Synthesis and biological evaluation of 2-(2-methyl-1H-pyrrol-3-yl)-2-oxo-N-(pyridine-3-yl) acetamide derivatives: in vitro α-glucosidase inhibition, and kinetic and molecular docking study

Article abstract of DOI:10.1007/s11696-019-00999-0

One of the therapeutic approaches in the management of type 2 diabetes is delaying the glucose absorption through α-glucosidase enzyme inhibition, which can reduce the occurrence of postprandial hyperglycemia. Based on this thought, a series of novel chloro-substituted 2-(2-methyl-1-phenyl-1H-pyrrol-3-yl)-2-oxo-N-(pyridin-3-yl) acetamide derivatives 5a–i were synthesized and their α-glucosidase inhibitory activities were evaluated. All the synthesized compounds have shown moderate to excellent in vitro α-glucosidase inhibitory activity with IC₅₀ values in the range of 111–673?μM) as compared to acarbose, the standard drug (750 ± 9?μM). Compound 5e (111 ± 12?μM), among the series, was the most potent inhibitor of α-glucosidase in a competitive mode of action based on the kinetic study. The molecular docking study of compounds 5e and 5a revealed that they have a lower free binding energy (? 4.27?kcal/mol and ? 3.17?kcal/mol, respectively) than acarbose (? 2.47?kcal/mol), which indicates that the target compound binds more easily to the enzyme than acarbose does. The outcomes from the molecular docking studies supported the results obtained from the in vitro assay. In conclusion, the overall results of our study reveal that the synthesized compounds could be a potential candidate in the search for novel α-glucosidase inhibitors to manage postprandial hyperglycemia incidence.

Full text of DOI:10.1007/s11696-019-00999-0

Chemical Papers
https://doi.org/10.1007/s11696-019-00999-0
ORIGINAL PAPER
Synthesis and biological evaluation
of 2‑(2‑methyl‑1H‑pyrrol‑3‑yl)‑2‑oxo‑N‑(pyridine‑3‑yl) acetamide
derivatives: in vitro α‑glucosidase inhibition, and kinetic
and molecular docking study
Tadesse Bekele Tafesse1,2,3 · Ebrahim Saeedian Moghadam2 · Mohammed Hussen Bule1,2,4 · Neda Abadian5 ·
Mohammad Abdollahi6 · Mohammad Ali Faramarzi5 · Mohsen Amini2
Received: 31 March 2019 / Accepted: 12 November 2019
© Institute of Chemistry, Slovak Academy of Sciences 2019
Abstract
One of the therapeutic approaches in the management of type 2 diabetes is delaying the glucose absorption through
α-glucosidase enzyme inhibition, which can reduce the occurrence of postprandial hyperglycemia. Based on this thought, a
series of novel chloro-substituted 2-(2-methyl-1-phenyl-1H-pyrrol-3-yl)-2-oxo-N-(pyridin-3-yl) acetamide derivatives 5a–i
were synthesized and their α-glucosidase inhibitory activities were evaluated. All the synthesized compounds have shown
moderate to excellent in vitro α-glucosidase inhibitory activity with IC50 values in the range of 111–673 µM) as compared
to acarbose, the standard drug (750 9 µM). Compound 5e (111 12 µM), among the series, was the most potent inhibitor
of α-glucosidase in a competitive mode of action based on the kinetic study. The molecular docking study of compounds
5e and 5a revealed that they have a lower free binding energy (−4.27 kcal/mol and − 3.17 kcal/mol, respectively) than
acarbose (−2.47 kcal/mol), which indicates that the target compound binds more easily to the enzyme than acarbose does.
The outcomes from the molecular docking studies supported the results obtained from the in vitro assay. In conclusion, the
overall results of our study reveal that the synthesized compounds could be a potential candidate in the search for novel
α-glucosidase inhibitors to manage postprandial hyperglycemia incidence.
Keywords α-Glucosidase activity · Docking · Kinetic study · Synthesis · Pyrrole
Introduction
Diabetes mellitus (DM) is a chronic progressive metabolic
disease worldwide due to carbohydrate, fat, and protein
metabolism that is characterized by hyperglycemia result-
Electronic supplementary material The online version of this
ing from defects of insulin secretion, insulin action, and/or
article (https://doi.org/10.1007/s11696-019-00999-0) contains
supplementary material, which is available to authorized users.
3
* Mohammad Ali Faramarzi
School of Pharmacy, College of Health & Medical Sciences,
Haramaya University, Harar, Ethiopia
faramarz@tums.ac.ir
4
5
* Mohsen Amini
Department of Pharmacy, College of Medicine and Health
Sciences, Ambo University, Ambo, Ethiopia
moamini@tums.ac.ir
Department of Pharmaceutical Biotechnology, Faculty
of Pharmacy and The Institute of Pharmaceutical Sciences,
Tehran University of Medical Sciences, Tehran, Iran
1
Department of Medicinal Chemistry, Faculty of Pharmacy,
Tehran University of Medical Sciences-International
Campus (IC-TUMS), Tehran, Iran
6
Department of Pharmacology and Toxicology, Faculty
of Pharmacy and The Institute of Pharmaceutical Sciences,
Tehran University of Medical Sciences, Tehran, Iran
2
Department of Medicinal Chemistry, Faculty of Pharmacy,
Drug Design and Development Research Center, The
Institute of Pharmaceutical Sciences (TIPS), Tehran
University of Medical Sciences, Tehran, Iran
Vol.:(0123456789)
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Chemical Papers
both (WHO 2016). Autoimmune destruction of the β cells
of the islets of Langerhans is the causative factor for type 1
DM, while a combination of genetic predisposition, physi-
cal inactivity, and obesity are the causes that contribute to
defects in insulin secretion and/or insulin resistance which
leads to type 2 DM (WHO 2016; Tundis et al. 2010). DM
leads to acute and chronic complications in many parts of
the body including diabetic ketoacidosis (DKA), hyperos-
molar hyperglycemic state (HHS), neuropathy, nephropathy,
retinopathy, ischemic heart disease, myocardial infarction,
stroke, and peripheral arterial disease (Powers et al. 2015;
Kitabchi et al. 2009; Deshpande et al. 2008). During the
digestion of food, α-glucosidase hydrolyzes carbohydrates
and produces α-d-glucose, which is absorbed in the blood
stream, increases postprandial blood glucose levels, and
causes diabetes. Therefore, for the control and prevention
of diabetes, α-glucosidase inhibitors are of particular inter-
est, as they can help to reduce the carbohydrate digestion and
subsequent monosaccharide absorption (Santos et al. 2018).
