# Design, Synthesis, Antihyperglycemic Studies, and Docking Simulations of Benzimidazole-Thiazolidinedione Hybrids

Authors: Abraham Gutierréz-Hernández; Yelzyn Galván-Ciprés; Elix Alberto Domínguez-Mendoza; Yoshajandith Aguirre-Vidal; Samuel Estrada-Soto; Julio César Almanza-Pérez; Gabriel Navarrete-Vázquez
Journal: Journal of Chemistry
 (2019)

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## Abstract

A simple and cheap three-step procedure for the synthesis of three (5Z)-5-[3(4)-(1H-benzimidazol-2-ylmethoxy)benzylidene]-1,3-thiazolidine-2,4-diones has been described via a SN2 reaction of generally recognized as safe hydroxybenzaldehydes and 2-(chloromethyl)-1H-benzimidazole, followed by a Knoevenagel condensation with thiazolidine-2,4-dione in moderated yields. All the newly synthesized compounds were characterized using analytical and spectral studies. In vitro treatment on adipocytes with compounds increased the mRNA expression of two proteins recognized as strategic targets in diabetes: PPARγ and GLUT-4. In silico studies were conducted in order to explain the interaction binding mode of the synthesized compounds on PPARγ. In vivo studies confirmed that compounds 1–3 have robust antihyperglycemic action linked to insulin sensitization mechanisms. The present study provides three compounds with a promising antidiabetic action.


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## Body

## 1. Introduction

Type 2 diabetes is a metabolic complication depicted by a hyperglycemia >120 mg/dL, initiated by a deficiency in production or action of insulin [1]. Drugs that improve insulin resistance are effective in controlling hyperglycemia. Peroxisome proliferator-activated receptor isotype gamma (PPARγ) is the protein target of thiazolidine-2,4-diones, a class of insulin-sensitizing drugs used as antihyperglycemic agents [2]. PPARγ controls target genes involved in several biological processes, for example, the facilitated glucose transporter GLUT-4 [3]. The thiazolidine-2,4-dione ring in most of the antidiabetic glitazones, such as pioglitazone and rosiglitazone, is accompanied by an additional nitrogen-containing heterocycle, for example, pyridine [4–6]. Thiazolidine-2,4-diones could be considered synthetic acid bioisosteres of natural antidiabetic p-coumaric acid [7, 8]. Azaheterocycles such as pyridine or benzimidazole are commonly found in nature. Benzimidazole core is a natural product which is part of vitamin B12 (Figure 1). In this work, we chose the benzimidazole azaheterocycle to generate the antihyperglycemic hybrids because this scaffold is of great importance due to its appreciated pharmacological actions in medicinal chemistry and applications in organic synthesis, acting as a privileged structure [3, 9–11], which can selectively modulate diverse targets associated with the pathogenesis of diabetes. On the other hand, the election of benzylidenethiazolidine-2,4-dione as p-coumaric acid bioisostere (the major natural component widely found in grapes, red wine, tomatoes, spinach, garlic, and coffee) was taken into account because several acid bioisosteres have demonstrated antidiabetic effects [4–8].Figure 1
Antidiabetic glitazones (pioglitazone and rosiglitazone) containing pyridine and thiazolidine-2,4-dione azaheterocycles. Natural vitamin B12 containing benzimidazole azaheterocycle (green). Natural antidiabetic p-coumaric acid and its inspired azaheterocyclic hybrids 1–3 designed in this work.In our current exploration on PPAR activators with antidiabetic effect, we describe in this manuscript the synthesis of hybrid benzimidazole heterocycles1–3 containing benzylidene-1,3-thiazolidine-2,4-dione (Figure 1). Also, the in vitro mRNA expression of GLUT-4 and PPARγ, in silico molecular docking simulations, and the in vivo antihyperglycemic action in a murine model have been evaluated.


## 2. Materials and Methods

### 2.1. Chemicals and Analytical Methods

The solvents and reagents were acquired from Sigma-Aldrich (Mexico) and were used without any further purification. Melting points were determined using an automated capillary apparatus (EZ-Melt) and are uncorrected. Chemical structures were confirmed using1H and 13C NMR spectral data, employing Varian Oxford (400 MHz) and (100 MHz) instruments, respectively. Mass spectra were recorded on a JEOL JM(S)-700 instrument, and elemental analyses have been performed using Elementar Vario ELIII instrument.


### 2.2. General Preparation of the Titled Compounds 1–3

In a stirred round bottom flask equipped with Dean–Stark apparatus for water removal and condenser, alkoxybenzaldehydes5–7 (0.3 g, 0.8 mmol), benzoic acid (0.03 g, 0.24 mmol, 30%), and piperidine (0.025 mL, 0.24 mmol, 30%) were dissolved in dry toluene (10 mL). The mixture was heated to 40°C for 10 min. Thiazolidine-2,4-dione (0.11 g, 0.9 mmol, 1.1 equiv.) was added, and the mixture was refluxed for 7 h. The reaction was monitored by thin-layer chromatography. After complete conversion, the resulting solids were filtered, washed with cold toluene, dried, and recrystallized from adequate solvents.


#### 2.2.1. (5Z)-5-[4-(1H-Benzimidazol-2-ylmethoxy)benzylidene]-1,3-thiazolidine-2,4-dione (1)

Yellow pale powder, mp 255°C–258.3°C; yield 76.3%.1H NMR (400 MHz, DMSO-d6) δ: 5.40 (s, 2H, OCH2), 7.17–7.19 (m, 2H, H5′, H6′), 7.23 (dd, 2H, H-3, H-5, Jm = 1.2, Jo = 8.8 Hz), 7.55–7.57 (m, 2H, H-4′, H-7′), 7.57 (dd, 2H, H-2, H-6, Jm = 1.2, Jo = 8.8 Hz), 7.67 (s, 1H, =C-H), and 12.68 (s, 1H, N-H) ppm. 13C NMR (100 MHz, DMSO-d6) δ: 64.4 (OCH2), 116.1 (C-3, C-5, C-4′, C-7′), 122.4 (C-5′, C-6′), 123.1 (=C-), 127.1 (C-1), 130.7 (=C-H), 132.3 (C-2, C-6), 138.6 (C-3a′, C-7a′), 150.1 (C-2′), 159.7 (C-4), 168.1 (N-C=O), 171.1 (S-C=O) ppm; MS/EI: m/z (% int. rel). 351 (M+, 1%), and 259 (100%). Anal. calcd. for C18H13N3O3S: C 61.53, H 3.73, N 11.96, S 9.13; found C 61.50, H 3.68, N 11.87, S 9.19.


#### 2.2.2. (5Z)-5-[4-(1H-Benzimidazol-2-ylmethoxy)-3-methoxybenzylidene]-1,3-thiazolidine-2,4-dione (2)

Yellow powder, mp 245.8–248.7°C; yield 85.5%.1H NMR (400 MHz, DMSO-d6) δ: 3.80 (s, 3H, OCH3), 5.36 (s, 2H, OCH2), 7.14 (d, 2H, H-5′, H-6′ Jo = 8.4 Hz), 7.18–7.20 (m, 2H, H-2, H-6), 7.30 (d, 1H, H-5, Jo = 8.8 Hz), 7.55–7.57 (m, 2H, H-4′, H-7′), 7.71 (s, 1H, =C-H), and 12.68 (s, 1H, N-H) ppm. 13C NMR (100 MHz, DMSO-d6) δ: 55.7 (OCH3), 64.7 (OCH2), 113.9 (C-5), 114.1 (C-2), 121.17 (=C-), 123.8 (=C-H), 127.1 (C-6), 128.6 (C-4′, C-7′), 129.1 (C-5′, C-6′), 132.1 (C-1), 138.6 (C-3a′, C-7a′), 149.8 (C-4), 149.8 (C-3), 149.5 (C-2′), 168.1 (N-C=O), and 168.6 (S-C=O) ppm; MS/EI: m/z (% int. rel). 381 (M+, 1%), 265 (80%), and 180 (100%). Anal. calcd. for C19H15N3O4S : C 59.83, H 3.96, N 11.02, S 8.41; found C 59.90, H 3.89, N 11.00, S 8.45.


