OPENING OF THE MACROCYCLIC RING IN 5,10-8,9-DISECOSTEROIDS (= STEROKLASTANES)

Catalytic hydrogenation of the DELTA-3-unsaturated (9R, 10R)- and (9S, 10S)-epoxyenol lactones 3a,b and 4a,b. respectively, affords, in addition to the expected saturated epoxylactones 5a, b and 7a, b, also open-chain products. i.e. the diastereoisomeric (9R, 10R)- and (9S, 10S)-9,10-epoxy-8-oxo-4,5-secosteroklastan-5-oic acids 6a, b and 8a, b. Alkaline hydrolysis of the lactone ring of compounds 5 and 7 and subsequent acetylation of the corresponding hydroxy derivatives give as the major products the open-chain, diastereoisomeric (9R, 10R)- and (9S, 10S)-4-acetoxy-9,10-epoxy-methyl esters 9a, b and 11a, b, respectively, and, but only in the androstane series, the tetrahydropyran derivatives 10a and 12a, as the minor components.