Corydalis B,a constituent of the Chinese plant CorydaLis ambihus,is a potent analgesic which also exhibits significant sedative activity.The chemical constitution of this alkaloid has been proved to be 2,3,9,10-tetramethoxy-5,6,13,13a-tetrahydro-8H-dibenzo [a,g] quinolizine (tetrahydropalmatin,Ⅰ).Pharmacological studies carried out in this institute revealed that replacement of the methoxy groups in I by other alkoxy or acyloxy groups caused substantial change in its pharmacological actions.