5-(1,1-dioxothiazepan-2-yl)-N-[1-(4-fluorophenyl)cyclopropyl]-8-hydroxy-3-methyl-1,6-naphthyridine-7-carboxamide;ethyl N-[3-(dimethylphosphorylmethoxy)-8-hydroxy-7-(naphthalen-2-ylmethylcarbamoyl)-1,6-naphthyridin-4-yl]-N-methylcarbamate;methyl 8-[tert-butyl(dimethyl)silyl]oxy-3-(dimethylphosphorylmethoxy)-1,6-naphthyridine-7-carboxylate;methyl 8-[tert-butyl(dimethyl)silyl]oxy-3-hydroxy-1,6-naphthyridine-7-carboxylate;methyl 8-[tert-butyl(dimethyl)silyl]oxy-3-methoxy-1,6-naphthyridine-7-carboxylate