Different pathways for the deoxygenation of the A-ring of natural triterpene compounds

Abstract

Some deoxygenation pathways were tested to remove the hydroxyl groups of the natural triterpenes oleanolic acid and maslinic acid to obtain a practical starting material for the semisynthesis of other interesting organic synthons. Different deoxygenation processes were carried out starting from these triterpenic acids or from several derivatives such as methyl esters and epoxy derivatives. The hydroxyl groups were transformed into some intermediate compounds including xanthyl, thiocarbonyl or tosyl derivatives. The opening of the oxirane ring between C-2 and C-3 was also achieved through different methods using deoxygenating reagents such as Me₃SiCl/NaI, WCl₄/n-BuLi and Cp₂TiCl.

Keywords:

• oleanolic acid
• maslinic acid
• triterpene
• deoxygenation

Acknowledgements

This work was supported by a grant from the Comisión Interministerial de Ciencia y Tecnologia and by a project from the Ministerio de Educacion y Cultura. We thank David Nesbitt for reviewing the article for English language.