22740
They differ from 4 by lacking an unstable hydroxyl group and by having an extra carboxyl moiety ; those differences endow thailanstatins with a significantly greater stability than 4 as tested in phosphate buffer at pH 7 . 4 .
 hydroxyl, carboxyl, thailanstatins, phosphate
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 hydroxyl, carboxyl, thailanstatins, phosphate