3, 4-seco-labdane diterpenoids from the leaves of Callicarpa nudiflora and their inhibitory effects on nitric oxide production.

As a part of our ongoing search for bioactive compounds from the leaves of Callicarpa nudiflora that inhibit nitric oxide (NO) production, the 90% EtOH fraction eluted by macroporous resin adsorption was found to show significant inhibitory activity against the production of NO in RAW 264.7 stimulated by lipopolysaccharide (LPS). Bioactivity-guided isolation of the fraction yielded three new bioactive diterpenoids, named ent-3, 4-seco-14-carbonyl-15, 16-epoxy-4(18), 8(17), 13(14)-labdatrien-3-oic acid (1), syn-3, 4-seco-12R-hydroxy-15, 16-epoxy-4(18), 8(17), 13(16), 14(15)-labdatetraen-3-oic acid (2) and syn-3, 4-seco-12S-hydroxy-15, 16-epoxy-4(18), 8(17), 13(16), 14(15)-labdatetraen-3-oic acid (3). Their structures and configurations were elucidated by comprehensive spectroscopic analysis. All the three compounds exhibited potent inhibitory activity on NO production in LPS-activated RAW 264.7 macrophage cells.