28905
A series of 2 ' - substituted analogues of the selective NMDA receptor ligand ( 2S , 1 ' R , 2 ' S ) - 2 - ( carboxycyclopropyl ) glycine ( ( S ) - CCG - IV ) have been designed , synthesized and pharmacologically characterized .
 NMDA, ( 2S , 1 ' R , 2 ' S ) - 2 - ( carboxycyclopropyl ) glycine, ( S ) - CCG - IV
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
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Answer:
 NMDA, ( 2S , 1 ' R , 2 ' S ) - 2 - ( carboxycyclopropyl ) glycine, ( S ) - CCG - IV