Application of the Ugi Reaction for the One-pot Synthesis of Uracil Polyoxin C Analogues

A simple, two-step synthesis of amide derivatives of uracil polyoxin C (UPOC) methyl ester using the Ugi reaction is described. The four components employed in the Ugi reaction are 2',3'-isopropylidine-protected uridine-5'-aldehyde, 2,4-dimethoxybenzylamine, an isoxazolecarboxylic acid, and the convertible isonitrile N-(2-{[(tert-butyldimethylsilyl)oxy]methyl}phenyl)carbonitrile. Following the Ugi reaction, treatment with HCl in MeOH achieves deprotection of the isopropylidene group and the N-benzyl group and conversion of the isonitrile-derived amide (the Ugi product) into the corresponding methyl ester. The procedure is amenable to automated multiparallel synthesis of novel compounds related to the polyoxin and nikkomycin nucleoside-peptide antibiotics.