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