Celastrol structures

Since the isolation of celastrol in 1936 by Chinese workers a variety of quinonemethides have been encountered in Celastraceae species and their structures and a wide range of biological activities have been reported thus far, resulting quite interesting activities against microorganisms and tumor cells [9,11]. 

From the root bark of T. wilfordii was isolated by Li et al. [26] a compound which exhibits a structure related to that of celastrol (52). It was named wilforic acid A (79), and its structure was established by applying spectroscopic methods. Besides IR absorption bands for hydroxyl (3402 cm ) and carbonyl (1702 cm 1) groups the compound showed UV absorption bands at 249 and 286 nm. The 1H-NMR spectrum showed six methyl groups (6 1.01 - 2.39 ppm), all of them as singlets,... 

The study of the outer root bark of T. hypoglaucum collected in China afforded three new structures of phenolic triterpenes. Duan et al. isolated triptohypol A (80), B (81) and C (82), a series of new phenolic compounds related to celastrol [29]. Triptohypol A (80) was isolated as an amorphous powder and spectroscopic means and chemical modification determined its structure. By HREIMS the formula C30H40O6 was determined, and H-NMR spectrum showed five methyl signals, a methoxy moiety, a methylene attached to an oxygen atom and two vinyl protons. Data from 13C-NMR experiments indicated the presence of a pair of carbonyl groups and was quite similar to that of wilforol A (78). The analysis of HMQC and HMBC experiments allowed to establish the structure for rings A and B, based on the correlations observed between the proton H-l (8 6.95 ppm) and the carbons C-3, C-5 and C-10. Finally, the position of the carbonyl group was established at C-6 based on a NOESY experiment of the dimethyl derivative. 

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. 

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