Deterministic 13C NMR analysis of oleanolic and ursolic acid derivatives based on application of 2D INADEQUATE NMR technique

This study focuses on the assignment of the 1H and 13C NMR spectra of four oleanene- and four ursene-type triterpenes, namely oleanolic acid (1), ursolic acid (2), 3-O-acetyloleanolic acid (3), 3-O-acetylursolic acid (4), 3-epi-oleanolic acid (5), 3-epi-ursolic acid (6), 3-O-epi-acetyloleanolic acid (7) and 3-O-epi-acetylursolic acid (8). Various NMR techniques were employed, such as 1D (1H, 13C), 2D (COSY, 1H -13C COSY, HMQC, HMBC, and INADEQUATE). These advanced approaches enabled the unambiguous assignment of the methyl proton signals and the carbon signals in the triterpene structures. These comprehensive spectral data provide essential reference information for future research on similar compounds from natural or synthetic sources.