Novel indolyl linked para-substituted benzylidene-based phenyl containing thiazolidienediones and their analogs as α-glucosidase inhibitors: synthesis, in vitro, and molecular docking studies

Article abstract of DOI:10.1007/s00044-017-2112-6

Synthesis of indolyl linked benzylidene-based para-substituted phenyl containing thiazolidinediones and acyclic analogs of isoxazolidinediones—a cyclic analog of thiazolidinedione (4a–7b) in an effort to develop novel α-glucosidase inhibitors in the manag

Full text of DOI:10.1007/s00044-017-2112-6

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res
DOI 10.1007/s00044-017-2112-6
ORIGINAL RESEARCH
Novel indolyl linked para-substituted benzylidene-based phenyl
containing thiazolidienediones and their analogs as α-glucosidase
inhibitors: synthesis, in vitro, and molecular docking studies
Jeewanjot Kaur1 Amanjot Singh1 Gagandeep Singh1 Raman K. Verma1
Rajiv Mall2
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Received: 11 August 2017 / Accepted: 3 November 2017
© Springer Science+Business Media, LLC, part of Springer Nature 2017
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Abstract Synthesis of indolyl linked benzylidene-based
para-substituted phenyl containing thiazolidinediones and
acyclic analogs of isoxazolidinediones—a cyclic analog of
thiazolidinedione (4a–7b) in an effort to develop novel
α-glucosidase inhibitors in the management of hypergly-
cemia for the treatment of type 2 diabetes is reported. The
structure of all the novel synthesized compounds was con-
firmed through the spectral studies (LC-MS, 1H-NMR, 13C-
NMR, FT-IR). Comparative evaluation of these compounds
revealed that the compound 5b showed maximum inhibi-
tory potential against α-amylase and α-glucosidase giving
an IC50 value of 0.51 0.01 µM. Furthermore, binding
affinities in terms of G score values and hydrogen bond
interactions between all the synthesized compounds and the
amino acid (AA) residues in the active site of the protein
(PDB code: 3TOP) to that of acarbose (standard drug) were
explored with the help of molecular docking studies.
Compound 5b was considered as promising candidate of
this series.
Keywords Antihyperglycemic Molecular docking
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Thiazolidenediones (TZD) Diethylmalonate (DEM)
Methylacetoacetate (MAA) Rhodanine (RHD)
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Introduction
Type 2 diabetes mellitus is a complex and chronic metabolic
disease due to insulin-resistance in body tissue (Lee et al.
2017). About 415 million people worldwide have diabetes
which is predicted to become one of the leading causes of
death in the world (Wei et al. 2016). Recently, a more
effective strategy for the treatment of type 2 diabetes mellitus
has involved the disturbance of dietary monosaccharide
absorption by inhibition of α-glucosidase (Kim et al. 2014).
α-Glucosidase is a membrane-bound enzyme located in the
epithelium of the human small intestine, and is a key enzyme
in carbohydrate digestion. It hydrolyzes the terminal, non-
reducing 1,4-linked α-D-glucose residues with release of α-
D-glucose and helps digestion and absorption of sugars. α-
Glucosidase inhibitors can be used as a first-line drug for the
treatment type 2 diabetes because they can lower the rate of
carbohydrate absorption and suppression of postprandial
hyperglycemia. Three α-glucosidase inhibitors, acarbose,
miglitol and voglibose, have been in clinical use for many
years. Furthermore, α-glucosidase may also be used as
therapeutic target for other carbohydrate mediated diseases
including cancer, HIV, and hepatitis. Therefore, discovery
and development of novel α-glucosidase inhibitors are
urgently needed (Wang et al. 2017). The literature survey
revealed that indole-based compounds have versatile and
many biological activities such as anti-cancer (El Sayed et al.
2015; Chao et al. 2007), antibacterial (Yamamoto and Kur-
azono 2007; Seefeld et al. 2001), anti-inflammatory (Radwan
Electronic supplementary material The online version of this article
(https://doi.org/10.1007/s00044-017-2112-6) contains supplementary
material, which is available to authorized users.
* Rajiv Mall
rajivmall@pbi.ac.in
1
Department of Chemistry, Synthetic Organic and Medicinal
Chemistry Laboratory, Punjabi University, Patiala 147002,
Punjab, India
2
Department of Basic and Applied Sciences, Punjabi University,
Patiala 147002, Punjab, India

Med Chem Res
CO2R3
O
points reported here were recorded using an open conc.
sulfuric acid bath and are uncorrected. The infrared and H
R1
1
X
N
nuclear magnetic resonance (NMR) spectra of the reported
compounds were recorded on Perkin-Elmer Spectrum RX
Fourier transform infrared (FTIR) spectrophotometer, and
AC400F, 400 MHz Bruker spectrometer, respectively at
SAIF, Panjab University, Chandigarh. LCMS of the com-
pounds were recorded on Waters Micromass Q-T of Micro
Spectrometer at SAIF, Panjab University, Chandigarh.
GCMS and Elemental analysis of these compounds were
carried out on Shimadzu GCMS-QP2010 Plus and Vario
Micro CHN Elemental Analyzer, respectively at Instru-
mental Laboratory, Department of Chemistry, Punjabi
University, Patiala. Thin layer chromatography analysis was
carried out on glass plates coated with silica gel-GF254
(Loba Chemie), and spots were visualized using a UV
cabinet (Perfit India). Column chromatography was per-
formed using silica gel 100–200 mesh (Loba Chemie).
Compound (1) was prepared as per reported procedure
(Verma et al. 2015).
NH
N
H
O
X = O, NH
N
R2
R2
R1
I
II
O
H
R
O
N
O
O
N
O
S
N
O
N
O
S
N
O
N
H
X
X= S, O
IV
R
III
Fig. 1 Representative examples for new class of α-glucosidase
inhibitors
et al. 2007; Fernandes et al. 2004), and antifungal (Khamna
et al. 2009; Dandia et al. 2006), antihelmintic (Davyt et al.
1998; Srivastava et al. 1999), and antidiabetic (Wang et al.
2012). Naureen et al. (2015) and Han et al. (2015) have
reported that a novel series of indole-based compounds
derivatives act as a new class of α-glucosidase inhibitors I
(Naureen et al. 2015) and II (Han et al. 2015) as shown in
Fig. 1. Thiazolidine-2,4-diones and their analogs are impor-
tant moieties due to their broad range of biological activities,
including antidiabetic (Lehmann et al. 1995), anticancer
(Blanquicett et al. 2008), anti-microbial (Dündar et al. 2007),
antioxidant (Nawale and Dhake 2012), and antibacterial
(Rekha and Chandrashekhara 2015; Chinthala et al. 2013).
