Convergent Total Synthesis of Kalmanol

Area of Science:

• Organic Chemistry
• Natural Product Synthesis

Background:

• Kalmane-type grayanoids are a class of natural products.
• Kalmanol is the first isolated kalmane-type grayanoid.
• It possesses a unique, highly oxidized tetracyclic carbon skeleton with 9 contiguous stereocenters.

Purpose of the Study:

• To achieve the first total synthesis of Kalmanol.
• To develop an efficient and asymmetric synthetic route.
• To explore a modular synthetic strategy for complex natural products.

Main Methods:

• Modular synthetic strategy.
• Convergent synthesis of a tetracyclic intermediate via Grignard reaction.
• Ring-closing metathesis of enantiomerically enriched fragments.
• Late-stage stereo- and regioselective oxidations for polyhydroxy group introduction.

Main Results:

• Successful and efficient total synthesis of Kalmanol (1).
• Synthesis completed in 16 steps from known compounds (20 steps from commercial materials).
• Established a highly oxidized 5/8/5/5 tetracyclic carbon skeleton with 9 stereocenters.

Conclusions:

• The developed synthetic strategy is effective for constructing complex kalmane-type grayanoids.
• This work provides access to Kalmanol and potentially related analogs.
• Highlights the power of modern synthetic methodologies in natural product chemistry.