['c1cnccn1', 'O=[N+]([O-])c1ccc(-c2nc[nH]n2)cc1', 'O=[N+]([O-])c1ccccc1', 'c1cnc(-c2ncn[nH]2)cn1']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is c1ccc(-c2n[nH]c(-c3cnccn3)n2)cc1.