New Trichothecenes Isolated from <i>Holarrhena </i><i>f</i><i>loribunda</i>

Bioassay-guided fractionation of an extract of <i>Holarrhena floribunda</i> stem, has led to the isolation of the new trichothecenes, 8-dihydrotrichothecinol A (<b>1</b>), loukacinol A (<b>2</b>), and loukacinol B (<b>3</b>), and the known compounds, trichothecolone (<b>4</b>), trichothecin (<b>5</b>), trichothecinol A (<b>6</b>), rosenonolactone (<b>7</b>), 6β-hydroxyrosenonolactone (<b>8</b>), and rosololactone (<b>9</b>). The structures were determined by spectral and chemical methods, and absolute configurations were established by a modified Horeau's method using HPLC. Compounds <b>1</b> and <b>6</b> exhibited significant cytotoxicity against several human tumor cell lines, whereas compound <b>8</b> showed moderate and weak antileishmanial activity toward extracellular and intracellular <i>Leishmania donovani</i>, respectively.