Chem. Pharm. Bull. 52(6) 739—746 (2004)

compounds from South American medicinal plants, we became interested in medicinal plants belonging to the genus Maytenus (Celastraceae). The plants of this genus are widely used in folk medicine in South America and are rich sources of terpenoids including dihydro-b-agarofuran sesquiterpenes, highly oxidized friedelane triterpenes, and several types of triterpene dimers. Among these, triterpene dimers constitute a rather unique class of compounds that are composed of two quinonemethide derived triterpenes such as pristimerin, tingenone, 22b-hydroxytingenone, and/or their congeners, joined by two ether linkages formed between the A rings or between the A and B rings of quinoid and aromatic triterpenes. At present, triterpene dimers have been reported exclusively by two groups of researchers, González et al. and us. A general methodology for elucidating the regioisomeric and stereoisomeric structures of triterpene dimers on the basis of a detailed comparison of Hand C-NMR chemical shifts, detection of NOE (or ROE) correlations in NOESY (ROESY), analysis of retro Diels–Alder type fragmentations in MS spectra, and interpretation of exciton couplings in CD spectra, has previously been established by us. Continued investigations of the triterpene dimers obtained from the Brazilian medicinal plant “xuxuá” (M. chuchuhuasca RAYMOND-HAMET et COLAS) have revealed the existence of additional minor triterpene dimers. Although the isolation and purification steps for these are difficult, several efforts during the preparative HPLC stages finally yielded nine triterpene dimers, xuxuarine Fa (1), isoxuxuarine Fa (2; cangorosin B), 7,8-dihydroisoxuxuarine Fa (3), isoxuxuarine Gb (4), 7,8-dihydroisoxuxuarine Ga (5), isoxuxuarine Eb (6), 7a-hydroxyisoxuxuarine Ea (7), 7 ,8 -dihydroxuxuarine Aa (8), and 7 ,8 -dihydroxuxuarine Db (9). June 2004 Chem. Pharm. Bull. 52(6) 739—746 (2004) 739