['CC(C)(C)O', 'Nc1c(Cl)ncnc1NCCNC=O', 'CC(C)(C)OC=O', 'NCCNc1ncnc(Cl)c1N', 'CC(C)C', 'Nc1c(Cl)ncnc1NCCNC(=O)O', 'CC(C)(C)OC(N)=O', 'CCNc1ncnc(Cl)c1N', 'Nc1ncnc(Cl)c1N', 'CCNC(=O)OC(C)(C)C', 'Nc1cncnc1Cl', 'CC(C)(C)OC(=O)NCCN']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is c1cncnc1.