Chemical ionization mass spectral characteristics of analogs of steviol, the aglycone of the plant-derived sweetening agent, stevioside

Abstract

The use the naturally occurring ent-kaurene diterpene glycoside, stevioside, as a sucrose substitute in several countries has resulted in the need for improved methods to analyze its potential metabolites. Altogether 21 diterpenes related in structure to steviol, the aglycone of stevioside, have been subjected to desorption chemical ionization mass spectrometry using methane, ammonia and dimethyl ether as reagent gases. Both methane and ammonia provided the molecular weights of these derivatives, but failed to produce any adduct ions of particular diagnositc value for differentiating compounds in the steviol series. On the other hand, dimethyl ether produced positive ion chemical ionization spectra that differed according to the nature of the functional groups represented among the steviol derivatives examined. Prominent adduct ions observed using dimethyl ether were [M + 1 − 18]+, [M + 1]+, [M + 45 − 32]+, [M + 45]+ and [M + 47]+. Mechanisms have been proposed for the formation of these adducts.