diethyl 8-ethyl-5,8-dihydro-5-oxofuro<2,3-b><1,8>naphthyridine-2,6-dicarboxylate

6-ethoxycarbonyl-8-ethyl-5,8-dihydro-5-oxofuro<2,3-b><1,8>naphthyridine-2-carboxylic acid

ethyl 7-ethoxy-1-ethyl-6-formyl-1,4-dihydro-4-oxo-1,8-naphthyridine-3-carboxylate

8-ethyl-5,8-dihydro-5-oxofuro<2,3-b><1,8>naphthyridine-2,8-dicarboxylic acid

8-ethyl-5,8-dihydro-5-oxofuro<2,3-b><1,8>naphthyridine-6-carboxylic acid