['CO', 'O=CCOc1cccc2c(=O)[nH]ccc12', 'COC(C)=O', 'O=c1[nH]ccc2c(O)cccc12', 'COC(=O)CO', 'O=c1[nH]ccc2ccccc12']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=c1[nH]ccc2ccccc12.