['O=[SH](=O)c1cnc[nH]1', 'O=C1CNCN1CC(F)(F)F', 'CC(F)(F)F', 'O=C1CN(S(=O)(=O)c2cnc[nH]2)CN1']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=C1CN(S(=O)(=O)c2cnc[nH]2)CN1.