Chemistry, anti-diabetic activity and structural analysis of substituted dihydropyrimidine analogues

Article abstract of DOI:10.1016/j.molstruc.2020.129412

In an effort to identify an anti-diabetic agent, a series of methyl/ethyl 4-(hydroxyphenyl)-6-methyl-2-oxo/thioxo-1,2,3,4 tetrahydropyrimidine-5-carboxylate analogues (4a-h) have been synthesized, purified, and characterized by using Fourier-Transform Inf

Full text of DOI:10.1016/j.molstruc.2020.129412

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Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstr
Chemistry, anti-diabetic activity and structural analysis of substituted
dihydropyrimidine analogues
Keshab M. Bairagia, Nancy Safwat Younisb,c, Promise Madu Emekab,
Katharigatta N. Venugopalab,d,∗, Osama I. Alwassile, Hany Ezzat Khalilb,f, Ekta Sangtanig,
Rajesh G. Gonnadeg, Viresh Mohanlalld, Susanta K. Nayaka,∗
a Department of Chemistry, Visvesvaraya National Institute of Technology, Nagpur 440 010, Maharashtra, India
b Department of Pharmaceutical Sciences, College of Clinical Pharmacy, King Faisal University, Al-Ahsa31982, Saudi Arabia
c Department of Pharmacology, Zagazig University, Zagazig 44519, Egypt
d Department of Biotechnology and Food Technology, Durban University of Technology, Durban 4001, South Africa
e Department of Pharmaceutical Sciences, College of Pharmacy, King Saud bin Abdulaziz University for Health Sciences, Riyadh 11481, Saudi Arabia
f Department of Pharmacognosy, Faculty of Pharmacy, Minia University, Minia, 61519, Egypt
g Centre for Materials Characterisation, CSIR-National Chemical Laboratory, Dr. HomiBhabha Road, Pune 411 008, India
a r t i c l e i n f o
a b s t r a c t
Article history:
In an effort to identify an anti-diabetic agent, a series of methyl/ethyl 4-(hydroxyphenyl)-6-methyl-2-
oxo/thioxo-1,2,3,4 tetrahydropyrimidine-5-carboxylate analogues (4a-h) have been synthesized, purified,
and characterized by using Fourier-Transform Infrared Spectroscopy (FT-IR) and NMR (1H and 13 C). The
synthesized compounds were screened for anti-hyperglycemic activity using Streptozotocin (STZ) induced
diabetic rat model. The anti-hyperglycemic activity of dihydropyrimidine (DHPM) compound is mainly
analyzed with the variation of substituents present on the phenyl ring and urea/thiourea group on phar-
macophoric features. Further, the crystal structure and supramolecular characteristics of two compounds
4c and 4f were analyzed through a single-crystal X-ray method and the Hirshfeld Surface Analysis, which
shows hydrogen bonding through N-H···O and N-H···S interactions with the formation of ring motif in
the crystal structure. It is interesting to note that among the title compounds, the 4a, 4e, 4f, and 4g
significantly displayed a better hypoglycemic effect in vivo rat model study.
Received 7 August 2020
Revised 24 September 2020
Accepted 5 October 2020
Available online xxx
Keywords:
Type-2 diabetes mellitus (T2DM)
Dihydropyrimidine (DHPM)
Hypoglycemia
Streptozotocin (STZ)
© 2020 Elsevier B.V. All rights reserved.
1. Introduction
since 1980, and it is mainly type 2 diabetes mellitus (T2DM) [7].
Currently, in South East Asia (SEA), 39.3 million people are suffer-
The metabolic complications like diabetes mellitus are increas-
ing health problems of the modern world, and they are now one
of the world’s most prevalent non-communicable diseases. Type 2
diabetes mellitus (T2DM) is a disorder that causes hyperglycemia
and glucose intolerance due to insufficient insulin secretion or
insulin resistance. Complications resulting from insulin disorders
such as cardiovascular disease, cerebrovascular disease, nephropa-
thy, renal failure, ulceration, and amputation leads to lower life ex-
pectancy [1–4]. According to the International Diabetes Federation
(IDF) Atlas report 2015, 415 million people were diagnosed world-
wide and will increase to 642 million in 2040, according to pre-
diction [5,6]. World Health Organization (WHO) has pointed out
that the number of people with diabetes mellitus has quadrupled
ing from T2DM; this number will likely increase to 81.6 in 2025
estimated by epidemiologists [5]. Various factors have been iden-
tified to be responsible for the increased incidence of type II di-
abetes mellitus. They include obesity, which is a risk factor for
type 2 diabetes mellitus along with high calories diet, an inactive
lifestyle, both of which could precipitate the condition of hyper-
glycemia. In addition to diabetes, impaired glucose tolerance (IGT)
has also been identified as a significant public health problem [6].
