Reaction Steps
To a suspension of 250 mg of 3-[(4-methoxy-3,5-dimethyl-2-pyridyl)oxomethyl]-1,2,4-thiadiazolo[4,5-a]benzimidazole in 125 mL methanol and 38 mL 0.1M hydrochloric acid was added 161 μL of 3-mercaptopropionic acid. After complete degradation of the starting material, the mixture was neutralized to pH 6 with aqueous sodium bicarbonate and extracted with ethyl acetate. The ethyl acetate was dried on anhydrous magnesium sulfate and evaporated. The crude material was purified by chromatography to give 93 mg of 2-imino-2-(2-mercapto-1-benzimidazolyl)-1-(4-methoxy-3,5-dimethyl-2-pyridyl) ethanone, 65 mg of 2-mercaptobenzimidazole and 61 mg of methyl 2-(4-methoxy-3,5-dimethyl-2-pyridyl)-2-oxoacetate. 2-Imino-2-(2-mercapto-1-benzimidazolyl)-1-(4-methoxy-3,5-dimethyl-2-pyridyl)ethanone: 1H NMR (CDCl3) δ10.55 (br s, 1H, NH or SH), 10.35 (br s, 1H, NH or SH), 8.10 (d, 1H, J=7 Hz, ArH), 7.80 (s, 1H, H6 of pyridyl), 7.35-7.20 (m, 2H, 2×ArH), 7.10 (d, 1H, J=7.9 Hz, ArH), 3.75 (s, 3H, OCH3), 2.60 (s, 3H, ARCH3), 2.15 (s, 3H, ArCH3) ppm; IR (KBr) ν3262, 1691, 1635, 1502, 1458, 1396, 1328, 1272, 1247, 1004, 746 cm-1 ; MS (electrospray)m/z 341 (MH+), 191 (MH+ -2-mercaptobenzimidazole). 2-Mercaptobenzimidazole: the material was found to be identical to an authentic sample purchased from Aldrich Chemical Co. by 1H NMR, IR and TLC. Methyl 2-(4-methoxy-3,5-dimethyl-2-pyridyl)-2-oxoacetate: 1H NMR (CDCl3) δ8.45 (s, 1H, ArH), 4.1 (s, 3H, OCH3), 3.85 (s, 3H, OCH3), 2.65 (s, 3H, ArCH3), 2.4 (s, 3H, ArCH3) ppm; IR (KBr) ν1747, 1703, 1468, 1394, 1310, 1242, 1206, 1120, 1004, 740 cm-1 ; MS m/z 224 (M+ +H), 164 (M+ -CO2Me), 136 (M+ -CO2Me-CO).
