New Bitter Diterpenes, Rabdosianone I and II, Isolated from Isodon japonicus Hara

Area of Science:

• Natural Product Chemistry
• Neuroscience
• Sensory Science

Background:

• Isodon japonicus, known as enmeiso, is a traditional Japanese herb.
• Bitter diterpenes are a class of natural compounds with diverse biological activities.
• Understanding the sensory properties of novel compounds is crucial for various applications.

Purpose of the Study:

• To isolate and characterize new bitter diterpenes from Isodon japonicus.
• To investigate the taste perception of these novel compounds using electrophysiological methods.
• To compare the bitterness intensity of a novel diterpene with a known bitter compound, quinine.

Main Methods:

• Isolation of compounds using chromatographic techniques.
• Structure elucidation of isolated diterpenes via spectroscopic analysis (e.g., NMR, MS).
• Electrophysiological recordings from chorda tympani nerves in Wistar rats to measure taste nerve responses.

Main Results:

• Two new bitter diterpenes, rabdosianone I (C20H24O5) and rabdosianone II (C22H28O6), were successfully isolated and their structures determined.
• Electrophysiological experiments demonstrated that rabdosianone I elicits a significantly smaller taste response compared to quinine.
• These findings suggest a potentially lower bitterness intensity for rabdosianone I relative to quinine.

Conclusions:

• Rabdosianone I and II represent novel bitter diterpenes from Isodon japonicus.
• Rabdosianone I exhibits a weaker bitter taste response than quinine in rat models.
• Further research can explore the structure-activity relationships of these diterpenes and their potential applications.