Rapid approach to complex boronic acids.

The compatibility of free boronic acid building blocks in multicomponent reactions to readily create large libraries of diverse and complex small molecules was investigated. Traditionally, boronic acid synthesis is sequential, synthetically demanding, and time-consuming, which leads to high target synthesis times and low coverage of the boronic acid chemical space. We have performed the synthesis of large libraries of boronic acid derivatives based on multiple chemistries and building blocks using acoustic dispensing technology. The synthesis was performed on a nanomole scale with high synthesis success rates. The discovery of a protease inhibitor underscores the usefulness of the approach. Our acoustic dispensing-enabled chemistry paves the way to highly accelerated synthesis and miniaturized reaction scouting, allowing access to unprecedented boronic acid libraries.

Acoustic Droplet Ejection Enabled Automated Reaction Scouting.

Miniaturization and acceleration of synthetic chemistry are critically important for rapid property optimization in pharmaceutical, agrochemical, and materials research and development. However, in most laboratories organic synthesis is still performed on a slow, sequential, and material-consuming scale and not validated for multiple substrate combinations. Herein, we introduce fast and touchless acoustic droplet ejection (ADE) technology into small-molecule chemistry to transfer building blocks by nL droplets and to scout a newly designed isoquinoline synthesis. With each compound in a discrete well, 384 random derivatives were synthesized in an automated fashion, and their quality was monitored by SFC-MS and TLC-UV-MS analysis. We exemplify a pipeline of fast and efficient nmol scouting to mmol- and mol-scale synthesis for the discovery of a useful novel reaction with great scope.

Acoustic Mist Ionization Platform for Direct and Contactless Ultrahigh-Throughput Mass Spectrometry Analysis of Liquid Samples.

Mass spectrometry (MS) has many advantages as a quantitative detection technology for applications within drug discovery. However, current methods of liquid sample introduction to a detector are slow and limit the use of mass spectrometry for kinetic and high-throughput applications. We present the development of an acoustic mist ionization (AMI) interface capable of contactless nanoliter-scale "infusion" of up to three individual samples per second into the mass detector. Installing simple plate handling automation allowed us to reach a throughput of 100 000 samples per day on a single mass spectrometer. We applied AMI-MS to identify inhibitors of a human histone deacetylase from AstraZeneca's collection of 2 million small molecules and measured their half-maximal inhibitory concentration. The speed, sensitivity, simplicity, robustness, and consumption of nanoliter volumes of sample suggest that this technology will have a major impact across many areas of basic and applied research.

Automated and Accelerated Synthesis of Indole Derivatives on a Nano-Scale.

Automated, miniaturized and accelerated synthesis for efficient property optimization is a formidable challenge for chemistry in the 21st century as it helps to reduce resources and waste and can deliver products in shorter time frames. Here, we used for the first-time acoustic droplet ejection (ADE) technology and fast quality control to screen efficiency of synthetic reactions on a nanomole scale in an automated and miniaturized fashion. The interrupted Fischer indole combined with Ugi-type reactions yielded several attractive drug-like scaffolds. In 384-well plates, a diverse set of interrupted Fischer indole intermediates were produced and reacted to the tricyclic hydantoin backbone by a 2-step sequence. Similarly, preformed Fischer indole intermediates were used to produce divers sets of Ugi products and the efficiency was compared to the in-situ method. Multiple reactions were resynthesized on a preparative millimole scale, showing scalability from nano to mg and thus synthetic utility. An unprecedented large number of building was used for fast scope and limitation studies (68 isocyanides, 72 carboxylic acids). Miniaturization and analysis of the generated big synthesis data enabled deeper exploration of the chemical space and permitted gain of knowledge that was previously impractical or impossible, such as the rapid survey of reactions, building block and functional group compatibility.

Acoustic Injectors for Drop-On-Demand Serial Femtosecond Crystallography.

X-ray free-electron lasers (XFELs) provide very intense X-ray pulses suitable for macromolecular crystallography. Each X-ray pulse typically lasts for tens of femtoseconds and the interval between pulses is many orders of magnitude longer. Here we describe two novel acoustic injection systems that use focused sound waves to eject picoliter to nanoliter crystal-containing droplets out of microplates and into the X-ray pulse from which diffraction data are collected. The on-demand droplet delivery is synchronized to the XFEL pulse scheme, resulting in X-ray pulses intersecting up to 88% of the droplets. We tested several types of samples in a range of crystallization conditions, wherein the overall crystal hit ratio (e.g., fraction of images with observable diffraction patterns) is a function of the microcrystal slurry concentration. We report crystal structures from lysozyme, thermolysin, and stachydrine demethylase (Stc2). Additional samples were screened to demonstrate that these methods can be applied to rare samples.

Dispensing processes impact apparent biological activity as determined by computational and statistical analyses.

Dispensing and dilution processes may profoundly influence estimates of biological activity of compounds. Published data show Ephrin type-B receptor 4 IC50 values obtained via tip-based serial dilution and dispensing versus acoustic dispensing with direct dilution differ by orders of magnitude with no correlation or ranking of datasets. We generated computational 3D pharmacophores based on data derived by both acoustic and tip-based transfer. The computed pharmacophores differ significantly depending upon dispensing and dilution methods. The acoustic dispensing-derived pharmacophore correctly identified active compounds in a subsequent test set where the tip-based method failed. Data from acoustic dispensing generates a pharmacophore containing two hydrophobic features, one hydrogen bond donor and one hydrogen bond acceptor. This is consistent with X-ray crystallography studies of ligand-protein interactions and automatically generated pharmacophores derived from this structural data. In contrast, the tip-based data suggest a pharmacophore with two hydrogen bond acceptors, one hydrogen bond donor and no hydrophobic features. This pharmacophore is inconsistent with the X-ray crystallographic studies and automatically generated pharmacophores. In short, traditional dispensing processes are another important source of error in high-throughput screening that impacts computational and statistical analyses. These findings have far-reaching implications in biological research.

Acoustically mounted microcrystals yield high-resolution X-ray structures.

We demonstrate a general strategy for determining structures from showers of microcrystals. It uses acoustic droplet ejection to transfer 2.5 nL droplets from the surface of microcrystal slurries, through the air, onto mounting micromesh pins. Individual microcrystals are located by raster-scanning a several-micrometer X-ray beam across the cryocooled micromeshes. X-ray diffraction data sets merged from several micrometer-sized crystals are used to determine 1.8 Ǻ resolution crystal structures.

Gradient, contact-free volume transfers minimize compound loss in dose-response experiments.

More accurate dose-response curves can be constructed by eliminating aqueous serial dilution of compounds. Traditional serial dilutions that use aqueous diluents can result in errors in dose-response values of up to 4 orders of magnitude for a significant percentage of a compound library. When DMSO is used as the diluent, the errors are reduced but not eliminated. The authors use acoustic drop ejection (ADE) to transfer different volumes of model library compounds, directly creating a concentration gradient series in the receiver assay plate. Sample losses and contamination associated with compound handling are therefore avoided or minimized, particularly in the case of less water-soluble compounds. ADE is particularly well suited for assay miniaturization, but gradient volume dispensing is not limited to miniaturized applications.