Structure of Dimeric Compounds Obtained from 3β-Acetoxy-21,22-dioxo-18α,19βH-ursan-28,20β-olide

Abstract

The triterpenoid α-diketone with oxabicyclo[2.2.2]octane system in the ring E (3β-acetoxy-21,22-dioxo-18α,19βH-ursan-28,20β-olide (I)) gives isopropylidenedioxy derivative II and dimeric compounds V and IX when submitted to chromatography on silica gel in the presence of acetone. Compounds V and IX were reduced with hydride to hydroxy derivatives VI, X, and XI; on reaction with diazomethane they gave dimeric compounds with spiroepoxide group at the position 21 (compound VII) or 22 (compound XII) which reacted further with diazomethane to give monomeric spiroepoxides VIII, XIII, and XIV. The structure of the compounds obtained was derived from their 1H and 13C NMR, IR, and FAB mass spectra.