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. 2011 Dec 16;6(12):e28976. doi: 10.1371/journal.pone.0028976

Figure 3. Chemical modification of the ureido group of a citrulline residue by 2,3-butanedione and antipyrine.

Figure 3

First 2,3-butanedione (a) reacts with the ureido group of citrulline to form a reactive imidazolone derivate (Mr+50). The first part of the reaction is followed by a nucleophilic addition of antipyrine (b) (Mr+188) to the imidazolone ring. The full reaction results in a total mass shift of +238Da.