Various oral hypoglycemic agents are currently used to
lower or maintain the blood glucose level to nearly nor-
mal with diferent therapeutic approaches (Ramprasad and
Madhusudhan 2016; Ghani 2015). One of the therapeutic
approaches in the management of type 2 diabetes is reducing
the postprandial hyperglycemia by slowing down the glucose
absorption through enzyme inhibition, α-glucosidase and
α-amylase, which hydrolyzes the carbohydrates in the diges-
tive tract (Gollapalli et al. 2018; Sugihara et al. 2014). Acar-
bose, miglitol, and voglibose are currently used to inhibit the
major carbohydrate-hydrolyzing enzymes (Joshi et al. 2015).
On the other hand, long-term high plasma level of glu-
cose causes impairment of the endogenous antioxidant
agents such as glutathione, coenzyme-Q, and α-lipoic acid.
Decreasing the level of this antioxidant increases the level
of reactive oxygen species (ROS) and hydroxyl and nitric
oxide (NO) radicals that induces pancreatic β-cell destruc-
tion. Furthermore, uncontrolled free radical generation leads
to various microvascular and macrovascular complications
(Rouzbehan et al. 2017; Ibrahim et al. 2014; Mccue et al.
2005). Consequently, the inhibition of α-glucosidase is the
most efective therapeutic approach to prevent the impact of
type 2 diabetes through controlling the postprandial glucose
levels and reducing postprandial hyperglycemia by delaying
the absorption of glucose (Gollapalli et al. 2018; Kim et al.
2008).
et al. 2000). Pyrroles and their derivatives are considered
as one of the most pharmaceutically signifcant hetero-
cyclic molecules and extensively used in drug discovery
(Abdelrazek & Metwally 2006). They have demonstrated
signifcant biological activities in various areas such as anti-
mycobacterial activity (Biava et al. 1999, 2009; Joshi et al.
2008), anti-infammatory and analgesic activity (Biava et al.
2010), HIV-1 non-nucleoside reverse transcriptase inhibition
(Famiglini et al. 2013), antibacterial and antifungal activities
(Joshi et al. 2008), acetylcholinesterase Inhibition (Sangnoi
et al. 2008), angiotensin AT1 receptor antagonist activities
(Wu et al. 2008), and hypoglycemic and hypotriglyceridemic
activities (Lohray and Lohray 2005; Mohamed et al. 2014).
Several pyrrole scafolds containing compounds have
been discovered and marketed to exhibit various therapeutic
properties, e.g., drugs tolmetin, atorvastatin, chlorfenapyr,
premazepam, pyrvinium, roseophilin, and zomepirac
(Domagala et al. 2015). On the other side, there are reports
on α-glucosidase inhibitory activity of diferent heterocy-
clic compounds (Dhameja and Gupata 2019). For example,
a series of 5,6-diphenyl-1,2,4-triazine derivatives (Fig. 1a)
showed good activity for inhibition of α-glucosidase enzyme
with IC50 ranging from 12 to 72 µM (Wang et al. 2017a).
The core of the heterocyclic ring, 1,2,4-triazine, was also
used to introduce other α-glucosidase inhibitors (Fig. 1b, c)
with diferent side chain length between the core and third
aryl group (Wang et al. 2016a, 2017b). Other heterocyclic
rings such as imidazole and pyrrole as central core contain-
ing 1,2-diaryl substitution (Fig. 1d, e) have been reported as
anti-hyperglycemic agents (Wang et al. 2016b; Goel et al.
2004).
With respect to the above background, in the search of
new, simple, and easily manageable compounds that could
be active against α-glucosidase, herein, we reported the
design and synthesis of new 1,5-cis-diaryl pyrrole deriva-
tives. As presented in Fig. 1, our designed structure has been
inspired from a and c derivatives. Pyridine ring was used as
the third aryl group at the end of the side chain to increase
water solubility of the target compounds. After structural
characterization, in vitro α-glucosidase inhibitory activity
and kinetic study were done for understanding the mode
of interaction of the most potent compounds with enzyme-
active site, and docking study was also performed.
Experimental
The currently available α-glucosidase inhibitors have
some side efects such as hypoglycemia at higher doses, liver
problems, meteorism, diarrhea, and lactic acidosis (Rouzbe-
han et al. 2017; Ibrahim et al. 2014). Therefore, the discov-
ery and development of potential α-glucosidase inhibitors
can be regarded as a promising topic in recent years.
All chemical compounds and reagents were purchased from
Merck (Darmstadt, Germany). Melting points were deter-
mined with a Kofer hot stage apparatus (Reichert, Vienna,
Austria) and are uncorrected. 1H NMR and 13C NMR spec-
tra were recorded with Bruker FT-400 and Bruker FT-100
spectrometer (Bruker, Darmstadt, Germany), respectively,
using TMS as the internal standard and CDCl3 as a solvent.
Pyrrole scafold is a key structural moiety in numerous
synthetic medicinal agents and natural products (Jacobi
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Chemical Papers
N
N
O
OH
N
Ph
Ph
N
N
S
Ph
Ph
N
N
S
Ph
Ph
N
N
S
N
O
N
H
R
HN
Ar
N
N
N
C
A
B
O
Ph
Ph
N
N
Ar
Ar
N
H
From C
N
N
N
O
CH3
N
CH3
NH
N
H
From E
D
5a-g
E
R
(This work)
Fig. 1 Chemical structures of some compounds with α-glucosidase inhibitory and anti-hyperglycemic activity
The chemical shift (δ) values were expressed in parts per
million (ppm), the coupling constants (J) in hertz, and spin
multiplicities as s (singlet), d (doublet), t (triplet), and m
(multiplet). Mass spectrum was performed with an Agilent
Technology (HP) mass spectrometer operating at an ioniza-
tion potential of 70 eV.
General procedure for the preparation of pyrrole
derivatives 4a–i
The diketones 3a–c (2.28 mmol) were dissolved in ethanol
(3 mL) in a round-bottom fask. A corresponding aniline
derivative (2.28 mmol) and a catalytic amount of para-
toluene sulfonic acid (pTSA) were added to the mixture
and allowed to refux for 8 h. The reaction progress was
inspected by TLC. The reaction becomes cyclized through
the process following the Paal–Knorr condensation to yield
the desired pyrrole derivatives 4a–i. The obtained crude
compounds were concentrated under reduced pressure and
purifed by column chromatography using hexane and ethyl
acetate as an eluent.
Chemistry
The synthetic route for preparation of 5a–I is outlined in
schemes 1 and 2.
