Alternative Identification of Glycosides Using MS/MS Matching with an In Silico-Modified Aglycone Mass Spectra Library

Glycosylation of metabolites serves multiple purposes.
Adding sugars
makes metabolites more water soluble and improves their biodistribution,
stability, and detoxification. In plants, the increase in melting
points enables storing otherwise volatile compounds that are released
by hydrolysis when needed. Classically, glycosylated metabolites were
identified by mass spectrometry (MS/MS) using [M-sugar] neutral losses.
Herein, we studied 71 pairs of glycosides with their respective aglycones,
including hexose, pentose, and glucuronide moieties. Using liquid
chromatography (LC) coupled to electrospray ionization high-resolution
mass spectrometry, we detected the classic [M-sugar] product ions
for only 68% of glycosides. Instead, we found that most aglycone MS/MS
product ions were conserved in the MS/MS spectra of their corresponding
glycosides, even when no [M-sugar] neutral losses were observed. We
added pentose and hexose units to the precursor masses of an MS/MS
library of 3057 aglycones to enable rapid identification of glycosylated
natural products with standard MS/MS search algorithms. When searching
unknown compounds in untargeted LC-MS/MS metabolomics data of chocolate
and tea, we structurally annotated 108 novel glycosides in standard
MS-DIAL data processing. We uploaded this new in silico-glycosylated
product MS/MS library to GitHub to enable users to detect natural
product glycosides without authentic chemical standards.