Synthesis, Characterization and In-Vitro Antidiabetic Studies of Vanadium Complexes derived from N₂O₂ donor Ligands

 

Shashikant P. Pawar¹, Tryambakrao J. Patil², Ratnamala S. Bendre³*

¹Smt. Narmadabai Nago Chaudhari, Arts Commerce and Science College, Kusumba, Dhule Maharashtra,  India

²Jai Hind Education Trust’s  Z. B.  Patil College, Dhule, Maharashtra, India

³School of Chemical Sciences, North Maharashtra University Jalgaon, Maharashtra, India

*Corresponding Author E-mail: bendrers@gmail.com

Trace elements are very essential for human health. Chemists have been attracted to prepare new potent inorganic pharmaceutical agents and these are used to treat chronic diseases. Vanadium complexes are used as good diagnostic tool for diabetes mellitus. The progress in the field of development in orally active antidiabetic vanadium complexes with different coordination structures using experimental diabetic animals and enzyme inhibitory action (α-amylase inhibition). In the present study we synthesized, characterized and evaluated % α- amylase inhibition by vanadium complexes having tetradentate Schiff base ligands–H₂L_1, H₂L₂ and H₂L₃. The mole ratio for preparation of complexes is 1:1. The synthesized vanadium complexes were characterized by sophisticated techniques and screened for antidiabetic activity by α-amylase inhibition assay. The data assigned to conclude that H₂L₁ shows lowest IC₅₀ value 0.786 mg/ml while L₂V shows highest IC₅₀ value 0.626 mg/ml.

 

 

 

INTRODUCTION:

Diabetes comprises a group of metabolic disorders characterized by chronic hyperglycemia with disorders in the metabolism of carbohydrate, fat and protein that result in defects in secretion and action of insulin [1]. The action dysfunction and failure of various organs, especially the eyes, kidneys, nerves, heart and the blood vessels are the usual complications of diabetes [2,3]. The literature study reveals that compounds of the trace element vanadium exert various insulino-mimetic and anti-diabetic effects in vitro and in vivo [4-8].

 

Metallotherapy is a new therapeutic strategy to treat diabetes with metal complexes. It is first studied by Coulson and Dandona in 1980 that ZnCl₂ stimulates lipogenesis in rat adipocytes similarly to the action of Insulin. During three decades many researchers reported insulin-mimetic activity, α-glucosidase and α-amylase inhibition with different transition metal complexes involving variety of ligands [9]. One of the current focuses is to create pharmaceutics that will take advantage of the insulinomimitic and anti-diabetic properties of vanadium in the place of insulin injections and synthetic drugs [10,11]. Schiff base metal complexes have been widely studied because they have industrial, antifungal, antibacterial, anticancer, antiviral and herbicidal applications [12-17]. The first report of vanadium salts being used as a metallotherapeutic agent appeared in 1899 [18]. Several vanadium complexes of the tetradentate Schiff base ligand N,N'-bis(salicylidene)ethylenediamine (salen) have been proposed for potential application as insulin mimetic agents [19].Salen type ligands (H₂L₁,H₂L₂) derived by reacting substituted benzaldehyde o-(thymoldehyde) with different diamines and a reduction product (H₂L₃) of one of the Schiff base (H₂L₁).

 

MATERIALS AND METHOD:

Chemicals

All reagents and chemicals were purchased from commercial sources and were used without further purification.  All the ligands and vanadium complexes were synthesized by the reported method. VOSO₄ and NaBH₄ was obtained from SRL Chemicals, ethylenediamine, o-phenylenediamine, 1,3-propylenediamine were purchased from sigma Aldrich chemicals, while methanol andethanol were purchased from Merck Co. (India). Acarbose, sodium phosphate buffer, starch, dinitrosalicylic acid (DNS) reagent and porcine pancreatic α-amylase were procured from SRL Co. (India). Double distilled water was used for all the experiments.

 

Experimental

The electronic spectra of ligand and complexes are recorded as DMSO solutions in the range 200–800 nm on a UV 2400 Series spectrophotometer. FT-IR spectra were recorded as KBr pellets on a SHIMADZU FT-IR-8400spectrometer in the range 4000–400 cm^-1. ¹H and ¹³C NMR spectra were measured with a BRUKER AVANCE III (400 MHz) spectrometer and proton chemical shifts have been recorded in ppm relative to tetramethyl silane as an internal standard using CDCl₃ as solvent, while the LC–MS spectra of complexes have been recorded on a Waters Micromass Q-Tof Micro instrument. The elemental analysis of ligands and complexes were carried out with a ThermoFinnigan elemental analyzer. Magnetic susceptibilities are measured at room temperature on a Guoy balance using Hg[Co(NCS)₄] as reference.

