13437
In contrast , the 3 - O - sidechains of 17 and 18 bend to the backside , the so - called hydrophobic side of the macrolide ring .
 Chemical: O
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: O