Studies on the constituents of Mikania hirsutissima (Compositae).

Two novel norhumulene-type sesquiterpenes, named mikaniahumulene I (1) and II (2) were isolated along with nine known compounds, seven kaurenic acid-type diterpenes (3-9), a coumarin (10) and a flavone (11), from the aerial parts of Mikania hirsutissima DC (Compositae). The structures of new norhumulenes were determined by spectroscopic means. The cytotoxic activities of isolated compounds against leukemia cells (L 1210) were investigated; among the isolated compounds, 1, 5, 8, and 11 showed relatively strong cytotoxicity.