A mixture of 1-tert-butyl 3-methyl 4-(3-hydroxypropyl)piperidine-1,3-dicarboxylate (Intermediate 133, 460 mg, 1.53 mmol) in dry dichloromethane (5 mL) and triethyl amine (0.3 mL, 2.14 mmol) was treated at 0° C. with a solution of methanesulfonyl chloride (0.14 mL, 1.83 mmol) in dichloromethane (5 mL). After 2 hours minutes the reaction was complete by TLC (dichloromethane:methanol 10:1). The reaction was diluted with ethyl acetate and water. The layers were separated. The organic layer was washed with 0.1N HCl, water, saturated sodium bicarbonate, dried over magnesium sulfate. The solvent was removed under reduced pressure and the crude preparation of the mesylate was used without delay for the next step.
