Characterization of various isomeric photoproducts of ergosterol and vitamin D2 generated by UV irradiation

Abstract

Vitamin D2 is produced from its precursor ergosterol under the impact of ultraviolet (UV) light which is also commercially carried out to increase vitamin D2 contents in mushrooms (‘Novel Food’). However, this process is accompanied by the formation of various isomers that partly co-elute with the target compound and are currently difficult to analyze. For this reason, vitamin D2 and ergosterol were irradiated with the goal to generate and characterize various isomeric photoproducts with three analytical methods. High-performance liquid chromatography with ultraviolet detection (HPLC–UV) was accompanied by using a chiral detector (CD) which was serially linked with the UV detector. Applied for the first time in this research area, HPLC-CD chromatograms provided complementary information which was crucial for the identification of several co-elutions that would have been overlooked without this approach. Additional information was derived from gas chromatography with mass spectrometry analysis. Diagnostic fragment ions in the GC/MS spectra allowed to distinguish four classes of tri- (n = 2), tetra-, and pentacyclic isomer groups. Despite several drawbacks of each of the applied methods, the shared evaluation allowed to characterize more than ten isomeric photoproducts of vitamin D2 including previtamin D2, lumisterol2, tachysterol2,trans-vitamin D2 isomers, and two pentacyclic isomers (suprasterols2 I and II), which were isolated and characterized by proton magnetic resonance spectroscopy (1H NMR).