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

Aconitum pendulum 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 (1), 12-epi-napelline (2), 12-acetyl-napelline (3), azitine (4), flavaconitine (5), nagarutine C (6), nagarutine D (7), 16-epi-pyroaconine (8), spicatine B (9), 3-deoxyaconitine (10), and napelline (11). Notably, compound 1 was characterized as a novel alkaloid. Additionally, compounds 3–9 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 10 and 11 exhibit notable anti-inflammatory activities. Moreover, given the structural analogy between the novel alkaloid 1 and the active compound 11, compound 1 is proposed as a promising lead for future structure–activity relationship studies and semi-synthetic modification.