New Esters of Ferrediol and Sideritriol in subsp. : Characterization and Antiproliferative Activity.

17-Isovalerate esters of ferrediol and sideritriol (compounds and ) and 17-(2-methylbutyrate) ferrediol (compound ), which have not been earlier described, were isolated along with five known -15-kaurene diterpenes (siderol, sideridiol, sideroxol, eubotriol, and -candicandiol), one -beyerene (flavovirol), and one phytosterol (β-sitosterol) from the aerial parts of subsp. (Boiss. & Heldr.) Baden that is a mountain tea species endemic to Northern Peloponnese in Greece. Compounds - exhibited weak antiproliferative activity against triple-negative MDA-MB-231 and Hs578T breast cancer cells. In MCF-7 breast cancer cells, compounds , , siderol, and sideridiol were equipotent to 5-fluorouracil (moderate antiproliferative activity).