Synthesis, in vitro α-glucosidase inhibitory activity and docking studies of novel chromone-isatin derivatives

Article abstract of DOI:10.1016/j.bmcl.2017.11.047

A novel series of chromone-isatin derivatives 6a–6p were designed, synthesized and characterized by ¹H NMR, ¹³C NMR and HRMS. These novel synthetic compounds were evaluated for inhibitory activity against yeast α-glucosidase enzyme. The results of biological test have shown that all tested compounds exhibited excellent to potent inhibitory activity in the range of IC₅₀ = 3.18 ± 0.12–16.59 ± 0.17 μM as compared to the standard drug acarbose (IC₅₀ = 817.38 ± 6.27 μM). Compound 6j (IC₅₀ = 3.18 ± 0.12 μM) with a hydroxyl group at the 7-position of chromone and a 4-bromobenzyl group at the N1-positions of isatin, was found to be the most active compound among the series. Furthermore, molecular docking study was performed to help understand binding interactions of the most active analogs with α-glucosidase enzyme. These results indicated that this class of compounds had potential for the development of anti-diabetic agents.

Full text of DOI:10.1016/j.bmcl.2017.11.047

Accepted Manuscript
Synthesis, in vitro α-glucosidase inhibitory activity and docking studies of novel
chromone-isatin derivatives
Guangcheng Wang, Ming Chen, Jie Qiu, Zhenzhen Xie, Anbai Cao
PII:
S0960-894X(17)31156-3
https://doi.org/10.1016/j.bmcl.2017.11.047
BMCL 25453
DOI:
Reference:
Bioorganic & Medicinal Chemistry Letters
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7 October 2017
25 November 2017
27 November 2017
Please cite this article as: Wang, G., Chen, M., Qiu, J., Xie, Z., Cao, A., Synthesis, in vitro α-glucosidase inhibitory
activity and docking studies of novel chromone-isatin derivatives, Bioorganic & Medicinal Chemistry Letters
(2017), doi: https://doi.org/10.1016/j.bmcl.2017.11.047
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Synthesis, in vitro α-glucosidase inhibitory activity
and docking studies of novel chromone-isatin
derivatives
Guangcheng Wanga,b,c,*, Ming Chend; Jie Qiud; Zhenzhen Xied; Anbai Caod
a Provincial Key Laboratory of Pharmaceutics in Guizhou Province, Guizhou Medical
University, 4 Beijing Road, Guiyang 550004, China.
b School of Pharmacy, Guizhou Medical University, 4 Beijing Road, Guiyang 550004,
China.
c
National Engineering Research Center of Miao’s Medicines, 4 Beijing Road,
Guiyang 550004, China.
d College of Chemistry and Chemical Engineering, Hunan Engineering Laboratory for
Analyse and Drugs Development of Ethnomedicine in Wuling Mountains, Jishou
University, Jishou 416000, PR China
*Corresponding Author
Tel.: +86 851 86908468
Fax: +86 851 86908468
E-mail address: wanggch123@163.com
1

Abstract.
A novel series of chromone-isatin derivatives 6a-6p were designed, synthesized and
characterized by 1H NMR, 13C NMR and HRMS. These novel synthetic compounds
were evaluated for inhibitory activity against yeast α-glucosidase enzyme. The
results of biological test have shown that all tested compounds exhibited excellent to
potent inhibitory activity in the range of IC50 = 3.18 0.12 - 16.59 0.17 µM as
compared to the standard drug acarbose (IC50 = 817.38 6.27 µM). Compound 6j
(IC50 = 3.18 0.12 µM) with a hydroxyl group at the 7-position of chromone and a
4-bromobenzyl group at the N1-positions of isatin, was found to be the most active
compound among the series. Furthermore, molecular docking study was performed to
help understand binding interactions of the most active analogs with α-glucosidase
enzyme. These results indicated that this class of compounds had potential for the
development of anti-diabetic agents.
Keywords: Chromone; Isatin; α-Glucosidase; Molecular docking
2

Diabetes mellitus is a chronic disease characterized by hyperglycemia with a lot of
serious complications. Type 2 diabetes is much more common and accounts for
1
around 90% of all diabetes cases worldwide . α-Glucosidase is a carbohydrate
2
hydrolyzing enzyme secreted from the intestinal chorionic epithelium . It hydrolyzes
glycosidic bond in polysaccharide chains to monosaccharide as glucose which is
3
mainly responsible to cause hyperglycemia . Thus, α-glucosidase is a therapeutic
target for type 2 diabetes by delay the absorption of glucose after meals, and some of
α-glucosidase inhibitors (acarbose, miglitol, and voglibose) have been used in clinical
4
for the treatment of type 2 diabetes (Figure 1) . Therefore, design and development
of new α-glucosidase inhibitors to treat diabetes mellitus is essential.
Chromone is a group of naturally occurring oxygen containing heterocyclic
compounds having a benzene ring fused with pyran ring, which can be used as
a privileged scaffold to design new molecules in drug discovery5. A wide spectrum of
pharmacological activities was associated with chromone such as anti-inflammatory 6,
8
9
antimicrobial7, anti-HIV , anticancer , antioxidant 10, and antibacterial activities11.
Furthermore, chromone derivatives also reported as α-glucosidase inhibitors (Figure
1, I and II)12, 13. More recently, our research group have also synthesized a series of
chromone hydrazone derivatives, and some of synthesized compounds displayed
potent α-glucosidase inhibitory activity with IC50 values in the range of 20.1 0.19 µM
to 45.7 0.23 µM, as compared to the standard drug acarbose (IC50 = 817.38 6.27
µM)14.
On the other hand, isatin is an important heterocyclic system, which is a core
3

