['CCC(=O)O', 'CC(=O)c1c(N)oc(C)cc1=O', 'NCCC(=O)O', 'CC(=O)c1coc(C)cc1=O', 'CC=O', 'Cc1cc(=O)cc(NCCC(=O)O)o1']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=c1ccocc1.