Ligand Optimization by Improving Shape Complementarity at a Hepatitis C Virus RNA Target.

Area of Science:

• Biochemistry
• Virology
• Medicinal Chemistry

Background:

• Hepatitis C virus (HCV) internal ribosome entry site (IRES) contains a conformational switch crucial for viral translation.
• Previous inhibitors, like 2-amino-benzimidazoles, bind to the IRES RNA in an elongated conformation.
• Understanding these interactions is key to developing effective antiviral therapies.

Discussion:

• Designed and synthesized novel quinazoline derivatives to improve binding to the HCV IRES RNA switch.
• Investigated the impact of structural modifications, specifically spiro-cyclopropyl and dimethyl substitutions, on ligand-RNA interactions.
• Utilized crystal structure analysis to elucidate the binding modes and shape complementarity.

Key Insights:

• A spiro-cyclopropyl modification significantly enhanced ligand affinity (5-fold increase) by optimally filling a hydrophobic pocket in the RNA binding site.
• A dimethyl substitution at the same position did not improve binding, highlighting the importance of precise shape complementarity.
• Demonstrated that hydrophobic interactions play a critical role in ligand binding, even within a predominantly hydrophilic RNA target site.

Outlook:

• Further optimization of quinazoline derivatives could lead to potent HCV inhibitors.
• This study provides a foundation for designing small molecules targeting RNA conformational switches.
• The findings contribute to the broader understanding of small molecule-RNA interactions in drug discovery.