['NC1CC1', 'O=CN1CC2COCC(C1)O2', 'O=CNC1CC1', 'C1NCC2COCC1O2', 'C1CC1', 'NC(=O)N1CC2COCC(C1)O2']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=C(NC1CC1)N1CC2COCC(C1)O2.