. Ranganatha, S.C. Raghavan,
K.S. Rangappa, Synthesis and identification of a new class of anti-leukemic
agents containing 2-(arylcarboxamide)-(S)-6-amino-4,5,6,7-tetra hydro-
benzo[d] thiazole, Eur. J. Med. Chem. 45 (2010) 5331e5336, https://doi.org/
10.1016/j.ejmech.2010.08.056.
[27] S.O. Pember, G.L. ejia, T.J. Price, R.J. Pasteris, Piperidinyl thiazole isoxazolines:
a new series of highly potent, slowly reversible FAAH inhibitors with anal-
gesic properties, Bioorg. Med. Chem. Lett. 26 (2016) 2965e2973, https://
doi.org/10.1016/j.bmcl.2016.02.061.
[28] M.F. Arshad, N. Siddiqui, A. Elkerdasy, A.H. Al Rohaimi, S.A. Khan, Anticon-
vulsant and neurotoxicity evaluation of some newly synthesized thiazolyl
coumarin derivatives, Am. J. Pharmacol. Toxicol. 9 (2014) 132e138, https://
doi.org/10.3844/ajptsp.2014.132.138.
[29] C.B. Mishra, S. Kumari, M. Tiwari, Thiazole: a promising heterocycle for the
development of potent CNS active agents, Eur. J. Med. Chem. 92 (2015) 1e34,
https://doi.org/10.1016/j.ejmech.2014.12.
[30] F. Chimenti, B. Bizzarri, E. Maccioni, D. Secci, A. Bolasco, P. Chimenti,
R. Fioravanti, A. Granese, S. Carradori, F. Tosi, P. Ballario, S. Vernarecci,
P. Filetici,
network:
A
novel histone acetyltransferase inhibitor modulating Gcn5
cyclopentylidene-[4-(4'-chlorophenyl) thiazol-2-yl)hydrazine,
[10] S.K. Bharti, K. Nath, R. Tilak, S.K. Singh, Synthesis, anti-bacterial and anti-
fungal activities of some novel Schiff bases containing 2, 4-disubstituted
thiazole ring, Eur. J. Med. Chem. 45 (2010) 651e660, https://doi.org/
10.1016/j.ejmech.2009.11.008.
[11] O.I. El-Sabbagh, M.M. Baraka, S.M. Ibrahim, C. Pannecouque, R. Snoeck,
J. Balzarini, A.A. Rashad, Synthesis and antiviral activity of new pyrazole and
thiazole derivatives, Eur. J. Med. Chem. 44 (2009) 3746e3753, https://doi.org/
10.1016/j.ejmech. 2009.03.038.
[12] G.H. Al-Ansary, M.A. Ismail, D.A. Abou El Ella, S. Eid, K.A. Abouzid, Molecular
design and synthesis of HCV inhibitors based on thiazolone scaffold, Eur. J.
Med. Chem. 68 (2013) 19e32, https://doi.org/10.1016/j.ejmech.2013.07.006.
[13] J. Das, P. Chen, D. Norris, R. Padmanabha, J. Lin, R.V. Moquin, Z. Shen, L.S. Cook,
A.M. Doweyko, S. Pitt, S. Pang, D.R. Shen, et al., 2-Aminothiazole as a novel
kinase inhibitor template. Structure activity relationship studies toward the
J. Med. Chem. 52 (2009) 530e536, https://doi.org/10.1021/jm800 885d.
[31] M.H. Khan, T. Akhtar, K.A. Yasin, N.A. Al-Masoudi, P.G. Jones, S. Hameed,
Synthesis, crystal structure and antiproliferative activity of 6-adamantyl-3-
aryl[1,2,4]triazolo[3,4-b][1,3,4] thiadiazoles, Z. Naturforschung 65b (2010)
178e184, https://doi.org/10.1515/znb-2010-0214.
[32] M.H. Khan, T. Akhtar, N.A. Al-Masoudi, H. Stoeckli-Evans, S. Hameed, Syn-
thesis, crystal structure and anti-HIV activity of 2-adamantyl/ada-
mantylmethyl-5-aryl-1,3,4-oxadiazoles, Med. Chem.
https://doi.org/10.2174/157340612804075232.
