Using CCC[C@H]1CC[C@H]([C@H]2CC[C@H](C(=O)O)CC2)CC1, CO to produce CCC[C@H]1CC[C@H]([C@H]2CC[C@H](C(=O)OC)CC2)CC1, please predict the agent for this reaction in SMILES notation in \boxed{$SMILES1, SMILES2, ...} format.