The diol system in the side-chain of ecdysteroids reacts with phenylboronic acid under formation of cyclic esters. Phenylboronates of ecdysteroids I - V were prepared. The regiospecific reaction course was confirmed by 1H NMR spectra of the products. The reaction conditions were studied for 20-hydroxyecdysone (I). The phenylboronate can be prepared in high yields even in aqueous solutions. The liberation of the ecdysteroid I from the corresponding phenylboronate VI was performed using various reagents - diols or carboxylic acids.
Regioselective Synthesis of 20-Hydroxyecdysone Glycosides. -The biologically interesting 2-, 3-, 22-and 25-β-D-glucopyranosides of 20-hydroxyecdysone (I) are regioselectively synthesized. A combination of protection of the 1,2-diol group as phenylboronate and of the hydroxy groups as acetates is used. -(PIS, J.; HYKL, J.; BUDESINSKY, M.; HARMATHA, J.; Tetrahedron 50 (1994) 32, 9679-9690; Inst. Org. Chem. Biochem., Acad. Sci. Czech Rep., 166 10 Prague, Czech Rep.; EN)
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