['CC', 'CCc1cnc2c(c1O)c(=O)[nH]c(=O)n2C', 'CCO', 'CCc1cnc2c(c1)c(=O)[nH]c(=O)n2C', 'CC', 'CCOc1ccnc2c1c(=O)[nH]c(=O)n2C']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=c1[nH]c(=O)c2cccnc2[nH]1.