Synthesis and Antiproliferative Activity of Thioxoflavones Mannich Base Derivatives

Two series of 12 novel thioxoflavones Mannich base derivatives 5a-f and 6a-f were synthesized via Mannich reaction of 4',7-dimethoxy-5-hydroxyflavothione (3) or 3',4',7-trimethoxy-5-hydroxyflavothione (4) with appropriate aliphatic amines or alicyclic amines and formaldehyde. Thioxoflavones 3 and 4 were prepared from 4',7-dimethoxy-5-hydroxyflavone (1) and 3',4',7-trimethoxy-5-hydroxyflavone (2) with Lawesson's reagent, respectively. Their antiproliferative activities in vitro were evaluated on a panel of three human cell lines (HeLa, HCC1954, and SK-OV-3) by CCK-8 assay. The results showed that most of the thioxoflavones and their Mannich base derivatives exhibited potential antiproliferative activities on the tested cancer cell lines, with IC₅₀ values ranging from 9.16 to 55.50 μM. In particular, thioxoflavone 4 and the thioxoflavone Mannich base derivatives 5a and 5d showed the best antiproliferative activity on all three human cancer cell lines; they are promising candidates worthy of further development. The structures of all synthesized compounds were confirmed by ¹ H NMR, ¹³ C NMR, IR, and MS techniques.