Abstract
Three undescribed pimarane-type diterpenoids, muhenrins A-C (1-3), along with a known analogue were isolated from the petroleum ether extract of Munronia henryi (Meliaceae). Their structures, including absolute configurations, were elucidated by means of various spectroscopic methods (IR, UV, HR-ESI-MS, NMR), single-crystal X-ray diffraction, ECD and NMR calculations. Muhenrin A (1) features a unique 6,7-seco pimarane skeleton, and its putative biosynthetic pathways have been proposed. Compounds 1-4 showed weak inhibitory activity against NO production in LPS-induced RAW 264.7 cells, with inhibition rates ranging from 13.73 - 32.35% at 50 μM concentrations.