RBE were synthesized according to a modified method by Neises and Steglich (1978) [24 (link)]. A mixture of trans-resveratrol (2.282 g, 10 mmol) and n-butyric acid (0.969 g, 11 mmol) was added to anhydrous tetrahydrofuran (THF) (Morris Plains, NJ, USA) (about 12 mL) in a three-neck flask with a magnetic stirrer. To perform the reaction in the dark, the flask was wrapped with aluminum foil. After all reactants were completely dissolved, predetermined amounts of EDC (1.708 g, 11 mmol) and DMPA (0.672 g, 5.5 mmol) were added into the solution. The esterification reaction was carried out by stirring the solution at room temperature under a nitrogen atmosphere for 60 h. Subsequently, the solution was poured into an excess amount of deionized water. Then, a viscous substance was precipitated. The viscous product was re-dissolved in acetone and collected, then the solvent was removed with a rotary vacuum concentrator. The concentrate of RBE was frozen at −80 °C and freeze-dried. Following freeze-drying, the light-yellow powder of RBE was obtained and stored in an opaque vial in a refrigerator at 4 °C.
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