12252
After aging and digestion with pepsin at pH 2 , peptide FGES198AGAAS from Sp - tabun thiocholine had a mass of 902 . 2 m / z in negative mode , indicating that it had aged by deamination , whereas peptide FGES198AGAAS from Rp - tabun thiocholine had a mass of 874 . 2 m / z in negative mode , indicating that it had aged by O - dealkylation .
 Chemical: Sp - tabun thiocholine; Chemical: Rp - tabun thiocholine; 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: Sp - tabun thiocholine; Chemical: Rp - tabun thiocholine; Chemical: O