Amino-acid conjugates of the hapten 2-phenyl-4-ethoxymethylene-5(4H)-oxazolone. Synthesis and confirmation of structure.

2-Phenyl-4-ethoxymethylene-5(4H)-oxazolone (PhOx = CHOEt) was reacted with methylamine, and 2-phenyloxazole-4-carboxylic acid was coupled with methylamine. The spectroscopic properties of the two products were compared in order to confirm that aminolysis of PhOx = CHOEt occurs by displacement of the ethoxy group to give 2-phenyl-4-(substituted-methylene)-5(4H)-oxazolones and not by attack at the oxazolone-carbonyl followed by rearrangement to give 2-phenyloxazole-4-carboxamides. Ten crystalline conjugates were prepared and characterized by reacting PhOx = CHOEt with an excess of unprotected di- and trifunctional amino acid anions followed by purification by washing them with hydrochloric acid.