Ureidopyrimidinones incorporating a functionalizable p-aminophenyl electron-donating group at C-6

2-Ureido-4-[1H]-pyrimidinones have been reported to dimerize via quadruple hydrogen bonding systems with dimerization constants > 10(6) M-1 in CDCl3. The dimerization constant, K-dim, is dependent on the solvent as well as the ring-substituents present, where previously alkyl (e.g., R-1 = Me) and aromatic moieties (e.g., R-1 = p-NO2C6H4, R-1 = C6H2(OC13H27)(3)) have been incorporated at the C-6 position. To assess the influence of alternative, functionalizable, electron-donating groups on the dimerization motif and tautomeric distribution of isomers, the synthesis of compounds possessing aminophenyl functionality at the C-6 position has been achieved. NMR spectroscopy chemical shift analysis revealed that compound 2 (R-1 = p-NH2C6H4, R-2 = C6H13) existed as the 2-ureido-4-pyrimidinol dimeric DADA array in DMSO-d(6), where a dimerization constant of 46 M-1 was determined. This is the first time that a ureidopyrimidinone quadruple hydrogen bonding DADA array has been observed in pure DMSO, a highly polar solvent. The azo-derivative 5 of compound 2 was prepared which also adopted the pyrimidin-4-ol form in DMSO-d(6). Compounds 7, 10 and 11 were then synthesized containing a more hydrophilic PEG unit in the lateral chain and the tautomeric distributions were determined.