RESUMO
A number of fatty acid (palmitic, myristic and lauric) esters (both 3α- and 3ß-isomers) of epibrassinolide has been prepared as reference compounds for metabolic studies. Selective protection of the three of four hydroxyl groups of epibrassinolide was successively performed first as cyclic 22,23-methylboronates and then as 2α-benzyl ethers. α,ß-Inversion of C-3 hydroxyl group was achieved through a consecutive oxidation-reduction reactions or by a nucleophilic substitution of the 3α-mesylates. Treatment of the 3α- and 3ß-alcohols with palmitic, myristinic or lauric acid chlorides gave the corresponding esters. The hydrolysis of 22,23-methylboronates was performed after their transformation into 2-hydroxy-1,3,2-dioxaborolanes using a cation exchange column with DOWEX 50WX8 in NH4(+) form. Hydrogenolysis of the benzyl ethers catalyzed by palladium yielded the target compounds. This article is part of a Special Issue entitled "Synthesis and biological testing of steroid derivatives as inhibitors".
Assuntos
Brassinosteroides/síntese química , Ácidos Graxos/síntese química , Esteroides Heterocíclicos/síntese química , Brassinosteroides/química , Ácidos Graxos/química , Espectroscopia de Ressonância Magnética , Espectrometria de Massas , Oxirredução , Esteroides Heterocíclicos/químicaRESUMO
Preparation of partially protected brassinosteroids is achieved through the reaction of the source material (24-epicastasterone and 24-epibrassinolide) with diol-specific reagents (2,2-dimethoxypropane and methylboronic acid). The obtained products were shown to be useful synthetic intermediates for further preparation of minor representatives of this class of natural phytohormones (such as 3,24-diepicastasterone and 3-dehydro-24-epibrassinolide).