pyroglutamic acid ethyl ester, Ethyl 5-oxo-2-pyrrolidinecarboxylate, 5-oxo-prolin-ethyl ester, 5-Oxo-DL-prolin-aethylester, 5-oxo-DL-prolin-ethyl ester, ethyl pyroglutamate, Ethyl L-pyroglutamate, Ethyl D-(-)-pyroglutamate, Ethyl DL-pyroglutamate, 5-Oxo-prolin-aethylester, Ethyl 5-oxo-DL-prolinate, Ethyl 5-oxo-L-prolinate, 5-oxo-proline ethyl ester