[NH2:1][C:2]1[C:3](=O)[C:4](=[O:9])[C:5]=1[O:6]CC.Br.[NH2:12][CH2:13][CH2:14][N:15]1[C:19](=[O:20])[NH:18][C:17](=[O:21])[O:16]1.[OH-].[Na+]>C(O)C>[NH2:1][C:2]1[C:5](=[O:6])[C:4](=[O:9])[C:3]=1[NH:12][CH2:13][CH2:14][N:15]1[C:19](=[O:20])[NH:18][C:17](=[O:21])[O:16]1A solution of 3-amino-4-ethoxy-3-cyclobutene-1,2-dione (0.56 g, 4.0 mmol) in ethanol (20 mL) was added to 2-(2-aminoethyl)-1,2,4-oxadiazolidine-3,5-dione hydrobromide (0.90 g, 4.0 mmol) in ethanol (100 mL). The reaction mixture was treated with 1N sodium hydroxide solution (8 mL, 8 mmol) and allowed to stir for 24 hours at room temperature. The resulting precipitate was filtered, dissolved in water and passed through an ion exchange column (AG 50W-X2, 100-200 mesh, H+ form), eluting with water. The eluent was freeze dried yielding the title compound as a cream colored solid, partial hydrate (0.45 g, 45%, mp 225° C. (dec)); IR (KBr, cm-1) 3300, 3140, 1820, 1740, 1720, 1640; MS (+FAB) 242 (MH+); 1H NMR (DMSO, 400 MHz): δ 12.4 (br s, NH), 7.5 (br s, 3 NH), 4.0- 3.5 (m, 4H); 13C NMR (DMSO, 400 MHz): ppm 183.72, 183.63, 170.06, 168.96, 158.17, 152.72, 50.41, 41.68.
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