['c1nnc(C2CC2)o1', 'CN1CCO[C@@H]2CNC[C@@H]21', 'C1CC1', 'CN1CCO[C@@H]2CN(c3nnco3)C[C@@H]21']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is C1CO[C@@H]2CN(c3nnc(C4CC4)o3)C[C@@H]2N1.