Chiral sensing by nonchiral tetrapyrroles

Area of Science:

• Organic Chemistry
• Analytical Chemistry
• Supramolecular Chemistry

Background:

• Enantiomeric excess (ee) is crucial for pharmaceuticals and catalysis.
• Traditional NMR methods for ee determination often require chiral auxiliaries and form diastereomeric complexes.
• Existing methods face challenges like tautomerism, macrocyclic inversion, and low-temperature requirements.

Purpose of the Study:

• To design and synthesize novel prochiral solvating agents for NMR-based ee determination.
• To overcome limitations of existing chiral solvating agents like oxoporphyrinogen (OxP) and tetraphenylporphyrin (TPP).
• To develop a versatile and efficient method for determining the enantiopurity of various chiral compounds.

Main Methods:

• Molecular design and synthesis of modified oxoporphyrinogen derivatives.
• Utilizing nuclear magnetic resonance (NMR) spectroscopy for chiral sensing.
• Investigating host-guest interactions and hydrogen bonding mechanisms.
• Employing regioselective N-alkylation to create the Bz2OxP host.

Main Results:

• Successfully synthesized Bz2OxP, a modified oxoporphyrinogen derivative.
• Bz2OxP acts as a chiral solvating agent, enabling 1:1 host-guest interactions.
• The Bz2OxP system allows for ee determination of various analytes (acids, esters, amines, ketones) at room temperature.
• The method does not rely on the formation of diastereomers and avoids issues like tautomerism.

Conclusions:

• Bz2OxP is an effective and versatile chiral solvating agent for NMR-based ee determination.
• This approach offers advantages over existing methods, including room-temperature operation and broader analyte compatibility.
• The study highlights the potential of symmetrical molecules as NMR probes for enantiopurity and provides insights into chirality principles.