Hydroxyphenylacetic acid → Pterostilbene

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Pterostilbene was synthesized as previously described (Joseph et al., supra). Briefly, pterostilbene was synthesized by condensation of 3,5-dimethoxybenzaldehyde and 4-hydroxyphenylacetic acid in acetic anhydride and triethylamine. The reaction mixture was heated (150° C.) under an atmosphere of nitrogen and continuously stirred. After 20 h, the reaction was stopped and cooled to room temperature, and concentrated hydrochloric acid (5 mL) was added. A precipitate formed, and this was dissolved in 50 mL of chloroform and then extracted with 10% aqueous sodium hydroxide. The aqueous extract was acidified to pH 1 with concentrated hydrochloric acid and stirred for at least 6 h, resulting in the precipitation of the intermediate product, α-[(3,5-dimethoxyphenyl)methylene]-4-hydroxy-(αZ)-benzeneacetic acid. This intermediate product was heated with 1.0 g of copper in 10 mL of quinoline (200° C., 6 h, under nitrogen). The reaction mixture was cooled to room temperature and filtered. To the filtrate was added 5 N hydrochloric acid (25 mL), which Was stirred for 1 h and then extracted with chloroform. The chloroform extract containing impure pterostilbene was purified by flash chromatography on a Horizon HPFC system (Biotage, Inc., Charlottesville, Va.), using a silica gel column and the solvent system ethyl acetate:hexane (linear gradient from 15:85 to 100% ethyl acetate). Fractions containing pure pterostilbene were combined and concentrated in vacuum. Pterostilbene was recrystallized in hexane, and its structure was confirmed from its spectroscopic data (UV, mass spectrometry, and nuclear magnetic resonance spectroscopy) (FIG. 1).

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