Nonetheless, as the disease burden gradually increases, there is a
need for effective treatment and control of T2DM. Typically, phar-
macological procedures are used to regulate T2DM by either re-
ducing blood sugar levels or removing glucose from the gastroin-
testinal tract and insulin sensitivity [8]. However, it has been a
challenging task to control blood glucose levels with oral hypogly-
caemic agents such as sulfonylureas and thiazolidinediones, along
with food, weight, and physical activity [9]. Currently, many orally
administered hypoglycemic agents (OHAs) are used in addition to
∗
Correspondence authors.
E-mail
addresses:
kvenugopala@kfu.edu.sa
(K.N.
Venugopala),
sknayak@chm.vnit.ac.in (S.K. Nayak).
https://doi.org/10.1016/j.molstruc.2020.129412
0022-2860/© 2020 Elsevier B.V. All rights reserved.
Please cite this article as: K.M. Bairagi, N.S. Younis, P.M. Emeka et al., Chemistry, anti-diabetic activity and structural analysis of substi-
tuted dihydropyrimidine analogues, Journal of Molecular Structure, https://doi.org/10.1016/j.molstruc.2020.129412

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Scheme 1. The synthetic scheme followed for obtaining DHPM.
insulin to manage this scourge [10]. However, orally administered
agents have many limitations, like adverse effects and high cost
[11]. Besides, 30–40% of patients have a compliance problem [9]. In
view of all these, there is need to formulate new drug molecules
that will effectively reduce blood glucose with minimal side effects
and enhance insulin level in the blood.
chromatography to purify the product. Heidolph rotary evapora-
tor was used to extract the solvent from the reaction mixture.
The obtained compound has dried under vacuum oven (Bio Tech-
nics India). The melting points of synthesized compounds were de-
termined using the DBK instrument, 230 V. The functional group
present in the compounds were identified using Bruker FT-IR spec-
trophotometer (Bruker IFS 55 equinox). The purity of compounds
was confirmed using Bruker NMR spectrometer 1H (400 MHz) and
13C (101 MHz) in DMSO solvents using TMS as an internal stan-
dard. The chemical shifts were recorded in ppm δ scale, coupling
constant (J) values are given in hertz (Hz). The crystal structural
data were collected on the Bruker D8 VENTURE Kappa Duo PHO-
TON II CPAD diffractometer with Mo micro-focused tube diffrac-
In this regard, we have formulated new DHPM derivatives by
using the known synthetic method [12], with a view of adding
an alternative agent to treat T2DM disease. The DHPM compounds
have been reported to possess various pharmacological proper-
ties such as anti-microbial [13,14], antioxidant [15], anti-malarial
[16,17], antitubercular [18–20], anti-mosquito [21], anti-diabetic
[22], anthelmintic [23], anticancer [24], and larvicidal activity [25–
27]. In our previous reports, we have remarked that the electron-
withdrawing group on the phenyl part of dihydropyrimidine shows
better larvicidal activity against Anopheles arabiensis. DHPM com-
pounds are commercially available and widely used for the treat-
ment of cardiovascular diseases such as hypertension [28], cardiac
arrhythmias, and angina [29]. Besides, it is also known that dihy-
dropyrimidine −5-carboxylate, also found in marine sources, play
a potent role in HIVgp-120-CD4 inhibition [30]. Niguldipine, tera-
zosin, and doxazosinare examples of commercially available DHPM
drugs that are used in the treatment of benign prostatic hyperpla-
sia (BPH) and cancers [31,32]. Streptozotocin (STZ) is an antibiotic
that induces pancreatic islet β-cell destruction, which producing
both type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus
(T2DM) in a dose-dependent fashion [33,34]. Due to the significant
biological activities observed with DHPM, the aim of this study is
to synthesize a series of new DHPM derived compounds contain-
ing hydroxyl functional groups using the known synthetic method
of Biginelli reaction (Scheme 1). Also, to screen these newly syn-
thesized compounds for hypoglycemic activity using streptozotocin
(STZ) -nicotinamide induced in vivo diabetic rat model for T2DM.
