Selective Aliphatic Aldimine Formation and Stabilization by a Hydrophobic Capsule in Water

Area of Science:

• Supramolecular Chemistry
• Organic Synthesis
• Biochemistry

Background:

• Aldol-type reactions are vital in biochemistry, often utilizing imines and enamines as intermediates due to their tunable acid/base properties near neutral pH.
• Generating aldimines in aqueous environments is challenging because the reaction equilibrium typically favors the starting materials (alkyl amines and aldehydes).

Purpose of the Study:

• To develop a method for the efficient generation, recognition, and stabilization of aldimines in water.
• To overcome the equilibrium limitations that hinder aldimine formation in aqueous solutions.

Main Methods:

• Utilizing a water-soluble capsule with a hydrophobic cavity to encapsulate aldimines.
• Employing Se-N chalcogen bonds to create a 'dry seam' interface, isolating the aldimines from the aqueous medium.
• Characterizing the formation and stability of various aldimines within the capsule.

Main Results:

• Successful in situ generation and rapid trapping of diverse aldimines in D2O with over 90% yield within 45 minutes at millimolar concentrations.
• Demonstrated long-term stability (at least one month) of encapsulated aldimines under ambient conditions.
• Achieved selective formation of aliphatic aldimines within the capsule, despite their lower stability in bulk solution compared to aromatic imines.
• Showcased the release of encapsulated aldimines using competitive guests like adamantane.

Conclusions:

• The water-soluble capsule effectively facilitates the generation, isolation, and stabilization of aldimines in aqueous media.
• This approach overcomes the thermodynamic barrier to aldimine formation in water, opening new possibilities for their use in biochemical reactions.
• The capsule provides a protective microenvironment, enabling the study and application of otherwise transient imine intermediates.