Synthesis of Five Known Brassinosteroid Analogs from Hyodeoxycholic Acid and Their Activities as Plant-Growth Regulators

Abstract

Brassinosteroids (BRs) are plant hormones that promote growth in different plant organs and tissues. The structural requirements that these compounds should possess to exhibit this biological activity have been studied. In this work, a series of known BR analogs 5–15, were synthesized starting from hyodeoxycholic acid 4, and maintaining the alkyl side chain as cholic acid or its methyl ester. The growth-promoting effects of brassinolide (1) and synthesized analogs were evaluated by using the rice lamina inclination assay at concentrations ranging from 1 × 10−8–1 × 10−6 M. Our results indicate that in this concentration range the induced bending angle of rice seedlings increases with increasing concentration of BRs. Analysis of the activities, determined at the lowest tested concentration, in terms of BR structures shows that the 2α,3α-dihydroxy-7-oxa-6-ketone moiety existing in brassinolide is required for the plant growing activity of these compounds, as it has been proposed by some structure-activity relationship studies. The effect of compound 8 on cell elongation was assessed by microscopy analysis, and the results indicate that the growth-promoting effect of analog 8 is mainly due to cell elongation of the adaxial sides, instead of an increase on cell number.

Biological Activities and Molecular Docking of Brassinosteroids 24-Norcholane Type Analogs

“…A number of bioassays, such as first bean internode, root growth, and rice lamina inclination have been developed to evaluate the growth-promoting activity of BR derivatives [6,37,45]. In this work, the activity of BR 24-norcholane-type analogs was evaluated using the rice lamina inclination test because of its specificity and high sensitivity for BL and related compounds [37,45,46]. Figure 2 shows some typical results obtained for BL, which were used as positive control, and the more active BRs analog (3 and 6) and the unresolved epimeric mixture (3/4).…”

“…The biological activity of the compounds was evaluated by the rice lamina inclination test [64,65], according to a previously described procedure [37] and using a Zafiro cultivar (Oryza sativa) provided by the Institute of Agricultural Research (INIA-Quilamapu-Chile). After soaking rice seeds in sterile distilled water for 24 h, the seeds were selected and cultivated at 22 • C in a plant growing chamber under a photoperiod of light (16 h)/darkness (8 h) in pots with soil and plenty of water.…”

“…One of these has been focused on the introduction of structural changes in the side alkyl chain but keeping common patterns of organic functions in the A/B rings and cis-trans fusion between them. In this way, BRs analogs with shorter side chains [19][20][21][22] and/or including a variety of substituents [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] have been reported. The biological activity of these synthetic BRs analogs seems to depend on the spatial distribution of oxygen atoms instead of the presence or absence of one specific functional group in the molecule [11,18], and consequently some new SAR have been proposed [40][41][42].…”

Synthesis and Structural Determination of New Brassinosteroid 24-Nor-5α-Cholane Type Analogs

“…In recent decades, much effort has been dedicated to the synthesis of new BRs analogs in which common patterns of organic functions in the A/B rings and cis-trans fusion between them are kept intact, but with important structural changes in the side chain. For example, BRs analogs with shorter side chains [10][11][12][13], spirostanic and furostanic [14][15][16][17][18][19][20][21], aromatic and cyclic substituents [22][23][24][25][26][27], esters and carboxylic acids [24,[28][29][30] have been reported. Despite these changes, these analogs have presented very important biological activity.…”

Inhibitors of Brassinosteroid Biosynthesis and Signal Transduction

“…To date several dozen of natural BRs are known with BL and CS being the biologically most active ones [72]. In addition, many synthetic BR analogs have been developed, which can be used as less expensive bioactive replacements for BL [305,306,307]. Also fluorescence labeled BR analogs have been developed, which have been useful for investigating endocytosis and endomembrane trafficking of the BR receptor BRI1 [308,309].…”