 

Synthesis of Ligands

I] Synthesis of 6,6’-{(1E,1E’) -(ethane-1,2-diylbis(azanylylidene)}bis(methanylylidene)bis(2-isopropyl-5-methylphenol) (H₂L₁)

The solution of 2-hydroxy-3-isopropyl-6-methylbenzaldehyde (0.002 M) in 15 ml ethanol was added to ethylenediamine (0.001 M) in 15 ml ethanol. The reaction mixture was refluxed on water bath for 8 hrs. The reaction mixture was allowed to cool; subjected to evaporate slowly and the yellow crystals formed was filtered, washed with cold ethanol and finally with petroleum ether. The product was recrystallized from ethanol [20]. Anal. Calc. for C₂₄H₃₂N₂O₂: Found: C, 75.50; H, 8.73; N, 7.26, O,8.51.  Calculated: C, 75.75; H, 8.48; N, 7.6, O,8.41. NMR (CDCl₃, d ppm) 1.27(d, 12H, gem 4CH₃), 2.34(s, 6H, 2Ar-CH₃), 3.32(heptet, 2H, 2CH), 3.91(s, 4H,CH₂-CH₂), 6.58(d, 2H, 2Ar-H, ortho to isopropyl gr), 7.09 (d, 2H, 2Ar-H ortho to methyl gr), 8.66 (s, 2H, 2CH=N). MS (m/z): Calc.: 380.25, Obs.: 381.3(Color- Yellow Solid, M.P.- 115 ^oC, M.W.-380, Yield-83%)

II] Synthesis of 6,6’-{1E,1E’)-(propane-1,3diylbis(azanylylidene)}bis(methanylylidene)bis(2-isopropyl-5-methylphenol) (H₂L₂)

Solution of 2-hydroxy-3-isopropyl-6-methylbenzaldehyde (0.002 M) in 15 ml ethanol and solution of 1,3-diamino propane (0.001 M) in 15 ml ethanol were mixed in round bottom flask. Reaction mixture was refluxed on water bath for 8 hrs.  The solution was concentrated to obtained dark green liquid. Anal. Calc. for C₂₅H₃₄N₂O₂: Found: C, 75.48; H, 8.85; N, 7.05, O,8.72.  Calculated: C, 76.10; H, 8.69; N, 7.10; O,8.11. NMR : δ 1.08-1.2 (12H,d), 2.40 (6H, s) 2.5 (2H, quin), 3.30 (2H, m), 3.73-3.77 (4H, t), 6.5-6.6 (2H,d), 7.12-7.24 (2H,d), 8.73 (2H, s, for OH), 14.68 (2H, s) ¹³CMR: 18.66, 22.50, 26.22, 31.67, 56.75, 115.81, 120.00, 129.04, 134.64, 135.92, 159.97, 167.52. MS (m/z): Calc. 394.26, Obs. 395.3 (Color- Yellow Solid, M.P.=80⁰C, M.W.=394, Yield=76 %)

 

III] Synthesis of 6,6’-{(ethane-1,2-diylbis(azanediyl)} bis(methylene)bis(2-isopropyl-5-methylphenol) (H₂L₃)

The solution of 2-hydroxy-3-isopropyl-6-methylbenzaldehyde(0.002 M) in 15 ml ethanol was transferred to ethylenediamine (0.001 M) in 15 ml ethanol and NaBH₄ (0.002 M) was added to it. The reaction mixture was refluxed on water bath for 2 hrs and the reaction mixture was allowed to cool; subjected to evaporate slowly and the yellow crystals formed were separated by filtration, washed with cold ethanol and finally with petroleum ether. The product was recrystallized from ethanol. Anal. Calc. for C₂₄H₃₆N₂O₂: Found: C, 75.48; H, 8.85; N, 7.05; O,8.72. Calculated: C, 76.10; H, 8.69; N, 7.10; O,8.11. NMR: δ 1.13-1.14 (12H, d), δ2.16 (6H, s), δ 2.51 (4H, s), δ3.16-3.23 (2H, m), δ 3.88 (2H, s, for OH), 6.47-6.51 (2H, d), 6.86-6.87 (2H,d), 8.13-814 (2H, s), ¹³CMR: 19.21, 22.47, 25.80, 47.13, 47.50, 119.99, 120.00, 123.69, 132.29, 132.32, 155.59. MS (m/z): Calc. 384.26, Obs. 385.3 (Color-White Solid, M.P. -161⁰C, M.W.-382, Yield-81%)

 

