In vitro biomass of Salvia corrugata: chemical analysis and evaluation of antimicrobial activity

The major diterpenoids of the exudate of the fresh aerial parts of Salvia corrugata Vahl., demethylfruticuline A (1) and fruticuline A (2), showed significant antibacterial activity [1] and inhibited in vitro the synthesis of biofilm of multiresistant strains of Staphylococcus and Enterococcus [2]. In order to identify efficient in vitro methods of production of these compounds, a protocol for micropropagation and for induction of adventitious shoots from the leaves of S. corrugata was developed. The percentage of nodal explants producing shoots was high in MS medium containing BA 1.5 µM or TDZ 3.0 µM, while the leaf explants showed a poorly suited source of explants for the induction of adventitious shoots. For the quantitative determination of 1 and 2 in the methanolic extracts of the two types of biomass an HPLC method was set up and validated. Regenerated shoots showed the presence of both 1 and 2, while micropropagated plants contained only 2. The yield of 2 was higher in regenerated shoots than in the exudate. In addition to 1 and 2, the two methanolic extracts afforded three new diterpenoids, an icetaxane (3) and two abietanes (4 and 5) with a royleanone skeleton, identified by UV, IR, 1D and 2D-NMR, and HR-MS analysis. 4 and 5 were active on multidrug resistant clinical strains of Staphilococcus aureus, S. epidermidis, Enterococcus faecalis and E. faecium displaying MIC values of 64 µg/mL.