A suspension of 500 mg 3-[(2S,4R,5R)-4-(4-methoxy-phenyl)-5-[4-(3-methoxy-propyl)-3,4-dihydro-2H-benzo[1,4]oxazin-6-ylmethoxy]-1-(toluene-4-sulfonyl)-piperidin-2-yl]-2,2-dimethyl-propionic acid (from example 65b), 111.2 mg ammonium chloride and 0.7 ml triethylamine in 5 ml tetrahydrofuran are cooled to −10° C. and 1.21 ml of a T3P® solution (50% in ethyl acetate) is added dropwise. The reaction mixture is warmed to room temperature and stirred for 8 hours. The resulting suspension is stirred at 70° C. for 2 days. During this time, the addition of 111.2 mg ammonium chloride, 0.7 ml triethylamine and 1.21 ml of a T3P® solution (50% in ethyl acetate) is repeated twice. The reaction mixture is quenched by addition of 5 ml of water and extracted with 50 ml ethyl acetate (3×). The combined organic layers are washed with brine and dried with sodium sulfate. The organic layer is filtered and evaporated under reduced pressure. The residue is purified by flash chromatography (SiO2 60 F) to afford the title compound as a colourless foam. Rf=0.12 (EtOAc-heptane 1:2); Rt=5.42.