Recently, Chinthala et al. (2013) and Wang et al. (2017) have
reported that a novel series of thiazolidinedione derivatives
act as a new class of α-glucosidase inhibitors III and IV
(Fig. 1). Acoordingly indole and thiazolidine-2,4-dione could
be used as pharmacophore to design new active compounds
for α-glucosidase inhibition. We report herein the design and
synthesis of a hybrid scaffold by incorporating indole with
thiazolidine-2,4-dione and their analogs into a single mole-
cule. Molecular docking was performed to investigate the
interaction of the synthesized compounds with the active site
of α-glucosidase. The synthesized compounds were tested for
their in vitro α-glucosidase inhibitory activity.
General procedure for the synthesis of different derivatives
of N-substituted ethyl 3-bromo-1H-indole-2-carboxylate
To a mechanically stirred mixture of (1) (27.97 mmol),
K2CO3 (83.91 mmol) and dry DMF (50 mL), benzyl bro-
mide or 4-chlorobenzyl bromide (30.77 mmol) was added
dropwise respectively. After stirring for 48 h, the solution
was filtered and the filtrate was extracted with ethyl acetate
(3 × 20 mL). The combined organic extracts were washed
with water (50 mL) and brine (50 mL), dried over sodium
sulfate and concentrated. The crude product was purified by
column chromatography using a mixture of ethyl acetate/
hexane (20:80) as eluent to give the title compounds (2a/b).
Ethyl 1-benzyl-3-bromo-1H-indole-2-carboxylate (2a)
Product was obtained as white solid (52% yield); mp:
75–78 °C; FTIR (KBr, cm−1) νmax: 2975 (Ar C–H), 1704
(C=O), 1606–1450 (Ar C=C), 695 (C–Br); 1H NMR (400
MHz, CDCl3): δ = 7.71 (m, 1H, Ar), 7.35 (m, 2H, Ar), 7.25
(m, 4H, Ar), 7.02 (m, 2H, Ar), 5.77 (s, 2H, benzylic), 4.39
(two overlapping quartets, 2H, –OCH2CH3), 1.38 (two
overlapping triplets, 3H, –OCH2CH3); 13C NMR (100
MHz, CDCl3): δ = 161.24 (COOCH2CH3), 138.11,
137.87, 128.71 (2C), 127.37, 127.00, 126.49, 126.24
(2C), 125.38, 121.66, 121.65, 110.92, 99.76 (C–Br), 61.32
(COOCH2CH3), 48.81 (N–CH2–C6H5), 14.24 (COOCH2
CH3); ESI-MS (m/z): 358.03 [M]+; anal. calcd. (%) for
C18H16BrNO2: C, 60.35; H, 4.50; N, 3.91. Found: C, 59.76;
H, 4.25; N, 3.77.
Materials and methods
Chemistry
All the chemicals used in the present work were purchased
from Aldrich and SD Fine chemicals. The melting/boiling
Ethyl 3-bromo-1-(4-chlorobenzyl)-1H-indole-2-carboxylate
(2b) Product was obtained as white solid (77% yield); mp:

Med Chem Res
80–82 °C; FTIR (KBr, cm−1) νmax: 2926 (Ar C–H), 1705
(C=O), 1504–1492 (Ar C=C), 803 (C–Cl), 742 (C–Br); 1H
NMR (400 MHz, CDCl3): δ = 7.72 (m, 1H, Ar), 7.37 (m,
1H, Ar), 7.31 (m, 1H, Ar), 7.27 (m, 1H, Ar), 7.23 (m, 2H,
Ar), 6.97 (m, 2H, Ar), 5.75 (s, 2H, benzylic), 4.39 (two
overlapping quartets, 2H, –OCH2CH3), 1.40 (two over-
lapping triplets, 3H, –OCH2CH3); 13C NMR (CDCl3, 100
MHz): δ = 161.21 (COOCH2CH3), 137.98, 136.42, 133.35,
128.87 (2C), 127.70 (2C), 127.04, 126.68, 125.16, 121.81,
121.79, 110.71, 100.06 (C–Br), 61.42 (COOCH2CH3),
48.20 (N–CH2–C6H4Cl), 14.28 (COOCH2CH3); ESI-MS
(m/z): 413.4 [M + Na]+; anal. calcd. (%) for
C18H15BrClNO2: C, 55.06; H, 3.85; N, 3.57. Found: C,
54.26; H, 3.25; N, 3.27.
yield); FTIR (KBr, cm−1) νmax: 3059 (Ar C–H), 2831 and
2735 (OC–H), 1701 (C=O), 1605–1457 (Ar C=C), 834
(C–Cl); 1H NMR (400 MHz, CDCl3): δ = 10.09 (s, 1H,
–CHO), 7.97 (d, 2H, J = 8.16 Hz, Ar), 7.64 (d, 2H, J =
8.08 Hz, Ar), 7.56 (d, 1H, J = 8.12 Hz, Ar), 7.38 (m, 2H,
Ar), 7.26 (m, 2H, Ar), 7.21 (m, 1H, Ar), 7.07 (d, 2H, Ar),
5.79 (s, 2H, benzylic), 4.14 (q, 2H, –OCH2CH3), 0.99 (t,
3H, –OCH2CH3); 13C NMR (100 MHz, CDCl3): δ =
192.46 (CHO), 162.08 (COOCH2CH3), 138.32, 136.72,
136.70, 136.67, 135.84, 133.12, 132.09, 128.89 (2C),
128.59, 128.41, 127.84 (2C), 126.75, 126.11, 124.54,
123.92, 121.60, 121.42, 110.70, 60.88 (COOCH2CH3),
47.79 (N–CH2–C6H4Cl), 13.65 (COOCH2CH3); ESI-MS
(m/z): 418.2 [M + 1]+, 440.2 [M + Na]+; anal. calcd. (%)
for C25H20ClNO3: C, 71.85; H, 4.82; N, 3.35. Found: C,
71.52; H, 4.55; N, 2.96.
