Dependence of 1H NMR chemical shifts of geminal protons of glycosyloxy methylene (H2-26) on the orientation of the 27-methyl group of furostane-type steroidal saponins

An approach based on the difference (Delta(ab) = delta(a) - delta(b)) between the H-1 NMR chemical shifts (delta(a), delta(b)) of the geminal protons of glycosyloxy methylene (H-2-26) (Delta(ab) = <0.48 for 25R; Delta(ab) = >0.57 for 25S) is proposed for ascertaining 25R/25S orientation of the 27-methyl group of furostane-type steroidal saponins. These studies suggested the 25R-orientation of the 27-Me group for the furostanol glycosides isolated by Wu et al. from Tribulus terrestris. Copyright (C) 2004 John Wiley Sons, Ltd.