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. Author manuscript; available in PMC: 2019 Jul 20.
Published in final edited form as: J Org Chem. 2018 May 30;83(14):7467–7479. doi: 10.1021/acs.joc.8b00625

Figure 4.

Figure 4.

Tandem mass spectrometry (MS/MS) on CBTag 1.0−CBTNAc demonstrates that modification is on the lysine residue. Top, predicted masses for MS/MS b and y product ions if the CBTNAc (purple star) is on the cysteine residue (left) or the lysine residue (right). Bottom, tandem MS/MS on the [M + CBTNAc + 2H]2+ ion shows product ions matching those predicted for lysine modification (green boxes).