Synthesis of 5-(2-hydroxyphenyl)-5-methyl-6H-benzo[c]carbazole-6-ones and their antitumor activities.

A concise and efficient photo-induced rearrangement and oxidation of 2-(3-methylbenzofuran-2-yl)-3-phenyl-1H-indoles 1 for the synthesis of 5-(2-hydroxyphenyl)-5-methyl-5,7-dihydro-6H-benzocarbazol-6-ones 2 is described. Irradiation of compounds 1 in anhydrous dichloromethane solution, using 313 nm UV light in an air atmosphere, resulted in the formation of compounds 2 with yields ranging from 55% to 98%. Using the 6π-electrocyclization strategy of compounds 1 containing a methyl, a quaternary carbon stereocenter was introduced in the compounds 2. The carbonyl group of compounds 2 was formed by the photo-induced oxidation of C-H bond to C-OH and hemiketal-keto tautomerization. Additionally, the antitumor activities of compounds 2 were evaluated and found to demonstrate equivalent or superior activity compared to Cisplatin against various tumor cell lines, including leukemia HL-60, lung cancer A549, liver cancer HepG2, breast cancer MDA-MB-231 and colon cancer SW480. The anticancer activity of compound 2f was particularly significant, with IC50 values of 2.99, 9.06, 6.81, 9.29, and 14.93 μM respectively, and its IC50 value of normal cells 11.18 μM. Compound 2k had a relatively high IC50 values against cancer cells, whereas its IC50 value greater than 40μM for normal cells.