Comprehensive 1H and 13C NMR assignment of 13 protobassic acid saponins

This study aimed to carry out complete H-1 and C-13 NMR assignment of 13 protobassic acid saponins, including arganins A-C (1-3) and F (4), butyrosides B-D (5-7), tieghemelin (8), 3 '-O-glucosyl-arganin C (9), Mi-saponins A-C (10-12), and mimusopsin (13), recorded in methanol-d(4). This was accomplished by the analysis of high-resolution one-dimensional (1D) NMR (H-1 and C-13), two-dimensional (2D) NMR (H-1-H-1 COSY, HSQC, and HMBC), and selectively excited 1D TOCSY spectra. Before this study, H-1 and C-13 NMR data of arganins A-C (1-3) and F (4) were partially assigned. Our effort leads to their complete assignment, especially the glycon residue, and revises some reported data. Some revisions of the H-1 and C-13 NMR data in the glycon part of butyroside C (6), tieghemelin (8), Mi-saponin A (10), and mimusopsin (13) were made. Those data of butyrosides B and D (5 & 7) and Mi-saponin B (11), which had not been recorded in methanol-d(4), are provided. In addition, the H-1 and C-13 NMR data of Mi-saponin C (12) are reported for the first time. These data, being recorded in methanol-d(4), should be more friendly for use as a reference for identifying the related triterpenoid saponins.