In the present study, we report the following: isolation and structural elucidation of two previously unknown in Thymelaea microphylla compounds, ethyl caffeate 1 and ladanein 2; evaluation of antioxidant properties and total phenolic content (TPC) of T. microphylla extracts; photoisomerization of cis/trans-tilirosides and structureantioxidant activity relationship of these two isomers. The petroleum ether and chloroform extracts were tested by DPPH•, ABTS •+ scavenging capacity (RSC) and ferric reducing antioxidant power (FRAP) assays. The results showed that there is a strong correlation between TPC and antioxidant activity of different T. microphylla extracts. Photoisomerization was induced by UV lamps at 365 nm, the percentage of cis-tiliroside was observed to increase up to 30%. Antioxidant activity was found to increase after phtoisomerization of tiliroside.
