[Synthesis]
Compound 17a (51 mg, 0.13 mmol) was used as starting material, which was dissolved in methanol (5 mL) and stirred at room temperature. Carbon tetrabromide (CBr4, 4.5 mg, 0.013 mmol) was added to this solution and the reaction mixture was subsequently heated to reflux with continuous stirring for 2.5 hours. The reaction process was monitored by thin layer chromatography (TLC). Upon completion of the reaction, the solvent was removed under reduced pressure using a rotary evaporator. The resulting residue was purified by preparative thin layer chromatography (PLC) with the eluent being a mixed solvent of hashane/ethyl acetate, resulting in the target product (E)-1-(2-hydroxy-4-methoxy-5-(3-methyl-2-buten-1-yl)phenyl)-3-(4-hydroxyphenyl)prop-2-en-1-one (Compound 5a, 35 mg, 84% yield) as yellow needle-like It is a yellow needle-like crystal. Its melting point is 169.9-170.1°C (EtOAc/hexane recrystallized); Rf value is 0.34 (33% EtOAc/hexane); infrared spectrum (KBr) νmax/cm-1: 3436, 3319, 3069, 2973, 2943, 2911, 2854, 2821, 2751, 2697, 2604, 1628, 1604, 1544, 1544, 1544, 1544, 1544, 1544, 1544, 1544, 1544, 1544, 1544, 1544, 1544, 1544, 1544, 1544, 1544, 1544, 1544, 1544, 1544 1628, 1604, 1544, 1508, 1443, 1363, 1306, 1284, 1205, 1170, 1130, 1105; NMR hydrogen spectra (acetone-d6) δH: 1.58 (3H, d, J = 1.0 Hz, CH3), 1.59 (3H, s, CH3), 3.13 (2H, d, J = 7.2 Hz, Ph-CH2CH), 3.78 (3H, s, OCH3), 5.12-5.17 (1H, m, CCHCH2), 6.34 (1H, s, C2'H), 6.80 (2H, d, J = 8.6 Hz, C3H and C5H), 7.56 (2H, d, J = 8.6 Hz, C2H and C6H), 7.59 (1H d, J = 15.4 Hz, CαH), 7.70 (1H, d, J = 15.4 Hz, CβH), 7.80 (1H, s, C6'H), 8.93 (1H, s, OH), 13.51 (1H, s, OH); NMR carbon (acetone-d6) δC: 17.89, 25.88, 29.28, 56.28, 100.00, 114.16, 118.35, 122.38, 123.78, 127.56, 131.21, 131.74, 132.50, 145.15, 161.08, 165.09, 166.44, 192.89; high-resolution mass spectrometry (HRMS): measured value [M]+ 338.1530, calculated value c21h22o4 338.1518. |