Discovery of Chemoselective and Biocompatible Reactions Using a High‐Throughput Immunoassay Screening

Abstract

The discovery of new chemical reactions is a long-standing goal of organic chemists. For decades, synthetic problems motivated the development of new methodologies to continuously expand the reaction toolkit in organic synthesis. As alternatives to purely rational approaches, strategies that offer more room for serendipity have recently emerged. In these approaches, the discovery is a result of the systematic exploration of a large number of chemical reactions through the use of robust high-throughput screening methods based either on mass spectrometry techniques [1] or on DNA technologies. [2] Although this strategy was already proven to be efficient with the discovery of several new interesting reactions, [3] this does not guarantee the potential impact of the discovered reactions. A more powerful approach would be the increase of the level of selection in a manner that only powerful reliable reactions are discovered. Such a highly demanding selection should therefore be based not only on reaction efficiencies, but also on other parameters that would ensure the usefulness of the discovered reaction. In 2001, K. B. Sharpless introduced the concept of "click chemistry", which has been widely and successfully applied since then, and listed a series of important criteria that may influence the extent and the impact of a chemical reaction. [4] Among them, chemoselectivity, simplicity of reaction conditions, and high efficiency, even in complex media, are probably the most important ones. This can be highlighted by the startling number of applications in organic synthesis, materials science, and biotechnology of the copper-catalyzed alkyne-azide cycloaddition reaction (CuAAC), which is one of the most powerful click reactions described to date. [5] Herein, we disclose an approach to accelerate the discovery of such important chemical reactions through the use of an immunoassay technique. As we previously described, [6] sandwich immunoassays can be successfully applied to monitor cross-coupling reactions by connecting small-molecule tags to chemically reactive groups. Products of bond-forming coupling reactions can then be specifically detected by two specific antitag monoclonal antibodies (mAbs) using standard ELISA techniques: one mAb captures the doubletagged coupling product on a solid phase and a second acts as a detector. We recently showed that the throughput of this adapted immunoassay (typically around 1000 analyses per day and person) allows the fast identification of new reactions among thousands of combinations of reactive functions and catalysts. [7] One crucial advantage of this screening method relies on the high specificity of mAbs, permitting the precise and sensitive quantification of the double-tagged crosscoupling products in complex mixtures without work-up. Here, we decided to fully exploit this advantage by designing a series of successive screening in order to identify new, efficient, chemoselective, and biocompatible [3+2] cycloaddition reactions. Our approach (Figure 1) involves three mai...

Synthesis of aminopyrazoles from sydnones and ynamides

“…12,45 The use of copper promoters has also been shown to affect regioselectivity and facilitate the cycloaddition reaction, commonly referred to as a Cu-mediated Sydnone Alkyne Cycloaddition (CuSAC). 11,13 Based on these reports, we decided to undertake a screening of readily available copper catalysts and study their effect on the cycloaddition between ynamides and sydnones. Although it is known that terminal sulfonyl ynamides are water sensitive, this was not a major concern during previous studies on metal-free systems, as the desired reactions outpaced any side-reactions.…”

“…1 Previously reported attempts to try to address these issues include the use of alkynylboronates 9,10 or copper promoters to direct the regioselectivity of the sydnone-alkyne cycloaddition reactions. [11][12][13] Due to the high interest towards new routes to fully functionalised pyrazoles, which are known to possess biological activities, 14,15 we were interested in expanding the scope of the sydnone-alkyne cycloaddition reaction to increase the tolerance for activated and electron-rich alkynes. To do so, we developed the synthesis of 4-aminopyrazoles from cycloaddition reactions between sydnones and ynamides, which have not been reported to date.…”

Sydnone Cycloaddition Route to Pyrazole-Based Analogs of Combretastatin A4

“…31 These cycloadditions can be highly regioselective and offer access to a wide range of pyrazoles. 32,33,34,35,36,37 In the context of developing novel VDAs, we envisaged that the sydnone cycloaddition strategy could be exploited to access a broad range of pyrazole templated combretastatin analogs from similar starting materials (Scheme 1). However, we recognized that a number of synthetic challenges needed to be met in order to achieve this goal: (1) access to 1,5-substituted pyrazoles theoretically required high temperature cycloaddition with acetylene gas; (2) 4,5-disubstituted…”

Synthesis and catalytic applications of C3-symmetric tris(triazolyl)methanol ligands and derivatives

“…Besides the applications of TTM ligands in CuAAC reactions, it is worth mentioning a very recently reported contribution by Taran et al 43 where the TTM ligand 6 was applied in the Cu-catalysed sydnone−alkyne cycloaddition (CuSAC). 44 …”