Dendrobium nobile Lindl. is registered in the Chinese Pharmacopoeia as a traditional medicine. Phytochemical investigation of the ethanol extract of D. nobile Lindl. stems yielded three alkaloid compounds, including two new compounds dendroxine B (2) and denrine B (3) as well as one known compound dendrobine (1). Here, we identified the structure of these compounds using spectroscopic analyses and compared them with those described in previous studies. Compounds 1-3 were found to show protective effect against amyloid-β 1−42 (Aβ 1−42 )-induced neurotoxicity in rat pheochromocytoma (PC12) cells, among which dendrobine exhibited the most significant neuroprotective effect. Hoechst 33342/propidium iodide staining indicated that dendrobine ameliorated Aβ 1−42 -induced apoptosis. Moreover, quantitative real-time polymerase chain reaction and western blot analysis analysis demonstrated that dendrobine suppressed the activation of cyclin-dependent kinase 5 (CDK5), upregulated Bcl-2 expression, and downregulated Bax, cyto-c, and caspase-3 expression. Molecular docking analysis and surface plasmon resonance assay suggested that dendrobine directly bound to CDK5 protein with a KD value of 2.05 × 10 −4 M. In summary, alkaloids are the neuroprotective constituents of D. nobile Lindl., and dendrobine protected PC12 cells against Aβ 1−42induced apoptosis by inhibiting CDK5 activation.

Gymnothecaoxazoles A and B (I) are isolated from the whole parts of endemic medicinal plant of Gymnotheca chinensis (Saururaceae).

Six lactone derivatives, including four α‐pyrones derivatives (1–4), two α‐furanone derivatives (5 and 6), were isolated from the Dendrobium pendulum. Structural elucidation of these undescribed lactone derivatives were accomplished on the basis of detailed nuclear magnetic resonance analysis, and the absolute configurations of compounds 1–4 were confirmed by electronic circular dichroism (ECD) techniques. The cytotoxic effects of isolated compounds on human breast cancer cell MDA‐MB‐231 were evaluated by the MTT assay.