Synthesis and biological evaluation of novel 2,4,5-triarylimidazole–1,2,3-triazole derivatives via click chemistry as α-glucosidase inhibitors

Article abstract of DOI:10.1016/j.bmcl.2016.10.057

A novel series of 2,4,5-triarylimidazole–1,2,3-triazole derivatives were synthesized via copper(I)-catalyzed azide–alkyne click chemistry, and evaluated for their α-glucosidase inhibitory activity. All tested compounds showed potent α-glucosidase inhibitory activity with IC₅₀ranging from 15.16 ± 0.18 to 48.15 ± 0.37 μM, in comparison to the standard drug, acarbose (IC₅₀= 817.38 ± 6.27 μM). Among all the tested compounds, 5j was found to be the most active compound with IC₅₀value of 15.16 ± 0.18 μM and behaved as a noncompetitive inhibitor with a K_iof 14.78 μM. In addition, molecular docking study was carried out to explore the binding interactions of these compounds with α-glucosidase enzyme.

Full text of DOI:10.1016/j.bmcl.2016.10.057

Accepted Manuscript
Synthesis and biological evaluation of novel 2,4,5-triarylimidazole-1,2,3-tria-
zole derivatives via click chemistry as α-glucosidase inhibitors
Guangcheng Wang, Zhiyun Peng, Jing Wang, Juan Li, Xin Li
PII:
S0960-894X(16)31095-2
DOI:
http://dx.doi.org/10.1016/j.bmcl.2016.10.057
BMCL 24360
Reference:
Bioorganic & Medicinal Chemistry Letters
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Received Date:
Revised Date:
Accepted Date:
10 June 2016
14 October 2016
20 October 2016
Please cite this article as: Wang, G., Peng, Z., Wang, J., Li, J., Li, X., Synthesis and biological evaluation of novel
2,4,5-triarylimidazole-1,2,3-triazole derivatives via click chemistry as α-glucosidase inhibitors, Bioorganic &
Medicinal Chemistry Letters (2016), doi: http://dx.doi.org/10.1016/j.bmcl.2016.10.057
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Synthesis and biological evaluation of novel
2,4,5-triarylimidazole-1,2,3-triazole derivatives via
click chemistry as α-glucosidase inhibitors
Guangcheng Wang*, Zhiyun Peng, Jing Wang, Juan Li, Xin Li
College of Chemistry and Chemical Engineering, Jishou University, Jishou 416000,
PR China
*Corresponding Author
Tel.: +86 743 8563911
Fax: +86 743 8563911
E-mail address: wanggch123@163.com
1

Abstract.
A novel series of 2,4,5-triarylimidazole-1,2,3-triazole derivatives were synthesized via
copper(I)-catalyzed azide-alkyne click chemistry, and evaluated for their
α-glucosidase inhibitory activity. All tested compounds showed potent α-glucosidase
inhibitory activity with IC50 ranging from 15.16±0.18 to 48.15±0.37 μM, in
comparison to the standard drug, acarbose (IC50 = 817.38±6.27 μM). Among all the
tested compounds, 5j was found to be the most active compound with IC50 value of
15.16±0.18 μM and behaved as a noncompetitive inhibitor with a Ki of 14.78 μM. In
addition, molecular docking study was carried out to explore the binding interactions
of these compounds with α-glucosidase enzyme.
Keywords: 2,4,5-Triarylimidazole; 1,2,3-Triazole; Click chemistry; α-Glucosidase
inhibitor; Enzyme kinetic study; Molecular docking
2

