Microbial transformation of bufotalin by Alternaria alternata AS 3.4578

The microbial transformation of a cytotoxic bufadienolide, bufotalin (1), was carried out. Three transformed products from 1 by Alternaria alternata were isolated. Their structures were characterized as 3-keto-bufotalin (2), 12β-hydroxyl-bufotalin (3), and 3-keto-12β-hydroxyl-bufotalin (4) based on the extensive NMR studies. Among them, 3 and 4 were new compounds with strong in vitro cytotoxic activities against HeLa cells.