Anti-neuroinflammatory terpenes from Magnolia grandiflora

Six previously undescribed sesquiterpenes, magnogranoides A–F (1–6), along with 10 known terpenes, were isolated from the leaves of Magnolia grandiflora L. Six previously undescribed sesquiterpene derivatives (11a–11e and 14a) were synthesized using chemical methods. Those structures were identified through extensive spectroscopic data and quantum chemical calculations. Notably, compound 1 represents the first sesquiterpene with a previously undescribed 8/5/5 tricyclic ring, and compound 2 was elucidated to be the first 13-norguaiane-type sesquiterpenoid with a 5/7/5 tricyclic ring system. Four compounds (3, 7, 8, and 16) exhibited better anti-neuroinflammatory activities in BV-2 cells with IC₅₀ values ranging from 3.23 ± 0.23 μM to 15.98 ± 1.79 μM than the positive control, minocycline (IC₅₀: 20.56 ± 0.93). Furthermore, the chemotaxonomic significance of the isolates was also discussed.