Extractives of Australian timbers. XII. Minor sapogenins of Castanospermum australe (Leguminosae). A stereospecific synthesis of methyl 2β,3β-Dihydroxyolean-12-en-28-oate

Abstract

The sapogenin mixture prepared from the extract of the wood of Castanospermum australe Cunn. & Fras. has been shown to contain the known triterpenes 2β,3β-dihydroxyolean-12-en-28-oic acid and 3β- hydroxyolean-12-ene-23,28-dioic acid; the latter also occurs as the free triterpene. The identity of methyl 2β,3β-dihydroxyolean-12-en-28- oic acid has been established by a high yielding stereospecific synthesis starting from methyl crategolate; this synthesis at the same time confirmed the revised configurations assigned from N.M.R. evidence¹ to the hydroxy groups in the two cis-2,3-diols of the isomeric methyl 2,3-dihydroxyolean-12-en-28-oates. The identity of methyl 3β- hydroxyolean-12-ene-23,28-dioate has been established by comparison with a specimen prepared by an unambiguous synthesis from dimethyl medicagenate.