['O=CC1CC2C=CC1C2', 'O=c1[nH]nc2n1CCNC2', 'C1=CC2CCC1C2', 'O=CN1CCn2c(n[nH]c2=O)C1']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=C(C1CC2C=CC1C2)N1CCn2c(n[nH]c2=O)C1.