['CC(C)C', 'CC(C)CNCC(=O)c1c(N)n(C)c(=O)n(C)c1=O', 'CC(C)CNCC(C)C', 'CC(=O)c1c(N)n(C)c(=O)n(C)c1=O', 'Cn1c(N)cc(=O)n(C)c1=O', 'CC(C)CN(CC=O)CC(C)C']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=c1cc[nH]c(=O)[nH]1.