General procedure for the synthesis of different derivatives
of ethyl N-substituted-1H-indole-2-carboxylate aldehyde
General procedure for the synthesis of target compounds
(4a/b) and (5a/b)
To a solution of (2a/2b) (2.3 mmol) and 4-formylphenyl
boronic acid (2.1 mmol) in 25 mL of dioxane:water (4:1)
K2CO3 (6.3 mmol) was added. The mixture was degassed
and stirred at ambient temperature for 20 min and catalytic
amount (0.005 mmol) of Pd(PPh3)4 was added. The mixture
was degassed and refluxed under nitrogen for 8 h and then
cooled and filtered through celite and extracted using ethyl
acetate (3 × 20 mL). The organic layer was dried over
anhydrous sodium sulfate, filtered and concentrated
to give oil which was subjected to column chromatography
using ethyl acetate/hexane (2:8) to afford the title com-
pounds (3a/3b).
A mixture of (3a/3b) (0.43 mmol), thiazolidine-2,4-dione
(0.43 mmol) or rhodanine (0.43 mmol) and catalytic
quantity of piperidinium acetate in toluene (25 mL) was
refluxed for 12 h using a Dean-Stark water separator for
continuous removal of water. The reaction mixture was
cooled to room temperature and then stored inside a
refrigerator overnight. The yellow precipitate was collected
by filtration under suction, dried and re-crystallized from
methanol to obtain the title compounds (4a/b) or (5a/b) as
pale yellow solids.
Ethyl 1-benzyl-3-(4-formylphenyl)-1H-indole-2-carboxy-
late (3a) Product was obtained as oil (82% yield); FTIR
(KBr, cm−1) νmax: 3029 (Ar C–H), 2851 and 2734 (OC–H),
Ethyl 1-benzyl-3-{4-[(2,4-dioxo-1,3-thiazolidin-5-ylidene)
methyl]phenyl}-1H-indole-2-carboxylate
(4a) Product
1
1699 (C=O), 1605–1455 (Ar C=C); H NMR (400 MHz,
was obtained as pale yellow solid (71% yield); mp:
120–125 °C; FTIR (KBr, cm−1) νmax: 3459 (N–H), 3181
(Ar C–H), 1742–1701 (C=O), 1545–1453 (Ar C=C), 1371
CDCl3): δ = 10.02 (s, 1H, –CHO), 7.90 (dd, 2H, Ar), 7.59
(d, 2H, J = 8.16 Hz, Ar), 7.49 (d, 1H, J = 8.12 Hz, Ar), 7.36
(1H, d, J = 8.44 Hz, Ar), 7.31 (1H, m, Ar), 7.21 (3H, m, Ar),
7.16 (1H, m, Ar), 7.05 (d, 2H, J = 7.00 Hz, Ar), 5.76
(s, 2H, benzylic), 4.07 (q, 2H, –OCH2CH3), 0.92 (t, 3H,
–OCH2CH3); 13C NMR (100 MHz, CDCl3): δ = 192.50
(CHO), 162.13 (COOCH2CH3), 138.45, 138.16, 136.76,
136.25, 136.00, 132.19, 128.74 (2C), 128.60, 128.29,
127.36, 126.70, 126.40 (2C), 125.94, 124.79, 123.65,
121.47, 121.29, 110.96, 60.83 (COOCH2CH3), 48.36
(N–CH2–C6H5), 13.68 (COOCH2CH3); ESI-MS (m/z):
383.9 [M]+, 406.7 [M + Na]+; anal. calcd. (%) for
C25H21NO3: C, 78.31; H, 5.52; N, 3.65. Found: C, 77.52;
H, 5.66; N, 3.57.
1
(C–N), 696 (C–S); H NMR (400 MHz, CDCl3): δ = 7.88
(s, 1H, benzylidene), 7.63 (m, 5H, Ar), 7.41 (m, 1H, Ar),
7.36 (m, 1H, Ar), 7.30 (m, 3H, Ar), 7.19 (m, 1H, Ar), 7.12
(m, 2H, Ar), 5.82 (s, 2H, benzylic), 4.15 (q, 2H,
–OCH2CH3), 1.00 (t, 3H, –OCH2CH3); 13C NMR (100
MHz, CDCl3): δ = 170.93 (C=O of thiazolidinedione ring),
168.38 (C=O of thiazolidinedione ring), 162.45 (C=O of
ester), 144.76, 138.72, 138.47, 136.99, 136.51, 136.29,
132.48, 129.07 (2C), 128.89, 128.59, 127.66, 126.96,
126.71 (2C), 126.27, 125.06, 123.98, 121.75, 121.58,
111.25, 105.41, 61.16 (COOCH2CH3), 48.68 (N–
CH2–C6H5), 13.95 (COOCH2CH3); ESI-MS (m/z): 483.39
[M + 1]+, 505.35 [M + Na]+; anal. calcd. (%) for
C28H22N2O4S: C, 69.69; H, 4.60; N, 5.81. Found: C, 58.99;
H, 4.44; N, 5.65.
Ethyl 1-(4-chlorobenzyl)-3-(4-formylphenyl)-1H-indole-2-
carboxylate (3b) Product was obtained as oil (79%

Med Chem Res
Ethyl 1-(4-chlorobenzyl)-3-{4-[(2,4-dioxo-1,3-thiazolidin-
5-ylidene)methyl]phenyl}-1H-indole-2-carboxylate (4b)
Product was obtained as pale yellow solid (79% yield); mp:
110–115 °C; FTIR (KBr, cm−1) νmax: 3463 (N–H), 3192
(Ar C–H), 1741–1699 (C=O), 1545–1456 (Ar C=C), 1333
(C–N), 799 (C–Cl), 741 (C–S); 1H NMR (400 MHz,
CDCl3): δ = 7.92 (s, 1H, benzylidene), 7.59 (m, 4H, Ar),
7.37 (m, 3H, Ar), 7.20 (m, 4H, Ar), 7.06 (d, 2H, J = 8.00
Hz, Ar), 5.78 (s, 2H, benzylic), 4.14 (q, 2H, –OCH2CH3),
1.02 (t, 3H, –OCH2CH3); 13C NMR (100 MHz, CDCl3): δ
= 170.87 (C=O of thiazolidinedione ring), 168.30 (C=O of
thiazolidinedione ring), 162.34 (C=O of ester), 144.67,
138.56, 136.96, 136.91, 136.84, 136.02, 133.33, 132.30,
129.01 (2C), 128.77, 128.62, 128.00 (2C), 126.96,
126.30, 124.72, 124.06, 121.79, 121.61, 110.89, 105.37,
60.99 (COOCH2CH3), 48.58 (N–CH2–C6H5), 13.86
(COOCH2CH3); ESI-MS (m/z): 517.14 [M + 1]+; anal.
calcd. (%) for C28H21ClN2O4S: C, 65.05; H, 4.09; N, 5.42.
