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.