Synthesis and activity of novel indirubin derivatives

A series of indirubin derivatives hydrochloride were obtained using a convenient and mild method from indirubin. The newly synthesized compounds and their derivatives were characterized by ¹ H NMR, ¹³ C NMR, and MS. Furthermore, we tested their IDO1 enzyme inhibitory activity and anti-proliferative activities in K562 tumor cells. The experimental results revealed that some of the compounds showed potential anti-enzyme and anti-tumor activity. Among of them, compound 4b exhibited certain inhibitory activity on IDO1 (IC₅₀ : 29.52 μmol/L), and compound 4a displayed activity similar to indirubin in K562 tumor cells (IC₅₀ : 24.96 μmol/L). This type of indirubin derivative is expected to have the potential to act as an immunologically active anti-tumor drug, indicating that further research will be worthwhile.