A mixture of methanesulfonic acid 6-tert-butoxycarbonylamino-pyridin-3-ylmethyl ester (Step 26.3) (0.8 g, 2.6 mmol), N-ethylpiperazine (0.37 mL, 2.9 mmol, 1.1 equiv), cesium carbonate (1 g, 3.2 mmol, 1.2 equiv), and DMF (10 ml) was stirred for 2 h at rt, diluted with EtOAc and H2O, and extracted with EtOAc. The organic phase was washed with H2O and brine, dried (Na2SO4), filtered and concentrated to provide a yellow solid. Trituration in Et2O afforded 0.75 g of the title compound as a white solid: ES-MS: 321.2 [M+H]+.
