LC–MS analysis of saponins of Achyranthes root in the Japanese market

LC–MS analyses of saponin fractions of Achyranthes roots in the Japanese market revealed that there were three patterns for the saponin fraction of their water extracts, i.e., the saponins with a sugar moiety at position 28 [achyranthosides B (3), C (4) and D (5)] were the major constituents, the saponins without sugar moiety at position 28 [betavulgarosides II (10) and IV (11)] were the major constituents, and mixtures of these saponins. In a decoction prepared from the sample which contained 10 and 11 as the major saponins, their amounts were largely decreased compared with those of the water extract. As large amounts of these saponins were found in the precipitates formed by heating of the water extract, these saponins were seemed to precipitate out under heating. When hot water was used for the extraction, 3, 4 and 5 were detected even from the samples whose water extract did not contain these saponins. This was attributed to inhibition of endogenous esterase which hydrolyzes the ester linkage at position 28. When saponins were extracted with reagent grade 1-butanol, in addition to the decrease of the amounts of highly polar saponins, oxidative decarboxylation of 3 and 10 occurred resulting in formation of achyranthoside E (6) and spinacoside D (12), respectively. As these changes were not observed with HPLC grade 1-butanol, which contain not more than 5 ppm of peroxide impurities, the change was attributable to the peroxide impurities contained in the reagent grade 1-butanol.