[Synthesis]
Procedure for the synthesis of Phellopterin (32): 50 mg (0.22 mmol) of compound 26 was dissolved in 2 mL of anhydrous DMF under argon protection, and 46 mg of K2CO3 and 33 μL (0.29 mmol) of 1-bromo-3-methyl-2-butene were added sequentially. The reaction mixture was heated to reflux and after 1 h of reaction, the mixture was poured into 20 mL of cold water and acidified with 1 M aqueous HCl. The product was extracted with ethyl acetate (3 x 5 mL), the organic layers were combined, and the solvent was removed by concentration under reduced pressure to give the crude product. The crude product was purified by column chromatography (eluent: ethyl acetate/hexane=1:1). The fraction containing the target compound was collected, concentrated and dried to give 32 as a pale yellow powder (50 mg, 77% yield). The structure of the product was confirmed by 1H NMR, 13C NMR and HR-FABMS.1H NMR (CDCl3, 500 MHz) δ 8.12 (1H, d, J = 9.7 Hz, H-4), 7.62 (1H, d, J = 2.2 Hz, H-9), 6.99 (1H, d, J = 2.2 Hz, H-10), 6.28 (1H, d, J = 9.7 Hz, H-10), 6.28 (1H, d, J = 9.7 Hz, H-10). = 9.7 Hz, H-3), 5.61 (1H, m, H-2'), 4.85 (2H, d, J = 7.5 Hz, H-1'), 4.18 (3H, s, OCH3), 1.74 (3H, brs, H-4'), 1.70 (3H, brs, H-5'); 13C NMR (CDCl3, 125 MHz) δ 160.5 (C, C-2), 150.8 (C, C-7), 145.1 (CH, C-9), 144.4 (C, C-5 or 8a), 144.3 (C, C-5 or 8a), 139.7 (C, C-3'), 139.4 (CH, C-4), 126.9 (C, C-8), 119.8 (CH, C-2'), 114.6 (C C-6), 112.8 (CH, C-3), 107.6 (C, C-4a), 105.0 (CH, C-10), 70.4 (CH2, C-1'), 60.8 (CH3, OCH3), 25.8 (CH3, C-4'), 18.1 (CH3, C-5'); HR-FABMS (pos) m/z 301.3174 [M + H]+ (calculated value C17H17O5, 301.3156). |