Uncarialins J—M from Uncaria rhynchophylla and Their Anti‐depression Mechanism in Unpredictable Chronic Mild Stress‐Induced Mice via Activating 5‐HT1A Receptor

Main observation and conclusion Uncaria rhynchophylla has been widely used to treat central nervous system diseases for a long history. After investigation of U. rhynchophylla , eleven monoterpene indole alkaloids, including four new compounds uncarialins J—M (1—4) and seven known analogues (5—11), were isolated and identified. Their structural characterization was conducted using HRESIMS, 1D and 2D NMR, electronic circular dichroism (ECD) spectra, and quantum chemical computations. Compounds 1, 2, 7, and 9—11 displayed significant agonistic effects towards 5‐HT 1A receptor, and their EC 50 values were 7.86, 7.32, 2.24, 1.18, 1.52, and 3.75 μmol/L, respectively. Furthermore, in vivo experimental results fully revealed that hirsuteine (7) displayed a significant antidepression effect in unpredictable chronic mild stress (UCMS)‐induced depression mice mainly via regulating 5‐HT 1A signaling pathway. Molecular docking and site‐directed amino acid mutation verified that amino acid residues Asp116 and Asn386 were the binding sites of hirsuteine (7) with 5‐HT 1A receptor. In addition, pre‐treatment of mice with WAY 100635 also blocked the anti‐depression effect of hirsuteine (7), which further demonstrated that 5‐HT 1A receptor was a potential target of hirsuteine (7) to effectively treat depression. These findings indicated the therapeutic material basis of U. rhynchophylla and the anti‐depression underlying mechanism of hirsuteine (7), and further provided the useful guidance for the development of hirsuteine (7) as a potential antidepressant candidate.