Method A: Benzaldehyde (466 mg, 4.4 mmol) was dissolved in DMF (1.5 mL) and acetic acid (0.5 mL) and the resulting solution was slowly added to solid 4,5-diamino-6-hydroxy-2-mercaptopyrimidine (316 mg, 2.0 mmol). The reaction mixture was heated under reflux conditions for 3 h and subsequently cooled to room temperature and 10 mL of ice water was slowly added. The precipitated yellow solid was collected by vacuum filtration and dried naturally. The dried solid was dissolved in 60 mL of chloroform and the chloroform solution was filtered to remove insoluble matter. The entire chloroform solution was upsampled onto a silica gel column pre-filled with dichloromethane, and the first yellow band was collected by column chromatography using dichloromethane:ethyl acetate (2:1, v/v) as eluent. The eluate was concentrated under reduced pressure to afford the target product 257 mg (0.77 mmol, 39% yield). The product was characterized as follows: 1H NMR (DMSO-d6) δ 13.42 (br.s, 1H), 12.82 (br.s, 1H), 7.43-7.34 (m, 10H); 13C NMR (DMSO-d6) δ 175.7, 158.5, 155.9, 149.1, 147.0, 137.7, 137.1, 129.8 (CH), 139.8 (CH), 137.1 (CH), 137.7, 137.1 (CH). 129.8 (CH), 129.7 (CH), 129.5 (CH), 128.8 (CH), 128.3 (CH), 128.2 (CH), 127.2; HRMS (ESI) m/z calcd for C18H13N4OS [M+H]+ 333.0810, found 333.0802; IR ( Nujol) νmax 3407 (br), 1698, 1633, 1552, 1126, 722, 695, 665 cm-1; mp 200-203 °C (dec.); UV/Vis λmax 380 nm (ε = 12,000 M-1 cm-1).