['O=C1CNCCN1', 'O=CCN1CCC2(CNC(=O)C2)C1', 'CC(=O)N1CCNC(=O)C1', 'O=C1CC2(CCNC2)CN1']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=C1CN(C(=O)CN2CCC3(CNC(=O)C3)C2)CCN1.