MAO-A inhibitors from Hypericum thasium Griseb

n-BuOH fraction from 80% ethanol extract of Hypericum thasium Griseb. have yielded two new compounds 3′,4,5′-trihydroxy-6-methoxy-2-O-α-arabinosylbenzophenone (1), and 3′,4,5′,6-tetrahydroxy-2-O-α-L-arabinosylbenzophenone (2), along with a known flavonoid glycoside quercetin-3-O-α-arabinose (3). The structures of the new compounds were elucidated by 1D and 2D NMR analysis as well as HR EIMS. The isolated compounds (1–3), as well as quercetin, and kaempferol previously isolated from EtOAc fraction were screened against MAO-A inhibitory activity. When tested against the MAO-A quercetin and kaempferol displayed IC₅₀ values of 19.6, and 17.5µM, respectively. The IC₅₀ values for MAO-A inhibition by compounds (1–3) were 310.3, 111.2, and 534.1µM, respectively. Standart inhibitor (clorgyline) exhibited MAO-A inhibition with an IC₅₀ value of 0.5µM.