UV‐Induced Tetrazole‐Thiol Reaction for Polymer Conjugation and Surface Functionalization

Abstract

A UV-induced 1,3-dipolar nucleophilic addition of tetrazoles to thiols is described. Under UV irradiation the reaction proceeds rapidly at room temperature, with high yields, without a catalyst, and in both polar protic and aprotic solvents, including water. This UV-induced tetrazole-thiol reaction was successfully applied for synthesis of small molecules, protein modification, and rapid and facile polymer-polymer conjugation.The reaction has been also demonstrated for the formation of micropatterns by site-selective surface functionalization. Superhydrophobic-hydrophilic micropatterns were successfully created by sequential modifications of a tetrazole-modified porous polymer surface with hydrophobic and hydrophilic thiols. A biotin functionalized surface could be fabricated in aqueous solutions under long-wavelength UV irradiation.Ever since the first reported photoreaction of an organic compound, santonin, in 1834 by Trommsdorf, [1] the spatially and temporally controllable photochemistry has found diverse and widespread applications, [2] including surface functionalization to create patterned or gradient immobilization of various substrates.[3] Photo-induced click reactions have been actively investigated during the last decade in attempts to combine the benefits of click reactions with the excellent spatial and temporal controllability of photochemical processes.[4] UV-induced thiolene and thiol-yne reactions are the most known radical photoclick reactions.[5] Non-radical photoreactions have also attracted a lot of attention in recent years.[6] For instance, Lin et al, [7] introduced a photo-click 1,3-dipolar tetrazole-ene reaction based on Huisgen's studies. [8] The tetrazole-ene reaction presents several advantages: simplicity of implementation, fast reaction kinetics, high yields, it is catalyst free, yields inoffensive byproducts (N2) and, therefore, bio-compatible. This and other photo reactions have been implemented in many different applications such as dendrimers synthesis, [9] bioconjugation, [6b, 6d, 6e, 10] in situ bio-labeling, [6c, 11] hydrogels formation, [12] surface functionalization [13] etc. Nevertheless, the implementation of photo reactions in bio-applications is still limited, partly because unnatural functional groups have to be first introduced to a biomolecule. In addition, only a few photo reactions could be applied for polymer-polymer coupling and site-selective conjugation of biomolecules on surfaces. [13b, 14] Thus, despite a progress in the field of photo-induced reactions, there is a clear need for novel efficient photo reactions that are selective to different types of functionalities, compatible with polymerpolymer conjugation and bioapplications. 50 years ago Huisgen et al. reported that thiophenol could be added to the intermediate nitrilimine generated from decomposition of 2,5-diphenyltetrazole in boiling thiophenol. [8a, 8b] Photolytic decomposition of tetrazoles with release of nitrogen and nitrilimines was also described.[8c] In this work, we repo...

Genetically Encoded Residue-Selective Photo-Crosslinker to Capture Protein-Protein Interactions in Living Cells

“…26,29 Recently, tetrazole derived unnatural amino acid (Uaa) was genetically encoded as an excellent photo-crosslinker (Figure 1B) (mPyTK) to achieve site-selective protein photo-crosslinking in living cells. 30,31 The tetrazoles are previously designed for photoclick reaction with alkenes, 32 while the nitrile imine intermediates photogenerated from tetrazoles could react with several nucleophilic groups (e.g., thiol groups, 33,34 carboxylic acids, 35,36 tryptophan, 37 amine, 35 and histidine 38 ) to give ligation products. Indeed, it is a creative strategy to develop Uaa from tetrazole to capture transient protein-protein interactions in living cells, however, photogenerated intermediate potentially reacts with above mentioned nucleophiles in addition to carboxylic acid residues, providing linkages with unpredictable selectivity in complex biological environments (Figure 1B).…”

Diphenyltetrazole Modified Bacterial Cellulose Film: Considerations on Heterogeneous Modification and Bioconjugation

“…Besides, the absorption pattern of the film used in the absence of UV light remained the same. It is important to show that a very similar UV-Vis pattern was found when this photoclick reaction was used to couple diphenyltetrazole and the molecule-containing thiol group 20 . However, the distinction between success and failure in coupling a protein structure in the presence of other aromatic groups, such as diphenyltetrazole appended onto cellulose, is reasonably reckless by UV-vis spectroscopy.…”

“…This is desirable so as to avoid protein denaturation, as well as for the reaction to be fast and selective to certain functional groups. Based on that, diphenyltetrazol 2 was coupled to the cellulose surface, considering that this molecule is able to promote photoclick conjugations with thiols 20 . BSA was chosen as the protein model, since it is known that this protein has a sulfidryl group facing the external face (Figure 1).…”

“…In this context, click chemistry reactions have been applied to functionalize different types of materials successfully [17][18][19] . In recent decades, photoclick reactions have been widely studied in the search of combining regioselectivity, the speed of the chemical process, and high yield 20,21 . The diaryltetrazole group was recognized as a versatile functional group for photoclick reactions.…”

“…The tetrazole ring is stable under normal conditions, but under ultraviolet irradiation it forms an intermediate that is highly reactive in the presence of some nucleophiles 22,23 . For instance, this methodology was used to promote selective coupling of thiols to a polyethyleneglycol diphenyltetrazole-modified polymer 20 . This procedure was proven to be very advantageous due to its occurrence in the absence of catalysts, and the only *e-mail: renatoviana@utfpr.edu.br byproduct formed was N 2 (g).…”