˚
tion source (Mo Kα λ = 0.7103 A), and data were refined using
SHELXL 2018/3. The general method of synthesis and spectral in-
formation are available in the electronic supporting information
file (ESI).
2.2. General experimental method for synthesis of
DHPMcompounds(4a-4h)
A combination of equimolar substituted hydroxy aryl alde-
hyde (0.0125 mol), urea/thiourea (0.0125 mol) and β-ketoester
(0.0125 mol) was taken in a 100 mL round bottom flask and re-
fluxed into 30 mL of ethanol solvent with constant stirring, in the
presence of concentrated hydrochloric acid in catalytic amount for
overnight (24 h). The reaction mixture was monitored using TLC
plate; after ensuring that the reaction contents were poured into
ice-cold water. The obtained white precipitate was filtered and
washed several times with distilled water to get the crude prod-
uct.
The crude product and small amount of silica and DCM were
added together and mixed homogenously for column chromatog-
raphy. The column chromatography was performed using sil-
ica gel with the combination of ethyl acetate:pet-ether solvents
(1:10) as an eluent. The purified eluent mixture was collected
in a round bottom flask and evaporated under a rotary evapo-
rator to obtain pure product and dried under a vacuum oven.
The percentage yield of the compound obtained was more than
65%. Furthermore, a slow evaporation method was used to get
the single crystal by dissolving the minimum amount (5 mg) of
a compound in different solvents and characterized using dif-
ferent spectrophotometry techniques. The physicochemical con-
stants of the substituted methyl/ethyl 4-(hydroxyphenyl)-6-methyl-
2-oxo/thioxo-1,2,3,4 tetrahydropyrimidine-5-carboxylate analogues
(4a-h) were listed in Table 1.
2. Materials and methods
2.1. Chemistry
All the chemicals for the synthesis were bought from Sigma-
Aldrich and Tokyo Chemical Industry (TCI) Co., Ltd., whereas sol-
vents were purchased from Fisher Scientific Corporation. The thin-
layer chromatography (TLC) plate for analysis of reaction mixture
was done on Merck aluminum plates (60 F254) coated with silica
gel. The product formed was confirmed by examining the spots
on the TLC plate under ultra-violet (UV cabinet, BTI 1429) irra-
diation (Bio Technico India, Biotech, BTI-49) at 254 and 366 nm.
The Merck silica gel of mesh size 100–120 was used for column
2

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Table 1
2.4. Crystal growth and single-crystal X-ray crystallographic study
The physicochemical constants of thesubstituted methyl/ethyl 4-(hydroxy-
phenyl)-6-methyl-2-oxo/thioxo-1,2,3,4 tetrahydropyrimidine-5-carboxylate ana-
logues (4a-h).
The minimum amount (5 mg) of the synthesized (4a-h), puri-
fied compound was taken in 5 mL beaker and dissolved in different
solvents and kept for a slow evaporation process at the optimum
temperature to achieve good quality single crystals. The obtained
single crystals were analyzed through Polarized Optical Microscope
(Nikon H600L). We have successfully obtained good single crystal
for compounds 4c and 4f for which single-crystal X-ray study was
carried out. A Bruker D8 VENTURE Kappa Duo PHOTON II CPAD
diffractometer was used to measure the single-crystal X-ray data.
