Preparation
Preparation of (-)-ASARININ: Total volatile oil extract of Asarum was obtained using a supercritical CO₂ extraction apparatus. The roots and/or rhizomes of Asarum were washed, air-dried and ground in a mill to produce a crude powder. The crude powder was placed into the loading flask of the extraction vessel, which was then loaded into the extraction vessel and sealed; The extraction vessel and separation vessel were heated separately. When the temperature of the extraction vessel reached 50 °C and the separation temperature of the separation vessel reached 40 °C, the valve of the extraction vessel was opened. Once the pressure inside the extraction vessel equalled that of the storage tank, the vent valve was opened to purge the air. The system was pressurised using a high-pressure pump. When the extraction vessel reached the set pressure of 35 MPa, and Separation Vessels I and II have each reached the set pressure of 5 MPa, regulate the CO₂ flow rate to 40 L/h and commence the extraction cycle; maintain the extraction temperature at 50 °C, the separation temperature in the separation vessels at 40 °C, and the extraction time at 180 minutes, yielding total essential oil from Asarum, with a yield of 2.5 per cent (mL/g); allow the total essential oil from Asarum to stand at –5 °C for 24 hours, then filter under reduced pressure to obtain crude (–)-asarinin; Take the crude (-)-asarinin and dissolve it in an equal volume of anhydrous ethanol; subject it to low-temperature recrystallisation twice at –20 to 4 °C; once white needle-like crystals have precipitated, the pure (-)-asarinin is obtained, with a yield of 1.5 per cent (g/mL).
