The homalium alkaloids: isolation, synthesis, and absolute configuration assignment.

Area of Science:

• Natural Product Chemistry
• Organic Synthesis
• Medicinal Chemistry

Background:

• Homalium alkaloids, including (-)-homaline, (-)-hopromine, (-)-hoprominol, and (-)-hopromalinol, are natural products characterized by bis-ζ-azalactam structures.
• These alkaloids were first isolated from Homalium pronyense Guillaum in New Caledonia.
• Structural variations among these alkaloids are limited to the side chains on their lactam rings.

Purpose of the Study:

• To establish a highly efficient and versatile synthetic strategy for the homalium alkaloid family.
• To enable the synthesis of both racemic and enantiopure forms of these bis-ζ-azalactam natural products.
• To explore stereoselective synthetic routes for complex natural products.

Main Methods:

• The primary synthetic strategy involves the conjugate addition of an enantiopure lithium amide reagent to an α,β-unsaturated ester.
• This conjugate addition serves as the key stereodefining step in the overall synthesis.
• The methodology has been successfully applied to the synthesis of all four known homalium alkaloids and their stereoisomers.

Main Results:

• A versatile and high-yielding synthetic route for homalium alkaloids has been developed.
• The conjugate addition strategy allows for precise control over stereochemistry.
• This approach has proven effective for synthesizing the entire family of homalium alkaloids and their related stereoisomers.

Conclusions:

• The conjugate addition of enantiopure lithium amide reagents represents a powerful and adaptable method for synthesizing bis-ζ-azalactam natural products.
• This methodology facilitates access to diverse homalium alkaloids and their stereoisomers.
• The developed strategy advances the field of natural product synthesis and medicinal chemistry.