['NC(N)=O', 'CN(CC=O)CC(=O)N(C)C', 'NC=O', 'CN(CC(N)=O)CC(=O)N(C)C', 'CNC', 'CN(CC=O)CC(=O)NC(N)=O', 'CC(=O)NC(N)=O', 'CNCC(=O)N(C)C', 'CC(=O)N(C)C', 'CNCC(=O)NC(N)=O']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is None.