Wilforic acid structure

The 13C spectrum of wilforic acid C was very similar to that from maytenoic acid (4) [28], except for the signals belonging to C-l, C-2, C-4 and C-10. The comparison of the spectroscopic data and molecular formula from both compounds led to establish the structure of wilforic acid C having an additional hydroxyl group located at C-2. The relative stereochemistry was determined as a by means of a ROESY experiment and the coupling constant of the geminal proton to the hydroxyl group (J = cal Hz). 

Triptocalline A (6) was found to have six methyls and two methines attached to hydroxyl groups. Additionally, the 13C NMR spectrum showed signals for a a,p-unsaturated carbonyl group at 5 200.1 and a second carbonyl group at 5 214.0. The spectral data of (6) were very similar to those of wilforic acid B, except for the signals due to D, and E rings, that were identical to those of 22p-hydroxytingenone [31]. From the evidence discussed the structure of (6) is showed in Fig. (4). 

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,... 

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