Found: C, 66.99; H, 4.54; N, 5.95.
124.91, 123.78, 121.64, 121.46, 111.07, 105.29, 61.00
(COOCH2CH3), 48.50 (N-CH2-C6H4Cl), 13.83 (COOCH2
CH3); ESI-MS (m/z): 556 [M + Na]+; anal. calcd. (%) for
C28H21ClN2O3S2: C, 63.09; H, 3.97; N, 5.26. Found: C,
63.35; H, 3.46; N, 5.48.
General procedure for the synthesis of target compounds
(6a/b) and (7a/b)
A mixture of (3a/3b) (0.54 mmol), Diethylmalonate (DEM)
(0.54 mmol) or methyl acetoacetate (0.56 mmol) and cata-
lytic amount of piperidinium acetate in toluene (25 mL)
were refluxed for 12 h with continuous removal of water
using a Dean-Stark water separator. After cooling to room
temperature, the solution was concentrated to crude reaction
mixture, which was purified by column chromatography
using ethyl acetate/hexane (1:9) as eluent to afford the title
compounds (6a/b) or (7a/b).
Ethyl 1-benzyl-3-{4-[3-ethoxy-2-(ethoxycarbonyl)-3-oxo-
Ethyl 1-benzyl-3-{4-[(4-oxo-2-thioxo-1,3-thiazolidin-5-yli-
dene)methyl]phenyl}-1H-indole-2-carboxylate (5a) Pro-
duct was obtained as pale yellow solid (81% yield); mp:
180–185 °C; FTIR (KBr, cm−1) νmax: 3437 (N–H), 1701
(C=O), 1496–1417 (Ar C=C), 1216 (C–N), 1177 (C=S),
prop-1-enyl]phenyl}-1H-indole-2-carboxylate (6a) Pro-
duct was obtained as oil (76% yield); FTIR (KBr, cm−1
)
νmax: 3063 (Ar C–H), 1711 (C=O), 1607–1454 (Ar C=C),
1
1367 (C–N), 1262–1178 (C–O–C); H NMR (400 MHz,
1
CDCl3): δ = 7.73 (s, 1H, benzylidene), 7.50 (m, 3H, Ar),
7.43 (m, 2H, Ar), 7.33 (m, 1H, Ar), 7.29 (m, 1H, Ar), 7.22
(m, 2H, Ar), 7.16 (m, 1H, Ar), 7.11 (m, 1H, Ar), 7.04 (m,
2H, Ar), 5.75 (s, 2H, benzylic), 4.33 (two overlapping
quartets, 4H, –OCH2CH3 of DEM), 4.06 (q, 2H,
–OCH2CH3), 1.30 (two overlapping triplets, 6H,
–OCH2CH3 of DEM), 0.92 (t, 3H, –OCH2CH3); 13C NMR
(100 MHz, CDCl3): δ = 166.92 (C=O of ester), 164.41
(C=O of ester), 162.58 (C=O of ester), 142.25, 138.57,
138.27, 136.88, 136.38, 136.06, 132.31, 128.86 (2C),
128.73, 128.42, 127.47, 126.83, 126.52 (2C), 126.07,
124.90, 123.78, 121.58, 121.39, 111.02, 110.36, 61.92
(COOCH2CH3), 61.80 (COOCH2CH3), 60.96 (COOCH2
CH3), 48.47 (N–CH2–C6H5), 14.34 (2x COOCH2CH3),
14.23 (COOCH2CH3); ESI-MS (m/z): 526.21 [M + 1]+,
548.13 [M + Na]+; anal. calcd. (%) for C32H31NO6: C,
73.13; H, 5.94; N, 2.66. Found: C, 72.23; H, 4.92; N, 2.26.
746 (C–S); H NMR (400 MHz, CDCl3): δ = 7.89 (s, 1H,
benzylidene), 7.59 (m, 3H, Ar), 7.43 (m, 3H, Ar), 7.30 (m,
5H, Ar), 7.18 (m, 2H, Ar), 5.83 (s, 2H, benzylic), 4.16 (q,
2H, –OCH2CH3), 1.01 (t, 3H, –OCH2CH3); 13C NMR (100
MHz, CDCl3): δ = 192.68 (C=S of rhodanine ring), 168.37
(C=O of rhodanine ring), 162.24 (C=O of ester), 144.70,
138.69, 138.40, 136.99, 136.46, 136.24, 132.43, 128.98
(2C), 128.86, 128.52, 127.62, 126.92, 126.65 (2C), 126.20,
124.79, 123.88, 121.71, 121.53, 111.20, 105.31, 61.09
(COOCH2CH3),
48.61
(N–CH2–C6H5),
13.94
(COOCH2CH3); ESI-MS (m/z): 521 [M + Na]+; anal.
calcd. (%) for C28H22N2O3S2: C, 67.45; H, 4.45; N, 5.62.
Found: C, 67.12; H, 5.13; N, 5.33.
