New cytotoxic guaianolides and derivatives from Grosheimia macrocephala.

Grosheimia macrocephala (Compositae) proved to be a very interesting natural source, not only of grosheimin (I), but also of cynaropicrin (III). Some derivatives from these two natural sesquiterpene gamma-lactones were prepared (Schemes 2 and 3) and two new natural guaianolides: 4'-deoxy-cynaropicrin (V) and 4'-nor-2'-metoxy-cynaropicrin (VI) were isolated and structurally identified. A series of these compounds were submitted to in vitro preliminary testing of cytostatic activity against KB cell lines and relationships between bioactivity and chemical features were investigated.