['CO', 'CC(=O)Cc1nc2ccccc2n1CC=O', 'COC(C)=O', 'CC(=O)Cc1nc2ccccc2[nH]1', 'CC(C)=O', 'COC(=O)Cn1cnc2ccccc21']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is c1ccc2[nH]cnc2c1.