(-)-Cytisine: Access to a stereochemically defined and functionally flexible piperidine scaffold

Area of Science:

• Organic Chemistry
• Synthetic Chemistry
• Medicinal Chemistry

Background:

• Cytisine derivatives are valuable scaffolds in medicinal chemistry.
• Efficient synthetic routes to functionalized piperidines are crucial for drug discovery.
• Exploring novel transformations of natural products like cytisine is of significant interest.

Purpose of the Study:

• To develop an efficient method for C(6)-N(7) cleavage of N-Benzyl cytisine.
• To generate a highly functionalized, enantiomerically pure cis-3,5-disubstituted piperidine core.
• To explore the synthetic utility and diversification potential of the resulting heterocyclic unit.

Main Methods:

• Directed C(6) lithiation, borylation, and oxidation of N-Benzyl cytisine.
• Selective manipulation of N(1), C(3"), and pyridone nitrogen.
• Pyridone core diversification via bromination and iridium-catalyzed C-H borylation.
• Evaluation of boronate-based 1,2-migration for C(6)-N(7) cleavage.

Main Results:

• Achieved efficient C(6)-N(7) cleavage to yield a privileged heterocyclic core.
• Established methods for selective functionalization at multiple positions (N(1), C(3"), pyridone N, C(4")).
• Demonstrated complementary diversification strategies including bromination and C-H activation.
• Identified limitations of boronate-based migration but revealed new pathways for cytisine elaboration.

Conclusions:

• The developed method provides access to a valuable, enantiomerically pure piperidine building block.
• The functionalized core allows for extensive exploration of chemical space.
• New synthetic pathways for cytisine elaboration were uncovered, enhancing its utility in synthesis.