New class of thio/semicarbazide-based benzyloxy derivatives as selective class of monoamine oxidase-B inhibitors

Abstract

Sixteen thio/semicarbazide-based benzyloxy derivatives (BT1-BT16) were synthesized and evaluated for their inhibitory activities against monoamine oxidases (MAOs). Most compounds showed better inhibitory activity against MAO-B than against MAO-A. BT1, BT3, and BT5 showed the greatest inhibitory activity with an identical IC₅₀ value of 0.11 µM against MAO-B, followed by BT6 and BT7 (IC₅₀ = 0.12 µM) and BT2 (IC₅₀ = 1.68 µM). The selectivity index of BT5 was the highest (363.64) for MAO-B, whereas that of BT1 was 88.73. BT1 and BT5 were reversible MAO-B inhibitors, based on the results of dialysis experiments. In inhibition kinetics, BT1 and BT5 were competitive MAO-B inhibitors with K_i values of 0.074 ± 0.0020 and 0.072 ± 0.0079 µM, respectively. Additionally, in the in-vitro parallel artificial membrane penetration assay, BT1 and BT5 crossed the blood-brain barrier. Cytotoxicity and possible neuroprotective effects of the lead compounds were assessed using IMR 32 cells. Levels of the antioxidant superoxide dismutase, catalase, and glutathione peroxidase in IMR 32 cells were increased by pretreatment with lead compounds. Five lead molecules (BT1, BT3, BT5, BT6, and BT7) were used for the docking studies. A significant pi-pi interaction with Tyr 326 was observed and molecular dynamics studies were performed for the most promising BT1-MAO-B complex. These results suggested that BT1 and BT5 could be used therapeutically for the treatment of various neurodegenerative diseases.

Keywords: Benzyloxy benzene-based thio/Semicarbazide derivatives; Kinetics; Molecular dynamics; Monoamine oxidase; Reversibility.

Fig. 1

Design strategy of benzyloxy benzene-based thio/semicarbazide derivatives.

Scheme 1

Synthesis of the BT series of compounds. Reaction condition: For thio derivatives: MW at 80 ֯C (5 min), For semicarbazide derivatives: MW at 80 ֯C to 120 ֯C (5–6 min).

Fig. 2

Structure–activity relationship of thio/semicarbazide-based benzyloxy derivatives.

Fig. 3

Lineweaver–Burk plots for MAO-B inhibitions by BT1 and BT5 (A and C), and their secondary plots (B and D) of the slopes vs. inhibitor concentrations. Results are expressed as the mean ± SD of triplicate experiments.

Fig. 4

Recovery of MAO-B inhibition by BT1 and BT5 in residual activities measeured before and after dialysis. Concentrations used were 2-times of their IC₅₀ values: BT1, BT5, and pargyline, 0.22 µM; safinamide, 0.038 µM.

Fig. 5

MTT viability assay of the lead compounds BT1, BT3, BT5, BT6, and BT7 using IMR 32 cells.

Fig. 6

Superoxide dismutase (SOD) levels observed in different concentrations of BT1, BT3, BT5, BT6, and BT7 treatment of IMR 32 cells. Std denotes standard.

Fig. 7

Glutathione peroxidase (GPX) levels observed in different concentrations of BT1, BT3, BT5, BT6, and BT7 treatment against the IMR 32 cells. Std denotes standard.

Fig. 8

Catalase (CAT) levels observed in different concentrations of BT1, BT3, BT5, BT6, and BT7 treatment against IMR 32 cells. Std denotes standard.

Fig. 9

Two-dimensional interaction of compound BT1 to the active site of MAO-B (PDB ID: 2V5Z).

Fig. 10

Three-dimensional interaction of compound BT1 to the active site of MAO-B (PDB ID: 2V5Z).

Fig. 11

MD simulation studies of BT1-MAO-B complex. The panels display root mean square deviation (RMSD) (A), root mean square fluctuation (RMSF) (B), two-dimensional interaction diagram of the complex (C), protein–ligand contact histogram of MD trajectory (D), and time-dependent RGyr of BT1-hMAO-B (E).