Intensity measurement was performed at 100 K temperature (us-
ing liquid nitrogen) with Mo micro-focused tube diffraction source
Compound code
R1
R2
X
m.p. (°C)
(%) Yield
4a
4b
4c
4d
4e
4f
3-Br, 6-OH
C2H5
C2H5
CH3
S
95
80.52
72.35
68.89
81.00
91.20
75.50
79.38
78.80
3-OH
O
O
O
S
165
152
145
137
170
172
158
3-OCH3, 2-OH
3-OCH3, 2-OH
3-OCH3, 2-OH
3-OC2H5, 4-OH
4-OCH3, 3-OH
4-OCH3, 2-OH
C2H5
CH3
C2H5
CH3
S
4g
4h
O
O
CH3
˚
(MoKα λ = 0.7103 A). Data collection, integration, unit cell mea-
surement, and crystal data absorption correction were performed
using Bruker Apex III software [38], and data reduction was made
by Bruker SAINT [39]. Direct technique SIR 2014 [40] has been
used to solve crystal structures, and complete matrix least square
method SHELXL 2018 [41] has been used to refine with WinGX
(version 2018/3) application suit [42]. The absorption correction
was implemented using SADABS. The crystallographic and refine-
ment detail of compounds 4c and 4f are shown in Table 2.
2.3. Ant-diabetic activity
2.3.1. Type 2 model of diabetes mellitus induction
This study was conducted with the use of Streptozotocin (STZ),
an agent that is known experimentally to induce both type 1 di-
abetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM) in
a dose-dependent fashion in animal models [35]. Newly synthe-
sized dihydropyrimidine compounds were evaluated for their anti-
hyperglycemic activities in STZ induced diabetic mice according to
the methods of Ghasemi et al., 2014 [36]. Diabetes was induced
in mice after an overnight fast by a single intraperitoneal (IP) in-
jection of nicotinamide (120 mg/kg body weight, dissolved in nor-
mal saline) 15 min before IP administration of STZ (50 mg/kg body
weight, dissolved in citrate buffer, pH 4.5) (Sigma Aldrich, USA)
[37]. The blood glucose levels were measured before and 72 h after
nicotinamide-STZ injection, for confirmation of hyperglycemia and
type 2 diabetes development. The mice that have a serum glucose
level above 200 mg/dL, as well as with polydipsia, polyuria, and
polyphagia, were selected and equally distributed into different di-
abetic treatment groups.
2.5. Hirshfeld Surface analysis
The Hirshfeld surfaces and two dimensional (2D) fingerprint
plots were developed using Crystal Explorer 17.5 application to vi-
sualize the intermolecular interaction in the crystal structure of 4c
and 4f molecule [43]. On the Hirshfeld surfaces, distance de and di
show the distances from the surfaces to the external nucleus and
surface to the internal nucleus, respectively. The normalized con-
tact distance (dnorm) appears on the surface as a white-red-blue
color scheme, where the bright red spot indicates the shorter con-
tact, the white area represents contacts around the van der Waals
distances, and the blue region is uncontacted.
2.3.2. Experimental design
3. Results and discussion
Male 57BL/6 mice (25–30 g) were purchased from Theodor Bil-
harzias Center, Cairo, Egypt. All experimental protocols were by
the guidelines and standards of animal care as approved by the
Ethical Committee for animal handling at Zagazig University (EC-
3.1. Synthesis and reaction mechanism for the title compounds
The present research includes the synthesis of title compounds
in ethanol as a solvent by the multi-component reaction between
hydroxy aryl aldehyde, β-ketoester, and urea/thiourea, as shown
in Scheme 1. The purity and structural elucidation of compounds
(4a-4h) were revealed by using FT-IR, 1H NMR, 13C NMR. The peak
range at 3300–3100 cm−1 and 1710–1640 cm−1 in FT-IR confirms
the presence of N-H and amide/ester carbonyl group, respectively.
The peak range at δ = 2.23–2.28 ppm and δ = 2.28–3.7 ppm in
1H NMR confirms the presence methyl group at dihydropyrimi-
dine and an ester methyl group, respectively. The methine hydro-
gen on the dihydropyrimidine ring is shown at the peak range of
δ = 5.04–5.50 ppm. The peak range at δ = 8.65–9.86 ppm con-
firms the presence of the N-H hydrogen atom in the compound.
The peak range at δ = 165–176 ppm in 13C NMR confirms the pres-
ence of carbonyl carbon in the title compounds.
AHZU). Mice were kept in cages at 20
4 °C temperature with
12 h light/dark cycle and given free access to water and food.
