Using O=[N+]([O-])[O-], O=C(O)c1cccc(C(=O)O)c1C(=O)O to produce O=C(O)c1cc([N+](=O)[O-])cc(C(=O)O)c1C(=O)O, please predict the agent for this reaction in SMILES notation in \boxed{$SMILES1, SMILES2, ...} format.