By utilizing the well known method, 1-[(5-chloro-1,3-benzothiazol-2-yl)methyl]-3-methyl-7-(2-butyn-1-yl)-8-bromo-xanthine 3b (460 mg, 0.96 mmol) was dissolved in N,N-dimethylformamide (12 ml). (R)-3-tert-butoxycarbonyl-aminopiperidine (193 mg, 0.96 mmol) and potassium carbonate (200 mg, 1.44 mmol) were added to give a reaction mixture. The reaction mixture was reacted at 75° C. for 2 hours, and TLC was used to monitor the reaction progress. After the reaction was completed, the obtained reaction mixture was cooled to room temperature. The cooled reaction solution was poured into cool water, suction filtered, and the obtained solid was washed with water, dried to give 1-[(5-chloro-1,3-benzothiazol-2-yl)methyl]-3-methyl-7-(2-butyn-1-yl)-8-[(R)-3-tert-butoxycarbonyl-amino-piperidin-1-yl]-xanthine 3c (417 mg, grey solid), yield: 72.6%.
