Total Synthesis of LL-A0341β₁

Area of Science:

• Organic chemistry
• Medicinal chemistry
• Molecular biology

Background:

• Cyclic depsipeptide antibiotics represent a crucial class of antimicrobial agents.
• LL-A0341β1 (LL) is a cyclic depsipeptide antibiotic with potential therapeutic applications.
• Understanding the stereochemical requirements and membrane interactions of LL is vital for drug development.

Purpose of the Study:

• To achieve the first total synthesis of the cyclic depsipeptide antibiotic LL-A0341β1 (LL).
• To determine the optimal stereoconfiguration of the β-methyltryptophan (β-MeTrp) residue for LL's antibiotic activity.
• To investigate the interaction of LL with bacterial cell membrane phospholipids.

Main Methods:

• Total synthesis of LL-A0341β1 utilizing Fmoc solid-phase peptide synthesis.
• Preparation and characterization of all four stereoisomers of Fmoc-β-methyltryptophan (Fmoc-β-MeTrp).
• Assay of synthesized LL variants for antibiotic activity and phospholipid interaction studies.

Main Results:

• Successful total synthesis of LL-A0341β1 (LL).
• Identification of the (2R,3R)-β-MeTrp stereoisomer as yielding the most active LL peptide.
• LL's antibiotic activity was significantly inhibited by cardiolipin (CL), but not other phospholipids, indicating specific CL interaction.

Conclusions:

• The stereochemistry of the β-methyltryptophan residue critically influences the antibiotic activity of LL.
• LL-A0341β1 exhibits specific binding to cardiolipin within bacterial membranes.
• These findings provide a foundation for the rational design of novel cyclic depsipeptide antibiotics targeting cardiolipin.