['c1cc2c(s1)CCNC2', 'C[C@@]12CCC(=O)N1[C@@H](C=O)CS2', 'C[C@@]12CCC(=O)N1CCS2', 'O=CN1CCc2sccc2C1']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=C([C@H]1CSC2CCC(=O)N21)N1CCc2sccc2C1.