Crystallographic evidence of Gly-d,l-Met oxidation to its sulfoxide in the presence of gold(III): Solid solution of the racemic mixture of two diastereo-isomers

Abstract

Crystallographic analysis of a solid solution of two diastereoisomers, i.e. ({(1S,R)-1-carb-oxy-3-[(R,S)-methyl-sul-fin-yl]propyl}amino-carbonyl) methanaminium tetra-chlorido-aur-ate(III) and ({(1S,R)-1-carb-oxy-3-[(S,R)- methyl-sulfinyl]propyl}amino-carbonyl)methanaminium tetra-chloridoaurate(III), (C7H15N2O4S)[AuCl4], has shown that in the presence of gold(III), the methio-nine part of the Gly-d,l-Met dipeptide is oxidized to sulfoxide, and no coordination to the AuIII cation through the S atom of the sulfoxide is observed. In view of our observation, literature reports that methio-nine acts as an N,S-bidentate donor ligand forming stable gold(III) complexes require verification. Moreover, it has been demonstrated that crystallization of the oxidation product leads to a substantial 77:23 excess of both S-methio-nine/R-sulfoxide and R-methio-nine/S-sulfoxide over S-methio-nine/S-sulfoxide and R-methio-nine/R-sulfoxide. The presence of two different di-astereoisomers at the same crystallographic site is a source of static disorder at this site. © 2010 International Union of Crystallography.