Synthesis of hexadeuterated 23-dehydroxybrassinosteroids.

Two hexadeuterated brassinosteroids (BS) ([26,27-2H(6)]-23-dehydroxycastasterone and [26,27-2H(6)]-cathasterone) containing a hydroxy group at C(22) instead of the 22R,23R-diol function characteristic for most compounds of this class were prepared for biochemical studies. The corresponding non-deuterated compounds are considered intermediates in brassinolide biosynthesis. The carbon skeleton of the side chain with proper stereochemistry at C(24) was prepared from commercially available (2R)-3-hydroxy-2-methylpropanoate. This low molecular fragment was coupled to the tetracyclic steroidal fragment through the reaction of the appropriate sulfone with C(22) aldehyde. Formation of the necessary configuration of the 22-hydroxy group was achieved by hydride reduction of the corresponding ketone. Deuterium atoms at C(26) and C(27) originated from [2H(3)]methyl iodide used for alkylation of the intermediate sulfone.