X-ray Crystallography-Guided Design and Synthesis of Cyclopentyl Heteroaryl Carboxylic Acid-Based Inhibitors of the SARS-CoV-2 Nsp3 Macrodomain (Mac1)

Mac1 is a conserved macrodomain enzyme in the nonstructural protein 3 (Nsp3) of SARS-CoV-2 and is part of the viral replication machinery. Mac1 is a target for small-molecule inhibitors that could ultimately enable new COVID-19 therapeutics to be developed. Here, we report the structure-guided design, synthesis, and Mac1 inhibition profiling of 25 analogues derived from a hit identified through crystallographic fragment screening. The heteroaryl group and scaffold (cis- and trans-cyclopentane and cyclopentene) were varied. Two new approaches to trans-cyclopentanes were developed: MacMillan's Ir/Ni-mediated photoredox cross-coupling of alcohols and Barluenga-Valdés' metal-free cross-coupling of sulfonyl hydrazones and boronic acids. X-ray crystal structures of 19 compounds bound to Mac1 were determined to guide the design and to rationalize the observed SAR. A new family of Mac1 inhibitors with benzothiazole or amino benzothiazoles was discovered and characterized, with IC₅₀ values of 6-8 μM and ligand efficiency values of up to 0.40.