['O=CO', 'Cc1nonc1Cn1ccccc1=O', 'Cc1nonc1C', 'O=C(O)c1ccc(=O)[nH]c1', 'Cc1cnon1', 'Cn1cc(C(=O)O)ccc1=O']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=c1ccccn1Cc1cnon1.