To a solution of methyl 4-[(4-{[(tert-butoxycarbonyl)amino]methyl}piperidine-1-yl)methyl]tetrahydro-2H-pyran-4-carboxylate (6.47 g, 17.5 mmol, step 3 of Example 8) in methanol (32 mL), 5 N NaOH aq (10 mL) was added at room temperature (exothermic). The resulting solution was stirred at 60° C. for 7 h, then cooled to 5˜10° C. in ice-cold bath. To this solution, 5 N HCl aq (10 added and the resulting solution (pH value was ca. 6) was concentrated. To the residue, 2-propanol (80 mL) was added. This solution was concentrated. To the residue, 2-propanol (80 mL) was added and it was concentrated again. The residue was diluted with ethanol (80 mL) and the mixture was stirred at room temperature for 2 h. It was filtered through a Celite pad (5.0 g) to remove NaCl. The Celite pad was washed with ethanol (20 mL) and the combined filtrate was concentrated. To the residue, CH3CN (40 mL) was added and it was concentrated. During this procedure, the formation of white precipitate was noticed. To the residue, CH3CN (40 mL) was added and the resulting suspension was stirred at room temperature for 2 h. This mixture was filtered and obtained solid was washed with CH3CN (10 mL), then dried under reduced pressure to give 4.1 g (65%) of the titled compound as white powder.
