Two new 18-carbon norditerpenoid alkaloids from Aconitum sinomontanum

Two new 18-carbon norditerpenoid alkaloids, sinaconitines A (1) and B (2), together with two known alkaloids, ranaconitine (3) and lappaconitine (4), were isolated from the roots of Aconitum sinomontanum. Their structures were elucidated on the basis of spectral evidences and X-ray crystallographic analysis for 1. Furthermore, the reversed ¹³C NMR assignments for C-10 and C-13 of 3, 4, puberanine, puberanidine and demethyllappaconitine were revised. Compounds 1–4 were evaluated for cyclooxygenase-2 (COX-2) enzyme inhibitory activity. However, they did not show any inhibition at 10 μM.