8 (2012) 1190e1197,
[33] M.H. Khan, S. Hameed, M. Farman, N.A. Al-Masoudi, H. Stoeckli-Evans, Syn-
thesis, anti HIV and molecular modeling study of 3-aryl-6-adamantyl-methyl-
[1,2,4]triazolo[3,4-b]thiazdiazole derivatives, Z. Naturforschung 70b (2015)
609e616, https://doi.org/10.1515/znb-2015-0032.
[34] M. Zahid, K.A. Yasin, T. Akhtar, N.H. Rama, S. Hameed, N.A. Al-Masoudi,
R. Loddo, P. La Colla, New 2-(4-aryl)-5-(2-adamantylthiazol-4-yl)-1,3,4-
oxadiazoles as potential antiproliferative and antiviral agents, Arkivoc xi
(2009) 85e93, https://doi.org/10.3998/ark.5550190. 0010.b08.
[35] T. Akhtar, S. Hameed, N.A. Al-Masoudi, R. Loddo, P. La Colla, In vitro antitumor
and antiviral activities of new benzothiazole and 1,3,4-oxadiazole-2-thione
derivatives, Acta Pharm. 58 (2008) 135e149, https://doi.org/10.2478/
v10007-008-0007-2.
discovery
of
N-(2-chloro-6-methylphenyl)-2-[[6-[4-(2-hydroxyethyl)-1-
piperazinyl)]-2-methyl-4-pyrimidinyl]amino)]-1,3-thiazole-5-carboxamide
(Dasatinib, BMS-354825) as a potent pan-Src kinase inhibitor, J. Med. Chem.
49 (2006) 6819e6832, https://doi.org/10.1021/jm060727j.
[14] D.J. Kempf, H.L. Sham, K.C. Marsh, C.A. Flentge, D. Betebenner, B.E. Green,
E. McDonald, S. Vasavanonda, A. Saldivar, N.E. Wideburg, W.M. Kati, L. Ruiz, et
al., Discovery of ritonavir, a potent inhibitor of HIV protease with high oral
bioavailability and clinical efficacy, J. Med. Chem. 41 (1998) 602e617, https://
doi.org/10.1021/jm970636.
[36] C. Pannecouque, D. Daelemans, E. De Clercq, Tetrazolium-based colorimetric
assay for the detection of HIV replication inhibitors: revisited, 20 years later,
Nat. Protoc. 3 (2008) 427e434, https://doi.org/10.1038/nprot.2007.517.
[37] M. Popovic, M.G. Sarngadharan, E. Read, R.C. Gallo, Detection, isolation, and
continuous production of cytopathic retroviruses (HTLV-III) from patients
with AIDS and pre-AIDS, Science 224 (1984) 497e500, https://doi.org/
10.1126/science.6200935.
[15] H.W. Manning, Process for preparing nizatidine, US Pat 5 (1997) 700, 945.
[16] Ø. Rist, M. Grimstrup, J.-M. Receveur, T.M. Frimurer, T. Ulven, E. Kontenis,
€
T. Hogberg, Novel selective thiazoleacetic acids as CRTH2 antagonists devel-
oped from in silico derived hits. Part 1, Bioorg. Med. Chem. Lett. 20 (2010)
1177e1180, https://doi.org/10.1016/j.bmcl.2009.12.008. https://www.ncbi.
nlm.nih.gov/pubmed/?term¼Rist%20%C3%98%5BAuthor%
ꢀ
[38] F. Barre-Sinoussi, J.C. Chermann, F. Rey, M.T. Nugeyre, S. Chamaret, J. Gruest,
5D&cauthor¼true&cauthor_uid¼20031403.
C. Dauguet, C. Axler-Blin, F. Vezinet-Brun, C. Rouzioux, W. Rozenbaum,
L. Montagnier, Isolation of a T-lymphotropic retrovirus from a patient at risk
for acquired immune deficiency syndrome (AIDS), Science 220 (1983)
868e871, https://doi.org/10.1126/science.6189183.
[17] Z. Xu, M. Ba, H. Zhou, Y. Cao, C. Tang, Y. Yang, R. He, Y. Liang, X. Zhang, Z. Li,
L. Zhu, Y. Guo, C. Guo, 2,4,5-Trisubstituted thiazole derivatives: a novel and
potent class of non-nucleoside inhibitors of wild type and mutant HIV-1
reverse transcriptase, Eur. J. Med. Chem. 85 (2014) 27e42, https://doi.org/
10.1016/j.ejmech.2014.07.072.
