O-(Benzotriazol-1-yl)-N,N,N',N'-tetramethyluronium tetrafluoroborate → (R)-N-{1-[(S)-4-(2,3-Dihydro-[1,4]dioxino[2,3-b]pyridin-3-yl)-benzyl]-piperidin-4-yl}-2-methylamino-propionamide

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A solution of Intermediate M (100 mg, 0.276 mmol), (R)-2-(tert-butoxycarbonyl-methyl-amino)-propionic acid (67 mg, 0.33 mmol), TEA (0.115 mL, 0.828 mmol), and TBTU (106 mg, 0.331 mmol) in DMF (2 mL) is heated at 60° C. overnight. The reaction is diluted with EtOAc, rinsed with sat. NaHCO3, and the organics dried and concentrated. The residue is purified by silica gel chromatography eluting with 0-10% MeOH/DCM. The pooled and concentrated product fractions are treated with 4M HCl in 1,4-dioxane (5 mL) and stirred overnight. The reaction is concentrated and purified by reverse phase HPLC eluting with 10-90% MeCN in water (0.1% TFA). The concentrated product fractions are dissolved in MeOH and eluted through a carbonate resin cartridge to afford the title compound 261. (LC/MS method 16: ES+ m/z 411.4 [M+H]+, Rt=0.33 min)

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