ent-Beyerane diterpenoids from the heartwood of Excoecaria parvifolia

• Published in: Phytochemistry (Oxford) 2007-02, Vol.68 (4), p.546-553
• Main Authors: Grace, Mary H., Faraldos, Juan A., Lila, Mary Ann, Coates, Robert M.
• Format: Article
• Language: English
• Subjects: anticarcinogenic activity; beyerane diterpenes; Biological and medical sciences; Chemical constitution; chemical structure; cultured cells; Cytotoxicity; Diosphenols; Diterpenes - chemistry; Diterpenes - isolation & purification; Diterpenoids; ent-Beyeranes; Euphorbiaceae; Euphorbiaceae - chemistry; Excoecaria; Excoecaria parvifolia; Fundamental and applied biological sciences. Psychology; Heartwood; L1210; lupeol; mice; Models, Molecular; Molecular Structure; phytochemicals; Plant Oils - chemistry; Plant physiology and development; spectral analysis; triterpenoids; Wood
• ISSN: 0031-9422; 1873-3700
• DOI: 10.1016/j.phytochem.2006.11.010

The heartwood of Excoecaria parvifolia afforded 12 beyerane diterpenes ( 1– 12), four of which ( 5– 7 and 12) have unusual structures: ent-3-oxa-beyer-15-en-2-one, ( 5); ent-15,16-epoxy-2-hydroxy-19-norbeyer-1,4-dien-3-one ( 6); methyl ent-2,4-seco-15,16-epoxy-4-oxo-3,19-dinorbeyer-15-en-2-oate ( 7); and ent-2,17-dihydroxy-19-norbeyer-1,4,15-trien-3-one ( 12). The isolated diterpenes were tested for their cytotoxic activity against leukemia cells (L1210), but only compounds 2 and 5 exhibited potent activity. Chromatographic fractionations of the toluene extract of the heartwood of Excoecaria parvifolia collected in Australia resulted in the isolation of 12 beyerane diterpenes ( 1– 12), and the triterpene, lupeol. Four of the isolated diterpenoids ( 5– 7 and 12) have unusual structures: ent-3-oxa-beyer-15-en-2-one, ( 5); ent-15,16-epoxy-2-hydroxy-19-norbeyer-1,4-dien-3-one ( 6); methyl ent-2,4-seco-15,16-epoxy-4-oxo-3,19-dinorbeyer-15-en-2-oate ( 7); and ent-2,17-dihydroxy-19-norbeyer-1,4,15-trien-3-one ( 12). The structures were established by spectroscopic analyses, NMR data comparisons with similar diterpenes, and chemical correlations. All the diterpenes are assumed to have the same absolute configuration as the co-occurring (+)-stachenol ( 4). Diosphenol 2 and nor-lactone 5 exhibited significant potency in bioassays for cytotoxic activity against leukemia cells (L1210). Plausible biosynthetic pathways are proposed to explain the origin of the diterpene metabolites.