['CO', 'Cc1ccccc1-n1nc(C(=O)O)ccc1=O', 'O=CO', 'COc1cnn(-c2ccccc2C)c(=O)c1', 'Cc1ccccc1', 'COc1cc(=O)[nH]nc1C(=O)O']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=c1cccnn1-c1ccccc1.