['CO', 'CC(C)n1cc(C(=O)O)c(=O)c2ccccc21', 'O=CO', 'COc1cccc2c(=O)ccn(C(C)C)c12', 'CCC', 'COc1cccc2c(=O)c(C(=O)O)c[nH]c12']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=c1cc[nH]c2ccccc12.