28910
This study demonstrates that it is possible to introduce substituents in the 2 ' - position of ( S ) - CCG - IV while maintaining agonist activity and that variation among NMDA receptor subtypes may be achieved by probing this region of the receptor .
 ( S ) - CCG - IV, NMDA
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 ( S ) - CCG - IV, NMDA