Orifluoroacetylation and dehydration of 20-hydroxyecdysone acetonides. Synthesis of stachisterone B

Orifluoroacetylation of the 25(OH)-group with subsequent dehydration of the 14(OH)-group takes place in the reaction of 20-hydroxyecdysone 20,22-acetonide and 2,3:20,22-diacetonide with trifluoroacetic anhydride in the presence of pyridine. Dehydration of the 14(OH)-group gives rise to stachisterone B derivatives, which are hydrolyzed to give the phytoecdysteroid stachisterone B.     

New method for trimethylsilylation of hydroxy-containing compounds. Synthesis of persilylated ecdysteroids and carbohydrates

A new method was developed for trimethylsilylation of alcohols by the reactions with (trifluoromethyl)trimethylsilane in the presence of tetrabutylammonium fluoride. The reactions of ecdysteroids (20-hydroxyecdysone, its 20,22-mono- and 2,3:20,22-diacetonides, and polypodine B) and carbohydrates (D-gluco-, D-galacto-, and D-xylopyranoses) afforded the corresponding persilylated derivatives.     

15-O-Deacetylrhaposerin and rhaserin -- new components of a lactone mixture from Rhaponticum serratuloides

As part of our continuing studies of lactones from the aerial part of the plant Rhaponticum serratuloides, 15-O-deacetylrhaposerin and new guaianolide called rhaserin were isolated along with the well-known loliolide. The configuration of the C(17) asymmetric center in 15-O-deacetylrhaposerin was established by X-ray diffraction analysis. The molecular structure of rhaserin was determined based on the data from ¹H and ¹³C NMR spectroscopy (including 2D NMR spectroscopy) of this lactone and its 4,15-O-isopropylidene derivative.     

Migration of the O-acetyl group in the acetonation of guaianolide rhaposerin

Acetonation of rhaposerin is accompanied by migration of the O-acetyl group. Acetonation of 15-O-deacetylrhaposerin afforded isomeric O-isopropylidene derivatives containing five- and six-membered rings.     

Novel ecdysteroid analogs with oxygen-containing heterocycles in the steroid skeleton

The reaction of ecdysteroids (20-hydroxyecdysone and its acetonides) with lithium in liquid ammonia gave novel analogs with an oxetane 9α,14α-oxacycle in the steroid skeleton. In aqueous alcohol solution the 9,14-oxa analogs rearrange to the more stable 9α,13α-oxa analogs through a 1,2-migration of the 18-Me group from the C-13 to the C-14 atom. Dedicated to Academician B. A. Trofimov in his 70^th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1339–1355, September, 2008.