['O=C1CC2(CCNC2)CN1', 'CCC(C=O)N1CCCC1=O', 'O=C1CCCN1', 'CCCC(=O)N1CCC2(CNC(=O)C2)C1']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=C1CC2(CCN(C(=O)CN3CCCC3=O)C2)CN1.