Larvicidal activities of 2-aryl-2,3-dihydroquinazolin -4-ones against malaria vector anopheles arabiensis, in silico ADMET prediction and molecular target investigation

Article abstract of DOI:10.3390/molecules25061316

Malaria, affecting all continents, remains one of the life-threatening diseases introduced by parasites that are transmitted to humans through the bites of infected Anopheles mosquitoes. Although insecticides are currently used to reduce malaria transmission, their safety concern for living systems, as well as the environment, is a growing problem. Therefore, the discovery of novel, less toxic, and environmentally safe molecules to effectively combat the control of these vectors is in high demand. In order to identify new potential larvicidal agents, a series of 2-aryl-1,2-dihydroquinazolin-4-one derivatives were synthesized and evaluated for their larvicidal activity against Anopheles arabiensis. The in silico absorption, distribution, metabolism, excretion, and toxicity (ADMET) properties of the compounds were also investigated and most of the derivatives possessed a favorable ADMET profile. Computational modeling studies of the title compounds demonstrated a favorable binding interaction against the acetylcholinesterase enzyme molecular target. Thus, 2-aryl-1,2-dihydroquinazolin-4-ones were identified as a novel class of Anopheles arabiensis insecticides which can be used as lead molecules for the further development of more potent and safer larvicidal agents for treating malaria.

Full text of DOI:10.3390/molecules25061316

molecules
Article
Larvicidal Activities of 2-Aryl-2,3-Dihydroquinazolin
-
4-ones against Malaria Vector Anopheles arabiensis,
In Silico ADMET Prediction and Molecular
Target Investigation
Katharigatta N. Venugopala 1 * , Pushpalatha Ramachandra , Christophe Tratrat ,
,2,
3
1
Raquel M. Gleiser 4 , Subhrajyoti Bhandary 5 , Deepak Chopra
, Mahesh Attimarad
, Pran Kishore Deb
Hany Ezzat Khalil 1 , Osama I. Alwassil
Ramachandra Palenge , Michelyne Haroun , Shinu Pottathil , Meravanige B. Girish
Sabah H. Akrawi 1 and Viresh Mohanlall 2
5
, Mohamed A. Morsy
1,6
,
1
1
, Anroop B. Nair 1 , Nagaraja Sreeharsha
, Sandeep Chandrashekharappa
1
Bandar E. Aldhubiab
Rashmi Venugopala
,
7
8
9
,
,10
11
8
8
, Sara Nidal Abed
, Yazan A. Bataineh ,
3
1
12
13
,
1
Department of Pharmaceutical Sciences, College of Clinical Pharmacy, King Faisal University, Al-Ahsa 31982,
Saudi Arabia; ctratrat@kfu.edu.sa (C.T.); momorsy@kfu.edu.sa (M.A.M.); baldhubiab@kfu.edu.sa (B.E.A.);
mattimarad@kfu.edu.sa (M.A.); anair@kfu.edu.sa (A.B.N.); sharsha@kfu.edu.sa (N.S.);
heahmed@kfu.edu.sa (H.E.K.); mharoun@kfu.edu.sa (M.H.); sakrawi@kfu.edu.sa (S.H.A.)
Department of Biotechnology and Food Technology, Durban University of Technology, Durban 4001,
South Africa; vireshm@dut.ac.za
2
3
4
5
Department of Chemistry, School of Applied Sciences, REVA University, Bangalore 560 064, India;
pushpalatha@reva.edu.in (P.R.); ramachandrap@reva.edu.in (R.P.)
CREAN-IMBIV (UNC-CONICET), Av. Valparaíso s.n., Córdoba, Argentina and FCEFyN, AV. Sarsfield 299,
Universidad Nacional de Cordoba, Cordoba 5000, Argentina; raquel.gleiser@unc.edu.ar
Department of Chemistry, Indian Institute of Science Education and Research Bhopal, Bhopal By-pass Road,
Bhauri, Bhopal 462 066, Madhya Pradesh, India; bhandarysj@gmail.com (S.B.); dchopra@iiserb.ac.in (D.C.)
Department of Pharmacology, Faculty of Medicine, Minia University, El-Minia 61511, Egypt
Department of Public Health Medicine, University of KwaZulu-Natal, Howard College Campus,
Durban 4001, South Africa; rashmivenugopala@gmail.com
6
7
8
9
Department of Pharmaceutical Sciences, Faculty of Pharmacy, Philadelphia University, P.O. Box 1,
Amman 19392, Jordan; pdeb@philadelphia.edu.jo (P.K.D.); sousanidal95@gmail.com (S.N.A.);
YBatineh@philadelphia.edu.jo (Y.A.B.)
Institute for Stem Cell Biology and Regenerative Medicine, NCBS, TIFR, GKVK, Bellary Road,
Bangalore 560 065, India; sandeepc@instem.res.in
Department of Pharmacognosy, Faculty of Pharmacy, Minia University, Minia 61519, Egypt
Department of Pharmaceutical Sciences, College of Pharmacy, King Saud bin Abdulaziz University for
Health Sciences, Riyadh 11481, Saudi Arabia; wassilo@ksau-hs.edu.sa
Department of Biomedical Sciences, College of Clinical Pharmacy, King Faisal University, Al-Ahsa 31982,
Saudi Arabia; spottathail@kfu.edu.sa
1
1
0
1
2
3
1
1
Department of Biomedical Sciences, College of Medicine, King Faisal University, Al-Ahsa 31982,
Saudi Arabia; gmeravanige@kfu.edu.sa
*
Correspondence: kvenugopala@kfu.edu.sa
ꢀ
ꢁꢂꢀꢃꢄꢅꢆꢇ
Academic Editor: Nuno Vale
Received: 22 February 2020; Accepted: 11 March 2020; Published: 13 March 2020
ꢀ
ꢁꢂꢃꢄꢅꢆ
Abstract: Malaria, affecting all continents, remains one of the life-threatening diseases introduced by
parasites that are transmitted to humans through the bites of infected Anopheles mosquitoes. Although
insecticides are currently used to reduce malaria transmission, their safety concern for living systems,
as well as the environment, is a growing problem. Therefore, the discovery of novel, less toxic,
and environmentally safe molecules to effectively combat the control of these vectors is in high demand.
In order to identify new potential larvicidal agents, a series of 2-aryl-1,2-dihydroquinazolin-4-one
Molecules 2020, 25, 1316; doi:10.3390/molecules25061316
www.mdpi.com/journal/molecules

Molecules 2020, 25, 1316
2 of 22
derivatives were synthesized and evaluated for their larvicidal activity against Anopheles arabiensis.
The in silico absorption, distribution, metabolism, excretion, and toxicity (ADMET) properties of the
compounds were also investigated and most of the derivatives possessed a favorable ADMET profile.
Computational modeling studies of the title compounds demonstrated a favorable binding interaction
against the acetylcholinesterase enzyme molecular target. Thus, 2-aryl-1,2-dihydroquinazolin-4-ones
were identified as a novel class of Anopheles arabiensis insecticides which can be used as lead molecules
for the further development of more potent and safer larvicidal agents for treating malaria.
Keywords: Anopheles arabiensis; larvicidal activity; 2,3-dihydroquinazolin-4-one; docking; ADMET;
crystallography; graphene oxide
1
. Introduction
Malaria is considered as one of the challenging life-threatening diseases initiated by parasites
that are transmitted to humans through the bites of infected Anopheles mosquitoes. Both genders
are affected, leading to severe health and socioeconomically negative impacts. Recently, the World
Health Organization (WHO) reported in 2018 that there were an estimated 228 million cases of
malaria that spread in 87 countries. The mortality rate of malaria was found to be 405,000 in 2018 [1].
The Anopheles arabiensis mosquito is considered as one of the major vectors of malaria. The origin of
infection starts with a bite from an infected female mosquito, where the parasite is delivered into the
circulatory system and ultimately to the liver, where it becomes mature and reproduces [2]. Many
approaches and strategies for the management of malaria were developed. One of the most effective
strategies is to eliminate the vector through environmental modifications, biological control, use of
long-lasting insecticidal nets (LLINs), and indoor residual spraying (IRS). Another effective strategy is
to eradicate mosquitos at the larval stage by preventing their development.
Organophosphates and carbamates are two major classes of synthetic insecticides known to
inactivate acetylcholinesterase (AChE), and they are currently used in combating malaria. However,
their use raises concerns regarding safety issues for the living system and the environment [3].
For instance, the most popular insecticide organophosphorus Temephos is a mutagenic compound and
is unsafe for human beings. In addition, insecticide resistance is becoming increasingly alarming and
threatens the management of vectors, thereby leading to prioritizing the development of new potent
and safer biologically active heterocyclic compounds as well as to aid in resistance management [
There are certain reports concerning the larvicidal activity of synthetic compounds [5–12].
4].
The 2,3-dihydroquinazolin-4(1H)-ones (2,3-DHQs) are fused heterocyclic compounds which exist in
natural products such as luotonins A, B, E, and F [13], tryptanthrin [14], and rutaecarpine [15]. 2,3-DHQs
possess a broad range of pharmacological properties such as anti-cancer [16,17], antidepressant [18],
antidiabetic [19], antifungal [20], antihypertensive [21 22], analgesic, anti-inflammatory [23
,
,
24],
antibacterial [25], antioxidant [26], and antiviral [27] activities; they also act as bronchodilator [28],
centrally acting muscle relaxant [29], diuretic [30], sedative, and hypnotic [31] agents (Figure 1).
Quinazoline derivatives were also reported as bactericides [32], fungicides [33], and insecticides [34].
In recent years, green and sustainable chemistry drew much attention for the generation of new
chemical methods with less environmental impact. In this regard, graphene oxide (GO), a carbocatalyst,
attracted our attention for the preparation of quinazoline derivatives due to its non-hazardous nature
and the fact that it is easy to remove from the reaction mixture.
In continuation of our efforts in developing larvicidal agents [35
heterocyclic compounds via green and microwave methods [41 43], we report herein the synthesis of
,3-dihydroquinazolin-4(1H)-one derivatives, a biological evaluation of their larvicidal activity against
–40] and pharmacologically active
–
2
Anopheles arabiensis, and an in silico evaluation of their absorption, distribution, metabolism, excretion,
and toxicity (ADMET) properties as well as molecular target investigation.

Molecules 2020, 25, 1316
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Figure 1. Representatives of 2,3-dihydroquinazolin-4(1H)-one derivatives as therapeutic agents.
. Results and Discussion
2
2
.1. Chemistry
An efficient protocol was reported for the synthesis of 2-(substituted phenyl)-2,3-dihydroquinazolin-
(1H)-ones using graphene oxide as carbocatalyst [44]. The title compounds (3a ) were prepared in
4
–n
excellent yields as racemic mixtures (Table 1) via direct one-pot condensation of anthranilamide (1)
with substituted aryl aldehydes (2) in the presence of GO, as depicted in Scheme 1.
The yields obtained were excellent in the range of 82–95%. The purity of the title compounds was
ascertained by high-performance liquid chromatography (HPLC), and it was found to be over 99%.
Fourier-transform infrared spectroscopy (FT-IR) of 2,3-dihydroquinazolin-4(1H) one analogues (3a
–n)
revealed a secondary amine and carbonyl carbon of six-membered heterocyclic rings in the ranges
−
1
of 3296–3382 and 1614–1660 cm , respectively. The title compounds 3c
,
3m, and 3n exhibited broad
−
1
peaks for a phenolic hydroxyl group at 3357, 3396, and 3355 cm , respectively. Stretching of the cyano
−
1
−1
group was observed at 2223 cm for compound 3b. Compound 3d exhibited a peak at 1163 cm
for carbon–fluorine stretching. Proton NMR spectra of the title compounds (3a–n) revealed a singlet
signal corresponding to methine proton (–CH–) of the six-membered heterocyclic rings in the range of
δ
= 5.57–6.08 ppm. Compounds 3a–j and 3l–n revealed a singlet for an amide –CONH– functional
group in the range of = 8.10–8.57 ppm, whereas derivative 3k revealed a singlet at = 8.09 ppm
for a secondary amine in the imidazole ring system. Title compounds 3c and 3n as mono-hydroxy
derivatives exhibited a singlet at = 9.53 ppm, whereas compound 3m exhibited a singlet for a hydroxy
group at = 11.66 ppm. For all the title compounds, aromatic protons were observed as a singlet,
doublet, doublet of a doublet, and multiplet depending on the substitution on the phenyl ring in the
range of = 8.18–5.57. Title compound 3a exhibited a singlet signal attributed to methoxy group
δ
δ
δ
δ
δ
at 3.75 ppm, whereas compound 3g exhibited two signals for methoxy group at 3.75 and 3.77 ppm.
The dimethylamino group was observed as a singlet for compound 3h at 2.88 ppm. Compound 3l
exhibited a singlet signal for methoxy at 3.98 ppm. 13C-NMR spectra of compounds 3a
–
n
exhibited a
= 163.39–163.86 ppm. The elemental
0.4% of the calculated values. ChemDraw 16.0.1.4v professional was
used to calculate the cLogP values of the title compounds (3a–n), and it was found to be in the range of
.1488–3.4428.
singlet signal corresponding to a carbonyl signal in the range of
analysis results were within
δ
±
0

