Transformations of Manool. Tri- and Tetracyclic Norditerpenoids with in Vitro Activity against Plasmodium falciparum

The known 17-norisopimar-15-ene-8beta,13beta-diol (5) and five new semisynthetic norditerpenoids, ethyl 17-norabiet-13(15)-E-en-8beta-ol-16-oate (6), ethyl 17-norabiet-13(15)-Z-en-8beta-ol-16-oate (7), 17-norpimaran-13alpha-ethoxy-8,16-olactone (8), 17-norisopimarane-8beta,15-diol (9), and 17-norarabiet-13(15)-ene-8beta,16-diol (10), were prepared from manool (11). Standard spectroscopic data including X-ray crystal analysis were used to determine the structures of 5-10. All five compounds exhibited in vitro antiplasmodial activity against the malarial parasite Plasmodium falciparum at varying microg mL(-1) concentrations.