C([O:4][C:5]1[CH:10]=[CH:9][C:8]([C:11]2[N:12]=[C:13]([CH2:21][C:22]3[CH:27]=[CH:26][CH:25]=[CH:24][CH:23]=3)[C:14]([NH:17][C:18](=[O:20])[CH3:19])=[N:15][CH:16]=2)=[CH:7][CH:6]=1)(=O)C.[OH-].[Na+].Cl>CO>[C:18]([NH:17][C:14]1[C:13]([CH2:21][C:22]2[CH:27]=[CH:26][CH:25]=[CH:24][CH:23]=2)=[N:12][C:11]([C:8]2[CH:7]=[CH:6][C:5]([OH:4])=[CH:10][CH:9]=2)=[CH:16][N:15]=1)(=[O:20])[CH3:19]5-(4-Acetoxyphenyl)-2-acetylamino-3-benzylpyrazine (c-33) (355 mg, 982 μmol) was dissolved in methanol (8 mL), to which was added 10% (w/v) aqueous solution of sodium hydroxide (1.8 mL) while stirring at room temperature and then stirred for an hour. To this was added 2 M hydrochloric acid to stop the reaction and extracted 3 times with ethyl acetate. The organic layer was washed with saturated brine and then dried over anhydrous sodium sulfate. After removing anhydrous sodium sulfate by filtration, the filtrate was concentrated under reduced pressure. After purifying the residue by column chromatography (37 g, n-hexane/ethyl acetate=1/2), the obtained solid was recrystallized from methanol to give 2-acetylamino-3-benzyl-5-(4-hydroxyphenyl)pyrazine (coelenteracetamide) (c-25) as a colorless solid (109 mg, 34.8%). Rf=0.23 (n-hexane/ethyl acetate=1/2). UV (MeOH) λmax (log ε) 332 (4.14), 294 (4.15), 275.5 (4.12). UV (pH 7.4 PB) λmax (log ε) 328 (4.14), 289.5 (4.03), 270 (4.08). 1H NMR (400 MHz, DMSO-d6) δ 2.03 (s, 3H), 4.13 (s, 2H), 6.84-6.89 (AA′BB′, 2H), 7.14-7.21 (m, 3H), 7.23-7.29 (m, 2H), 7.89-7.94 (AA′BB′, 2H), 8.80 (s, 1H), 9.91 (s, 1H), 10.21 (s, 1H). IR (KBr, cm−1) 592, 631, 702, 746, 837, 1128, 1157, 1173, 1211, 1231, 1279, 1314, 1368, 1435, 1497, 1518, 1543, 1582, 1591, 1611, 1672, 3026, 3073, 3254. HRMS (FAB+) m/z 320.1399 (M+H, C19H18N3O2 requires 320.1399).
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