Animal’s selection was performed randomly. Animals were allo-
cated into 11 groups (n = 6); group 1 animals were adminis-
tered with 0.5% CMC (0.5 mL) (vehicle); group 2 were the strep-
tozotocin (STZ)/nicotinamide diabetic control (DC) group and un-
treated, group 3, diabetic animals were treated with gliclazide
50 mg/kg and act as a reference drug group. The rest of the groups
of the diabetic animals were given the newly synthesized dihy-
dropyrimidine compounds (50 mg/kg orally, daily for seven days).
At the end of the experiment, their blood samples were collected
after an overnight fast via retro-orbital plexus under ether anes-
thesia, and the level of fasting serum glucose was measured using
diagnostic strips.
2.3.3. Data analysis
3.2. Anti-diabetic activity
Data are hereby presented as mean
standard deviation (SD).
Anti-hyperglycemic were compared with control and standard drug
treatment. One-way ANOVA followed by Dunnett’s multiple com-
parisons test was performed using Graph Pad Prism version 8.2.0
for Windows, Graph Pad Software, San Diego, California USA. Also,
Paired t-test was used to compare the percentage reductions in
blood glucose levels amongst newly synthesized compounds. Lev-
els of significance was determined at p < 0.05 -p < 0.01.
Results of hypoglycaemic activities of newly synthesized dihy-
dropyrimidine analogues are presented in Fig. 1. These agents were
given in equal dose as the standard drug (STD), gliclazide. Statisti-
cal analysis of the data obtained by one-way analysis of variance
shows that there is a significant difference (p < 0.01) between
the means of the treatment groups and the STZ group, indicat-
ing hypoglycaemic activity. Also, from the results, it shows that all
3

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Table 2
Single crystal X-ray data and refinement detail for the compounds 4c and 4f.
DATA
4c
4f
Formula
C
14H16O5N2
C16H20O4N2S
336.41
Formula weight
CCDC
280.7
2020234
100
2020235
100
Temperature/K
˚
Wavelength(A)
0.71073
Monoclinic
P21/c
0.71073
Monoclinic
P21/c
Crystal system
Space group
˚
a(A)
11.6727(74)
11.6512(65)
20.0564(7)
90
10.9797(6)
17.0410(11)
8.4730(4)
90
˚
b(A)
˚
c(A)
α (˚)
β (˚)
γ (˚)
92.338(24)
90
107.125(2)
90
3
˚
V (A )
2725.42(39)
2,8
1515.05(10)
1, 4
Z’, Z
Density (g cm−3
)
1.39
1.47
μ (mm−1
)
0.101
0.237
F (000)
1196.0
712
θ (min, max)
hmin, kmin,
2.5, 28.8
(−15, 15)(−15, 13)(−26, 25)
31722
2.4, 30.5
lmin,
max.
(−13, 15)(−23, 21)(−12, 11)
max,
max,
No. of refl.
20845
No of unique ref./Obs. ref.
No. parameters
Rall, Robs
7022/5543
534
4551/3592
256
0.098, 0.076
0.174, 0.163
−0.35, 0.59
1.139
0.080, 0.062
0.200, 0.184
2.06, 0.93
1.054
wRall,wRobs
−3
)
˚
ꢀρmin
G.O.O.F.
,
(eA
max
500
400
300
200
100
0
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
B
AF B
BF AF B
A
B
A
A
BF A
B
B
AF
A
B
A
f
c B
4c
e A
4f
4e 4
4d
Z A
g
u
d
g B
4
4 4g 4h 4h
4a 4a
4
4b 4b
4
T
STZS rug
d
r
ntrol
o
ontrol
C
D d
T
D
T
C
S
S
Treatment groups
Fig. 1. Anti-diabetic activity of 4a-h on induced hyperglycemia in mice in comparison to STZ and STD (Standard drug).
the newly synthesized dihydropyrimidine compounds had an ef-
21.76, and 20.64, respectively. Therefore, the attenuation of STZ in-
duced hyperglycemia by these new compounds is a clear indication
that they have the potential to lower high blood glucose levels. The
details of the analysis result are listed in Table-S1 (ESI).
fect on the blood glucose levels post diabetic induction. The stan-
dard drug at the dose of 50 mg/kg showed a better lowering effect
compared to the newly synthesized compounds (dose by dose).
