The new bitter diterpenes, rabdosianone I (C20H24O5) and II (C22H28O6), were isolated from Isodon japonicus (Japanese name, enmeiso), and their structures were elucidated by spectroscopic methods. Electrophysiological experiments were performed to compare rabdosianone I with quinine. The taste responses of chorda tympani nerves to rabdosianone I were smaller than those to quinine in Wistar rats.
