Hierarchical Key for the LC-MSn Identification of All Ten Regio- and Stereoisomers of Caffeoylglucose

A chromatographic method was developed to separate all 10 regio- and stereoisomers of caffeoylglucose. Following chromatographic separation on reversed phase, the fragmentation behavior of all 10 regio- and stereoisomers of caffeoylglucose has been investigated using LC-MSn. It is possible to discriminate between each of the isomers based on their characteristic fragment spectra and order of elution, including those for which commercial standards are not available. On the basis of the synthesis of authentic standards for 6-caffeoylglucose and 3-caffeoylglucose and nonselective further synthesis of suitable mixtures of isomers, it was possible to fully assign regiochemistry of all 10 isomeric compounds and stereochemistry of eight isomeric compounds. Their fragmentation pattern was rationalized based on assuming different hydrogen-bonding arrays of gas-phase ions opening distinct fragmentation pathways. An analysis of yerba mate extract showed all 10 regio- and stereoisomers of caffeoylglucose to be present in this dietary material, which could all be assigned to regioisomeric level and eight to stereoisomeric level.