constituent of many alkaloids and drugs as well as dyes, pesticides and analytical
reagents 15, 16. In the past few decades, a large number of isatin derivatives have been
reported to exhibit various biological activities including anticancer17, antibacterial18,
antiviral19, anticonvulsant20, anti-inflammatory21, antifungal activity22. It is import to
point out that isatin core is a privileged scaffold for the design and development
of new α-glucosidase inhibitors and number of isatin derivatives have been reported
to exhibit α-glucosidase inhibitory activity (Figure 1, III - V) 23-25
.
Figure 1. Chemical structures of acarbose and some α-glucosidase inhibitors
In our previous study, we have reported that some chromone derivatives exhibited
potent α-glucosidase inhibitory activity14 as well as also reported isatin derivatives as
a potential α-glucosidase inhibitors (Figure 2)25-27. As part of our continuing research
program28-31, we report herein the design and synthesis of a hybrid scaffold by
4

incorporating chromone and isatin in a single molecule (Figure 2). The synthesized
compounds were evaluated for their α-glucosidase inhibitory activity.
Figure 2. Rationale design of the title compounds of this study.
The chromone-isatin derivatives 6a-6p were synthesized as shown in Scheme 1. The
starting material isatin 1 was treated with various substituted alkyl halide to form
N-alkyl isatin 2. Then reaction compound 2 with hydrazine hydrate to give the
corresponding hydrazine derivatives 3. On the other hand, substituted
3-formylchromones 5 were prepared according to Vilsmeier-Haack reaction by
reaction of the corresponding o-hydroxyacetophenones with the Vilsmeier-Haack
reagent (DMF/POCl3). Finally, condensation of substituted 3-formylchromones 5 with
appropriate 3-hydrazino-isatins 3 in refluxing ethanol and in the presence of acetic
acid as catalyst to afford the ethanolate of the corresponding title compounds 6a-6p in
moderate to high yields. The structure of synthesized compounds was elucidated and
has been proven using spectral methods such as 1H NMR and 13C NMR. All the newly
synthesized compounds were in good agreement with the proposed structures
(Supplemental Material). To the best of our knowledge, all synthetic hybrid molecules
5

6a-6p have not yet been reported in the literature.
Scheme 1. (a) R1Cl, R1Br or R1I, K2CO3, DMF, room temperature, 4 h; (b)
NH2NH2·H2O, MeOH, reflux, 3 h; (c) POCl3, DMF, 50 oC, 4 h; (d) EtOH, AcOH (c.),
reflux, 6 h.
All the synthesized chromone-isatin derivatives 6a-6p were screened to evaluate their
in vitro α-glucosidase inhibitory activity (Table 1). All tested compounds exhibited
excellent to potent inhibitory activity in the range of IC50 = 3.18 0.12 - 16.59
0.17 µM as compared to the standard drug acarbose (IC50 = 817.38
6.27 µM).
Among the series, compound 6j (IC50 = 3.18 0.12 µM) with a hydroxyl group at the
7-position of chromone and a 4-bromobenzyl group at the N1-positions of isatin, was
found to be the most active compound. As shown in Table 1, compounds 6a-6h shown
excellent inhibitory activity against α-glucosidase with IC50 values ranging from 8.17
0.18 to 16.59 0.17 µM. Compounds 6i-6p displayed potent inhibitory activity with
6

IC50 values of 4.25 0.14, 3.18 0.12, 3.90 0.14, 4.17 0.16, 4.57 0.13, 3.82
0.11, 4.73 0.18 and 5.51 0.21 µM, respectively. Compared the inhibitory activity
of 6a-6h with 6i-6p and found that the introduction of hydroxyl group into the
chromone ring results in dramatically increased inhibitory activity. The results were
suggested that the substitution on the chromone ring is very important for the
α-glucosidase inhibitory activity in this series. Furthermore, introduction of various
alkyl group at N1 position of isatin ring resulted in a slight increase or decrease of the
biological activity, which indicated that the N1 alkyl group is not important for
activity.
Table 1. α-Glucosidase inhibitory activities of chromone-isatin derivatives 6a-6p
Compound
R1
R2
H
IC50 (µM)
8.17 0.18
11.81 0.20
16.59 0.17
16.18 0.24
15.96 0.25
14.02 0.19
9.80 0.21
13.54 0.24
4.25 0.14
3.18 0.12
3.90 0.14
4-bromobenzyl
methyl
6a
6b
6c
6d
6e
6f
H
4-chlorobenzyl
H
H
H
3-fluorobenzyl
2-fluorobenzyl
4-fluorobenzyl
2-chlorobenzyl
2,4-dichlorobenzyl
4-bromobenzyl
4-chlorobenzyl
H
H
H
6g
6h
6i
H
OH
OH
OH
6j
6k
7