#### 2.2.3. (5Z)-5-[3-(1H-Benzimidazol-2-ylmethoxy)-4-methoxybenzylidene]-1,3-thiazolidine-2,4-dione (3)

Yellow powder, mp 246.9°C (dec); yield 31%.1H NMR (400 MHz, DMSO-d6) δ: 3.85 (s, 3H, OCH3), 5.34 (s, 2H, OCH2), 7.17 (s, 1H, H-5, Jo = 8.6 Hz), 7.18–7.20 (m, 2H, H-5′, H-6′), 7.23 (dd, 1H, H-6, Jm = 1.02, Jo = 8.6 Hz), 7.37 (d, 1H, H-2, Jm = 1.02 Hz), 7.56–7.58 (m, 2H, H-4′, H-7′), 7.69 (s, 1H, =C-H), and 12.68 (s, 1H, N-H) ppm. 13C NMR (100 MHz, DMSO-d6) δ: 55.7 (OCH3), 64.4 (OCH2), 112.5 (C-5), 115.2 (C-2), 122.1 (=C-), 124.6 (C-6), 125.7 (=C-H), 128.5 (C-4′, C-7′), 129.2 (C-5′, C-6′), 131.3 (C-1), 138.6 (C-3a′, C-7a′), 147.5 (C-3), 149.5 (C-4), 150.1 (C-2′), 168.4 (N-C=O), and 168.8 (S-C=O) ppm; MS/EI: m/z (% int. rel). 381 (M+, 1%), anal. calcd. for C19H15N3O4S : C 59.83, H 3.96, N 11.02, S 8.41; found C 59.76, H 3.89, N 11.00, S 8.36.


### 2.3. Preparation of 2-(Chloromethyl)-1H-benzimidazole (4)

1,2-Phenylenediamine (1 g, 0. 8 mmol), 1.3 equivalents of chloroacetic acid, and 10 mL of 1 M HCl were heated at 90°C in a nitrogen atmosphere for 10 h. The cooled mixture was basified with saturated NaHCO3 solution, and the crude product was extracted with AcOEt. Solvent was removed and the solids filtrated. Yellow powder, mp 147.8–148.2°C (Lit. 142°C–144°C); yield 53.2%. 1H NMR (400 MHz, DMSO-d6) δ: 4.90 (s, 2H, ClCH2), 7.18–7.20 (m, 2H, H-5′, H-6′), and 7.54–7.55 (m, 2H, H-4′, H-7′) ppm. MS/EI: m/z (% int. rel). 165 (M+, 45%), 131 (100%), and 180 (100%).


### 2.4. General Preparation of Precursors 5–7

A solution of generally recognized as safe hydroxybenzaldehydes (0.25 mmol of 4-hydroxybenzaldehyde (8), vanillin (9), or isovanillin (10)) and K2CO3 (0.51 mmol, 2 equiv.) in 5 mL of acetonitrile was heated at 50°C for 30 min. After that, 2-(chloromethyl)-1H-benzimidazole (4) (0.275 mmol, 1.1 equiv.) in acetonitrile was added drop by drop. The reaction was heated for 2–9 h. Acetonitrile was removed using a rotavapor. 10 mL of ice-water was added and stirred for 10 min. The emulsion was extracted with EtAcO (3 × 15 mL), and the organic layer was evaporated to give a solid, which was recrystallizated from suitable solvent.


#### 2.4.1. 4-(1H-Benzimidazol-2-ylmethoxy)benzaldehyde (5)

Brown powder, ethanol, mp 179°C–181.9°C; yield 95%.1H NMR (400 MHz, DMSO-d6) δ: 5.45 (s, 2H, OCH2), 7.17–7.20 (m, 2H, H-5′, H-6′), 7.29 (dd, 2H, H-3, H-5, Jm = 1.2, Jo = 8.8 Hz), 7.54–7.56 (m, 2H, H-4′, H-7′), 7.88 (dd, 2H, H-2, H-6, Jm = 1.2, Jo = 8.8 Hz), and 9.87 (s, 1H, CHO) ppm. MS/EI: m/z (% int. rel). 252 (M+, 24%) and 131 (100%).


#### 2.4.2. 4-(1H-Benzimidazol-2-ylmethoxy)-3-methoxybenzaldehyde (6)

Brown powder, ethanol, mp 71.7–74.7°; yield 48.7%.1H NMR (400 MHz, DMSO-d6) δ: 3.82 (s, 3H, OCH3), 5.41 (s, 2H, OCH2), 7.16–7.18 (m, 2H, H-5′, H-6′), 7.37 (d, 1H, H-5, Jo = 8.8 Hz), 7.41 (d, 1H, H-2, Jm = 2.1 Hz), 7.53 (dd, 1H, H-6, Jm = 2.1, Jo = 8.8 Hz), 7.53–7.55 (m, 2H, H-4′, H-7′), and 9.83 (s, 1H, CHO) ppm. MS/EI: m/z (% int. rel) 282 (M+, 1%) and 131 (100%).


#### 2.4.3. 3-(1H-Benzimidazol-2-ylmethoxy)-4-methoxybenzaldehyde (7)

Brown powder, ethanol, mp 80.9°C (dec); yield 59%.1H NMR (400 MHz, DMSO-d6) δ: 3.89 (s, 3H, OCH3), 5.37 (s, 2H, OCH2), 7.13 (d, 1H, H-5, Jo = 8.7 Hz), 7.19 (m, 2H, H-4′, H-7′), 7.23 (d, 1H, H-6 Jo = 8.7 Hz), 7.37 (s, 1H, H-2), and 9.82 (s, 1H, CHO) ppm. MS/EI: m/z (% int. rel) 282 (M+, 2%) and 131 (100%).


### 2.5. Biological Activity

#### 2.5.1. PPARγ and GLUT-4 Determination

Assays were performed as described elsewhere [3, 12, 13]. Briefly, 3T3-L1 murine fibroblasts were cultured, and cell viability was measured using the MTT assay at three increasing concentrations (1, 10, and 100 μM) of hybrids 1–3. Confluent cultures of fibroblasts were differentiated to the adipocyte phenotype for 48 h employing 0.5 mM of 3-isobutyl-1-methylxanthine, 0.25 μM of dexamethasone acetate, and 0.8 μM of murine insulin, enriched by additional insulin charge. After 8 to 10 days, the cells acquire the mature adipocyte phenotype and were treated for 24 h to observe the effects of heterocycles 1–3 on PPARγ and GLUT-4 mRNA expression. Total mRNA was isolated from adipocytes, and 2 μg was reverse transcribed. The cDNA was amplified using SYBR Green Master Mix (Roche) containing 0.5 mM of customized primers for PPARγ (GenBank accession no.: NM 011146.1) and GLUT-4 (GenBank accession no.: NM009204.2). PCR was used for individually sample calculating the threshold cycles (Ct) and the ΔCt values. The amount of mRNA for each gene was normalized according to the amount of mRNA encoding ribosomal protein 36B4 (GenBank accession no.: NM_007475.2). The ΔCt values were calculated in every sample for each gene of interest as follows: Ct gene of interest—Ct reference gene with 36B4 as the reference gene (mRNA of reference remained stable throughout the experiments). Fluctuations in the relative expression levels of individual specific genes (ΔΔCt) were measured and graphed [2, 12].


