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

Natural brassinosteroids possess a 22R, 23R configuration that appears essential for biological activity. It is, therefore, interesting to elucidate if the activity of brassinosteroids with a short side chain depends on the C22 configuration. Herein, we describe the synthesis of new brassinosteroids analogs with 24-norcholane type of side chain and R configuration at C22. The initial reaction is the dihydroxylation of a terminal olefin that leads to S/R epimers. Three different methods were tested in order to evaluate the obtained S/R ratio and the reaction yields. The results indicate that Upjohn dihydroxylation is the most selective reaction giving a 1.0:0.24 S/R ratio, whereas a Sharpless reaction leads to a mixture of 1.0:0.90 S/R with 95% yield. Using the latter mixture and following a previous reported method, benzoylated derivatives and both S and R brassinosteroids analogs were synthesized. All synthesized compounds were completely characterized by NMR spectroscopy, and HRMS of new compounds are also given. In conclusion, a synthetic route for preparation of new analogs of brassinosteroids of 24-norcholane type and R configuration at C22 were described. It is expected that this will help to elucidate if a configuration at C22 is a structural requirement for hormonal growth activity in plants.

Effect of combination of cisplatin with brassinosteroids on the growth of cancer cells

In this work, the effect of brassinosteroids on the antitumor activity of classical cytostatic cisplatin in tumor cell lines A549 (human lung carcinoma) and Hep G2 (human hepatocellular carcinoma) was evaluated. Natural brassinosteroids 24-epibrassinolide and 28-homocastasterone, as well as their synthetic analogues (22S,23S)-24-epibrassinolide and (22S,23S)-28-homocastasterone were used. All four compounds with cisplatin inhibited the growth of cancer cells more effectively than cisplatin alone. Combinations with low concentrations of synthetic brassinosteroids were more effecient, and at 1 µM decreased the IC50 of cisplatin by almost 2 times. The results suggest a possible benefit of combinations of classical antitumor drugs with brassinosteroids in overcoming the negative effects of chemotherapy by reducing their effective doses.

Synthesis and Mass Spectral Fragmentation Patterns of Brassinolide Early Biosynthetic Precursors Labeled at C-26

New analogues of brassinolide biosynthetic precursors with three deuterium atoms at non-exchangeable positions have been synthesized to be used as standards for quantification of natural brassinosteroids by liquid chromatography-mass spectrometry. [26-2H3](22 R,23 R,24 S)-22,23-Dihydroxy-6β-methoxy-24-methyl-3α,5-cyclo-5α-cholestane was used as a starting material for the preparation of campestane derivatives having a 22 R,23 R-diol functionality and either a hydroxy or keto group at C-3 and labeled at C-26. The mass spectrometric behavior of the newly synthesized compounds has been studied.