3-fluorobenzyl
2-fluorobenzyl
4-fluorobenzyl
2-bromobenzyl
2-chlorobenzyl
OH
OH
OH
OH
OH
4.17 0.16
4.57 0.13
3.82 0.11
4.73 0.18
5.51 0.21
817.38 6.27
6l
6m
6n
6o
6p
Acarbose
To investigate the binding mode of these compounds with α-glucosidase, molecular
docking study was carried out by using Autodock VINA 1.1.2. The 3D structure of
α-glucosidase of Saccharomyces cerevisiae have been predicted using homology
modeling in our previous report30. The theoretical binding mode between 6a and
Saccharomyces cerevisiae α-glucosidase was shown in Figure 3. Compound 6a
adopted a “U-shaped” conformation in the pocket of the α-glucosidase. The
4-bromophenyl group of 6a was located at the hydrophobic pocket, surrounded by the
residues Phe-157, Phe-177, Ala-278 and Phe-300, forming a stable hydrophobic
binding. Detailed analysis showed that the 4-bromophenyl group of 6a formed π-π
stacking and CH-π interactions with the residues Phe-157 and Phe-177, respectively,
while the benzopyrone group of 6a formed π-π stacking interaction with the residue
Phe-300. In addition, the benzopyrone group of 6a formed the cation-π interaction and
anion-π interaction with the residues Arg-312 and Asp-349, respectively. It was shown
that the residue His-279 (bond length: 2.7 Å) formed a hydrogen bond with 6a, which
was the main interaction between 6a and α-glucosidase. All these interactions helped
6a to anchor in the binding site of the α-glucosidase.
8

Figure 3. The binding mode between compound 6a and the binding site of the
Saccharomyces cerevisiae α-glucosidase.
To explain the activity order of 6a and 6j against α-glucosidase, 6j was then docked
into the binding site of α-glucosidase, and the theoretical binding mode between 6j
and α-glucosidase was shown in Figure 4A. The interaction between 6j and
α-glucosidase was almost the same as the precursor 6a. The only difference was that
the hydroxyl group of 6j formed an extra hydrogen bond with the residue Gln-350 of
α-glucosidase when compared with 6a, which made 6j was more active than 6a
against α-glucosidase (Figure 4B). In addition, the estimated binding energies were
-8.1 kcal·mol−1 for 6a and -8.8 kcal·mol−1 for 6j, respectively, which was consistent
with the results of the in vitro anti-α-glucosidase assay. In summary, the above
9

molecular simulations give us rational explanation of the interactions between 6a, 6j
and α-glucosidase, which provided valuable information for further development of
α-glucosidase inhibitors.
Figure 4. (A) The binding mode between compound 6j and the binding site of the
Saccharomyces cerevisiae α-glucosidase. (B) The binding mode between compounds
6a and 6j and the binding site of the Saccharomyces cerevisiae α-glucosidase.
(overlapped).
A novel series of chromone-isatin derivatives 6a-6p were synthesized and their in
vitro α-glucosidase inhibitory activity were evaluated. All the synthesized compounds
shown excellent to potent inhibitory activity in the range of IC50 = 3.18 0.12 - 16.59
0.17 µM as compared to the standard drug acarbose (IC50 = 817.38 6.27 µM).
Molecular docking study was performed to investigate the possible binding mode
of compounds with the active site of enzyme. The results of this study suggest
that these compounds may serve as lead molecules for further α-glucosidase
inhibitors development.
Acknowledgments
10

This work was supported by Natural Science Foundation of Jishou University
(Jdx17012); the Open Project Program of Hunan Engineering Laboratory for Analyse
and Drugs Development of Ethnomedicine in Wuling Mountains; the Open Project
Program of Key Laboratory of Hunan Forest and Chemical Industry Engineering
(JDZ201705).
Supplementary material
Supplementary data associated with this article can be found, in the online version, at
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Highlights
► A novel series of chromone-isatin derivatives were designed and synthesized.
► The IC50 in the range of 3.18 0.12 - 16.59 0.17 µM.
► The structure-activity relationship has been discussed.
► The introduction of hydroxyl into the chromone results in increased activity.
► Molecular docking study was carried out.
14