New Stemona alkaloids from the roots of Stemona tuberosa and structural revision of stemonatuberone B

Three new Stemona alkaloids (1-3), along with five known compounds (4-8), were isolated from the roots of Stemona tuberosa. Their structures were unambiguously elucidated by spectroscopic analysis and single-crystal X-ray crystallography. Atrop-tuberostemonone (1) is a stable conformational isomer of tuberostemonone (4), which features a new type of atropisomerism in one-carbon bridged lactam with a [6.4.1] scaffold. The reported structure of stemonatuberone B was revised to 4. The inhibitory activities of all the isolates against acetylcholinesterase were evaluated. (C) 2020 Elsevier Ltd. All rights reserved.