A general protocol for creating high-throughput screening assays for reaction yield and enantiomeric excess applied to hydrobenzoin

Abstract

A general approach to high-throughput screening of enantiomeric excess (ee) and concentration was developed by using indicator displacement assays (IDAs), and the protocol was then applied to the vicinal diol hydrobenzoin. The method involves the sequential utilization of what we define herein as screening, training, and analysis plates. Several enantioselective boronic acid-based receptors were screened by using 96-well plates, both for their ability to discriminate the enantiomers of hydrobenzoin and to find their optimal pairing with indicators resulting in the largest optical responses. The best receptor/indicator combination was then used to train an artificial neural network to determine concentration and ee. To prove the practicality of the developed protocol, analysis plates were created containing true unknown samples of hydrobenzoin generated by established Sharpless asymmetric dihydroxylation reactions, and the best ligand was correctly identified.artificial neural networks ͉ catalyst discovery ͉ enantioselective indicator displacement assay ͉ supramolecular chemistry T he unique role of chiral bioactive therapeutic substances is a source of inspiration for the design of efficient asymmetric catalytic processes (1). To this end, combinatorial synthesis and stockpiles of chiral ligands can afford large libraries of molecules as a potential source of new and improved catalysts (2, 3). Traditionally, the search for asymmetric catalysts has relied on iterative approaches wherein a single catalyst is designed, synthesized, tested, and optimized. This cycle is repeated until a catalytically active system is obtained with the desired level of enantioselectivity. In contrast, if a high-throughput screening (HTS) strategy for ee determination existed, it would enable one to rapidly identify effective asymmetric catalysts, thus allowing for a much broader range of catalyst candidates and experimental conditions to be evaluated (4, 5). However, most of these methods require prior derivatization of the analyte or require expensive instrumentation, and many are still quite slow. Herein, we report a colorimetric strategy based on indicator displacement assays (IDAs) for creating HTS protocols that can be used for the rapid determination of molecular chirality as well as the yield of a reaction.An indicator displacement assay relies on a colorimetric or fluorescent indicator that changes optical or electrochemical properties when bound to a host relative to being free in the bulk medium (6). The most commonly used indicators are pH indicators (7). The competition between an indicator and the guest of interest for the binding site of the host allows the determination of total guest (or analyte) concentration [G] t [Scheme 1 (Eq.1)]. An IDA both eliminates the need to incorporate the chromophore or fluorophore into the structure of the host, thus simplifying the synthesis of the host molecule, and allows one to tune the sensitivity of the assay because of the ability to change the identity and concentration of the ind...

Chiral Amine Enantiomeric Excess Determination Using Self‐Assembled Octahedral Fe(II)‐Imine Complexes

“…Our group, 8,9 as well as others, 3,10-12 have combined self-assembling receptors with optical techniques for the rapid screening of ee . Optical instrumentation is an attractive method for ee determination because the analysis is typically fast, inexpensive, and familiar to most organic chemists – all of which lower the barrier to its widespread adoption.…”

Discrimination and Classification of Ginsenosides and Ginsengs Using Bis‐Boronic Acid Receptors in Dynamic Multicomponent Indicator Displacement Sensor Arrays

“…When H4 was added to an Alizarin Red S (ARS) solution (200 mm) at pH 7.4, the intensity of the peak at 451 nm increased with isosbestic points at 332 and 415 nm ( These observations are consistent with titrations conducted before with mono-boronic acid. [38] However, different behavior was observed during titration of H4 into Pyrocatechol Violet (PV) (100 mm) solution (see the Supporting Information, Figure 2 S). The peak at 432 nm decreased, whereas the peak at 610 nm increased, and after 60 mm of H4 the trend reversed (Figure 1 C).…”

“…Methanol was chosen as a solvent because the lower polarity of methanol compared to water increases the binding affinity between boronic acid and diols and thereby increases the sensitivity of the assay. [38] All methanolic solutions were buffered by para-toluenesulfonic acid and Hunigs base at pH 7.4.…”

An ESI-MS Method to Determine Yield and Enantioselectivity in a Single Assay

“…Various optical strategies have been employed as a rapid and efficient method to determine both concentration and % ee in a single assay [27][28][29][30][31][32][33][34][35]. NMR assays have been developed to determine both concentration and enantioselectivity of a reaction [36].…”