[39] I. Miyoshi, H. Taguchi, I. Kobonishi, S. Yoshimoto, Y. Ohtsuki, Y. Shiraishi,
T. Akagi, Type C virus-producing cell lines derived from adult T cell leukemia,
Gann Monogr. Cancer Res. 28 (1982) 219e228.
[18] M. Zia, T. Akhtar, S. Hameed, N.A. Al-Masoudi, New aryl-1,3-thiazole-4-
carbohydr-azides, their 1,3,4-oxadiazole-2-thione-1,2,4-triazole, isatin-3-
ylidene and carboxamide derivatives: synthesis and anti-HIV activity,
Z. Naturforschung 67b (2012) 747e758, https://doi.org/10.5560/ZNB.2012-
0095.
ꢀ
[40] U.C. Kassehin, F.A. Gbaguidi, C.N. Kapanda, C.R. McCurdy, J.H. Poupaert, Sol-
vent effect and catalysis in the synthesis of thiosemicarbazone derivatives
from ketones and 4’-phenylthiosemicarbazide, Afr. J. Pure Appl. Chem. 8
(2014) 110e115, https://doi.org/10.5897/AJPAC 2014.0575.
[19] K. Mahmood-ul-Hassan, S. Hameed, A. Tashfeen, N.A. Al-Masoudi, Synthesis,
crystal structure, anti-HIV, and antiproliferative activity of new oxadiazole
and thiazole analogs, Med. Chem. Res. 25 (2016) 2399e2409, https://doi.org/
10.1007/s00044-016-1669-9.
[20] S.M. Gomha, M.G. Badrey, M.M. Abdalla, R.K. Arafa, Novel anti-HIV-1 NNRTIs
based on a pyrazolo[4,3-d]isoxazole backbone scaffold: design, synthesis and
insights into the molecular basis of action, Med. MedChemCommun. 5 (2014)
1685e1692, https://doi.org/10.1039/C4MD00282B.
[21] K.M. Dawood, T.M. Eldebss, H.S. El-Zahabi, M.H. Yousef, P. Metz, Synthesis of
some new pyrazole-based 1,3-thiazoles and 1,3,4-thiadiazoles as anticancer
agents, Eur. J. Med. Chem. 70 (2013) 740e749, https://doi.org/10.1016/
j.ejmech.2013.10.042.
[41] K.D. Hargrave, J.R. Proudfoot, K.G. Grozinger, E. Cullen, S.R. Kapadia, U.R. Patel,
V.U. Fuchs, S.C. Mauldin, J. Vitous, M.L. Behnke, J.M. Klunder, K. Pal, J.W. Skiles,
D.W. McNeil, J.M. Rose, G.C. Chow, et al., Novel nonnucleoside inhibitors of
HIV-1 reverse transcriptase. 1. Tricyclic pyridobenzo- and dipyr-
idodiazepinones, J. Med. Chem. 34 (1991) 2231e2241, https://doi.org/
10.1021/jm00111a045.
[42] H. Mitsuya, K.J. Weinhold, P.A. Furman, M.H. St Clair, S.N. Lehrmann, R. Gallo,
30-Azido-30-deoxythymidine (BW A509U), an antiviral agent that inihibits the
ineffectivity and cytopathic effect of human T-lymphotropic virus type III/
lymphadenopathy associates virus in vitro, Proc. Natl. Acad. Sci. U.S.A. 82
(1985) 7096e7100, https://doi.org/10.1073/pnas.82.20.7096.
[43] O.J. D'Cruz, F.M. Uckun, Dawn of non-nucleoside inhibitor-based anti-HIV
microbicides, J. Antimicrob. Chemother. 57 (2006) 411e423, https://doi.org/
10.1093/jac/dki464.
[44] O.J. D'Cruz, F.M. Uckun, Discovery of 2,5-dimethoxy-substituted 5-
bromopyridyl thiourea (PHI-236) as a potent broad-spectrum anti-human
immunodeficiency virus microbicide, Mol. Hum. Reprod. 11 (2005) 767e777,
https://doi.org/10.1093/molehr/gah236.
