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) (Δab = <0.2 for 25 R; Δab = >0.5 for 25 S) is proposed for ascertaining 25 R/25 S orientation of the 27-methyl group for (22 R)-spirostane-type steroidal sapogenins and steroidal saponins. These studies suggested the 25 R-orientation of the 27-Me group for the steroidal saponins isolated by Temraz et al. from Tribulus alatus.