['O=C1NCCN1', 'CC(C)(C)c1nnnn1CC=O', 'CC(=O)N1CCNC1=O', 'CC(C)(C)c1nnn[nH]1', 'CC(C)C', 'O=C(Cn1cnnn1)N1CCNC1=O']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=C(Cn1cnnn1)N1CCNC1=O.