To a stirred solution of oxalyl chloride (5 eq) in DCM (0.3 M) at −78° C. was added a solution of DMSO (10 eq) in DCM (0.5M). The reaction mixture was stirred at −78° C. for 30 min. A solution of tert-butyl (2R,5R)-5-(hydroxymethyl)-2-[2-(2-{[N-(methoxycarbonyl)-β-phenyl-L-phenylalanyl]amino}phenyl)ethyl]morpholine-4-carboxylate (Example 185, step 10) (1 eq) in CH2Cl2 (0.2M) was added dropwise and stirred at −40° C. for 1.5 hours. It was then cooled to −78° C. and triethylamine (10 eq)) was added and the reaction mixture was stirred at 0° C. for 1 h. Water was added and the reaction mixture was warmed to rt for 30 min. The mixture was poured into aqueous sodium hydrogen carbonate and the aqueous layer was extracted with CH2Cl2. The combined organic layers were washed with brine, dried with MgSO4 and concentrated under vacuum to afford the title compound as a yellow gum. The material was used in the subsequent step without further purification.
