Synthesis and Structural Characterization of Three Novel 23,24-Dinorcholane Brassinosteroid Analogs Bearing Benzoate Groups and Halogen Substituents

Brassinosteroids are an important family of plant hormones involved in various processes of plant growth and development. They also play a crucial role in plant stress responses, improving tolerance to abiotic factors such as temperature extremes, drought, and salinity, and contributing to resistance against biotic stresses. This work describes the synthesis and full structural characterization of three new 23,24-dinorcholane-type brassinosteroid analogs bearing benzoate groups at C-22 and substituted with fluorine and chlorine atoms, while maintaining the structural features of the A/B rings present in active natural brassinosteroids such as castasterone. The synthesis was achieved in two steps: an esterification reaction with acyl chlorides, followed by a stereospecific Sharpless dihydroxylation. Both reactions proceeded with good yields.