['C#CCN', 'O=CCn1c(=O)[nH]c(=O)c2ccccc21', 'C#CC', 'NC(=O)Cn1c(=O)[nH]c(=O)c2ccccc21', 'C#CCNC(C)=O', 'O=c1[nH]c(=O)c2ccccc2[nH]1']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=c1[nH]c(=O)c2ccccc2[nH]1.