On the diterpenoids of Andrographis paniculata: X-ray crystallographic analysis of andrographolide and structure determination of new minor diterpenoids.

The crystal structure of andrographolide (8) was determined and the absoluted configuration at C-14, which was previously undecided, was established as R. Reexamination of the constituents of Andrographis paniculata NEES resulted in the isolation of three new diterpenoids of ent-labdane type, and rographanin, andropanoside, and 14-deoxy-12-methoxy-andrographolide, together with three known compounds, 14-deoxyandrographolide (4), neoandrographolide (5) and andrographolide (8). The structures of the new diterpenoids were determined to be 1, 2, and 3 on the basis of spectral and chemical evidence.