['c1ccccc1', 'O=Cc1cc[n+](-c2c([O-])c(=O)c2=O)cc1', 'O=Cc1ccccc1', 'O=c1c([O-])c(-[n+]2ccccc2)c1=O']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=C(c1ccccc1)c1cc[n+](-c2cc(=O)c2=O)cc1.