Brassinosteroid analogs

Table L Biological Activity of Selected Brassinosteroid Analogs in the Rice Lamina Inclination Test...

However, some side chain epimers like 24-epibrassinolide 2, trisepi-brassinolide and (22S,23S)-homobrassinolide 3 show remarkable activity and are therefore used widely for biological experiments. Furthermore several structural analogs with a shortened side chain moiety are active in specific test systems (7). Thus, structure-activity relationships of brassinosteroids are a field of continual development and require further examination. 

For an interaction to occur with a putative brassinosteroid receptor, both stereospeciflcally arranged vicinal diol functions in the ring A, as well as in the side chain, can be assumed as important. In our synthetic program for modified brassinosteroids, we were especially interested in new types of analogs with the ring A- and B-seco structure to study the influence of the geometry of this molecular adaptation on biological activity. 

Sucrose Absorption by Vascular Bundles. Sucrose uptake into 2-4 mm long pieces of vascular bundles isolated from the petiole of Cyclamen persicum was described in detail in (5). Briefly, the tissue material was preincubated (30 min) with brassinosteroids or related compounds, which were also present during the following incubation with 1 mM 1AC-labelled sucrose (30 min). All solutions contained 1 mM CaSO, 1 mM KC1 and 10 mM morpholinoethanesulfonic acid and were adjusted with NaOH to pH 5.0. After a 5-min-washing procedure and extraction in methanol the uptake rate for sucrose was determined analogously to the experiments with leaves. 

Table I Water content of transformed tobacco callus-cultures grown on brassinosteroid-containing medium for 3 weeks. The brassinosteroid employed (BR-1) is a synthetic 225,235,245-analog of the naturally occurring brassinolide. The concentration of BR-1 was varied from IO 10 M to KT6 M CV <5%...

We developed several methods for construction of the side chain and the A/B ring of brassinosteroids, and synthesized more than fifty analogs (6). In order to obtain the structure-activity relationship, those analogs were subjected to bioassay in the rice-lamina inclination (7), Raphanus, and tomato tests (5). In general, die structural... 

The discovery of brassinolide by scientists at USDA led to the development of a new group of plant growth substances, termed brassinosteroids, which have the potential for increasing crop yields and biomass. The chapter summarizes the USDA s contributions to brassinosteroids, which include isolation and identification of brassinolide, synthesis of brassinolide and its analogs, and limited biological and field studies on brassinosteroids. An overview of the current data requirements for the registration of brassinosteroids as biochemical pesticides under the Federal Insecticide, Fungicide, and Rodenticide Act is presented. 

Synthesis of Brassinosteroids. USDA scientists were the first to report the synthesis of various brassinolide analogs, some of which were later found to be present in plants. This work led to, in addition to identifying new brassinosteroids from plants, establishing the structure—activity relationship of brassinosteroids. The reasons for undertaking the synthesis were (a) to ascertain that brassinolide was indeed the active ingredient of the pollen, (b) to determine structure—activity relationships, and (c) to provide quantities of the active ingredient(s) sufficient for biological studies and field work. 

Our synthetic work on brassinosteroids showed that the stereochemistry in the steroid molecule is very important to retain the biological activity. We found that, of the 13 asymmetric centers in the molecule, only 3 asymmetric centers (at C-22, C-23, and C-24) can be altered. On the basis of this information, we prepared brassinolide and all the analogs (23) by using the general synthetic scheme (Figure 3). Additionally, we prepared compounds having different substituents (H, CH3, and C2H5) at C-24 (2, 7). 

The brassinosteroids are essential for many growth and development processes in plants. However, relatively little is known about the effects of BRs and their synthetic analogs on animal cells [89]. It has been reported that cultured hybridoma mouse cells treated with 24-epiBL exhibit certain interesting effects, including an increase in the mitochondrial membrane potential, a decrease in the abundance of intracellular antibodies, an increase in the fraction of the cells in the Gq/Gi phase, and a corresponding decrease in the proportion of cells in S phase. Moreover, treatment with 24-epiBL at concentrations of 10 and 10 mol/1 significantly increased the density of viable cells relative to controls [90],... 

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