To a stirred solution of (S)-3,5-dichloro-4-(2-(3-(cyclopropylmethoxy)-4-(difluoromethoxy)phenyl)-2-((4-nitrophenoxy)carbonyloxy)ethyl)pyridine 1-oxide (prepared in an analogous manner as described in Scheme 3, Step 1) (0.150 g, 0.256 mmol) in DCM (10 ml), DMAP (0.0156 g, 0.128 mmol) was added followed by tert-butyl 2-(cyclopropylmethoxy)-4-(hydroxymethyl)phenyl(methylsulfonyl)carbamate (0.124 g, 0.333 mmol), and the resulting mixture was stirred at RT for 3 hours. HCl 4M in dioxane (3 ml, 12 mmol) was added and the reaction was stirred at RT for additional 5 hours. The solvent was removed under vacuum and the residue was purified by flash chromatography on silica gel column (DCM:MeOH=10:0.15). A further purification by flash chromatography on silica gel column (DCM:acetone=10:1) was required to obtain (S)-3,5-dichloro-4-(2-(3-(cyclopropylmethoxy)-4-(difluoromethoxy)phenyl)-2-((3-(cyclopropylmethoxy)-4-(methylsulfonamido)-benzyloxy)carbonyloxy)ethyl)pyridine 1-oxide as a white solid (0.073 g, 0.102 mmol, 39.7% yield, MS/ESI+ 716.93 [MH]+, [αD]=−11.84, c=0.495, DCM).
