Structure-Activity Relationship and Crystallographic Study of New Monobactams

Area of Science:

• Medicinal Chemistry
• Structural Biology
• Microbiology

Background:

• Monobactams are β-lactam antibiotics with a unique monocyclic structure.
• They exhibit resistance to metallo-β-lactamases, offering a therapeutic advantage.
• Aztreonam is a key monobactam antibiotic.

Purpose of the Study:

• To conduct an in silico structure-activity relationship (SAR) investigation of aztreonam-related monobactams.
• To synthesize and evaluate novel monobactam derivatives for penicillin-binding protein (PBP) inhibition and antibacterial activity.
• To explore potential therapeutic applications against resistant bacterial strains.

Main Methods:

• In silico SAR investigation and focused library synthesis of monobactam derivatives.
• Enzymatic assays for PBP inhibition and antibacterial activity testing.
• Crystallization of ten compounds, including aztreonam, with PBP1b from Streptococcus pneumoniae.
• 2D similarity search for identifying potent inhibitors against specific bacterial species.

Main Results:

• Potent PBP1b inhibitors were developed, though enzymatic potency did not always correlate with antibacterial activity.
• Several derivatives demonstrated activity against Staphylococcus aureus, a typically resistant bacterium.
• Inhibitors effective against Escherichia coli, Klebsiella pneumoniae, and Acinetobacter baumannii were identified.
• Crystal structures revealed novel binding interactions, including a halogen bond with a conserved threonine residue.

Conclusions:

• Aztreonam-related monobactams can be optimized for potent PBP inhibition.
• Novel derivatives show promise against challenging Gram-negative pathogens and Staphylococcus aureus.
• Understanding unique binding interactions, like halogen bonds, can guide the development of next-generation monobactam antibiotics.