A mixture of 7-(4-methyl-1H-imidazol-1-yl)-2-{(2S)-1-[4-nitro-2-(pentafluoro-λ6-sulfanyl)phenoxy]propan-2-yl}-3,4-dihydro-2H-pyrido[1,2-a]pyrazine-1,6-dione (C55) (790 mg, 1.44 mmol) and ethanol (10 mL) was heated to 55° C. Iron powder (99%, 243 mg, 4.31 mmol) and a solution of ammonium chloride (462 mg, 8.64 mmol) in water (2.5 mL) were added, and the reaction mixture was stirred at reflux for 3 hours. The reaction mixture was allowed to cool to room temperature, concentrated in vacuo, treated with ethyl acetate and saturated aqueous sodium bicarbonate solution and filtered through Celite. The filter pad was rinsed with water and ethyl acetate; the organic portion of the filtrate was washed with saturated aqueous sodium chloride solution, dried over magnesium sulfate, filtered, and concentrated under reduced pressure. Purification via silica gel chromatography (Gradient: 5% to 10% methanol in ethyl acetate) provided the product as a light yellow foam. Yield: 507 mg, 0.98 mmol, 68%. LCMS m/z 520.2 (M+1). 1H NMR (400 MHz, CDCl3), characteristic peaks: δ 1.48 (d, J=7.2 Hz, 3H), 3.71-3.79 (m, 1H) 3.85-3.92 (m, 1H), 4.05 (dd, J=9.6, 5.5 Hz, 1H), 4.99-5.08 (m, 1H), 6.80 (dd, half of ABX pattern, J=8.8, 2.6 Hz, 1H), 6.86 (br d, half of AB quartet, J=8.8 Hz, 1H), 7.06 (d, J=2.6 Hz, 1H).
