['O=C(O)C1CCNCC1', 'FC(F)(F)c1nncs1', 'O=CO', 'FC(F)(F)c1nnc(N2CCCCC2)s1', 'FC(F)F', 'O=C(O)C1CCN(c2nncs2)CC1']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is c1nnc(N2CCCCC2)s1.