Revisit to 25R/25S stereochemical analysis of spirostane-type steroidal sapogenins and steroidal saponins via 1H NMR chemical shift data

Abstract

An approach based on the difference (Δab = δa - δb) between 1H NMR chemical shifts (δa, δb) of the geminal protons of oxymethylene (H2-26) (Δab2 = <0.2 for 25R; Δab = >0.5 for 25S) is proposed for ascertaining 25R/25S orientation of the 27-methyl group for (22R)-spirostane-type steroidal sapogenins and steroidal saponins. These studies suggested the 25R-orientation of the 27-Me group for the steroidal saponins isolated by Temraz et al. from Tribulus alatus.