Molecules 2020, 25, 1316
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Table 1. Physicochemical characteristics of 2-(substituted phenyl)-2,3-dihydroquinazolin-4(1H)-ones (3a–n).
◦
◦
Compound
Code
Molecular Formula
(Molecular Mass)
Yield
(%)
m.p ( C)
mp ( C)
Ar
cLogP
References
CAS Number
Reported
Found
3
a
4-OCH -Ph
4-CN-Ph
3-OH-Ph
C H N O (254)
95
92
91
94
92
87
88
93
91
91
87
93
89
95
182–183
178–180
184–186
194–196
–
197–198
214–216
209–211
192–194
196–198
–
181–182
178–180
185–187
195–196
153–155
198–199
213–215
210–211
192–1193
197–198
156–158
149–151
245–246
210–211
2.2388
1.7528
1.6528
3.3478
3.4428
3.0328
1.9778
2.4848
2.0628
2.4628
0.1488
2.2818
1.9818
1.6528
[45]
[44]
[46]
[47]
61195-16-2
219619-59-7
107922-06-5
685505-75-3
3
15 14
2
2
3
b
C H N O (249)
15 11 3
3
c
C H N O (240)
14 12 2 2
3
d
4-OCF -Ph
C H F N O (308)
3
15 11 3 2 2
3
e
3-I-Ph
4-Cl-Ph
C H IN O (349)
Novel Compound
1
4
11
2
3
f
C H ClN O (258)
[44]
[46]
[48]
[44]
[48]
13165-11-2
126492-17-9
66181-66-6
26029-30-1
359605-44-0
1
4
11
2
3
g
3,4-diOCH -Ph
C H N O (284)
3
16 16 2 3
3
h
4-N,N dimethyl-Ph
C H N O (267)
16 17 3
3
3
i
j
3-NO -Ph
C H N O (269)
2
14 11 3 3
4-F-Ph
Imidazole
C H FN O (242)
14 11 2
3
k
C H N O (214)
Novel Compound
Novel Compound
[49]
[50]
1
1
10
4
3
l
2-OCH -4-NO -Ph
C H N O (299)
–
3
2
15 13
3
4
3
m
2-OH, 5-NO -Ph
C14H N O (285)
244–246
209–211
1794721-69-9
107920-18-3
2
11
3
4
3
n
4-OH-Ph
C H N O (240)
14 12 2 2
Ar: Aromatic; m.p: Melting point; CAS: Chemical Abstracts Service.

Molecules 2020, 25, 1316
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Scheme 1. Synthetic scheme for the construction of 2-(substituted phenyl)-2,3-dihydroquinazolin-
(1H)-ones (3a ). Reagents and conditions: ( ) graphene oxide (2.5%), water, stirred at room
4
–
n
a
temperature; yield 82–95%.
2
.2. Crystallography
Crystal Structure Analysis of 2-(3,4-Dimethoxyphenyl)-2,3-dihydroquinazolin-4(1H)-one (3g)
The compound 3g crystallized in the monoclinic centrosymmetric space group P2 /n with Z = 4
1
(Table 2). Figure 2 gives the Oak Ridge Thermal Ellipsoid Plot (ORTEP) view of the title compound
and crystal data was deposited in Cambridge Crystallographic Data Centre (CCDC) with its number
983734. The molecular conformation of the central ring exists in the envelope conformation, with the
displacement of the atom C8 from the mean plane passing through C1–C6–C7–N2–N1 being around
.624 (3) Å. The torsion angle N1–C8–C9–C10 is 44.3(3) indicating conformational flexibility of the
1
0
molecule with respect to the C8–C9 bond. The crystal structure is connected via strong N–H···
O
hydrogen bonds (H-bonds) (involving H2/O3) along with C–H···O interactions (involving H16C/O1)
forming a dimer (Table 3). This dimer is further supported via additional N–H···O H-bonds (involving
H1/O2) and C–H···O intermolecular interactions (involving H2C/H3 with O1 and H2C with O3),
forming a tetramer which is further connected with similar tetramers via van der Waals interactions
(Figure 3).
Table 2. Single-crystal X-ray data of title compound 2-(3,4-dimethoxyphenyl)-2,3-dihydroquinazolin-
(1H)-one (3g).
4
CCDC Number
1983734
C H N O
3
Molecular Formula
Molecular weight
Temperature
1
6
16
2
284.31
173(2)
Crystal Size (mm)
0.2, 0.110, 0.040
Absorption coefficient (mm 1)
−
0.096
Tmin, Tmax
0.981, 0.996
Crystal system
Monoclinic
Lattice parameters: a (Å), b (Å), c (Å)
7.8881(6), 20.2194 (13), 8.9638 (6)
90, 104.887(3), 90
◦
α, β, γ ( )
0
Space Group, Density, Z, Z
P2 /n, 1.367, 4, 1
1
hmin, max; kmin, max; lmin, max
Number of total/unique/observed reflections
No. of parameters
;
−8, 10; −26, 26; −11, 11
13,538, 3403, 2321
200
Independent reflections, Rint
Rall, Robs
3403, 0.0482
0.0879, 0.0544
0.1425, 0.1221
0.541, −0.269
1.029
wR2all, wR2
obs
−
∆
ρ
(eÅ 3)
max, min
goodness-of-fit (G.o.F)

Molecules 2020, 25, 1316
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Figure 2. ORTEP representation (with 50% displacement ellipsoids) of the title compound (3g) showing
the atom numbering scheme.
Table 3. List of intermolecular interactions in the crystal structure of 2-(3,4-dimethoxyphenyl)-2,3-
dihydroquinazolin-4(1H)-one (3g).
Interaction
N1–H1···O2
N2–H2···O3
C16–H16C···O1
C3–H3···O1
C2–H2C···O1
C2–H2C···O3
H···A (Å)
2.30
D···A (Å)
3.176
∠D–H···A (◦)
Symmetry Code
−x + 1, −y, −z + 2
−x, −y, −z + 2
−x, −y, −z + 2
x + 1,+y,+z
170
148
137
124
122
140
2.30
3.070
2.66
3.441
2.54
3.167
2.57
3.180
x + 1,+y,+z
2.64
3.421
−x + 1, −y, −z + 2
a
b
0
c
Figure 3. Packing arrangement of molecules in the crystal structure via formation of tetramers involving
N–H···O hydrogen bonds (H-bonds), C–H···O interactions, and π–π stacking interactions.

Molecules 2020, 25, 1316
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2
.3. Larvicidal Activity
The larvicidal test of the racemic title compounds (3a–n) was conducted at a concentration of
µg/mL, where the positive control Temephos demonstrated 99% to 100% mortality. The larvicidal
4
action of the title compounds (3a–n) is described in Table 4. Significant larvicidal effects of the
compounds were observed (F = 26.48, p < 0.0001), with all the compounds resulting in a higher larval
mortality than exposure to the negative control. Moreover, there was no significant effect of exposure
time (F = 3.73, p = 0.06) on larval mortality, i.e., mortality did not significantly increase from 24 h to 48 h.
Compound 3d was the most lethal, resulting in 93% mortality, which was not statistically different from
exposure to the positive control Temephos (99% to 100% mortality). Compounds 3b
not statistically different from 3d, resulting in larval mortalities ranging from 87% to 91% mortality after
8 h. The least lethal compounds (3c 3i 3h 3k, and 3n) resulted in mortalities ranging from 43% to 57%.
, 3e, 3f, and 3j were
4
,
,
,
On the basis of the functionalization of aryl ring and the observed larvicidal effect, it would be possible
to establish the structure–activity relationships (SAR) of the title 2,3-dihydroquinazolin-4(1H)-one
analogues (3a–n). The SAR indicated that the presence of halogen at the para and meta position of
aryl was favorable for the bioactivity (3e (3-I), 3f (4-Cl), 3j (4-F)). The presence of the cyano group
(3b) and methoxy group (3a) at the 4-position of the aryl exhibited interesting insecticide action.
The replacement of the methoxy at the 4-position by a trifluoromethoxy group considerably enhanced
the larvicidal activity. However, the replacement of trifluoromethoxy by a hydroxyl group at the
4
-position of aryl (3n) was detrimental to the activity. Similarly, weak activity was observed for the
compound 3c with a hydroxyl group at the meta position. When 3-OH was replaced by the nitro group
3i), no bioactivity improvement was identified. Disubstituted aryl compounds 3g 3l, and 3m showed
moderate activity against larvae. The presence of the dimethylamino group at the para position (4h
(
,
)
was the least favorable substituent for the larvicidal activity. Lastly, the introduction of an imidazole
ring at the 2-position of quinazoline was unfavorable for the activity, showing only 46% mortality.
Additional information, such as ADMET properties and binding interactions, is needed in order to
explain the observed activity of the compound.
Table 4. Mortality of Anopheles arabiensis larvae exposed to test compounds 3a–n at 4 µg/mL.
Compound
a (4-OCH3)
b (4-CN)
c (3-OH)
d (4-OCF3)
e (3-I)
f (4-Cl)
g (3,4-diOCH3)
24-h Mortality
48-h Mortality
d,e,f
c,d,e
3
0.77 ± 0.04
0.83 ± 0.04
b,c,d,e
b,c,d
3
3
0.86 ± 0.04
0.88 ± 0.03
h,i,j,k,l,m
h,i,j,k,l
0.51 ± 0.05
0.57 ± 0.05
b,c
a,b
3
0.91 ± 0.03
0.93 ± 0.03
c,d,e
b,c,d
3
0.82 ± 0.04
0.87 ± 0.04
b,c,d
b,c
3
0.87 ± 0.04
0.91 ± 0.03
g,h,i,j
f,g,h
3
0.62 ± 0.05
0.66 ± 0.05
m
l,m
3
h (4-N(CH ) )
0.41 ± 0.05
0.43 ± 0.05
3
2
h,i,j,k,l,m
h,i,j,k,l,m
3
i (3-NO2)
0.52 ± 0.05
0.54 ± 0.05
b,c
b,c
3
j (4-F)
k (imidazole)
l (2-OCH , 4-NO )
0.89 ± 0.03
0.91 ± 0.03
k,l,m
j,k,l,m
3
0.46 ± 0.05
0.48 ± 0.05
e,f,g
d,e,f
3
0.74 ± 0.05
0.77 ± 0.04
3
2
h,i,j,k
f,g,h,i
3
m (2-OH, 5-NO2)
n (4-OH)
0.59 ± 0.05
0.64 ± 0.05
i,j,k,l,m
h,i,j,k,l,m
3
0.50 ± 0.05
0.52 ± 0.05
a
a
Temephos
Acetone
0.99 ± 0.01
1.00 ± 0.00
m
n
0.01 ± 0.01
0.04 ± 0.02
a–m
Means ± standard errors are shown.
Compounds sharing a letter do not differ significantly (p > 0.05).
2
.4. In Silico Absorption, Distribution, Metabolism, Excretion, and Toxicity (ADMET) Analysis
The ADMET properties of the derivatives (3a–n) were predicted using Accelrys Discovery
Studio 4.0 client, and they are reported in Table 5. This study revealed that many compounds were
predicted to possess good to excellent drug-likeness properties with the exception of compounds 3d