α-Glucosidases (EC 3.2.1.20) are a family of enzymes, which play an important role
in the digestion of carbohydrates in the body.1 Inhibition of the activity of
α-glucosidase could reduce postprandial plasma glucose levels and suppression of
postprandial hyperglycemia, and thus α-glucosidase has been considered as an
important target for the treatment type II diabetes.2, 3 Furthermore, α-glucosidase has
been recognized as a therapeutic target for other carbohydrate mediated diseases
including cancer,4 hepatitis5 and HIV.6, 7 Currently, there are three α-glucosidase
inhibitors (acarbose, voglibose and miglitol) have been approved for clinical use.
Hence, the search of novel molecules with potent α-glucosidase inhibitory activity is
still in progress.
In recent years, imidazole and its derivatives have attracted much attention for their
9
versatile properties in chemistry and pharmacology.8,
Imidazole-containing
compounds have been reported to exhibit a variety of biological activities such as
antitumor,10 antibacterial,11 antihypertensive,12 antimicrobial,13 and antitubercular
properties.14 Moreover, some imidazole derivatives have been identified to possess
α-glucosidase inhibitory activity (Figure 1).15-18
Over the last decade, 1,2,3-triazoles have received increasing attention in the drug
discovery field since the "click chemistry" concept was introduced by Sharpless.19-23
Several compounds possessing the 1,2,3-triazole ring display broad spectrum of
biological properties such as antibacterial,24 antimalarial,25 anticancer,26 anti-HIV27
and antitubercular activities.28 Furthermore, Ferreira et al reported the synthesis of a
3

series of 4-substituted 1,2,3-triazoles conjugated with sugars and the most active
compounds showing up to 25-fold higher inhibitory potency than standard acarbose.29
Particularly, Jabeen et al have recently reported that 1,4-disubstituted-1,2,3-triazoles
showed promising activity against α-glucosidase (Figure 1).30
Figure 1. Chemical structures of some α-glucosidase inhibitors containing imidazole
or 1,2,3-triazole rings.
Over the last few years, the molecular hybridization approach has received
considerable attention in discovery of new biological agents which containing two or
more bioactive pharmacophores.31, 32 Based on these things mentioned above, and in
continuation of our interest in the synthesis of biologically active heterocyclic
compounds, herein we reported the synthesis of
a
novel series of
2,4,5-triarylimidazole-1,2,3-triazole derivatives by the copper(I)-catalyzed
azide-alkyne click chemistry and evaluated for their α-glucosidase inhibitory activity.
Furthermore, molecular docking was also performed to understand the interaction
modes of these compounds with the active site of α-glucosidase.
4

The synthetic pathway to achieve the title compounds 5a-5r is shown in Scheme 1.
Condensation of benzil with appropriate aromatic aldehydes in the presence of
NH4OAc/AcOH to afford the corresponding 2,4,5-triarylimidazoles (2a-2k) in high
yields. Treatment of 2a-2k with 3-bromo-1-propyne and K2CO3 in anhydrous DMF to
give compounds 3a-3k. Finally, according to Huisgen 1,3-dipolar cycloaddition
reaction (click reaction),19 intermediate 3a-3k was reacted with substituted
2-azido-N-phenylacetamide 4a-4j, sodium ascorbate and CuSO4·5H2O in DMF at
room temperature to afford the target compounds 5a-5r. Structures of the title
1
compounds were elucidated by spectral data. For instance, the H NMR spectrum of
5a shown two singlets at δ 1.91 and 2.19 ppm due to CH3 proton of the phenyl ring.
The methylene protons of –CH2– and –CH2–CO– appeared as two singlets at δ 4.89
and 5.00 ppm. Eighteen aromatic hydrogen atoms were appeared as multiplet signals
at 7.06-7.44 ppm. The single peak of NH proton of –CO–NH– was observed at 7.74
ppm. The total number of protons matched perfectly with its structure. Moreover, in
13
their C NMR spectra, the number of signals equals the number of different carbons
in the molecule.
5