#### 2.5.2. In Vivo Oral Glucose Tolerance Assay

All animal procedures were conducted in accordance with the Official Mexican Rules for Animal Experimentation and Care (SAGARPA, NOM-062-ZOO-1999), ratified by the Institutional Animal Care and Use Committee of the Universidad Autónoma Metropolitana (dictum 1857), based on US National Institutes of Health Publication #85-23, revised 1985.Normoglycemic mice (ICR strain) were divided into 3 groups of 6 mice (n = 6). 30 minutes after administration of heterocycles 1–3, a dose of 2 g/kg of glucose solution was administered to individual mouse. Samples of blood were collected from the caudal vein at 0, 0.5, 1, 1.5, and 2 hours, followed by the oral administration of vehicle (Tween 80, 10%), heterocycles 1–3, or glibenclamide. Glucose concentration was estimated using a commercial glucometer test strips [3, 12].


### 2.6. Statistical Analysis

To analyze the fluctuations in the percent variation of plasmatic glucose and thein vitro PPARγ and GLUT-4 determinations, we employed ANOVA, complemented with a Dunnett’s multiple test. All values are expressed as the mean ± SEM, p<0.05 (statistically significant). GraphPad Prism 5.0 was used for the analysis.


### 2.7. In Silico Docking Calculations

Molecular operation environment software (MOE) [14] and Pymol version 1.0 were employed for visualization. The crystal coordinates of PPARγ were retrieved from the protein databank (PDB) with the accession code 5U5L. Docking simulations were performed with AutoDock, ver.4.2. The program conducts numerous runs in each docking experiment. H2O molecules and cocrystal ligands were extracted from the crystallographic coordinates, and Gasteiger charges were assigned for the compounds and PPARγ. All torsions were permitted to rotate during the calculation. The program AutoGrid created the grid maps, placed at the coordinates of the crystallographic ligand with dimensions of 60 × 60 × 60 Å and points separated by 0.375 Å. The number of docking runs was 100. After computational calculations, all solutions were clustered into groups with RMSD <2.0 Å and by the lowest energy.


#### 2.7.1. Docking Validation

The docking protocols were validated by redocking of rivoglitazone (cocrystal ligand) into the PPARγ ligand binding site of 5U5L. The root mean square deviation (RMSD) between the cocrystal ligand and the rivoglitazone docked was 0.433 Å. This value specifies that the parameters for docking calculations are reproducing conformation and orientation in the X-ray crystal of PPARγ.


## 2.1. Chemicals and Analytical Methods

The solvents and reagents were acquired from Sigma-Aldrich (Mexico) and were used without any further purification. Melting points were determined using an automated capillary apparatus (EZ-Melt) and are uncorrected. Chemical structures were confirmed using1H and 13C NMR spectral data, employing Varian Oxford (400 MHz) and (100 MHz) instruments, respectively. Mass spectra were recorded on a JEOL JM(S)-700 instrument, and elemental analyses have been performed using Elementar Vario ELIII instrument.


## 2.2. General Preparation of the Titled Compounds 1–3

In a stirred round bottom flask equipped with Dean–Stark apparatus for water removal and condenser, alkoxybenzaldehydes5–7 (0.3 g, 0.8 mmol), benzoic acid (0.03 g, 0.24 mmol, 30%), and piperidine (0.025 mL, 0.24 mmol, 30%) were dissolved in dry toluene (10 mL). The mixture was heated to 40°C for 10 min. Thiazolidine-2,4-dione (0.11 g, 0.9 mmol, 1.1 equiv.) was added, and the mixture was refluxed for 7 h. The reaction was monitored by thin-layer chromatography. After complete conversion, the resulting solids were filtered, washed with cold toluene, dried, and recrystallized from adequate solvents.


### 2.2.1. (5Z)-5-[4-(1H-Benzimidazol-2-ylmethoxy)benzylidene]-1,3-thiazolidine-2,4-dione (1)

Yellow pale powder, mp 255°C–258.3°C; yield 76.3%.1H NMR (400 MHz, DMSO-d6) δ: 5.40 (s, 2H, OCH2), 7.17–7.19 (m, 2H, H5′, H6′), 7.23 (dd, 2H, H-3, H-5, Jm = 1.2, Jo = 8.8 Hz), 7.55–7.57 (m, 2H, H-4′, H-7′), 7.57 (dd, 2H, H-2, H-6, Jm = 1.2, Jo = 8.8 Hz), 7.67 (s, 1H, =C-H), and 12.68 (s, 1H, N-H) ppm. 13C NMR (100 MHz, DMSO-d6) δ: 64.4 (OCH2), 116.1 (C-3, C-5, C-4′, C-7′), 122.4 (C-5′, C-6′), 123.1 (=C-), 127.1 (C-1), 130.7 (=C-H), 132.3 (C-2, C-6), 138.6 (C-3a′, C-7a′), 150.1 (C-2′), 159.7 (C-4), 168.1 (N-C=O), 171.1 (S-C=O) ppm; MS/EI: m/z (% int. rel). 351 (M+, 1%), and 259 (100%). Anal. calcd. for C18H13N3O3S: C 61.53, H 3.73, N 11.96, S 9.13; found C 61.50, H 3.68, N 11.87, S 9.19.


### 2.2.2. (5Z)-5-[4-(1H-Benzimidazol-2-ylmethoxy)-3-methoxybenzylidene]-1,3-thiazolidine-2,4-dione (2)

Yellow powder, mp 245.8–248.7°C; yield 85.5%.1H NMR (400 MHz, DMSO-d6) δ: 3.80 (s, 3H, OCH3), 5.36 (s, 2H, OCH2), 7.14 (d, 2H, H-5′, H-6′ Jo = 8.4 Hz), 7.18–7.20 (m, 2H, H-2, H-6), 7.30 (d, 1H, H-5, Jo = 8.8 Hz), 7.55–7.57 (m, 2H, H-4′, H-7′), 7.71 (s, 1H, =C-H), and 12.68 (s, 1H, N-H) ppm. 13C NMR (100 MHz, DMSO-d6) δ: 55.7 (OCH3), 64.7 (OCH2), 113.9 (C-5), 114.1 (C-2), 121.17 (=C-), 123.8 (=C-H), 127.1 (C-6), 128.6 (C-4′, C-7′), 129.1 (C-5′, C-6′), 132.1 (C-1), 138.6 (C-3a′, C-7a′), 149.8 (C-4), 149.8 (C-3), 149.5 (C-2′), 168.1 (N-C=O), and 168.6 (S-C=O) ppm; MS/EI: m/z (% int. rel). 381 (M+, 1%), 265 (80%), and 180 (100%). Anal. calcd. for C19H15N3O4S : C 59.83, H 3.96, N 11.02, S 8.41; found C 59.90, H 3.89, N 11.00, S 8.45.


