NOVEL BRASSINOSTEROID ANALOGS WITH BENZYL FUNCTIONS AT C-22 AND BIOLOGICAL EVALUATIONS IN THE RICE LAMINA INCLINATION TEST

Abstract

Brassinosteroids (BRs) are an important group of polyhydroxylated natural occurring steroidal phytohormones found in the plant kingdom in extremely low amounts. Due to the low concentrations in which these compounds are found, much effort has been dedicated to synthesizing these compounds or their structural analogues using natural and abundant sterols. In this work we report the synthesis of seven new brassinosteroid analogs, obtained from a derivative of dinorcholenic acid 3b-acetate, with benzyl functions at side chain (C-22 positions) and o-p-substituted chlorine and fluorine. Plant growth activities of these compounds were evaluated by Rice Lamina Inclination Test (RLIT). Results show that unsubstituted benzylated compound is less active than the benzoylated analog.  However, the incorporation of a fluorine atom on -para position of aromatic ring, produces a significant increase in biological activity and p-F benzyl analog becomes three times more active than the respective benzoylated compound. Interestingly, substitution in the aromatic ring with F or Cl atom induce important changes on activity, which strongly depends on the substitution position in the benzylated function.