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Part-IExperimental(1H, d, CH at imidazole, J = 8.92), 12.47 (1H, br s, NH), 13.45(1H, s, NH).MS m/e : 416(M + ), 383, 210, 180.5. Synthesis of ethyl 2-((1H-benzo[d]imidazol-2-ylthio)methyl)-5-methyl-4-oxo-3,4-dihydrothieno[2,3-d]pyrimidine 6-carboxylate (IIIv)2-Mercaptobenzimidazole (1.5 gm; 0.01 mole) was dissolved in 25 ml of 10% sodiumhydroxide solution by stirring at room temperature. To this clear solution pinch of TEBAchloride was added and stirring was further continued for 10 min. To this well stirredsolution, added clear solution of ethyl 2-(chloromethyl)-3,4-dihydro-5-methyl-4-oxothieno[2,3-d]pyrimidine 6-carboxylate (IIiii, 2.86 gm; 0.01 mole) in methylenedichloride (25 ml), over a period of 15-20 min. Reaction was worked up as described forthe compound IIIi to get the title compound.M.P. : 270-272 o C; Yield: 52%.Mol. Formula : C 18 H 16 N 4 O 3 S 2 ; Mol. Wt. 400.IR(KBr) cm -1 : 3237(γ NH ), 2945(γ C-H ), 1716(γ COOEt ), 1673(γ CONH ), 740(γ C-S ).MS m/e : 400(M + ), 372, 296, 150.6. Synthesis of ethyl 2-{[(5-methoxy-1H-benzimidazol-2-yl)thio]methyl}-5-methyl-4-oxo-3,4-dihydrothieno[2,3-d]pyrimidine 6-carboxylate (IIIvi)2-Mercapto-5-methoxybenzimidazole (1.8 g; 0.01 mole) was dissolved in 25 ml of 10%sodium hydroxide solution by stirring at room temperature. To this clear solution pinch ofTEBA chloride was added and stirring was further continued for 10 min. To this wellstirred solution, added clear solution of ethyl 2-(chloromethyl)-3,4-dihydro-5-methyl-4-oxothieno[2,3-d]pyrimidine 6-carboxylate (IIiii, 2.86 gm; 0.01 mole) in methylenedichloride (25 ml), over a period of 15-20 min. Reaction was worked up as described forcompound the IIIi to get the title compound.M.P. : 257-260 o C; Yield: 65%.Mol. Formula : C 19 H 18 N 4 O 4 S 2 ; Mol. Wt. 430.5.IR (KBr) cm -1 : 3247(γ NH ), 2985(γ C-H ), 1690(γ CONH ), 650(γ C-S ).NMR (DMSO-d 6 )δppm : 1.38 (3H, t, CH 3 of CH 3 -CH 2 -O-, J = 6), 2.67 (3H, s, CH 3 at 5),3.84 (3H, s, OCH 3 ), 4.20-4-38 (4H, m, CH 3 -CH 2 -O and SCH 2 ),188