Ethyl 1-(4-chlorobenzyl)-3-{4-[(4-oxo-2-thioxo-1,3-thiazo-
lidin-5-ylidene)methyl]phenyl}-1H-indole-2-carboxylate
(5b) Product was obtained as pale yellow solid (83%
yield); mp: 165–168 °C; FTIR (KBr, cm−1) νmax: 3435
(N–H), 1700 (C=O), 1491–1417 (Ar C=C), 1215 (C–N),
Ethyl 1-(4-chlorobenzyl)-3-{4-[3-ethoxy-2-(ethoxycarbo-
nyl)-3-oxoprop-1-enyl]phenyl}-1H-indole-2-carboxylate
(6b) Product was obtained as oil (74% yield); FTIR (KBr,
cm−1) νmax: 3053 (Ar C–H), 2982 (–OCH2CH3, C–H),
2918 (–OCH2CH3, C–H), 1727–1704 (C=O), 1607–1492
(Ar C=C), 1260–1177 (C–O–C), 801 (C–Cl); 1H NMR
(400 MHz, CDCl3): δ = 7.80 (s, 1H, benzylidene), 7.57 (m,
3H, Ar), 7.49 (m, 2H, Ar), 7.36 (d, 2H, J = 3.72 Hz, Ar),
7.25 (m, 2H, Ar), 7.19 (m, 1H, Ar), 7.06 (d, 2H, J = 8.40
Hz, Ar), 5.78 (s, 2H, benzylic), 4.41 (two overlapping
1
1175 (C=S), 798 (C–S), 851 (C–Cl); H NMR (400 MHz,
CDCl3): δ = 7.88 (s, 1H, benzylidene), 7.63 (3H, s, Ar),
7.55 (2H, m, Ar), 7.37 (2H, m, Ar), 7.24 (2H, m, Ar), 7.18
(m, Ar), 7.07 (m, 2H, Ar), 5.78 (s, 2H, benzylic), 4,15 (q,
2H, –OCH2CH3), 1.01 (t, 3H, –OCH2CH3); 13C NMR (100
MHz, CDCl3): δ = 192.35 (C=S of rhodanine ring), 168.28
(C=O of rhodanine ring), 162.30 (C=O of ester), 144.57,
138.59, 138.32, 136.92, 136.38, 136.15, 132.29, 128.87
(2C), 128.74, 128.42, 127.50, 126.85, 126.56 (2C), 126.11,

Med Chem Res
quartet, 4H, –OCH2CH3 of DEM), 4.13 (q, 2H, –OCH2
CH3), 1.37 (two overlapping triplets, 6H, –OCH2CH3 of
DEM), 0.99 (t, 3H, –OCH2CH3); 13C NMR (100 MHz,
CDCl3): δ = 170.86 (C=O of thiazolidinedione ring),
168.20 (C=O of thiazolidinedione ring), 162.20 (C=O of
ester), 144.53, 138.41, 136.77, 136.74, 136.70, 135.88,
133.16, 132.14, 128.93 (2C), 128.65, 128.46, 127.90 (2C),
126.82, 126.19, 124.61, 124.00, 121.65, 121.48, 110.75,
110.31, 61.85 (COOCH2CH3), 61.78 (COOCH2CH3),
60.88 (COOCH2CH3), 48.43 (N–CH2–C6H4Cl), 14.26 (2x
COOCH2CH3), 14.21 (COOCH2CH3); ESI-MS (m/z):
560.28 [M]+, 583.23 [M + Na]+; anal. calcd. (%) for
C32H30ClNO6: C, 68.63; H, 5.40; N, 2.50. Found: C, 68.12;
H, 5.80; N, 2.05.
δ = 207.99 and 207.86 (C=O of COCH3), 168.96 and
168.79 (C=O of COOCH3), 158.90 and 158.75 (C=O of
ester), 140.27 and 140.05, 138.21 and 138.07, 136.71 and
136.60, 136.55 and 136.50, 136.44 and 136.31, 135.69 and
135.56, 133.14 and 133.00, 132.09 and 131.94, 128.91 and
128.77 (2C), 128.61 and 128.47, 128.43 and 128.24, 127.84
(2C), 126.75, 126.11, 124.54, 123.92, 121.60, 121.44 and
121.30, 110.72 and 110.57, 110.24 and 110.11, 61.98 and
61.58 (COOCH2CH3), 57.45 and 54.41 (COOCH3), 48.36
and 48.11 (N–CH2–C6H4Cl), 29.87 and 29.72 (COCH3),
14.30 and 14.03 (COOCH2CH3); ESI-MS (m/z): 516 [M +
1]+, 538 [M + Na]+; anal. calcd. (%) for C30H26ClNO5: C,
69.83; H, 5.08; N, 2.71. Found: C, 68.23; H, 5.14; N, 3.18.
Molecular docking methods
Ethyl 1-benzyl-3-{4-[2-(methoxycarbonyl)-3-oxobut-1-en-
1-yl]phenyl}-1H-indole-2-carboxylate (7a) Product was
obtained as oil (69% yield); FTIR (KBr, cm−1) νmax: 2954
(Ar C–H), 1703 (C=O), 1541–1454 (Ar C=C), 1246–1175
The crystal structure of C-terminal domain of human intest-
inal α-glucosidase (PDB code: 3TOP) was used as molecular
target. The crystal structure complexed with an original
ligand (Acarbose) was downloaded from RCSB Protein Data
Bank. Water molecules were removed from enzyme structure
whereas, hydrogens added, energy minimized using
Gasteiger–Huckel charges and Tripos force field in the Sybyl
software suite (Sybyl 2006, Verma et al. 2012a, b, 2013a, b,
c, 2015 and Mall et al. 2017). Synthesized compounds were
assigned Gasteiger–Huckel charges and subsequently mini-
mized using the Powel method by using SYBYL 7.3 soft-
ware. The energy-optimized sketched compound were
subjected to docking run at the ligand binding site of α-
glucosidase by Surflex dock in SYBYL7.3. Docking analysis
was conducted using the Surflexdock module to predict and
examine the binding modes of the synthesized derivatives at
the active site of α-glucosidase. The hydrogen bonding
interactions (amino acid residues and bond distances) of the
synthesized molecules at the respective active sites were also
compared to those of standard inhibitor Acarbose (Fig. 2).
1
(C–O–C); H NMR (400 MHz, CDCl3): δ = 7.76 and 7.64
(two singlets, 1H, benzylidene), 7.56 (m, 1H, Ar), 7.51 (m,
2H, Ar), 7.49 (m, 2H, Ar), 7.41 (m, 1H, Ar), 7.36 (m, 1H,
Ar), 7.29 (m, 2H, Ar), 7.23 (m, 1H, Ar), 7.18 (m, 1H, Ar),
7.11 (m, 2H, Ar), 5.82 (s, 2H, benzylic), 4.14 (q, 2H,
–OCH2CH3), 3.89 (d, 3H, –OCH3), 2.45 (d, 3H, COCH3),
1.00 (overlapping triplets, 3H, –OCH2CH3); 13C NMR
(100 MHz, CDCl3, mixture of E and Z isomers): δ = 208.16
and 208.02 (C=O of COCH3), 169.28 and 169.16 (C=O of
COOCH3), 159.39 and 159.27 (C=O of ester), 140.96 and
140.80, 138.47 and 138.30, 138.19 and 138.06, 136.78 and
136.66, 136.27 and 136.09, 136.02 and 135.90, 132.17 and
132.02, 128.76 and 128.63 (2C), 128.62 and 128.50, 128.31
and 128.18, 127.38 and 127.26, 126.72 and 126.58, 126.42
and 126.28 (2C), 125.96 and 125.80, 124.81 and 124.68,
123.67 and 123.50, 121.49 and 121.36, 121.29 and 121.15,
110.98 and 110.85, 110.26 and 110.11, 62.27 and 62.10
(COOCH2CH3), 57.75 and 54.59 (COOCH3), 48.38 and
48.25 (N–CH2–C6H5), 30.14 and 29.99 (COCH3), 14.23
and 14.09 (COOCH2CH3); ESI-MS (m/z): 482 [M + 1]+,
504 [M + Na]+; anal. calcd. (%) for C30H27NO5: C, 74.83;
H, 5.65; N, 2.91. Found: C, 74.25; H, 6.05; N, 2.53.
