['CO', 'O=C(O)Cc1nnnn1-c1ccccc1', 'CC(=O)O', 'COc1ccc(-n2cnnn2)cc1', 'COc1ccccc1', 'O=C(O)Cc1nnn[nH]1']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is c1ccc(-n2cnnn2)cc1.