The genus Sideritis (Lamiaceae) includes more than 150 species, which are distributed widely in the Mediterranean area. Sideritis species are traditionally used for the treatment of several disorders, e.g. ulcers, spasm and pain. Although Sideritis species are considered to be abundant source of diterpenoids, until now only siderol was described from S. montana L. Previously, iridoid glycosides (ajugol, ajugoside and melittoside), diosmetin, and verbascoside have also been isolated from the plant.
The present study focused on the phytochemical and pharmacological investigation of S. montana. From the methanol extract of the plant, four abietane-type diterpenes (1–4) were isolated. The compounds are substituted with hydroxyl, methyl and isopropyl groups, two of them, sideritins A and B (1, 2), are new natural products. Further diterpenes [9α,13α-epi-dioxiabiet-8(14)-en-18-ol (3) and pomiferin E (4)], a lignan (paulownin, 5), a flavonoid (6-methoxysakuranetin, 6), a megastigmane (3-oxo-α-ionol, 7) and a phenol-glucoside (dictamnoside A, 8) were also identified. All of the compounds were isolated for the first time from the plant.
Several diterpenoids have been reported to exhibit remarkable antiproliferative activity, but there were no previous data of the cytotoxic effects of metabolites from S. montana. All of the isolated compounds were tested in vitro on human cervical cancer cell lines (HeLa, SiHa and C33A) using the MTT assay. Among the isolated compounds, pomiferin E (4) and 6-methoxysakuranetin (6) showed considerable activity [inhibition (%) ± SEM: 46.93±2.35 on HeLa (4), and 51.52±2.45 on C33A (6)] at 30 µM concentration.
Acknowledgement: This work was supported by the GINOP-2.3.2-15-2016-00012, and a János Bolyai Research Scholarship of the Hungarian Academy of Sciences.