General procedure for the preparation of pentane‑1,
4‑dione derivatives (3a, b)
General procedure for the synthesis of target com‑
pounds 5a–i
An appropriate solution of benzaldehyde 1a, b (31.2g,
294 mmol) in DMF (150 mL) was added dropwise over
10 min to vigorously stirred sodium cyanide (1.5g,
30.6 mmol) in DMF (100 mL) at 35 °C in a round-bottom
fask under N2 according to the Stetter reaction. The reaction
mixture was stirred for 10 min and then methyl vinyl ketone
(16.0g, 228 mmol) in DMF (150 mL) was added dropwise
within 20 min with continued vigorous stirring at the same
temperature leading to 3a, b formation (Peloquin et al. 2012;
Biava et al. 2008; Stetter 1976). The obtained compound
was concentrated under reduced pressure and purifed with
column chromatography using ethyl acetate and hexane as
an eluent.
To the mixture of appropriate pyrrole derivatives 4a–i
(4.82 mmol) in dichloromethane (5 mL) and triethylamine
(4.82 mmol), 4.82 mmol of oxalyl chloride was added
dropwise at 0 °C. The reaction mixture was stirred for
5 h at room temperature. After 5 h, the reaction mixture
was concentrated under reduced pressure to remove the
excess oxalyl chloride, and the corresponding α-keto acid
chloride was formed as an intermediate at C-3 of the pyr-
role nucleus. Then, the residue was dissolved in dichlo-
romethane (5 mL) and para-aminopyridine (6.4 mmol)
and triethylamine (1.2 mmol) were added to the mixture
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Chemical Papers
Scheme 1 Synthesis pathway of the target compounds 5a–g
Scheme 2 Synthesis pathway of
the target compounds 5 h, 5i
in the presence of a catalytic amount of 4-N,N-dimethyl-
aminopyridine to obtain the target compounds. The reac-
tion mixture was refluxed for 12 h at 45 °C. After the
12 h reflux, the reaction progress was inspected by TLC.
The mixture was concentrated and the resulting residue
was purified with column chromatography using silica gel
Merck 60 F254 in hexane/ethyl acetate (3:1 v/v) as eluent.
Finally, the purified residue was crystallized to obtain the
corresponding target compounds 5a–i from diethyl ether.
1 3

Chemical Papers
Ar), 7.38–7.43 (m, 3H, pyridine), 7.59 (s, 1H, Ar), 7.82 (s,
1H, Pyrrole), 8.60 (s, 1H, pyridine), 9.62 (s, 1H, NH). 13C-
NMR (125 MHz, CDCl3) δ: 13.23, 112.98, 113.66, 116.54,
125.41, 127.77, 128.81, 129.13, 130.19, 130.40, 134.13,
134.14, 136.32, 143.29, 143.98, 150.84, 161.18, 180.37.
Mass, m/z (%): 415 (<1), 328 (37), 264(10), 149 (15), 129
(18), 97 (40), 71 (60), 55(100).
2‑(1‑(2, 4‑dichlorophenyl)‑2‑methyl‑5‑phe‑
nyl‑1H‑pyrrol‑3‑yl)‑2‑oxo‑N‑(pyridin‑3‑yl) acetamide
(5a)
1
Yellow solid; yield 45%; m.p. 197–199 °C; H-NMR
(500 MHz, CDCl3) δ: 2.42 (s, 3H, CH3), 7.33 (s, 1H, Ar),
7.34–7.37 (m, 3H, Ar), 7.38-7.39 (m, 3H, Ar), 7.48 (d,
J=2.0 Hz, 1H, Ar), 8.23-8.25 (m, 1H, pyridine), 8.41 (d,
J=9.0 Hz, 1H, pyridine), 8.48 (d, J=4.5 Hz, 1H, pyridine),
8.82 (s, 1H, Pyrrole), 9.32 (s, 1H, pyridine), 9.88 (s, 1H,
NH). 13C-NMR (125 MHz, CDCl3) δ: 13.29, 112.44, 113.70,
117.02, 127.55, 128.20, 128.26, 128.35, 130.41, 131.17,
133.92, 134.14, 135.23, 135.99, 143.97, 144.10, 150.83,
160.91, 180.79. Mass, m/z (%): 449 (9), 328(40), 290 (47),
83(59), 55(100).
2‑(5‑(4‑chlorophenyl)‑1‑(2, 4‑dichlorophenyl)‑2‑me‑
thyl‑1H‑pyrrol‑3‑yl)‑2‑oxo‑N‑(pyridin‑3‑yl) aceta‑
mide (5e)
Yellow solid; yield 87%; m.p. 98–100 °C; 1H-NMR
(500 MHz, CDCl3) δ: 2.42 (s, 3H, CH3), 7.33–7.34 (m,
2H, Ar), 7.37 (s, 1H, Ar), 7.38 (d, J=4.5 Hz, 2H, Ar), 7.48
(d, J=2.0 Hz, 2H, Ar), 8.25 (d, J=9.0 Hz, 1H, pyridine),
8.39–8.41 (m, 1H, pyridine), 8.48 (d, J=4.5 Hz, 1H, pyri-
dine), 8.82 (s, 1H, Pyrrole), 9.24 (s, 1H, pyridine), 9.85 (s,
1H, NH). 13C-NMR (125 MHz, CDCl3) δ: 13.23, 112.87,
117.23, 123.73, 126.75, 128.25, 128.37, 128.47, 128.60,
129.12, 129.34, 129.72, 130.25, 130.36, 130.52, 131.46,
133.48, 133.70, 133.82, 133.87, 134.10, 136.18, 141.44,
144.10, 145.85, 160.70, 181.20. Mass, m/z (%): 483 (11),
362 (100), 324(5), 149 (50), 55(75).
2‑(1‑(2, 5‑dichlorophenyl)‑2‑methyl‑5‑phe‑
nyl‑1H‑pyrrol‑3‑yl)‑2‑oxo‑N‑(pyridin‑3‑yl) acetamide
(5b)
1
Yellow solid; yield 47%; m.p. 107–109 °C; H-NMR
(500 MHz, CDCl3) δ: 2.43 (s, 3H, CH3), 7.14 (d, J=2.0 Hz,
1H, Ar), 7.16 (d, J = 2.5 Hz, 1H, Ar), 7.31 (s, 1H, Ar),
7.37–7.39 (m, 3H, Ar), 8.26-8.28 (m, 2H, Ar), 8.48-8.50 (m,
1H, pyridine), 8.51 (d, J=5.0 Hz, 1H, pyridine), 8.54 (d,
J=2.5 Hz, 1H, pyridine), 8.87 (s, 1H, H- Pyrrole), 9.38 (s, 1H,
pyridine), 9.90 (s, 1H, NH). 13C-NMR (125 MHz, CDCl3) δ:
13.23, 120.61, 121.69, 125.20, 127.08, 127.29, 128.00, 128.55,
128.99, 129.60, 129.93, 130.12, 133.14, 133.38, 134.61,
158.23, 160.50, 181.20. Mass, m/z (%): 449 (52), 330 (100),
293 (10), 264 (32), 230 (12), 128 (56), 78 (27), 51(10).
