[NH:1]([C:5]1[CH:9]=[CH:8][O:7][C:6]=1[C:10]([O:12]CC)=O)[C:2]([NH2:4])=[O:3].[OH-].[Na+].Cl>CO>[N:1]1[C:5]2[CH:9]=[CH:8][O:7][C:6]=2[C:10]([OH:12])=[N:4][C:2]=1[OH:3]Ethyl 3-ureidofuran-2-carboxylate 35 (120 mg, 1.0 eq) was suspended in methanol (6 ml) and treated with 1.5 M NaOH (1.5 ml). Reaction mixture was heated to reflux for 90 minutes. Reaction mixture was allowed to cool down to room temperature, and was acidified with 6N HCl up to pH 3. Mixture was concentrated. Methanol was added to residue and solid was filtered and dried at 95° C. under high vacuum for 24 h to yield furo[3,2-d]pyrimidine-2,4-diol 36 (90 mg, 91%) which was used in the next reaction without further purification.
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