Synthesis and Cytotoxic Activity of a Series of Functionalized Maleopimarimides

New functionalized maleopimarimides were prepared. Their cytotoxicity against tumor cell lines (HeLa, HEp-2) was studied. Diterpenoids 6, 9, and 10 with allene fragments possessed the greatest cytotoxicity and could be considered lead compounds with potential antitumor activity.