2‑(5‑(4‑chlorophenyl)‑1‑(2, 5‑dichlorophenyl)‑2‑me‑
thyl‑1H‑pyrrol‑3‑yl)‑2‑oxo‑N‑(pyridin‑3‑yl) aceta‑
mide (5f)
1
Yellow solid; yield 84%; m.p. 101–103 °C; H-NMR
(500 MHz, CDCl3) δ: 2.43 (s, 3H, CH3), 7.06 (d, J=8.5 Hz,
1H, Ar), 7.20 (d, J = 8.0 Hz, 2H, Ar), 7.23 (d, J = 1.5 Hz,
1H, Ar), 7.42 (d, J = 8.5 Hz, 2H, Ar), 7.46–7.48 (m, 2H,
pyridine), 7.61 (s, 1H, Ar), 8.47 (d, J = 4.5 Hz, 1H, pyri-
dine), 8.56 (s, 1H, Pyrrole), 9.11 (s, 1H, pyridine), 9.72 (s,
1H, NH). 13C-NMR (125 MHz, CDCl3) δ: 13.23, 112.91,
117.25, 123.72, 126.76, 128.24, 128.49, 128.61, 129.05,
129.28, 129.63, 130.38, 130.84, 131.36, 131.48, 133.48,
133.74, 133.88, 134.83, 136.05, 141.46, 145.85, 160.69,
181.25. Mass, m/z (%): 483 (8), 362 (100), 264(4), 163 (9),
126 (38), 78(10).
2‑(1‑(3, 4‑dichlorophenyl)‑2‑methyl‑5‑phe‑
nyl‑1H‑pyrrol‑3‑yl)‑2‑oxo‑N‑(pyridin‑3‑yl) acetamide
(5c)
1
Yellow solid; yield 57%; m.p. 213–215 °C; H-NMR
(500 MHz, CDCl3) δ: 2.51 (s, 3H, CH3), 7.01 (d, J=7.0 Hz,
1H, Ar), 7.10 (d, J=7.0 Hz, 1H, Ar), 7.22–7.23(m, 5H, Ar),
7.26-7.33 (m, 1H, pyridine), 7.50 (d, J=8.5 Hz, 1H, pyri-
dine), 7.63 (s, 1H, Ar), 8.33 (d, J=7.5 Hz, 1H, pyridine),
8.43 (s, 1H, Pyrrole), 8.79 (s, 1H, pyridine), 9.30 (s, 1H,
NH). 13C-NMR (125 MHz, CDCl3) δ: 13.77, 112.79, 113.72,
117.12, 127.45, 127.61, 128.36, 128.40, 129.96, 131.00,
131.06, 133.34, 133.41, 135.00, 136.22, 143.39, 143.96,
150.8, 150.83, 160.97, 180.88. Mass, m/z (%): 449 (10), 328
(100), 264 (50), 163 (7), 128 (12), 78 (8), 51(4).
2‑(5‑(4‑chlorophenyl)‑1‑(3, 4‑dichlorophenyl)‑2‑me‑
thyl‑1H‑pyrrol‑3‑yl)‑2‑oxo‑N‑(pyridin‑3‑yl) aceta‑
mide (5 g)
1
Yellow solid; yield 76%; m.p. 176–178 °C; H-NMR
(500 MHz, CDCl3) δ: 2.49 (s, 3H, CH3), 6.98 (d, J=2.5 Hz,
1H, Ar), 7.00 (d, J=2.5 Hz, 1H, Ar), 7.02 (d, J=8.5 Hz, 2H,
Ar), 7.21 (d, J =8.5 Hz, 2H, Ar), 7.36–7.38 (m, 1H, pyri-
dine), 7.52 (d, J=8.5 Hz, 1H, pyridine), 7.61 (s, 1H, Ar),
8.35 (d, J=8.0 Hz, 1H, pyridine), 8.43 (s, 1H, Pyrrole), 8.84
(s, 1H, pyridine), 9.39 (s, 1H, NH). 13C-NMR (125 MHz,
2‑(1‑(3‑chlorophenyl)‑2‑methyl‑5‑phenyl‑1H‑pyr‑
rol‑3‑yl)‑2‑oxo‑N‑(pyridin‑3‑yl)acetamide (5d)
1
Yellow solid; yield 54%; m.p. 164–166 °C; H-NMR
(500 MHz, CDCl3) δ: 2.50 (s, 3H, CH3), 7.02–7.26 (m, 8H,
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Chemical Papers
CDCl3) δ: 13.77, 113.17, 113.76, 113.95, 117.19, 119.36,
121.83, 127.58, 128.71, 129.51, 129.94, 130.83, 131.28,
133.48, 133.67, 133.75, 136.29, 143.94, 150.87, 160.88,
180.85. Mass, m/z (%): 483 (11), 362 (100), 327 (5), 298(7),
264 (7), 163 (10), 78 (12), 51(9).
10 min. Then, 25 µL of 4 mM p‐nitrophenyl‐α‐d‐glucopyra-
noside solution in 0.05 M phosphate bufer (pH=6.8) was
added to each well and the reaction mixture was allowed
to incubate for 20 min at 37 °C. Finally, the reaction was
terminated by adding 50 µL of 0.2 M sodium carbonate solu-
tion and then the change in absorbance was measured at
405 nm with a spectrophotometer (Gen5, Power wave xs2,
BioTek, America). DMSO and acarbose were used as the
control and standard inhibitor, respectively. Three independ-
ent assays were performed in each concentration. The mean
of three experiments was used to calculate IC50. The α‐glu-
cosidase inhibitory activity was expressed as the percentage
of enzyme inhibition for each synthesized compound and
calculated by the following formula (Rouzbehan et al. 2017;
Hati et al. 2015):
2‑(1‑(2, 4‑dichlorophenyl)‑2, 5‑dimethyl‑1H‑pyrrol‑3
‑yl)‑2‑oxo‑N‑(pyridin‑3‑yl) acetamide (5 h)
1
Yellow solid; yield 44%; m.p. 140–142 °C; H-NMR
(500 MHz, CDCl3) δ: 1.95 (s, 3H, CH3), 2.32 (s, 3H, CH3),
7.21–7.24 (m, 1H, pyridine), 7.25 (d, J = 1 Hz, 1H, Ar),
7.36 (d, J=4.5 Hz, 1H, Ar), 7.44 (d, J =8.5 Hz, 1H, pyri-
dine), 7.62 (s, 1H, Ar), 8.33 (d, J=7.0 Hz, 1H, pyridine),
8.41 (s, 1H, Pyrrole), 8.83 (s, 1H, pyridine), 9.36 (s, 1H,
NH). 13C-NMR (125 MHz, CDCl3) δ: 12.15, 13.22, 110.46,
116.35, 121.81, 123.67, 127.15, 128.42, 129.68, 130.72,
131.76, 133.40, 134.12, 136.18, 142.26, 146.57, 157.09,
161.19, 181.03. Mass, m/z (%): 387 (31), 266 (100), 231
(5), 202(37), 167 (20), 78 (18), 51(14).
