['CO', 'CCCN1CCc2[nH]c3c(C=O)cccc3c2C1', 'CCC', 'COC(=O)c1cccc2c3c([nH]c12)CCNC3', 'COC=O', 'CCCN1CCc2[nH]c3ccccc3c2C1']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is c1ccc2c3c([nH]c2c1)CCNC3.