Triazolecarbaldehyde Reagents for One‐Step N‐Terminal Protein Modification

Site‐specific modification of peptides and proteins is a key aspect of protein engineering. We developed a method for modification of the N terminus of proteins using 1H‐1,2,3‐triazole‐4‐carbaldehyde (TA4C) derivatives, which can be prepared in one step. The N‐terminal specific labeling of bioactive peptides and proteins with the TA4C derivatives proceeds under mild reaction conditions in excellent conversion (angiotensin I: 92 %, ribonuclease A: 90 %). This method enables site‐specific conjugation of various functional molecules such as fluorophores, biotin, and polyethylene glycol attached to the triazole ring to the N terminus. Furthermore, a functional molecule modified with a primary amine moiety can be directly converted into a TA4C derivative through a Dimroth rearrangement reaction with 1‐(4‐nitrophenyl)‐1H‐1,2,3‐triazole‐4‐carbaldehyde. This method can be used to obtain N‐terminal‐modified proteins via only two steps: 1) convenient preparation of a TA4C derivative with a functional group and 2) modification of the N terminus of the protein with the TA4C derivative. Reagents for bioconjugation: A one‐step N‐terminal protein modification proceeds using 1H‐1,2,3‐triazole‐4‐carbaldehyde (TA4C) derivatives tethering a functional molecule. Furthermore, a Dimroth rearrangement enables direct preparation of TA4C derivatives from a functional‐group‐attached amine. The modified protein with a tag at the N terminus is easily obtained by a two‐step process.