STRUCTURE ELUCIDATION OF SECALOSIDE-A AND SECALOSIDE-B BY NMR-SPECTROSCOPY

The constitution of secalosides A and B was elucidated through NMR spe ctroscopy using fast BD-NMR experiments with pulsed-field gradients fo r coherence selection. Secalosides A and B are epimers at center C-3' of aglycon I and have the constitution shown as 1. The presence of a s accharose unit was confirmed independently by mild basic hydrolysis an d enzymatic quantification. The relative configuration of the stereoge nic centers of aglycon II could be deduced from ROESY data. Assignment s of the two epimers to the R- and S- configurations at C-3' in aglyco n I, as well as the absolute configuration of aglycon II remain to be determined.