9α-hydroxylation of 25-fluoroponasterone a diacetonide in lithium-ammonia solution

Abstract

25-FluoroponasteroneA diacetonide reacted with lithium in liquid ammonia to give 25-fluoro-9α,20-dihydroxyecdysone diacetonide whose hydrolysis afforded 25-fluoro-9α,20-dihydroxyecdysone 20,22-acetonide. Nonfluorinated analog of the latter was isolated previously from Silene italica ssp. nemoralis.Lithium in liquid ammonia is widely used for selective reduction of double bond in cyclic conjugated enones, including those belonging to the steroid series [1,2]. Analogous reactions with ecdysteroids have been poorly studied; however, it is known [3,4] that the reaction of 20-hydroxyecdysone and its acetonides with lithium in liquid ammonia and subsequent treatment with ammonium chloride and evaporation of ammonia on exposure to air gives ecdysteroids with an ether bridge in the C ring instead of expected 7,8-dihydro derivatives. For instance, 20-hydroxyecdysone diacetonide I is thus converted into oxetane II and 14α-hydroperoxide III [3] (Scheme 1).It may be expected that 25-deoxy-25-fluoro-20-hydroxyecdysone diacetonide (IV) (25-fluoroponasterone A diacetonide [5]) could be converted under analogous