Two New Thiophenes from Echinops latifolius and their Phototoxic Activities

Two new thiophenes, 5-{4-[4-(5-pent-1,3-diynylthiophen-2-yl)-but-3-ynyloxy]-but-1-ynyl}-2,2'-bithiophene (1) and 5-(4-hydroxybut-1-one)-2,2'-bithiophene (2), together with two known thiophenes 5-(4-hydroxybut-1-ynyl)-2,2'-bithiophene (3) and 5-(3,4-dihydroxybut-1-ynyl)-2,2'-bithiophene (4), were isolated from the roots of Echinops latifolius Tausch. Their structures were elucidated based on the detailed NMR spectroscopic analysis and comparison with literature values. Compounds 1 and 2 showed significant inhibition activities against human cancer cell lines A375-S2 and HeLa with IC(50) values from 3.1 to 13.5 micromol/L, depending on their exposure to long wavelength ultraviolet light.