It has been reported that several toxic diterpenoids, Pieristoxins and Asebotoxins, were isolated from the flowers of Pieris japonica D. Don (Ericaceae). The structures of Asebotoxin-I, II, III, IV, V and VII are known, but those of Pieristoxin A, B, C and D are unknown. We isolated five diterpenoids, compound-I, II, III, IV and V, from the same flowers. The structures of these compounds were investigated. From the comparison of the spectral data and the chemical facts, compound-I, mp 190-191°, and compound-II were found to be identical with Asebotoxin-I C23H38O7, mp 196-198°, and Asebotoxin-VII C25H38O10, respectively. The IR spectrum of compound-III (mp 257-260°) was identical with that of Pieristoxin-B (mp 257°). Compound-ID: was hydrolysed to give lactic acid and desacyl Pieristoxin-B (Pieristoxin-E, mp 280-282°), which showed the same IR spectrum with compound-IV (mp 260-276°). The analysis of the NMR spectrurm of Pieristoxin-E showed the presence of the same functional groups to those of Rhodojaponin-III C20H32O6 (desacyl Asebotoxin-III, mp 285-287°). The melting point of Pieristoxin-E is close to that of Rhodojaponin-III, but those of monoacetyl Pieristoxin-E (mp 280-283°) and diacetyl Pieristoxin-E (mp 236-238°) differ from those of monoacetyl Rhodojaponin-III (Rhodojaponin-II mp 294.5-296°) and diacetyl Rhodojaponin-III(Rhodojaponin-I, mp 248.5-250°), respectively. The C-14 hydrogen signal (6.18 ppm) in the NMR spectrum of Pieristoxin-B indicates that Pieristoxin-B is 14-lactoyl Pieristoxin-E. The NMR spectrum of Pieristoxin-B is similar to that of Rhodojaponin-V (14-acetyl Rhodojaponin-III except that the signals due to the O-acetyl group in the latter is replaced by the signals due to the O-lactoyl group in the former. It is likely that Pieristoxin-B and E are identical with Asebotoxin-III and Rhodojaponin-III, respectively. The structure of compound-V C25H40O9, mp 203-205°, was shown by the chemical and spectral characteristics to be 7-acetoxy-14-propionyl Grayanotoxin-III or 7-propionyloxy-14-acetyl Grayanotoxin-III
