['CO', 'Cn1c(C=O)c(N)c2ccc(C(F)(F)F)nc21', 'COC=O', 'Cn1cc(N)c2ccc(C(F)(F)F)nc21', 'FC(F)F', 'COC(=O)c1c(N)c2cccnc2n1C']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is c1cnc2[nH]ccc2c1.