The South American Simaba cuspidata Spruce and North Indian Ailanthus grandis Prain were investigated as sources of potentially useful antineoplastic agents. Both of these Simaroubaceae plant species were found to produce 6 alpha-tigloyloxychaparrinone (4a) and the new quassinoid 6 alpha-tigloyloxychaparrin (3b). The latter structure was determined by interpretation of spectral data and oxidation to 6 alpha-tigloyloxychaparrinone (4a). While both glycol 3b and alpha-ketol 4a were found to significantly inhibit growth of the murine P388 lymphocytic leukemia cell line, only the alpha-ketol (4a) inhibited growth of the corresponding in vivo system.