Pristimerin structures

The structure of the methylene quinonoid triterpenoid pristimerin (114) has been confirmed by X-ray analysis. The full details of the crystal structure of the triterpenoid dimethyl ester s-lactone from dammar resin have appeared. ... 

A possible biogenetic route to triterpene quinones with an extra double bond (e.g., netzahualcoyone and derivatives) may involve dehydrogenation and subsequent pristimerin regrouping. Indeed, (Table V) two epimeric di-triterpene quinone ethers umbelatin a and p (118,119) have been isolated from the roots of Rzedowskia tolantonguensis [68]. The structures of pristimerin and netzahualcoyone were ascertained by the standard spectral methods. The H... 

A number of quinonemethides with structures related to pristimerin, tingenone (54) iguesterine (55) and isoiguesterine (56) had been described in these years. All of them are characterized by a conjugated system involving rings A and B, which is named non-extended conjugation, Fig. (30). 

From two Maytenus species collected in Paraguay, two new pristimerin-related compounds were isolated, 15-a-hydroxypristimerin (57), from M. scutioides [72], and 15-a-hydroxy-21-keto-pristimerin (58) from M. catingarum [73], the last one isolated in our laboratory. The structure of compound (57) was elucidated by spectroscopic means, including MS, h and 13C - NMR, and H - 13C heteronuclear... 

Bearing a 7-oxoquinonemethide structure, but with a skeleton related to tingenone insted of pristimerin, as exhibited by dispermoquinone, a new celastroloid (73) of this uncommon type was isolated from the roots of M. amazonica by Chavez et al. [81]. The structure was elucidated by spectroscopic evidences, exhibiting a molecular formula C28H32O5, and characteristic features of 7-oxo-quinonemethides in the H NMR spectrum as the signals of H-l and H-6 as non-interchangeable with D2O... 

The first natural celastroloid-related structure described bearing a phenolic system in ring A was zeylasterone (75), isolated from Kokoona zeylanica [82]. That compound was characterized as a 6-oxo-diphenol derivative of pristimerin (53). 

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) showed a molecular formula of CeoHgoOs, based on HRFAB-MS analysis and its l3C-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). 

Quite different are the chemical features of some newer antiperoxidative triterpenoids from Trypterigium wilfordii, because they have highly unsaturated A and B rings with a quinonoid-like structure over a friedooleanane skeleton. The main datum to be noted is that celastrol, the most representative compound of this series, inhibits mitochondrial LP, with an IC50 - 7 iM. Its potency is then 15 times higher than that of a-tocoferol. Furthermore, it has been observed that while celastrol and its acetyl derivative affect the radical chain reaction in a biphasic manner, a-tocoferol and pristimerin, a celastrol-methyl ester, do it monotonously. 

The structurally related cephalosporin and helvolic acid do not appear to have the same antibacterial potency as fusidic acid [271, 336, 337] and so would not seem destined for equivalent status in medicine. Similarly the antibacterial potency of the triterpenoid antibiotics polyporenic acid A [338] and polyporenic acid C [339], like that [340] of pristimerin (LXI) [341, 342], which is one of the most highly oxidised naturally occurring pentacyclic triterpenes... 

Harada, R., H. Kakisawa, S. Kobayashi, M. Musya, K. Nakanishi, and Y. Taka-HASHi Structure of pristimerin, a quinonoid triterpene. Tetrahedron Letters 14, 603 (1962). 

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