The invention discloses a novel synthetic method of a CDK-4 / 6 inhibitor. The method comprises the steps of mixing 1:2,4-dichloro, 5-acetyl
pyrimidine and alkali in a
solvent, reacting and carrying out
crystallization and suction
filtration to obtain a compound 2-chloro-4-cyclopentylamine-5-acetyl
pyrimidine; dissolving fructone into
anhydrous tetrahydrofuran, and performing recrystallization with
ethyl acetate to obtain a compound 4,6-acetyl-2-chloro-8-cyclopentyl-5-methylpyridine (2,3-d) pyrimidino-7(8H)-
ketone; mixing the 4,6-acetyl-2-chloro-8-cyclopentyl-5-methylpyridine (2,3-d) pyrimidino-7(8H)-
ketone with alkali and a compound 5 tert-butyl4-(6-aminopyridine-3-yl)
piperazine-1-carboxyl tert-butyl ester in DMF, methylbenzene and dimethylsulfoxide, heating and reacting to obtain a compound 6 4-(6-(8-cyclopentyl-5-methyl-6-(2-methyl-1,3-dioxolame-2-yl)-7-oxo-7,8-dihydropyridino-(2,3-d)
pyrimidine-2-yl) amino)
pyridine-3-yl)
piperazine-1-carboxyl tert-butyl ester; and finally, adding the compound 6 4-(6-(8-cyclopentyl-5-methyl-6-(2-methyl-1,3-dioxolame-2-yl)-7-oxo-7,8-dihydropyridino-(2,3-d) pyrimidine-2-yl) amino)
pyridine-3-yl)
piperazine-1-carboxyl tert-butyl ester into acid liquid, and reacting to obtain the corresponding salt of 6-acetyl-8-cyclopentyl-5-methyl-2-((5(piperazine-1-yl)
pyridine-2-yl) amino) pyridino-(2,3-d) pyrimidine-7(8H)-
ketone. The synthetic process is low in cost, is simple and environment-friendly and is suitable for industrial volume production.