In vitro enzymatic starch digestion assay
For in vitro enzymatic starch digestion method of Granfeldt
et al. (1992) was followed with some modifications. Hun-
dred milligram corn starch was put and gelatinized in 3 mL
distilled water with or without test compound or Acarbose.
To this solution 4 µg α-amylase was put, vortexed and the
mixture was incubated for 20 min at 80 °C. Then, 3 mL
mixture was diluted to 10 mL with distilled water. Then 1
mL of this solution was taken and added to 2 mL of 0.1 M
sodium acetate buffer (pH 4.75). To this 3 mL mixture, 30
µg of α-amyloglucosidase was added and the mixture was
incubated for 30 min at 60 °C. Samples were removed to ice
to inhibit the thermophilic enzymes. Control samples were
having neither Acarbose nor test compound. The inhibitory
Ethyl
1-(4-chlorobenzyl)-3-{4-[2-(methoxycarbonyl)-3-
oxobut-1-en-1-yl]phenyl}-1H-indole-2-carboxylate (7b)
Product was obtained as oil (70% yield); FTIR (KBr, cm−1
)
νmax: 2953 (Ar C–H), 1703 (C=O), 1546–1457 (Ar C=C),
1247–1176 (C–O–C), 825 (C–Cl); 1H NMR (400 MHz,
CDCl3): δ = 7.76 and 7.65 (two singlets, 1H, benzylidene),
7.55 (m, 1H, Ar), 7.51 (m, 3H, Ar), 7.37 (m, 2H, Ar), 7.26
(m, 3H, Ar), 7.20 (m, 1H, Ar), 7.06 (m, 2H, Ar), 5.78 (s,
2H, benzylic), 4.12 (q, 2H, –OCH2CH3), 3.89 (d, 3H,
–OCH3), 2.46 (d, 3H, –COCH3), 1.00 (dt, 3H, –OCH2CH3);
13C NMR (100 MHz, CDCl3, mixture of E and Z isomers):

Med Chem Res
Fig. 2 Molecular interactions of
standard inhibitor Acarbose and
indole derivatives in the active
site of α-glucosidase through
hydrogen bonding with potent
amino acid residues a Acarbose,
b compound 4a, c compound
4b, d compound 5a, e
compound 5b, f compound 6a, g
compound 6b, h compound 7a
rate of test compound on enzymatic starch digestion was
calculated by the following equation
where Ao is the absorbance of control sample, Ai is the
absorbance given by test compound.
EC50 value (µM) was defined as the amount of test
compound reducing the breakdown of starch to glucose by
ð%Þ inhibition of enzymatic starch digestion ¼ ½Ao À Ai=AoŠ  100;

Med Chem Res
50% in comparison to the control sample. It was determined
by the plotting the graph between percentage inhibition of
starch digestion verse various concentrations of test
compounds.
440 (100) in the mass spectrum further confirmed the
structure.
All the targeted benzylidene-based new chemical entities
(NCEs) were prepared in fairly good yields through
‘Knoevenagel Condensation’ of the thiazolidinediones
(TZD) or rhodanine (RHD) or diethyl malonate (DEM) or
methyl acetoacetate (MAA) based hydrogen bonding parts
with the appropriate heterocyclyl linked benzaldehydes 3a
and 3b as per synthetic (Scheme 2) while using piper-
idinium acetate/toluene as base under reflux conditions.
The appearance of the bands corresponding to the N–H
and C–S stretch of the thiazolidinedione moiety present in
these molecules at 3459, 3463 cm−1 and at 696, 741 cm−1
along with the two carbonyls of the thiazolidinedione
appearing at 1742, 1701 cm−1 and at 1741, 1699 cm−1
respectively in the IR spectrum of 4a and 4b confirm
their structure. The presence of benzylidene-based proton
present in these molecules was also confirmed from the
appearance of a 1H singlet at 7.88, 7.92 ppm respectively
in the NMR spectrum. The presence of [M + 1]+ peak at
m/z 483 (100), m/z 517 (100) in the mass spectrum
provide additional support to the structure assigned to these
molecules.
Results and discussion
Chemistry
The direct linked N-benzylindol-2-yl based 4-substituted
benzaldehydes (3a/3b) were synthesized by Suzuki cou-
pling of (2a/2b) with 4-formylphenylboronic acid
(Scheme 1). The (2a/2b) required in this strategy was pre-
pared by N-benzylation of ethyl 3-bromo-1H-indole-2-car-
boxylate (1) while using benzyl bromide and 4-chloro
benzyl bromide respectively in the presence of sodium
hydride taken in dry DMF as shown in (Scheme 1).
The presence of two weak bands representing the cou-
pled doublet characteristic of aldehydic C–H stretch at 2851
and 2734 cm−1 along with C=O stretch at 1699 cm−1 for
esteric and aldehydic carbonyl in the infrared (IR) spectrum
of this molecule confirm the structure assigned to 3a. Fur-
ther support to this structure assigned is indicated by the
presence of a 1H singlet for the aldehydic proton at 10.02
ppm in the 1H NMR spectrum along with a peak at m/z 383
[M]+ in the mass spectrum.
The C=O stretch at 1701, 1700 cm−1 and the bands
corresponding to the N–H and C–S stretch of the rhodanine
moiety present in the molecules at 3437, 3435 cm−1 and at
746, 798 cm−1 along with C=S stretching at 1177, 1175
cm−1 respectively in the IR spectrum of 5a and 5b confirm
their structure. Moreover, the appearance of a 1H singlet in
the NMR spectrum at 7.89, 7.88 ppm, respectively con-
firmed the benzylidene based proton. Further the structures
were also confirmed by the presence of [M + Na]+ peak at
m/z 521 (100), m/z 556 (100) in the mass spectrum.
