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. Author manuscript; available in PMC: 2014 Jun 12.
Published in final edited form as: J Am Chem Soc. 2013 May 30;135(23):8692–8701. doi: 10.1021/ja4029507

Figure 1.

Figure 1

Azoline heterocycles are versatile intermediates for selective peptide labeling. A general scheme for TOMM heterocycle biogenesis is displayed. Select Cys, Ser, and Thr residues are cyclized by the ATP-dependent cyclodehydratase (complex of C and D proteins). Azoline heterocycles can then be oxidized by a flavin-dependent dehydrogenase to afford the aromatic azole. Alternatively, the electrophilic azoline heterocycle can be exploited for the installation of oxygen isotopes and thioamides using [18O]-H2O and potassium hydrosulfide (KHS) as nucleophilic ring-opening agents, respectively. The mass shift relative to unmodified peptide is displayed underneath each product.