TIANFU CHEM- 4-[6-(6-BROMO-8-CYCLOPENTYL-5-METHYL-7-OXO-7,8-DIHYDRO-PYRIDO[2,3-D]PYRIMIDIN-2-YLAMINO)-PYRIDIN-3-YL]-PIPERAZINE-1-CARBOXYLIC ACID TERT-BUTYL ESTER