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For evaluation of C(18)- and C(19)-diterpenoid alkaloids as analgesics, three C(19)-diterpenoid alkaloids were isolated from the roots of Aconitum hemsleyanum var. circinatum and A. transsecutum; and twenty-five semisynthetic C(18)- or C(19)-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 (ED(50)=0.0972 mg/kg) and 8-O-ethylyunaconitine (ED(50)=0.0591 mg/kg) were the most potent analgesics relative to the reference drugs lappaconitine (ED(50)=3.50 mg/kg) and crassicauline A (ED(50)=0.0480 mg/kg). Analgesic activity data of these C(18)- and C(19)-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 C(19)-diterpenoid alkaloids.

In the title study, the synthesis of the vital intermediate C-nor-aconanone (3) from 4 was completed through 11 steps, mainly including semipinacol rearrangement, formation of the imines by the treatment of 10 or 20 with NBS, the cleavage of N-C19 bonds in 11 or 21 by treatment with m-CPBA and subsequently with LTA, as well as the rupture of the N-C17 bonds in 22 by a modified Nef reaction (NaH/t-BuOH --> KMnO4/H2O). One-pot procedure was successfully developed starting from 11 or 21 to afford the N,19-seco-C-nor product 15 or 22, respectively, in reasonably good yields.

From the roots of Delphinium potaninii var. jiufengshanense, two new lycoctonine-type C(19)-diterpenoid alkaloids called jiufengdine (1) and jiufengtine (4) have been isolated. The structures of the new alkaloids (1, 4) were established by 1D and 2D NMR spectra.