Revisiting ring-degenerate rearrangements of 1-substituted-4-imino-1,2,3-triazoles

1-(4-Nitrophenyl)-1H-1,2,3-Triazole-4-carbaldehyde: Scalable Synthesis and Its Use in the Preparation of 1-Alkyl-4-Formyl-1,2,3-triazoles

1,2,3-Triazole-4-carbaldehydes are useful synthetic intermediates which may play an important role in the discovery of novel applications of the 1,2,3-triazole moiety. In this work, a one-step multigram scale synthesis of 4-formyl-1-(4-nitrophenyl)-1H-1,2,3-triazole (FNPT) as a preferred reagent for the synthesis of 1-alkyl-4-formyltriazoles is described, making use of the commercially available 3-dimethylaminoacrolein and 4-nitrophenyl azide. Next, the earlier reported reaction of FNPT with alkylamines is further explored, and for hexylamine, the one-pot sequential cycloaddition and Cornforth rearrangement is demonstrated. In addition, a useful protocol for the in situ diazotization of 4-nitroaniline is provided. This facilitated the complete hydrolysis of rearranged 4-iminomethyl-1,2,3-triazoles and allowed for the recycling of 4-nitrophenyl azide.

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.