['NCC=O', 'Cn1c(CN)cc(=O)n(C)c1=O', 'NCC(N)=O', 'Cc1cc(=O)n(C)c(=O)n1C', 'CNC(=O)CN', 'Cn1ccc(=O)n(C)c1=O']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=c1cc[nH]c(=O)[nH]1.