7-(1-Aminoethyl)-6-bromo-3-methyl-5H-thiazolo[3,2-a]pyrimidin-5-one (18.8 g, 65.2 mmol) was dissolved in isopropanol (375 mL) at reflux and then (S)-(+)-mandelic acid (4.84 g, 31.8 mmol) in isopropanol (375 mL) was added dropwise to the amine solution over 35 min. The reaction mixture was allowed to cool to about 72° C. and solid precipitation was observed. The slurry was cooled to room temperature and stirred for 1 hour. The solid product was collected by filtration. The wet cake was washed with isopropanol (100 mL) and dried on the filter under suction for 1 h to give the product (S)-1-(6-bromo-3-methyl-5-oxo-5H-thiazolo[3,2-a]pyrimidin-7-yl)ethanaminium (S)-2-hydroxy-2-phenylacetate (11.9 g) as a white solid. Chiral HPLC analysis was performed on a Lux Cellulose-2, 4.6×250 mm, 5 micron column using 60% ethanol/40% hexanes as the mobile phase at a flow rate of 1 mL/min. The major enantiomer eluted at retention time 11.21 min (99.0 area %). The minor enantiomer eluted at retention time 14.31 min (0.96 area %). The e.e. of the desired product was 98.08%.
