['c1ccccc1', 'Nc1ncncc1-c1ccc([N+](=O)[O-])cc1', 'O=[N+]([O-])c1ccccc1', 'Nc1ccnc(-c2ccccc2)n1']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is c1ccc(-c2cnc(-c3ccccc3)nc2)cc1.