Acetic Anhydride → 5-(4-Acetoxyphenyl)-2-amino-3-benzylpyrazine

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Under an argon atmosphere, 2-amino-3-benzyl-5-(4-hydroxyphenyl)pyrazine (coelenteramine) (c-5) (prepared by the method described in Adamczyk, M. et al., Org. Prep. Proced. Int., 33, 477-485 (2001)) (303 mg, 1.09 mmol) was dissolved in pyridine (2 mL) and cooled to 0° C. To this was added acetic anhydride (133 μL, 1.40 mmol) and stirred for an hour after warming to room temperature. To the mixture was added saturated aqueous solution of sodium bicarbonate and ethyl acetate to stop the reaction. After separating the aqueous layer and organic layer, it was extracted 3 times with ethyl acetate. The organic layer was washed 3 times with water and once with saturated brine, and then dried over anhydrous sodium sulfate. After removing anhydrous sodium sulfate by filtration, the filtrate was concentrated under reduced pressure with a rotary evaporator. The residue was purified by column chromatography (50 g, n-hexane/ethyl acetate=1/1) to give 5-(4-acetoxyphenyl)-2-amino-3-benzylpyrazine (c-19) as a pale yellow solid (337 mg, 96.7%). Rf=0.31 (n-hexane/ethyl acetate=3/2). Mp. 183.5-185.5° C. 1H NMR (400 MHz, DMSO-d6) δ 2.27 (s, 3H), 4.07 (s, 2H), 6.42 (s, 2H), 7.12-7.17 (AA′BB′, 2H), 7.19 (d, J=7.2 Hz, 1H), 7.27 (t, J=7.5 Hz, 2H), 7.33 (d, J=7.0 Hz, 2H), 7.90-7.95 (AA′BB′, 2H), 8.41 (s, 1H). IR (KBr, cm−1) 513, 596, 640, 654, 710, 746, 851, 910, 1016, 1136, 1167, 1198, 1217, 1373, 1423, 1452, 1466, 1493, 1508, 1535, 1630, 1746, 3148, 3289.

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