(control absorption − sample absorption)
% Inhibition =
× 100.
control absorption
The concentration of the target compounds required
to inhibit 50% of the enzyme activity (IC50) values was
obtained from non-linear regression curve using the logit
method.
2‑(1‑(3, 4‑dichlorophenyl)‑2, 5‑dimethyl‑1H‑pyrrol‑3
‑yl)‑2‑oxo‑N‑(pyridin‑3‑yl) acetamide (5i)
Kinetic study
1
Yellow solid; yield 36%; m.p. 150–152 °C; H-NMR
(500 MHz, CDCl3) δ: 2.02 (s, 3H, CH3), 2.39 (s, 3H, CH3),
7.10 (d, J=8.5 Hz, 1H, Ar), 7.21–7.27 (m, 1H, pyridine),
7.27 (s, 1H, Ar), 7.37 (d, J = 7.5 Hz, 1H, Ar), 7.64 (d,
J=8.5 Hz, 1H, pyridine), 8.34 (d, J=8.0 Hz, 1H, pyridine),
8.42 (s, 1H, Pyrrole), 8.82 (s, 1H, pyridine), 9.36 (s, 1H,
NH). 13C-NMR (125 MHz, CDCl3) δ: 12.65, 13.71, 110.63,
113.66, 116.15, 127.29, 129.86, 129.94, 131.40, 133.79,
133.85, 136.15, 142.22, 144.01, 150.82, 161.14, 180.48.
Mass, m/z (%): 387 (5), 266 (100), 231 (4), 202(7), 167 (5),
78 (8), 51(4).
The inhibition mode of the most potent compound 5e as
identified with its lowest IC50 was investigated against
α-glucosidase activity. The enzyme solution (1 U/mL, 20
µL) was incubated with diferent concentrations (0, 70, 95,
and 111 µM) of compound 5e (20 µL) at 30 °C for 15 min.
The reaction was initiated by adding diferent concentra-
tions of p-nitrophenyl α-d glucopyranoside (1–10 mM) as
substrate, and change in absorbance was measured in the
absence and presence of compound 5e for 20 min at 405 nm
by using a spectrophotometer (Gen5, Power wave xs2,
BioTek, USA) (Nikookar et al. 2018). A Lineweaver–Burk
plot was produced to identify the mode of inhibition and the
Michaelis–Menten constant (Km) value was determined from
the plot between the reciprocal of the substrate concentration
(1/[S]) and the reciprocal of enzyme rate (1/V) over various
inhibitor concentrations. The value of inhibition constant
(Ki) was made by secondary plots of the inhibitor concentra-
tion [I] versus Km.
Biological evaluation
In vitro α‑glucosidase inhibition activity
The α-glucosidase inhibitory activity of the synthesized
compounds was evaluated using p-nitrophenyl‐α‐d‐glu-
copyranoside (pNPG) as a substrate based on a previously
reported method (Nikookar et al. 2018). The α-glucosidase
enzyme (EC3.2.1.20, Saccharomyces cerevisiae, 20 U/mg)
and substrate (pNPG) were purchased from Sigma-Aldrich.
The desired concentrations of enzyme were prepared in
potassium phosphate bufer (pH 6.8, 50 mM), and the target
compounds 5a–i were dissolved in DMSO (10% fnal con-
centration). A volume of 20 μL of α‐glucosidase solution
(0.5 U/mL), diferent concentrations of the target compounds
5a–i (20 μL), and 135 μL of potassium phosphate bufer
were added to the 96-well plate and incubated at 37 °C for
Molecular docking studies
Molecular docking studies were performed to comprehend
the possible interactions of the most potent compounds
with the amino acid residues on the active site of the tar-
get enzyme. AutoDock version 4.2.6, AutoDock Tools
(ADT) version 1.5.6 and Discovery studio v16.1.0.15350
were used to conduct the docking studies. The most potent
1 3

Chemical Papers
compounds from the series were generated as a ligand with
their 3D structure, 5e and 5a and the reference drug, acar-
bose, using ChemDraw Ultra 12.0.2 version of Cambridge
University. To perform the docking studies, we retrieved the
three-dimensional structure of isomaltase from Saccharo-
myces cerevisiae (PDB ID: 3A4A; Resolution 1.6 Å) from
the Brookhaven protein database (www.rcsb.org/pdb/) as
there is no report yet about the three-dimensional structure
of α-glucosidase from Saccharomyces cerevisiae. Then, the
protein structure was prepared by removing the water mol-
ecules and original inhibitors. Subsequently, the AutoDock
format of protein and potent compounds was prepared and
then the attained structure of the enzyme was used as an
input for the AutoGrid program. AutoGrid was used to pre-
pare the grid map using a grid box. The dimension of the
grid size was set to 60×60×60 with a grid spacing of 0.375
Å. The center of grid box was designated in coordinates
x = 21.272, y = −0.751, and z = 18.633. Fifty runs of the
AUTODOCK search by the Lamarckian genetic algorithm
were performed for each docked system. To analyze the
interactions between the target enzyme and the inhibitor, the
best pose of each ligand was designated and the results were
visualized with Discovery Studio Visualizer v16.1.0.15350
(Accelrys, San Diego, USA).
Then, after removing the unreacted oxalyl chloride with a
rotary evaporator, the residue was dissolved in DCM and
reacted with 3-aminopyridine in the presence of Et3N and a
catalytic amount of 4-N,N-dimethylaminopyridine at 45 °C
for 12 h. After 12 h, the reaction progress was examined by
thin layer chromatography and UV light. Finally, the excess
solvents were removed under reduced pressure and the tar-
get compounds 5a–i were purifed with column chromatog-
raphy using hexane/ethyl acetate (3:1, v/v) as eluent and
recrystallized from diethyl ether. Altogether, nine new target
compounds (5a–i) were synthesized in good to moderate
yields. The chemical structure of the fnal compounds was
confrmed by 1HNMR, 13CNMR, and mass spectroscopy.
