['NC=O', 'CC1(C)CCC[C@]1(C)[C@@H]1NC(=O)NC1=O', 'O=C1CNC(=O)N1', 'C[C@H]1CC[C@@H](C(N)=O)C1(C)C']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=C1NC(=O)[C@H](C2CCCC2)N1.