Synthesis, molecular modeling, selective aldose reductase inhibition and hypoglycemic activity of novel meglitinides

Article abstract of DOI:10.1016/j.bioorg.2021.104909

In the present study, a novel generation of selective aldose reductase ALR2 inhibitors with significant hypoglycemic activities was designed and modulated based on rhodanine scaffold joined to an acetamide linker in between two lipophilic moieties. The synthesis of the novel compounds was accomplished throughout simple chemical pathways. Molecular docking was performed on B-cell membrane protein SUR1, aldehyde reductase ALR1 and aldose reductase ALR2 active sites. Compounds 10B, 11B, 12B, 15C, 16C, 26F and 27F displayed the highest hypoglycemic activities with 80.7, 85.2, 87, 82.3, 83.5, 81.4 and 85.3% reduction in blood glucose levels, respectively. They were more potent than the standard hypoglycemic agent repaglinide with 65.4% reduction in blood glucose level. Compounds 12B and 15C with IC₅₀ 0.29 and 0.35 μM were more potent than the standard ALR2 inhibitor epalrestat with IC₅₀ 0.40 μM. They were selective towards ALR2 over ALR1 134 and 116 folds, respectively. Molecular docking studies matched with the in-vitro and in-vivo results to elucidate the dual activities of both compounds 12B and 15C as potent antagonists for ALR2 over ALR1 and good agonists for the SUR1 protein.

Full text of DOI:10.1016/j.bioorg.2021.104909

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Bioorganic Chemistry 111 (2021) 104909
Contents lists available at ScienceDirect
Bioorganic Chemistry
journal homepage: www.elsevier.com/locate/bioorg
Synthesis, molecular modeling, selective aldose reductase inhibition and
hypoglycemic activity of novel meglitinides
,
,
Manar G. Salema, Yasmine M. Abdel Aziza *, Marwa Elewaa *, Mohamed S. Nafieb,
Hosam A. Elshihawya *, Mohamed M. Saida
,
a Pharmaceutical Organic Chemistry Department, Faculty of Pharmacy, Suez Canal University, P.O. 41522 Ismailia, Egypt
b Chemistry Department, Faculty of Science, Suez Canal University, Ismailia 41522, Egypt
A R T I C L E I N F O
A B S T R A C T
Keywords:
Meglitinides
Eparlestat
Repaglinide
ALR2
In the present study, a novel generation of selective aldose reductase ALR2 inhibitors with significant hypo-
glycemic activities was designed and modulated based on rhodanine scaffold joined to an acetamide linker in
between two lipophilic moieties. The synthesis of the novel compounds was accomplished throughout simple
chemical pathways. Molecular docking was performed on B-cell membrane protein SUR1, aldehyde reductase
ALR1 and aldose reductase ALR2 active sites. Compounds 10B, 11B, 12B, 15C, 16C, 26F and 27F displayed the
highest hypoglycemic activities with 80.7, 85.2, 87, 82.3, 83.5, 81.4 and 85.3% reduction in blood glucose levels,
respectively. They were more potent than the standard hypoglycemic agent repaglinide with 65.4% reduction in
blood glucose level. Compounds 12B and 15C with IC50 0.29 and 0.35 µM were more potent than the standard
ALR2 inhibitor epalrestat with IC50 0.40 µM. They were selective towards ALR2 over ALR1 134 and 116 folds,
respectively. Molecular docking studies matched with the in-vitro and in-vivo results to elucidate the dual ac-
tivities of both compounds 12B and 15C as potent antagonists for ALR2 over ALR1 and good agonists for the
SUR1 protein.
