A solution of (2R,3R)-3-(2,4-difluorophenyl)-3-hydroxy-2-methyl-4-(1H-1,2,4-triazol-1-yl)butanoic acid (50 mg, 0.17 mmol) (obtained in reference example 30) and triethylamine (0.35 mL, 0.25 mmol) in tert-butanol (3 mL) was treated with diphenylphosphoryl azide (0.44 mL, 0.20 mmol) and the reaction mixture was heated at reflux for 25 h. Removal of the volatiles under reduced pressure afforded a crude product that was partitioned between chloroform and saturated NaHCO3 aqueous solution. The organic phase was dried over anhydrous Na2SO4, filtered and the filtrate was concentrated in vacuo to a brown oil that was dissolved in methanol (2 mL) and 1N aqueous KOH (1 mL) and then heated at 70° C. during 15 h. The volatiles were removed in vacuo and the aqueous residue was acidified to pH 1 by addition of 1N aqueous HCl and washed with CHCl3. The aqueous phase was basified with saturated Na2CO3, saturated with NaCl and extracted (3x) with CHCl3. The collected organic phases were dried over anhydrous Na2SO4, the drying agent was filtered and the filtrate was concentrated to afford the title product (18.8 mg) pure by TLC analysis. An analytical sample was obtained by chromatography on silica gel (CHCl3 : MeOH 5:1) as a white solid.
