Synthesis of 3()-phosphonoacetyl-2()-piperidinecarboxylic acid, a conformationally-restricted glutamate antagonist

The synthesis of the conformationally-restricted β-ketophosphonic acid, 3(S)-phosphonoacetyl-2(R)-piperidinecarboxylic acid (4) is described. This compound is a competitive, glutamate antagonist (IC50 = 40 nM vs [3H]CPP) of the NMDA receptor complex.