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We report the discovery of a novel series of ATP - competitive Janus kinase 3 ( JAK3 ) inhibitors based on the 5H - pyrrolo [ 2 , 3 - b ] pyrazine scaffold .
 ATP, 5H - pyrrolo [ 2 , 3 - b ] pyrazine
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 ATP, 5H - pyrrolo [ 2 , 3 - b ] pyrazine