Doo-Ha Yoon

Alkylative Ring Opening of N-Methylaziridinium Ions and a Formal Synthesis of Tyroscherin

Alkylative ring-opening reactions of stable 2-substituted N-methylaziridinium ions proceeded with various alkyl- or arylmagnesium bromides in the presence of CuI to yield synthetically valuable and optically pure alkylated acyclic amines in a completely regio- and stereoselective manner. This was applied to a formal synthesis of the cytotoxic natural product tyroscherin.

Nucleophile‐Dependent Regio‐ and Stereoselective Ring Opening of 1‐Azoniabicyclo[3.1.0]hexane Tosylate

1-[(1R)-(1-Phenylethyl)]-1-azoniabicyclo[3.1.0]hexane tosylate was generated as a stable bicyclic aziridinium salt from the corresponding 2-(3-hydroxypropyl)aziridine upon reaction with p-toluenesulfonyl anhydride. This bicyclic aziridinium ion was then treated with various nucleophiles including halides, azide, acetate, and cyanide in CH3CN to afford either piperidines or pyrrolidines through regio- and stereoselective ring opening, mediated by the characteristics of the applied nucleophile. On the basis of DFT calculations, ring-opening reactions under thermodynamic control yield piperidines, whereas reactions under kinetic control can yield both piperidines and pyrrolidines depending on the activation energies for both pathways.

Ratiometric fluorescence probes based on a Michael acceptor type of coumarin and their application for the multichannel imaging of in vivo glutathione

A series of Michael acceptors based on a coumarin moiety, were developed as fluorescent probes for ratiometric detection of in vivo glutathione. The α,β-unsaturated Michael acceptors were transformed into non-conjugated molecules through the Michael addition of biothiols. The resulting UV-vis and fluorescence spectra of the probes revealed characteristic ratiometric responses, which were successfully applied for the multichannel imaging of in vivo glutathione.