Brassinolide analogs, synthesis

Synthesis of Brassinosteroids. USDA scientists were the first to report the synthesis of various brassinolide analogs, some of which were later found to be present in plants. This work led to, in addition to identifying new brassinosteroids from plants, establishing the structure—activity relationship of brassinosteroids. The reasons for undertaking the synthesis were (a) to ascertain that brassinolide was indeed the active ingredient of the pollen, (b) to determine structure—activity relationships, and (c) to provide quantities of the active ingredient(s) sufficient for biological studies and field work. 

Subsequent to our use of butenolide anions in aldol reactions to construct sidechains of steroids, two groups have reported a similar method for synthesis of brassinolide or its analogs. Kametani and co-workers employed the dianion of 3-isopropyltetronic acid which was reacted with a 20-keto steroid. The aldol product was dehydrated and the product hydrogenated to furnish the brassinolide sidechain (28,29). Zhou and Tian have used the reaction of a C-22 aldehyde derived from... 

The discovery of brassinolide by scientists at USDA led to the development of a new group of plant growth substances, termed brassinosteroids, which have the potential for increasing crop yields and biomass. The chapter summarizes the USDA s contributions to brassinosteroids, which include isolation and identification of brassinolide, synthesis of brassinolide and its analogs, and limited biological and field studies on brassinosteroids. An overview of the current data requirements for the registration of brassinosteroids as biochemical pesticides under the Federal Insecticide, Fungicide, and Rodenticide Act is presented. 

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