Pinostilbene

The stilbenoid derivatives to be tested (1–19, Table 1) were isolated from natural sources or obtained commercially. The naturally occurring stilbenoids trans-resveratrol (1), pinostilbene (2), thunalbene (3), piceatannol (4), piceatannol-3’-O-β-glucopyranoside (5), batatasin III (6), pinostilbenoside (7), 1-(2,4-dihydroxyphenyl)-2-(4-hydroxyfenyl)-ethanone (10), 3,5-dimethoxystilbene (11), pterostilbene (15), pinosylvin monomethyl ether (17), and isorhapontigenin (18) were obtained from Sigma-Aldrich, synthetic compounds trans-stilbene (12), cis–stilbene (13), 4-stilbenecarboxylic acid (14), trans-α-methylstilbene (16), and 2,4,3´,5´-tetramethoxystilbene (19) were purchased from Sigma-Aldrich (Steinheim, Germany). The compounds 2-carboxyl-3-O-methyl-4´-β-d-glucopyranosyl-dihydroresveratrol (8) and 3-O-caffeoyl-(9→5)-β-apiosyl-(1→6)-β-glucopyranosyl-5,3´-O-dimethyldihydropiceatannol (9) were kindly provided by Dr. Sebastian Granica (Medical University of Warsaw, Warsaw, Poland) who had isolated them from Tragopogon tommasinii Sch.Bip. (Asteraceae, Cichorieae) [7 (link)].

Hexane, chloroform, ethylchloroformate, trans-RSV, and pinostilbene (internal standard) were purchased from Sigma-Aldrich (Germany). Standard stock solutions were prepared by dissolving trans-RSV and pinostilbene in ethanol. All calibrations were performed by diluting the stock solutions in wine-like matrix (50 mL final volume containing: 150 mg disodium tartrate, 6.5 mL ethanol (13% final concentration), 43.5 mL H₂O adjusted to pH 3.3 with an aqueous tartaric acid solution). cis-RSV standard solution was prepared according to Francioso et al. [13 (link)]. Briefly, 30 μg/mL trans-RSV in wine-like matrix were exposed for 2 min to UV light (20 cm from the irradiation source, with a 14.7 W UV-B fluorescent tube emitting at wavelengths of 270−320 nm with a peak at 312 nm). Conversion rate was estimated using GC–MS by comparing trans-RSV peak areas before and after the treatment with UV light.