Molecules 2020, 25, 1316
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(4-OCF3), 3e (3-I), and 3f (4-Cl). Blood–brain barrier penetration prediction indicated that only 3d,
3
e, and 3f might have the ability to readily cross the brain cell membrane; hence, they may interact
with the central nervous system (CNS). The remaining compounds also showed favorable cell brain
permeability with the exception of derivatives 3i (2-OCH , 4-NO ), 3k (imidazole), and 3m (2-OH,
3
2
5
-NO ). Moreover, these compounds demonstrated elevated polar surface area (PSA) 2D, indicating
2
poor cell membrane penetration ability. All compounds were predicted to be absorbed through the
intestine to reach the bloodstream circulation and be transported through the plasma-binding carrier
protein to reach the desired molecular target with the exception of compound 3k (imidazole). As for
the drug metabolism aspect, no inhibition against Cytochrome P450 (CYP450) was predicted for
all the compounds, indicating favorable metabolic stability against CYP450 enzymes. However, all
compounds might demonstrate some toxicity toward liver cells, as indicated from the hepatotoxicity
prediction. In general, most of the compounds were observed to have a favorable ADMET profile.
As for the insecticide Temephos ADMET profile, it showed that Temephos was predicted to be a highly
penetrant molecule towards the cell brain membrane, explaining why Temephos provides its action to
the CNS as a potent acetylcholesterase inhibitor. On the basis of ADMET analysis, this study revealed
a clear correlation between the larvicidal activity and the blood–brain permeability of the compounds.
Indeed, the most potent derivatives 3d (4-OCF3), 3e (3-I), and 3f (4-Cl) were predicted to be highly
permeable towards the brain cell membrane, and the permeability of less active compounds was
predicted to be low and medium. This study indicates that the quinazolinones are more likely to act in
the CNS of larvae.
Table 5. In silico ADMET properties of quinazolines (3a–n) and Temephos.
Blood–Brain
Barrier
Penetration
Intestinal
Hepatotoxicity Absorption
Level
Plasma
Protein
Binding
Solubility
Level
CYP450
Inhibition
Entry
AlogP PSA 2D
(
BBB) Level
Temephos
a (4-OCH3)
2
3
3
3
1
2
2
3
3
3
3
4
3
3
3
0
2
2
2
1
1
1
2
2
3
2
3
2
3
2
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
+
+
+
+
+
+
+
+
+
+
+
-
5.656
2.432
2.327
2.206
4.568
3.026
3.113
2.415
2.610
2.343
2.654
0.632
2.326
2.101
2.206
53.58
51.851
65.856
63.736
51.851
42.921
42.921
60.781
46.273
85.744
42.921
69.237
94.674
106.559
63.736
3
3
b (4-CN)
c (3-OH)
d (4-OCF3)
e (3-I)
f (4-Cl)
g (3,4-diOCH3)
h (4-N(CH3)2)
i (3-NO2)
j (4-F)
k (imidazole)
l (2-OCH3, 4-NO2)
m (2-OH, 5-NO2)
n (4-OH)
3
3
3
3
3
3
3
3
3
3
+
+
+
3
3
Criteria: solubility level/drug-likeness: 0, extremely low/no; 1, very low/possible; 2, low/yes; 3, good/yes;
, optimal/yes. BBB level (blood–brain barrier): 0, very high penetrant; 1, high; 2, medium; 3, low; 4, undefined.
HIA level (human intestinal absorption): 0, good; 1, moderate; 2, poor; 3, very poor. PBB: plasma protein binding.
4
2
.5. Molecular Modeling
On the basis of the preliminary structure–activity relationship of the 2,3-dihydroquinazolin-
(1H)-one derivatives, we explored a variety of enzyme molecular targets in an attempt to identify
4
the mode of action via which the compounds exert their larvicidal effect. It is well known that AChE
represents the main molecular target of insecticides [51 55] and can be associated with the larvicidal
–
action of our compounds. However, some insecticide enzyme targets other than AChE were reported.
For instance, larvicidal inhibitors have the ability to bind to sterol carrier protein-2 [56], juvenile
hormone-binding protein [57], D7r4 a salivary biogenic amine-binding protein [58], calcium-dependent
protein kinase-1 [59], or purine nucleoside phosphorylase targets [60]. The binding investigation of the
dihydroquinazolines against the above-mentioned molecular targets allowed us to identify AChE as the
most plausible molecular target which corroborated with the predicted brain cell permeability [51
–60].
No crystal structures of Anopheles arabienesis AChE from mosquito are deposited in the Protein Data

Molecules 2020, 25, 1316
9 of 22
Bank (PDB) so far. A crystal structure of Anopheles gambiae AChE of the malaria mosquito was recently
reported with a low structure resolution of 3.4 Å that may not be exploitable for docking study [61].
Another crystal structure of Anopheles gambiae AChE of the malaria insecticide-resistant mosquito
harboring a G119S mutation was deposited with a better resolution (2.26 Å) [54]. This mutation does
not appear to perturb the other amino acids in the catalytic site. Knutsson et al. reported the synthesis
and the larvicidal activity of some phenoxyacetamide derivatives [55]. An enzymatic assay of these
derivatives was conducted against four AChE1 enzymes (Anopheles gambiae mosquito, G119S mutation
Anopheles gambiae mosquito, mouse, and human), and it demonstrated good selectivity in favor of
both mosquito AChE1 enzymes as compared to that of human AChE. Moreover, the tested derivatives
showed a similar inhibition profile between the mosquito AChE1 and insecticide-resistant mutant
mosquito AChE1, as well as between the mouse and human AChE. In light of the enzymatic assay, it
appeared that the structure of insecticide resistant mutant mosquito AChE1 showed high structural
similarity to the non-mutant one. Hence, the insecticide-resistant mutant receptor would appear to be
a suitable receptor that can be used as a template for providing a structural understanding of the title
compounds’ potency.
The computational study was then conducted using the co-crystal enzyme G199S mutant AChE1
mosquito (PDB code: 6ARY), with Table 6 presenting the binding energy and the residue interactions.
It should be noted that the dihydroquinazoline derivatives 3a–n, possessing a chiral center in the
2-position of the quinazoline ring, exist as R and S stereoisomer. Therefore, the docking interaction
against the AChE target was conducted for each stereoisomer. The molecular modeling study revealed
that the binding energies of some dihydroquinazolines were greater than the binding energy of the
native ligand found in the co-crystal AChE 1. As for Temephos, we were unable to dock it in the
AChE active site of the insecticide-resistant mosquito, which corroborates its resistance to insecticide.
It was also predicted that, for the majority of derivatives, the R form was more tightly bound in the
receptor than the S form, with the exception of compounds 3a, 3i, and 3n. This may indicate that
the R stereoisomer would be more potent than its enantiomer. The docking analysis revealed that
the hydrophilic and the hydrophobic interactions contributed more or less equally to the observed
larvicidal effect of the derivatives with the exception of quinazoline 3f R (4-Cl). The potency of this
compound might be explained by its involvement in
π–π interactions with residues Tyr 282 and Tyr
489, as well as the chlorine interaction involvement with the amino acid Trp 245. Another halogen
interaction was also observed for quinazoline 3e R (3-I) with residue Asn 246 and for 3d R (4-OCF3)
with residues Gly 278 and Glu 359. The quinazoline ring appeared to be an important pharmacophore
due to its capability of forming hydrogen bond donors from the NH and acceptors from the carbonyl,
as well as a hydrophobic interaction through
π
–
π
stacking with the fused aryl ring of quinazoline.
110.82 kJ/mol for the
R enantiomer, displaying three hydrogen bonding interactions with residues Gly 278 (CF ), Tyr 291
The most potent compound 3d (4-OCF ) displayed very good binding energy of
−
3
3
(
CF ), and Tyr 489 (NH quinazoline), as well as stacking interactions with residues Trp 245 and Tyr 282.
3
In general, the amino-acid residues Trp 245, Tyr 282, and Tyr 489 were implicated in
with the quinazoline ring and the aromatic ring at the 2-position of the derivatives. The halogenated
compounds 3e (3-I), 3f (4-Cl), and 3j (4-F), exhibiting high larvicidal action, showed interactions
π–π interactions
π–π
with residues Trp 245, Tyr 282, and Tyr 489 of the AChE active site. They also demonstrated hydrogen
bonding involvement with residues Tyr 489 (NH) for 3e (3-I), 3f (4-Cl), and 3j (4-F), and Ser 283 (NHCO)
for 3f (4-Cl) and 3j (4-F). The importance of the hydrogen bonding contribution to the bioactivity
of the compounds can also be observed. For instance, the couple 3a (4-OCH )/3d (4-OCF ) as an R
3
3
stereoisomer adopted a similar binding mode in which the pendant aryl ring was located facing the
edge of residue Trp 245 in which OCF and OCH groups were oriented toward the backbone of Gly
3
3
2
78 participating in H-bonding with only quinazoline 3d (4-OCF ). Other residues were also involved
3
in H-bonding with the ligands, such as Gly 279, Gly 359, Asp 233, Ser 280, Tyr 281, and Tyr 291.

Molecules 2020, 25, 1316
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Table 6. Binding energy and residue interactions of 2,3-dihydroquinazolin-4(1H)-one derivatives (3a–n) against G199S mutant acetylcholinesterase 1 (AChE1) (Protein
Data Bank (PDB) code: 6ARY).
Residues Interaction
Binding Energy
Entry
Larvicidal Activity
Stereoisomer
(kJ/mol)
H-Bond (Interacting Atom)
Hydrophobic (π–π)
Gly 279, Trp 285,
Tyr 489
Native ligand
Temephos
-
-
-
−46.68
Ser 280, Tyr 282
-
0
-
-
R
−93.21
Trp 245 (NH), Tyr 489 (NHCO)
Trp 245, His 600
3
a (4-OCH3)
0.77
Gly 279 (NHCO), Ser 280 (NHCO)
Tyr 489 (NH)
S
−114.50
Tyr 282, Trp 245, Tyr 489
Ser 283 (NHCO), Tyr 489 (NH)
Tyr 291 (CN)
Trp 245, Tyr 282, Asp 233
(ion-pi)
R
−98.03
3
b (4-CN)
0.86
Trp 245 (NH), Tyr 291 (CN)
Gly 278 (CN), Tyr 282 (NHCO)
Tyr 489 (NHCO)
S
−81.74
Trp 245
Ser 289 (NHCO), Tyr 291 (OH)
Glu 359 (OH)
R
S
R
S
−99.16
−89.42
Trp 245, Tyr 489
Trp 245, Tyr 489
3
c (3-OH)
0.51
0.91
Ser 280 (OH), Tyr 282 (OH)
Ser 283 (NHCO), Tyr 289 (NH)
Gly 278 (CF ), Tyr 291 (CF )
Trp 245, Tyr 282, Asp 233
(ion-pi), Glu 359 (F), Gly 278 (F)
3
3
−110.82
−106.47
3
d (4-OCF3)
Tyr 489 (NH)
Ser 283 (NHCO)
Tyr 489 (NH)
Trp 245, Tyr 282, Tyr 489
Trp 245, Tyr 282, Tyr 489, Asn
246 (I)
R
S
−105.04
−75.88
Tyr 489 (NH)
Trp 245 (NH)
3
e (3-I)
0.82
0.87
Trp 245
Ser 283 (NHCO)
Tyr 489 (NH)
Tyr 282, Trp 245, Asp 233
(ion-pi)
R
−108.19
3
f (4-Cl)
Trp 245 (NH), Tyr 282 (NHCO)
Tyr 489 (NHCO), Glu 359 (Cl)
S
−81.59
Tyr 245

Molecules 2020, 25, 1316
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Table 6. Cont.
Residues Interaction
H-Bond (Interacting Atom)
Binding Energy
kJ/mol)
Entry
Larvicidal Activity
Stereoisomer
(
Hydrophobic (π–π)
Ser 283 (NHCO)
Tyr 489 (NH)
R
−95.90
Trp 245, Tyr 282, Tyr 489
3
g (3,4-diOCH3)
0.62
Trp 245 (NH), Tyr 282 (NHCO)
Tyr 489 (NHCO)
S
R
S
−91.29
−92.98
−91.01
Tyr 245
Tyr 489 (NH)
Trp 245, Tyr 282, Tyr 489
Trp 245, Tyr 489
3
h (4-N(CH ) )
0.41
0.52
3
2
Ser 283 (NHCO)
Tyr 489 (NH)
Asp 233 (NO ), Ser 283 (NHCO)
2
R
S
R
S
R
S
R
S
R
S
R
S
−108.38
−131.24
−101.15
−76.85
−91.64
−80.14
−120.40
−89.15
−127.01
−113.14
−91.36
−121.58
Trp 245, Tyr 282, Tyr 489
Trp 245, Tyr 282
Trp 245, Tyr 489
Trp 245, Tyr 489
Trp 245
3
i (3-NO2)
Tyr 489 (NH)
Ser 280 (NHCO)
Tyr 489 (NH)
Ser 283 (NHCO)
Tyr 489 (NH)
3
j (4-F)
0.89
0.46
Tyr 291 (NHCO)
Tyr 489 (NH)
Ser 283 (NHCO)
Tyr 489 (NH)
3
k (imidazole)
Ser 283 (NHCO)
Tyr 489 (NH)
Trp 245, Tyr 489
Gly 279 (NHCO), Ser 289 (NHCO)
Ser 289 (OCH3)
Trp 245, Tyr 489, His 600, Glu
359 (ion-pi)
3
l (2-OCH3,
-NO2)
0
.74
4
Ser 283 (NHCO)
Tyr 489 (NH)
Trp 245, Tyr 282, Tyr 489, Tyr
493 (ion-pi)
Ser 283 (NHCO), Tyr 489 (NH)
Tyr 489 (OH)
Trp 245, Tyr 282, Tyr 489
3
m (2-OH, 5-NO2)
0.59
0.50
Trp 245 (NH)
Ser 283 (OH)
Trp 245, Glu 359 (ion-pi), His
600 (ion-pi)
Ser 280 (NHCO), Tyr 291 (OH)
Glu 359 (OH)
Trp 245, Tyr 282, Tyr 489
Trp 245
3
n (4-OH)
Ser 280 (NHCO), Tyr 291 (OH)
Glu 359 (OH)