ALR1
SUR1
1. Introduction
the polyol pathway, triggering severe complications, such as cardio-
vascular disorders, kidney, eye and nerve damages. The main enzyme of
Meglitinides are non-sulfonylureas hypoglycemic agents. They have
the potential to stimulate pancreatic B-cells to secret more insulin and to
improve insulin resistance in target tissues. It is well known that the
pathological mechanisms of type 2 diabetes mellitus DM are mainly
owing to reduced insulin secretion and insulin resistance in target tis-
sues. As a result, meglitinides represent a single active treatment for type
2 DM with dual mechanisms of action [1]. Repaglinide (Fig. 1) is the
most famous example of meglitinides. It is mainly metabolized in the
liver and so it is safe for patients with renal impairment [2]. Repaglinide
binds to site B of sulfonylurea receptor 1 SUR1 in pancreatic B-cells
rather than site A that is targeted by sulfonylureas hypoglycemic agents
such as gliclazide [3] (Fig. 1). Consequently, repaglinide has fast onset
and duration of action. Thereby, it can normalize blood glucose level
and eliminates the risk of drug-induced hypoglycemia. Despite all trials
to develop novel hypoglycemic agents, long-term diabetic complications
still life-threatening for diabetic patients [4]. Hyperglycemia stimulates
the polyol pathway is aldose reductase ALR2 [5]. It is worth to mention
that ALR2 has around 65% similarity in structure with aldehyde
reductase ALR1 [6,7]. ALR1 is responsible for a crucial detoxification
mechanism in human body [7]. Accordingly, the non-selective inhibi-
tion of both AR enzymes leads to serious adverse effects. Selective aldose
reductase inhibitors ARIs such as epalrestat seem to be effective treat-
ments for diabetic complications [6] with minimal undesirable effects.
The recent study aimed to design a single drug, according to mixed
pharmacophore theory, that can normalize glucose level in plasma and
control chronic diabetic complications through selective ALR2 inhibi-
tion [8]. This was established through the modification of the only ARI
approved drug, epalrestat (Fig. 2). In the present study, epalrestat
scaffold was mainly modified according to three strategies. Strategy (A)
was using simple lipophilic moieties attached to rhodanine core such as
substituted benzylidene moieties in place of Baylise-Hillman adducts
found in epalrestat structure [9]. Strategy (B) was keeping the rhodanine
* Corresponding authors.
E-mail addresses: yassmin_morsy@pharm.suez.edu.eg (Y.M. Abdel Aziz), marwa_elewa@pharm.suez.edu.eg (M. Elewa), hosamelshihawy74@hotmail.com
(H.A. Elshihawy).
https://doi.org/10.1016/j.bioorg.2021.104909
Received 27 December 2020; Received in revised form 6 April 2021; Accepted 7 April 2021
Available online 20 April 2021
0045-2068/© 2021 Elsevier Inc. All rights reserved.

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M.G. Salem et al.
Bioorganic Chemistry 111 (2021) 104909
(A-G) and intermediate compounds, 2-chloro-N-phenylacetamide de-
rivatives 3(A-D) in DMF [15]. The target compounds [series (A-G] were
synthesized via the simplest and the most economic chemical pathway.
Microanalyses and spectral data (IR, 1H NMR, 13C NMR and EI-MS)
were used to elucidate the structure of the synthesized compounds 6A-
–
33G. The IR Spectra for Series A and G showed collectively NH and C
O
–
stretching at around 3300–3500 cmꢀ 1 and 1630–1700 cmꢀ 1 respec-
tively, the appearance of (Ar-H, sp2) stretching at 3000–3100 cmꢀ 1
,
ꢀ 1
3
–
–
(=C H) stretching at 3010–3100 cm , (C H, sp , alkyl) stretching at
2850–3000 cmꢀ 1, overtones weak bands at 2000–1665 cmꢀ 1, (N-C O)
–
–
at around 1665–1710 cmꢀ 1, (Ar C C) stretching at around 1450–1600
–
–
cmꢀ 1 and (N-C S) at around 1025–1225 cmꢀ 1. Besides, the appearance
–
–
of (O-CH3, ether) stretching at 1150 cmꢀ 1 and 1170 cmꢀ 1 in compounds
8A and 32G respectively. On the other hand, the IR spectra for series B
and F illustrated the same bands as series A except for (O-CH3, ether)
stretching at 1050–1250 cmꢀ 1. IR Spectra of series C showed same bands
ꢀ 1
–
–
as series A except for (O H) stretching at 3200–3400 cm and (C O,
alcoholic) stretching at around 1050–1250 cmꢀ 1. Concerning series D,
(C N, amine) stretching appeared at 1080–1360 cmꢀ 1. In series E, two
–
–
strong stretching related to (N O, nitro) were observed at 1515–1560
and 1345–1385 cmꢀ 1
.
