Nagarines A and B, two novel 8,15-seco diterpenoid alkaloids from Aconitum nagarum

Two novel 8,15-seco C-19-diterpenoid alkaloids, nagarines A (1) and B (2), were isolated from the roots of Aconitum nagarum Stapf (Ranunculaceae), a folk herbal medicine used to treat rheumatism and arthritis in Southwestern China, Northern Burma and Northeastern India. They are the first C-19-diterpenoid alkaloids possessing unprecedented opened D ring formed by the cleavage of the bond between C-8 and C-15. Compounds 1 and 2 showed certain inhibition activities of interleukin-6 in LPS-activated RAW 264.7 cells with IC50 values of 72.63 +/- 0.39 mu M and 52.98 +/- 0.50 mu M, respectively.