8-amino-7-ethoxycarbonyl-5-(3,4-dimethoxyphenyl)-1,2,3,4,5,6,7,10-octahydropyrimido[4,5-b][1,8]naphthyridine-2,4,6-trione   、                                                                                      
硫脲                                                                                                                                                                                              以
                                                                                         
N,N-二甲基甲酰胺                                                                                  为溶剂,
                                                                                                                                                                                        以42%的产率得到5-amino-12-(3,4-dimethoxyphenyl)-2-thioxo-2,3,4,4a,7,8,9,10,11,12-decahydro dipyrimido[4,5-b;4',5'-f][1,8]naphthyridine-4,9,11-trione