To a mixture of 3-{7-amino-2-[(2,4-dimethoxypyrimidin-5-yl)amino]-1H-benzimidazol-1-yl}propan-1-ol (99 mg, 0.287 mmol), acetaldehyde (90%, 0.178 mL, 2.87 mmol) and acetic acid (0.066 mL, 1.15 mmol) in tetrahydrofuran (2.0 mL) was added sodium triacetoxyborohydride (384 mg, 1.72 mmol) portionwise at 0° C. The mixture was warmed to room temperature and stirred for 14 hr. Aqueous sodium bicarbonate was added and the mixture was extracted with ethyl acetate. Organic layer was washed with brine, dried over sodium sulfate and concentrated in vacuo. The residue was purified by flash chromatography on silica gel eluting with a 5.0-100% ethyl acetate/n-hexane gradient mixture. The filtrate was concentrated in vacuo to give the title compound (90 mg, 0.224 mmol, 78%) as a colorless amorphous.
