(R)-7-chloro-5-cyclopentyl-4-ethyl-4,5-dihydro-[1,2,4]triazolo[4,3-f]pteridine (70 mg, 0.23 mmol), cyclopropylamine (0.5 ml, 7.18 mmol), DIPEA (0.16 ml, 0.918 mmol) in nBuOH (2 ml) were heated in a sealed tube in the microwave at 140° C. for 90 minutes. The reaction mixture was concentrated in vacuo, and purified by reverse phase preparative HPLC [Waters Sunfire C18, 10 M, 100 Å column, gradient 10%-95% B (solvent A: 0.05% TFA in water; solvent B: CH3CN) over 16 minutes at 25 mL/min] to afford the title compound as an off-white powder. The free base was generated using a bicarbonate resin, and was freeze-dried to give the title compound as a colourless solid (25.6 mg, 34% yield)
