New clerodane diterpenoids from Salvia buchananii Hedge

S. buchananii Hedge (Lamiaceae) (subgenus Calosphace) is a Mexican perennial herbaceous species with almost glabrous petiolate and spathulate leaves and large corollas. The antimicrobial activity of the surface exudate obtained by rinsing the aerial parts of with CH2Cl2 was preliminary evaluated by testing 10 µl of 2-fold dilutions (ranging from 1000 mg/L to 64 mg/L) on selected multi-drug-resistant Gram-positive strains, appropriately seeded on agar plates. A clear halo of inhibition was observed on Staphylococcus epidermidis, Staphylococcus aureus (minimum active concentrations for both strains 125 mg/L) and, particularly, on Enterococcus faecium and Enterococcus faecalis (minimum active concentrations for both strains 64 mg/L). The exudate extract, subjected to repeated column chromatography on Sephadex LH-20 and silica gel and to semi-preparative RP-HPLC, yielded two new clerodane diterpenoids, identified by IR and NMR analysis, including TOCSY, COSY, HSQC, HMBC and ROESY experiments, and ESI-TRAP-MS and HR-MS analysis.