Molecules 2020, 25, 1316
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It can be noted that compounds 3i S (3-NO ) and 3m R (2-OH, 5-NO ) exhibited a very strong
2
2
binding affinity to the receptor. However, 3i and 3m demonstrated modest larvicidal activities of
.52 and 0.59, respectively. The lack of correlation between the bioactivity and the docking results
0
may be associated with the lipophilicity of the compounds. Indeed, from the ADMET properties,
both compounds were predicted to weakly cross the brain cell membrane, preventing their full action
toward the CNS of the larvae. It is interesting to note that, for all other compounds, the docking results
for the R enantiomer were in agreement with the larvicidal effect of the compounds with the exception
of 3n (4-OH), showing a high predicted binding energy of
−
121.58 for the S stereoisomer. The less
potent compounds, 3h (4-N(CH ) ) and 3k (imidazole), demonstrated weaker binding energies as
3
2
compared to their congeners.
The binding interactions of the most active compound 3d with the G199S mutant AChE receptor
are illustrated in Figure 4, showing a different binding mode for each enantiomer. The binding mode
of 3d R demonstrated three hydrogen bonding interactions with amino-acid residues Tyr 291 and Gly
278 with the fluorine atom, and residue Tyr 489 with the NH of the quinazoline ring. Additionally,
several fluorine interactions were also observed with residues Gly 278 and Glu 359. Furthermore,
π–π
hydrophobic interactions were predicted between the aryl of the quinazoline at the 2-position and
both rings of tryptamine residue Trp 245 facing its edge, and the quinazoline moiety was involved in a
T-shaped
the binding mode of enantiomer 3d S was predicted to be inverted, in which the quinazoline ring
interacted with residue Trp 245 facing its edge via interaction, while the aryl ring showed two
interactions with residues Tyr 282 and Tyr 489. Two hydrogen bonding interactions were also
predicted with the two NH groups of the quinazoline ring and residues Gly 279 and Tyr 489.
π–π interaction with Tyr 282 and a π–ion interaction with amino acid Asp 233. In contrast,
π–π
π–π
3
d R form
3d S form
Figure 4. Predicted binding mode of both enantiomers of 3d in the G199S mutant AChE receptor (PDB:
ARY). The molecular interactions are represented as green dotted lines for H-bonds, magenta dotted
6
lines for π–π stacking interactions, and cyan dotted lines for fluorine contacts.
Our molecular modeling input revealed that the AChE enzyme target might be the plausible
enzyme target and the R enantiomer would be the principal active compound for larvicidal activity
contribution. This study may also indicate that our compounds might be potentially active
against insecticide-resistant mosquitos due to the good fitting observed with the active site of
the G199S mutant AChE receptor. However, future work should address the identification of the
enzyme target, the enantiomer responsible for the insecticidal effect, and the potency against the
insecticide-resistant mosquito.

Molecules 2020, 25, 1316
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3
. Materials and Methods
3
.1. General
The chemicals reported here were obtained from Sigma-Aldrich Co. (St. Louis, MO, USA), while
the solvents were obtained from Millipore Sigma (Burlington, MA, USA). Thin-layer chromatography
TLC) using silica gel (Sigma-Aldrich Co.) on aluminum foil was employed to observe the chemical
(
reactions; n-hexane and ethyl acetate (4:6) were used as solvents. The reactions were visualized
under an ultraviolet (UV)-light/iodine chamber. B-545 was used to measure the melting points (Büchi,
Labortechnik, Flawil, Switzerland). Fourier-transform infrared (FT-IR) spectra were recorded on a
1
13
Shimadzu FT-IR spectrophotometer. Furthermore, H-and C-NMR spectra were recorded on Bruker
AVANCE III 400 MHz instruments using dimethyl sulfoxide (DMSO)-d6 as a solvent. Chemical shifts
(δ) were recorded in parts per million (ppm) downfield from tetramethylsilane, while the coupling
constants (J) were recorded in Hz. The splitting pattern was documented as follows: s, singlet;
d, doublet; q, quartet; m, multiplet. Liquid chromatography–mass spectrometry (LC–MS; Agilent 1100
series) was used to measure the mass spectra in conjunction with the mass selective detector (MSD),
as well as 0.1% aqueous trifluoroacetic acid in an acetonitrile system on the C18-BDS column. Then,
elemental analysis was carried out using the analyzer FLASH EA 1112 CHN (Thermo Finnigan LLC,
New York, NY, USA). A single-crystal X-ray diffraction study was performed using a Bruker KAPPA
APEX II DUO diffractometer equipped with a charge coupled device (CCD) detector; monochromated
Mo K
α radiation (λ = 0.71073 Å) was used. Data collection was carried out at 173(2) K using an Oxford
Cryostream cooling system featuring the Bruker Apex II software.
3
.2. General Procedure for the Synthesis of 2-(Substituted phenyl)-2,3-dihydroquinazolin-4(1H)-ones (3a–n)
A mixture of aryl aldehyde (1.5 mmoL) and 2-aminobenzamide (1 mmoL) in 10 mL of water
was stirred in a round-bottom flask with graphene oxide (2.5%) at room temperature, as depicted in
Scheme 1. The progress of the reaction was monitored with TLC. After completion of the reaction,
the insoluble precipitate obtained was separated and filtrated, and the crude product was washed with
5
0% cold ethanol. The crude product was recrystallized from 75% ethyl alcohol to obtain 65% of the title
compound 2-(4-fluorophenyl)-2,3-dihydroquinazolin-4(1H)-one at 98% purity [44]. Physicochemical
1
13
characteristics of the title compounds are tabulated in Table 1. FT-IR, H and C-NMR of the title
compounds (3a–n) are available as electronic supplementary information.
3
.2.1. 2-(4-Methoxyphenyl)-2, 3-dihydroquinazolin-4(1H)-one (3a)
FT-IR (KBr, cm 1) 3298, 3182, 2862, 1658, 1610, 1508, 1483, 1298, 1174, 802, 611. H-NMR (400 MHz,
DMSO-d6) = 8.20 (s, 1H), 7.64–7.62 (dd, J = 8 Hz, 1.6 Hz,1H), 7.45–7.42 (m, 2H), 7.27–7.23 (m, 1H),
.02 (s, 1H), 6.97–6.94 (m, 2H), 6.77–6.70 (m,1H), 6.68–6.66 (m, 1H), 5.72 (s, 1H), 3.75 (s, 3H); C-NMR
100 MHz, DMSO-d6) = 163.70, 159.41, 147.99, 133.42, 133.22, 128.19, 127.32, 117.07, 114.97, 114.39,
13.60, 66.29, 55.13. Analytically calculated for C H N O : C, 70.85; H, 5.55; N, 11.02; found: C, 70.75;
−
1
δ
13
7
(
1
δ
15
14
2
2
H, 5.50; N, 10.98.
3
.2.2. 4-(4-Oxo-1,2,3,4-tetrahydroquinazolin-2-yl)benzonitrile (3b)
−
1
1
FT-IR (KBr, cm ) 3440, 2223, 1664, 1610, 1502, 1373, 1153, 858, 771, 619. H-NMR (400 MHz,
DMSO-d6) = 8.52 (s, 1H), 7.88–7.86 (d, J = 8 Hz, 2H), 7.71–7.69 (d, J = 8.4 Hz, 2H), 7.66–7.64 (d,
J = 7.6 Hz, 1H), 7.30–7.25 (m, 2H), 6.81–6.79 (d, J = 8.4 Hz, 1H), 6.72–6.70 (d, J = 8.0 Hz,1H), 5.89 (s, 1H);
δ
13
C-NMR (100 MHz, DMSO-d6)
δ = 163.40, 147.31, 147.24, 133.55, 132.36, 132.36, 127.68, 127.68, 127.41,
1
1
18.62, 117.45, 114.87, 114.52, 111.10, 65.59. Analytically calculated for C H N O: C, 72.28; H, 4.45; N,
6.86; found: C, 72.15; H, 4.40; N, 16.78.
15
11
3

Molecules 2020, 25, 1316
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3
.2.3. 2-(3-Hydroxyphenyl)-2,3-dihydroquinazolin-4(1H)-one (3c)
FT-IR (KBr, cm 1) 3357, 3296, 1631, 1606, 1506, 1483, 1305, 1155, 1035, 865, 752. H-NMR (400 MHz,
DMSO-d6) = 9.53 (s, 1H), 8.28 (s, 1H), 7.66–7.64 (d, J = 7.6 Hz, 1H), 7. 27–7.17 (m, 2H), 7.10 (s, 1H),
.95–6.92 (m, 2H), 6.78–6.76 (br d, J = 8.4 Hz, 2H), 6.71–6.67 (m, 1H), 5.69 (s, 1H); 13C-NMR (100 MHz,
−
1
δ
6
DMSO-d6) δ = 163.57, 157.34, 147.80, 143.17, 133.30, 129.32, 127.34, 117.44, 117.01, 115.36, 114.81, 114.34,
1
13.63, 66.47. Analytically calculated for C H N O : C, 69.99; H, 5.03; N, 11.66; found: C, 69.85; H,
14 12 2 2
4
.96; N, 11.58.
3
.2.4. 2-(4-(Trifluoromethoxy)phenyl)-2,3-dihydroquinazolin-4(1H)-one (3d)
FT-IR (KBr, cm 1) 3296, 3184, 3074, 1652, 1614, 1510, 1440, 1278, 1163, 1018, 813, 792, 675. H-NMR
400 MHz, DMSO-d6) = 8.36 (s, 1H), 7.66–7.63 (m, 3H), 7.42–7.40 (d, J = 8 Hz, 2H), 7.29–7.24 (m, 1H),
.17 (s, 1H), 6.78–6.76 (br d, J = 8.4 Hz, 1H), 6.72–6.68 (m,1H), 5.84 (s, 1H); 13C-NMR (100 MHz,
= 163.49, 148.30, 148.28, 147.93, 133.38, 128.91, 127.36, 121.30, 118.76, 117.29, 114.88, 114.42,
5.82. Analytically calculated for C H F N O : C, 58.45; H, 3.60; N, 9.09; found: C, 58.05; H, 3.46;
−
1
(
7
δ
DMSO-d6)
6
δ
15
11
3
2
2
N, 8.88.
3
.2.5. 2-(3-Iodophenyl)-2,3-dihydroquinazolin-4(1H)-one (3e)
FT-IR (KBr, cm 1) 3282, 3078, 2925, 1649, 1614, 1514, 1446, 1296, 1159, 811, 790, 754, 696. H-NMR
400 MHz, DMSO-d6) = 8.39 (s, 1H), 7.88 (s, 1H), 7.72–7.70 (d, J = 8.0 Hz, 1H), 7.65–7.63 (dd, J = 8.0,
.6 Hz, 1H), 7.54–7.51 (d, J = 7.2 Hz, 1H), 7.29–7.17 (m, 3H), 6.79–6.77(d, J = 6.8 Hz, 1H), 6.72–6.68 (m,
H), 5.77 (s, 1H); 13C-NMR (100 MHz, DMSO-d6)
= 163.45, 147.51, 144.35, 137.02, 135.50, 133.45,
30.54, 127.38, 126.17, 117.31, 114.84, 114.45, 94.76, 65.51. Analytically calculated for C H IN O: C,
−
1
(
δ
1
1
1
4
δ
14
11
2
8.02; H, 3.17; N, 8.00; found: C, 47.90; H, 3.06; N, 7.88.
3
.2.6. 2-(4-Chlorophenyl)-2,3-dihydroquinazolin-4(1H)-one (3f)
−
1
FT-IR (KBr, cm ) 3450, 3307, 3190, 3064, 2933, 1658, 1608, 1485, 1386, 1153, 838, 795, 752, 667.
H-NMR (400 MHz, DMSO-d6) = 8.37 (s, 1H), 7.66–7.64 (d, J = 7.6 Hz, 1H), 7.55–7.53 (m, 2H), 7.48–7.45
1
δ
(
m, 2H), 7.29–7.24 (m, 1H), 7.16 (s, 1H), 6.79–6.77 (d, J = 8.0 Hz, 1H), 6.72–6.68 (m,1H), 5.80 (s, 1H);
1
3
C-NMR (100 MHz, DMSO-d6)
δ = 163.53, 147.64, 140.61, 133.39, 133.00, 128.74, 128.29, 127.37, 117.29,
1
6
14.92, 114.46, 65.59. Analytically calculated for C H ClN O: C, 65.00; H, 4.29; N, 10.83; found: C,
4.90; H, 4.16; N, 10.68.
14
11
2
3
.2.7. 2-(3,4-Dimethoxyphenyl)-2,3-dihydroquinazolin-4(1H)-one (3g)
−
1
FT-IR (KBr, cm ) 3450, 3330, 3299, 2933, 1660, 1610, 1510, 1488, 1369 1262, 1232, 1140, 1091, 810.
H-NMR (400 MHz, DMSO-d6) = 8.21 (s, 1H), 7.65–7.63 (d, J = 7.0 Hz,1H), 7.28–7.26 (m, 1H), 7.16–7.15
1
δ
(
5
d, J = 1.6 Hz, 1H), 7.03–7.01 (m, 2H), 6.96–6.94 (m, 1H), 6.79–6.77 (d, J = 8.0 Hz,1H), 6.71–6.68 (m, 1H),
.72 (s, 1H), 3.77 (s, 3H), 3.75 (s, 3H); 13C-NMR (100 MHz, DMSO-d6)
δ = 163.76, 148.99, 148.58, 148.05,
133.55, 133.22, 127.33, 119.20, 117.14, 115.03, 114.43, 111.24, 110.60, 66.55, 55.54, 55.43. Analytically
calculated for C H N O : C, 67.59; H, 5.67; N, 9.85; found: C, 66.90; H, 5.36; N, 09.68.
16
16
2
3
3
.2.8. 2-(4-(Dimethylamino)phenyl)-2,3-dihydroquinazolin-4(1H)-one (3h)
−
1
FT-IR (KBr, cm ) 3450, 3296, 3193, 3060, 2932, 1658, 1614, 1485, 1357, 1296, 1161, 1064, 817,
1
7
54. H-NMR (400 MHz, DMSO-d )
δ
= 8.10 (s, 1H), 7.66–7.64 (dd, J = 8.4, 1.2 Hz, 1H), 7.34–7.32 (d,
6
13
J = 8.8 Hz, 2H), 7.27–7.22 (m, 1H), 6.94 (s, 1H), 6.78–6.67 (m, 4H), 5.67 (s, 1H), 2.88 (s, 6H); C-NMR
100 MHz, DMSO-d6) = 163.86, 150.67, 148.21, 133.12, 128.59, 127.70, 127.34, 116.94, 115.03, 114.38,
11.90, 111.90, 66.68, 40.12. Analytically calculated for C H N O: C, 71.89; H, 6.41; N, 15.72; found:
(
1
δ
16
17
3
C, 71.40; H, 6.36; N, 15.48.