### 2.2.3. (5Z)-5-[3-(1H-Benzimidazol-2-ylmethoxy)-4-methoxybenzylidene]-1,3-thiazolidine-2,4-dione (3)

Yellow powder, mp 246.9°C (dec); yield 31%.1H NMR (400 MHz, DMSO-d6) δ: 3.85 (s, 3H, OCH3), 5.34 (s, 2H, OCH2), 7.17 (s, 1H, H-5, Jo = 8.6 Hz), 7.18–7.20 (m, 2H, H-5′, H-6′), 7.23 (dd, 1H, H-6, Jm = 1.02, Jo = 8.6 Hz), 7.37 (d, 1H, H-2, Jm = 1.02 Hz), 7.56–7.58 (m, 2H, H-4′, H-7′), 7.69 (s, 1H, =C-H), and 12.68 (s, 1H, N-H) ppm. 13C NMR (100 MHz, DMSO-d6) δ: 55.7 (OCH3), 64.4 (OCH2), 112.5 (C-5), 115.2 (C-2), 122.1 (=C-), 124.6 (C-6), 125.7 (=C-H), 128.5 (C-4′, C-7′), 129.2 (C-5′, C-6′), 131.3 (C-1), 138.6 (C-3a′, C-7a′), 147.5 (C-3), 149.5 (C-4), 150.1 (C-2′), 168.4 (N-C=O), and 168.8 (S-C=O) ppm; MS/EI: m/z (% int. rel). 381 (M+, 1%), anal. calcd. for C19H15N3O4S : C 59.83, H 3.96, N 11.02, S 8.41; found C 59.76, H 3.89, N 11.00, S 8.36.


## 2.2.1. (5Z)-5-[4-(1H-Benzimidazol-2-ylmethoxy)benzylidene]-1,3-thiazolidine-2,4-dione (1)

Yellow pale powder, mp 255°C–258.3°C; yield 76.3%.1H NMR (400 MHz, DMSO-d6) δ: 5.40 (s, 2H, OCH2), 7.17–7.19 (m, 2H, H5′, H6′), 7.23 (dd, 2H, H-3, H-5, Jm = 1.2, Jo = 8.8 Hz), 7.55–7.57 (m, 2H, H-4′, H-7′), 7.57 (dd, 2H, H-2, H-6, Jm = 1.2, Jo = 8.8 Hz), 7.67 (s, 1H, =C-H), and 12.68 (s, 1H, N-H) ppm. 13C NMR (100 MHz, DMSO-d6) δ: 64.4 (OCH2), 116.1 (C-3, C-5, C-4′, C-7′), 122.4 (C-5′, C-6′), 123.1 (=C-), 127.1 (C-1), 130.7 (=C-H), 132.3 (C-2, C-6), 138.6 (C-3a′, C-7a′), 150.1 (C-2′), 159.7 (C-4), 168.1 (N-C=O), 171.1 (S-C=O) ppm; MS/EI: m/z (% int. rel). 351 (M+, 1%), and 259 (100%). Anal. calcd. for C18H13N3O3S: C 61.53, H 3.73, N 11.96, S 9.13; found C 61.50, H 3.68, N 11.87, S 9.19.


## 2.2.2. (5Z)-5-[4-(1H-Benzimidazol-2-ylmethoxy)-3-methoxybenzylidene]-1,3-thiazolidine-2,4-dione (2)

Yellow powder, mp 245.8–248.7°C; yield 85.5%.1H NMR (400 MHz, DMSO-d6) δ: 3.80 (s, 3H, OCH3), 5.36 (s, 2H, OCH2), 7.14 (d, 2H, H-5′, H-6′ Jo = 8.4 Hz), 7.18–7.20 (m, 2H, H-2, H-6), 7.30 (d, 1H, H-5, Jo = 8.8 Hz), 7.55–7.57 (m, 2H, H-4′, H-7′), 7.71 (s, 1H, =C-H), and 12.68 (s, 1H, N-H) ppm. 13C NMR (100 MHz, DMSO-d6) δ: 55.7 (OCH3), 64.7 (OCH2), 113.9 (C-5), 114.1 (C-2), 121.17 (=C-), 123.8 (=C-H), 127.1 (C-6), 128.6 (C-4′, C-7′), 129.1 (C-5′, C-6′), 132.1 (C-1), 138.6 (C-3a′, C-7a′), 149.8 (C-4), 149.8 (C-3), 149.5 (C-2′), 168.1 (N-C=O), and 168.6 (S-C=O) ppm; MS/EI: m/z (% int. rel). 381 (M+, 1%), 265 (80%), and 180 (100%). Anal. calcd. for C19H15N3O4S : C 59.83, H 3.96, N 11.02, S 8.41; found C 59.90, H 3.89, N 11.00, S 8.45.


## 2.2.3. (5Z)-5-[3-(1H-Benzimidazol-2-ylmethoxy)-4-methoxybenzylidene]-1,3-thiazolidine-2,4-dione (3)

Yellow powder, mp 246.9°C (dec); yield 31%.1H NMR (400 MHz, DMSO-d6) δ: 3.85 (s, 3H, OCH3), 5.34 (s, 2H, OCH2), 7.17 (s, 1H, H-5, Jo = 8.6 Hz), 7.18–7.20 (m, 2H, H-5′, H-6′), 7.23 (dd, 1H, H-6, Jm = 1.02, Jo = 8.6 Hz), 7.37 (d, 1H, H-2, Jm = 1.02 Hz), 7.56–7.58 (m, 2H, H-4′, H-7′), 7.69 (s, 1H, =C-H), and 12.68 (s, 1H, N-H) ppm. 13C NMR (100 MHz, DMSO-d6) δ: 55.7 (OCH3), 64.4 (OCH2), 112.5 (C-5), 115.2 (C-2), 122.1 (=C-), 124.6 (C-6), 125.7 (=C-H), 128.5 (C-4′, C-7′), 129.2 (C-5′, C-6′), 131.3 (C-1), 138.6 (C-3a′, C-7a′), 147.5 (C-3), 149.5 (C-4), 150.1 (C-2′), 168.4 (N-C=O), and 168.8 (S-C=O) ppm; MS/EI: m/z (% int. rel). 381 (M+, 1%), anal. calcd. for C19H15N3O4S : C 59.83, H 3.96, N 11.02, S 8.41; found C 59.76, H 3.89, N 11.00, S 8.36.


## 2.3. Preparation of 2-(Chloromethyl)-1H-benzimidazole (4)

1,2-Phenylenediamine (1 g, 0. 8 mmol), 1.3 equivalents of chloroacetic acid, and 10 mL of 1 M HCl were heated at 90°C in a nitrogen atmosphere for 10 h. The cooled mixture was basified with saturated NaHCO3 solution, and the crude product was extracted with AcOEt. Solvent was removed and the solids filtrated. Yellow powder, mp 147.8–148.2°C (Lit. 142°C–144°C); yield 53.2%. 1H NMR (400 MHz, DMSO-d6) δ: 4.90 (s, 2H, ClCH2), 7.18–7.20 (m, 2H, H-5′, H-6′), and 7.54–7.55 (m, 2H, H-4′, H-7′) ppm. MS/EI: m/z (% int. rel). 165 (M+, 45%), 131 (100%), and 180 (100%).


## 2.4. General Preparation of Precursors 5–7

A solution of generally recognized as safe hydroxybenzaldehydes (0.25 mmol of 4-hydroxybenzaldehyde (8), vanillin (9), or isovanillin (10)) and K2CO3 (0.51 mmol, 2 equiv.) in 5 mL of acetonitrile was heated at 50°C for 30 min. After that, 2-(chloromethyl)-1H-benzimidazole (4) (0.275 mmol, 1.1 equiv.) in acetonitrile was added drop by drop. The reaction was heated for 2–9 h. Acetonitrile was removed using a rotavapor. 10 mL of ice-water was added and stirred for 10 min. The emulsion was extracted with EtAcO (3 × 15 mL), and the organic layer was evaporated to give a solid, which was recrystallizated from suitable solvent.


