Structures of polygalacin-D and -D2, platycodin-D and -D2, and their monoacetates, saponins isolated from Platycodon grandiflorum A. DC., determined by carbon-13 nuclear magnetic resonance spectroscopy.

Abstract

The structure of new nine saponins isolated from Platycodon grandiflorum A. DC. have been elucidated by comparison of their 13C nuclear magnetic resonance spectra with those of the known prosapogenins and that of platycodin-D (1). All the saponins proved to possess the same sugar chain as that of 1 at C-28 position. Eight of the nine (2, 3, 5, 6, 8, 9, 11, and 12) have an O-acetyl group which was found to migrate easily and reversibly between 2-O- and 3-O-position of the rhamnose moiety in their sugar chain. The other one is an acetyl-free saponin named polygalacin-D2 (10). Two new deacetylated saponins, platycodin-D2 (4) and polygalacin-D (7), were prepared from 5 (6) and 8 (9), respectively.