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A reversible pH-dependent intramolecular pyridine-aldehyde cyclization.

Xiao-an Zhang1, Datong Song, Stephen J Lippard

  • 1Department of Chemistry, Massachusetts Institute of Technology. Cambridge, Massachusetts 02139, USA.

The Journal of Organic Chemistry
|December 18, 2007
PubMed
Summary

Dipicolylamine (DPA) with an aldehyde undergoes reversible cyclization to a pyridinium-fused heterocycle, pH-dependently. This masked aldehyde enables the synthesis of diverse DPA-based metal chelators.

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Area of Science:

  • Organic Chemistry
  • Supramolecular Chemistry
  • Coordination Chemistry

Background:

  • Dipicolylamine (DPA) is a versatile chelating unit.
  • Aldehyde functionalities are key for molecular construction.
  • pH-responsive systems offer dynamic control in chemical processes.

Purpose of the Study:

  • To investigate the intramolecular cyclization of DPA-aldehyde conjugates.
  • To explore the pH-dependent equilibrium of the resulting heterocycle.
  • To establish the utility of the cyclized form as a masked aldehyde for synthesizing functional DPA derivatives.

Main Methods:

  • Synthesis of DPA-aldehyde conjugate.
  • Characterization of the cyclization reaction using NMR spectroscopy.
  • pH-controlled studies to determine equilibrium conditions.
  • Demonstration of the masked aldehyde reactivity for metal chelator synthesis.

Main Results:

  • A novel pyridinium-fused heterocycle is formed via intramolecular cyclization of DPA-aldehyde.
  • The cyclization is reversible and highly pH-dependent, favoring the closed form under acidic conditions and the open form under basic conditions.
  • The fused-ring heterocycle serves as a stable, masked aldehyde precursor.
  • Successful synthesis of various functional metal chelators incorporating the DPA unit was achieved.

Conclusions:

  • The pH-controlled reversible cyclization of DPA-aldehyde provides a dynamic covalent strategy.
  • The masked aldehyde approach offers a versatile route to functionalized DPA-based metal chelators.
  • This methodology expands the toolkit for designing sophisticated ligands for metal ion coordination.