### 2.4.1. 4-(1H-Benzimidazol-2-ylmethoxy)benzaldehyde (5)

Brown powder, ethanol, mp 179°C–181.9°C; yield 95%.1H NMR (400 MHz, DMSO-d6) δ: 5.45 (s, 2H, OCH2), 7.17–7.20 (m, 2H, H-5′, H-6′), 7.29 (dd, 2H, H-3, H-5, Jm = 1.2, Jo = 8.8 Hz), 7.54–7.56 (m, 2H, H-4′, H-7′), 7.88 (dd, 2H, H-2, H-6, Jm = 1.2, Jo = 8.8 Hz), and 9.87 (s, 1H, CHO) ppm. MS/EI: m/z (% int. rel). 252 (M+, 24%) and 131 (100%).


### 2.4.2. 4-(1H-Benzimidazol-2-ylmethoxy)-3-methoxybenzaldehyde (6)

Brown powder, ethanol, mp 71.7–74.7°; yield 48.7%.1H NMR (400 MHz, DMSO-d6) δ: 3.82 (s, 3H, OCH3), 5.41 (s, 2H, OCH2), 7.16–7.18 (m, 2H, H-5′, H-6′), 7.37 (d, 1H, H-5, Jo = 8.8 Hz), 7.41 (d, 1H, H-2, Jm = 2.1 Hz), 7.53 (dd, 1H, H-6, Jm = 2.1, Jo = 8.8 Hz), 7.53–7.55 (m, 2H, H-4′, H-7′), and 9.83 (s, 1H, CHO) ppm. MS/EI: m/z (% int. rel) 282 (M+, 1%) and 131 (100%).


### 2.4.3. 3-(1H-Benzimidazol-2-ylmethoxy)-4-methoxybenzaldehyde (7)

Brown powder, ethanol, mp 80.9°C (dec); yield 59%.1H NMR (400 MHz, DMSO-d6) δ: 3.89 (s, 3H, OCH3), 5.37 (s, 2H, OCH2), 7.13 (d, 1H, H-5, Jo = 8.7 Hz), 7.19 (m, 2H, H-4′, H-7′), 7.23 (d, 1H, H-6 Jo = 8.7 Hz), 7.37 (s, 1H, H-2), and 9.82 (s, 1H, CHO) ppm. MS/EI: m/z (% int. rel) 282 (M+, 2%) and 131 (100%).


## 2.4.1. 4-(1H-Benzimidazol-2-ylmethoxy)benzaldehyde (5)

Brown powder, ethanol, mp 179°C–181.9°C; yield 95%.1H NMR (400 MHz, DMSO-d6) δ: 5.45 (s, 2H, OCH2), 7.17–7.20 (m, 2H, H-5′, H-6′), 7.29 (dd, 2H, H-3, H-5, Jm = 1.2, Jo = 8.8 Hz), 7.54–7.56 (m, 2H, H-4′, H-7′), 7.88 (dd, 2H, H-2, H-6, Jm = 1.2, Jo = 8.8 Hz), and 9.87 (s, 1H, CHO) ppm. MS/EI: m/z (% int. rel). 252 (M+, 24%) and 131 (100%).


## 2.4.2. 4-(1H-Benzimidazol-2-ylmethoxy)-3-methoxybenzaldehyde (6)

Brown powder, ethanol, mp 71.7–74.7°; yield 48.7%.1H NMR (400 MHz, DMSO-d6) δ: 3.82 (s, 3H, OCH3), 5.41 (s, 2H, OCH2), 7.16–7.18 (m, 2H, H-5′, H-6′), 7.37 (d, 1H, H-5, Jo = 8.8 Hz), 7.41 (d, 1H, H-2, Jm = 2.1 Hz), 7.53 (dd, 1H, H-6, Jm = 2.1, Jo = 8.8 Hz), 7.53–7.55 (m, 2H, H-4′, H-7′), and 9.83 (s, 1H, CHO) ppm. MS/EI: m/z (% int. rel) 282 (M+, 1%) and 131 (100%).


## 2.4.3. 3-(1H-Benzimidazol-2-ylmethoxy)-4-methoxybenzaldehyde (7)

Brown powder, ethanol, mp 80.9°C (dec); yield 59%.1H NMR (400 MHz, DMSO-d6) δ: 3.89 (s, 3H, OCH3), 5.37 (s, 2H, OCH2), 7.13 (d, 1H, H-5, Jo = 8.7 Hz), 7.19 (m, 2H, H-4′, H-7′), 7.23 (d, 1H, H-6 Jo = 8.7 Hz), 7.37 (s, 1H, H-2), and 9.82 (s, 1H, CHO) ppm. MS/EI: m/z (% int. rel) 282 (M+, 2%) and 131 (100%).


## 2.5. Biological Activity

### 2.5.1. PPARγ and GLUT-4 Determination

Assays were performed as described elsewhere [3, 12, 13]. Briefly, 3T3-L1 murine fibroblasts were cultured, and cell viability was measured using the MTT assay at three increasing concentrations (1, 10, and 100 μM) of hybrids 1–3. Confluent cultures of fibroblasts were differentiated to the adipocyte phenotype for 48 h employing 0.5 mM of 3-isobutyl-1-methylxanthine, 0.25 μM of dexamethasone acetate, and 0.8 μM of murine insulin, enriched by additional insulin charge. After 8 to 10 days, the cells acquire the mature adipocyte phenotype and were treated for 24 h to observe the effects of heterocycles 1–3 on PPARγ and GLUT-4 mRNA expression. Total mRNA was isolated from adipocytes, and 2 μg was reverse transcribed. The cDNA was amplified using SYBR Green Master Mix (Roche) containing 0.5 mM of customized primers for PPARγ (GenBank accession no.: NM 011146.1) and GLUT-4 (GenBank accession no.: NM009204.2). PCR was used for individually sample calculating the threshold cycles (Ct) and the ΔCt values. The amount of mRNA for each gene was normalized according to the amount of mRNA encoding ribosomal protein 36B4 (GenBank accession no.: NM_007475.2). The ΔCt values were calculated in every sample for each gene of interest as follows: Ct gene of interest—Ct reference gene with 36B4 as the reference gene (mRNA of reference remained stable throughout the experiments). Fluctuations in the relative expression levels of individual specific genes (ΔΔCt) were measured and graphed [2, 12].


### 2.5.2. In Vivo Oral Glucose Tolerance Assay

All animal procedures were conducted in accordance with the Official Mexican Rules for Animal Experimentation and Care (SAGARPA, NOM-062-ZOO-1999), ratified by the Institutional Animal Care and Use Committee of the Universidad Autónoma Metropolitana (dictum 1857), based on US National Institutes of Health Publication #85-23, revised 1985.Normoglycemic mice (ICR strain) were divided into 3 groups of 6 mice (n = 6). 30 minutes after administration of heterocycles 1–3, a dose of 2 g/kg of glucose solution was administered to individual mouse. Samples of blood were collected from the caudal vein at 0, 0.5, 1, 1.5, and 2 hours, followed by the oral administration of vehicle (Tween 80, 10%), heterocycles 1–3, or glibenclamide. Glucose concentration was estimated using a commercial glucometer test strips [3, 12].