Synthesis of Complexes

Synthesis of [L₁V]

A 40 ml ethanolic solution of H₂L₁ (0.001M) and 40 ml of ethanolic solution of vanadium sulphate (0.001M) were mixed and refluxed for 3-4 h. The solvent was allowed to evaporate slowly and the precipitated compound was filtered, washed with cold ethanol, water and finally with petroleum ether. Color: Dark Black solid; Yield: 79%; Anal. Calc. for VC₂₄H₃₀N₂O₂: Found: C, 67.12; H, 7.04; N, 6.52; O, 7.45;  V, 11.86. Calculated: C, 67.40; H, 7.80; N, 6.42; O, 7.85; V, 11.54.μ_eff: 1.46 B.M.; Conductance (ʌ_M, Ώ^-1 cm² mol^-1) in DMSO: 17.4. ESI-MS m/z, ion 445.1 [M]^+.

 

 

Synthesis of [L₂V] and [L₃V]

Complexes 2 and 3 were prepared by similar procedure as for complex 1. Complex 2, (Pale Orange): yield, 62%. Anal. Calc. for VC₂₅H₃₂N₂O₂,Found: C, 67.71; H, 7.27; N, 6.32; O, 7.22; V, 11.49 %.Calculated: C, 67.55; H, 7.93; N, 6.42; O, 7.70; V, 11.80.μ_eff: 1.72 B.M.; Conductance (ʌ_M, Ώ^-1 cm² mol^-1) in DMSO: 37.0. ESI-MS m/z, ion 482.1 [M]⁺.   Complex 3, (Grey violet): yield: 78%. Anal.Calc. forVC₂₄H₃₂N₂O₂.  Found: C, 66.81; H, 7.48; N, 6.49; O, 7.42; V, 11.81%.Calculated: C, 66.70; H, 7.89; N, 6.45; O, 7.70; V, 11.40.μ_eff: 1.83 B.M.; Conductance (ʌ_M, Ώ^-1 cm² mol^-1) in DMSO: 9.0; ESI-MS m/z, ion 449.2 [M]⁺. The solvent was allowed to evaporate slowly and the precipitated compound was filtered, washed with cold ethanol and finally with petroleum ether.

 

Biological Activity

α-amylase Inhibition assay

Appropriate dilution of 500μl vanadium complexes and 500 μl of 0.02M sodium phosphate buffer (pH 6.9 with 0.006 M NaCl) containing porcine pancreatic α-amylase (0.5 mg/ml) were incubated at 25⁰C for 10 minutes. Then 500μl of 1% starch solution in 0.02 M sodium phosphate buffer (pH 6.9 with 0.006 M NaCl) was added to each tube. The reaction mixtures were incubated at 25⁰C for 10 minutes and stopped with 1.0 ml of dinitrosalicylic acid color reagent. Thereafter, the mixture was incubated in a boiling water bath for 5 minutes and cooled to room temperature. The reaction mixture was then diluted by adding 10 ml of distilled water and absorbance was measured at 540 nm [21-22].

 

All the samples were run in triplicate, acarbose was taken as standard reference compound. Several dilutions of primary solution (0.5mg/ml DMSO) were made and assayed accordingly to obtain concentration of the test sample required to inhibit 50% activity (IC₅₀) of the enzyme.

 

RESULTS AND DISCUSSION:

The N₂O₂ donor symmetrical Schiff bases [H₂L_1, H₂L₂] were prepared by condensation of 2-hydroxy-3-isopropyl-6-methylbenzaldehyde with, ethylenediamine and propane-1,3-diamine in 2:1 M ratio in ethanolic solution and [H₂L₃] by reduction of [H₂L₁] . [L₁V], [L₂V] and [L₃V] complexes were synthesized by refluxing ligand with equimolar amount of metal sulphate in methanol in 1:1 ratio. The spectral analysis agrees with proposed structure of the complexes.

 

The synthesized ligands H₂L_1, H₂L₂ and H₂L₃ and their vanadium complexes were screened for in vitro antidiabetic study by α-amylase inhibition assay

 

IV)  Synthesis of Vanadium Complex

 

Where H₂L= H₂L₁/ H₂L₂/ H₂L₃

 

 

A lot of literatures were reviewed and it was found that several complexes have been prepared to evaluate their antidiabetic activity for the development of a clinically useful metallopharmaceutics. However the  research of Vanadium complexes on the long-term toxicity including their side effects and clear-cut evidence of target molecules for the in vivo as well as in vitro pharmacological action and good pharmacokinetic property are highly essential [9-11]. Many vanadium complexes have been prepared to examine their α-amylase inhibition activity. In present investigation we have examined their α-amylase inhibition of three ligands and their V (IV) complexes. Table 3 demonstrates the IC₅₀ value of Acarbose, ligands and vanadium complexes. Table 4 (a) and (b) shows the absorbance of standard acarbose, ligands and vanadium complexes. Table 5 (a) and (b) represents the α-amylase inhibition of standard acarbose, ligands and vanadium complexes. Fig. 1 and Fig. 2 represent absorbance and % inhibition at various concentrations of ligands and vanadium complexes.

