Amino group transfer recent developments

One of the major points of interest in the chemistry of glutathione has been the chemistry of the mercaptan group. More recently, there has been an additional interest developed in the possibility of glutathione being a common intermediate in the synthesis of all peptide links, particularly in view of the existence of enzyme systems which transfer this 7-glutamyl residue to a whole variety of other amino acids. However, this is not the part of the subject to which I will be addressed. We will limit ourselves, then, to a discussion of sulfur chemistry. 

Further great advancements in the field of asymmetric alkylation reactions have been made by several groups for the chiral phase transfer-catalyzed alkylation of glycinates. This type of reaction offers attractive access to enantiomerically pure, particularly nonproteinogenic a-amino acids. A pioneer in this field is the O Donnell group (O Donnell et al. 1989 for an excellent recent review, see O Donnell 2001) who developed the first a-amino acid ester synthesis by means of this methodology. Notably, this group also reported a first scale up of the synthesis in... 

Several groups have investigated the synthesis of such compounds, for instance the cationic metallo-macrocycles [(t -ring)M(Aa)]3[BF4]3 (Aa = amino acidate) act as catalysts for hydrogen transfer to ketones while the neutral metallo-macrocycles [( -ring)ML]3 are efficient hosts for alkali metals (Li and Na). However, the chiral aspect of these species in solution was not investigated and only Yamanari and coworkers have reported diastereomeric separations, but no NMR studies have been made to differentiate these chiral macrocycles by the use of a chiral auxiliary. Recently the chemistry of these macrocycles was reviewed by Severin, who contributed largely to the development of this field. 

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