[OH:1][C:2]1[CH:3]=[C:4]([CH:10]=[CH:11][C:12]=1[OH:13])[CH2:5][CH2:6][C:7]([OH:9])=O.CN1CCOCC1.C(OC(Cl)=O)C(C)C.[NH2:29][C:30]1[CH:39]=[CH:38][C:33]([C:34]([O:36][CH3:37])=[O:35])=[CH:32][CH:31]=1>C1COCC1>[OH:1][C:2]1[CH:3]=[C:4]([CH2:5][CH2:6][C:7]([NH:29][C:30]2[CH:31]=[CH:32][C:33]([C:34]([O:36][CH3:37])=[O:35])=[CH:38][CH:39]=2)=[O:9])[CH:10]=[CH:11][C:12]=1[OH:13]To a solution of 3,4-dihydroxyhydrocinnamic acid (723 mg, 3.97 mmol) in anhydrous THF (20 mL) were added N-methylmorpholine (0.44 mL, 3.97 mmol) and isobutylchloroformate (0.52 mL,3.97 mmol) at 0° C. After 45 min, at 0° C., a solution of methyl 4-aminobenzoate (500 mg, 3.31 mmol) in anhydrous THF (4 mL) was added to the reaction mixture. After 5 min the temperature was allowed to warm up to rt and stir overnight. After extraction with EtOAc (100 mL), washing with HCl (0.1N, 50 mL) and a saturated aqueous solution of NaHCO3 (50 mL), the organic layer was dryed over sodium sulfate and evaporated under vacuo to give a yellow oil. Purification by flash chromatography using DCM/MeOH (95/5) as eluant gave the title compound as a colourless oil (22%) in a 94.8% purity by HPLC (MaxPlot detection between 230 and 400 nm).
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