['Cc1n[nH]c(C)c1C', 'CCN1CNCC1=O', 'CC', 'Cc1n[nH]c(C)c1CN1CNC(=O)C1', 'Cc1cc(C)[nH]n1', 'CCN1CN(C)CC1=O']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=C1CN(Cc2cn[nH]c2)CN1.