['O=CO', 'CC(C)c1nnc(-c2ccccc2)o1', 'CCC', 'O=C(O)c1ccccc1-c1nnco1', 'CC(C)c1nnco1', 'O=C(O)c1ccccc1']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is c1ccc(-c2nnco2)cc1.