A mass spectrometry study of the self-association of glycyrrhetinic acid molecules

The formation of self-associates of glycyrrhetinic acid (GLA), an aglycone of glycyrrhizic acid (GA), has been studied by electrospray ionization mass spectrometry. It has been shown for the first time that, analogously to triterpene saponins having free carboxyl groups, GLA stereoisomers can form self-associates. The capacity of GLA to form self-associates has been confirmed by the mass spectrometry data. It has been found that the ionization of GLA self-associates with the formation of an anion proceeds rather weakly. The ionization of GLA in the positive ion mode goes on effectively and makes it possible to record multidimensional structures of one to eight 18 alpha-GLA molecules and from one to nine 18 beta-GLA molecules. The structure of GLA associates and their stability are demonstrated most comprehensively in positive ion mass spectra. As a whole, the sets and intensity of peaks for 18 alpha- and 18 beta-GLA correlate well. The results of the mass spectrometry study show the capacity of 18 alpha- and 18 beta-GLA stereoisomers to form self-associates, which indicates a high potentiality of GLA in providing noncovalent interactions during the formation of supramolecular complexes. Similarly to the saponins of licorice and ivy, GLA stereoisomers may form a potential basis for the synthesis of a new generation of noncovalent molecular complexes and novel highly effective medicinal substances owing to a possible improvement in bioaccessibility and possible synergistic effects.