Carbon-13 NMR spectra of a number of (-)-ent-kauranoids have been studied. An unambiguous selfconsistent assignment of resonances has been made by considering the changes in chemical shifts produced by the change of substituent(s).A new kauranoid diterpene, didymooblongin (1) was isolated' along with (-)-enf-16-kauren-19-oic acid' (2) and (-)-ent-16a-kaurano13 (3) from the whole plant Didymocarpus oblonga. Didymooblongin [(-)-ent-7P-hydroxy-16-kauren-19-oic acid] has been shown4 to be an intermediate in the metabolic transformation of (-)-ent-kaur-16-ene to gibberellic acids in the mould Gibberella fujikuroi. We report here the I3C NMR spectral assignments of 1 and 2 as well as those of some closely related compounds (4-12). Carbon-13 N M R data of (-)-ent-16-kauranyl acetate (13) are also presented. The assignments were made by comparing the effects of the change of one functional group to another. Once the spectral assignments of (-)-ent-16-kauren-19-oic acid (2) were made it was very simple9 R' = COOH, R2 = a-H, 6-OAc, R3 = CH, 10 R' = COOH, R2 = 0, R3 = CH, 12 R' = CH,OAc, RZ = a-H, (3-OAc, R' = CH, 13 R' = CH,, R2 = H,, R3 = a-OAc, @-CH, 14 R' = CH,, R2 = H,, R3 = CH, 15 R' = CH,, R2 = H,, R' = 0 16 R' = COOH, RZ = H,, R3 = 0 11 R'=CH,OH, R 2 = a -H , @-OH, R'=CH,
