Synthesis of HCV Replicase Inhibitors: Base-Catalyzed Synthesis of Protected α-Hydrazino Esters and Selective Aerobic Oxidation with Catalytic Pt/Bi/C for Synthesis of Imidazole-4,5-dicarbaldehyde
作者:Roy K. Bowman、Andrew D. Brown、Jannine H. Cobb、John F. Eaddy、Mark A. Hatcher、Martin R. Leivers、John F. Miller、Mark B. Mitchell、Daniel E. Patterson、Matthew A. Toczko、Shiping Xie
DOI:10.1021/jo4014595
日期:2013.12.6
A robust convergent synthesis of the prodrugs of HCV replicase inhibitors 1-5 is described. The central 5H-imidazo[4,S-d]pyridazine core was formed from acid-catalyzed cyclocondensation of an imidazole-4,5-dicarbaldehyde (20) and a alpha-hydrazino ester, generated in situ from the bis-BOC-protected precursors 25 and 33. The acidic conditions not only released the otherwise unstable alpha-hydrazino esters but also were the key to avoid facile decarboxylation to the parent drugs from the carboxylic ester prodrugs 1-5. The bis-BOC alpha-hydrazino esters 25 and 33 were prepared by addition of ester enolates (from 23 and 32) to di-tert-butyl azodicarboxylate via catalysis with mild inorganic bases, such as Li2CO3. A selective aerobic oxidation with catalytic 5% Pt-Bi/C in aqueous KOH was developed to provide the dicarbaldehyde 20 from the diol 27.