Daphnane diterpenoid resistant to prostate cancer and preparation method thereof

A method for treatment or adjuvant treatment of a castration-resistant prostate cancer in a patient, comprising:

• determining whether the patient suffers from the castration-resistant prostate cancer, and
• administering to the patient a therapeutic amount of a daphnane diterpenoid compound of formula I or a pharmaceutically acceptable salt thereof;
• wherein:
• in the formula I, a bond between C-1 and C-2 is a double bond, a bond between C-6 and C-7 is a single bond, and a bond between C-15 and C-16 is a double bond;
• R1 is absent;
• R2 is carbonyl;
• R3 is hydroxyl;
• R4 is hydroxyl;
• R5 is fluorine, chlorine, bromine, or iodine;
• R6 is fluorine, chlorine, bromine, or iodine;
• R7 is phenyl;
• R8 is absent;
• and
• R9 is hydrogen, hydroxyl, acetyl, benzoyl, isobutyryl, butyryl, or propionyl.