Sodium Bicarbonate → 2,5,6-Trichloro-3-(N-hydroxyiminomethylidene)-1-(beta-D-ribofuranosyl)indole

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To a solution of 2,5,6-trichloro-3-formyl-1-(β-D-ribofuranosyl)indole (4.3, 170 mg, 0.45 mmol) in MeOH (10 mL) was added a solution of methoxylamine hydrochloride (39 mg, 0.56 mmol) and sodium bicarbonate (49 mg, 0.48 mmol) in water (2.0 mL). The resulting mixture was stirred at room temperature for 16 h, then the solvent was evaporated to provide a pale yellow residue. The residue was suspended in 20 mL of 5% aqueous sodium thiosulfate and extracted with EtOAc (2×50 mL). The combined organic extracts were washed with brine (25 mL), dried over MgSO4, filtered and evaporated to yield a pink residue. The residue was subjected to column chromatography (40×350 mm) on C18 reverse-phase silica gel with 75% MeOH/H2O. The appropriate UV-active fractions were pooled and evaporated to yield 124 mg (70%) of 4.29 as a white powder. A portion was recrystallized from Et2O/hexane to yield a white crystalline solid: mp 208-209 C; Rf 0.2 (10% MeOH/CHCl3); 1H NMR (500 MHz, DMSO-d6) δ 11.31 (s, 1H), 8.54 (s, 1H), 8.22 (s, 1H), 8.19 (s, 1H), 5.93 (d, 1H), 5.37 (m, 2H, D2O exch.), 5.25 (m, 1H, D2O exch.), 4.43 (m, 1H), 4.16 (m, 1H), 3.99 (m, 1H), 3.73 (m, 2H). 13C NMR (125 MHz, DMSO-d6) δ 141.30, 133.03, 128.48, 125.85, 124.73, 124.05, 121.76, 115.31, 106.70, 88.81, 86.02, 71.39, 69.65, 61.11. HRMS (EI) m/z calcd. for C14H13Cl3N2O5 393.9890, found 393.9892. Anal calcd for C14H13Cl3N2O5·½Et2O: C, 44.41; H, 4.19; N, 6.47. Found: C, 44.16; H, 4.18; N, 6.48.

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