Separation, determination and identification of the diastereoisomers of podophyllotoxin and its esters by high-performance liquid chromatography/tandem mass spectrometry

A rapid and stable high-performance liquid chromatography–diode array detection (HPLC–DAD) and a high-performance liquid chromatography–electrospray ionization tandem mass spectrometry (HPLC–ESI/MS/MS) method were developed and validated for the separation, determination, and identification of eight pairs of diastereoisomers of podophyllotoxin and its esters at C-2 position. The separation was carried out on BDS Hypersil C18 column with CH3OH–CH3CN–H2O as the mobile phase in a gradient program. Interestingly, every 2α-H compound migrated before its corresponding 2β-H epimer under optimum conditions. Also, the [M+NH4]+ of all eight pairs of compounds was observed in the HPLC–ESI/MS spectra. The characteristic elimination from the precursor protonated ions and the product ions at m/z 397, 313, 282, and 229 were the common diagnostic masses. The ion ratios of relative abundance [M−ROH+H]+ (ion 397) to [M+NH4]+, [A+H]+ (ion 313) to [M−ROH+H]+, and [M−ROH−ArH+H]+ (ion 229) to [M−ROH+H]+ in the ESI/MS/MS spectra of each pair of diastereoisomers of the lignans specifically exhibited a stereochemical effect. Thus, by using identical sample solutions and chromatographic conditions (including the same columns and gradient programs), the combination of DAD and MS/MS data permitted the separation and identification of the eight pairs of diastereoisomers of the podophyllotoxin and its esters in the mixture. The method could be used in rapidly identifying the purity and monitoring of the epimerization of 2-H of podophyllotoxin and its analogues from natural products, chemical reactions, and pharmaceutical metabolism.