Sesterterpenes from Salvia tingitana Etl. (Lamiaceae)

Salvia tingitana Etl. is an aromatic woody-based perennial shrub original from the Arabian region [1]. The plant was historically used as rubefacient, solving, digestive, and against colds and drunkenness [2]. In the course of our research on new plant compounds from Salvia species able to face the constantly increasing resistance to antibiotics [3], the antimicrobial properties of the dichloromethane extract obtained from the aerial parts of S. tingitana was investigated following a bioassay-oriented fractionation approach. The surface extract showed moderate antimicrobial activity against Gram positive multi-resistant bacterial strains; no activity was observed on the Gram-negative strains or on Candida albicans. The hexane insoluble fraction of the crude extract was separated by silica gel column chromatography into six fractions (Ia-VIa); the hexane soluble fraction was separated into seven fractions (Ib-VIIb); all fractions were evaluated at doses corresponding to that of the crude extract. Among the tested fractions, fraction IVa Va Va were active against various Staphylococcus spp including S. aureus and S. epidermidis. Fractions IIIb and IVb were active against various Staphylococcus spp. and Enterococcus faecium, and fraction Vb was active against Staphylococcus spp. The chemical separation of the fractions afforded eight new and five known sesterterpenes, along with other known compounds including five labdane and one abietane diterpenes, one sesquiterpene and four polymethoxylated flavonoids, identified by IR, 1D and 2D NMR, HRMS analysis. The antimicrobial activity of the pure compounds was analysed on several Gram positive multi-resistant bacterial strains, also of marine origin (S. aureus, S. epidermidis, S. haemoliticus, S. hominis, S. capitis, S. lugdunensis, S. saprophyticus, S. mitis, E. faecium, E. faecalis, E. durans, E. gallinarum, E. casseliflavus, E. gallolyticus). The compounds showed various antimicrobial activities against Gram positive bacteria, with the exception of manool and sclareol, which exhibited MIC values ranging from 4 to 64 g/mL.