Crude 2-(4-tert-Butyl-phenyl)-5-piperazin-1-yl-imidazo[1,2-a]pyridine (0.100 g, 0.298 mmol) and pyrido[2,3-b]pyrazine-3-carbaldehyde (0.062 g, 0.378 mmol) was dissolved in NMP (5 mL). The mixture was treated with 3 drops of glacial acetic acid, followed by sodium triacetoxyborohydride (0.126 g, 0.596 mmol.) The mixture was stirred at room temperature overnight and then purified by semipreparative RP-HPLC (Method C) followed by basification as in example 18 to obtain 0.0155 g of the title compound (11%). HPLC (Method B): r.t.=9.0 min., purity 85.2% at 210-370 nm, 81.1% at 252 nm. HRMS: calcd for C29H31N7+H+, 478.27137; found (ESI, [M+H]+), 478.271.
