Synthesis, Characterization and Assessment of Antioxidant and Melanogenic Inhibitory Properties of Edaravone Derivatives

Abstract

A series of edaravone derivatives and the corresponding Cu(II) complexes were synthesized and characterized using spectroscopic and analytical techniques such as IR, UV, NMR and elemental analysis. Antioxidant activities of all compounds were examined using free radical scavenging methods such as hydrogen peroxide scavenging activity (HPSA), 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2-2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS) assays. All of the tested compounds exhibited good antioxidant activity. Further, the frontier orbital energy levels, as well as various chemical properties, were determined using the density functional theory (DFT) calculations. The MEP maps of all of the derivatives were plotted to identify the nucleophilic and electrophilic reactive sites. Further, binding energies of all of the organic compounds with the protein tyrosinase was investigated to determine their potential anti-melanogenic applications. The selected ligand, L6 was subjected to molecular dynamics simulation analysis to determine the stability of the ligand-protein complex. The MD simulation was performed (150 ns) to estimate the stability of the tyrosinase-L6 complex. Other key parameters, such as, RMSD, RMSF, Rg, hydrogen bonds, SASA and MMPBSA were also analyzed to understand the interaction of L6 with the tyrosinase protein.

Keywords: antioxidant activity; copper(II) complexes; edaravone derivatives; melanogenic inhibition activity; molecular docking; molecular dynamics simulation; tyrosinase-binding.

Figure 1

Proposed structures of copper complexes C1–C9 (based on the spectral and analytical characterization).

Scheme 1

Synthetic route of compounds L2–L9. Reaction conditions (i) AcCl, Ca(OH)_2, THF, 4 h, reflux; (ii) aniline, MeOH, H⁺, 12 h, reflux; (iii) phenyl hydrazine, MeOH, H⁺, 12 h, reflux; (iv) 2-aminopyridine, MeOH, H⁺, 12 h, reflux; (v) semicarbazide, MeOH, H⁺, 12 h, reflux; (vi) hydroxylamine, MeOH, H⁺, 12 h, reflux; (vii) NH₄SCN, K₂S₂O₈, MeOH, 12 h, RT; and (viii) Isatin, NaOH, MeOH, 12 h, reflux.

Figure 2

Results of the HPSA of edaravone derivatives (L1–L9) and their Cu(II) complexes (C1–C9). Values are presented as IC₅₀, µg.mL⁻¹. Ascorbic acid (IC₅₀ = 24.84 µg.mL⁻¹) was used as a standard. Different letters for the same method indicate significant difference at p < 0.05 levels by Duncan’s test. Duncan’s test allows us to use edaravone (L1) as a standard by which to compare the antioxidant activity of its derivatives (L1–L9) and Cu(II) complexes (C1–C9).

Figure 3

Results of DPPH assay of edaravone derivatives (L1–L9) and their Cu(II) complexes (C1–C9). Values are presented as IC₅₀, µg.mL⁻¹. Edaravone (L1) was used as a standard. Different letters for the same method indicate significant difference at p < 0.05 levels by Duncan’s test.

Figure 4

Results of ABTS assay of edaravone derivatives (L1–L9) and their Cu(II) complexes (C1–C9). Values are presented as IC₅₀, µg.mL⁻¹. Edaravone (L1) was used as a standard. Different letters for the same method indicate significant difference at p < 0.05 levels by Duncan’s test.

Figure 5

HOMO–LUMO plots of DFT optimized structures of (a) L1, (b) L2, (c) L3, (d) L4, (e) L5, (f) L6, (g) L7, (h) L8, and (i) L9.

Figure 6

The molecular electrostatic potential (MEP) plots of the organic compounds (color code: carbon – grey, nitrogen – blue, oxygen – red, hydrogen – white, sulfur – yellow) (a) L1, (b) L2, (c) L3, (d) L4, (e) L5, (f) L6, (g) L7, (h) L8, and (i) L9.

Figure 7

Interaction plots of 3NM8 with (a) L1, (b) L2, (c) L3, (d) L4, (e) L5, (f) L6, (g) L7, (h) L8, and (i) L9.

Figure 8

Root mean square deviation of the backbone atoms of 3NM8 and 3NM8–L6 complex.

Figure 9

Root mean square fluctuation of the c-alpha atoms of 3NM8 and 3NM8–L6.

Figure 10

Rg of the backbone atoms of 3NM8 and 3NM8–L6.

Figure 11

SASA of the backbone atoms of 3NM8 and 3NM8–L6.

Figure 12

H-bonds of complex 3NM8–L6.

Figure 13

(a) Last frame of MD trajectory (150 ns). (b) Active site MMPBSA values of 3NM8–L6.