Scheme 1. Reagents and conditions: (a) ammonium acetate, acetic acid, reflux, 6 h; (b)
K2CO3, DMF, 80 oC, 48 h; (c) sodium ascorbate, CuSO4·5H2O, DMF, r.t, 2 h.
All the synthesized 2,4,5-triarylimidazole-1,2,3-triazole derivatives 5a-5r were
evaluated for in vitro inhibition activities against α-glucosidase enzyme. The results
were presented in Table 1. All tested compounds showed potent α-glucosidase
inhibitory activity with IC50 ranging from 15.16±0.18 to 48.15±0.37 μM, in
comparison to the standard drug, acarbose (IC50 = 817.38±6.27 μM, The value of IC50
is similar to previous literature report33, 34). Compound 5j (IC50 = 15.16±0.18 μM),
bearing 3-bromophenyl at the 2-position of the imidazole ring and 2-ethoxyl
substitution at phenylacetamide, was found to be the most active compound in the
series of 2,4,5-triarylimidazole-1,2,3-triazole derivatives 5a-5r, with fifty-two folds
more active than the standard drug acarbose (IC50 = 817.38±6.27 μM). The
replacement of the 3-bromophenyl with different fluoro-substituted phenyl (5c, 5d, 5k
and 5l,), chloro-substituted phenyl (5f and 5r), methoxyl-substituted phenyl (5g, 5m,
5n and 5q) or thiophen-2-yl (5i) resulted in a decrease of the inhibitory activity. These
results indicated the 3-bromophenyl substitution at imidazole ring seems to be the
6

optimal group of this class of compounds. A decrease in activity was observed for 5h
(IC50 = 19.62 ± 0.29 μM) in which 2-ethoxyl substituted is replaced with 4-ethoxyl
substituted at phenylacetamide. Compound 5o (IC50 = 17.03 ± 0.25 μM), which has
4-(methoxycarbonyl)phenyl substitution at the 2-position of the imidazole ring,
4-ethoxyl substitution on phenylacetamide moiety, was found to be the second most
active member of the series. The introduction of strong electron-withdrawing
2,5-dichloro substitution (5p, IC50 = 20.23 ± 0.26 μM) into the phenylacetamide
moiety can decrease the inhibitory activity.
Table 1. α-Glucosidase inhibitory activities of 2,4,5-triarylimidazole-1,2,3-triazole
derivatives 5a-5r.
Compound
Ar
R
IC50 (μM)a
2,4-Me2
38.49±0.31
5a
4-F
22.03±0.29
30.12±0.31
32.14±0.28
5b
5c
5d
2,4-Me2
2-Me
7

2-Me
4-OEt
2,4-Cl2
4-OEt
4-OMe
2-OEt
2-OEt
2,4-Cl2
3-Me
29.27±0.29
44.24±0.35
21.63±0.24
19.62±0.29
24.22±0.19
15.16±0.18
36.91±0.26
22.76±0.17
20.33±0.28
5e
5f
5g
5h
5i
5j
5k
5l
5m
4-Cl
29.21±0.34
5n
4-OEt
2,5-Cl2
4-Me
17.03±0.25
20.23±0.26
26.99±0.32
5o
5p
5q
8

4-OMe
48.15±0.37
5r
817.38±6.27
Acarbose
a Acarbose is standard for α-glucosidase inhibition activity.
To gain insight into the mechanism of the α-glucosidase inhibitory activity of the
newly synthesized 2,4,5-triarylimidazole-1,2,3-triazole derivatives, compound 5j was
selected as a representative for the kinetic study. We measured the reaction rates in the
presence of four concentration of 5j (0, 12, 15, 18 and 21 μM) with various
concentrations of p-nitrophenyl α-D-glucopyranoside (pNGP) as a substrate. The
inhibition type on the enzyme was assayed by Lineweaver-Burk plots of inverse of
velocities (1/v) versus inverse of substrate concentration 1/[pNGP (mM)] (Figure 2A).
As shown in Figure 2A, Vmax values for all the substrates gradually decreased with
increasing the concentrations of inhibitors, while Km values did not change,
indicating that 5j was a noncompetitive inhibitor of α-glucosidase. The Ki values were
calculated by plotting the slope of each line in the Lineweaver-Burk plots against the
different concentration of compounds (Figure 2B). Enzyme kinetic analysis indicated
that 5j is a noncompetitive inhibitor of α-glucosidase with a Ki of 14.78 μM.
9

