['CC(C)(C)O', 'CCn1cnc2c1c(=O)n(C)c(=O)n2C', 'CC(C)C', 'Cn1c(=O)c2c(ncn2CCO)n(C)c1=O', 'CCOC(C)(C)C', 'Cn1c(=O)c2[nH]cnc2n(C)c1=O']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=c1[nH]c(=O)c2[nH]cnc2[nH]1.