12605
The structures of M - 1 , M - 2 , M - 3 , and M - 4 were elucidated by spectroscopic methods including ESI - TOF - MS , 1D , and 2D NMR experiments .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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