The structure of O-phospho- l-threonine in different chemical environments

Abstract

The crystal and molecular structures of the potassium ( I), ammonium ( II) and diammonium ( III) salts of O-phospho- l-threonine were determined by X-ray methods. The crystal structure of I contains two independent monoanions [denoted as (1) and (2)] and that of II four independent monoanions [denoted as (1), (2), (3) and (4)], while III contains one independent dianion in an asymmetric unit. The monoanions of O-phospho- l-threonine contain the ionized carboxyl group (more acidic) and singly protonated phosphate group which is double ionized in the dianion of III. The overall conformation of the threonine moiety in all anions is similar to that found in the zwitterions of phosphothreonine but differs from that in l-threonine. The carbon atom chains adopt antiperiplanar conformation in all anions of O-phospho- l-threonine. The anions differ slightly in the orientation of the terminal phosphate O atoms with regard to the threonine moiety. In all three crystals, the molecules are arranged in three-dimensional networks via N–H⋯O [and O–H⋯O in I and II] hydrogen bonds in which all N-bonded [and O-bonded in I and II] H atoms are involved. Additionally, the crystal structures are stabilized by C–H⋯O interactions of less than 3.5 Å.