Synthesis and biological evaluation of esculetin derivatives as potential anti-HBV agents

Previous in vivo and in vitro studies revealed that esculetin (Fig. 1) has anti-hepatitis B virus (anti-HBV) activity as well as a protective effect on liver damage caused by duck hepatitis B virus. We designed and synthesized a series of esculetin derivatives, introduced side chains containing various amino groups into site 7 of the parent structure, and synthesized C-4 and C-8 substituted derivatives with the goal of investigating their anti-HBV activities. In vitro anti-HBV activity was performed against HepG2.2.15 cells by using Enzyme-Linked Immunosorbent Assay(ELISA) kit and cytotoxicity was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay with lamivudine as the positive control. The results demonstrated that several compounds showed moderate anti-HBV activity, while the introduction of morpholine groups could significantly inhibit the expression of hepatitis B e antigen (HBeAg) and the introduction of the 2-methylimidazole group could significantly inhibit the expression of Hepatitis B surface antigen (HBsAg). Among all tested compounds, compound 4a demonstrated the best anti-HBeAg activity (IC₅₀ = 15.8 ± 4.2 μM), while compound 6d demonstrated the best anti-HBsAg activity (IC₅₀ = 21.4 ± 2.8 μM). Compounds 6b and 6c showed moderate anti-HBV activity and HBsAg inhibition. Compounds 4b showed moderate anti-HBV activity and an inhibitory effect on HBeAg. In addition, compounds 4a, 4c, 4d, 6b, 6c and 6d showed improved metabolic stability. This study provides useful guidance for the discovery of anti-HBV drugs, which merits further investigation.