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The most active derivative in this study against both tested cell lines was the Schiff ' s base 4e with IC50 of 4 . 7 and 4 . 6 mu M against HT29 and MDA - MB231 , respectively .
 Schiff ' s base
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 Schiff ' s base