Synthesis and spectroscopic characterization of protected N-phosphonomethylglycine dipeptides

A series of terminally blocked dipeptides containing C-terminal N-phosphonomethylglycine (glyphosate, an extremely effective non-selective post-emergence herbicide) have been synthesized by a solution method. The presence of their two conformers, cis (syn) and trans (anti), was shown in solutions by NMR spectroscopy. Molecular structures of the peptides were also determined in the solid state by X-ray diffraction. The attempts for the selective and total removal of the groups protecting amino, carboxylic and phosphonate functions were in many cases unsuccessful due to the formation of cyclic structures and breakage of the phosphorus-to-carbon bond.