Figure 2. (A) Lineweaver–Burk plot of the inhibition kinetics of α-glucosidase by 5j.
Concentrations of 5j were 0, 12, 15, 18 and 21 μM, respectively. Substrate
p-nitrophenyl α-D-glucopyranoside (pNGP) concentrations were 0.25, 0.5, 1 and 2
mM, respectively. (B) Secondary re-plot of Lineweaver-Burk plot between the slopes
of each line on Lineweaver-Burk plot versus various concentrations of 5j.
The crystallographic structure of Saccharomyces cerevisiae α-glucosidase enzyme has
not been published yet, a number of homology models of α-glucosidase have been
reported in the literature.34, 35 The procedure of homology modeling was followed by
literature procedure,34, 35 which comprised three sequential steps: (1) the sequence in
FASTA format of α-glucosidase was retrieved from UniProt (http://www.uniprot.org/,
access code P53341); (2) the crystallographic structure of Saccharomyces cerevisiae
isomaltase (PDB ID: 3AJ7) with 72.4% was selected as the template for modeling; (3)
the 3D structure of α-glucosidase was built by means of modeller 9.15 homology
modeling software (http://salilab.org/modeller/).
To understand the mechanism of α-glucosidase inhibition and binding mode of these
10

novel 2,4,5-triarylimidazole-1,2,3-triazole derivatives with the active site of
α-glucosidase and to confirm the experimental results, molecular docking studies
were performed. The theoretical binding mode between 5j and Saccharomyces
cerevisiae α-glucosidase was shown in Figure 3. Compound 5j adopted a compact
conformation in the pocket of the α-glucosidase. The ethyoxylphenyl group of 5j bind
at the bottom of the α-glucosidase pocket and made a high density of van der Waals
contacts, whereas the triphenylimidazolyl group of 5j was positioned near the
entrance of the pocket and made only a few contacts. Detailed analysis showed that
the ethyoxylphenyl group of 5j formed arene-cation interaction with residue Arg-439
and CH-π interaction with residue Tyr-71. The bromophenyl group at the 2-position of
the imidazolyl group located at the hydrophobic pocket, surrounded by residues
Leu-176, Leu-218, Phe-177 and Pro-240. Also, a CH-π interaction was observed
between the phenyl group at the 4-position of imidazolyl group and the residue
His-239. In addition, the phenyl group at the 5-position of the imidazolyl group
formed arene-cation interaction with residue Arg-312 and CH-π interactions with
residues Phe-157 and Phe-300, respectively. Importantly, amide group of 5j formed
hydrogen bonds with both residues Glu-276 (bond length: 2.1 Å) and Asp-214 (bond
length: 2.5 Å), while the triazole ring of 5j formed hydrogen bond with Thr-215 (bond
length: 3.5 Å). All these interactions helped 5j to anchor in the binding site of
α-glucosidase. All in all, the above molecular simulations give us a rational
explanation of the interactions between 5j and α-glucosidase, which provided
11

valuable information for further development of α-glucosidase inhibitors.
Figure 3. Compound 5j was docked into the binding pocket of the Saccharomyces
cerevisiae α-glucosidase.
In summary, a novel series of 2,4,5-triarylimidazole-1,2,3-triazole derivatives have
been synthesized via copper(I)-catalyzed azide-alkyne click chemistry, and their
inhibitory activities against α-glucosidase were evaluated. All tested compounds
(5a-5r) were found to be potent inhibitors of α-glucosidase (IC50 = 15.16±0.18 -
48.15±0.37 μM), more active than the standard drug acarbose (IC50 = 817.38±6.27
μM). Enzyme kinetic study revealed that synthesized compounds inhibit
α-glucosidase via a noncompetitive mechanism. Furthermore, molecular docking
study showed that the compounds had high binding affinities for the active site of
12

α-glucosidase enzyme. Hence, this study identified a new structural type of
α-glucosidase inhibitors, which could be used as lead compound for the further
development of α-glucosidase inhibitors.
Conflict of Interest
The authors confirm that this article content has no conflict of interest.
Acknowledgments
This work was supported by National Natural Science Foundation of China (Grant No
81660574), Hunan Provincial Natural Science Foundation of China (2015JJ3099),
Scientific Research Fund of Hunan Provincial Education Department (15B194).
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Graphic Abstract
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