To a solution of (R)-(1-(5,6-diaminopyridin-2-yl)piperidin-3-yl)(pyrrolidin-1-yl)methanone (135.9 mg, 0.5 mmol) in ethanol was added 2-cyclobutylpyrimidine-4-carbaldehyde (76.2 mg, 0.5 mmol), sulfur (30.1 mg, 0.9 mmol) and acetic acid (0.15 mL) at room temperature under nitrogen. The reaction mixture was stirred for 16 h at reflux. The solvent was removed under reduced pressure. Water was added to the residue and the mixture was extracted with ethyl acetate. The combined organics were dried over sodium sulfate and concentrated under reduced pressure. The crude material was purified via preparative TLC to afford the title compound as a yellow solid. MS (ES+APCI) (M+H) 432.1; LCMS retention time 2.567 min (Method G).
