Aromatic triterpene pristimerin

Dimers are a class of compounds isolated from only seven species of Celastraceae family [8,88]. These triterpene dimers were found to be composed of one quinoid type and one aromatic type of triterpene derived from pristimerin, tingenone and / or their congeners joined together by two ether linkages formed between the two A rings or between the A and B rings. From the methylene chloride soluble portion of a methanolic extract of Maytenus chuchuhuasca, four dimeric compounds were isolated by Shirota et al. [88]. 

Compound (90) showed a molecular formula of C60H80O9, determined by HRFAB-MS. The H and 13C NMR spectra of (90) showed that two pristimerin-type triterpene units composed it, one in the quinoid form and the other in the aromatic form. The units were different that those from scutidin aA [89] and xuxuarine Ep [90]. From the spectroscopic data, it... 

Compounds (91), (92) and (93) had an identical molecular formula C58H74O8, which was established by HRFAB-MS. The NMR spectral data, which were similar to those of cangorosin B [7], suggested that each consisted of two different types of triterpene units, tingenone and pristimerin, one in the quinoid form and the other in the aromatic form. The stereochemistry was confirmed by means of ROES Y and CD spectral studies. The FAB-MS data enabled to determine whether the pristimerin and the tingenone type triterpene were in the quinoid form or in the aromatic form. Considering the spectroscopic evidences, the structures of (91), (92) and (93) were assigned to xuxuarines Fp, Ga and Gp respectively, Fig. (49). 

Compound (94) has a molecular formula CeoHgoOg, based on HRFASMS analysis and its 13C-NMR spectrum. According to the data obtained from its H and 13C-NMR spectra suggested that (94) was a triterpene dimer composed of two pristimerin-type triterpenes with one subunit in the quinoid form and the other in the aromatic form. Confirmation of the structure was made by analysis of the 2D NMR spectroscopic data. The absolute configuration was determined from its CD spectrum. According to the above data, the authors concluded that (94) was a regioisomer of scutionin aA [89], and it was called scutionin aB, Fig. (50). 

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