| CPC C07K 1/13 (2013.01) [C07K 1/113 (2013.01); C07K 14/00 (2013.01); C07K 2319/21 (2013.01)] | 15 Claims |

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1. A method of labeling a protein comprising:
Reacting the protein with a thiophosphorodichloridate reagent under conditions to effect chemoselective histidine conjugation and form a resultant conjugate of the protein and the thiophosphorodichloridate reagent;
wherein the thiophosphorodichloridate reagent is selected form the group consisting of:
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