Soluble Epoxide Hydrolase Inhibitory Constituents from Selaginella tamariscina

A novel norneolignan, tamariscinol T (1), and six known compounds, protocatechuic acid (2), vanillic acid (3), caffeic acid (4), amentoflavone (5), 2,3-dihydroamentoflavone (6), and 2 '',3 ''-dihydroamentoflavone (7), were isolated from Selaginella tamariscina. Their structures were elucidated using 1D/2D NMR, high-resolution electrospray ionization mass spectrometry (HR-ESI-MS), and infrared (IR), ultraviolet (UV), and circular dichroism (CD) spectroscopy. The effects of the isolated compounds on soluble epoxide hydrolase (sEH) activity were then evaluated. Compounds 5-7 potently inhibited sEH activity with IC50 values of 24.3 +/- 1.6, 5.4 +/- 0.1, and 11.9 +/- 0.1 mu M, respectively. In addition, analysis of the kinetics of compounds 5-7 revealed that their inhibitory actions were noncompetitive, with inhibition constants (K-i) of 24.4 +/- 1.2, 8.6 +/- 0.4, and 5.3 +/- 0.6 mu M, respectively.