Molecules 2020, 25, 1316
15 of 22
3
.2.9. 2-(3-Nitrophenyl)-2,3-dihydroquinazolin-4(1H)-one (3i)
−
1
FT-IR (KBr, cm ) 3296, 3193, 3074, 2923, 1652, 1610, 1530, 1485, 1352, 1257, 1153, 1033, 904, 752.
H-NMR (400 MHz, DMSO-d6) = 8.57 (s, 1H), 8.39 (s, 1H), 8.22–8.19 (m, 1H), 7.97–7.95 (d, J = 8.0 Hz,
H), 7.71–7.63 (m, 2H), 7.36 (s, 1H), 7.30–7.26 (m, 1H), 6.82–6.80 (d, J = 8.0 Hz, 1H), 6.72–6.69 (m, 1H),
1
δ
1
5
.98 (s, 1H); 13C-NMR (100 MHz, DMSO-d6)
δ
= 163.39, 147.68, 147.27, 144.24, 133.57, 133.32, 129.97,
1
27.41, 123.23, 121.55, 117.53, 114.91, 114.58, 65.19. Analytically calculated for C H N O : C, 62.45;
14
11
3
3
H, 4.12; N, 15.61; found: C, 62.06; H, 4.06; N, 15.37.
3
.2.10. 2-(4-Fluorophenyl)-2,3-dihydroquinazolin-4(1H)-one (3j)
−
1
FT-IR (KBr, cm ) 3400, 3299, 3184, 3130, 2931, 1658, 1610, 1508, 1485, 1389, 1234, 1159, 836, 750,
75. 1H-NMR (400 MHz, DMSO-d6)
= 8.31 (s, 1H), 7.65–7.63 (dd, J = 8.8, 1.2 Hz, 1H), 7.58–7.55
6
δ
(
m, 2H), 7.26–7.21 (m, 3H), 7.12 (s, 1H), 6.78–6.76 (d, J = 8.0 Hz, 1H), 6.72–6.68 (m, 1H), 5.80 (s, 1H);
1
3
C-NMR (100 MHz, DMSO-d6)
δ = 163.57, 147.78, 137.76, 137.73, 133.34, 129.06, 128.97, 127.35, 117.24,
1
15.17, 114.96, 114.92, 114.43, 65.93. Analytically calculated for C H FN O: C, 69.41; H, 4.58; N, 11.56;
14
11
2
found: C, 69.06; H, 4.46; N, 11.37.
3
.2.11. 2-(1H-Imidazol-4-yl)-2,3-dihydroquinazolin-4(1H)-one (3k)
−
1
1
FT-IR (KBr, cm ) 3247, 3130, 1614, 1579, 1515, 1440; H-NMR (400 MHz, DMSO-d )
δ
= 8.09
s, 1H), 7.49–7.48 (dd, J = 6.4, 1.2 Hz, 2H), 7.09–7.05 (m, 1H), 6.89, (s, 1H), 6.85, (s, 1H), 6.64–6.62 (d,
J = 8.0, 1H), 6.53–6.50 (m, 1H), 5.57 (s, 1H); 13C-NMR (100 MHz, DMSO-d6)
= 163.84, 147.96, 135.37,
6
(
δ
1
33.08, 127.30, 117.07, 115.19, 114.59, 61.67. Analytically calculated for C H N O: C, 61.67; H, 4.71; N,
11
10
4
2
6.15; found: C, 61.06; H, 4.56; N, 25.37.
3
.2.12. 2-(2-Methoxy-4-nitrophenyl)-2,3-dihydroquinazolin-4(1H)-one (3l)
−
1
FT-IR (KBr, cm ) 3371, 3022, 2929, 1649, 1616, 1519, 1485, 1348, 1253, 1163, 1089, 887, 765, 740.
H-NMR (400 MHz, DMSO-d6) = 8.23 (s, 1H), 7.87–7.85 (dd, J = 8.4, 2.4 Hz, 1H), 7.81–7.80 (m, 1H),
.66–7.60 (m, 2H), 7.27–7.23 (m, 1H), 6.99 (s, 1H), 6.80–6.78 (d, J = 8.0 Hz, 1H), 6.71–6.67 (m, 1H),
.08 (s, 1H) 3.98 (s, 3H); 13C-NMR (100 MHz, DMSO-d6)
= 163.53, 156.76, 148.37, 147.32, 136.36,
33.46, 127.56, 127.32, 117.35, 115.38, 114.54, 114.49, 105.84, 60.71, 56.33. Analytically calculated for
C H N O : C, 60.20; H, 4.38; N, 14.04; found: C, 60.06; H, 4.16; N, 13.87.
1
δ
7
6
1
δ
15
13
3
4
3
.2.13. 2-(2-Hydroxy-5-nitrophenyl)-2,3-dihydroquinazolin-4(1H)-one (3m)
−
1
FT-IR (KBr, cm ) 3396, 3195, 2925, 1645, 1623, 1515, 1392, 1336, 1284, 1164, 1089, 833, 757, 628.
H-NMR (400 MHz, DMSO-d6) = 11.66 (s, 1H), 8.24–8.23 (d, J = 7.2 Hz, 1H), 8.18–8.12 (m, 2H),
.67–7.65 (d, J = 7.6 Hz, 1H), 7.28–7.24 (m, 1H), 7.07–7.05 (d, J = 9.2 Hz, 1H), 6.95 (s, 1H), 6.82–6.80 (d,
1
δ
7
13
J = 8.0 Hz,1H), 6.73–6.69 (m, 1H) 6.05–6.04 (m, 1H); C-NMR (100 MHz, DMSO-d6)
47.60, 139.19, 133.44, 128.28, 127.37, 125.78, 123.31, 117.44, 115.95, 114.60, 114.60, 60.80. Analytically
calculated for C H N O : C, 58.95; H, 3.89; N, 14.73; found: C, 58.77; H, 3.77; N, 14.43.
δ = 163.69, 161.30,
1
14
11
3
4
3
.2.14. 2-(4-Hydroxyphenyl)-2,3-dihydroquinazolin-4(1H)-one (3n)
−
1
1
FT-IR (KBr, cm ) 3355, 3296, 1631, 1606, 1506, 1481, 1463, 1278, 1157, 1130, 865, 752. H-NMR
(
2
δ
400 MHz, DMSO-d6) δ = 9.53 (s, 1H), 8.12 (s, 1H), 7.65–7.63 (d, J = 7.2 Hz, 1H), 7.34–7.32 (d, J = 8.4 Hz,
H), 7.27–7.25 (m, 1H), 6.95–6,92 (m, 1H), 6.80–6.75 (m, 4H), 5.68 (s, 1H); 13C-NMR (100 MHz, DMSO-d6)
= 163.78, 157.67, 148.14, 133.23, 131.56, 128.28, 127.34, 117.04, 114.92, 114.37, 66.65. Analytically
calculated for C H N O : C, 69.99; H, 5.03; N, 11.66; found: C, 69.56; H, 5.87; N, 11.43.
14
12
2
2
3
.3. Crystallographic Studies
Single-crystal X-ray diffraction data were collected on a Bruker KAPPA APEX II DUO diffractometer
using graphite monochromated Mo Kα radiation (χ = 0.71073 Å). Data collection was carried out at

Molecules 2020, 25, 1316
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1
73(2) K. Temperature was controlled by an Oxford Cryostream cooling system (Oxford Cryostat). Cell
refinement and data reduction were performed using the program SAINT [62]. The data were scaled,
and absorption correction was performed using SADABS [62].
The structure was solved via direct methods using SHELXS-18 [63] and refined via the full-matrix
2
least-squares method based on F using SHELXL-2018 [63]. The program WinGx [64] was used to prepare
molecular graphic images. All non-hydrogen atoms were refined anisotropically. All hydrogen atoms,
except H1 and H2, were placed in idealized positions and refined in riding models with Uiso assigned
1
.2 or 1.5 times the Ueq of their parent atoms, and the C–H bond distances were constrained to 0.95 Å for
aromatic hydrogen and 1.00 Å for methyl hydrogen. The amino hydrogens H1 and H2 were located in
the difference electron density maps and refined independently. There was a solvent-accessible void of
3
3
4
11.3 Å per unit cell volume of 2587.0 Å (~15.9%). Attempts to model the solvent molecule as discrete
atomic sites failed. PLATON SQUEEZE [65] was employed to calculate the contribution to the diffraction
from the missing solvent molecules, and it produced a set of partial solvent-free diffraction intensities.
This set of intensities was used for final refinements. SQUEEZE estimated a total count of 99 electrons
per unit cell, which were contributed by the missing solvents. The structure was refined to an R factor of
0
.0544. The parameters for crystal data collection and structure refinement and the list of intermolecular
interactions in the crystal structure 2-(3,4-dimethoxyphenyl)-2,3-dihydroquinazolin-4(1H)-one (3g) are
given in Tables 2 and 3, respectively.
3
.4. Larvicidal Activity
Anopheles arabiensis was used in the study according to the protocol described by WHO (1975)
◦
guidelines [66] in an insectary, simulating the temperature (27.5 C), humidity (70%), and lighting
(12/12) of a malaria-endemic environment. One milliliter of test compound (1 mg/mL) was added to
distilled water (250 mL) to obtain a final concentration of 4 g/mL. Thirty instar larvae were introduced
µ
into a container. A negative control was set up using the solvent (Acetone), and distilled water, as
well as a positive control Temephos, which is an active emulsified organophosphate larvicidal drug in
malaria control programs. Larval mortality was examined for each container separately for 24 h and
4
8 h, and larvae were fed specially made cat food that contained less oil/fat content. The percentage
mortality was determined relative to the initial number of larvae exposed. The bioassay was performed
in triplicate, and the results are tabulated in Table 4.
3
.5. Data Analysis
Differences in larval mortality between treatments were assessed with generalized linear models
using a binomial link function [67]. The dependent variable was A. arabiensis mortality, while fixed
effects were test compound (test compounds 3a , and both controls) and observation period (24 and
8 h). A p-value <0.05 was considered statistically significant. Throughout the text, the results are
presented as the adjusted mean ±the standard error.
–
n
4
3
.6. In silico ADMET Prediction
ADMET properties of the derivatives (3a–n) were predicted using the software Accelry’s Discovery
Studio 4.0 Client [68]. ADMET-related descriptors such as drug-likeness, permeability, intestine
absorption, plasma binding, liver toxicity, and CYP450 inhibition were investigated. The in silico
ADMET properties of quinazolines (3a–n) and Temephos are tabulated in Table 5.
3
.7. Molecular Modeling
Docking simulation was conducted with the software Accelry’s Discovery Studio 4.0 client
employing the CHARMm force field algorithm following our earlier reported procedure [69,70]. In this
study, the X-ray co-crystal acetylcholinesterase receptor (PDB: 6ARY) was retrieved from the Protein
Data Bank (PDB) [71] and subjected to the following steps: removal of all ligands and water; adding
hydrogen and missing amino acids. The binding domain was defined by inserting the original ligand

