['CO', 'CC(=O)N1CCc2c(sc(N)c2C=O)C1', 'CC=O', 'COC(=O)c1c(N)sc2c1CCNC2', 'COC=O', 'CC(=O)N1CCc2cc(N)sc2C1']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is c1cc2c(s1)CNCC2.