C(OC([N:8]1[CH2:15][C:14]2[C:10](=[N:11][NH:12][C:13]=2[NH2:16])[CH2:9]1)=O)(C)(C)C.[Cl:17][CH:18]([CH:22](OCC)OCC)[C:19](=O)[CH3:20]>CC(O)=O>[Cl:17][C:18]1[C:19]([CH3:20])=[N:16][C:13]2[N:12]([N:11]=[C:10]3[CH2:9][NH:8][CH2:15][C:14]3=2)[CH:22]=1A solution of 3-amino-2,6-dihydro-4H-pyrrolo[3,4-c]pyrazole-5-carboxylic acid tert-butyl ester (5.8 g; 25.9 mmol; 1 eq.) and 3-chloro-4,4-diethoxy-butan-2-one (5.6 g; 25.9 mmol; 1 eq.) in AcOH (26 mL) was stirred at room temperature for 16 hours then concentrated in vacuo. The residue was poured onto sat. aq. NaHCO3 and the formed precipitate was filtered off and dried. Purification by column chromatography (30% EA in heptane) afforded the title compound (1.7 g, 22%) as a white solid. 1H NMR (DMSO-d6) δ 9.48 (s, 1H), 4.62-4.54 (m, 4H), 2.60-2.57 (m, 3H), 1.48 (s, 9H). HPLC (max plot) 97.0%, Rt 3.93 min. UPLC/MS: (MS+) 309.3 ([M+H]+).
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