Molecules 2020, 25, 1316
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into the prepared protein. To validate the active site, the original ligand was re-docked to ensure
proper binding interactions with respect to those reported for PDB 6FSD. CDocker protocol was used to
predict the binding mode of compounds. The active amino-acid residues of the receptor were kept rigid
during the docking run. The conformation of the best 10 binding poses was ranked according to the
CDocker energy score. The most proper binding mode was selected according to the highest-scoring
functions PLP1, PLP2, Jain, and PMF [70]. The binding energy of the selected ligand binding pose was
determined by applying the in situ ligand minimization energy step in the CDocker protocol.
4
. Conclusions
The 2,3-dihydroquinazolin-4(1H)-one represents a privileged scaffold exhibiting various
pharmacological activities. The functionalization of the quinazoline at the 2-position with aryl
led to potent medicinal agents with anti-tubulin, antifungal, anti-tuberculosis, and antiviral activities,
among others. Thus, the 2-aryl-2,3-dihydroquinazolin-4-one scaffold makes compounds attractive
in terms of exploring novel activity. The novel series of 2-aryl-2,3-dihydroquinazolin-4-ones were
identified as potent insecticides against larvae Anopheles arabiensis. These compounds exhibited potent
larvicidal effects for the control of malaria vectors due to their toxicity towards larvae, when exposed
to a concentration of 4 µg/mL. The most promising compound was found to be 3d, substituted in
the para position with an OCF group, which displayed a similar toxicity to that of Temephos, an
3
active emulsified organophosphate larvicidal used by malaria control programs. The next two potent
compounds were 3j and 3f, which resulted in over 90% larval mortalities after 24- to 48-h exposure.
The ADMET profile for the majority of the compounds was acceptable. The docking input revealed
that AChE would be the appropriate enzyme molecular target upon demonstrating a favorable binding
interaction, and the title compounds may find application for treating insecticide-resistant mosquitos.
In general, the R enantiomer was predicted to strongly bind to the AChE receptor. Based on ADMET
and docking analysis, the title compounds are investigated as potential AChE inhibitors, and the brain
cell permeability was an important parameter for the activity. However, elucidation of the molecular
target and the enantiomer responsible for larvicidal activity remains to be addressed in order to design
more potent and safer 2,3-dihydroquinazolin-4(1H)-ones. Therefore, the dihydroquinazolinone scaffold
having a para trifluoromethoxy functionality on the phenyl ring was identified as the lead compound,
which can serve as the starting point for the development of novel larvicidal agents.
Supplementary Materials: The following are available online at http://www.mdpi.com/1420-3049/25/6/1316/s1:
1
Figure S1: FT-IR of 2-(4-methoxyphenyl)-2,3-dihydroquinazolin-4(1H)-one (3
a
); Figure S2: H-NMR of
1
3
2
-(4-methoxyphenyl)-2,3-dihydroquinazolin-4(1H)-one (3a); Figure S3: C-NMR of 2-(4-methoxyphenyl)-2,3-
dihydroquinazolin-4(1H)-one (3
a
); Figure S4: FT-IR of 4-(4-oxo-1,2,3,4-tetrahydroquinazolin-2-yl)benzonitrile
1
13
(
3
b); Figure S5: H-NMR of 4-(4-oxo-1,2,3,4-tetrahydroquinazolin-2-yl)benzonitrile (3
b
); Figure S6: C-NMR
); Figure S7: FT-IR of 2-(3- hydroxyphenyl)-2,3-
); Figure S8: H-NMR of 2-(3- hydroxyphenyl)-2,3- dihydroquinazolin-
of 4-(4-oxo-1,2,3,4-tetrahydroquinazolin-2-yl)benzonitrile (3
b
1
dihydroquinazolin- 4(1H)-one (3
(1H)-one (3
FT-IR of 2-(4- (trifluoromethoxy)phenyl)-2,3- dihydroquinazolin- 4(1H)-one (3
c
4
c
); Figure S9: 13C-NMR of 2-(3- hydroxyphenyl)-2,3- dihydroquinazolin- 4(1H)-one (3
c
); Figure S10:
); Figure S11: H-NMR
C-NMR of 2-(4-
); Figure S13: FT-IR of 2-(3- iodophenyl)-2,3-
1
d
1
3
of 2-(4- (trifluoromethoxy)phenyl)-2,3- dihydroquinazolin- 4(1H)-one (3
d
); Figure S12:
(
trifluoromethoxy)phenyl)-2,3- dihydroquinazolin- 4(1H)-one (3
d
1
dihydroquinazolin- 4(1H)-one (3
e
); Figure S14: H-NMR of 2-(3- iodophenyl)-2,3- dihydroquinazolin- 4(1H)-one
(3
e
); Figure S15: 13C-NMR of 2-(3- iodophenyl)- 2,3-dihydroquinazolin- 4(1H)-one (3
-(4- chlorophenyl)-2,3- dihydroquinazolin- 4(1H)-one (3
e
); Figure S16: FT-IR of
); Figure S17: H-NMR of 2-(4- chlorophenyl)-2,3-
1
2
f
1
3
dihydroquinazolin- 4(1H)-one (3
f
); Figure S18:
C-NMR of 2-(4- chlorophenyl)-2,3- dihydroquinazolin-
4
(1H)-one (3
f
); Figure S19: FT-IR of 2-(3,4- dimethoxyphenyl)-2,3- dihydroquinazolin- 4(1H)-one (3
g); Figure S20:
1
13
H-NMR of 2-(3,4- dimethoxyphenyl)-2,3- dihydroquinazolin- 4(1H)-one (3
g
); Figure S21: C-NMR of 2-(3,4-
); Figure S22: FT-IR of 2-(4- (dimethylamino)phenyl)-2,3-
); Figure S23: H-NMR of 2-(4- (dimethylamino)phenyl)-2,3- dihydroquinazolin-
C-NMR of 2-(4- (dimethylamino)phenyl)-2,3- dihydroquinazolin- 4(1H)-one
dimethoxyphenyl)-2,3- dihydroquinazolin- 4(1H)-one (3
g
1
dihydroquinazolin- 4(1H)-one (3
h
13
4(1H)-one (3
h); Figure S24:
1
(
3h); Figure S25: FT-IR of 2-(3- nitrophenyl)-2,3- dihydroquinazolin- 4(1H)-one (3
i
); Figure S26: H-NMR
1
3
of 2-(3- nitrophenyl)-2,3- dihydroquinazolin- 4(1H)-one (3i); Figure S27: C-NMR of 2-(3- nitrophenyl)-2,3-
dihydroquinazolin- 4(1H)-one (3i); Figure S28: FT-IR of 2-(4- fluorophenyl)-2,3- dihydroquinazolin- 4(1H)-one

Molecules 2020, 25, 1316
18 of 22
1
); Figure S30: 13C-NMR
(
3
j
); Figure S29: H-NMR of 2-(4- fluorophenyl)-2,3- dihydroquinazolin- 4(1H)-one (3
j
of 2-(4- fluorophenyl)-2,3- dihydroquinazolin- 4(1H)-one (3
dihydroquinazolin- 4(1H)-one (3
j
); Figure S31: FT-IR of 2-(1H-imidazol- 4-yl)-2,3-
1
k
); Figure S32: H-NMR of 2-(1H- imidazol-4-yl)-2,3- dihydroquinazolin-
13
4
(1H)-one (3
k
); Figure S33:
C-NMR of 2-(1H- imidazol-4-yl)-2,3- dihydroquinazolin- 4(1H)-one (3
k);
Figure S34: FT-IR of 2-(2-methoxy-4-nitrophenyl)-2,3- dihydroquinazolin- 4(1H)-one (3
l); Figure S35:
1
13
H-NMR of 2-(2-methoxy-4-nitrophenyl)-2,3- dihydroquinazolin- 4(1H)-one (3
-(2-methoxy-4-nitrophenyl)-2,3- dihydroquinazolin- 4(1H)-one (3
nitrophenyl)-2,3- dihydroquinazolin- 4(1H)-one (3
l
); Figure S36:
C-NMR of
2
l
); Figure S37: FT-IR of 2-(2-hydroxy- 5-
1
m
); Figure S38: H-NMR of 2-(2-hydroxy- 5- nitrophenyl)-2,3-
1
3
dihydroquinazolin- 4(1H)-one (3m); Figure S39: C-NMR of 2-(2-hydroxy- 5- nitrophenyl)-2,3- dihydroquinazolin-
4
(1H)-one (3
m
); Figure S40: FT-IR of 2-(4- hydroxyphenyl)-2,3- dihydroquinazolin- 4(1H)-one (3
n);
1
13
Figure S41: H-NMR of 2-(4-hydroxyphenyl)-2,3-dihydroquinazolin- 4(1H)-one (3
of 2-(4-hydroxyphenyl)-2,3-dihydroquinazolin- 4(1H)-one (3n).
n
); Figure S42: C-NMR
Author Contributions: Conceptualization, K.N.V., C.T., R.M.G., and S.C.; methodology, K.N.V., P.R., C.T., R.M.G.,
S.B., D.C., M.A.M., M.A., A.B.N., N.S., R.V., P.K.D., S.C., O.I.A., S.N.A., Y.A.B., R.P., M.H., S.P., M.B.G., S.H.A.,
and V.M.; software, K.N.V., C.T., S.B., D.C., and P.K.D.; validation, K.N.V., P.R., C.T., S.B., M.A.M., S.C., H.E.K.,
and M.H.; formal analysis, K.N.V., C.T., S.B., D.C., M.A., N.S., S.C., H.E.K., M.B.G., and S.H.A.; investigation,
K.N.V., P.R., C.T., R.M.G., A.B.N., P.K.D., S.C., S.N.A., Y.A.B., R.P., S.P., and V.M.; resources, K.N.V., D.C., B.E.A.,
R.V., P.K.D., S.C., H.E.K., and O.I.A.; data curation, K.N.V., C.T., M.A.M., S.C., and O.I.A.; writing—original draft
preparation, K.N.V., P.R., C.T., R.M.G., S.B., M.A.M., B.E.A., M.A., N.S., R.V., P.K.D., O.I.A., S.N.A., Y.A.B., R.P.,
M.H., S.P., M.B.G., S.H.A., and V.M.; writing—review and editing, K.N.V., C.T., D.C., R.M.G., B.E.A., A.B.N.,
P.K.D., R.V., H.E.K., and S.C.; visualization, K.N.V., C.T., and D.C.; supervision, K.N.V., D.C., and S.C.; project
administration, K.N.V.; funding acquisition, K.N.V., B.E.A., M.A., A.B.N., N.S., and D.C. All authors have read
and agreed to the published version of the manuscript.
Funding: This research was funded by the Deanship of Scientific Research at King Faisal University, Al-Ahsa,
Saudi Arabia (Research Group grant number 17122011).
Acknowledgments: The authors are grateful to the Deanship of Scientific Research, King Faisal University,
Kingdom of Saudi Arabia for financial support and encouragement. The authors thank Hong Su, Center for
Supramolecular Chemistry Research, Department of Chemistry, University of Cape Town, Rodenbosch 7701, for
single-crystal X-ray data collection and Shiva Kumar, School of Applied Sciences, REVA University, Bangalore for
providing carbocatalyst. D.C. and S.B. thank IISER Bhopal for research facilities and infrastructure. R.M.G. is a
researcher of CONICET.
Conflicts of Interest: The authors declare no conflicts of interest. The funders had no role in the design of the
study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to
publish the results.
References
1
.
WHO. World Malaria Report; WHO: Geneva, Switzerland, 2019. Available online: https://www.who.int/
publications-detail/world-malaria-report-2019 (accessed on 11 December 2019).
2
.
Venugopala, K.N.; Gleiser, R.M.; Chalannavar, R.K.; Odhav, B. Antimosquito properties of 2-substituted
phenyl/benzylamino-6-(4-chlorophenyl)-5-methoxycarbonyl-4-methyl-3,6-dihydropyrimidin-1-ium
chlorides against Anopheles arabiensis. Med. Chem. 2014, 10, 211–219.
3.
4.
5.
Mohankumar, T.K.; Shivanna, K.S.; Achuttan, V.V. Screening of Methanolic Plant extracts against larvae of
Aedes aegypti and Anopheles stephensi in Mysore. J. Arthropod Borne Dis. 2016, 10, 303–314. [PubMed]
Hemingway, J.; Ranson, H. Insecticide resistance in insect vectors of human disease. Annu. Rev. Entomol.
2
000, 45, 371–391. [CrossRef] [PubMed]
Abdalla, H.; Wilding, C.S.; Nardini, L.; Pignatelli, P.; Koekemoer, L.L.; Ranson, H.; Coetzee, M. Insecticide
resistance in Anopheles arabiensis in Sudan: Temporal trends and underlying mechanisms. Parasites Vectors
2
014, 7, 213. [CrossRef] [PubMed]
Zhao, Q.; Sun, R.; Liu, Y.; Chen, P.; Li, Y.; Yang, S.; Wang, Q. Synthesis and insecticidal activity studies of
novel phenylpyrazole derivatives containing arylimine or carbimidate moiety. Bioorg. Med. Chem. 2019
7, 115092. [CrossRef] [PubMed]
Huang, Y.; Liu, Y.; Liu, Y.; Song, H.; Wang, Q. C ring may be dispensable for
6
7
8
.
.
.
,
2
β
-carboline: Design, synthesis,
and bioactivities evaluation of tryptophan analog derivatives based on the biosynthesis of β-carboline
alkaloids. Bioorg. Med. Chem. 2016, 24, 462–473. [CrossRef] [PubMed]
da Silva, J.B.; Navarro, D.M.; da Silva, A.G.; Santos, G.K.; Dutra, K.A.; Moreira, D.R.; Ramos, M.N.;
Espindola, J.W.; de Oliveira, A.D.; Brondani, D.J.; et al. Thiosemicarbazones as Aedes aegypti larvicidal. Eur. J.
Med. Chem. 2015, 100, 162–175. [CrossRef]

