Triterpenes of Japanese White Birch and the Configuration at C-24 of Ocotillol II and Its Related Compounds

抄録

A new triterpene named now betulafolientriol oxide I (IV), mp 237-240°, [α]²²_D+2.6° (CHCl₃), was isolated from the leaves of Betula platyphylla SUKATCHEV var. japonica HARA in addition to betulafolientriol (I), hydroxyhopanone (II), and dammar-24-ene-12β, 20(S)-diol-3-one (III). The isolation of III was the first example of its occurrence in nature. The chemical and spectrometric investigation of IV and its derivatives showed that IV is a derivative of I, having a modified side chain of a substituted tetrahydrofuran ring. The oxidation of betulafolientriol (I) with perbenzoic acid gave betulafolientriol oxide I (IV) along with its C-24-epimer (XIV). The structure of XIV including its all stereochemistries was clarified by the derivation of XIV from 25-bromo-20 (S), 24 (S)-epoxy-dammarane-3α, 12β-diol (XV). Accordingly, the structure of betulafolientriol oxide I (IV) was established as 20 (S), 24 (R)-epoxy-dammarane-3α, 12β, 25-triol. The achievement of chemical conversion of IV into ocotillone II (XII) showed that the stereochemistry at C-24 of ocotillol II (VIII) and its derivatives is expressed in term of (R) configuration (the methyl at C-20/ the hydroxyisopropyl at C-24 : trans).