Kleinhospitine E and Cycloartane Triterpenoids from <i>Kleinhovia hospita</i>

A novel cycloartane triterpenoid alkaloid, kleinhospitine E (<b>1</b>), six new cycloartane triterpenoids (<b>2</b>–<b>7</b>), three known cycloartane triterpenoids (<b>8</b>–<b>10</b>), and taraxerone (<b>11</b>) were isolated from a methanol extract of <i>Kleinhovia hospita</i>. Their structures were elucidated by 1D- and 2D-NMR spectroscopy as well as HRMS analysis. The absolute configurations of all isolated compounds were determined from their ECD spectra by comparison with theoretical values. Kleinhospitine E (<b>1</b>) is the first cycloartane alkaloid possessing an unusual γ-lactam with an oxopropylidene side chain. Compounds <b>2</b>, <b>3</b>, and <b>6</b> were assigned as cycloartane triterpenoids with a 9α,10α-cyclopropyl ring, which is found rarely among naturally occurring compounds, while <b>4</b> and <b>5</b> were established as isomers of compound <b>3</b> containing a 21,23-diacetal side chain. Biological evaluation revealed that compounds <b>4</b> and <b>9</b> exhibited more potent antiproliferative activities against a multidrug-resistant tumor cell line compared with its parent chemosensitive cell line. Furthermore, compound <b>6</b> exhibited submicromolar anti-HIV activity