Thymol derivatives from the roots of Xerolekia speciosissima an endemic species of the pre-Alpine area

A chloroform extract from roots of Xerolekia speciosissima, except for commonly distributed phenolic compounds, i.e.: syringaldehyde and 2,6-dimethoxy-p-benzoquinone, yielded five thymol derivatives. Two of the compounds, namely: 8-hydroxy-9-isobutyryloxy-10-isovaleryloxythymol (1) and 8-hydroxy-9,10-diisovaleryloxythymol (2) have not been previously reported and their structures were elucidated based on 1D and 2D NMR, HRESIMS and other spectral data. Three known thymol derivatives: 8-hydroxy-9,10-diisobutyryloxythymol (3), 7,10-diiso-butyryloxy-8,9-epoxythymol isobutyrate (4) and 10-isobutyryloxy-7-isovaleryloxy-8,9-epoxythymol isobutyrate (5) were formerly isolated from other taxa of the Inulae tribe (Asteraceae). Activities of 1 and 5 against Staphylococcus aureus were preliminarily evaluated by Kirby-Bauer disk diffusion method using novobiocin as a positive control.