Biotinylated Cyclophane: Synthesis, Cyclophane-Avidin Conjugates, and Their Enhanced Guest-Binding Affinity

Area of Science:

• Supramolecular Chemistry
• Bioconjugation Chemistry

Background:

• Cyclophanes are versatile host molecules with tunable properties.
• Biotinylation is a common strategy for targeting avidin and related proteins.

Purpose of the Study:

• To synthesize cationic and anionic cyclophanes with biotin moieties.
• To investigate the binding of these cyclophanes with avidin.
• To evaluate the effect of avidin conjugation on the guest binding properties of the cyclophanes.

Main Methods:

• Synthesis of cationic (1a) and anionic (1b) biotinylated cyclophanes.
• Surface plasmon resonance (SPR) for binding constant determination.
• Guest binding studies with fluorescent molecules (TNS, 2,6-ANS).
• Computer-aided molecular modeling.

Main Results:

• Both 1a and 1b strongly bind avidin (K = 1.3 × 10^8 M^-1).
• The 1a-avidin conjugate exhibits a ~19-fold increase in binding affinity for fluorescent guests compared to free 1a.
• Molecular modeling suggests favorable hydrophobic and electrostatic interactions in the 1a-avidin-TNS complex.
• Anionic 1b-avidin conjugate showed no significant enhancement due to electrostatic repulsion.

Conclusions:

• Cationic biotinylated cyclophanes can form conjugates with avidin that exhibit enhanced guest binding.
• The observed enhancement is attributed to favorable interactions within the conjugate complex.
• Electrostatic interactions play a crucial role in the binding properties of these conjugates.