Rare oxoisoaporphine alkaloids from Menispermum dauricum with potential anti-inflammatory activity

Eleven alkaloids including four previously undescribed oxoisoaporphine alkaloids, menisoxoisoaporphines A-D (1–4), four known analogues (5–8), and three aporphine alkaloids (9–11), were isolated and identified from the rhizomes of Menispermum dauricum. Their structures were elucidated by extensive spectroscopic data and single-crystal X-ray diffraction analyses. Among them, compounds 1 and 4 were the first samples of oxoisoaporphine with C-6 isopentylamino moiety, and 2 was a rare C-4 methylation product of oxoisoaporphine alkaloid. The in vitro anti-inflammatory activity of compounds 1–11 was performed by evaluating the inhibition of NO level in LPS-induced RAW264.7 macrophages. Among them, compound 4 exhibited the most potent NO inhibition activity with an IC₅₀ value of 1.95 ± 0.33 μM. The key structure-activity relationships of those oxoisoaporphine alkaloids for anti-inflammatory effects have been summarized.