Using CCO, CCCc1c(O)ccc2c(=O)cc(-c3ccc(C(=O)O)cc3)oc12 to produce CCCc1c(O)ccc2c(=O)cc(-c3ccc(C(=O)OCC)cc3)oc12, please predict the agent for this reaction in SMILES notation in \boxed{$SMILES1, SMILES2, ...} format.