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

Abstract

AbstractThis study aimed to carry out complete 1H and 13C 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‐d4. This was accomplished by the analysis of high‐resolution one‐dimensional (1D) NMR (1H and 13C), two‐dimensional (2D) NMR (1H–1H COSY, HSQC, and HMBC), and selectively excited 1D TOCSY spectra. Before this study, 1H and 13C 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 1H and 13C 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‐d4, are provided. In addition, the 1H and 13C NMR data of Mi‐saponin C (12) are reported for the first time. These data, being recorded in methanol‐d4, should be more friendly for use as a reference for identifying the related triterpenoid saponins.