1,1-Dimethylethyl N-{2-[(3-amino[1,5]naphthyridin-4-yl)amino]ethyl}carbamate 0.6 g, 2 mmol), trimethyl orthovalerate (0.35 g, 2.1 mmol), and toluene (25 mL) were combined and heated at reflux for 2 hours. Additional trimethyl orthovalerate (1 eq.) was added and the reaction mixture was heated at reflux overnight. Xylene was added and the toluene was distilled off. The reaction was heated at reflux for an additional 8 hours. The bulk of the xylene was distilled off leaving a volume of about 5 mL. The reaction mixture was allowed to cool. The resulting precipitate was isolated by filtration, washed with heptane and dried to provide 0.35 g of 1,1-dimethylethyl N-[2-(2-butyl-1H-imidazo[4,5-c][1,5]naphthyridin-1-yl)ethyl]carbamate as an ivory powder, m.p. 198-199° C. Analysis: Calculated for C20H27N5O2: %C, 65.01; %H, 7.36; %N, 18.95. Found: %C, 64.75; %N, 7.57; %N, 19.09.
