['CO', 'O=C(O)Cn1cnc(-c2ccccc2)cc1=O', 'CC(=O)O', 'COc1ccc(-c2cc(=O)[nH]cn2)cc1', 'COc1ccccc1', 'O=C(O)Cn1cnccc1=O']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=c1cc(-c2ccccc2)nc[nH]1.