Tumor Inhibitors XL. The Isolation and Structural Elucidation of Elephantin and Elephantopin, Two Novel Sesquiterpenoid Tumor Inhibitors from Elephantopus elatus

Abstract

Evidence is presented for the assignment of structures for elephantin (3) and elephantopin (4), two tumorinhibitory sesquiterpene dilactones isolated from Elephantopus elatus Bertol. Elemental analysis and highresolution mass spectrometry supported a C20H22O7 molecular formula for elephantin (3) and a C19H20O7 molecular formula for elephantopin (4). Chemical and spectral evidence indicated the presence of α,β-unsaturated lactone, α,β-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 (d). Alkaline hydrolysis of 6 gave dihydroelephantol (8) and isobutyric acid. Acylation of 5 with methacrylic anhydride gave elephantol methacrylate (11), 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. © 1969, American Chemical Society. All rights reserved.