['O=CCn1cnnn1', 'O=C1NC[C@H]2NCCC[C@@H]12', 'c1nnn[nH]1', 'CC(=O)N1CCC[C@H]2C(=O)NC[C@H]21']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=C1NC[C@@H]2[C@H]1CCCN2C(=O)Cn1cnnn1.