Using O=C(O)c1cnc(C(=O)c2cn(Cc3ccc(Cl)cc3)c3ccccc23)[nH]1, CO to produce COC(=O)c1cnc(C(=O)c2cn(Cc3ccc(Cl)cc3)c3ccccc23)[nH]1, please predict the agent for this reaction in SMILES notation in \boxed{$SMILES1, SMILES2, ...} format.