To a solution of 5-amino-8-[3-(tert-butyl-dimethyl-silanyloxy)-propyl]-2-methylsulfanyl-8H-pyrido[2,3-d]pyrimidin-7-one (150 mg, 0.395 mmol) in DCM (9 mL) was added 3-chloroperoxybenzoic acid (77% max., 106 mg, 0.474 mmol) at RT under argon atmosphere and the resulting mixture was stirred for 40 min. The reaction mixture was then evaporated under reduced pressure and the residue was dissolved in anhydrous dimethyl sulfoxide (ca. 9 mL). Cyclohexylamine (0.226 mL, 1.975 mmol) was then added at RT and the resulting mixture was stirred at 80° C. for 1.5 h. The reaction mixture was then quenched with water (70 mL) and an aqueous saturated solution of ammonium chloride (30 mL). The resulting mixture was extracted with EtOAc; the organic extracts were washed twice with water (50 mL), dried over MgSO4, filtered and evaporated under reduced pressure. To the residue, dissolved in THF, was added a solution of tetrabutylammonium fluoride (1 M in THF, 0.59 mL) at RT and the resulting mixture was stirred overnight. The solid formed was collected by filtration, washed with hexane and purified by preparative TLC (DCM/MeOH, 90/10) to give 30 mg of 5-amino-2-cyclohexylamino-8-(3-hydroxy-propyl)-8H-pyrido[2,3-d]pyrimidin-7-one as a yellow powder. MS=318 [M+H]+; MP=131.0-132.5° C.
