['c1ccncc1', 'CN1C(=O)N(C2CCNC2)C(=O)C1(C)C', 'CN1C(=O)NC(=O)C1(C)C', 'c1ccc(N2CCCC2)nc1']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=C1CNC(=O)N1C1CCN(c2ccccn2)C1.