Novel Alkaloids from the Roots of Stemona sessilifolia

Abstract

Four new Stemona alkaloids, sessilistemonamines A–C (1–3, resp.) and dihydrostemoninine (4), were isolated from the roots of Stemona sessilifolia. Their structures and relative configurations were elucidated by means of in-depth 1D- and 2D-NMR-spectroscopic as well as mass-spectrometric experiments; and the structure of 4 was solved by X-ray single-crystal diffraction. The stereoisomeric compounds 1–3 share an unprecedented tetracyclic decahydro-1H-furo[2′,3′:4,5]cyclopenta[1,2-b]pyrrolo[1,2-a]azepine nucleus. Compounds 1 and 2 were found to be moderately active in terms of acetylcholinesterase (AchE) inhibition, with IC₅₀ values of 68.8±9.5 and 17.1±2.5 μM, resp.