Design, synthesis and biological evaluation of new rhodacyanine analogues as potential antitumor agents

In an attempt to develop potent antitumor agents, new rhodacyanine analogues containing the pyridinium ring (5a–5h), the isoquinolinium ring (6a–6c) and the quinolinium ring (7a–7e) linked to the rhodanine ring via N–N covalent bond were designed, synthesized and evaluated for antitumor activity against human lung cancer cell line (H460) by MTT assay in vitro. Most of the tested compounds showed enhanced antitumor activity with IC50 values ranging from 0.006 to 9.2 μmol/L as compared to the lead compound MKT-077. Among them, the most promising compound 7d (IC50 = 0.006 μmol/L) was 216.7 times more active than MKT-077 (IC50 = 1.3 μmol/L). The preliminary structure–activity relationship of the target compounds was discussed.