Molecules 2020, 25, 1316
19 of 22
9
1
.
Castelino, P.A.; Naik, P.; Dasappa, J.P.; Sujayraj, R.S.; Sharath Chandra, K.; Chaluvaiah, K.; Nair, R.; Sandya
Kumari, M.V.; Kalthur, G.; Adiga, S.K. Synthesis of novel thiadiazolotriazin-4-ones and study of their
mosquito-larvicidal and antibacterial properties. Eur. J. Med. Chem. 2014, 84, 194–199. [CrossRef]
0. Oliveira, V.S.; Pimenteira, C.; da Silva-Alves, D.C.; Leal, L.L.; Neves-Filho, R.A.; Navarro, D.M.; Santos, G.K.;
Dutra, K.A.; dos Anjos, J.V.; Soares, T.A. The enzyme 3-hydroxykynurenine transaminase as potential target
for 1,2,4-oxadiazoles with larvicide activity against the dengue vector Aedes aegypti. Bioorg. Med. Chem. 2013
,
2
1, 6996–7003. [CrossRef]
1
1
1. Mao, M.; Li, Y.; Liu, Q.; Zhou, Y.; Zhang, X.; Xiong, L.; Li, Y.; Li, Z. Synthesis and insecticidal evaluation
of novel N-pyridylpyrazolecarboxamides containing cyano substituent in the ortho-position. Bioorg. Med.
Chem. Lett. 2013, 23, 42–46. [CrossRef]
2. Abass, M.; Mostafa, B.B. Synthesis and evaluation of molluscicidal and larvicidal activities of some novel
enaminones derived from 4-hydroxyquinolinones: Part IX. Bioorg. Med. Chem. 2005, 13, 6133–6144.
[
CrossRef] [PubMed]
3. Liang, J.L.; Cha, H.C.; Jahng, Y. Recent advances in the studies on luotonins. Molecules 2011, 16, 4861–4883.
CrossRef] [PubMed]
4. Lee, S.; Kim, D.-C.; Baek, H.Y.; Lee, K.-D.; Kim, Y.-C.; Oh, H. Anti-neuroinflammatory effects of tryptanthrin
from Polygonum tinctorium Lour. in lipopolysaccharide-stimulated BV2 microglial cells. Arch. Pharmacal Res.
1
1
[
2
018, 41, 419–430. [CrossRef] [PubMed]
1
5. Tian, K.-M.; Li, J.-J.; Xu, S.-W. Rutaecarpine: A promising cardiovascular protective alkaloid from
Evodia rutaecarpa (Wu Zhu Yu). Pharmacol. Res. 2019, 141, 541–550. [CrossRef] [PubMed]
1
6. Estlin, E.J.; Pinkerton, C.R.; Lewis, I.J.; Lashford, L.; McDowell, H.; Morland, B.; Kohler, J.; Newell, D.R.;
Boddy, A.V.; Taylor, G.A.; et al. A phase I study of nolatrexed dihydrochloride in children with advanced cancer.
A United Kingdom Children’s Cancer Study Group Investigation. Br. J. Cancer 2001, 84, 11–18. [CrossRef]
7. Gudimella, K.K.; Bonige, K.B.; Gundla, R.; Katari, N.K.; Yamajala, B.; Battula, V.R. 2,4-Diphenyl-1,2-
dihydroquinazoline derivatives: Synthesis, anticancer activity and docking studies. ChemistrySelect 2019, 4,
1
1
1
2
2
2
2
1
2528–12533. [CrossRef]
8. Iyer, K.A.; Alix, K.; Eltit, J.M.; Solis, E., Jr.; Pan, X.; Argade, M.D.; Khatri, S.; De Felice, L.J.; Sweet, D.H.;
Schulte, M.K.; et al. Multi-modal antidepressant-like action of 6- and 7-chloro-2-aminodihydroquinazolines
in the mouse tail suspension test. Psychopharmacology (Berl) 2019, 236, 2093–2104. [CrossRef]
9. Barmak, A.; Niknam, K.; Mohebbi, G. Synthesis, structural studies, and α-Glucosidase inhibitory, antidiabetic,
and antioxidant activities of 2,3-Dihydroquinazolin-4(1H)-ones derived from Pyrazol-4-carbaldehyde and
anilines. ACS Omega 2019, 4, 18087–18099. [CrossRef]
0. Guillon, R.; Pagniez, F.; Picot, C.; Hédou, D.; Tonnerre, A.; Chosson, E.; Duflos, M.; Besson, T.; Logé, C.;
Le Pape, P. Discovery of a novel broad-spectrum antifungal agent derived from albaconazole. ACS Med.
Chem. Lett. 2013, 4, 288–292. [CrossRef]
1. Mujeeb Ur, R.; Rathore, A.; Siddiqui, A.A.; Parveen, G.; Yar, M.S. Synthesis and characterization of quinazoline
derivatives: Search for hybrid molecule as diuretic and antihypertensive agents. J. Enzym. Inhib Med. Chem.
2
014, 29, 733–743. [CrossRef]
2. Obase, H.; Takai, H.; Teranishi, M.; Nakamizo, N. Synthesis of (1-substituted piperidin-4-yl)-1H-
benzimidazoles and (1-substituted piperidin-4-yl)-3,4-dihydroquinazolines as possible antihypertensive
agents. J. Heterocycl. Chem. 1983, 20, 565–573. [CrossRef]
3. El-Sabbagh, O.I.; Ibrahim, S.M.; Baraka, M.M.; Kothayer, H. Synthesis of new 2,3-dihydroquinazolin-
4
(1H)-one derivatives for analgesic and anti-inflammatory evaluation. Arch. Der Pharm. 2010, 343, 274–281.
[CrossRef] [PubMed]
2
2
4. Clissold, S.P.; Beresford, R. Proquazone. A review of its pharmacodynamic and pharmacokinetic properties,
and therapeutic efficacy in rheumatic diseases and pain states. Drugs 1987, 33, 478–502. [CrossRef] [PubMed]
5. Kamal, A.; Babu, K.S.; Poornachandra, Y.; Nagaraju, B.; Ali Hussaini, S.M.; Shaik, S.P.; Ganesh Kumar, C.;
Alarifi, A. Efficient and green sulfamic acid catalyzed synthesis of new 1,2-dihydroquinazoline derivatives
with antibacterial potential. Arab. J. Chem. 2015. [CrossRef]
2
6. Salehi, P.; Ayyari, M.; Bararjanian, M.; Ebrahimi, S.N.; Aliahmadi, A. Synthesis, antibacterial and antioxidant
activity of novel 2,3-dihydroquinazolin-4(1H)-one derivatives of dehydroabietylamine diterpene. J. Iran.
Chem. Soc. 2014, 11, 607–613. [CrossRef]

