Late-Stage Functionalization via Thianthrenation: A Reaction Enabling Rapid Preparation of Drug Beads for Chemical Pulldown.

A major bottleneck in identifying the molecular targets of phenotypically active compounds via affinity pulldown is the chemical synthesis of functionalized probes suitable for attachment to solid supports. This process often requires time-intensive, multistep synthesis. A more direct approach would be to use late-stage functionalization chemistry to directly modify the phenotypic hit/lead. We report a proof-of-concept workflow adapting the thianthrenation late-stage functionalization reaction to expedite the preparation of probes. A high-throughput experimental approach allowed rapid assessment of substrate suitability for this chemical reaction. Twenty-four compounds with activity against the protozoan parasite Leishmania donovani were progressed through this workflow. Five compounds were identified as thianthrenation substrates, and four were functionalized to prepare affinity probes. Compound 9b was advanced to target identification in L. donovani, with molecular targets identified with high confidence. These studies highlight the utility of late-stage functionalization reactions to expedite the synthesis of functionalized tool compounds for multiple downstream applications.