Yuliang Ma

Characterization of flavone and flavonol aglycones by collision‐induced dissociation tandem mass spectrometry

A mass spectrometric method based on the combined use of fast atom bombardment collisionally-induced dissociation (CID) and tandem mass spectrometry has been used for the structural characterization of free and conjugated flavone and flavonol aglycones. Low-energy CID spectra of the [M + H]+ (or Y+0) ions show simple fragmentation patterns, which allow characterization of the substituents in the A and B rings and, in particular, differentiation between flavones and flavonols. A systematic nomenclature for product ions produced from protonated molecules under CID conditions is proposed.

Internal glucose residue loss in protonated O-diglycosyl flavonoids upon low-energy collision-induced dissociation

The low-energy collision-induced dissociation of protonated flavonoid O-diglycosides, i.e., flavonoid O-rutinosides and O-neohesperidosides, containing different aglycone types has been studied. The results indicate that the unusual [M + H − 162]+ ion formed by internal glucose residue loss, which in a previous study was shown to be a rearrangement ion, is strongly dependent upon the aglycone type. For 7-O-diglycosides, the internal glucose loss is very pronounced for aglycones of the flavanone type, but is completely absent for aglycones of the flavone and flavonol types. Internal glucose residue loss was found to correspond to a minor fragmentation pathway for flavonol 3-O-diglycosides. A plausible mechanism is proposed based on proton mobilization from the aglycone to the disaccharidic part of the flavonoid O-diglycosides which is supported by theoretical calculations and model building.

Characterization of 3-methoxyflavones using fast-atom bombardment and collision-induced dissociation tandem mass spectrometry

A mass spectrometric method based on the combined use of fast-atom bombardment (FAB), collision-induced dissociation (CID) and linked scanning at constant B/E has been used for the analysis of the fragmentation behavior of protonated 3-methoxyflavones (3-MFs). It is shown that several diagnostic ions such as (1,3)A (+) and (0,2)B (+) ions allow for an unambiguous localization of functions in the A- and B-rings and that the position of an additional methoxy group in the B-ring could be determined by a detailed analysis of the spectral patterns. Isomeric 3-MFs can be differentiated using this methodology. General fragmentation patterns of 3-MFs are discussed and plausible formation mechanisms of relatively abundant fragment ions are proposed.

INDUCTION OF A p-COUMAROYL TRIHYDROXY TRITERPENE ACID IN Psylla-INFESTED AND MECHANICALLY DAMAGED PEAR TREES

The pattern of induction and the chemical structure of phenolic compounds in pear trees (Pyrus communis, cv. Conference) that were either infested by pear leaf suckers Psylla pyricola and P. pyri or mechanically damaged, or both, were studied. Chromatographic (HPLC) and mass spectral analysis performed on extracts of leaf samples collected at various time intervals from trees subjected to three treatments demonstrated the induction (and/or amplification) of a phenolic compound, identified as 3-O-trans-p-coumaroyltormentic acid (I). New mass spectrometric data on this phenolic compound are presented. HPLC revealed different peak patterns in the course of the period of Psylla infestation and the lapse of time since mechanical damage was inflicted, compared to a control tree. The new phenolic compound became apparent after 12 hr and reached the highest level 30 days after damage by pear leaf suckers. It was also observed after 24 hr at lower intensity in samples from a mechanically damaged tree and exclusively on day 30 at very low intensity in the leaf extracts from the uninfested control trees. We conclude that damage by pear leaf suckers, and to a lesser extent also mechanical damage, induce the synthesis of the new, late-eluting phenolic compound. We propose that this compound is involved in plant defense against pear leaf suckers.

Flavonoid glucuronides from Picria fel-terrae

Abstract Three flavonoid glucuronides are reported from a n-BuOH extract of Picria fel-terrae (Scrophulariaceae). The structures were established by UV, one- and two-dimensional NMR and mass spectrometry as apigenin 7-O-β-glucuronide, luteolin 7-O-β-glucuronide and apigenin 7-O-β-(2″-O-α-rhamnosyl)glucuronide, the latter one being a new compound.

Mass spectrometric methods for characterization and differentiation of isomeric **O**-diglycosyl flavonoids

Tandem mass spectrometric methods have been evaluated for the characterisation of the type and the differentiation of the interglycosidic linkage of isomeric flavonoid O-diglycosides. Based on the occurrence of internal monosaccharide residue loss and the relative abundances of Y-type ions formed by fragmentation at glycosidic bonds, four pairs of isomeric flavonoid O-diglycosides can be unambiguously differentiated. The different techniques used, i.e. linked scanning at constant B/E without collisional activation and low-energy collision-induced dissociation using methane or helium as collision gas, have been shown to be useful for distinguishing the two most common (1, 2- and 1, 6-) interglycosidic linkages, e.g. flavonoid O-neohesperidosides and O-rutinosides.