## 2.5.1. PPARγ and GLUT-4 Determination

Assays were performed as described elsewhere [3, 12, 13]. Briefly, 3T3-L1 murine fibroblasts were cultured, and cell viability was measured using the MTT assay at three increasing concentrations (1, 10, and 100 μM) of hybrids 1–3. Confluent cultures of fibroblasts were differentiated to the adipocyte phenotype for 48 h employing 0.5 mM of 3-isobutyl-1-methylxanthine, 0.25 μM of dexamethasone acetate, and 0.8 μM of murine insulin, enriched by additional insulin charge. After 8 to 10 days, the cells acquire the mature adipocyte phenotype and were treated for 24 h to observe the effects of heterocycles 1–3 on PPARγ and GLUT-4 mRNA expression. Total mRNA was isolated from adipocytes, and 2 μg was reverse transcribed. The cDNA was amplified using SYBR Green Master Mix (Roche) containing 0.5 mM of customized primers for PPARγ (GenBank accession no.: NM 011146.1) and GLUT-4 (GenBank accession no.: NM009204.2). PCR was used for individually sample calculating the threshold cycles (Ct) and the ΔCt values. The amount of mRNA for each gene was normalized according to the amount of mRNA encoding ribosomal protein 36B4 (GenBank accession no.: NM_007475.2). The ΔCt values were calculated in every sample for each gene of interest as follows: Ct gene of interest—Ct reference gene with 36B4 as the reference gene (mRNA of reference remained stable throughout the experiments). Fluctuations in the relative expression levels of individual specific genes (ΔΔCt) were measured and graphed [2, 12].


## 2.5.2. In Vivo Oral Glucose Tolerance Assay

All animal procedures were conducted in accordance with the Official Mexican Rules for Animal Experimentation and Care (SAGARPA, NOM-062-ZOO-1999), ratified by the Institutional Animal Care and Use Committee of the Universidad Autónoma Metropolitana (dictum 1857), based on US National Institutes of Health Publication #85-23, revised 1985.Normoglycemic mice (ICR strain) were divided into 3 groups of 6 mice (n = 6). 30 minutes after administration of heterocycles 1–3, a dose of 2 g/kg of glucose solution was administered to individual mouse. Samples of blood were collected from the caudal vein at 0, 0.5, 1, 1.5, and 2 hours, followed by the oral administration of vehicle (Tween 80, 10%), heterocycles 1–3, or glibenclamide. Glucose concentration was estimated using a commercial glucometer test strips [3, 12].


## 2.6. Statistical Analysis

To analyze the fluctuations in the percent variation of plasmatic glucose and thein vitro PPARγ and GLUT-4 determinations, we employed ANOVA, complemented with a Dunnett’s multiple test. All values are expressed as the mean ± SEM, p<0.05 (statistically significant). GraphPad Prism 5.0 was used for the analysis.


## 2.7. In Silico Docking Calculations

Molecular operation environment software (MOE) [14] and Pymol version 1.0 were employed for visualization. The crystal coordinates of PPARγ were retrieved from the protein databank (PDB) with the accession code 5U5L. Docking simulations were performed with AutoDock, ver.4.2. The program conducts numerous runs in each docking experiment. H2O molecules and cocrystal ligands were extracted from the crystallographic coordinates, and Gasteiger charges were assigned for the compounds and PPARγ. All torsions were permitted to rotate during the calculation. The program AutoGrid created the grid maps, placed at the coordinates of the crystallographic ligand with dimensions of 60 × 60 × 60 Å and points separated by 0.375 Å. The number of docking runs was 100. After computational calculations, all solutions were clustered into groups with RMSD <2.0 Å and by the lowest energy.


### 2.7.1. Docking Validation

The docking protocols were validated by redocking of rivoglitazone (cocrystal ligand) into the PPARγ ligand binding site of 5U5L. The root mean square deviation (RMSD) between the cocrystal ligand and the rivoglitazone docked was 0.433 Å. This value specifies that the parameters for docking calculations are reproducing conformation and orientation in the X-ray crystal of PPARγ.


## 2.7.1. Docking Validation

The docking protocols were validated by redocking of rivoglitazone (cocrystal ligand) into the PPARγ ligand binding site of 5U5L. The root mean square deviation (RMSD) between the cocrystal ligand and the rivoglitazone docked was 0.433 Å. This value specifies that the parameters for docking calculations are reproducing conformation and orientation in the X-ray crystal of PPARγ.


## 3. Results and Discussion

### 3.1. Chemistry

The synthetic route for the preparation of hybrid compounds1–3 is described in Figure 2. For achieving the synthesis of the titled compounds involved the preliminary preparation of 2-chloromethyl-1H-benzimidazole (4). In this step, starting from 1,2-phenylenediamine (13) upon treating with chloroacetic acid (12) in 10 mL of HCl 1 M as solvent generated 4 in moderated yield (53%). Later, the aforementioned reaction mixture was heated in acetonitrile with 4-hydroxybenzaldehyde (8), vanillin (9), or isovanillin (10), three generally recognized as safe compounds, in the presence of anhydrous K2CO3, yielded alkoxybenzaldehydes 5–7. In the last step, a mixture of alkoxybenzaldehydes 5–7, piperidinium benzoate (30% mol), and thiazolidine-2,4-dione (11), in toluene was heated under reflux with constant elimination of H2O employing a Dean–Stark apparatus. After the reaction was completed by TLC, the mixture was cooled to room temperature and the solids were separated by filtration affording the corresponding compounds 1–3, which were recovered with 31–85% yields and purified by recrystallization. Chemical structures were established by spectroscopic (1H, 13C NMR) and spectrometric analysis. In the nuclear magnetic resonance spectra, the signals of the respective hydrogens of the titled heterocycles were assigned identifying the chemical shifts, multiplicities, and coupling constants (J). All compounds exhibited a single signal ranging from δΗ 5.34 to 5.40 ppm, attributed to CH2 of the ether bridge. Compounds 2 and 3 displayed the characteristic signals of trisubstituted benzene, whereas compound 1 showed signals for disubstituted benzene. The aromatic region of the 1H NMR spectrum of compounds 1–3 contained an A2B2 pattern signals ranging from δΗ 7.14 to 7.20 ppm (d, Jortho = 8.4 Hz) and 7.55 to 7.58 ppm (d, Jortho = 8.4 Hz) attributed to the equivalents H-5′, H-6′ and H-4′, H-7′, respectively, of the benzimidazole tautomeric ring. The displacement for methoxy group in compounds 2 and 3 was found in 3.80 and 3.85 ppm (singlet), respectively. In all compounds, a singlet signal for benzylidene hydrogen was found ranging from δH 7.67 to 7.71 ppm, and the last signal of the spectra was found in 12.68 ppm, corresponding to N-H of the thiazolidine-2,4-dione ring. For the 13C nuclear magnetic resonance spectra, constant signals were found for the benzimidazole nucleus: one signal ranging from δC 116.1 to 128.7 ppm, attributed to C-4′ and C-7′, and additional signal ranging from δC 122.4 to 129.2 ppm, assigned to C-5′and C-6′. Another frequent signal was found in downfield shifts from δC 149.5 to 150.1 ppm endorsed to C-2′, found in all compounds. The thiazolidine-2,4-dione scaffold also showed constant signals: δC 168.6 to 171.1 ppm attributed to S-C=O, δC 168.1 to 168.6 ppm endorsed to N-C=O, and δC 121.1 to 123.1 ppm assigned to =C-S. Benzylidene signal was found in δC 123.8 to 130.7 ppm, whereas the signal for methyleneoxy bridge was constant in 64.4 to 64.7 ppm.Figure 2
Synthesis of compounds1–3: (i) HCl 1 M reflux; (ii) K2CO3, acetonitrile; (iii) piperidinium benzoate (30% mol), toluene, and Dean–Stark apparatus.


