Localization of malonyl and acetyl on substituted saikosaponins according to the full‐scan mass spectra and the fragmentation of sodium‐adduct ions in the positive mode

Abstract

Rationale It's a long‐lasting unsettled issue to discriminate between aglycone‐substituted and saccharide‐substituted saikosaponins by LC‐MSⁿ. It's necessary to characterize the two types of substituted saikosaponins taking into consideration their potential significant difference in bioactivity. Methods Taking the substituents of malonyl and acetyl as example, we developed a MS strategy to discriminate between the aglycone‐substituted and saccharide‐substituted saikosaponins through comparing their Y₀‐nH₂O (n=1‐2) ions from the protonated molecules in the full‐scan mass spectra and their B ions in the MS² spectra of sodium‐adduct molecules in the positive mode. Results Both the aglycone‐substituted and saccharide‐substituted saikosaponins presented similar fragmentation patterns from the deprotonated molecules in the negative mode, which could not discriminate whether the substitutes located on the aglycone or saccharide. On the contrary, the Y₀‐nH₂O (n=1‐2) ions containing or no substitute were observed respectively in the mass fragmentation of the protonated molecules of aglycone‐substituted or saccharide‐substituted saikosaponins in the positive mode. And the B ions containing or no substitute were observed respectively in the mass fragmentation of the sodium‐adduct molecules of the saccharide‐substituted or aglycone‐substituted saikosaponins in the positive mode. Two aglycone‐malonylated saikosaponins were first reported. Conclusions Whether the substitutes located on the aglycone or saccharide could be determined according to the Y₀‐nH₂O (n=1‐2) ions from the protonated molecules in the full‐scan mass spectra and the B ions in the MS² spectra of sodium‐adduct molecules in the positive mode. Our results updated the mass fragmentation patterns of substituted saikosaponins, which is helpful for quality control of pharmaceutical preparations containing saikosaponins. More importantly, this MS strategy should be able to be extended for characterizing other substituted saponins of bioactive significance in future study.