['CCCCCN', 'O=Cc1cc2ccccc2c(=O)[nH]1', 'CCCCC', 'NC(=O)c1cc2ccccc2c(=O)[nH]1', 'CCCCCNC=O', 'O=c1[nH]ccc2ccccc12']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=c1[nH]ccc2ccccc12.