In vitro α‑glucosidase inhibition activity
α-Glucosidase activities are associated with two small intes-
tinal membrane-bound enzymes: maltase-glucoamylase
(MGAM) and sucrase-isomaltase (SI). As they are involved
in the breakdown of dietary sugars and starches, MGAM
and SI are attractive targets for inhibition, as a means of
controlling blood glucose levels in individuals with type 2
diabetes (Santos et al. 2018; Flores-Bocanegra et al. 2015;
Palcic et al. 1999). Therefore, the discovery and develop-
ment of potential α-glucosidase inhibitors can be regarded
as a promising topic in recent years.
Results and discussion
The activity of the target compounds 5a–i was assessed
in vitro against yeast α-glucosidase (EC 3.2.1.20) inhibition.
The usage of this source of enzyme has been reported for
inhibitory properties of α-glucosidase in numerous papers
(Guerreiro et al. 2013; Nikookar et al. 2018; Wang et al.,
2016a, Wang et al., 2016b; Wang et al. 2017a; Wang et al.
2017b). Chiba and Shimomura proposed a slightly diferent
classifcation of α-glucosidases that is based on recognition
of homologous sites of the enzymes’ amino acid sequences.
According to the mentioned classifcation, E. coli and other
bacterial species constitute family I of α-glucosidases, and
α-glucosidases from mammalian tissues, plants, and fungi
constitute family II. Three-dimensional structures have also
been obtained for the enzymes from A. oryzae, pig pan-
creas, A. niger, barley, and Pseudomonas stutzeri. All these
structures have similar topological features. In all these
enzymes, the active site is a slit formed at the C-terminus of
the β-sheet of the (β/α) eight barrel (Chiba and Shimomura
1978; Krasikov et al. 2001; Ghasemi and Mehraban 2015).
However, some structural features appear to have been con-
served between α-glucosidase from lower and higher eukar-
yotes. Alignment of the plant and yeast glucosidase with
their mammalian counterparts (Homo sapiens Swiss-Prot
Q13724, Mus musculus Swiss-Prot Q9Z2W5, and Rattus
rattus Swiss-Prot O88941) and the enzyme from C. elegans
(Swiss-Prot Q19426) shows Ala and His residues at the
binding site of α-glucosidases (Faridmoayer and Scaman
Chemistry
The general procedure for synthesis of the final target
compounds 5a–i is described in Schemes 1 and 2. Briefy,
pentane-1,4-dione derivatives 3a, b were obtained by react-
ing appropriate benzaldehydes 1a, b with methyl vinyl
ketone 2 in the presence of sodium cyanide as a catalyst
in dimethylformamide (DMF) at 35 °C following Stetter
reaction and other previously reported methods (Peloquin
et al. 2012; Biava et al. 2008; Stetter 1976). The correspond-
ing diketones 3a–c (3c was purchased) were dissolved in
ethanol (EtOH) and refuxed for 8 h with aniline deriva-
tives (3-chloroaniline, 2,4-dichloroaniline, 2,5-dichloroani-
line, and 3,4-dichloroaniline) in the presence of a catalytic
amount of p-toluenesulfonic acid (PTSA). Following the
Paal–Knorr condensation, the reaction mixture was cyclized
to yield the corresponding 1 N-phenylpyrrole derivatives
4a–i (Biava et al. 2011; Stetter 1976). The target compounds
5a–i were achieved with a two-step reaction. Primarily, the
1 N-phenylpyrrole derivatives 4a–i dissolved in dichlo-
romethane (DCM) and oxalyl chloride and triethylamine
(Et3N) were added dropwise to the reaction mixture in an
ice bath. The corresponding α-keto acid chloride was formed
through regioselective acylation as the side chain of 4a–i
at C3 of the pyrrole ring reacted with the oxalyl chloride.
1 3

Chemical Papers
Table 1 In vitro α-glucosidase inhibitory activities of compounds
2005). In Saccharomyces cerevisiae, CWH41 encodes pro-
cessing α-glucosidase (Cwh41p) (Romero et al. 1997) which
is a member of family 63 of the glycoside hydrolases (Can-
tarel et al. 2009). Cwh41p is a type II membrane glycopro-
tein with a proposed domain orientation comparable to its
mammalian counterpart (Shailubhai et al. 1991; Kalz-Fuller
et al.1995; Jiang et al. 1996). Sequence comparison between
enzyme orthologs (i.e., human, Caenorhabditis elegans and
S. cerevisiae) shows higher identity (34–49%) at the end of
the C-terminus domain where the putative catalytic domain
is located (Romero et al. 1997).
5a–i
N
O
HN
O
CH3
R
N
X
Compounds
R
X
IC50 (µM)a
Furthermore, the similar results have been reported for
assessment of α-glucosidase inhibitory activity using two
diferent kinds of enzymes (α-glucosidase EC 3.2.1.20;
Sigma, and rat intestinal α-glucosidase source). For kaemp-
ferol, a natural product separated from herb, IC50 were
61 µM and 59 µM, respectively. The percentage of enzyme
inhibition at concentrations of 0.83 µM was reported as 68%
and 55%, respectively (Kang et al. 2011).
5a
5b
5c
5d
5e
5f
5 g
5 h
Phenyl
Phenyl
Phenyl
Phenyl
4-Chlorophenyl
4-Chlorophenyl
2,4-dichloro
2,5-dichloro
3,4-dichloro
3-chloro
2,4-dichloro
2,5-dichloro
3,4-dichloro
2,4-dichloro
3,4-dichloro
–
196 10
663 11
197 9
276 11
111 12
573 12
639 13
4-Chlorophenyl
CH3
CH3
–
494
673 12
750
9
Compound 5e was bound to active site on the enzyme and
competed with the substrate for binding to the active site, so
the type of inhibition was competitive inhibition. The results
were compared with acarbose, the marketed α-glucosidase
inhibitor, as a standard drug. The activity of acarbose has
been reported in a range of 600–800 µM related to the
source of the enzyme. In our experiments, 750 9 µM was
found for IC50 of acarbose in triplicated tests. The in vitro
α-glucosidase inhibitory activity was carried out based on
the previously reported method (Nikookar et al. 2018). The
results were described as the concentration of the target
compounds required to inhibit 50% of the α-glucosidase
activity (IC50 values) (Sun et al. 2017; Biava et al. 2011) and
are summarized in Table 1. Accordingly, a careful remark of
the bioactivity data revealed that all the target compounds
5a–i exhibited better inhibitory activity than the standard
drug, acarbose. Optimization of the α-glucosidase inhibitory
activity of 2-(2-methyl-1-phenyl-1H-pyrrol-3-yl)-2-oxo-N-
(priding-3-yl) acetamide derivatives 5a–i was performed
using chloride substituents on a diferent position of the
phenyl rings. The diferences in the pattern of inhibition of
the synthesized compounds are mainly due to the position
of the substituents on the phenyl moiety.
