Small molecule inhibitors of the SARS-CoV Nsp15 endoribonuclease

The severe acute respiratory syndrome (SARS) virus encodes several unusual RNA processing enzymes, including Nsp15, an endoribonuclease that preferentially cleaves 3’ of uridylates through a ribonuclease A (RNase A)-like mechanism. Crystal structures of Nsp15 confirmed that the Nsp15 active site is structurally similar to that of RNase A. These similarities and our molecular docking analysis lead us to hypothesize that previously characterized RNase A inhibitors will also inhibit the SARS-CoV Nsp15. Benzopurpurin B, C-467929, C-473872, N-306711, N-65828, N-103019 and congo red were tested for effects on Nsp15 endoribonuclease activity. A fluorescence assay revealed that the IC50 values for inhibiting endoribonuclease activity were between 0.2 µM and 40 µM. These compounds were demonstrated to bind SARS-CoV Nsp15 by a differential scanning fluorimetry assay. Benzopurpurin B also inhibited the endoribonuclease activities of the Nsp15 orthologs from two other coronaviruses: mouse hepatitis virus (MHV) and infectious bronchitis virus (IBV). Benzopurpurin B, C-473872, and congo red reduced infectivity of MHV in L2 cells by 8- to 26- fold. The more effective drugs caused a decrease in MHV RNA accumulation. All three compounds reduced the infectivity of the SARS-CoV in Vero cells

Novel Transthyretin Amyloid Fibril Formation Inhibitors: Synthesis, Biological Evaluation, and X-Ray Structural Analysis

Transthyretin (TTR) is one of thirty non-homologous proteins whose misfolding, dissociation, aggregation, and deposition is linked to human amyloid diseases. Previous studies have identified that TTR amyloidogenesis can be inhibited through stabilization of the native tetramer state by small molecule binding to the thyroid hormone sites of TTR. We have evaluated a new series of β-aminoxypropionic acids (compounds 5–21), with a single aromatic moiety (aryl or fluorenyl) linked through a flexible oxime tether to a carboxylic acid. These compounds are structurally distinct from the native ligand thyroxine and typical halogenated biaryl NSAID-like inhibitors to avoid off-target hormonal or anti-inflammatory activity. Based on an in vitro fibril formation assay, five of these compounds showed significant inhibition of TTR amyloidogenesis, with two fluorenyl compounds displaying inhibitor efficacy comparable to the well-known TTR inhibitor diflunisal. Fluorenyl 15 is the most potent compound in this series and importantly does not show off-target anti-inflammatory activity. Crystal structures of the TTR∶inhibitor complexes, in agreement with molecular docking studies, revealed that the aromatic moiety, linked to the sp(2)-hybridized oxime carbon, specifically directed the ligand in either a forward or reverse binding mode. Compared to the aryl family members, the bulkier fluorenyl analogs achieved more extensive interactions with the binding pockets of TTR and demonstrated better inhibitory activity in the fibril formation assay. Preliminary optimization efforts are described that focused on replacement of the C-terminal acid in both the aryl and fluorenyl series (compounds 22–32). The compounds presented here constitute a new class of TTR inhibitors that may hold promise in treating amyloid diseases associated with TTR misfolding

Novel Transthyretin Amyloid Fibril Formation Inhibitors: Synthesis, Biological Evaluation, and X-Ray Structural Analysis

Transthyretin (TTR) is one of thirty non-homologous proteins whose misfolding, dissocn., aggregation, and deposition is linked to human amyloid diseases. Previous studies have identified that TTR amyloidogenesis can be inhibited through stabilization of the native tetramer state by small mol. binding to the thyroid hormone sites of TTR. We have evaluated a new series of b-aminoxypropionic acids (compds. 5-21), with a single arom. moiety (aryl or fluorenyl) linked through a flexible oxime tether to a carboxylic acid. These compds. are structurally distinct from the native ligand thyroxine and typical halogenated biaryl NSAID-like inhibitors to avoid off-target hormonal or anti-inflammatory activity. Based on an in vitro fibril formation assay, five of these compds. showed significant inhibition of TTR amyloidogenesis, with two fluorenyl compds. displaying inhibitor efficacy comparable to the well-known TTR inhibitor diflunisal. Fluorenyl 15 is the most potent compd. in this series and importantly does not show off-target antiinflammatory activity. Crystal structures of the TTR:inhibitor complexes, in agreement with mol. docking studies, revealed that the arom. moiety, linked to the sp2-hybridized oxime carbon, specifically directed the ligand in either a forward or reverse binding mode. Compared to the aryl family members, the bulkier fluorenyl analogs achieved more extensive interactions with the binding pockets of TTR and demonstrated better inhibitory activity in the fibril formation assay. Preliminary optimization efforts are described that focused on replacement of the C-terminal acid in both the aryl and fluorenyl series (compds. 22-32). The compds. presented here constitute a new class of TTR inhibitors that may hold promise in treating amyloid diseases assocd. with TTR misfolding