Bioactive norditerpenoids and neolignans from the roots of salvia miltiorrhiza
Two new norditerpenoids, miltiolactones A and B (1a, 1b); seven new neolignans, miltiolignanolides A–G (2a, 2b and 3a, 3b and 4a, 4b, and 5) were obtained from the root extract of Salvia miltiorrhiza. Using HPLC separation with a chiral column, compounds 1–4 were found to exist as four pairs of enantiomers. Compounds 2–5 are novel neolignans with a dibenzocycloheptatriene ring system, which form an unprecedented 6/7/6 carbon skeleton. The structures were established via extensive spectroscopic analysis, and experimental and calculated electronic circular dichroism (ECD) spectra, and compound 1 was also elucidated by X-ray diffraction experiments. Compounds 2a and 2b significantly increased the viability of H9c2 cells from H2O2-induced cell death, and 3a showed significant antioxidant activity in an ABTS assay. In addition, compounds 2a, 2b and 3a, 3b display moderate inhibitory effects on nitric oxide (NO) production in LPS-induced microglial cells.