ꢀ
ꢀ
ꢀ
[22] M. Popsavin, L. Torovic, M. Svircev, V. Kojic, G. Bogdanovic, V. Popsavin,
Synthesis and antiproliferative activity of two new tiazofurin analogues with
2'-amido functionalities, Bioorg. Med. Chem. Lett 16 (2006) 2773e2776,
https://doi.org/10.1016/j.bmcl.2006.02.001.
[23] K.J. Wilson, C.R. Illig, N. Subasinghe, J.B. Hoffman, M.J. Rudolf, R. Soll, C. Molloy,
R. Bone, D. Green, T. Randall, M. Zhang, F.A. Lewandowski, et al., Synthesis of
thiophene-2-carboxamidines containing 2-aminothiazoles and their biolog-
ical evaluation as urokinase inhibitors, Bioorg. Med. Chem. Lett 11 (2001)
915e918, https://doi.org/10.1016/S0960-894X(01) 00102-0.
[24] C.M. Dario, C.G. Gian, M. Nova, F. Viviana US patent 0, 284,017 (1988).
[25] T.N. Minh An, M. A Kumar, S.H. Chang, M.Y. Kim, J.-A. Kim, K.D. Lee, Synthesis,
anticancer and antioxidant activity of novel 2,4-disubstituted thiazoles, Bull.
Korean Chem. Soc. 35 (2014) 1619e1624, https://doi.org/10.5012/
bkcs.2014.35.6.1619.
[45] E.A. Sudbeck, J.D. Jennissen, T.K. Venkatachalam, F.M. Uckun, Inhibitor of HIV-
1 reverse transcriptase: N'-(5-bromo-2-pyridyl)-N-[2-(2,5-dimethoxyphenyl)
ethyl]thiourea, Acta Crystallogr. C55 (1999) 2122e2124, https://doi.org/
10.1107/S0108270199012044.
€
[46] A.S. Cantrell, P. Engelhardt, M. Hogberg, S.R. Jaskunas, N.G. Johansson,
€
C.L. Jordan, J. Kangasmetsa, M.D. Kinnick, P. Lind, J.M. Morin, M.A. Muesing,
€
ꢀ
R. Noreen, B. Oberg, P. Pranc, C. Sahlberg, R.J. Ternansky, R.T. Vasileff, L. Vrang,
S.J. West, H. Zang, Phenethylthiazolyl thiourea (PETT) compounds as a new
class of HIV-1 reverse transcriptase inhibitors. 2. Synthesis and further
[26] R.D. Kamble, R.J. Meshram, S.V. Hese, R.A. More, S.S. Kamble, R.N. Gacche,

8
A. Rauf et al. / Journal of Molecular Structure 1198 (2019) 126866
structure-activity relationship studies of PETT analogs, J. Med. Chem. 39
(1996) 4261e4274, https://doi.org/10.1021/jm950639r.
[47] Molecular Operating Enviroment (MOE), 2013.08, Chemical Computing Group
ULC, 1010 Sherbooks St. West, Suit #910, 2R7, Canada, H3A, Montreal, QC,
2018.
[48] J. Ren, P.P. Chamberlain, A. Stamp, S.A. Short, K.L. Weaver, K.R. Romines,
R. Hazen, A. Freeman, R.G. Ferris, C.W. Andrews, L. Boone, J.H. Chan,
D.K. Stammers, Structural basis for the improved drug resistance profile of
new generation benzophenone non-nucleoside HIV-1 reverse transcriptase
inhibitors, J. Med. Chem. 51 (2008) 5000e5008, https://doi.org/10.1021/
jm800 4493.
[49] X. Barril, S.D. Morley, Unveiling the full potential of flexible receptor docking
using multiple crystallographic structures, J. Med. Chem. 48 (2005)
4432e4443, https://doi.org/10.1021/jm048972v.
[50] D. Rogers, A.J. Hopfinger, Application of genetic function approximation to
quantitative structure-activity relationships and quantitative structure-
property relationships, J. Chem. Inf. Comput. Sci. 34 (1994) 854e866,
https://doi.org/10.1021/ci00020a020.
[51] K.F. Khaled, Modeling corrosion inhibition of iron in acid medium by genetic
function approximation method:
a QSAR model, Corros. Sci. 53 (2011)
3457e3465, https://doi.org/10.1016/j.corsci.2011.01.035.