Activity-guided fractionation of the n-hexane and ${CHCl_3}-soluble$ fractions of Sindora sumatrana using a bioassay based on the inhibition of lipopolysaccharide (LPS)-induced nitric oxide (NO) production by inducible nitric oxide synthase (iNOS) in murine macrophage RAW 264.7 cells led to the isolation of the known compound, $(+)-7{eta}-acetoxy-15,16-epoxy-3$, 13(16), 14-clero-datriene-18-oic acid (2) as an active constituent. In addition, a new trans-clerodane diterpenoid, (+)-2-oxokolavenic acid (1), together with six known compounds, (+)-3, 13-clerodadiene-16,15-olide-18-oic acid (3), $(+)-7{eta}-acetoxy-3$,13-clerodadiene-16,15-olide-18-oic acid (4), $(+)-7{eta}-acetoxy-16-hydroxy-3$,13-clerodadiene-16, 15-olide-18-oic acid (5), ${eta}-caryophyllene$ oxide (6), $clovane-2{eta},9{eta}-diol (7),{;}and{;}caryolane-1,9{eta}-diol$ (8) were isolated and found to be inactive. The structure of compound 1 was determined using physical and spectroscopic methods such as 1D and 2D-NMR experiments. The known compounds 2-8 were identified by the spectroscopic data and by comparison with the published values. Of eight isolates (1-8), only compound 2 exhibited an iNOS inhibitory activity with $IC_{50}$/ value of $51.6{;}mu extrm{m}M$.