Synthesis of New Brassinosteroid 24-Norcholane Type Analogs Conjugated in C-3 with Benzoate Groups.

Karoll Ferrer,Mauricio Cuellar,Katy Díaz,Miroslav Kvasnica,Andrés F Olea,Luis Espinoza

doi:10.3390/molecules26041173

Abstract

The metabolism of brassinosteroid leads to structural modifications in the ring skeleton or the side alkyl chain. The esterification and glycosylation at C-3 are the most common metabolic pathways, and it has been suggested that conjugate brassinosteroids are less active or inactive. In this way, plants regulate the content of active brassinosteroids. In this work, the synthesis of brassinosteroid 24-norcholane type analogs conjugated at C-3 with benzoate groups, carrying electron donor and electron attractant substituents on the aromatic ring, is described. Additionally, their growth-promoting activities were evaluated using the Rice Lamina Inclination Test (RLIT) and compared with that exhibited by brassinolide (used as positive control) and non-conjugated analogs. The results indicate that at the lowest tested concentrations (10−8–10−7 M), all analogs conjugated at C-3 exhibit similar or higher activities than brassinolide, and the diasteroisomers with S configuration at C-22 are the more active ones. Increasing concentration (10−6 M) reduces the biological activities of analogs as compared to brassinolide.

Highlights

Brassinosteroids (BRs) are an important group of polyhydroxylated sterol plant growth regulators in multiple developmental processes, at nanomolar to micromolar concentration, including cell division, cell elongation, vascular differentiation, reproductive development, and modulation of gene expression [1]
The results indicate that at the lowest tested concentrations (10−8–10−7 M), all analogs conjugated at C-3 exhibit similar or higher activities than brassinolide, and the diasteroisomers with S configuration at C-22 are the more active ones
To obtain the new BR analogs conjugated in C-3 (18a, 18b, 19a, and 19b, Figure 2), the synthetic strategy shown in Scheme 1 was developed

Summary

Introduction

Brassinosteroids (BRs) are an important group of polyhydroxylated sterol plant growth regulators in multiple developmental processes, at nanomolar to micromolar concentration, including cell division, cell elongation, vascular differentiation, reproductive development, and modulation of gene expression [1]. BRs influence various other developmental processes such as the germination of seeds, rhizogenesis, flowering, senescence, abscission, and maturation. They confer resistance to plants against various abiotic and biotic stresses [2,3,4,5]. The other eleven conjugated metabolites are formed by glycosylation at C-2, C-3, C-23, C-25, or C-26 [8,13,14,15,16,17,18,19,20] The natural conjugates 3, 4 (Figure 1) were synthesized from 24-epibrassinolide (2) [21]

Methods

Results

Conclusion