Studies on the Constituents of Asclepiadaceae Plants. XXXVI. Component of Marsdenia tomentosa DECNE : Structure of Tomentonin, Tomentodin, and Dehydrotomentosin and Difference in the Reactivity between Utendin and Tomentogenin Diesters on Mild Alkaline Hydrolysis

Abstract

Three new polyoxypregnane derivatives, tomentonin (12β-O-dihydrotigloyl-20-O-acetyltomentogenin), tomentodin (12β-O-cinnamoyl-20-O-acetyltomentogenin), and dehydrotomentosin (12β-O-tigloyl-20-O-acetylutendin), were isolated from the stem of Marsdenia tomentosa DECNE. Dehydrotomentosin underwent an internal acyl migration from C-12β-OH to C-20-OH on mild alkaline hydrolysis to afford a monoester, but tomentonin and tomentodin did not. The remarkable difference in the reactivity between toementogenin and utendin diesters on this condition was discussed. Tomentonin is the first example of a tomentogenin derivative with an ester linking of dihydrotiglic acid or 2-methylbutyric acid isolated from Asclepiadaceae plants.