A solution of 2-methylthio-4-(3-chloro-4-methoxybenzylamino)-5-formylpyrimidine (prepared in Example 84-(2)) 2.057 g in chloroform 20 ml is treated at 0° C. for 30 minutes with m-chloroperbenzoic acid (80%) 1.468 g. L-(S)-Prolinol 0.901 g and then triethylamine 1.33 ml are added thereto. The reaction is carried out at 0° C. for 1 hour. The reaction mixture is elevated to room temperature, diluted with ethyl acetate, washed with an aqueous sodium hydrogen carbonate solution, water and a saturated sodium chloride solution, and dried over anhydrous sodium sulfate. The precipitate is filtered off and the filtrate is concentrated in vacuo to give (S)-2-(2-hydroxymethyl-1-pyrrolidinyl)-4-(3-chloro-4-methoxybenzylamino)-5-formylpyrimidine as a colorless amorphous, 1.9990 g. MS(m/z): 377(M+H)+
