Synthesis of hexadeuterated 23-dehydroxybrassinosteroids

Two hexadeuterated brassinosteroids (BS) ([26, 27- 2 H 6 ]-23-dehydroxycastasterone and [26, 27- 2 H 6 ]-cathasterone) containing a hydroxy group at C 22 instead of the 22 R,23 R-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 (2 R)-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 [ 2 H 3 ]methyl iodide used for alkylation of the intermediate sulfone.