Synthesis of Spiro-Isoxazolidine Derivatives of Methyl α-Isocostate

Background: In recent decades, natural products are an important source of chemotherapeutics as more than half of the effective cancer drugs can be traced to natural origins. Objective: Moreover, the modification of natural products is one of the most common and fruitful approaches to obtain novel therapeutic agents in medicinal chemistry. Methods: Continuing with a research project based on the support of Moroccan plant resources. we report herein the use of α-isocostic acid extracted in enantiomerically pure form from Dittrichia viscosa as a convenient starting material for the synthesis of new eudesmane derivatives. Results: Novel spiro derivatives with a natural scaffold were prepared. Spiro-isoxazolidine derivatives were generated on the exocyclic double bond adjacent to the ester α,β-unsaturated function by 1,3-dipolar cycloaddition of methyl α-isocostate 1 derived from sesquiterpenic isocostic acid, with nitrones 2. Conclusion: This procedure allowed us to generate enantiomerically pure spiro compounds in one diastereoisomer form with a limited number of steps. These compounds were fully characterized by spectroscopic methods.