Labradorins with Antibacterial Activity Produced by Pseudomonas sp

Area of Science:

• Natural Product Chemistry
• Microbiology
• Medicinal Chemistry

Background:

• The rise of antibiotic resistance necessitates the discovery of novel antibacterial agents.
• Microorganisms are a historically rich source of clinically relevant antibiotics.
• Renewed interest in microbial natural products is crucial for addressing the urgent need for new drugs.

Purpose of the Study:

• To isolate and characterize novel antibacterial compounds from *Pseudomonas* species.
• To evaluate the antibacterial activity and cytotoxicity of newly discovered alkaloids.
• To determine the potential of these compounds as leads for new antibiotic development.

Main Methods:

• Bioassay-guided isolation of alkaloids from *Pseudomonas* isolates.
• Structure elucidation using Nuclear Magnetic Resonance (NMR) spectroscopy and Mass Spectrometry (MS).
• Confirmation of structures through chemical synthesis.
• Determination of Minimal Inhibitory Concentrations (MIC) against bacterial pathogens.
• Assessment of cytotoxicity using liver (HEP-G2) and T-cell (MT4) lines.

Main Results:

• Two new oxazolylindole alkaloids, labradorins 5 (1) and 6 (2), were isolated and characterized.
• Compounds 1 and 2 exhibited antibacterial activity against *Staphylococcus aureus* and *Acinetobacter baumannii*.
• MIC values for *S. aureus* were 12 μg·mL⁻¹ for compound 1 and 50 μg·mL⁻¹ for compound 2.
• Cytotoxicity (CC₅₀) values for compound 1 were 30 μg·mL⁻¹ (HEP-G2) and 20 μg·mL⁻¹ (MT4); for compound 2, they were >100 μg·mL⁻¹ (HEP-G2) and 20 μg·mL⁻¹ (MT4).

Conclusions:

• Labradorins 5 and 6 possess moderate antibacterial activity against specific pathogens.
• The observed cytotoxicity and limited potency of labradorins 5 and 6 preclude their further development as antibiotics.
• This study highlights the ongoing exploration of microbial natural products for drug discovery, despite challenges with specific isolates.