22569
The structure of 1 was determined via mass spectrometry and 1D and 2D NMR spectroscopy , while its absolute configuration was determined via X - ray crystallographic analysis performed on its methyl ester derivative 2 .
 Chemical: methyl ester
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: methyl ester