Synthesis and biological activity of ring-A difluorinated brassinosteroids

In this paper we report the synthesis of four ring-A difluorinated analogs of brassinosteroids. The bioactivity of these new compounds was evaluated using the rice lamina inclination test. The results show that one of these analogs elicits a bioactivity comparable to that of 28-homocastasterone, a highly active natural brassinosteroid. This finding suggests that both hydroxyls at C-2 and C-3 in active brassinosteroids are involved as hydrogen bond acceptors in their interactions with the cellular receptor.

► Ring-A difluorinated brassinosteroids analogs were synthesised for the first time.
► Fluorination at C-2 and C-3 leads to a highly active compound.
► Difluorination at C-3 yields a completely inactive analog.