Abstract
For evaluation of C18- and C19-diterpenoid alkaloids as analgesics, three C19-diterpenoid alkaloids were isolated from the roots of Aconitum hemsleyanum var. circinatum and A. transsecutum; and twenty-five semisynthetic C18- or C19-diterpenoid alkaloids were prepared from lappaconitine, crassicauline A or yunaconitine. In a mice acetic acid-induced abdominal constriction assay, four crassicauline A analogs and three yunaconitine analogs exhibited good analgesic activities with 77.8—94.1% inhibition range in 0.1—10 mg/kg subcutaneous (s.c.) dose range at the point of 20 min after drug administration. Among them, 8-O-deacetyl-8-O-ethylcrassicauline A (ED50=0.0972 mg/kg) and 8-O-ethylyunaconitine (ED50=0.0591 mg/kg) were the most potent analgesics relative to the reference drugs lappaconitine (ED50=3.50 mg/kg) and crassicauline A (ED50=0.0480 mg/kg). Analgesic activity data of these C18- and C19-diterpenoid alkaloids indicate that a tertiary amine in ring A, an acetoxyl or an ethoxyl group at C-8, an aromatic ester at C-14, and the saturation state of the ring D are important structural features necessary to the analgesic activity of the C19-diterpenoid alkaloids.
