Analysis of Acyl Solamines in Tuber Periderm of Cultivated and Wild Potatoes Using Liquid Chromatography Coupled With Electrospray Ionization Quadrupole Time-of-Flight Mass Spectrometry

Abstract

Acyl solamines are a poorly investigated class of alkaloids found in several solanaceous plants. A general screening approach on the basis of all-ion fragmentation is proposed for this compound class using reversed-phase ultra-high performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight mass spectrometry. When applied to tuber periderm extracts of Solanum tuberosum, Solanum pinnatisectum, and Solanum cardiophyllum, this approach resulted in the annotation of over 20 acyl solamines including short- and medium-chain fatty acyl solamines, hydroxycinnamoyl solamines, and other aromatic acyl solamines. In addition, minor derivatives with N-oxidized solamine moieties (acyl solamine-N-oxides and di-N-oxides) and N-demethylated solamine moieties (acyl nor- and dinor-solamines) were detected. The annotated compounds formed singly and doubly protonated molecules under positive ion electrospray conditions. Upon collision-induced dissociation (CID), protonated acyl solamines and derivatives with modified solamine moieties produced informative and readily interpretable product ion spectra. This enabled the structural characterization of the solamine head group and, in some cases, of the acyl moiety. To localize the positions of the carbon–carbon double bonds, major unsaturated medium-chain fatty acyl solamines were isolated in small quantities from S. tuberosum tuber periderm and derivatized with meta-chloroperbenzoic acid. Analysis of the CID mass spectra obtained from the protonated oxidation products provided valuable information for the further structural characterization of these compounds.