1H NMR spectra of the newly synthesized com-
pounds of series (A-G) showed NH singlets at δH [9.76–10.50 ppm].
–
Besides, the proton of the methylidene group (=C H) appeared as
downfield singlets at δH [7.30–8.63 ppm]. 1H NMR Spectra were char-
acterized by two important regions: a highly shielded region consisting
of aliphatic characteristic signals corresponding to methylene of acet-
amide moiety at δH [3.82–4.50 ppm] and a deshielded region consisting
of aromatic multiplets corresponding to substituted phenyl and
substituted benzylidene rings at δH [6–8.5 ppm]. In addition, in series B
and F, singlets at δH [3–3.5 ppm] were observed that referred to the
three protons of methoxy group (O-CH3). Regarding the 1H NMR spectra
of series C, singlets at δH [10–10.5 ppm] were detected that referred to
the hydroxyl group (OH). Compounds of series D obtained dimethyla-
mino group (N-(CH3)2) that was observed as singlets at δH [3–3.5 ppm]
that referred to six equivalent protons. The 13C NMR spectra showed
characteristic decoupled signals for 5-benzylidene rhodanine, phenyl
rings and acetamide moiety at the expected regions. In the rang δC
[160–195 ppm] several characteristic peaks were observed that referred
Fig. 1. Pharmacophoric model for gliclazide binding with site A and repagli-
nide binding with site B of SUR1.
–
–
–
–
to (C S), (C O, acetamide) and (C O, rhodanine). Besides, the aro-
–
–
moiety intact as it is essential for ARI activity. Strategy (C) involved the
bioisosteric replacement of the carboxylic acid moiety of epalrestat with
various substituted N-phenyl acetamide moieties. In this way, our
designed structures fulfill the minimum pharmacophoric criterion for
improving hypoglycemic activity which is the presence of acetamide
moiety in between two lipophilic centers [10]. This acetamide moiety
ionizes at the physiological pH to give an anionic center that plays a
crucial role in enhancing the binding affinity to SUR1 [10]. This study
aimed to the synthesis of 7 Series (A-G) of novel hypoglycemic com-
pounds as well as selective ALR2 inhibitors, inspired by epalrestat [11]
and repaglinide structures, throughout simple chemical pathways [12]
(Fig. 2).
matic carbons were observed at δC [111–158 ppm]. Aliphatic carbons of
(methylene group of acetamide, methoxy group and dimethylamino
group) were elucidated at δC [40–55 ppm].
2.2. Biological activity
In-vivo hypoglycemic activity of novel compounds was evaluated. In
addition, the potential inhibitory activity against ALR1 and ALR2 en-
zymes as well as selectivity indices were determined. Most of the
screened compounds might serve as suitable candidates to treat diabetes
and diabetic complications by using a single medication with dual
activity.
2. Results and discussion
2.2.1. In-vivo hypoglycemic activity
The in-vivo studies for compounds of series (A-G) representing
meglitinide were performed on BALB/c mice. Diabetes was induced, the
blood samples were collected at time intervals 0, 2, 4, 6 and 8 h and the
blood glucose levels were measured. The results are listed in Table 1.
Most of the tested compounds of series (A-G) possessed potent
glucose lowering activities as hypoglycemic agents. Compounds 10B,
11B, 12B, 15C, 16C, 26F and 27F displayed the highest activities with
80.7, 85.2, 87, 82.3, 83.5, 81.4 and 85.3% reduction in blood glucose
levels, respectively. They were more potent than standard 2 with 65.4%
reduction and comparable to standard 1. It was observed that these
compounds of series B, C and F obtained methoxy and hydroxyl sub-
stituents on the benzylidene rhodanine moiety. Compounds of series D
and E, with N, N-dimethyl amino and nitro substituents at p-position of
2.1. Chemistry
Scheme I illustrated the synthetic route developed for the synthesis
of 4 intermediate compounds, 2-chloro-N-phenylacetamide derivatives
3(A-D), through the reaction of chloroacetyl chloride with various an-
iline derivatives 2(A-D) in glacial acetic acid at 100 ◦C [13,14]. Scheme
II involved the synthesis of 5-arylidenerhodanine compounds 5(A-G)
through the addition of 2-thioxothiazolidin-4-one, different aldehydes 4
(A-G) and anhydrous sodium acetate in glacial acetic acid [9,11].
