Structural analysis of complex saponins of Balanites aegyptiaca by 800 MHz 1 H NMR spectroscopy

The main saponin (1) present in the mesocarp of Balanites aegyptiaca fruit is a mixture of 22 R and 22 S epimers of 26‐( O ‐β‐ D ‐glucopyranosyl)‐3‐β‐[4‐ O ‐(β‐ D ‐glucopyranosyl)‐2‐ O ‐(α‐ L ‐rhamnopyranosyl)‐β‐ D ‐glucopyranosyloxy]‐22,26‐dihydroxyfurost‐5‐ene. This structure differs from a previously reported saponin isolated from this source by the site of attachment of the rhamnosyl residue, and presumably represents a structural revision of the latter. The main saponin (2) present in the kernel is a xylopyranosyl derivative of 1. The use of high‐field NMR enabled the practically complete assignment of 1 H and 13 C chemical shifts of these complex saponins, existing as a mixture of C‐22 epimers. Moreover, the work represents a new approach to structural elucidation of saponins: direct preparative‐scale HPLC‐RID of crude extracts followed by high‐field NMR investigations supported by ESI‐MS n . Copyright © 2006 John Wiley & Sons, Ltd.