New spin labeled analogues of podophyllotoxin as potential antitumor agents.

Four new nitroxyl labeled derivatives of podophyllotoxin, 4-(2, 2, 6, 6-tetramethyl-1-oxyl-4-piperidyl)oxy-epipodophyllotoxin (4), 4-(2, 2, 6, 6-tetramethyl-1-oxyl-4-piperidyl)oxy-4'-demethylepipodophyllotoxin (5), 4-(2, 2, 5, 5-tetramethyl-1-oxyl-3-pyrrolinyl)formyloxy-epipodophyllotox in (6) and 4-(2, 2, 5, 5-tetramethyl-1-oxyl-3-pyrrolinyl)formyloxy-4'-demethylep ipodophyllotoxin (7), have been synthesized and evaluated for their antitumor activity in vitro. Compounds 5 and 7 showed superior activity to clinically used etoposide (VP-16,2) in their inhibition of leukemia P388, lung cancer A549 and stomach carcinoma SGC-7901 cells. 4'-Demethyl-epipodophyllotoxins 5 and 7 was found to be more active than eipodophyllotoxins 4 and 6 lacking a free phenolic hydroxyl group at C-4'.