Three new diterpenes from the roots of Salvia miltiorrhiza and their cytotoxicity.

Two undescribed oxazole-containing diterpenoids (1-2) and a new diterpenoid (3) were isolated from the roots of Salvia miltiorrhiza. Their structures were elucidated by extensive HRESIMS and NMR spectroscopic analysis, and the absolute configurations of 1 and 3 were confirmed by comparison of the calculated and experimental electronic circular dichroism (ECD) spectra. Compound 1 represents the first example of an abietane diterpenoid with a benzo[d]oxazole unit fused in the ring B of the abietane skeleton. The cytotoxicity of 1-3 was evaluated against four human tumor cell lines (A549, MCF-7, HepG2, and PC-3), and 1-2 showed weak cytotoxic activities.