Triflic anhydride (13.6 g, 48.3 mmol) was added dropwise with stirring to a 0° C. solution of N,N-bis-(2-hydroxyethyl)-2-nitrobenzenesulfonamide (7.00 g, 24.1 mmol) from Example 16A and 2,4,6-collidine (5.85 g, 48.3 mmol) in anhydrous methylene chloride (50 mL) (J. A. Kozlowski, et al., Bioorg. Med. Chem. Lett. 12: 791-794, 2002). Reaction stirred two hours at 0° C. and then overnight at room temperature. Reaction diluted with chloroform, washed with saturated NaHCO3 and brine, dried over Na2SO4, filtered, and concentrated under reduced pressure. The residue was purified by normal phase HPLC on a Biotage pre-packed silica gel column cluting with 3:1 hexane:ethyl acetate to afford the title compound. MS (ESI) m/z 555 (M+H)+.
