The crude extract of Eurycoma longifolia Jack (Simaroubaceae) has long been used as one of traditional folk medicines in the Southeast Asia. During the survey of cytotoxic antitumor compounds from the title plant, three novel cytotoxic squalene-type triterpene ethers, named eurylene (1), 14-deacetyl eurylene (2) and longilene peroxide (3), and 14 novel quassinoids were isolated from the woods together with teurilene (4). Their structure were elucidated by spectroscopic data, chemical evidence and X-ray analysis. The absolute stereostructure of 1 was determined by an advanced Mosher's method. Molecular conformation of 1 with linear form was different from those of 3 and 4 with a turn structure. Conformational analysis of 2 showed that 2 possess the similar turn structure with an intramolecular hydrogen bonding to 3 and 4. The new skeleton C_<19>-type quassinoids, named as longilactone and 6-dehydroxylongilactone, were found to form a lactonic linkage at C-7 and many C_<20>-type quassinoids were isolated. These structures were elucidated by spectroscopic methods and X-ray analysis. The cytotoxic activities of these squalene-type triterpene ethers and quassinoids are also discussed.
