['CO', 'O=C(O)CCc1nnnn1-c1ccccc1', 'CCC(=O)O', 'COc1ccc(-n2cnnn2)cc1', 'COc1ccccc1', 'O=C(O)CCc1nnn[nH]1']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is c1ccc(-n2cnnn2)cc1.