Cell-surface Labeling via Bioorthogonal Host-Guest Chemistry.

Area of Science:

• Chemical Biology
• Bioorganic Chemistry
• Supramolecular Chemistry

Background:

• The bioorthogonal chemical reporter strategy has transformed chemical biology.
• Challenges remain in translating this strategy to living mammals due to reporter size, stability, and reaction kinetics.
• Traditional optimization focuses on developing new bioorthogonal reactions.

Purpose of the Study:

• To introduce and validate a novel bioorthogonal strategy termed 'bioorthogonal complexation'.
• To leverage intermolecular host-guest interactions for bioorthogonal labeling.
• To demonstrate the efficacy of bioorthogonal complexation in mammalian systems.

Main Methods:

• Utilized the cucurbit[7]uril (CB[7]) scaffold to create bioorthogonal host-guest pairs.
• Investigated medium-affinity guests (K_a ≈ 10⁸-10⁹ M^-1) for cell surface labeling.
• Metabolically incorporated *ortho*-carborane into cell-surface glycans.
• Detected labeled glycans using a CB[7]-fluorescein conjugate.

Main Results:

• Bioorthogonal complexation does not require activated functional groups or second-order rate constants.
• Medium-affinity CB[7] guests demonstrated efficient cell surface labeling.
• The bioorthogonal complexation approach outperformed strain-promoted azide-alkyne cycloaddition in labeling efficiency.
• Successful implementation of bioorthogonal complexation for detecting metabolically incorporated *ortho*-carborane.

Conclusions:

• Bioorthogonal complexation offers a promising alternative to traditional bioorthogonal reactions for mammalian applications.
• This host-guest approach overcomes key limitations associated with reporter size, stability, and reaction kinetics.
• The strategy enables efficient and specific labeling of cell surfaces in a biological context.