(1aS,3aR,6bS)-5-(carbamoyloxymethyl)-1-oxo-1,1a,2,3,3a,6b-hexahydro-4-oxa-2,6a-diazacyclobut[cd]indene-6-carboxylic acid   、                                                                                      
4-氨基甲酰基苯胺甲酸琥珀酰亚胺酯                                                                                                                                                                                                                                                                                                          以61%的产率得到(1aS,3aR,6bS)-2-(4-Carbamoyl-phenylcarbamoyl)-5-(carbamoyloxymethyl)-1-oxo-1,1a,2,3,3a,6b-hexahydro-4-oxa-2,6a-diazacyclobut[cd]indene-6-carboxylic acid sodium salt