Unresolved rearrangement of thiazoline form of glutathione

The thiazoline form of glutathione was investigated with regard to its unresolved instability under neutral conditions. A simple method was developed for production of the thiazoline in stable solid form, thereby facilitating preparation of its neutral solution without using excess base and enabling isolation of the reaction product in quantity by ion‐exchange chromatography. Analysis of the product by HPLC, infrared and ultraviolet absorption spectroscopy, mass spectrometry and proton magnetic resonance led to the identification of a cyclic amidine form of glutathione. The instability of the thiazoline is, therefore, due to an intramolecular rearrangement reaction, rather than hydrolysis. Once formed, the amidine is stable at pH 5–7 and in concentrated HCl, showing no tendency to rearrange back to either the original thiazoline or glutathione under these conditions.