Scheme III showed the synthesis of acetamide derivatives of 5-arylide-
nerhodanine compounds [series (A-G] through the addition of sodium
bicarbonate and sodium iodide to 5-arylidenerhodanine compounds 5
2

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M.G. Salem et al.
Bioorganic Chemistry 111 (2021) 104909
the benzylidene rhodanine moiety respectively, obtained moderate ac-
tivities with 75.9–62.3% reduction. Both of series A and G exhibited
weak hypoglycemic activities. Compounds 7A and 33G displayed the
lowest activity. This might be attributed to the absence of o- or p-sub-
stitution on benzylidene rhodanine moiety.
15C with IC50 0.29 and 0.35 µM were more potent than epalrestat, with
IC50 0.40 µM. They were selective towards ALR2 over ALR1 134 and 116
folds, respectively. This therapeutic potential might be attributed to the
presence of 4-OCH3 and 2-OH substituents attached to the benzylidene
moiety in addition to 4-OCH3 and 2,4-diCl attached to the phenyl ring in
compounds 12B and 15C, respectively. On the other hand, the
replacement of methoxy substituent at para-position on benzylidene
moiety by the same one at meta-position of arylidene moiety in series F
render the compounds very weak than their analogs in series B.
Regarding series C, the presence of a hydroxyl substituent at ortho-po-
sition slightly affected the activity of the compounds as inhibitors for
ALR2. Therefore, the compounds of series C were still active inhibitors
compared to the standard. Moreover, the compounds of series D and E
obtained moderated potencies and IC50 of 0.94 to 8.42 µM. Compounds
2.2.2. ALR1 and ALR2 activity
Inhibitory activities of the novel compounds were screened in-vitro
against ALR1 and ALR2 using UV spectrophotometer on the basis of
measuring the decrease in the UV absorption by NADPH at 340 nm [16].
The positive control was valproic acid for ALR1 [10] and epalrestat for
ALR2 [9]. The results are listed in Table 2.
Among the 7 series, series B was the most active one as potent in-
hibitor for ALR2 with exciting selectivity index. Compounds 12B and
Fig. 2. The proposed scaffolds of hypoglycemic agents [series (A-G)].
3

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M.G. Salem et al.
Bioorganic Chemistry 111 (2021) 104909
binding energy ꢀ 24.11 Kcal/mol, it formed 2H-bonds with His 110, and
Trp 111 and two arene-arene with Tyr 209 and Trp 111 as the co-
crystallized ligand NADP, but it was docked inside the 3H4G with
lower binding energy ꢀ 11.2 Kcal/mol, and it did not form any inter-
active hydrogen bond (H-bond) like NADP, it only formed week in-
teractions of one arene-arene with Trp 22. While compound 15C, was
docked inside the 4QR6 with a good binding energy ꢀ 16.43 Kcal/mol, it
formed 2H-bonds with His 110, and Tyr 48 and One arene-arene with
Trp 20 as the co-crystallized ligand NADP, but it was docked inside the
3H4G with lower binding energy ꢀ 11.9 Kcal/mol, and it did not form
any interactive H-bond like NADP, it only formed week interactions of
one arene-arene interaction with Trp 22.
Scheme I. Synthesis of 2-chloro-N-arylacetamide derivatives (intermediates) 3
Moreover, as seen in Fig. 3A, it was noticed that ligand 12B tightly
bounded itself inside the binding site by two distinct H-bonds with
His110 (with bond length 1.72 Å) and Trp11 (with bond length 1.45 Å)
through the oxygen atoms as H-bond acceptors of rhodamine and
acetamide, respectively. Also, compound 15C, as seen on Fig. 3B, tightly
bounded itself inside the binding site by two strong H-bonds with His110
(with bond length 1.82 Å) and Tyr48 (with bond length 2.06 Å) through
the oxygen atom as H-bond acceptor acetamide. These strong H-bond
interactions were deterministic in targeting ALR2. In addition, it showed
significant interactions with both polar and hydrophobic residues of
ALR2 that further increased its binding affinity.
(A-D).
