[One new ent-kaurane diterpenoid from Isodon serra].

Isodon serra, a Chinese medicinal herb widely used in the Lingnan region, has extensive pharmacological activities. However, its chemical constituents remain to be studied. In this study, a variety of modern chromatographic separation techniques were used to isolate five compounds from 95% ethanol extract of the aboveground part of I. serra. Their planar structures were determined by ultraviolet spectroscopy(UV), infrared spectroscopy(IR), high resolution-electrospray ionization-mass spectrometry(HR-ESI-MS), 1D and 2D nuclear magnetic resonance(1D NMR and 2D NMR), single-crystal X-ray diffraction(SC-XRD), and literature analysis. The compounds were identified as five 6,7-seco-ent-kaurane diterpenoids: isodon I(1), epi-nodosinol(2), carpalasionin(3), epi-nodosin(4), and enmein(5), among which compound 1 was a new one. The results of the pharmacological activity evaluation showed that compound 5 significantly inhibited nitric oxide(NO) release in RAW264.7 cells exposed to lipopolysaccharide(LPS).