Triterpenoide, 5. Synthese und Strukturaufklärung einiger neuer 18α-Oleanolsäurederivate

Triterpenoids, 5. — Synthesis and Structure Elucidation of Some New 18α-Oleanolic Acid Derivatives On treatment with hydrogen bromide, 3β-acetoxy-11-oxoolean-12-en-28-oic acid methyl ester (1) affords the expected 18α-diastereomer 2 and the unknown 3-isopropyl-11-oxo-4-nor-18α-oleana-3(5),12-dien-28-oic acid methyl ester (3) as product of a Wagner-Meerwein rearrangement accompanied by the migration of the new introduced exocyclic double bond. Alkaline hydrolysis of 2 gives the known methyl ester 5 together with the new 3β,11-dihydroxy-12-oxooleana-9(11),13(18)-dien-28-oic acid methyl ester (4). The byproducts 3 and 4 can also be obtained by treatment of 5 with acetic anhydride (3) or KOH/ethanol (4), respectively. The structure elucidation of 3 and 4 is described. The structure of 4 was confirmed by X-ray analysis.