27466
A series of structurally novel aryl ureas was derived from optimization of the HTS lead as selective histamine H3 receptor ( H3R ) antagonists .
 Chemical: aryl ureas; Chemical: histamine
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: aryl ureas; Chemical: histamine