### 3.2. In Vitro mRNA Expression of PPARγ and GLUT-4

For thein vitro mRNA expression of selected targets, murine fibroblasts (3T3-L1) were differentiated to adipocytes to observe the effect of title compounds on PPARγ and GLUT-4 mRNA concentration. Adipocytes were processed for 24 hours with 10 μM of heterocycles 1–3 and agonist control drug (pioglitazone, PIO) [12, 13]. Previously, the viability of 3T3-L1 cells was examined at 1, 10, and 100 μM of compounds 1–3 using the MTT assay reported in reference [15]. No cytotoxicity was observed in any of the three concentrations tested (data not shown). Then, fluctuation in the mRNA expression level was evaluated by qPCR. Figure 3 shows that compounds 2, 3, and pioglitazone (PIO) augmented with statistical significance, the mRNA expression of PPARγ (around 2.7- to 3.2-fold), and its downstream gene GLUT-4 (3.5-fold). On the other hand, the increased levels of PPARγ and another glucose transporter (GLUT-2) were previously reported for p-coumaric acid [7, 8].Figure 3
Changes in the expression of PPARγ (a) and GLUT-4 (b) induced by hybrid bioisosteres 1–3 and pioglitazone. ANOVA with post hoc Dunnett’s test (n = 5, mean ± SEM, p<0.001 compared with CTRL group).
(a)
(b)Agonism of PPARγ could decrease glycemia in diabetic individuals through an improvement in insulin sensitization, and the increments in GLUT-4 levels in the striated muscle are crucial for glucose regulation [16]. The results obtained here suggest that compounds 2 and 3 prompt GLUT-4 mRNA concentration greater than pioglitazone (Figure 3(b)).Furthermore, compound1 did not provoke a statistically significant rise in the mRNA expression level of PPARγ, but a slight increase in GLUT-4 expression (2.1-fold). These results suggest that increments in the concentration of the downstream genes are not always dependent on high expression of PPARγ, instead the activation is the most important process.


### 3.3. In Vivo Oral Glucose Tolerance Test (OGTT)

To confirm the possible hypoglycemic and/or antihyperglycemic action of hybrids1–3, we performed an OGTT in normal glycemic mice using glibenclamide (Gli) as hypoglycemic control drug. Figure 4 shows the results of these experiments. All compounds administered at 100 mg/kg significantly decreased glycemia sixty minutes after glucose ingestion (2 g/kg) in comparison with the vehicle (Tween 80, 10%) that showed the maximum hyperglycemia at the first hour. The AUC graph (area under the curve) established the efficacy of heterocycles 1–3, which decreased with statistical significance the AUC of the control (vehicle) around 75% (Figure 4). Throughout the assay, glucose concentrations did not diminish beyond normal levels as glibenclamide did, demonstrating that compounds 1–3 have an antihyperglycemic effect in agreement with insulin sensitization provoked by PPAR agonism [16, 17].Figure 4
Oral glucose tolerance test (a) and AUC (b) of heterocycles1–3. ∗Statistical significance compared with control (n = 6, mean ± SEM, p<0.05).
(a)
(b)


### 3.4. Molecular Docking Simulations

Once established thein vitro PPAR activation and in vivo antihyperglycemic action, compounds 1–3 were subjected to an in silico docking analysis, in order to explain the experimental effects on PPARγ. Docking simulation exposed that hybrids 1–3 enter into the ligand binding site of PPARγ (PDB ID: 5U5L) and produce a net of hydrogen bonds with His-323, and several contact with Tyr-327, Cys-285, Ser-289, and Arg-288, the important amino acids for the PPARγ activation (Figure 5). Rivoglitazone was previously cocrystallized with PPARγ and shared the same contacts, where only one oxygen atom from the thiazolidine-2,4-dione participates in the hydrogen-bonding network with His-323 [6]. p-Coumaric acid was also docked over PPARγ for comparative purposes with its inspired hybrids 1–3, showing less affinity than its bioisosteres, but maintaining the key polar interaction with His-323 (Table 1). Validation of docking yielded an RMSD value of 0.433 Å. MOE [14] and Pymol version 1.7.4 were employed for visualization.Figure 5
3-D binding diagram (a) and 2-D overlay (b) of1 (red) and 2 (green) into the PPARγ ligand site, sharing the same orientation.
(a)
(b)Table 1
Molecular docking binding energies, calculated affinities, and qualitative pharmacological activities of compounds1–3.
Compound
PPARγ ΔG (kcal/mol)
Ki (μM)
In vitro activity
In vivo effect
1
−7.98
1.346
++
++
2
−8.17
0.976
+++
+++
3
−8.96
0.256
+++
+++
p-Coumaric acid∗
−4.64
385.9
+ [8]
+ [8]
Rivoglitazone∗
−7.33
4.261
++ [6]
++ [18]
∗References [6], [8], and [18].Hybrids1 and 2 assume a similar conformation within the PPARγ ligand binding site mediated by hydrogen bonds with His-323 and π-sp3 interactions with His-449 (Figure 5).Compound3 (obtained from isovanillin) displayed a different conformation than its regioisomer 2 (obtained from vanillin). Although the thiazolidine-2,4-dione heterocycle was correctly oriented to interact with the His-323, the part of the benzimidazole ring was adapted to the side arm of the PPAR cavity, displaying several extra interactions with Arg-288, His-449, and Tyr-327 (Figure 6).Figure 6
Comparison of the 3-D binding mode of regioisomers2 and 3 (a) and 2-D map interaction of 3 with the PPARγ ligand site (b).
(a)
(b)Both molecular docking scores (binding energies) and calculated affinities (Ki) correspond to the performance of heterocycles 1–3, p-coumaric acid, and rivoglitazone in the in vitro and in vivo pharmacological tests (Table 1), suggesting that chemoinformatic simulations are very useful in drug discovery, to explain the potential mode of action of bioactive compounds.


## 3.1. Chemistry

The synthetic route for the preparation of hybrid compounds1–3 is described in Figure 2. For achieving the synthesis of the titled compounds involved the preliminary preparation of 2-chloromethyl-1H-benzimidazole (4). In this step, starting from 1,2-phenylenediamine (13) upon treating with chloroacetic acid (12) in 10 mL of HCl 1 M as solvent generated 4 in moderated yield (53%). Later, the aforementioned reaction mixture was heated in acetonitrile with 4-hydroxybenzaldehyde (8), vanillin (9), or isovanillin (10), three generally recognized as safe compounds, in the presence of anhydrous K2CO3, yielded alkoxybenzaldehydes 5–7. In the last step, a mixture of alkoxybenzaldehydes 5–7, piperidinium benzoate (30% mol), and thiazolidine-2,4-dione (11), in toluene was heated under reflux with constant elimination of H2O employing a Dean–Stark apparatus. After the reaction was completed by TLC, the mixture was cooled to room temperature and the solids were separated by filtration affording the corresponding compounds 1–3, which were recovered with 31–85% yields and purified by recrystallization. Chemical structures were established by spectroscopic (1H, 13C NMR) and spectrometric analysis. In the nuclear magnetic resonance spectra, the signals of the respective hydrogens of the titled heterocycles were assigned identifying the chemical shifts, multiplicities, and coupling constants (J). All compounds exhibited a single signal ranging from δΗ 5.34 to 5.40 ppm, attributed to CH2 of the ether bridge. Compounds 2 and 3 displayed the characteristic signals of trisubstituted benzene, whereas compound 1 showed signals for disubstituted benzene. The aromatic region of the 1H NMR spectrum of compounds 1–3 contained an A2B2 pattern signals ranging from δΗ 7.14 to 7.20 ppm (d, Jortho = 8.4 Hz) and 7.55 to 7.58 ppm (d, Jortho = 8.4 Hz) attributed to the equivalents H-5′, H-6′ and H-4′, H-7′, respectively, of the benzimidazole tautomeric ring. The displacement for methoxy group in compounds 2 and 3 was found in 3.80 and 3.85 ppm (singlet), respectively. In all compounds, a singlet signal for benzylidene hydrogen was found ranging from δH 7.67 to 7.71 ppm, and the last signal of the spectra was found in 12.68 ppm, corresponding to N-H of the thiazolidine-2,4-dione ring. For the 13C nuclear magnetic resonance spectra, constant signals were found for the benzimidazole nucleus: one signal ranging from δC 116.1 to 128.7 ppm, attributed to C-4′ and C-7′, and additional signal ranging from δC 122.4 to 129.2 ppm, assigned to C-5′and C-6′. Another frequent signal was found in downfield shifts from δC 149.5 to 150.1 ppm endorsed to C-2′, found in all compounds. The thiazolidine-2,4-dione scaffold also showed constant signals: δC 168.6 to 171.1 ppm attributed to S-C=O, δC 168.1 to 168.6 ppm endorsed to N-C=O, and δC 121.1 to 123.1 ppm assigned to =C-S. Benzylidene signal was found in δC 123.8 to 130.7 ppm, whereas the signal for methyleneoxy bridge was constant in 64.4 to 64.7 ppm.Figure 2
Synthesis of compounds1–3: (i) HCl 1 M reflux; (ii) K2CO3, acetonitrile; (iii) piperidinium benzoate (30% mol), toluene, and Dean–Stark apparatus.


