Total Synthesis of Aquatolide

Area of Science:

• Organic Chemistry
• Natural Product Synthesis
• Photochemistry

Background:

• Sesquiterpene lactones are a diverse class of natural products with significant biological activities.
• Aquatolide is a complex sesquiterpene lactone whose total synthesis presents a considerable synthetic challenge.
• Developing efficient synthetic routes to complex natural products is crucial for medicinal chemistry and drug discovery.

Purpose of the Study:

• To achieve the first total synthesis of the sesquiterpene lactone aquatolide.
• To explore the utility of intramolecular [2 + 2]-photocycloaddition in constructing complex ring systems.
• To establish a robust synthetic pathway amenable to further derivatization and analogue synthesis.

Main Methods:

• The synthesis employed a strategic intramolecular [2 + 2]-photocycloaddition of an allene onto an α,β-unsaturated δ-lactone as the key ring-forming step.
• Lactone ring closure was achieved via an intramolecular Horner-Wadsworth-Emmons reaction.
• Construction of the eight-membered ring was accomplished using an intramolecular Mukaiyama-type aldol reaction.
• Racemic aquatolide was resolved into its enantiomers using preparative High-Performance Liquid Chromatography (HPLC).

Main Results:

• Successful total synthesis of racemic aquatolide was accomplished.
• The [2 + 2]-photocycloaddition proved effective for constructing the core structure.
• The sequence of intramolecular reactions efficiently assembled the complex polycyclic framework.
• Preparative HPLC enabled the separation of enantiomers, yielding pure racemic aquatolide.

Conclusions:

• The total synthesis of aquatolide demonstrates the power of modern synthetic methodologies, particularly photochemical cycloadditions.
• This work provides a valuable synthetic route to aquatolide and related compounds, facilitating further biological evaluation.
• The developed strategy offers a blueprint for the synthesis of other complex sesquiterpene lactones.