['FC(F)F', 'Cc1cc(-n2cnc3cc(F)c(F)cc32)n2ncnc2n1', 'Fc1cc2nc[nH]c2cc1F', 'Cc1ccn2nc(C(F)(F)F)nc2n1']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is c1ccc2c(c1)ncn2-c1ccnc2ncnn12.