The aldehydic C–H stretch at 2831 and 2735 cm−1 along
with C=O stretch at 1701 cm−1 for esteric and aldehydic
carbonyl and C–Cl stretch at 834 cm−1 in the IR spectrum
of this molecule confirm the structure assigned to 3b. The
presence of 1H singlet at 10.09 ppm for the aldehydic
proton in the 1H NMR spectrum and [M + Na]+ peak at m/z
CHO
CHO
Br
O
H
Br
Br
B
O
X
H
COOEt
COOEt
COOEt
b
c
N
N
N
H
1
X
X
2a/b
3a/b
a
compound
X
2a
2b
3a
3b
H
Cl
H
COOEt
N
H
Cl
Scheme 1 Reagents and conditions: a NBS, dry DMF b K2CO3, dry DMF c Pd(PPh3)4, dioxane:water

Med Chem Res
O
Scheme 2 Reagent and
conditions: a piperidinium
acetate, toluene
S
N
H
S
O
O
N
H
O
COOEt
N
X
4a/b
S
S
N
H
O
S
S
N
H
O
COOEt
N
CHO
X
5a/b
a
C
COOEt
H
3
O
N
O
X
3a/b
O
C
H
3
O
O
O
CH
CH
3
3
O
O
compound
X
H
Cl
H
3a
3b
4a
4b
5a
5b
6a
6b
7a
7b
COOEt
N
X
6a/b
Cl
H
O
O
Cl
H
C
H3
C
H3
O
Cl
H
O
O
O
C
H
3
C
H
Cl
3
COOEt
N
X
7a/b
The formation of 6a and 6b were confirmed by the bands
corresponding to the ester carbonyl C=O stretch at 1711,
1704 cm−1 in the IR spectrum along with the presence of
benzylidene-based proton as 1H singlet at 7.73, 7.80 ppm,
respectively along with the presence of a 4H (2H each)
overlapping quartets at 4.33, 4.41 ppm and one 6H

Med Chem Res
overlapping triplet at 1.30, 1.37 ppm, respectively in the
NMR spectrum for the diethyl malonate-based structural
units present in these molecules. The presence of [M +
Na]+ peak at m/z 548(100), m/z 583(100) in the mass
spectrum provided additional support to the structure
assigned.
7.76–7.65 ppm for the benzylidene proton; two 3H doublet
signals for methyl ester at δ (ppm) 3.89–2.45, 3.89–2.46
along with signals for the protons of the acyl groups and
aromatic protons at their expected positions. The structures
were also confirmed from the presence of [M + Na]+ peak
at m/z 504(100) and 538(100) in the mass spectrum.
The C=O stretch was recorded at 1703, 1703 cm−1 and
other bands near their expected positions in the IR spectra
of 7a and 7b. Characteristic bands for the functional groups
were found near to their expected positions in the IR
spectrum. The NMR strongly indicated the formation of
products as mixture of two geometric isomers as the
appearance of two 1H singlet signals at 7.76–7.64,
Molecular docking studies
The docking results in terms of Gold score energies (G
score) and H-bond interactions of the studied compounds
with protein (PDB code: 3TOP) were given in (Table 1).
The docking interactions for the selected ligands 4a, 4b, 5a,
Table 1 Docking results of the
Compound G score
H-bonding interactions between the ligands and the active site amino acid (AA)
residues
synthesized targeted compounds
as compared to acarbose
(standard drug) at the active site
of α-glucosidase
Atoms of ligandsa
AA residues Bond distance (Å) No. of H-bonds
Acarbose
−160.51 O–H
ASP1279
HIS1584
ASP1526
ASP1526
ARG1510
ARG1510
ARG1510
ASP1157
ASP1157
ASP1157
LYS1460
1.99
1.95
2.65
1.85
2.41
2.63
2.08
1.91
1.85
2.75
2.59
2.05
2.23
1.91
2.16
2.31
1.87
2.48
2.69
2.74
2.18
2.03
2.61
2.20
2.58
2.65
1.96
1.93
1.95
2.02
2.02
–
11
O–H
O–H
O–H
O–H
O–H
O–H
O–H
O–H
O–H
O–H
4a
4b
−220.32 O=C–OC2H5 of indole THR1586
3
3
4-C=O of TZD
N–H of TZD
LYS1460
ASP1157
GLN1158
LYS1460
ARG1156
ASP1157
ARG1510
ARG1510
−242.9
4-C=O of TZD
4-C=O of TZD
4-C=O of TZD
5a
5b
−255.41 N–H of Rh
−241.42 C=O of RH
C=O of RH
1
3
O=C–OC2H5 of indole LYS1460
6a
−140.53 O=C–OC2H5
LYS1460
GLN1158
LYS1164
LYS1164
GLN1158
5
3
O=C–OC2H5
O=C–OC2H5
O=C–OC2H5
O=C–OC2H5
6b
7a
−199.3
O=C–OC2H5 of indole LYS1460
O=C–OC2H5
O=C–OC2H5
LYS1164
LYS1164
−158.00 O=C–OC2H5 of indole TRP1369
2
O=C–CH3
LYS1460
7b
−142.69
–
–
–
a
The particular atom involved in hydrogen bond formation has been indicated by bold face

Med Chem Res
5b, 6a, and 6b in comparison to acarbose (standard drug)
were illustrated in (Fig. 2). All the final synthesized com-
pounds (4a–7b) were docked (with Surflex dock module of
Sybyl 7.3, Tripose Inc. software available at our in silico
drug design Laboratory) at the binding site of C-terminal
domain of human intestinal α-glucosidase (PDB Code:
3TOP) for the prediction of binding affinities in reference to
standard molecule (acarbose). It was found from the ana-
lysis of docking results that the binding affinity of Acarbose
in term of G-score is −160.51 and it binds through
hydrogen bonds formation with ASP1526, ASP1279,
ASP1157, HIS1584, ARG1510, and LYS1460 amino acid
residues. The comparison of the predicted binding affinities
in terms of G score of the synthesized ligands with that of
Acarbose (the standard ligand in this study) showed that all
RHD and TZD-based compounds 4a (−220.32), 4b
(−242.90), 5a (−255.41) and 5b (−241.42) have higher
binding affinities than that of acarbose (−160.51) (Table 1)
which is expected as RHD and TZD derivatives are known
to possess antidiabetic activities. Furthermore out of these
TZD and RHD-based compounds, RHD linked compounds
have higher binding affinities which is also in accordance
with biological activity studies. The DEM-based compound
6a (−140.53) exhibited lesser binding affinity while com-
pound 6b (−199.30) have higher binding affinity than that
of acarbose (−160.51). The MAA-based compounds 7a
(−158.00) and 7b (−142.69) showed comparable binding
affinities to that of acarbose (−160.51). Docking analysis
showed that mostly 4-chlorobenzyl N-substituted com-
pounds 4b (−242.90), 5b (−241.42), and 6b (−199.30)
showed higher binding affinity in comparison to their
benzyl N-substituted compounds 4a (−220.32), 5a
(−255.41), and 6a (−140.53) except in case of methyla-
cetoacetate based compounds (7a–b). The hydrogen bond
interactions between the synthesized ligands and the AA
residues in the active sites of 3TOP were explored and
compared with those of Acarbose to explain the binding
modes and binding affinities of the ligands. The hydrogen
bonds for each of the novel ligands are less in number
compared to acarbose (eleven hydrogen bonds) at the active
site. The interacting AA residues were all similar to that of
acarbose, as the new ligands occupy a same region in the
binding cavity (Fig. 2). The H-bond distances (Å) between
the ligands and the interacting AA residues are in range and
in most of the cases are shorter than those of Acarbose.
