Average Electron Density: A Quantitative Tool for Evaluating Non-Classical Bioisosteres of Amides

Area of Science:

• Medicinal Chemistry
• Computational Chemistry
• Drug Design

Background:

• Bioisosterism is a key strategy in drug design to optimize molecular properties.
• The average electron density (AED) tool has successfully quantified similarities for carboxylic acid bioisosteres.
• Evaluating amide bioisosterism, particularly amide-to-1,2,3-triazole, requires robust quantitative methods.

Purpose of the Study:

• To apply the AED tool for quantifying similarities among nonclassical amide bioisosteres, specifically amide-to-1,2,3-triazole.
• To assess the influence of isomerism (cis/trans amides, 1,4/1,5-triazoles) and environmental factors on bioisosterism.
• To compare the AED tool's quantitative approach with traditional qualitative methods like electrostatic potential maps.

Main Methods:

• Utilized the average electron density (AED) tool to calculate and compare electron densities of amide and 1,2,3-triazole moieties.
• Investigated various isomers of amide (cis, trans) and 1,2,3-triazole (1,4, 1,5-disubstituted).
• Incorporated different R groups (methyl, hydrogen, chloro) to simulate diverse chemical environments, including within the drug imatinib.

Main Results:

• The AED tool demonstrated significant similarities between amide and 1,2,3-triazole bioisosteres, with differences not exceeding 4%.
• AED values were transferable across different environments with a maximum difference of 2.6%.
• Isomeric differences were quantified: 1,4/1,5-triazoles differed by 0.52% and cis/trans amides by 1.31% in AED.
• Electrostatic potential maps failed to show similarities between these bioisosteres under varying conditions.

Conclusions:

• The AED tool effectively quantifies amide-to-1,2,3-triazole bioisosterism, extending its utility beyond carboxylic acid analogs.
• This quantitative method accurately evaluates the impact of structural variations and molecular environments on bioisosteric relationships.
• The AED tool provides a powerful, predictive capability for bioisosteric evaluation in drug design, outperforming qualitative methods.