Brassinosteroids: Synthesis and activity of some fluoro analogues

Three types of 5 alpha-androstane and ergostane analogues of brassinolide, containing a fluorine atom in either the 3 alpha or the 5 alpha positions or in 3 alpha and 5 alpha positions, were prepared using standard operations (reaction of 3 beta-alcohols with (diethylamino)sulfur trifluoride, cleavage of epoxide with HF in py or BF(3)center dot Et(2)O). The 5 alpha-fluorine was found to affect chemical reactivity (e.g., electrophilic addition to the Delta(2)-double bond) as well as physical properties (e.g., NMR, chromatographic behavior) of the products. Cytotoxicity of the products was studied using human normal and cancer cell lines with 28-homocastasterone as positive control and their brassinolide type activity was established using the bean second-internode test with 24-epibrassinolide as standard. The equivalence of F and OH groups was observed in some of the active compounds. The anticancer and the brassinolide-type activity do not correlate with each other: ergostane derivatives were most active in the former test while androstane derivatives were best in the latter.