A mixture of 1-[2-(4-amino-1-piperidinyl)ethyl]-7-fluoro-1,5-naphthyridin-2(1H)-one (Intermediate 21: 38.9 mg, 0.134 mmol) and 5-chloro-6-(hydroxymethyl)-3-pyridinecarbaldehyde (Intermediate 39: 23 mg, 0.134 mmol) in 1,2-Dichloroethane (2.5 ml) was stirred under N2 at room temperature for 1 h. Then, sodium triacetoxy borohydride (85 mg, 0.402 mmol) was added and the mixture was stirred at RT overnight. LCMS showed desired compound and imine. An excess of sodium triacetoxy borohydride (85 mg, 0.401 mmol) was added and the mixture was stirred at rt 6 h. LCMS showed desired compound and imine. An excess of sodium triacetoxy borohydride (85 mg, 0.401 mmol) was added. The mixture was stirred at room temperature overnight. LCMS showed desired compound and imine. An excess of sodium triacetoxy borohydride (85 mg, 0.401 mmol) was added and the mixture was stirred at room temperature overnight. LCMS did not show imine and showed desired compound. NaHCO3 sat. was added and the aqueous phase was extracted twice with DCM. The combined organic phases were washed with sat. NaCl, dried over anhydrous Na2SO4 and concentrated under reduced pressure. The residue was purified by Flash-Master chromatography on a 2 g silica gel cartridge using DCM/MeOH 95:5 as eluent to obtain two fractions. The first was 9 mg of white solid consistent with the desired compound by HNMR. The second was 4 mg white solid consistent with desired compound but not enough pure by HNMR and LCMS. This second fraction was discarded.
