Thrombin inhibitory constituents from Duranta repens

The C-alkylated flavonoids 3,7,4′-trihydroxy-3′-(4-hydroxy-3-methylbutyl)-5,6-dimethoxyflavone (1), 3,7-dihydroxy-3′-(4-hydroxy-3-methylbutyl)-5,6,4′-trimethoxyflavone (2) and the trans-clerodane diterpenoids 6β-hydroxy-15,16-epoxy-5β,8β,9β,10α-cleroda-3,13(16),14-trien-18-oic acid (3) and 2β-hydroxy-15,16-epoxy-5β,8β,9β,10α-cleroda-3,13(16),14-trien-18-oic acid (4) were isolated from Duranta repens. Their structures and the relative configuration of 3 and 4 were determined by spectroscopic methods (1H- and 13C-NMR, IR, and MS) and 2D-NMR experiments. The known flavonoid 5 is also reported for the first time from this species. The compounds 1, 3, and 5 showed significant enzyme-inhibitory activity against thrombin.