Molecules 2020, 25, 1316
20 of 22
2
7. Chung, C.K.; Liu, Z.; Lexa, K.W.; Andreani, T.; Xu, Y.; Ji, Y.; DiRocco, D.A.; Humphrey, G.R.; Ruck, R.T.
Asymmetric hydrogen bonding catalysis for the synthesis of dihydroquinazoline-containing antiviral,
letermovir. J. Am. Chem. Soc. 2017, 139, 10637–10640. [CrossRef]
2
2
3
3
3
8. Mehta, D.R.; Naravane, J.S.; Desai, R.M. Vasicinone. A Bronchodilator Principle from Adhatoda vasica Nees
(N. O. Acanthaceae). J. Org. Chem. 1963, 28, 445–448. [CrossRef]
9. Yamamura, M.; Ochiai, T.; Ishida, R. [Effects of afloqualone, a new centrally acting muscle relaxant, on DRL
response and CER in rats (author’s transl)]. Nihon Yakurigaku Zasshi 1981, 78, 381–392. [CrossRef]
0. Ferrando, C.; Foy, J.M.; Pratt, C.N.F.W.; Purvis, J.R. On the pharmacological actions of a diuretic, fenquizone,
with particular reference to its site of action. J. Pharm. Pharmacol. 1981, 33, 219–222. [CrossRef]
1. Van Zyl, E.F. A survey of reported synthesis of methaqualone and some positional and structural isomers.
Forensic Sci. Int. 2001, 122, 142–149. [CrossRef]
2. Jafari, E.; Khajouei, M.R.; Hassanzadeh, F.; Hakimelahi, G.H.; Khodarahmi, G.A. Quinazolinone and
quinazoline derivatives: Recent structures with potent antimicrobial and cytotoxic activities. Res. Pharm. Sci.
2
016, 11, 1–14. [PubMed]
3
3
3
3. Li, W.J.; Li, Q.; Liu, D.L.; Ding, M.W. Synthesis, fungicidal activity, and sterol 14alpha-demethylase binding
interaction of 2-azolyl-3,4-dihydroquinazolines on Penicillium digitatum. J. Agric. Food Chem. 2013, 61,
1
419–1426. [CrossRef] [PubMed]
4. Zhou, Y.; Feng, Q.; Di, F.; Liu, Q.; Wang, D.; Chen, Y.; Xiong, L.; Song, H.; Li, Y.; Li, Z. Synthesis and
insecticidal activities of 2,3-dihydroquinazolin-4(1H)-one derivatives targeting calcium channel. Bioorg. Med.
Chem. 2013, 21, 4968–4975. [CrossRef] [PubMed]
5. Chandrashekharappa, S.; Venugopala, K.N.; Nayak, S.K.; Gleiser, R.M.; García, D.A.; Kumalo, H.M.;
Kulkarni, R.S.; Mahomoodally, F.M.; Venugopala, R.; Mohan, M.K.; et al. One-pot microwave assisted
synthesis and structural elucidation of novel ethyl 3-substituted-7-methylindolizine-1-carboxylates with
larvicidal activity against Anopheles arabiensis. J. Mol. Struct. 2018, 1156, 377–384. [CrossRef]
3
3
3
3
4
6. Bairagi, K.M.; Venugopala, K.N.; Mondal, P.K.; Gleiser, R.M.; Chopra, D.; García, D.; Odhav, B.; Nayak, S.K.
Larvicidal study of tetrahydropyrimidine scaffolds against Anopheles arabiensis and structural insight by
single crystal X-ray studies. Chem. Biol. Drug Des. 2018, 92, 1924–1932. [CrossRef] [PubMed]
7. Dharma Rao, B.D.; Bhandary, S.; Chopra, D.; Venugopala, K.N.; Gleiser, R.M.; Kasumbwe, K.; Odhav, B.
Synthesis and characterization of a novel series of 1,4-dihydropyridine analogues for larvicidal activity
against Anopheles arabiensis. Chem. Biol. Drug Des. 2017, 90, 397–405. [CrossRef] [PubMed]
8. Sanchez-Borzone, M.E.; Mariani, M.E.; Miguel, V.; Gleiser, R.M.; Odhav, B.; Venugopala, K.N.; Garcia, D.A.
Membrane effects of dihydropyrimidine analogues with larvicidal activity. Colloids Surf. B Biointerfaces 2017
50, 106–113. [CrossRef]
,
1
9. Sandeep, C.; Venugopala, K.N.; Gleiser, R.M.; Chetram, A.; Padmashali, B.; Kulkarni, R.S.; Venugopala, R.;
Odhav, B. Greener synthesis of indolizine analogues using water as a base and solvent: Study for larvicidal
activity against Anopheles arabiensis. Chem. Biol. Drug Des. 2016, 88, 899–904. [CrossRef]
0. Venugopala, K.N.; Krishnappa, M.; Nayak, S.K.; Subrahmanya, B.K.; Vaderapura, J.P.; Chalannavar, R.K.;
Gleiser, R.M.; Odhav, B. Synthesis and antimosquito properties of 2,6-substituted benzo[d]thiazole and
2
,4-substituted benzo[d]thiazole analogues against Anopheles arabiensis. Eur. J. Med. Chem. 2013, 65, 295–303.
[CrossRef]
4
4
4
4
1. Venugopala, K.N. Synthesis and structural elucidation of novel 2, 4-disubstituted 1, 3-oxazole analogues for
pharmacological properties. Asian J. Chem. 2018, 30, 684–688. [CrossRef]
2. Venugopala, K.N. Design, microwave assisted synthesis and characterization of substituted 1, 2, 4-oxadiazole
analogues as promising pharmacological agents. Asian J. Chem. 2017, 29, 1767–1770. [CrossRef]
3. Venugopala, K.N.; Jayashree, B.S. Microwave-induced synthesis of Schiff bases of aminothiazolyl
bromocoumarins as antibacterials. Indian J. Pharm. Sci. 2008, 70, 88–91. [CrossRef] [PubMed]
4. Kausar, N.; Roy, I.; Chattopadhyay, D.; Das, A.R. Synthesis of 2,3-dihydroquinazolinones and
quinazolin-4(3H)- ones catalyzed by graphene oxide nanosheets in an aqueous medium: “on-water”
synthesis accompanied by carbocatalysis and selective C–C bond cleavage. RSC Adv. 2016, 6, 22320–22330.
[CrossRef]
4
5. Bahekar, S.P.; Dahake, N.D.; Sarode, P.B.; Chandak, H.S. Efficient access to 2, 3-dihydroquinazolin-4 (1H)-ones
by environmentally benign l-proline nitrate as recyclable catalyst. Synlett 2015, 26, 2575–2577. [CrossRef]

Molecules 2020, 25, 1316
21 of 22
4
4
4
6. Shiri, L.; Heidari, L.; Kazemi, M. Magnetic Fe3O4 nanoparticles supported imine/Thiophene-nickel (II)
complex: A new and highly active heterogeneous catalyst for the synthesis of polyhydroquinolines and 2,
-dihydroquinazoline-4(1H)-ones. Appl. Organomet. Chem. 2018, 32, e3943. [CrossRef]
7. Bunce, R.A.; Nammalwar, B. New conditions for synthesis of ( )-2-monosubstituted and (
,3-dihydro-4(1H)-quinazolinones from 2-nitro- and 2-aminobenzamide. J. Heterocycl. Chem. 2011, 48,
91–997. [CrossRef]
8. Shiri, L.; Ghorbani-Choghamarani, A.; Kazemi, M. Synthesis and characterization of bromine source
supported on magnetic Fe3O4 nanoparticles: A new, versatile and efficient magnetically separable catalyst
for organic synthesis. Appl. Organomet. Chem. 2017, 31, e3634. [CrossRef]
3
±
±
)-2,2-disubstituted
2
9
4
9. Ramesh, R.; Sankar, G.; Małecki, J.; Lalitha, A. Carbon–SO3H derived from glycerol: A green recyclable
catalyst for synthesis of 2,3-dihydroquinazolin-4(1H)-ones. J. Iran. Chem. Soc. 2017, 15. [CrossRef]
0. Dhanunjaya Rao, A.V.; Vykunteswararao, B.P.; Bhaskarkumar, T.; Jogdand, N.R.; Kalita, D.; Lilakar, J.K.D.;
Siddaiah, V.; Douglas Sanasi, P.; Raghunadh, A. Sulfonic acid functionalized Wang resin (Wang-OSO3H) as
polymeric acidic catalyst for the eco-friendly synthesis of 2,3-dihydroquinazolin-4(1H)-ones. Tetrahedron Lett.
5
2
015, 56, 4714–4717. [CrossRef]
5
5
5
5
5
5
5
5
5
1. Bhatt, S.; Gething, P.W.; Brady, O.J.; Messina, J.P.; Farlow, A.W.; Moyes, C.L.; Drake, J.M.; Brownstein, J.S.;
Hoen, A.G.; Sankoh, O.; et al. The global distribution and burden of dengue. Nature 2013, 496, 504–507.
[CrossRef]
2. Loza-Mejia, M.A.; Salazar, J.R.; Sanchez-Tejeda, J.F. In Silico studies on compounds derived from Calceolaria:
Phenylethanoid glycosides as potential multitarget inhibitors for the development of pesticides. Biomolecules
2
018, 8, 121. [CrossRef] [PubMed]
3. El Yazal, J.; Rao, S.N.; Mehl, A.; Slikker, W., Jr. Prediction of organophosphorus acetylcholinesterase inhibition
using three-dimensional quantitative structure-activity relationship (3D-QSAR) methods. Toxicol. Sci. 2001
3, 223–232. [CrossRef] [PubMed]
,
6
4. Cheung, J.; Mahmood, A.; Kalathur, R.; Liu, L.; Carlier, P.R. Structure of the G119S mutant acetylcholinesterase
of the malaria vector Anopheles gambiae reveals basis of insecticide resistance. Structure 2018, 26, 130–136.e132.
[CrossRef] [PubMed]
5. Knutsson, S.; Engdahl, C.; Kumari, R.; Forsgren, N.; Lindgren, C.; Kindahl, T.; Kitur, S.; Wachira, L.; Kamau, L.;
Ekström, F.; et al. Noncovalent inhibitors of mosquito acetylcholinesterase 1 with resistance-breaking potency.
J. Med. Chem. 2018, 61, 10545–10557. [CrossRef] [PubMed]
6. Dyer, D.H.; Lovell, S.; Thoden, J.B.; Holden, H.M.; Rayment, I.; Lan, Q. The structural determination of an
insect sterol carrier protein-2 with a ligand-bound C16 fatty acid at 1.35-A resolution. J. Biol. Chem. 2003, 278,
3
9085–39091. [CrossRef]
7. Kim, I.H.; Pham, V.; Jablonka, W.; Goodman, W.G.; Ribeiro, J.M.C.; Andersen, J.F. A mosquito hemolymph
odorant-binding protein family member specifically binds juvenile hormone. J. Biol. Chem. 2017, 292,
1
5329–15339. [CrossRef]
8. Mans, B.J.; Calvo, E.; Ribeiro, J.M.; Andersen, J.F. The crystal structure of D7r4, a salivary biogenic
amine-binding protein from the malaria mosquito Anopheles gambiae. J. Biol. Chem. 2007, 282, 36626–36633.
[CrossRef]
9. Vidadala, R.S.; Ojo, K.K.; Johnson, S.M.; Zhang, Z.; Leonard, S.E.; Mitra, A.; Choi, R.; Reid, M.C.; Keyloun, K.R.;
Fox, A.M.; et al. Development of potent and selective Plasmodium falciparum calcium-dependent protein
kinase 4 (PfCDPK4) inhibitors that block the transmission of malaria to mosquitoes. Eur. J. Med. Chem. 2014
4, 562–573. [CrossRef]
0. Taylor, E.A.; Rinaldo-Matthis, A.; Li, L.; Ghanem, M.; Hazleton, K.Z.; Cassera, M.B.; Almo, S.C.; Schramm, V.L.
Anopheles gambiae purine nucleoside phosphorylase: Catalysis, structure, and inhibition. Biochemistry 2007
6, 12405–12415. [CrossRef]
,
7
6
6
,
4
1. Han, Q.; Wong, D.M.; Robinson, H.; Ding, H.; Lam, P.C.H.; Totrov, M.M.; Carlier, P.R.; Li, J. Crystal structure
of acetylcholinesterase catalytic subunits of the malaria vector Anopheles gambiae. Insect Sci. 2018, 25, 721–724.
[CrossRef]
6
6
6
2. SAINT Version 7.60a; Bruker AXS Inc.: Madison, WI, USA, 2012.
3. Sheldrick, G. Crystal structure refinement with SHELXL. Acta Crystallogr. Sect. C 2015, 71, 3–8. [CrossRef]
4. Farrugia, L. WinGX and ORTEP for Windows: An update. J. Appl. Crystallogr. 2012, 45, 849–854. [CrossRef]

Molecules 2020, 25, 1316
22 of 22
6
6
6
5. Spek, A. PLATON SQUEEZE: A tool for the calculation of the disordered solvent contribution to the
calculated structure factors. Acta Crystallogr. Sect. C 2015, 71, 9–18. [CrossRef]
6. Service, M.W. Management of vectors. In Pest and Vectors Management in Tropics; Youdeowei, A., Service, M.W.,
Eds.; Longman: London, UK, 1983; pp. 265–280.
7. DiRienzo, J.A.; Casanoves, F.; Balzarini, M.G.; Gonzalez, L.; Tabalada, M.; Robledo, C.W. InfoStat Version
2014; Group InfoStat, FCA, Universidad Nacional de Cordoba: Argentina. Available online: http://www.
infostat.com.ar/ (accessed on 7 December 2019).
6
8. Venugopala, K.N.; Tratrat, C.; Chandrashekharappa, S.; Attimarad, M.; Sreeharsha, N.; Nair, A.B.;
Pottathil, S.; Venugopala, R.; Al-Attraqchi, O.H.A.; Morsy, M.A.; et al. Anti-tubercular potency and
computationally-assessed drug-likeness and toxicology of diversely substituted indolizines. Indian J. Pharma.
Educ. Res. 2019, 53, 545–552. [CrossRef]
6
9. Pran Kishore, D.; Anuradha, K.; Poonam, P.; Raghuram Rao, A. Molecular docking and receptor specific
3
D-QSAR studies of acetylcholinesterase Inhibitors. Mol. Diver. 2012, 16, 803–823.
7
0. Chandrashekharappa, S.; Venugopala, K.N.; Tratrat, C.; Mahomoodally, F.M.; Aldhubiab, B.E.; Haroun, M.;
Venugopala, R.; Mohan, M.K.; Kulkarni, R.S.; Attimarad, M.V. Efficient synthesis and characterization of
novel indolizines: Exploration of in vitro COX-2 inhibitory activity and molecular modelling studies. New J.
Chem. 2018, 42, 4893–4901. [CrossRef]
7
1. Available online: https://www.rcsb.org/structure/6ary (accessed on 4 March 2020).
Sample Availability: Samples of the compounds 3a–n are available from the authors.
©
2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (http://creativecommons.org/licenses/by/4.0/).