20919
Practical synthesis of a chromene analog for use as a retinoic acid receptor alpha antagonist lead compound .
 Chemical: chromene; Chemical: retinoic acid
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: chromene; Chemical: retinoic acid