5i
Acarbose
9
a Values are mean SD. All experiments were performed in triplet
1N-phenyl ring. The presence of a para-chloro substituent on
the 5-phenyl ring of 5e improves its binding interaction with
the amino acid residue in the active site of the enzyme through
hydrophobic interaction as the experimental fndings were
confrmed by molecular docking studies. However, when the
position of 2,4-dichloro substituents of compound 5e on the
1N-phenyl ring was shifted to 2,5-dichloro and 3,4-dichloro
positions on the same moiety as in the case of compound 5f
(IC50 =573 12 µM) and compound 5 g (IC50 =639 13 µM),
respectively, the inhibitory activity noticeably diminished by
more than fvefold as compared to the most active compound
5e. Even though the inhibitory activity of these compounds
is reduced in comparison with the most potent one, they have
still a better inhibitory activity than the standard drug, acar-
bose (IC50 =750 9 µM). This result indicates that the orien-
tation of the substituents on the phenyl ring has a great impact
on the α-glucosidase inhibitory activity.
The most potent compounds were 5e, 5a, and 5c with
IC50 values 111 12, 196 10, and 197 8 µM, respectively,
while the IC50 value of acarbose was 750 8 µM (Table 1).
The other target compounds showed a moderate inhibitory
activity around 1.11- to 2.72-fold more than acarbose with
the IC50 values in the range of 276 10 to 673 12 µM. The
greater inhibitory activity of compound 5e over compound 5a
might be due to the introduction of an electron-withdrawing
group through its strong inductive efect as a para substitu-
ent on the aromatic ring attached to the pyrrole moiety, as
both compounds contain 2, 4-dichloro substituents on the
Similarly, when the position of 2,4-dichloro substituents
of compound 5a (IC50 = 196 10 µM) on the 1N-phenyl
ring was shifted to 2,5-dichloro as in the case of compound
5b (IC50 =663 11 µM), the inhibitory activity decreased
by more than threefold, whereas there was no diference
when it was shifted to position 3,4-dichloro as in compound
5c (IC50 = 197 8 µM). On the other hand, the replace-
ment of substituted 5-phenyl moiety of the pyrrole ring
with methyl moiety reduces the inhibitory activity greatly
as in the case of compound 5 h (IC50 = 494 10 µM) and
5i (IC50 = 673 12 µM); however, the inhibition potency
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Chemical Papers
Fig. 2 Kinetics of α-glucosidase
inhibition by compound 5e. a
The Lineweaver–Burk plot in
the absence and presence of
diferent concentrations of com-
pound 5e (µM); b the secondary
plot between Km and diferent
concentrations of compound 5e
was still better than that of acarbose. This indicated that
the nature of substituents at position 5 of the pyrrole ring
exhibited a signifcant efect on the inhibition potency of the
α-glucosidase enzyme.
Between a large numbers of the related structure (Kasturi
et al. 2017, Damsud et al. 2013, and Guerreiro et al. 2013),
only two compounds were active, namely 3-hydroxypyrro-
lidine-2,5-diyl)dimethanol, a polyhydroxylated pyrrolidine,
and 6-hydroxy-5-(hydroxymethyl)tetrahydro-1H-pyrrolizin-
3(2H)-one (an oxapyrrolizidine molecule). On the other
hand, Damsud et al. 2013 isolated three new phenylpro-
panoyl amides: chaplupyrrolidones a and b, which contain
a 5-oxygenated-∆3-2-pyrrolidone moiety, and deacetyl-
sarmentamide b (a dihydroxy pyrrolidine derivative). The
chaplupyrrolidones a and b displayed a weak α-glucosidase
inhibitory activity with IC50 values of 7820 and 430 µM,
respectively, while deacetylsarmentamide b was inac-
tive as compared to acarbose (Damsud et al. 2013). Five-
membered iminocyclitol α-glucosidase inhibitors were
As shown in Fig. 1, a heterocyclic core containing di-
aryl rings (a, b, c) or tri-aryl rings (d, e) have been reported
as either α-glucosidase inhibitor or anti-hyperglycemic
agents. For a–d derivatives (Fig. 1), a 5–70 μM range of
IC50 was reported that shows the triazine or imidazole
served as a suitable core for design of α-glucosidase inhibi-
tor with high potency. For pyrrole derivatives (e, Fig. 1),
the study involved an in vivo test (goel et al. 2004) with-
out any data related to α-glucosidase inhibitory activity. On
the other hand, there are several reports that have shown
α-glucosidase inhibitory activity of pyrrolidine derivatives.
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Chemical Papers
Fig. 3 Kinetics of α-gluosidase
inhibition by acarbose. The
Lineweaver–Burk plot in the
absence and presence of difer-
ent concentrations of acarbose
Fig. 4 The predicted binding
mode of acarbose in the active
site pocket
reported (Guerreiro et al. 2013) that indicates the reported
compounds were weaker than acarbose with IC50 ranging
from 10.9 to 38 mM. Some studies showed that the pyrro-
lidine derivatives exhibited either moderate α-glucosidase
inhibitory activity or were totally inactive as compared to
acarbose.
Kinetic study
The mechanism of enzyme inhibition of the most potent
compound 5e on α-glucosidase was evaluated using a kinetic
study. The inhibition mode and value of inhibition con-
stant (Ki) were determined by Lineweaver–Burk plots and
secondary re-plot of Lineweaver–Burk plots, respectively
(Nikookar et al. 2018).
However, our compounds showed less activity than tria-
zole or imidazole derivatives, and the pyrrole scafold illus-
trated remarkable better α-glucosidase inhibitory efects
when compared with the activity of pyrrolidine derivatives.
In the presence of different concentrations of com-
pound 5e, the Lineweaver–Burk plot showed that the
1 3

Chemical Papers
Fig. 5 The predicted mode of binding of compounds 5e and 5a in the active site pocket. a The interactions between compound 5e and the active
site of the modeled α-glucosidase b The interactions between compound 5a and the active site of the modeled α-glucosidase
Michaelis–Menten constant (Km) gradually increased while
Vmax remained unafected (Fig. 2a), which indicates that the
type of inhibition is competitive. The same mechanism for
enzyme inhibition of acarbose was observed and the results
are presented in Fig. 3. Again, the gradual increase of Km and
unchanged Vmax indicates competitive inhibition for acar-
bose. This result suggests that compound 5e competes with
the substrate for binding to the active site of the enzyme.
