A CH2Cl2-MeOH (1: 1) extract prepared from the whole plant of Nidema boothii inhibited spontaneous contractions (IC50= 6.26±2.5 μg/mL) of the guinea-pig ileum. Bioassay-guided fractionation of the active extract led to the isolation of the novel spiro compound 1, which was given the trivial name nidemone, and the new dihydrophenanthrene 3, characterized as 1, 5, 7-trimethoxy-9, 10-dihydrophenanthrene-2, 6-diol. In addition, the known stilbenoids ...