Design, Synthesis, and Biological Evaluation of 2-Mercaptobenzoxazole Derivatives as Potential Multi-Kinase Inhibitors

Abstract

A series of 12 compounds was designed and synthesized, based on 2-mercaptobenzoxazole derivatives containing either the substituted benzenes 4a-d, substituted isatins 5a-f, or heterocycles 6a-b. The in vitro antiproliferative activity of the compounds was evaluated against hepatocellular carcinoma (HepG2), mammary gland cancer (MCF-7), breast cancer (MDA-MB-231), and the epithelioid cervix carcinoma (HeLa) cancer cell lines. Compounds 4b, 4d, 5d, and 6b had the most potent antiproliferative activity, with IC₅₀ values ranging from 2.14 to 19.34 µM, compared to the reference drugs, doxorubicin and sunitinib. Compound 6b revealed a remarkably broad antitumor activity pattern against HepG2 (IC₅₀ 6.83 µM), MCF-7 (IC₅₀ 3.64 µM), MDA-MB-231 (IC₅₀ 2.14 µM), and HeLa (IC₅₀ 5.18 µM). In addition, compound 6b showed potent inhibitory activities against EGFR, HER2, VEGFR2, and the CDK2 protein kinase enzymes, with IC₅₀ values of 0.279, 0.224, 0.565, and 0.886 µM, respectively. Moreover, compound 6b induced caspase-dependent apoptosis and cell cycle arrest at the G2/M phase. Finally, a molecular docking simulation was performed for compound 6b to predict the potential ligand-protein interactions with the active sites of the EGFR, HER2, and VEGFR2 proteins.

Keywords: N-acylhydrazone (NAH); anticancer; benzoxazole; docking; isatins; protein kinases.

Figure 1

The reported and proposed benzoxazole, hydrazone, and isatin conjugates with anticancer activity.

Scheme 1

Synthesis of the target hybrid compounds, 4a–d, 5a–f, and 6a–b. Reagents and conditions: (a) ethyl chloroacetate, K₂CO₃, acetone, reflux, 5–10 h. (b) N₂H₄.H₂O, EtOH, reflux, 6–10 h. (c) appropriate isatin or aldehyde, AcOH, EtOH, reflux 3–5 h.

Figure 2

Schematic 2D and 3D depictions of the molecular simulation of erlotinib (A) and compound 6b (B) within the ATP-binding site of EGFR (PDB ID: 4HJO). Green dotted lines represent hydrogen bonding.

Figure 3

Schematic 2D and 3D depictions of the molecular simulation of sorafenib (A) and compound 6b (B) within the ATP-binding site of VEGFR2 (PDB ID: 4ASD). Green dotted lines represent hydrogen bonding.

Figure 4

Schematic 2D and 3D depictions of the molecular simulation of lapatinib (A) and compound 6b (B) within the ATP-binding site of HER2 (PDB ID: 3RCD). Green dotted lines represent hydrogen bonding.

Figure 5

The cell cycle analysis of HepG2 cells treated with compound 6b for 24 h, using flow cytometry.

Figure 6

Effect of compound 6b on the percentage of annexin propidium iodide-positive staining in HepG2 cells. (A) Control cells. (B) Cells treated with compound 6b.