Synthesis of 2,24-Diepicastasterone and 3,24-Diepicastasterone as Potential Brassinosteroid Metabolites of the Cockroach Periplaneta americana

Investigations of the metabolic conversion of the phytohormone 24-epicastasterone ( 1 ) in the cockroach Periplaneta americana (L.) required the synthesis of 2,24-diepicastasterone ( 4 ), 3,24-diepicastasterone ( 7b ) and 2-dehydro-3,24-diepicastasterone ( 9 ) as reference standards. 2,24-Diepicastasterone ( 4 ) was synthesized from 2α,3α-epoxy derivative 2 as well as from the 2β,3β-epoxy-22,23-diol 3 by acid-catalyzed water addition to the epoxy function leading to the desired 2β,3α- trans functionality. 3,24-Diepicastasterone ( 7b ) was prepared by NaBH 4 -reduction of the 3-oxo derivative 6 . Upon deprotection conditions from the ketol acetonides 6 and 8 in both cases 2-dehydro-3,24-diepicastasterone ( 9 ) was obtained. The structure of 2,24-diepicastasterone ( 4 ) was confirmed by X-ray analysis.