Development of High-Throughput Experimentation Approaches for Rapid Radiochemical Exploration

Abstract

Positron emission tomography is a widely used imaging platform for studying physiological processes. Despite the proliferation of modern synthetic methodologies for radiolabeling, the optimization of these reactions still primarily relies on inefficient one-factor-at-a-time approaches. High-throughput experimentation (HTE) has proven to be a powerful approach for optimizing reactions in many areas of chemical synthesis. However, to date, HTE has rarely been applied to radiochemistry. This is largely because of the short lifetime of common radioisotopes, which presents major challenges for efficient parallel reaction setup and analysis using standard equipment and workflows. Herein, we demonstrate an effective HTE workflow and apply it to the optimization of copper-mediated radiofluorination of pharmaceutically relevant boronate ester substrates. The workflow utilizes commercial equipment and allows for rapid analysis of reactions for optimizing reactions, exploring chemical space using pharmaceutically relevant aryl boronates for radiofluorinations, and constructing large radiochemistry data sets.

Figure 1.

HTE Radiochemistry

Figure 2:

Adapted apparatus for HTE radiolabeling. Commercial apparatus may be obtained from Analytical Sales and Services, Inc. (analytical-sales.com).

Figure 3:

Exploration and Validation of SPE-based HTE Radiochemistry. a) Substrate set for protocol validation. Manual and HTE radiofluorinations reactions were conducted using Condition D. b) Correlation between RCCs measured by SPE-based separation techniques and standard radioTLC. c) Heatmap data for radioTLC determined RCC, PET Scanner determined RCC, Gamma Counter Determined RCC, and Autoradiography determined RCC (CPM). Data are the average of two individual reactions on the same plate.

Figure 4:

Informer Library Evaluation. a) Informer library of (hetero)aryl boronate pinacol esters evaluated; b) correlation analysis between SPE analytical techniques (gamma counter and PET/CT scanner) and radioTLC; c) heatmaps demonstrating similarity of trends between the analytical techniques.

Figure 5.

Optimization and Manual Validation. a) Target molecules and variables for optimization via HTE; b) Acquired radiochemical conversions across multiple analytical protocols identified improved conditions; c) Manual validation of improved conditions at 25 μmol scale.