['CO', 'Cc1cn2nc(N3CCC(C=O)CC3)sc2n1', 'Cc1cn2ncsc2n1', 'COC(=O)C1CCNCC1', 'COC=O', 'Cc1cn2nc(N3CCCCC3)sc2n1']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is c1cn2nc(N3CCCCC3)sc2n1.