: N-(tert-Butoxycarbonyl)-L-pyroglutamic Acid Ethyl Ester, Ethyl (S)-1-(tert-Butoxycarbonyl)-5-oxopyrrolidine-2-carboxylate, (S)-1-(tert-Butoxycarbonyl)-5-oxopyrrolidine-2-carboxylic Acid Ethyl Ester, Ethyl N-Boc-L-pyroglutamate, N-Boc-L-pyroglutamic Acid Ethyl Ester, Ethyl (S)-1-Boc-5-oxopyrrolidine-2-carboxylate