Spinosyn g: proof of structure by semisynthesis

Area of Science:

• Natural Product Chemistry
• Organic Synthesis
• Insecticide Development

Background:

• Spinosyn G, a minor component of the insecticide spinosad, was previously identified with an uncertain structure.
• Tentative structural assignments were based on NMR data, but isomers could not be definitively excluded.

Purpose of the Study:

• To unambiguously synthesize spinosyn G (3) and its isomer (4).
• To definitively establish the correct structure of the natural product spinosyn G.
• To develop novel synthetic methodologies for spinosyn derivatives.

Main Methods:

• Synthesis of compound 4 involved oxidative deamination of spinosyn A to a ketone, followed by stereoselective reduction and nitrogen incorporation.
• Synthesis of compound 3 utilized coupling of spinosyn A pseudoaglycone with a protected dihydropyran derivative.
• Purification and characterization of synthesized compounds using spectroscopic methods.

Main Results:

• Compound 3 was synthesized and confirmed to be identical to the natural product spinosyn G.
• Compound 4 was synthesized through a novel multi-step process from spinosyn A.
• The synthesis provided unambiguous proof of structure for both isomers.

Conclusions:

• The structure of spinosyn G was definitively confirmed as 5'-epispinosyn A (3).
• Novel synthetic routes were established for spinosyn derivatives, including a unique oxidative deamination and stereoselective reduction sequence.
• This work provides essential chemical tools for further research on spinosyns and their applications.