SYNTHESIS AND PHARMACOLOGICAL CHARACTERIZATION OF ALL SIXTEEN STEREOISOMERS OF 2-(2'-CARBOXY-3'-PHENYLCYCLOPROPYL)GLYCINE. FOCUS ON (2S,1'S,2'S,3'R)-2-(2'-CARBOXY-3'-PHENYLCYCLOPROPYL)GLYCINE, A NOVEL AND SELECTIVE GROUP II METABOTROPIC GLUTAMATE RECEPTOR ANTAGONIST