Substructure replacement using RDKit

[Sowmya-R-Krishnan]

Hi all. I was trying to write a function to replace a specific instance of a substructure using RDKit. For example, the following molecule has 2 benzene rings: CCC(=O)C(CC(C)N(C)C)(c1ccccc1)c1ccccc1

I want to specifically replace the benzene ring attached to the 12th atom with a furan ring. I have written the following function based on RDKit documentation.

#Replacing an atom with a different functional group in SMILES
def replace_groups_in_smiles(smiles, group_fragment, fgroup_smiles, replace_with):
    core_mol = Chem.MolFromSmiles(smiles)
    pattern_mol = Chem.MolFromSmiles(group_fragment)
    replacement_mol = Chem.MolFromSmiles(replace_with)
    
    products = AllChem.ReplaceSubstructs(core_mol, pattern_mol, replacement_mol)
    replaced_smiles = Chem.MolToSmiles(products[0])

    return replaced_smiles

Here, core_mol is the SMILES of the molecule, pattern_mol is the functional group to be replaced (c1ccccc1 for benzene) and replace_with is the new functional group (c1ccoc1 for furan). On using the above function, only the first instance of the benzene ring is replaced.

Before replacement

After replacement

In the above image, I want to replace the second benzene connected to 12th atom. I'm not able to understand how to use the function when there are multiple instances of the same substructure (benzene) in the molecule. Is this possible in RDKit? Any suggestions would be really helpful.