Table 1.

Brief summary of the currently available chemical toolbox for site‐selective protein functionalization.

AA residues	Methods
Cysteine	Halocarbonyl, [9] Maleimide derivatives,[ 33 , 36 ] Sulfone derivatives,[ 37 , 38 ] Metal‐mediated arylation[ 39 , 40 , 41 ] Thiol–ene/yne reactions,[ 42 , 43 ] Dichlorotetrazine [44] Vinylphosphonothiolate, [45] Ethnylbenziodoxolones [46]
Disulfide	Allyl sulfone, [38] Dibromomaleimide, [47] Oxetane, [48] Divinylpyridine, [49] Dibromopyridazinediones [50]
N‐terminus	2‐Formylphenylboronic derivatives,[ 51 , 52 ] 2‐Pyridinecarboxyaldehyde, [53] 2‐Ethynylbenzaldehydes, [54] o‐Aminophenols, [55] 2‐Cyanobenzothiazole, [56] Pictet–Spengler reaction, [57] Ketenes [58]
Methionine	Hypervalent iodine reagent, [59] Oxaziridines, [60] Epoxide [61]
Tyrosine	Diazonium, [62] Mannich‐type reaction, [63] Pd‐mediated alkylation, [64] Trizoline‐diones [65]
Tryptophan	Rhodium‐carbenoid, [66] Keto‐ABNO, [67] Metal‐mediated arylation/alkynylation[ 68 , 69 , 70 , 71 ]
Serine	Salicylaldehyde ester [72] Phosphorus–sulfur incorporation reagents [73]
Arginine	Glyoxal reagents [74]