 

 

 

Table 1: IR Spectral data (cm^-1) of ligands and their metal complexes

 

Table 2: Electronic spectra data (nm) of ligands and vanadium complexes

 

 

Table 3: IC₅₀ values of standard, ligands and vanadium complexes

 

Table 4 (a): Absorbance of ligands at various concentrations

 

 

Table 4 (b): Absorbance of standard and vanadium complexes

 

Table5 (a): % of α-amylase inhibition of  ligands

 

Table 5 (b): % of α-amylase inhibition of  vanadium complexes

 

 

Figure 1: Representing graph between concentration (mg/ml) and absorbance

 

Fig. 2:  % Inhibition curve of α-amylase v/s concentration of samples

 

Spectral Characterization

Electronic Spectra

The electronic spectra of synthesized ligands and its vanadium complexes were recorded in DMSO solutions at different concentrations in the range 200-800 nm. The spectral data of Schiff  bases shows two bands in the range of 265-280 nm and 280-344 nm due to  π⟶π* and ɳ ⟶π*  transitions [23]. The electronic spectra of complex (1) shows absorption bands having a  λ_max  270 nm assigned to π⟶π* of aromatic ring and 327 nm assigned to ɳ ⟶π* transition of –C=N [24]. The electronic spectra of complex (2) shows absorption bands having λ _max 273 nm assigned to the π⟶π* of aromatic ring and 288 nm assigned to ɳ ⟶π*   transition of –C=N-,  the 378 nm band assigned to ligand to metal ion charge transfer and d-d transition at 551 nm of the  complex indicating square planar geometry [25-27]. The electronic spectra of complex (3) shows absorption bands having λ _max  269 nm assigned to the  π⟶π* of aromatic ring and 326 nm assigned to ɳ ⟶π*   transition of –C=N-,  the 374 nm band assigned to ligand to metal charge transfer and 549 nm band assigned to the ²B_{1g  ⟶}²A_1g transition showing square planar geometry [28,29].

 

FT-IR Spectra

The IR spectra of the ligand and complexes compared to conform the coordination of the ligand. The band at 1610 cm^-1 attributed to the –C=N in the Schiff base ligand was observed to shift to lower frequency region, 1610-1546 cm^-1 in all complexes illustrating participation of the azomethine nitrogen atom in coordination. The peak at 3220 cm^-1 appear for the phenolic-OH group. The peak appearing in the ligand at 1260cm^-1 due to C-O was shifted to 1260-1378 cm^-1 upon complexation. The weak and low frequency bands appearing in the range 400-600 cm^-1 corresponds to presence of M-O and M-N in coordination with metal [27].

 

Magnetic Susceptibility

The all three vanadium complexes shows magnetic moment in the range of 1.46 to 1.83 B.M. corresponding to square planar geometry showing one unpaired electron [30,31].

 

Molar Conductivity

The molar conductivities ʌ_M of metal complexes dissolved in DMSO at 10^-3 Mol concentration were found to be in the range of 9-37Ώ^-1 cm² mol^-1. The low values indicate that all these complexes are non-electrolyte in nature due to absence of any counter ions in their structures [30].

 

CONCLUSION:

In above investigation we are reporting the synthesis and characterization of ligands and their Vanadium complexes. It has been observed that Vanadium complexes posses higher activity than their respected ligands. The ligands and their vanadium complexes were screened for their in vitro antidiabetic activity. Sharp intense peak around 1600 cm^-1in IR spectra shows the formation of complexes. All ligands and complexes shows α-amylase inhibition activity, data assign to conclude that H₂L₁ shows lowest IC₅₀ value 0.786 mg/ml while L₂V show highest IC₅₀ value 0.626 mg/ml activity. All the ligands and vanadium complexes have IC₅₀ less than 1 mg/ml, the values are close to standard drug Acarbose.

 

ACKNOWLEDGEMENT:

The Authors would like to thank North Maharashtra University, Jalgaon, Maharashtra for  financial assistant through VCRMS Scheme.

 

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Received on 27.01.2018         Modified on 02.02.2018

Accepted on 14.02.2018         © AJRC All right reserved