Reaction Steps
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)) (199 mg, 718 μmol) was dissolved in pyridine (1.5 mL) and to this was added 4-(dimethylamino)pyridine (9.0 mg, 74 μmol) and cooled to 0° C. To this was added p-toluenesulfonyl chloride (410 mg, 2.15 mmol) and stirred for 2 h after warming to room temperature. To this were added 2 M hydrochloric acid and dichloromethane to stop the reaction and, after separating the aqueous layer and organic layer, it was extracted 3 times with dichloromethane and was washed with saturated aqueous solution of sodium sulfate 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 dissolved in methanol (5 mL) and to this was added 10% (w/v) aqueous, solution of sodium hydroxide (1.2 mL) while stirring at room temperature and stirred at 65° C. for 30 min. After cooling to room temperature, to this was added 2 M hydrochloric acid to stop reaction and extracted 3 times with ethyl acetate. The organic layer was washed with saturated brine and 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 (23 g, n-hexane/ethyl acetate=3/2) to give 3-benzyl-5-(4-hydroxyphenyl)-2-[(4-methylphenyl)sulfonylamino]pyrazine (coelentera-p-tosylamide) (c-35) as a yellow solid (155 mg, 37.1% (2 steps)). Rf=0.25 (n-hexane/ethyl acetate=3/2). Mp. 181-182.5° C. UV (MeOH) λmax (log ε) 336.5 (4.10), 291.5 (4.26), 277 (4.27). UV (pH 7.4 PB) λmax (log ε) 351 (4.14), 282.5 (4.37). 1H NMR (400 MHz, DMSO-d6) δ 2.36 (s, 3H), 4.27 (s, 2H), 6.81 (d, J=8.7 Hz, 2H), 7.17-7.24 (m, 1H), 7.25-7.32 (m, 4H), 7.36 (d, J=7.6 Hz, 2H), 7.79 (t, J=8.7 Hz, 4H), 8.53 (s, 1H), 9.77 (s, 1H), 10.74 (s, 1H). IR (KBr, cm−1) 474, 525, 546, 567, 610, 667, 698, 743, 816, 839, 876, 941, 1088, 1148, 1165, 1215, 1269, 1321, 1364, 1404, 1447, 1495, 1516, 1593, 1609, 3283. HRMS (FAB+) m/z 432.1382 (M+H, C24H22N3O3S requires 432.1382).
