Fig. 3. Different types of backbone modifications on PNAs to aid delivery into cells. In some cases, lipophilic transporter molecules were attached to the terminal of the PNA backbone like (A) adamantyl acetic acid, (B) triphenylphosphonium cations, (C) diaminobutanoic acid dendrons, and (D) cholic acids. On the other hand, in some cases, different cationic side chains were substituted at the alpha or gamma positions on the PNA backbone, such as (E) aminomethylene, (F) aminopropylene, (G) ethyleneguanidino, (H) arginine side chain, and (I) tetrahydrofuran.