## 3.2. In Vitro mRNA Expression of PPARγ and GLUT-4

For thein vitro mRNA expression of selected targets, murine fibroblasts (3T3-L1) were differentiated to adipocytes to observe the effect of title compounds on PPARγ and GLUT-4 mRNA concentration. Adipocytes were processed for 24 hours with 10 μM of heterocycles 1–3 and agonist control drug (pioglitazone, PIO) [12, 13]. Previously, the viability of 3T3-L1 cells was examined at 1, 10, and 100 μM of compounds 1–3 using the MTT assay reported in reference [15]. No cytotoxicity was observed in any of the three concentrations tested (data not shown). Then, fluctuation in the mRNA expression level was evaluated by qPCR. Figure 3 shows that compounds 2, 3, and pioglitazone (PIO) augmented with statistical significance, the mRNA expression of PPARγ (around 2.7- to 3.2-fold), and its downstream gene GLUT-4 (3.5-fold). On the other hand, the increased levels of PPARγ and another glucose transporter (GLUT-2) were previously reported for p-coumaric acid [7, 8].Figure 3
Changes in the expression of PPARγ (a) and GLUT-4 (b) induced by hybrid bioisosteres 1–3 and pioglitazone. ANOVA with post hoc Dunnett’s test (n = 5, mean ± SEM, p<0.001 compared with CTRL group).
(a)
(b)Agonism of PPARγ could decrease glycemia in diabetic individuals through an improvement in insulin sensitization, and the increments in GLUT-4 levels in the striated muscle are crucial for glucose regulation [16]. The results obtained here suggest that compounds 2 and 3 prompt GLUT-4 mRNA concentration greater than pioglitazone (Figure 3(b)).Furthermore, compound1 did not provoke a statistically significant rise in the mRNA expression level of PPARγ, but a slight increase in GLUT-4 expression (2.1-fold). These results suggest that increments in the concentration of the downstream genes are not always dependent on high expression of PPARγ, instead the activation is the most important process.


## 3.3. In Vivo Oral Glucose Tolerance Test (OGTT)

To confirm the possible hypoglycemic and/or antihyperglycemic action of hybrids1–3, we performed an OGTT in normal glycemic mice using glibenclamide (Gli) as hypoglycemic control drug. Figure 4 shows the results of these experiments. All compounds administered at 100 mg/kg significantly decreased glycemia sixty minutes after glucose ingestion (2 g/kg) in comparison with the vehicle (Tween 80, 10%) that showed the maximum hyperglycemia at the first hour. The AUC graph (area under the curve) established the efficacy of heterocycles 1–3, which decreased with statistical significance the AUC of the control (vehicle) around 75% (Figure 4). Throughout the assay, glucose concentrations did not diminish beyond normal levels as glibenclamide did, demonstrating that compounds 1–3 have an antihyperglycemic effect in agreement with insulin sensitization provoked by PPAR agonism [16, 17].Figure 4
Oral glucose tolerance test (a) and AUC (b) of heterocycles1–3. ∗Statistical significance compared with control (n = 6, mean ± SEM, p<0.05).
(a)
(b)


## 3.4. Molecular Docking Simulations

Once established thein vitro PPAR activation and in vivo antihyperglycemic action, compounds 1–3 were subjected to an in silico docking analysis, in order to explain the experimental effects on PPARγ. Docking simulation exposed that hybrids 1–3 enter into the ligand binding site of PPARγ (PDB ID: 5U5L) and produce a net of hydrogen bonds with His-323, and several contact with Tyr-327, Cys-285, Ser-289, and Arg-288, the important amino acids for the PPARγ activation (Figure 5). Rivoglitazone was previously cocrystallized with PPARγ and shared the same contacts, where only one oxygen atom from the thiazolidine-2,4-dione participates in the hydrogen-bonding network with His-323 [6]. p-Coumaric acid was also docked over PPARγ for comparative purposes with its inspired hybrids 1–3, showing less affinity than its bioisosteres, but maintaining the key polar interaction with His-323 (Table 1). Validation of docking yielded an RMSD value of 0.433 Å. MOE [14] and Pymol version 1.7.4 were employed for visualization.Figure 5
3-D binding diagram (a) and 2-D overlay (b) of1 (red) and 2 (green) into the PPARγ ligand site, sharing the same orientation.
(a)
(b)Table 1
Molecular docking binding energies, calculated affinities, and qualitative pharmacological activities of compounds1–3.
Compound
PPARγ ΔG (kcal/mol)
Ki (μM)
In vitro activity
In vivo effect
1
−7.98
1.346
++
++
2
−8.17
0.976
+++
+++
3
−8.96
0.256
+++
+++
p-Coumaric acid∗
−4.64
385.9
+ [8]
+ [8]
Rivoglitazone∗
−7.33
4.261
++ [6]
++ [18]
∗References [6], [8], and [18].Hybrids1 and 2 assume a similar conformation within the PPARγ ligand binding site mediated by hydrogen bonds with His-323 and π-sp3 interactions with His-449 (Figure 5).Compound3 (obtained from isovanillin) displayed a different conformation than its regioisomer 2 (obtained from vanillin). Although the thiazolidine-2,4-dione heterocycle was correctly oriented to interact with the His-323, the part of the benzimidazole ring was adapted to the side arm of the PPAR cavity, displaying several extra interactions with Arg-288, His-449, and Tyr-327 (Figure 6).Figure 6
Comparison of the 3-D binding mode of regioisomers2 and 3 (a) and 2-D map interaction of 3 with the PPARγ ligand site (b).
(a)
(b)Both molecular docking scores (binding energies) and calculated affinities (Ki) correspond to the performance of heterocycles 1–3, p-coumaric acid, and rivoglitazone in the in vitro and in vivo pharmacological tests (Table 1), suggesting that chemoinformatic simulations are very useful in drug discovery, to explain the potential mode of action of bioactive compounds.


## 4. Conclusion

In summary, three hybrids composed of benzimidazole and thiazolidine-2,4-dione have been synthesized, offering the following advantages over current antidiabetic glitazone drugs: preparation in fewer steps, use of safe and nontoxic raw materials (generally recognized as safe aldehydes: vanillin, isovanillin, and 4-hydroxybenzaldehyde), and comparable antihyperglycemic action. Hybrid bioisosteres1–3 significantly augmented the mRNA expression of PPARγ and GLUT-4 greater than pioglitazone and in vivo reduced blood glucose concentration with antihyperglycemic effect linked to insulin sensitization mode of action.



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*Source: 1650145-2019-10-15.xml*