However, as represented in Fig. 2, the compounds 4a, 4e, 4f, and
4g significantly (p < 0.05) reduced the blood glucose levels when
compared with STZ treated group and with other newly synthe-
sized compounds. The study indeed has shown that the newly syn-
thesized compounds of dihydropyrimidine possess hypoglycaemic
potentials. The mean percentage reduction obtained for gliclazide
was 47.9%, whereas that of 4a, 4e, 4f, and 4g were 18.06, 21.66,
3.3. Analysis of the crystal structure of compounds 4c and 4f
Rod-shaped single crystals of 4c were obtained from Ethanol
solvent by slow evaporation method at room temperature (Fig. S9).
The crystal size of 0.26 × 0.18 × 0.10 mm3 was chosen for single-
crystal X-ray diffraction analysis, which shows that 4c crystallizes
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˚
60
40
20
0
structure, the N-H···S hydrogen bonds N1-H1···S1 [2.52 A, 162°]
˚
and N2-H2···S1 [2.62 A, 170°] form close ring dimer with graph set
motif R22(8) (Fig. 4b). The 4-hydroxy hydrogen atom form hydrogen
˚
bond with ester oxygen through O4-H4A···O1 [2.14 A, 130°] and
form R22(20) ring motif. The molecule also forms C-H···π through
˚
C16-H16B···π [2.88 A, 123°] and π···π interactions between the
phenyl ring, which propagate along the b-axis (Fig. 4c). Further, the
˚
crystal packing also strengthens by C7-H7A···O4 [2.58 A, 155°] and
˚
C13-H13···O2 [256 A, 149°] intermolecular interaction in the crystal
structure. The prominent intermolecular interaction present in the
molecule is tabulated in Table 3.
-20
STD 4a 4b 4c 4d 4e 4f 4g 4h STZ
Treatment groups
3.4. Hirshfeld surface analysis
Fig. 2. Showing percentage reduction of glucose levels in diabetic induced mice by
The Hirshfeld surface and 2D fingerprint plot were used to un-
derstand the role of intermolecular interactions present in their
crystal structure. Here, we have developed the Hirshfeld surface
for the compounds 4c and 4f to analyze the intermolecular inter-
actions present in the molecule (Fig. 5a and 5b). The compound
4c shows red spot is due to N-H···O, O-H···O, C-H···O hydrogen
bonding in the molecule, whereas S-H···O, O-H···O, C-H···O hydro-
gen bonding in 4f. Further, the existence of intermolecular in-
teractions is clearly shown by the sharp spike in 2D fingerprint
plots for both the compounds (Fig. 5c and 5d). The fingerprint
plots show the H···H intermolecular contacts contribute relatively
high for both the molecules, 45% and 47.5% for the compounds 4c
and 4f, respectively (Fig. 5c and 5d). The percentage contribution
of other intermolecular interactions in the title compound 4c are
as follows: O···H/H···O (30.1%), C···H/H···C(16.3%), N···H/H···N(3%),
C···C(2.5%), C···O/O···C(1.8%), O···O(1%), O···N/N···O(0.2%) and for the
compound 4f are as follows: O···H/H···O(16.1%), S···H/H···S(15.3%),
C···H/H···C(11.3%), C···O/O···C(3.2%), C···C(2.4%), N···H/H···N(2.3%),
O···N/N···O(0.9%), O···O(0.9%). Fig. 6 showed that after H···H in-
teractions, 4c shows O···H interaction as the major contribution,
whereas 4f prefers equal contribution of O···H and S···H interac-
tions in their molecular assembly.
4a-h in comparison to STZ and STD.
Fig. 3. (a) Oak Ridge Thermal Ellipsoid Plot (ORTEP) of compound 4c drawn at 50%
–
probability) N H···O hydrogen bonds form a dimer in the crystal packing)π···π in-
teractions in the crystal packing along bc plane.
The Cambridge Structural Database (CSD) (Conquest version 5.4;
CCDC version 5.40) [45] shows that the crystal structures of the
series of molecules (Scheme 1) were not yet reported elsewhere.
