Six Amino Acids: Accessing OAS1 Inhibitors Open Access
Marecheau-Miller, Tamecka (Spring 2024)
Abstract
As of 2022, there are 485 known types of inborn errors of immunity. These conditions are marked by vastly diverse autoimmune irregularities in the human body ranging from increased infection susceptibility to autoimmune disorders (Tangye et al., 2022). One type of inborn error of immunity is caused by a mutant form of the OAS1 enzyme, the OAS1 Gain-of-Function enzyme, that demonstrates unregulated RNA cleavage activity. This unregulated activity ultimately results in the cleavage of human RNA and the development of downstream autoinflammatory immunodeficiencies.
The OAS1 enzyme plays a vital role in the human immune response by conducting a double-stranded RNA (dsRNA) dependent cleavage of viral and host RNA during viral infection. In the presence of dsRNA, the OAS1 enzyme catalyzes the formation of the 2’, 5’-oligoadenylate species, which activate the latent RNAse enzyme to cleave RNA. However, the Gain-of-Function mutant OAS1 (OAS1 GoF) enzyme is dsRNA-independent, resulting in unregulated RNA cleavage. The unregulated activity of the GoF mutant can cause inborn errors of immunity, for which treatment options largely include lifelong symptom management or stem cell therapy. Inhibition of the OAS1 enzyme via a small-molecule compound can pose a more targeted, as well as a potentially safer and more cost-effective, treatment route for this condition. Aliphatic, polar-protected, and aromatic amino-acid-derived analogs of inhibitor scaffold have been successfully synthesized and docked. In the quest for a potent OAS1 enzyme inhibitor, diverse analog synthesis, structure-activity relationship analysis, and reaction route optimization are ongoing. In this work, I delineate my progress toward the effective synthesis of diverse analogs of an OAS1 inhibitor scaffold.
Table of Contents
Introduction 1
Inborn errors of immunity 1
OAS1 wild type and gain of function enzymes 1
Molecular Dynamics, the OAS pathway, and Gain of Function mutants 2
Figure 1. OAS1 active site, allosteric pocket, and important residues 3
Complexities of treatment of OAS1 Gain of Function enzymes 4
OAS1 protein allosteric inhibitors 5
Synthesizing OAS1 allosteric inhibitors 5
Overview 5
Figure 2. Compound 13 and its retrosynthetic scheme with amino acids 5
Synthesis of Compound 13 6
Figure 3. Compound 13 synthetic route 6
Figure 4. Compound 13 IC50 values, R and S enantiomers 7
Validation of necessity of acid moiety 7
Figure 5. IC50 values for Compound 13 and two ester analogs 7
Aliphatic benzimidazole synthesis 8
Figure 6. Reaction scheme for achiral benzimidazoles with limited steric
hindrance of the amine 9
Aliphatic amino acid analog synthesis 9
Figure 7. IC50 values of analog 8e, analog 8c, and Compound 13 (8a) 10
Figure 8. Synthetic scheme of analog 8e 11
Figure 9. Analog 8f synthetic scheme 12
Figure 10. Analog 8g synthetic scheme 15
Figure 11. Histidine-derived analog synthetic scheme 17
The allosteric target 18
Figure 12. First view of OAS1 allosteric pocket and interactions with Compound
13 18
Figure 13. A different perspective on the allosteric site with Compound 13 bound 20
Figure 14. Analog 8c in the allosteric site 21
Figure 15. Analog 8d in the allosteric site 22
Figure 16. Analog 8e in the allosteric site 23
Figure 17. Analog 8f in the allosteric site 24
Figure 18. Analog 8g in the allosteric site 26
Figure 19. Analog 8h in the allosteric site 28
Figure 20. Summary of all analogs synthesized and data 30
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