['O=[N+]([O-])c1ccccc1', 'S=c1[nH]cc(-c2ccc(Cl)cc2Cl)o1', 'Clc1cccc(Cl)c1', 'O=[N+]([O-])c1cccc(-n2ccoc2=S)c1']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is S=c1oc(-c2ccccc2)cn1-c1ccccc1.