['CCC(C)O', 'Cc1sc2ncn(CC=O)c(=O)c2c1C', 'CCCC', 'Cc1sc2ncn(CC(=O)O)c(=O)c2c1C', 'CCC(C)OC(C)=O', 'Cc1sc2nc[nH]c(=O)c2c1C']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=c1[nH]cnc2sccc12.