A mixture of optical pure 7-(1-aminoethyl)-6-(3,5-difluorophenyl)-3-methyl-5H-[1,3]thiazolo[3,2-a]pyrimidin-5-one (0.13 g, 0.40 mmol) made from above, 2-amino-6-bromopurine (0.10 g, 0.47 mmol), and N,N-diisopropylethylamine (0.085 mL, 0.49 mmol) in ethanol (1 mL) was heated at 110° C. overnight. LCMS showed incomplete conversion. An additional 0.5 equivalent of 2-amino-6-bromopurine and 1.0 equivalent of N,N-diisopropylethylamine was added, and the mixture was stirred at 110° C. for another day. The solid was shown to be 2-amino-6-bromopurine by LCMS. The mixture was filtered, and the filtrates were purified on preparative-LCMS ((XBridge C18 Column, eluting with a gradient of acetonitrile/water containing 0.15% NH4OH) to give the desired product (0.095 g, 52%). LCMS calculated for C20H17F2N8OS (M+H)+: m/z=455.1. Found: 455.1 1H NMR (DMSO-d6, 400 MHz) δ 7.67 (1H, s), 7.27 (1H, m), 7.17 (3H, m), 7.07 (1H, s), 6.89 (1H, br s), 5.45 (2H, br s), 5.03 (1H, m), 2.63 (3H, s), 1.30 (3H, d, J=6.8 Hz) ppm. 19F NMR (DMSO-d6, 376.3 MHz) δ −111 ppm.
