Synthesis
Ammonium thiocyanate (17.8 g, 0.234 mol) was dissolved in anhydrous acetone (200 mL) under nitrogen protection and cooled to 0°C. Benzoyl chloride (30 g, 0.213 mol) was slowly added dropwise over 15 min, keeping the reaction temperature at 0 °C. After the dropwise addition was completed, the reaction mixture was warmed to room temperature and stirring was continued for 30 min, followed by filtration. To the filtrate, 2-aminopyrazine (16.2 g, 0.17 mol) was added and the reaction was stirred at room temperature for 3 hours. After completion of the reaction, the solvent was removed by distillation under reduced pressure and the residue was diluted with water to precipitate a solid. The solid was collected by filtration and dried to give N-[(pyrazin-2-ylamino)thiocarbonyl]benzamide (33 g, 76% yield).TLC conditions: chloroform/methanol (9:1), Rf=0.5.N-[(pyrazin-2-ylamino)thiocarbonyl]benzamide (25 g, 0.096 mol) was dissolved in 10% NaOH solution (200 mL) and stirred at 80°C for 20 min. and stirred at 80 °C for 20 min. The reaction mixture was cooled and the solvent was removed under reduced pressure. The residue was acidified to pH=1 with 2 M HCl and subsequently alkalized with ammonium hydroxide. The precipitated solid was collected by filtration and dried by suction to give 1-(pyrazin-2-yl)thiourea (12 g, 80% yield). Product characterization: 1H NMR (DMSO-d6, 300 MHz): δ 8.24 (br s, 2H), 8.54 (s, 1H), 9.10 (m, 1H), 9.95 (m, 1H), 10.66 (br s, 1H). Mass Spectrometry (ESI): m/z 154.9 [M+H]+. HPLC (Method B): retention time 3.47 min (purity 98.23%). TLC: Chloroform/methanol (9:1), Rf=0.25. Melting point: 234-235°C.
References
[1] Patent: WO2006/125805, 2006, A1. Location in patent: Page/Page column 50-51
[2] Bioorganic and Medicinal Chemistry Letters, 2003, vol. 13, # 16, p. 2641 - 2645
[3] Bioorganic and Medicinal Chemistry Letters, 2005, vol. 15, # 12, p. 3081 - 3085
[4] Bioorganic and Medicinal Chemistry Letters, 2006, vol. 16, # 14, p. 3706 - 3712
[5] Tetrahedron Letters, 2018, vol. 59, # 17, p. 1623 - 1626
