Improved Synthesis of 28-Norbrassinolide

Abstract

An improved procedure for the preparation of 28-norbrassinolide is described. The key step of the whole process was the construction of the side-chain carbon skeleton, which was achieved by successive addition of C₂₃–C₂₄ and C₂₅–C₂₇ fragments to 22C-steroidal aldehyde via the Normant reaction and Claisen rearrangement. The method affords the title compound in 16% overall yield from stigmasterol and represents a significant improvement over literature procedures.

Keywords:

• Brassinosteroids
• Claisen rearrangement
• 28-norbrassinolide
• Normant reaction

ACKNOWLEDGMENT

The authors are indebted to the International Science and Technology Center (Project No. 1332) for financial support of this research.