However, similar type of other DHPM derivatives was reported
[12]. Using urea and thiourea moiety, we have searched in CSD and
observed that there are 121 DHPM has been reported. However, at
different positions on the benzene ring, only the crystal structure
of twenty DHPM derivatives has been reported with hydroxyl sub-
stituent. It is commonly observed that the DHPM with a hydroxyl
group at 4th position on the benzene ring are crystallized with wa-
ter and form hydrate in their crystal structures [46,47] whereas,
the hydrate form was not being observed in the hydroxyl group
at 2nd and 3rd position on the benzene ring of DHPM [48,49]. All
the DHPM have shown a similar kind of synthon and form dim-
mer through N-H···O and N-H···S interaction. It is noted that only
five crystal data on the benzene ring of DHPM are recorded with
2–hydroxy and all the compound form dimer through N-H···O in-
teraction with one N-H bond and other N-H bond is free of any
interaction [50,51]. However, in the reported crystal 4c and 4f, the
π···π interaction is present in the crystal system, which is being
absent in the CSD reported DHPM crystal. It is further noted the
4-OH with 3-ethoxy on benzene ring containing DHPM derivative
not form dimer [52]; however, the dimer is observed in the re-
ported crystal 4f through N-H···S short contact.
in the monoclinic space group P21/c with eight molecules in the
unit cell and two molecules in the asymmetric unit (Z=8, Z’=2).
The dihedral angles between the planes of the six-membered dihy-
dropyrimidine ring with its 2-hydroxy 3-methoxyphenyl ring and
ester substituents are observed at 70.85° (4) and 16.75° (5), re-
spectively for one molecule, whereas 89.57° (3) and 12.12° (12) are
observed for the second molecule (Fig. 3a). In the crystal struc-
ture, pyrimidine carbonyl oxygen is involved in the generation of
significant dimeric structure through two N-H···O hydrogen bonds,
˚
˚
N2-H2N···O6(2.13 A, 172°) and N4-H4N···O1 (2.09 A, 168°) with the
formation of R22(8) graph-set cyclic ring motif [44] (Fig. 3b). Fur-
ther, the results of the dimer form chain which propagates along
the b-axis. Besides the hydrogen bonding, the π···π interactions
between the benzene ring of two individual DHPM molecule con-
solidate the molecular packing, which also strengthens the crystal
packing along the bc plane (Fig. 3c). The crystallographic refine-
ment details and intermolecular interactions are listed in Table-2
and Table-3, respectively.
The compound 4f crystallizes with block-shaped single crys-
tals, which were obtained from ethanol solvent by slow evap-
oration method at room temperature (Fig. S10). Crystal size of
0.25×0.14×0.09mm3) was taken for a single-crystal X-ray study,
which crystallizes in the monoclinic space group P21/c with four
molecules in the unit cell and one molecule in the asymmetric
unit (Z=4, Z’=1). The dihedral angle between hydropyrimidine ring
with 4-hydroxy-3-ethoxy phenyl ring and ester group are observed
at 80.31(0.8)° and 29.84(17)°, respectively (Fig. 4a). In the crystal
Analyzing the variation in their substituent’s, it is observed
that the reduction of glucose level from the blood is mainly in-
fluenced by the following reasons (i) thiourea analogues (4a, 4e,
and 4f) showed prominent glucose reduction compared to other
compounds (4b, 4c, 4d, and 4h); (ii) The para-methoxy and meta-
5

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–
–
Fig. 4. (a) Oak Ridge Thermal Ellipsoid Plot (ORTEP) of compound 4f drawn at 50% probability, (b) the N H···S hydrogen bonds and O H···O form ring motif in the crystal
–
structure, (c) the C H···π connected through π···π interactions in the crystal packing along b-axis.
Fig. 5. (a) Hirshfeld surface of the compound 4c mapped over dnorm. (b) Hirshfeld surface of the compound 4f mapped over dnorm. (c) and (d) Two-dimensional fingerprint
plots and relative contributions of various interactions to the Hirshfeld surface of the compounds 4c and 4f, respectively.
Fig. 6. Relative contributions of various intermolecular contacts to the Hirshfeld surface area in 4c and 4f.
6

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Table 3
Intermolecular interaction of the title compounds 4c and 4f.