Generally, the acidic units of the ligands are involved in
hydrogen bond formation in all the cases. The TZD-based
compounds 4a and 4b interacts with important AA residues
(THR1586, LYS1460 and GLN1158, LYS1460 and
ARG1156, respectively) through carbonyl group and NH of
TZD. The RHD based compounds 5a and 5b form H-bonds
with ASP1157, ARG1510, and LYS1460. The DEM-based
compounds 6a and 6b interacts with important AA residue
LYS1460, LYS 1164, and GLN1158 through oxygen of
ethoxy. Compound 7a used carbonyl group of methyl
acetoacetate for H-bonding with LYS1460. The results for
the hydrogen bond interactions also support the G score
values. The results of molecular docking studies are found
to be in accordance with in vitro studies and hence, sup-
ported the biological activity.
In vitro studies
All the eight newly synthesized targeted compounds (4a–b,
5a–b, 6a–b, and 7a–b) were evaluated for their in vitro α-
amylase and α-glucosidase inhibitory activity using acar-
bose as positive control (IC50 value of 11.4 0.70 µM)
(Table 2). The compounds (4a, 4b, 5a, 5b, and 6b) were
more inhibitive to these enzymes than the rest of the tested
compounds with IC50 values of much lower than that of the
positive control (standard drug acarbose). It was revealed
from the biological activity studies that presence of chlorine
(an electron withdrawing group) and H-bonding part (such
as RHD, TZD, DEM, and MAA), both play an effective
role in this assay. It has been seen from biological activity
results that N-4-chlorobenzylindolyl-based compounds have
better inhibitory effect than there corresponding N-benzy-
lindolyl-based compounds. It has also been concluded from
biological results that RHD and TZD based compounds 5a
(IC50 0.91 0.01 µM), 5b (IC50 0.51 0.01 µM), 4a (IC50
5.30 0.38 µM), and 4b (IC50 3.67 0.19 µM) have better
inhibition than standard drug (IC50 11.4 0.70 µM). Further
out of these compounds, compounds 5b and 4b with elec-
tron withdrawing atom Chlorine on benzyl have more
inhibition potential than corresponding compounds 5a and
4a without chlorine on benzyl respectively. DEM-based
compound 6b (IC50 9.3 0.66 µM) has good inhibition
potential while compound 6a (IC50 21.4 1.20 µM) has
lesser inhibition potential in comparison to standard drug
(IC50 11.4 0.70 µM). MAA-based compound 7a (11.8
0.61 µM) showed comparable while 7b (IC50 19.6 0.77
Table 2 α-Glucosidase inhibitory activity of the synthesized
compounds
Compound
IC50 (µM)
4a
5.30 0.38
3.67 0.19
0.91 0.01
0.51 0.01
21.4 1.20
9.3 0.66
4b
5a
5b
6a
6b
7a
11.8 0.61
19.6 0.77
11.4 0.70
7b
Acarbose

Med Chem Res
µM) showed much lesser inhibition potential than standard
drug (IC50 11.4 0.70 µM) because of less number of
electronegative atom in MAA moiety than in DEM, RHD,
and TZD moiety. The binding interactions of promising
compounds 4a, 4b, 5a, 5b, 6a, and 6b were proved by using
molecular docking studies. Molecular docking studies in
terms of G score values and binding interaction of novel
targeted compounds in comparison to standard drug (acar-
bose) in active site of enzyme has also supported the bio-
logical activity studies. Overall a significant correlation was
found between the docking studies and α-glucosidase
inhibition of active compounds by displaying a good cor-
relation coefficient (r2 = 0.900) between G score and IC50
values. The correlation curve and the value of correlation
coefficient are given in (Fig. 3).
The structure–activity relationship of these compounds
has been established. The results suggested that the thia-
zolidine-2,4-dione or rhodanine group located at the 4-
position of the phenyl ring resulted in the best activity
(4a–b and 5a–b). Replacement of the TZD/RHD group
(4a–b, 5a–b) with DEM and MAA group (6a–b and 7a–b)
which are acyclic analogs of isoxazolidinediones i.e., fur-
ther a cyclic analog of thiazolidinedione, decreased the
activity drastically. The results demonstrated that H-
bonding part and presence of chlorine (an electron with-
drawing group), both play a key role in the activity of these
compounds. Introduction of an electron-withdrawing group
such as Cl (4b, 5b) into the 4-position of the benzyl ring
results in an increase in the inhibitory activity. It has also
been concluded that N-4-chlorobenzylindolyl based com-
pounds have better results than there corresponding N-
benzylindolyl based compounds. In summary, the obtained
structure–activity relationship information is useful in future
structural optimization. The binding interactions of the most
active molecules with the active site of α-glucosidase were
confirmed through molecular docking studies.
Conclusions
A novel series of compounds (4a–7b) were synthesized and
evaluated for their inhibitory action against α-amylase and
α-amyloglucosidase. Comparative evaluation of these
compounds revealed that the compound 5b showed max-
imum inhibitory potential against α-amylase and α-gluco-
sidase giving an IC50 of 0.51 0.01 µM. The compounds
(4a, 4b, 5a, 5b, and 6b) were stronger inhibitors against the
enzyme than the rest of the tested compounds with IC50
values of much lower than that of the positive control
(acarbose, standard drug). The results of molecular docking
studies have also supported the in vitro studies.
Acknowledgements The authors are thankful to the Punjabi Uni-
versity, Patiala authorities for providing the necessary research facil-
ities. We are also grateful to Director and Mr. Avtar Singh of
Sophisticated Analytical Instrumentation Facility (SAIF), Panjab
University, Chandigarh, respectively, for extending the facilities for
spectral analysis of the compounds reported in this paper.
Compliance with ethical standards
Conflict of interest The authors declare that they have no competing
interests.
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