Synthesis of 19-hydroxyaldosterone and the 3β-hydroxy-5-ENE analog of aldosterone, active mineralocorticoids

Abstract

19-Hydroxyaldosterone ( 20) and the 3β-hydroxy-5-ene analog of aldosterone (HAA) ( 8) were synthesized from 21-acetoxy-4-pregnene-3,20-dion-20-ethylene ketal-18,11β-lactone ( 2) as follows: the double bond was transposed from the 4,5 to the 5,6-position by enol acetylation to 3, followed by sodium borohydride reduction. Further reduction of the resulting lactone 4a with diisobutylaluminum hydride (DIBAH) furnished the 20-ketal of HAA 6, from which free HAA ( 8) and the 18,21-anhydro compound 7 were obtained by acid treatment. The [ 1H]NMR spectrum of 8 in CDCl 3 showed it to be a mixture of two isomeric forms. Correlation with the known aldosterone-γ-etiolactone ( 10) was established by periodate oxidation of HAA to the corresponding etiolactone 9 followed by chromic acid oxidation. The preparation of 20 was next effected in the following manner: the diacetate 4b was converted into the 6β,19-oxido compound 13b by addition of hypobromous acid followed by the hypoiodite reaction of the bromohydrin 11. Mild saponification of 13b lead to the corresponcling diol 13a, and was followed by selective oxidation to the 3-one 14, readily dehydrobrominated to 15a. Reductive ring opening furnished a mixture of the 19,21-diol 16a and its 5-ene isomer 16b, which was directly converted to the diketal 17. Reduction with DIBAH gave the hemiacetal 18, and hydrolysis of the latter 19-hydroxyaldosterone ( 20) as a water-soluble solid, accompanied by the 18,21-anhydro compound 19. 19-Hydroxyaldosterone exists in CHCl 3 and water as a mixture of mainly two isomers. Periodate oxidation furnished the etiolactone 21. Preliminary results indicate that HAA and 19-hydroxyaldosterone are active mineralocorticoids in the Kagawa bioassay and short-circuit current measurements.