Chlorosulfonic acid → 5-[3-Ethoxy-5-(4-methylpiperazinylsulfonyl)-thiophene-2-yl]-1-methyl-3-n-propyl-6,7-dihydro-1H-pyrazolo-[4,3-d]pyrimidin-7-one

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Reaction Conditions

Reaction Steps

Compound 4 (165 mg, 0.517 mmol) was added to chlorosulfonic acid (0.35 mL, 5.2 mmol) at 0° C. The mixture was stirred under nitrogen at 50° C. for 24 h. Ice was added and the mixture was extracted with a mixture of CH2Cl2 /MeOH (9:1), dried with Na2SO4. After evaporation of the solvent, a white solid was obtained which, by NMR analysis contained predominantly 5-(5-chlorosulfonyl-3-ethoxythiophene-2-yl)-1-methyl-3-n-propyl-6,7-dihydro-1H-pyrazolo-[4,3-d]pyrimidin-7-one and a small amount of 5-(5-chlorosulfonyl-3-hydroxythiophene-2-yl)-1-methyl-3-n-propyl-6,7-dihydro-1H-pyrazolo-[4,3-d]pyrimidin-7-one. This white solid (90 mg, 0.456 mmol) was added to a solution of methylpiperazine (137 mg, 1.37 mmol) in methanol (abs. 15 mL) and stirred at rt for 4 days. The solvent was evaporated, and the residue was dissolved in CH2Cl2 /MeOH (9:1) and washed with saturated Na2CO3. The aqueous layer was extracted with CH2Cl2 /MeOH (9:1). The organic layers were combined and dried with MgSO4. The residue obtained after evaporation of the solvent contained two compounds. Separation and purification was carried out by column chromatography (silica gel). Compound 5 was obtained as a white solid by elution with ethyl acetate; mp: 219-220° C.; 1H NMR (DMSO-d6) δ 0.94(t, J=7 Hz, 3H), 1.42(t, J=7 Hz,3 H), 1.74(sxt, J=7 Hz, 2 H), 2.18 (s, 3 H), 2.40 (m, 4 H), 2.76 (t, J=7 Hz, 2 H), 3.35 (m, 4 H), 4.14 (s, 3 H), 4.44 (q, J=7 Hz, 2 H), 7.72 (s, 1 H), 10.79 (br s, 1H); MS (m/z): 481 (MH+). The hydrochloride salt was prepared by adding a solution of HCl in dioxane (4.0 M, 0.2 mL) to a suspension of the free base (6.0 mg) in MeOH (1 mL) and stirring for 1 h. Following removal of the solvents under vacuum a white solid was obtained; mp: 225° C. (dec.).

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