12-epi-Turpelline, a Novel C20 Diterpene Alkaloid Isolated from Zanba Stir-Fried Tiebangchui

<i>Aconitum pendulum</i> Busch (Tiebangchui), a traditional Chinese medicinal herb, is recognized for its diverse pharmacological properties and for its significant toxicity. The Zanba stir-frying processing method is commonly employed to mitigate toxicity and enhance efficacy; however, the underlying chemical principles remain insufficiently studied. In order to address this issue, a phytochemical investigation was conducted on the diterpenoid alkaloids present in Zanba-processed Tiebangchui. Eleven diterpenoid alkaloids were isolated by means of chromatographic techniques, including silica gel column chromatography. Their structures were elucidated by extensive spectroscopic analysis (single-crystal X-ray diffraction, IR, HR-ESI-MS) and comparison with literature data. The compounds were identified as 12-epi-turpelline (<b>1</b>), 12-epi-napelline (<b>2</b>), 12-acetyl-napelline (<b>3</b>), azitine (<b>4</b>), flavaconitine (<b>5</b>), nagarutine C (<b>6</b>), nagarutine D (<b>7</b>), 16-epi-pyroaconine (<b>8</b>), spicatine B (<b>9</b>), 3-deoxyaconitine (<b>10</b>), and napelline (<b>11</b>). Notably, compound <b>1</b> was characterized as a novel alkaloid. Additionally, compounds <b>3</b>-<b>9</b> were isolated from this processed material for the first time. These findings provide crucial chemical insights into the detoxification mechanism of Zanba processing. Subsequent pharmacological evaluation revealed that compounds <b>10</b> and <b>11</b> exhibit notable anti-inflammatory activities. Moreover, given the structural analogy between the novel alkaloid <b>1</b> and the active compound <b>11</b>, compound <b>1</b> is proposed as a promising lead for future structure-activity relationship studies and semi-synthetic modification.