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Part-IExperimentalNMR (DMSO-d 6 )δppm : 2.67 (3H, s, CH 3 at 5), 3.88 (3H, s, OCH 3 ), 3.87 (3H, s, CH 3 -O-CO-), 5.50 (2H, s, CH 2 at SCH 2 ), 7.03 (1H, dd, CH at imidazole,J = 2.30 & 6.62), 7.17 (1H, d, CH at imidazole, J = 2.2), 7.52(1H, d, CH at imidazole, J = 8), 12.40 (1H, br s, NH), 13.20 (1H,s, NH).5. Synthesis of ethyl 2-((1H-benzo[d]imidazol-2-ylsulfinyl)methyl)-5-methyl-4-oxo-3,4-dihydro-thieno[2,3-d]pyrimidine-6-carboxylate (IVv)Ethyl 2-((1H-benzo[d]imidazol-2-ylthio)methyl)-5-methyl-4-oxo-3,4-dihydro-thieno[2,3-d]pyrimidine 6-carboxylate (IIIv, 2.16 gm; 0.0054 mole) was dissolved in 125 mlmethanol and 100 ml methylene dichloride by stirring at room temprature. Thereafter, thereaction mixture was chilled in an ice salt bath while maintaining the temperature below0 o C. To this clear solution, methanolic solution of m-CPBA (1.16 gm; 0.0065 mole) wasadded while stirring and the reation was continued for 30-45 mins. After completion ofthe reaction, worked up was done as for the compound IVi.M.P. : 220-222 o C; Yield: 41%.Mol. formula : C 18 H 16 N 4 O 4 S 2 ; Mol. Wt. 416.IR(KBr) cm -1 : 3239(γ NH ), 2946(γ C-H ), 1717(γ COOEt ), 1670(γ CONH ), 1038(γ S-O ), 741(γ C-S ).6. Synthesis of ethyl 2-{[(5-methoxy-1H-benzimidazol-2-yl)sulfinyl]methyl}-5-methyl-4-oxo-3,4-dihydrothieno[2,3-d]pyrimidine 6-carboxylate (IVvi)Ethyl 2-{[(5-methoxy-1H-benzimidazol-2-yl)thio]methyl}-5-methyl-4-oxo-3,4-dihydrothieno[2,3-d]pyrimidine6-carboxylate (IIIvi, 2.30 gm; 0.0054 mole) was dissolved in 125ml methanol and 100 ml methylene dichloride by stirring at room temprature. Thereafter,the reaction mixture was chilled in an ice salt bath while maintaining the temperaturebelow 0 o C. To this clear solution, methanolic solution of m-CPBA (1.16 gm; 0.0065mole) was added while stirring and the reation was continued for 30-45 mins. Aftercompletion of the reaction, worked up was done as for the compound IVi.M.P. : 200-207 o C; Yield: 43%.Mol. formula : C 19 H 18 N 4 O 5 S 2 ; Mol. Wt. 446.5.IR (KBr) cm -1 : 3175(γ NH ), 2978(γ C-H ), 1715(γ COO- ), 1659(γ CONH ), 1029(γ S-O ), 754(γ C-S ).205