['CCN1CNCC1=O', 'Cn1cc(C#N)c(=O)n(C)c1=O', 'CC', 'Cn1c(N2CNC(=O)C2)c(C#N)c(=O)n(C)c1=O']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=C1CN(c2cc(=O)[nH]c(=O)[nH]2)CN1.