Comparative Phytochemical Studies on the Aerial Parts of Teucrium davaeanum Coss. and Teucrium zanonii Pamp.

Phytochemical studies performed on the aerial parts of Teucrium davaeanum Coss. resulted in the isolation of an iridoid diglycoside, teucardoside; two phenylethanoid triglycosides, poliumoside and 3-O-methyl-poliumoside; a flavon C-diglycoside, vicenin-2 (apigenin-6,8-di-C-glycoside); and a newly described bisdesmosidic oleanane-type triterpene saponin, davaeanoside. Structure elucidations of all isolated metabolites are based on extensive spectroscopic analysis and chemical derivatizations. The extract and isolated compounds (1–5) were tested for α-amylase and α-glucosidase inhibitory activity. IC50 values were measured for all extracts and compounds and compared against acarbose. Results revealed weak or moderate α-amylase and α-glucosidase inhibitory activity at the tested concentrations of the isolated compounds, especially compound 5. However, these findings do not exclude antidiabetic activity mediated by other mechanisms such as modulation of insulin signaling, enhancement of glucose uptake, or antioxidant effects. Further studies are warranted to explore these potential pathways. In addition, the essential oils of T. davaeanum and T. zanonii were obtained by hydrodistillation and simultaneously analyzed by GC-FID and GC/MS. The major compounds of T. davaeanum essential oil were germacrene D (31.4%) and bicyclogermacrene (15.9%); the main compounds of T. zanonii were β-pinene (19.5%), α-muurolene (13.4%), oxo-7,8-dihydro-β-ionol (9.2%), and α-pinene (6.9%).