<D-X···A(o)
Symmetry code
˚
˚
˚
D-X···A
D-X(A)
X···A(A)
D···A(A)
4c
N1-H1N···O7
N2-H2N···O6
N3-H3N···O7
N4-H4N···O1
O4-H4O···O6
O9-H9O···O1
π···π
0.85(3)
0.84(3)
0.93(3)
0.80(3)
0.85(4)
0.85(4)
–
2.47(3)
2.13(3)
2.54(3)
2.09(3)
2.01(4)
2.08(4)
3.79(5)
3.268(3)
2.965(3)
3.383(3)
2.872(3)
2.826(3)
2.873(3)
–
158(2)
172(3)
150(3)
168(3)
160(3)
154(3)
–
x,y,z
1-x,1-y,-z
1-x,−1/2 + y,1/2-z
1-x,1-y,-z
1-x,1/2 + y,1/2-z
1-x,−1/2 + y,1/2-z
1- x,−1/2 + y,1/2-z
π= centroid between six member of C8-C9-C10-C11-C12-C13 and C22-C23-C24-C25-C26-C27 phenyl ring
4f
N1-H1···S1
N2-H2···S1
O4-H4A···O1
C7-H7A···O4
C13-H13···O2
C16-H16B···π
π···π
0.80
0.83
0.90
0.98
1.01
0.98
–
2.52
2.62
2.14
2.58
2.56
2.88
3.877
3.2895(3)
3.4405(2)
2.7958(2)
3.4889(2)
3.4696(2)
3.5050(2)
–
162
170
130
155
149
123
–
x,1/2-y,−1/2 + z
x,1/2-y,1/2 + z
1-x,-y,1-z
1-x,−1/2 + y,3/2-z
1-x,-y,2-z
x,1/2-y,−1/2 + z
1-x,-y,1-z
π= centroid between six members of C9-C10-C11-C12-C13-C14.
hydroxy group, along with urea-based DHPM (4g) showed better
anti-diabetic activity than others, however, it is lower activity than
4e and 4f in the absence of sulfur (thiourea) moiety; (iii) bromine
at meta position instead of methoxy/methoxy group and a hydroxyl
group at ortho position along with thiourea (4a) showed little re-
duction in its activity in comparison to 4e and 4f; (iv) ethyl or
methyl substitution in ester part of this DHPM (4a-h) appears has
no influence in its anti-diabetic activity. From their crystal struc-
ture analysis, 4f showed nearly same percentage of O···H (16.1%)
and S···H (15.3%) interactions whereas, 4c preferred the dominate
O···H (30.1%) interactions which clearly suggest that sulfur, because
of large size and high polarizability in comparison to oxygen plays
an important role for the enhancement of anti-diabetic activity.
analysis, Investigation. Hany Ezzat Khalil: Formal analysis, Inves-
tigation, Resources. Ekta Sangtani: Software, Resources. Rajesh G.
Gonnade: Data curation, Investigation. Viresh Mohanlall: Formal
analysis, Methodology, Resources, Investigation. Susanta K. Nayak:
Supervision, Project administration, Funding acquisition, Writing -
original draft, Writing - review & editing.
Acknowledgments
The authors are grateful for the research supported by the
Durban University of Technology, National Research Foundation,
South Africa (Project No. 98884), Department of Chemistry, VNIT,
Nagpur supported by DST FIST Project No. SR/FST/CSI-279/2016 and
SERB, DST, Government of India (Project No. ECR/2016/001820).
4. Conclusion
References
A series of eight DHPM compounds (4a-h) have been syn-
thesized and characterized successfully. The single-crystal study
showed that 4c prefers to form dimer through strong N-H···O hy-
drogen bonding whereas, the crystal 4f form dimer through N-H···S
hydrogen bonding. Both the crystal structures (4c and 4f) shows
π···π interaction to consolidate the molecular packing, whereas 4f
showed additional C-H···π interaction. The Hirshfeld surface anal-
ysis confirms the major contribution of H···O and S···H contacts in
the crystal structure, which played a significant role to explain the
strength and nature of intermolecular interaction associate in the
crystal structure. Current structure-activity comparisons study re-
vealed that the S···H interactions of thiourea derivative play ma-
jor role in a significant lowering of glucose level in blood.. Further
studies are required to improve the anti-diabetic activity and cor-
relate the structure-activity relationship.
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The authors declare that they have no known competing finan-
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