Two New Terpenoids From <i>Isodon serra</i> and Their Anti‐Alzheimer's Disease Activity

Phytochemical investigation of the 95% ethanol extract of the whole plants of Isodon serra (Lamiaceae) led to the isolation of a new ent-kaurane diterpenoid isoserrone A (1) and a new 2,3-seco-ursane-type triterpenoid isoserric acid A (2), along with four known compounds (3-6). Except for compound 4, the remaining compounds were obtained from I. serra for the first time. The structures of the new compounds were established based on the analysis of HRESIMS, IR, 1D, and 2D NMR spectroscopic data. The absolute configurations of 1 and 2 were elucidated by electronic circular dichroism (ECD) and single-crystal X-ray diffraction analysis, respectively. To our knowledge, this article provides the first reported single-crystal X-ray diffraction data of known compounds 4-6. Moreover, using a transgenic Caenorhabditis elegans Alzheimer's disease (AD) pathological model, we evaluated the in vivo anti-AD activities of compounds 1-4 and 6. The biological evaluation revealed that 3 and 6 delayed the paralysis process in CL4176 nematodes at the concentration of 100 µM, suggesting their potential as anti-AD therapeutic candidates.