Evidence is presented for the assignment of structures for elephantin (3) and elephantopin (4), two tumorinhibitory sesquiterpene dilactones isolated from Elephantopus elutus Bertol. Elemental analysis and highresolution mass spectrometry supported a CZOHI~O~ molecular formula for elephantin (3) and a CIBHZOO~ molecular formula for elephantopin (4). Chemical and spectral evidence indicated the presence of cu,&unsaturated lactone, cr,@-unsaturated ester, and epoxide groupings in 3 and 4. Alkaline hydrolysis of 3 gave elephantol (5) and dimethylacrylic acid, while, under the same conditions, 4 gave elephantol (5) and methacrylic acid. Catalytic hydrogenation of elephantol (5) gave tetrahydroelephantol (9). Treatment of elephantol(5) with p-bromobenzoyl chloride gave elephantol p-bromobenzoate (14). X-Ray crystallographic analysis established the structure and stereochemistry of 14 and 5. Hydrogenation of elephantopin (4) gave tetrahydroelephantopin (6). Alkaline hydrolysis of 6 gave dihydroelephantol (8) and isobutyric acid. Acylation of 5 with methacrylic anhydride gave elephantol methacrylate (ll), while acylation of 8 with isobutyric anhydride gave elephantol isobutyrate (12). Acid hydrolysis of 6 gave dihydroelephantolide (13), which on acylation with isobutyric anhydride gave 6. Low-and high-resolution mass spectra of elephantin (3) and elephantopin (4) and a number of derivatives ( 5 , 6 , 8 , 10, 11, 12, and 13) are discussed.Elephantin and elephantopin are cytotoxic sesquiterpene lactones from Elephantopus elatus Bertol., and their isolation and characterization have recently been reported.*s5 It is the purpose of this paper to present in detail the fractionation of the active extract of E. elatus and the isolation and structural elucidation of the active constituents, elephantin and elephantopin! Fractionation of the concentrated ethanol extract (A in Chart I), guided by assay against KB revealed that the active principles were concentrated (Table I) in the chloroform phase (D) of a chloroformwater partition. Partition of this residue between 10% aqueous methanol and petroleum ether concentrated the activity in the aqueous methanol layer (G). Fraction G was chromatographed on a silicic (1) (a) University of Wisconsin. Part XXXIX: 8. M. Kupchan, W.

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