['Cn1cnc(=O)[nH]1', 'Cc1nnnn1C(C)(C)C', 'CC(C)C', 'Cn1cnc(=O)n1Cc1nnn[nH]1', 'Cn1cnc(=O)n1C', 'CC(C)(C)n1cnnn1']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=c1nc[nH]n1Cc1nnn[nH]1.