Analysis of Triterpenoids in Ganoderma lucidum Using Liquid Chromatography Coupled with Electrospray Ionization Mass Spectrometry

Triterpenoids extracted from Ganoderma lucidum (Leyss. ex Fr.) Karst were separated and characterized using optimized reversed-phase liquid chromatography with diode array detection and electrospray ion trap tandem mass spectrometry (HPLC-DAD-ESI-MSⁿ). They could be classified into five types depending on the fragmentation behavior. All triterpenoids gave [M - H]^- and [2M - H]^- ions by electrospray ionization monitored in the negative ion mode; in addition, compounds of types III and IV gave prominent [M - H - H₂O]^- ions and the unsaturated bond at C-20, 22 would reduce the abundance of [M - H - H₂O]^- ion. The key fragmentation information was cleavage at C- and D-rings despite the predominant losses of H₂O and CO₂. Compounds with hydroxyls at C-7 and C-15 would produce a list of b, b - 1, b - 2, and b - 16 ions attributed to cleavage of D-ring; if the second alcohol at C-15 were oxidized to ketone, the prominent cleavage would occur at C-ring and produce a group of ions of a; if C-7 were oxidized to ketone, transference of two hydrogen atoms would occur during the cleavage of rings and a list of ions about a + 2 and/or b + 2 would appear instead. The above fragmentations and regularities in fragmentation pathways were reported for the first time, and were implemented for the analysis of triterpenoids in G. lucidum. The chloroform extract was separated on a Zorbax SB-C₁₈ column, eluting with an acetonitrile-0.2% acetic acid gradient. A total of 32 triterpenoids, including six new ones, were identified or tentatively characterized based on the tandem mass spectra of the HPLC peaks.