O-phospho-DL-threonine and O-phospho-L-threonine compared with their serine analogs

In crystals of O-phospho-DL-threonine and O-phospho-L-threonine, the molecules are zwitterions HO3-POCH(CH3)CH(NH3+)CO2H linked by three-dimensional networks of strong P-O-H ... O=P, C-O-H ... O=P, N-H ... O=P and N-H ... O=C hydrogen bonds with [O ... O]=2.55(3)Angstrom and [N ... O]=2.84(4)Angstrom. Both the molecular conformations and the nearest-neighbor hydrogen-bonded surroundings are very similar in the racemic and enantiomeric crystals of the threonine compounds, but earlier studies of crystals of the analogous serine compounds have shown that the serine zwitterions HO3-POCH2CH(NH3+)CO2H have different conformations about the C beta-O gamma-P phosphate ester bonds and different hydrogen-bonded surroundings.