Moreover, the plot of Km versus various concentrations of
compound 5e presented an estimate of the value of inhibition
constant Ki as 106 µM (Fig. 2b).
an infuential tool, if handled properly, to convey a consistent
structural data of biological macromolecules and regulate
the structure and position of the active center, which assists
in comprehending in what way the protein recognizes and
binds to the ligand fragments (Rhodes 2006). But, when
the crystal structure of a specifed molecule is not manage-
able, homology modeling can be an outstanding replace-
ment to upkeep drug discovery determinations (Levoin et al.
2011). Hence, we used the three-dimensional structure of
isomaltase from Saccharomyces cerevisiae (PDB ID: 3A4A;
Resolution 1.6 Å) to prepare the protein for docking, which
has a 71% identity and 84% similarity to the α-glucosidase
from Saccharomyces cerevisiae (Leong et al. 2018; Sun
et al. 2017). The binding mode of acarbose, as shown in
Fig. 4, demonstrates that it interacts with the active site of
isomaltase via ten hydrogen bonds, two carbon–hydrogen
bonds, and one hydrophobic interaction with the residues
Asp69, Phe159, Gln182, Asp215, Asp242, Glu277, Asp307,
Arg315, Gln353, Glu411, and Arg442.
Molecular docking
Molecular docking study was carried out on the possible
interaction of the target compounds with the amino acid resi-
dues in the active site of the modeled α-glucosidase. The
most active compounds 5e and 5a and the reference drug,
acarbose were docked using AutoDock Tools version 1.5.6.
To date, there has been no report regarding the crystal struc-
ture of α-glucosidase from Saccharomyces cerevisiae. It is
obvious that molecular models attained from crystallography
are used widely as a tool for enlightening molecular informa-
tion of life progressions. All methods that might be obtained
from a model have their own weakness and strength; how-
ever, the majority of crystal structures are formed identical
to the aqueous structure. Furthermore, it yields high atomic
resolution irrespective of the molecular weight of the sam-
ple and is also more suitable for membrane proteins, water-
soluble proteins, and macromolecular complexes. It is also
Compound 5e, the most active one from the target com-
pounds, recognized hydrogen bond interaction with the
active site residue His280 through the carbonyl oxygen of
the amide unit of the acetamide chain (Fig. 5). π– π T-shaped
interaction was formed with Tyr158 through the 5-phenyl
ring. The pyridine ring established π–anion interactions with
Asp307 residue, while the 5-phenyl and 1N-phenyl rings of
compound 5e formed the same interaction with the Asp352
residue. Moreover, the para-chloro substituents of 5-phenyl
and 1N-phenyl rings of compound 5e created π–alkyl inter-
actions with the residues Phe178 and Phe303, respectively
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Chemical Papers
Bonding distance (Å)
4.02
Table 2 Molecular docking data
resulting from compounds 5e
and 5a in α-glucosidase
Structure of the compounds
Interacting amino
acid residue
Bond type
N
Phe178
Hydrophobic
HN
O
N
O
CH3
Cl
Cl
Cl
Val216
Phe303
Arg315
Arg442
His280
Asp307
Asp352
Tyr158
Tyr158
Hydrophobic
Hydrophobic
Hydrophobic
Hydrophobic
Hydrogen bonding
π–anion
π–anion
π–π T shaped
Hydrophobic
5.43
4.10, 5.19
5.30
4.90
1.90
3.90
3.69, 4.80
5.54
Compound 5e
N
5.75
HN
O
N
O
CH3
Cl
Cl
Cl
Val216
His280
Phe303
Arg315
Arg442
Arg315
Glu411
Phe178
Phe303
Hydrophobic
Hydrophobic
Hydrophobic
Hydrophobic
Hydrogen bonding
π–cation
π–anion
π–π stacked
π–π stacked
4.78
4.79
4.96
4.55
4.21
4.33
4.12
3.92
3.98
Compound 5a
(Fig. 5a). Other hydrophobic interactions were also detected
through the 5-phenyl ring with the residue Val216, 2-methyl
substituent of pyrrole ring with the residue Phe303, pyridine
ring with the residue Arg315, and the ortho-chloro substitu-
ent of the 1N-phenyl ring with the residue Arg442 (Table 2).
Compound 5a, the second most active of the series,
interacted with the active site residue Arg442 via hydrogen
bond with the carbonyl oxygen of the acetamide chain. π–π
stacked interaction was formed with the residues Phe303
and Phe178 through the 5-phenyl and pyridine rings, respec-
tively. Hydrophobic interactions were also observed with
the residues Tyr158, Val216, His280, Phe303, and Arg315
(Fig. 5b). The hydrophobic interactions of residues Tyr158,
His280, and Phe303 were observed via 2-chloro substituent
of the 1N-phenyl ring, while residues Arg315 and Val216
formed the hydrophobic interaction through 1N-phenyl and
pyridine rings, respectively. Moreover, residues Arg315 and
Glu411 made π–cation and π–anion interactions with the
5-phenyl and pyrrole rings, respectively.
On top of their interactions, the binding energies of
compounds 5e, 5a, and acarbose, as observed from the best
docking conformations, showed that both compounds 5e and
5a have a lower free binding energy (− 4.27 kcal/mol and
−3.17 kcal/mol, respectively) than acarbose (2.47 kcal/mol).
Therefore, the results emphasize that the target compounds
bind more easily to the target enzyme (α-glucosidase) than
the reference drug, acarbose. In general, the outcomes from
the molecular docking studies supported the results obtained
from the in vitro assay.
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Chemical Papers
synthesis and in vitro and in vivo biological evaluation. J Med
Chem 53:723–733
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Biava M, Porretta GC, Poce G, Battilocchio C, Alfonso S, Rovini
M et al (2011) Novel analgesic/anti-infammatory agents: dia-
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properties. J Med Chem 54:7759–7771
The reported derivatives exhibited α-glucosidase inhibi-
tion activity better than the reference compound (acarbose).
Compounds 5e, 5a, and 5c showed potent activity among
the series. Compound 5e bearing a 2,4-dichloro substitu-
ent on 1N-phenyl ring and para-chloro substituent of the
5-phenyl ring of the pyrrole scafold exhibited the most
potent α-glucosidase inhibitory activity with an IC50 value
of 111 11 μM. The outcomes from the molecular dock-
ing studies of compounds 5e and 5a supported the results
obtained from the in vitro assay. Moreover, these compounds
have a lower free binding energy than the reference drug,
acarbose, which indicates that they bind easily to the target
enzyme than acarbose. This might be the best clue for the
good inhibitory activity of the compounds. In conclusion,
the synthesized compounds of this class of heterocyclic
motifs have shown promising results for further develop-
ment of potent, selective, and efcacious inhibitors against
the α-glucosidase enzyme that could be a potential candidate
for the treatment of diabetes.
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