So, from the strong interactive binding modes of the two docked
compounds inside the two rested proteins, we could conclude the over
selectivity against the 4QR6 over 3H4G, this in agreement with the in-
vitro inhibitory biological results of both compound 12B and 15C to-
wards ALR2 with IC50 of 0.29 and 0.35 µM, respectively compared to
Epalrestate (IC50 = 0.40 µM) and AlR1 with IC50 of 39.11 and 40.72 µM,
respectively compared to Valproic acid (IC50 = 57.4 µM).
To predict the mode of action of the docked compounds 12B and 15C
compared with the co-crystallized ligand (Repaglinide), they were
evaluated as agonists for their binding affinities towards the molecular
target (PDB: 6PZ9) as a SUR1 membrane protein in pancreatic B-cell to
stimulate insulin secretion [18]. As seen in Table 4 with the two- and
three-dimensional representation of the overall interaction inside the
binding site of the target molecule, compound 12B was docked inside
the receptor binding site with binding energy –22.63 Kcal/mol, to form
2H-bonds with Asn 437 (bond length 2.16 Å) and Arg 1248 (1.75 Å) as
Scheme II. Synthesis of 5-arylidenerhodanine compounds (intermediates) 5
(A-G).
of D and E series obtained N, N-dimethyl amino and nitro substituents at
para-position on benzylidene moiety respectively. The weakest com-
pounds were in series A, F and G. These series obtained no substitution
(series A) or contained m-substituents on benzylidene ring (series F and
G) which resulted in a decreased interaction with the active site of ALR2.
–
H-bond acceptors through (–OCH ) substituents and C O group of
–
3
acetamide group, respectively. While compound 15C, was docked inside
the receptor binding site with binding energy ꢀ 21.41 Kcal/mol, to form
1H-bonds with Asn 437 (bond length 2.34 Å) as H-bond acceptor
2.2.3. The selectivity indices of the novel compounds
The selective inhibition of the novel compounds was calculated in
terms of their IC50 values against ALR1 versus ALR2. In all series,
remarkable selectivity indices were observed for compounds 10B, 11B,
12B, 15C and 22E with 39, 45, 134, 116 and 38 folds, respectively.
These compounds were more selective towards ALR2. Therefore, com-
pounds of series B might be considered potent and selective inhibitors
with minor side effects. According to the previous three parameters, in-
vivo hypoglycemic activity, in-vitro ALR1 and ALR2 inhibitory activity
and the selectivity indices of the novel compounds, the most active
compounds were 12B and 15C.
–
through C O group of acetamide group.
–
So, the molecular docking study elucidates the feasible mechanism of
binding of both compounds 12B and 15C to act as agonist inside the
6PZ9 (SUR1) protein, which explains their high biological activity as a
hypoglycemic agent (87% and 82.3% reduction in blood glucose,
respectively).
3. Bioinformatics study
Bioinformatics studies were conducted to establish physicochemical
properties and drug-like properties for compounds 10B, 11B, 12B, 15C,
16C, 26F and 27F that exhibited the most potent hypoglycemic activ-
ities. The examined compounds showed promising drug-likeness grads
and good physicochemical properties according to Lipinsiki’s rule of five
[17]. These physicochemical properties included molecular weight,
number of rotatable bonds, H-bond donor and acceptors along with
number of violations. Furthermore, acceptable pharmacokinetics such
as permeability and intestinal absorption were observed too. For good
drug absorbance through intestine, the value of topological polar surface
area (TPSA) should be as low as 140. Blood brain barrier (BBB) should be
as low as 90 Å2 [18]. The examined compounds showed good absorption
and permeability. As shown in Table 5, the tested compounds had 1–2H-
bond donors and 5–6H-bond acceptors. Besides, all tested compounds
2.3. In silico studies
2.3.1. Molecular modeling
Molecular docking study was performed to rationalize the in-vivo and
in-vitro biological results and give insights into the possible binding
modes of compounds of the 7 series (A-G) together with the co-
crystallized ligands within the active sites of 6PZ9 (SUR1), aldose
reductase (4QR6) and aldehyde reductase enzymes (3H4G).
Among the highest active compounds 12B and 15C were highlighted
for their binding mode inside the 4QR6 (ALR2) and 3H4G (ALR1) to
elucidate their over selectivity towards the ALR2 over the AlR1. As seen
in Table 3, compound 12B was docked inside the 4QR6 with a strong
4